• 

(ed note: this paper is about streams of water drops impacting a pool of water instead of laser pulse trains impacting human flesh, but the effects are similar.)

When a water droplet impacts a free surface with sufficient velocity, the momentum transfer results in the formation of a hemispherical cavity expanding radially from the point of impact. This cavity continues to expand until the kinetic energy is completely converted to potential energy. Pumphrey and Elmore equated the potential energy of this subsurface cavity with the kinetic energy of the impacting droplet, concluding that the magnitude of the cavity radius is proportional to impact velocity and droplet diameter.

Less is known about the effect of several droplets impacting a water surface in rapid succession. The first impacting droplet creates a subsurface cavity as described above; the second droplet creates a very similar result, but with the cavity initiating from the base of the first. A third droplet and a fourth droplet expand the depth and compound nature of the cavity. We refer to the nested cavity shape formed in the wake of multiple droplets as a matryoshka cavity (named after Russian nesting dolls). This phenomenon is only observed when a series of droplets impacts a free surface with a sufficiently high temporal frequency such that subsequent cavities form before the initial cavity closes. One may be inclined to conclude that the ideal droplet frequency should involve a droplet impacting just as the previously formed cavity has reached its apogee. However, this would result in the lower portions of this complex cavity forming as the upper levels collapse. We conjecture that the ideal frequency is higher than this definition, allowing the top of the cavity to continue to expand outward while the bottom is extending downward. Of course, the upper bound on droplet frequency would be the case where the droplets are so close together that they coalesce to form a single jet, which results in a different impact event.

See video here

As we approach this ideal impact frequency, larger compound cavities can be formed, extending much deeper below the free surface and lasting longer than a cavity generated from a single droplet impact. Rather than producing the spherical cavity observed by Worthington, a droplet stream produces a long conical cavity. Fig. 2 presents an extensive cavity formed by approximately 15 droplets impacting the water surface in succession, and is approximately 14 times deeper than a cavity created by a single droplet. It is likely that this image does not represent the upper limit of the cavity proportions that can be achieved.

Dr. Schilling

Whether you use lasers or particle beams, you'll need a bit over a kilojoule of output energy to reliably incapacitate a human target. In the case of a laser weapon, that energy would be subdivided into ~1 joule pulses at ~5 microsecond intervals, to achieve penetration in the face of a laser's natural tendency to deposit energy at the target's surface. Particle beams don't have that problem; boost the electrons up to a few hundred MeV, and you can dump the whole kilojoule's worth at once.

The plasma clears away easily in that time frame; debris is the real issue, and the driving force between the 5 microsecond pulse rate. That allows roughly 90% of the debris to clear the beam path, assuming a 1mm beam and instantaneous 1J pulses. 1 joule every 5 microseconds is optimal against soft tissue, other materials will want different pulse trains.

I'm assuming a weapon designed to penetrate ~30cm in soft body tissue. This gives about 15cm in bone or plastic, 5cm in brick or concrete, or 2.5cm in steel or most ceramics. Synthetics won't be very good at stopping energy weapons, even tough ones like kevlar, but you might be able to find a ceramic that could stop a laser beam with a centimeter's thickness or so. Particle beams are tougher to stop; it mostly comes down to sticking mass in the way without regard to material properties.

(ed note: if my slide rule is not lying to me, 1000 pulses at 5 microseconds per pulse will take 0.005 seconds. 1000 joules in 0.005 seconds is equivalent to 200 kilowatts)

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Luke Campbell

Keep in mind that in tissue, the cavity blasted out will collapse back on itself in a few milliseconds (and probably re-expand and collapse again in pulse-like oscillations for a few cycles).

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Dr. Schilling

Yes, and this is a problem if you want to push the penetration much above the 30cm I specified. If your pulses come fast enough to gouge out a meter-deep path before the surrounding tissue recoils back into the cavity and blocks the beam, they come too fast for the per-shot debris to clear the beam.

In soft materials, vapor expansion will carve out a hole much larger than the original one millimeter — I got four centimeters maximum hole diameter for soft body tissue, so the effect should be at least equal to a modern high-velocity pistol bullet, and perhaps comparable to a small centerfire rifle. Brittle materials are likely to shatter within a similar radius, tough stuff like steel will show little effect beyond the original hole.

And no, mirrors will not work as armor. The best finish you can reasonably expect to keep on an exterior surface, will still absorb 10-20% of the incident energy, which will be enough to burn through the outer layer on the first pulse. And the rough and now hot interior will be even less reflective.

I also mentioned earlier that lasers would likely have to have pulse energy and frequency tuned to the specific material being targeted. It might be possible to do this automatically, based on crude spectoanalysis of the material vaporized in each pulse, but if not expect penetration to be roughly halved if a laser weapon is fired at a target it has not been optimized for. Target-shooting lasers won't be optimized for flesh, and certainly not for ceramic armor, so there may be legal implications here. Particle beams are less likely to suffer such inconveniences.

Taking into account the inefficiency of the system, the input energy will likely be somewhere between two and five kilojoules per shot. So you could get fifty to a hundred shots from a pistol-sized non rechargeable energy source, or half that with a rechargeable battery. Automatic fire at anywhere up to 20 Hz (1200 rpm) shouldn't be a problem in the short term, though might cause cooling problems if you keep it up.

You also need to focus the energy on the target, with a spot size of a millimeter or less. With a laser, that gets kind of tricky. A 5-centimeter mirror, about the largest you can really imagine on a pistol, gives an effective range of perhaps sixty meters, beyond which the weapon starts losing penetration quite rapidly.

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Luke Campbell

If you are already talking about the laser excavating cavities several centimeters in diameter, sub-millimeter spot sizes do not seem necessary, you just need a moderate fraction of the cavity's maximum size.

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Dr. Schilling

No, you still need to get down to a millimeter or so to flash-boil water in a layer ~one optical depth in thickness. Once you do that, the steam will expand and spread the damage around, but if you don't hit the threshold for turning water into steam all you do is warm up the target.

And the mirror needs to adjust for target range - adaptive optics (flexible mirror with microactuators)coupled to a laser range finder seems to be the way to go here - you've already got the pulsed laser part of the rangefinder.

• 

Luke Campbell

{amount of damage caused by battle laser shot: 10 kJ per shot, made up of 50 pulses of 200 J each, spaced 10 microsecond apart} I use my damage calculator here which lays out all of my physical assumptions and approximations, but which I think captures the basic physical processes of crater gouging. Since stress is concentrated at the tips of cracks, you may get individual cracks propagating beyond the distances listed below in brittle materials, but severe pulverization should be limited to approximately the distances given (as observed in impact and explosive craters).

Incident on meat, the aforementioned pulse train will blast out a hole 53 cm deep and 2.2 cm across (this is probably reported to one more significant figure than is justified). The diameter of the temporary cavity will be about 10 cm, but since muscle is highly elastic this will probably cause only bruising beyond the 2.2 cm permanent hole. Adding gristle and bone doesn't change this much - you get the same permanent cavity and depth in gristle, while bone will be drilled through to a depth of 29 cm, a permanent cavity diameter of 1.2 cm, and shattering and fracturing out to 1.45 cm diameter. Note that a typical person will be about 20 cm to 30 cm through the torso (depending on orientation), so this pulse would not only shoot through a person, but through the guy behind him as well.

Incident on plastic — in this case high density polyethylene — the pulse train will blast out a 32 cm deep and 1.3 cm across hole, with possible plastic flow out to 2.43 cm diameter.

Incident on sandstone, you get a 25 cm deep hole, 1.1 cm across, with shattering and cracking out to 2.1 cm. On granite, the hole is essentially the same except that shattering and fracturing is limited to 1.5 cm diameter. On concrete, the hole is again about the same depth and width, but now you can expect shattering out to about 3 cm.

Against structural steel, you get a 16 cm deep hole that is 0.65 cm across, and possible cracks or permanent deformation out to 1.1 cm. The very strongest maraging steels have the same size hole, but will lack any permanent deformations in the vicinity of the hole.

A representative titanium alloy might get an 18 cm deep hole 0.74 cm across, with possible permanent damage out to 0.84 cm diameter. Aluminum alloys will get drilled to 19 cm and 0.79 cm across, with possible permanent deformation out to 1.5 cm diameter.

High tech armor is likely to be some sort of carbon, perhaps diamondoid, fullerite, or nanotube weave. Against diamond I get a hole depth of 6.1 cm and a 0.26 cm hole diameter. Expect permanent damage out to 4 cm in the form of shattering and cracks. Against fullerite and nanotubes, the hole will be 7.7 cm deep and 0.32 cm in diameter, with possible permanent damage out to 0.41 cm.

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Anthony Jackson

(Luke Campbell: 10 kJ per shot, made up of 50 pulses of 200 J each, spaced 10 microsecond apart)

Why that level of overkill? You should get the same penetration out of 100 pulses of 25J each, spaced 5 microseconds apart. You'll just have a hole that's half as wide, and you've just dramatically cut the energy requirements.

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• 

Luke Campbell

Two reasons, all relating to the fact that the hole is half as wide.

First, very large aspect ratio holes may be problematic to drill, based on issues of the ejecta interacting with the beam and the hole. With the pulse parameters I used, I'm looking at a 25:1 aspect ratio - which is probably doable although the hole will likely have constricted significantly near the end. At half the width, the aspect ratio will be more like 50:1, which is pretty extreme and may be unachievable. Also, if the hole is constricted, each subsequent pulse will produce a smaller bang, which will gouge out a smaller crater, which will in turn reduce the penetration from this optimistic assessment. In the limit of lots of small pulses, this should give a penetration that depends on the logarithm of the number of pulses, which quickly reaches a point of diminishing return.

Second, your range for maximum effect is cut in half, since you need to focus the pulses to within half the width to efficiently blast out the crater. Against diamondoid armor, the 200 J pulses require a 0.26 cm spot size for maximum effect and a 1 micron wavelength, 6 cm aperture laser will be able to be effective out to about 120 meters with a perfect Gaussian beam. If the craters are only half as wide, you would need to be twice as close.

Although now that I think about it, all my previous figures on the beam power were from the figures on power consumption, not beam power. Since I assumed by lasers were 50% efficient, all the previously stated beam powers are too large by a factor of 2 (and the details on the pulse trains which I retro-fitted to give the right beam power will be off as well). Ah well, I plead that I was distracted (I had just learned that I was going to be a daddy).

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Anthony Jackson

(Luke Campbell: First, very large aspect ratio holes may be problematic to drill...)

Hm. On reflection, this suggests that the ideal number of pulses in a blast may be fixed (probably somewhere in the 20-100 range), since the aspect ratio is basically about half of the number of pulses.

(Luke Campbell: In the limit of lots of small pulses, this should give a penetration that depends on the logarithm of the number of pulses...)

Pretty sure it's order 1/3, since the lost energy tends to go towards making the hole wider.

(Luke Campbell: Second, your range for maximum effect is cut in half, since you need to focus the pulses to within half the width to efficiently blast out the crater...)

On reflection, this may be problematic for unrelated reasons. Air breakdown in clean air occurs at upwards of 10¹⁰W/cm², but in dirty air it can drop down to 10⁸W/cm² or so. Your 0.26 cm spot size is 0.05 cm², so the dirty air limit is around 10⁷W or 10J/microsecond. For clean air, the 200J pulses are likely not a problem.

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Luke Campbell

(Anthony Jackson: Hm. On reflection, this suggests that the ideal number of pulses in a blast may be fixed, probably somewhere in the 20-100 range)

Yeah, that's the conclusion I've been coming to.

(Anthony Jackson: Pretty sure it's order 1/3, since the lost energy tends to go towards making the hole wider)

I can see this is true if you are mainly working via melting or evaporation of the material. If the pulses are blasting out a void, however, the energy deposited on the sides of the hole may not be sufficiently intense to deform the material. Of course, the hypersonic jet of ejecta may be able to strip material from the sides of the hole. So we are looking at penetration scaling at somewhere between the 1/3 power and logarithmically for large numbers of pulses. For small numbers of pulses we should, of course, be in a linear regime.

Looking at pictures of various aspect ratio laser drilled holes, the opening to the hole looks to have about the same radius regardless of aspect ratio, which is about the same as the width of the beam. As the aspect ratio of the hole increases, the hole constricts with depth, eventually becoming significantly narrower than the beam.

I am not sure if the same mechanisms that operate in close focus laser drilling necessarily take place in holes drilled as part of an attack by a laser weapon. For example, in laser machining the walls of the hole are often used as a waveguide to extend the depth of field of the laser beam. For weapons, this will be irrelevant at significant ranges. If loss due to multiple reflections down the waveguide is responsible for much of the constriction, then this will not be as much of an issue for laser weapons.

For pulse lasers, as long as you can get most of the energy of the pulse into a given area of the target material, you will blast out a full sized crater. So suppose the crater is 1 cm across (and thus you have a maximum spot size of 1 cm in which to focus your beam for maximum effect), and also suppose your beam is focused to 1 mm. You will continue to blast out full sized craters until ejecta deposition constricts some part of the hole to less than 1 mm. This will result in a much deeper hole than if your beam started out close to the threshold limit of 1 cm.

(Anthony Jackson: On reflection, this may be problematic for unrelated reasons. Air breakdown in clean air occurs at upwards of 10¹⁰W/cm², but in dirty air it can drop down to 10⁸W/cm² or so. Your 0.26 cm spot size is 0.05 cm², so the dirty air limit is around 10⁷W or 10J/microsecond. For clean air, the 200J pulses are likely not a problem.)

This is a very interesting observation. It may be that in air we can never be able to reliably penetrate carbon-armor materials.

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Anthony Jackson

Beam divergence for a near-IR laser (such as neodymium-doped yttrium aluminium garnet (Nd:YaG)) can be estimated as on the order of 1mm per (aperture in mm) meters, and focus tighter than 1-2mm is probably not useful due to issues of hole aspect ratio, so the range at which these weapons would retain full penetration is reasonable for their apparent roles (as assault rifle, SMG, pistol), though rather sharply capped as compared to conventional rifles (which, while not very effective beyond a few hundred meters, don't drop to irrelevance).

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Luke Campbell

I was envisioning these as pulsed lasers. With a pulse, so long as the light is delivered into a smaller spot than the crater which is excavated, the crater will explode to full effect. Since higher energy pulses explode to give bigger craters, higher energy beams will have longer range for the same primary aperture.

So take the battle laser, with a 6 cm aperture and 200 J pulses (fired in bursts of 50 pulses spaced a few microseconds apart). At 200 J, the crater blown out of a good structural steel is about 6.5 mm. So suppose we want the beam to focus into a 6 mm spot. If the beam wavelength is around 1 micron, we get a range of about 275 meters. As the materials get less strong, the crater gets bigger and the range of the laser gets longer — about 470 meters in concrete, or about 940 meters for meat. Stronger materials need you to be closer — for sooper carbon nano stuff, you will want to be closer than about 140 meters.

• 

• 

      WINCHELL CHUNG Luke Campbell, a question if you please, sir!
     The classic Colt .45 automatic pistol has a classic name. "Colt" is the manufacturer, and .45 is the caliber of the weapon.
     In essence, the .45 is a crude measure of the destructive power of the weapon. Since both the mass of the bullet and the amount of gunpowder charge is roughly proportional to the damage energy inflicted on the target.
     So if I was to name the item below, what would it be?
     The manufacturer be something along the lines of "Campbell", but what about the weapon designation? Would it be "3 cm" (aperture), "4 μs" (pulse interval), or "3.2 kJ" (beam energy)? Or would there be another more logical specification number?

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     BRIAN RENNINGER Super 8 sounds kind of deadly.

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     JENNIFER LINSKY the Campbell collimator.

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     MATTER BEAM Perhaps pulse energy with a pulse length descriptor? Like a Campbell 100 Short, for 100 joules over a typically short pulse length?

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     JUAN OCHOA Gods I love you people.

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     JASON FRITZ "In essence, the .45 is a crude measure of the destructive power of the weapon." Well, the designator ".45" was never meant to be indicative of the power of the weapon, but the caliber of the ammunition it fired.

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     DAN THOMPSON I think it really needs a two-number designation because it's going to deliver an amount of energy over an amount of time. Saying it's a 10kilojoule is meaningless without knowing that if it's delivered over a nanosecond or over an hour. So, first number would be energy (assume kilojoules) and the second number would be the number of nanoseconds it's delivered over. Better weapons have big first numbers and small second numbers, so a 100@5 would be much better than a 50@12.

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     WINCHELL CHUNG Dan Thompson, so it would be a Hundred-aught-Five ? {grin}

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     ISAAC KUO I would think in terms of marketing, and the culture/society we're dealing with. Is this a civilian weapon? Is this a military weapon? Is it, like here currently in the USA, a situation where the military weapon has civilian versions, so the naming will more likely be dominated by the civilian naming?
     Is this just one weapon in a huge array of weapons supplied by this manufacturer? Or is it only one or two? If the latter, then the manufacturer's name will likely become the common name. Think Armalite, or Baretta, or whatever.
     Or depending on the circumstances, it's more likely a simple military designation that becomes the common name (like M2 or M60 or whatever)...

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     JOHN REIHER I think before I, as a military commander, would field a laser weapon, I would want to know if the laser was capable of delivering 1100 joules at about 100m. That's the yield of a 7.62 round fired from a standard military assault rifle. 100 meters is the iron site engagement range for most military assault rifles.
     Now, if you're assuming that you're barrel sighting with a laser weapon, (And why not? You make your laser weapon the same as a SLR camera.), you'd have a greater range, but as person who used to shoot targets with a scope, it takes longer to sight in your target the farther away they are. So, I'd stay with the 100m range. That means for me to switch over to laser rifles, I'd have to be assured of two things: Rate of fire down range is at least the same, and the accuracy is comparable.
     If I can only get one of those, then it's worthless. A FN-SCAR has a ROF of 3 a second for a 3 round burst. So, if your laser assault rifle has a ROF of 1 a second, it's worthless for me. But you say, "But the accuracy is much better!"
     Yeah, but that's only important if every soldier is a crack marksman. But they are not. They jerk, they twitch, and at 200m, they'll miss their target. But a soldier with an ballistic assault rifle will get off a 3 round burst and one of those bullets have a good chance of hitting.
     Now, I'd use a laser rifle for snipers. There it will excel. No drop-off, no worrying about wind, and it delivers most of its energy on target. And it's absolutely silent. That's where I'd employ laser weapons.

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     BRIAN RENNINGER Probably want to add a third parameter — some measure of divergence. So, energy/release time/divergence. Similar to a shot gun: shot size or type/dram equivalent of powder/and choke setting. Though, divergence, like choke, may be an adjustable setting.

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     JOHN REIHER 30kj is about 3 Wetherby elephant rounds, .460 cal. Not bad. But, as Brian points out, what's the divergence on your pulse rifle at 100m? 200m? Would a light fog complete defeat your weapon? A mylar shield? The uniform is designed to reflect infrared light?

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     ISAAC KUO I really don't think miitary users would care about beam energy — simply doesn't matter. There are too many other variables when it comes to actual effectiveness — which is what matters. What's the practical range? What sorts of targets are it effective against? That's what matters.
     As for an energy rating, there actually is a place where that number is useful, but it's on the other end of the equation — energy consumption. Today, we already give battery ratings in terms of how much energy they store. This gives us a useful standard for feeling how much battery life we've got.
     Energy consumption tells you how many shots your battery is worth. To put it mildly, your amount of "ammunition" is kind of a big deal to know.
     So, if you've got a pulsed laser rifle "in the 40 watt range", it's going to be talking about 40 watt consumption rather than 40 watt beam power.

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     JOHN REIHER It's much like most modern assault weapons have fully automatic ROF that is a useless metric. The FN-SCAR has a FA ROF of 300 rounds a minute. With a 30 round magazine, that's only 5 seconds of wasting ammo.
     And that's the first thing you're taught in the military. "See that 'auto' setting? Never use it." You're trained to fire in bursts for a couple of reasons. A well placed 3rnd burst will have a good chance of hitting a target. Second, if you're standing there for 5 seconds spraying and praying, the sharpshooter on the other side can target you and take you out.

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     TODD ZIRCHER Yeah, the Terminator already set the stage. From a marketing perspective, what would be the watts delivered with a single trigger pull ala what does a .45 deliver with a single round. Not sure what the numbers would look like but that is how I would SELL a zap gun.
     So a Campbell 45 would deliver 45 watts and things like ammo capacity, rate of fire, alternate firing modes, beam diameter and spread would all be on the text after you got the reader's attention.
     "(ed note: if my slide rule is not lying to me, 1000 pulses at 5 microseconds per pulse will take 0.005 seconds. 1000 joules in 0.005 seconds is equivalent to 200 kilowatts)"
     Okay, that's a Campbell 200k then. Maybe the Terminator dropped the 'k' like all the cool kids do.

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     MATT WILSON I think Isaac is on the right track. The military will call it whatever version number it is (M4, M9, M16), and the consumer model will have either a neato descriptive name like the Wilson Lasers "Sharknado" personal defense face pulverizer or a more serious model number (Walther P99, Glock 17, etc). They'll do focus groups for the names and test for arousal. "Hmm when we said Sharknado the ambient room temp went up 2 degrees, looks like we have a winner."
     In terms of describing destructive power, I bet there will be a shorthand, or common outputs, because human beings are lazy af. Maybe there will be thread wars similar to 9mm vs. 45 about which combo is best. "Laserstatic shock, you morons! Beam aperture matters!"
     And of course the brochures will tell you that the lens on the Sharknado is coated with Focusbrite^tm for a 14% greater zapification, and there will be one of those comparison charts that show you how the Sharknado has all these extra features you won't find in other laser pistols, like rubberized grip and fresh pine scent.

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     JOHN REIHER The Zzzapmatic 3000! Capable of delivering eleven hundred joules a second on target! 23 angstrom focusing reticle and inline targeting system! Only 23,099 CR! Get yours now!

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     LUKE CAMPBELL In my Vergeworlds setting, that looks like it is in the Sòng family of weapons, fitting into the "heavy laser pistol" category. So call it the Sòng XL-P 238 "Durendal", in the standard 3-1.5 configuration (here, Sòng is the manufacturer, XL-P 238 is the model number, Durendal is what everyone calls it, and 3-1.5 designates a 3 cm aperture and a 1.5 kJ beam pulse. As everyone else is saying, there's a lot more detail that goes into a full description of the weapon's utility — beam duration, beam quality, firing latency, beam stabilization algorithms, durability, heat rejection, solenoid power storage, etcetera. But then, Colt .45 just tells you the projectile diameter, not its muzzle velocity, projectile length, projectile mass, action (single action revolver, unless you are talking about the Colt M1911 automatic pistol, which fires a different .45 caliber cartridge), ammunition capacity, weight, rifling twist, ergonomics, reliability, or the duration of the waiting period in the state you buy it in. And if you try to put the .45 ACP bullets for your Colt M1911 into your Colt Single Action Army revolver (the classic Colt .45 of the old west) you'll be in for a nasty shock).

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     PETER KISNER 3.2 kilo Joule?
     Nah, man! Joules are that New World Order SI crap. Here in America we arm ourselves with the Campbell .76 μt (that's pronounced you-tee).
     The ol' Campbell 76!
     That's 760 nano-tons of TNT to protect your home and property in the hard fighting, freedom loving spirit of 1776. (well, 760 micro-tons of TNT, actually, but the idea is the important thing)

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     JUAN OCHOA U niversal L aser W eapon P rofile a la Traveller?

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     JOHN REIHER So, those weapons can be had for a... Sòng?

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     LUKE CAMPBELL John Reiher, hah! Yeah. I remember thinking of the same pun when daydreaming about the really cute girl in my Judo class with the last name of Sòng. I totally didn't name one of the major electronics manufacturers in the Verge after her.
     Isaac Kuo, energy might not matter to the military grunt schlepping around one of these things, but bullet diameter probably doesn't either — and they still call cartridges things like 7.62mm NATO and 5.56mm NATO and such.
     In my Vergeworlds setting, an energy storage solenoid can store such a ridiculous amount of energy that ammunition capacity is not that much of a worry for lasers (typically, you would expect about 1000 shots per charge, and due to issues with dissipating the heat most lasers only shoot semi-automatic. So you are not likely to run out of energy during a firefight).

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     JOHN REIHER So, what happens if someone manages to peg that solenoid with a more or less full charge?

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     LUKE CAMPBELL John Reiher, at least it would be quick. If it is any consolation, if the pulse was a few centimeters off and drilled you through the torso instead you would be just as dead.
     It also helps that by their nature, the solenoids are very well armored. They need to withstand the field-current interaction that is constantly trying to burst them open. The current-carrying superconductor is actually just a fairly thin layer lining the empty central torroid where the field is contained. Everything else is a super-tough, super-strong backing of carbon nano-stuff that compresses the solenoid and keeps its insides on the inside. And of course engineers build in a satisfactory safety tolerance. So by the very nature of the way they work, solenoids can withstand quite a bit of abuse.
     But probably not a full powered pulse from a laser weapon.

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     TOBIAS KLAUSMANN (BLACKBIRD) It's a laser, which today are put into classes that designate how dangerous they are to retinas, essentially.
     So it'd be a Campbell class 5 (or whatever, the class system would need to be made up going from LTL all the way to "melts people in 5µs" or whatever the pinnacle of photon delivery is).
     Note that even today, people don't say, for example "Glock .45", but rather "A Glock in .45", possibly adding if it's a full-frame pistol. The "Colt .45" works mostly because without further qualifiers, everybody assumes something 1911-patterned.
     With rifles, the variations are much wider, including barrel length, bullpup vs. traditional, control style (even though Ar15 is everywhere, it's not everything), and of course ammo: there are a lot more rifle cartridges (not just calibers!) that have sizable market share than there are handgun calibers in common use (basically, it's .45, 9x19 and .40S&W plus a few revolver cartridges and oddballs like 5.7x28).
     If you want to go the cartridge route for lasers, people would classify the weapons by their laser module and possibly wattage. From a narrative point of view, this gives variation for use cases: not all modules would be good for high-energy pulse fire, or would suck at sustained use (cooling etc).

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     ISAAC KUO Luke Campbell, okay, but if we're assuming plausible near future technologies, the number of shots available from a lithium-ion battery is likely going to be in the single to double digits.

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     BENJAMIN BAUGH Many gun names are abbreviations for some of its features or for terms of art used in its branding. Like in a H&K VP70 the VP stands for "Volkspistole" — people's pistol.
     So here, this might be a Campbell J32-P (Called Little Campy by fans) — a Campbell Arms 3.2J Pulsed weapon, series J.

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     MICHAEL EARL The caliber designation we tend to use for firearms don't just tell you how much damage they do (although they do do that), it tells you what you need to reload it. I suspect portable laser weapons would be labelled by the output specification of the swappable power pack ("Campbell 30 Amp" or, yes, "plasma rifle in the 40 watt range") or maybe by the required external cooling for a man-portable crew served weapon equivalent to our current medium machine guns ("Campbell 10/15" for a heavy laser rifle requiring a cooling system that can dissipate 10Kw at 1500 Kelvin).

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     STEPHEN WHITEHEAD You need a letter and a number. The letter has some relation to what it is or does, so it could be P for "pulsed laser". The number is non-specific but probably has some connection with a physical property, at least initially. It can be incremented arbitrarily for improved models, with a letter suffix for the major tweaks. It wants to be fairly short and snappy — decimal points or zeroes best avoided especially for military use. So I think this is a Campbell P32.

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     JOHN POWELL Different manufacturers will have different naming conventions and a popular or novel weapon with an awkward designation will gain a nickname. A really popular brand may become a generic term for the class of weapon. “Blaster” could have been a manufacturer’s brand for hand held energy weapons.

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     JOHN REIHER Hmm, "Blaster" might be considered to "kitschy". But then some marketing droid comes up with "Blazer" which keeps the blaster esthetic, but makes it sound more like a laser.

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     JOHN POWELL Pictured in the original post is the classic iGun Sierra 3. Love the retro Late 20th Century look!

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ISAAC KUO Luke Campbell: "Energy might not matter to the military grunt schlepping around one of these things, but bullet diameter probably doesn't either — and they still call cartridges things like 7.62mm NATO and 5.56mm NATO and such."     Reading this more carefully...it did indeed matter. Remember, earlier military guns were muzzle loaders. So, bullet diameter alone determined what ammunition would fit in your musket/pistol/rifle.
     As cartridge ammunition was developed, cartridges were originally loaded in a way that legacy bullets would still be used when wrapped up into cartridges.
     Preloaded cartridges used diameter to describe them because that's what was already used.
     With modern cartridges, diameter is no longer entirely adequate. We've resorted to slightly lying about diameter in order to distinguish incompatibly shaped cartridges which happen to use the same diameter bullets (.357 Magnum vs .38 special for example). It's easier to develop new cartridges that use the same bullets and rifling diameters as already standard.
     The point is, it's not an illogical decision — it's something that was logical at the time.
     So, we need to think about the legacy of how things got to where they are at the time of the setting.
     With current technology, we have numerous incompatible lithium-ion battery packs for power tools. Are these the sorts of things that would be used for laser weapons?
     I'm guessing not. We may need huge backpacks for anything useful. In that case, a standard power cord connector might be what's relevant rather than a battery form factor that fits within a laser weapon itself...

---

     ROB CONLEY My day job is writing and maintaining software for the metal cutting machines my company manufactures. In the US but we say 1 1/4 inches and generally use inches for human scale measurements. The rest of the world use mils for millimeters.
     So I would call it the Campbell 60 mil. And note regardless of the name the technical reference will be using millimeters not centimeters.
     "The aperture is a 60 mil window protecting a 60 mill lens."

---

     JOHN REIHER Isaac Kuo, exactly, though the military would put a stop to multiple different connectors and power controllers. They would force an industry standard for power supplies so that the armorer doesn't have to stock 20 different power supplies and connectors for them.
     But milspec systems might get restricted to the military and the civilian market might have unique systems with controllers that only work with specific model lasers. Much like the printer ink market, after market or "generic" power systems would be available but would violate the warranty on your Camp0-32.
     And as man spreads out in system and in other star systems, local manufacturers might "adapt" big market systems for their homegrown weapons. So a Ceres Chungster 0-36 might use the same system used by the Campbell line of lasers, just with some minor modifications. Can you use a Chungster power supply on your Campy? Maybe... possibly...

---

     RAYMOND McVAY The Campbell Aught-three Peacekeeper

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     KERR Well, we could use some regime of energies and average power output to roughly define the weapon. Similar to how you would differentiate a carbine and an SMG. The aperture size describes the physical "bore" of the laser and can be related to range and to some degree also damage. As for the ammunition, I think we can assume that those devices have some sort of integrated capacitor which feds into a quasi-CW laser that pumps the Q-switched cavities. So you could use an appropriately powerful battery as long as it fits (doesn't mean you would survive a fight by plugging your li-ion battery into the laser pistol).
     Cam-bell .30 ?

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     ROB GARITTA I suggest the brand followed by mm dash output (kJ!). Like thirty aught six names and he diameter an the year of introduction only this tells you enough to stat it for a game. Ex: Campbell 30-3.5 thirty three point five or just thirty three five. As opposed to thirty five (a heavy weapon by output).

---

     MICHAEL EARL Ship-mounted weapons are of course a different animal, but for what it's worth: in the (relatively hard) 'Children of a Dead Earth' video game, laser designs being discussed are generally referred to by designer and power input requirement ("Apophis 100Mw", "jt Gigawatt"), or if you're really getting into the nitty gritty, by the diameter of beam and distance at the point where the laser intensity drops below a specific threshold:
     "What's the spot size on that JT one gigawatt anyway?"
     "6 meters at 3.5 Megameters."
     "!@#$. How many railgun drones are our carriers packing these days, exactly?"

(If you have droplets of water/ oil / mud on the lens and your first pulse hits it could the resulting steam eventually degrade the lens?)

An interesting question. For the parameters I assumed for these devices, a single shot is about 5 kJ in 0.5 milliseconds, or 10 MW of power time averaged over the pulse. At the lens it is spread out over a 6 cm diameter spot (since the lens is 6 cm in diameter). Since 100 J distributed over a 6 cm spot is not likely to give an impulsive shock wave, I'll treat this as if a 10 MW beam was incident on the lens debris.

I turn to the calculator and look at what 10 MW in 6 cm will do to granite — assume a piece of dust is equivalent to a tiny granite fleck. I find that the vapor pressure is 242 kPa — a bit less than two and a half atmospheres. This is much less than the structural strength of any reasonable lens material, so the evaporating dust fleck will not blast a hole in the lens (material strength of strong refractory materials are measured in tens of GPa or more — hundreds of thousands or millions of atmospheres). The temperature is 2584 K. This will burn unprotected diamond, so we will have to assume that the surface of the lens is not diamond. Zirconia has a melting point of 2986 K, so we can make a thin film covering out of that, with diamond underneath (diamond has excellent thermal conductivity and transparency). Silicon carbide is another possibility for a lens coating. In the half a millisecond of laser irradiation, the dust will evaporate to a depth of 0.06 mm.

So what looks like will happen to a bit of dust on the lens is that a thin layer of the dust will be heated to vapor. The vapor will expand, acting like a rocket to launch the dust off the lens. With a proper selection of materials, the lens will be undamaged.

Repeating the calculation with perfectly absorbing water (a model for mud), I find a pressure of about 6 atmospheres (615 kPa), a temperature of 433 K (a bit over boiling), and vaporization to a depth of 0.6 mm. This comes nowhere near harming the lens, and blasts the water off the lens with a puff of steam. In practice, the water is likely to be mostly transparent, and might boil throughout its volume or even transmit the beam without significant heating for very pure water rather than having a bottom layer evaporating.

Oops — SiC also burns when it gets too hot. It looks like zirconia will need to be the lens coating material.

Or rather than zirconia, cubic boron nitride could be used as a coating, since it is just about as hard as diamond, has extraordinary chemical stability, thermal conductivity, and thermal stability. Maybe you could make the entire lens out of cubic boron nitride rather than diamond.

(ed note: in 2015 somebody asked Luke Campbell how far in the future such laser sidearms are.)

My best guess about the time span for pulsed lasers is maybe about thirty years, plus or minus fifty.

This would be for ship-board and vehicular weapons. Getting a laser into a rifle-sized package sounds like a much more challenging task.

Although over the last several decades laser power levels have been advancing faster than Moore's law, so who knows? Admittedly, that's for instantaneous power rather than time average power. And you would need to put a few kilojoules into a pulse train about a microsecond long, with individual pulses of tens of joules energy and nanoseconds duration. Modern pulse lasers that fit on a tabletop (as opposed to an ICF facility) are doing really good if they reach millijoules (1/1000^th of a joule) in a nanosecond, in a package much larger than a rifle, so they've got a long ways to go.)

(ed note: in 2017 somebody asked me if the ejecta from a laser wound would appreciably thrust or tumble a target who was in free fall. I asked Dr. Campbell. TL;DR: nope.)

Luke Campbell

I'll work this out when I get a chance to go over my high energy laser absorption code. It should calculate the speed and mass of the ejecta as part of the intermediate calculations. I'll just have it print that out.

Incidentally, I find the lasers tend to work better with about 100 pulses than 1000.

The conceptual weapon fires over a one millisecond time period. That's roughly the period of oscillation of impulsive cavities in flesh (but a bit shorter, the cavities tend to collapse and oscillate with a period of several milliseconds), so a one millisecond beam could drill through a person without having the beam interrupted by the cavity produced by the violent vapor expansion collapsing back.

This one millisecond pulse is broken up into a number (about 100 or 1000) of individual "micropulses", each on the order of a nanosecond duration.

(Dr. Campbell returns from his calculations)

The easy one first. If you take a 1 MW beam and focus it to a 1 mm wide spot on a person for 1 millisecond, it is just about as effective at blasting out a hole on them as if you break the beam up into hundreds of nanosecond pulses (the armor penetration will not be as good, but still better than a bullet). My calculator tells us that the pressure of the laser-irradiated spot is 224 MPa. With a 1 mm diameter spot, this means the force is 176 Newtons. The beam lasts for 1 ms, but the hole it drills in meat is 71 cm deep — and most people are not that thick. Since you have constant drilling speed, and a typical cross section across the human body is 25 cm, you will be getting that force over about 1/3 of a millisecond. This gives an impulse of 0.06 N s. A 75 kg human would be sent moving at the blistering speed of 0.08 mm/s (about 2 minutes to move one centimeter). If you shot someone at a distance of 1 meter from their center of mass and were drilling the hole more-or-less perpendicular to the vector from their center of mass to the point of incidence, and assuming we can calculate the moment of inertia as if the person were a uniform rigid rod 1.6 meters long (for I = 16 kg m²), the target would be set rotating at a speed of about 0.004 radians per second (or about 1500 seconds for a full revolution). (so it would take 25 minutes for a full revolution. This is about twice as fast as the minute-hand on an analog clock for those of you old enough to have seen a non-digital clock)

Now consider breaking that 1 MW, 1 ms pulse up into 100 pulses of 1 ns duration and 10 J each, separated by 10 microseconds (for the same total pulse duration and beam energy). The pressure in the irradiated spot is 228 GPa so the force is 180 kN. Over 1 ns, that's an impulse of about 1.8×10^-4 N s. It will take about 20 of these pulses to blast through your target, so the total momentum transferred is 0.0036 N s. So you would get roughly 1/15th the impulse, 1/15th the change in speed (0.005 mm/s, 33 minutes to move 1 cm), and 1/15th the rotation (2.7×10^-4 radians per second, 22,500 seconds or 6.25 hours for a full revolution) as from a single pulse.

I suspect that the splatter of blood and guts will deliver significantly more momentum to your poor target than the evaporate, but that's well beyond the level of simple calculations.

---

Luke Miller

As you drill deeper, would you have less evaporate as more energy is transfered into surrounding tissues?

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Luke Campbell

To some extent. Laser drilled holes tend to be limited to aspect ratios of 1:20 to 1:30 or less. In metal, the surface of the drill-hole tapers inward. This intercepts more and more of the beam. The losses are not as bad as it might seem at first, because the sides are still somewhat reflective and form a wave guide that funnels the beam to the end of the hole. Still, too deep of a hole can interfere with drilling even deeper.

In meat, it is not quite as clear what's going on. For obvious reasons, this is not something people nowadays have a lot of experience with. You have the evaporation of the meat producing a high vapor pressure, which expands out the surrounding meat to produce a big hole or cavity. The laser beam is much narrower than the cavity, so it might be able to just sail through and hit the back wall, producing even more high pressure vapor to dig out and deepen the cavity. Experiments might reveal complications to this model — if anyone wants to fund me to buy a megawatt laser and drill holes in slabs of meat, I'm listening.

Any interesting battery material for a laser gun would be more usefully deployed as an explosive warhead.

I make a point of noting — although mine are superconducting batteries — that the distinction between "battery" and "grenade" is essentially disabling the safety circuits that stop it from discharging Much Too Fast and causing a sudden, catastrophic, energy-dumping quench. But nevertheless, energy storage with that sort of energy density is just too useful not to use — so a lot of work has gone into very good, no-fail safety circuits.

(In ISS agent and special forces training, of course, they teach you how do to exactly this: Explosive Overclocking)

That said, they don't worry about it much for military applications, either, because you have to be a very good, very cocky sniper with an amazingly good gun to successfully hit a target that small in just the right way to break through the deliberately-hardened-against-this-scenario shell and fracture the loops.

Strength in other divisions at Samsung helped offset the financial hit the company took in the third quarter as a result of its unprecedented Galaxy Note 7 recall. But if a new claim pans out and a “safe” Note 7 issued as a replacement did in fact catch fire aboard an airplane earlier this week, Samsung’s initial recall might just be the beginning.

As we know all too well at this point, a major manufacturing defect has completely spoiled Samsung’s Galaxy Note 7 launch over the past two months. The issue, which is believed to only have affected a small number of Note 7 devices, can cause the phone’s battery to overheat and explode. So far, Note 7 fires have injured people, destroyed cars and even burnt down one family’s house. Now, it’s time to get up-close and personal with an exploding Note 7 to see exactly what it looks like when Samsung’s flagship phablet explodes.

In a safe and controlled lab environment, the researchers applied pressure to the Galaxy Note 7’s battery. They continued to apply an increasing amount of pressure until finally, the phone burst into flames. While the test doesn’t simulate the exact conditions under which a defective Note 7 might combust, the result is the same: Smoke, then a huge ball of fire, then the charred remains of a one-beautiful smartphone.

Photos of the lab’s test, which were posted by The Telegraph, follow below. First, the phone begins to smoke:

• 

Where there’s smoke, there’s fire…

• 

Lots of fire…

• 

And finally, the charred remains:

• 

Again, this test was performed in a lab and outside pressure was applied to the battery. But unfortunately, this is also what happens when a defective Note 7 explodes on its own, and that’s why we recommend that no one should purchase a Galaxy Note 7 right now under any circumstances.

MATTERBEAM:

     Luke Campbell, Hi!
     I and some others were wondering on the ToughSF discord: What is the peak output of the 'blaster' designs you created a few years ago?
     You mention that the battle laser design produces '50 pulses of 200J spaced by 10 microseconds'. We guessed that Q-switching allowed for very high peak output, but we could not find details on the pulse duration.
     The reason why is because if the pulses were nanoseconds in length, like suggested by your RPG page, the peak output works out to gigawatts of power — we don't know of any energy storage system could deliver this in handheld devices, let alone handle it without superconductors.

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LUKE CAMPBELL

     The intended pulse duration would be between 1 and 10 nanoseconds in length — the exact amount probably isn't all that important for the terminal effects, at that energy and duration you will get much of the pulse energy in the form of a blast. The advantage to slightly longer pulse lengths is to avoid atmospheric self-focusing.
     And yes, the peak power will be on the order of gigawatts. You don't need to supply gigawatt pulses of electricity, however. A few megawatts can serve to energize the lasing medium, storing up energy in the excited states of the material to be released in a nanosecond pulse when the lasing cavity is made resonating via the Q-switch mechanism.

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OMG its WTF

     Hello! I am a content manager on MatterBeam's discord and I started the conversation because of the laser weapons ideas I occasionally mention. A XM-25 sized laser blaster using 20J pulses with a length of 10 nanoseconds was the reason. I thought the power of the lasing medium is equal to the pulse energy times the time between each pulse. For example one pulse every 40 microseconds leds to a pumping power of 500kW, is this the correct way to calculate it? Also I am interested how the lens/focusing mirror avoids LDT at those powers?

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LUKE CAMPBELL

     There are two power levels you need to worry about, the time averaged power and the instantaneous power.

     The TIME AVERAGE POWER is the total length of the pulse train. For example, if you have a 1 millisecond long pulse train (consisting of, say, 100 pulses each separated by 10 microseconds), and each pulse has 10 joules, then the total pulse train energy is 1 kilojoule and the time averaged power is 1 kilojoule / 1 millisecond = 1 megawatt. This is the power than needs to be provided by your power supply, such as a capacitor or inductor (in addition to any inefficiencies in the system — if the laser is 50% efficient at turning electricity into light, then the power supply will need to provide 2 megawatts). The power supply provides this energy constantly over the millisecond of the pulse train — the lasing medium being energized up to its capacity over 10 microseconds and then emitting a 10 joule pulse, over and over for 100 times.

     The PEAK POWER, or INSTANTANEOUS POWER will be the energy per pulse divided by the pulse duration. So if each of those 10 joule pulses last 10 nanoseconds, the peak power is 10 joules / 10 nanoseconds = 1 gigawatt. (This is a bit of a simplification, since the pulse time profile is unlikely to be square, so the maximum peak energy is going to be somewhat bigger, but it gives an idea of the order of magnitude of the power.)

     The way to make the optics work is to use highly robust materials for your optics with very little absorption, and to spread the pulse out over a large area on your optics. Dielectric layer mirrors, for example, are on the order of 99.999% reflective, so a GW pulse with a total energy of 10 J will only have something like 10 kW and 100 uJ absorbed by the optics. If your optical focusing lens is, say, 5 cm across (for a total area of roughly 20 cm^2), it will be exposed to a thermal flux of 500 W/cm^2 and a thermal fluence of 5 uJ/cm^2. This is within the published limits for dielectric layer mirrors, although pushing close to the limits in terms of flux (typically a few tens of uJ/cm^2 and several tens to hundreds of W/cm^2).

(ed note: spread pulse out over larger area of optics so there are more square mm of lens or mirror surface. This means each square mm has to deal with a smaller fraction of the total laser energy. All the energy is eventually focused down to a tiny dot on the hapless target. This means the laser muzzle will be somewhat large, 5 cm diameter in the example.)

     If you are using a lens, use similar methods — a wide area lens made of a highly transparent highly refractory high bandgap material with high thermal conductivity (diamond, for example, would be ideal) would be able to handle the heat load.

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OMG its WTF

     20J * 10μs = 2MW
     20J * 100 = 2kJ
     2kJ * 1ms = 2MW
Alright thank you.

     Do you think that using a small phased array makes sense? A 40mm wide lens emitting at 450nm requires 800 emitters to produce a steering angle of 1 mrad. Resulting in a steering distance of 1cm/10m. Vibrations from the user and the cooling system could throw the beam off the drilling spot and thereby decrease penetration. Or at least how I'd imagine it.

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Luke Campbell

     A phased array certainly makes sense — if you have the tech for it. The ability to flick the beam well off-axis would be nice for any automatic targeting system.

     But if all you want is to suppress vibrations — we can do that already like we do with high end autostabilized cameras. You just need a moveable mirror in the beam path, with a fast response and feedback to adjust its tilt so as to counteract the jitter in the device. You will probably also want a deformable mirror in the beam path, in order to pre-focus the beam so that the fluctuations in atmospheric density that normally defocus the beam just act to refocus the beam to the diffraction limited spot at the target. This is called adaptive optics, and is used on modern astronomy telescopes and laser weapons. But it can also be done just using a phased array.

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OMG its WTF

     You also mentioned that the exact length of the pulse duration isn't so important, could you explain why? Shorter pulses result in higher intensities and vapor pressures, increasing kinetic damage of the laser beams. Which can be 4x as penetrative than ideal case continuous wave beams.

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Luke Campbell

     Once you get to nanosecond-scale beams, the beam is over before the material can repond to the additional energy just dumped into it. Before the material even has time to deform, all the energy of the beam is absorbed (or partially reflected) to create a thin layer of plasma at the surface. So the net result is that whether your beam is 1 ns or 10 ns long, you end up with the same physical condition — a layer of plasma of the same dimensions with the same energy. As this plasma explosively expands, it will gouge out the same sized crater.

     But there are other effects where the pulse length does matter. If you exceed a threshold power level, you can initiate catastrophic self-focusing where the beam's interactions with air (via the optical Kerr effect ) will result in the beam converging well before it is supposed to, possibly causing filamentation.
     In addition, lower power levels can also keep the beam below the critical power threshold for your optical elements in the beam, preventing damage to your lenses and mirrors.

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OMG its WTF

     My worries regarding movement are not only from the laser weapon itself, but also from a moving target. A lateral movement of 5km/h could throw off the beam spot so much that penetration is cut in half or worse.
     Interesting, although this image seems to imply that pico/femtosecond pulses create major shockwaves in the target material.

• 

     So where should I put my benchmark when creating a pulsed laser weapon? Your calculator indicates that ideal pulse length scales of intensity, with vapor pressures exceeding the cavity strength by over 200% being a mark of near ideal pulse length. And if that is true, would variable pulse length be possible by utilizing something like a "dynamic" q-switch?

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LUKE CAMPBELL

     I figured that laser weaponry would get a fix on the rate of lateral displacement of whatever they were aimed at at the moment of firing. Then the autostabilization mechanism would instead track the target for the millisecond or so duration of the target. This would keep the beam focused on the same spot.
     Pico- and femtosecond duration laser pulses are weird. During the time of laser irradiation, they heat up only the electrons of the material, leading to a situation where the target material has two different temperatures - one for the electron system and one for the ions in the lattice. It is only after the laser is done that the hot electrons come into thermal equilibrium with the rest of the material. This tends to lead to very "clean" craters, with less roughness than from nanosecond pulses.Using picosecond or shorter pulses for weapons would be problematic — when each pulse has on the order of a joule of energy or more, the instantaneous power level would be so high it would be hard to avoid damaging the optics or producing a self-focused filamented beam (the later effect may or may not be bad — it would let you overcome depth of focus limitations, but would give away your position, would likely have less control over the beam propagation, and could significantly decrease the range).
     The duration of the pulse train should be around a millisecond or a few — much shorter than this and the tissue of the human body does not have time to respond and all you get is a shallow surface crater. For the individual pulses, around a nanosecond is probably the best compromise for putting enough power on the target but not so much power that you damage your weapon or have unwanted interactions with the air.

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OMG its WTF

     I think we have the same communications problem again regarding pulses and pulsetrains, I am talking about the individual pulses not the pulse train as a whole. My question is if ideal laser pulse length depends on a certain "intensity threshold"

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LUKE CAMPBELL

     For the individual pulses, I suspect that for pulse energies of several joules to several tens of joules, you will want nanosecond scale durations (for the reasons I outlined above) This will put you well above the threshold intensity for flashing a thin layer of the surface to plasma, having the plasma absorb the beam and become highly energized, and then having the energized plasma explode to create a crater.

“We know where we stand, then.” She popped the charge pack out of her weapon, placed it in sunlight. “That might pick up enough power for one or two shots before dark. Give me yours.”

AnyKaat’s weapon had power enough for three more shots. Just enough. “Somebody comes along, you don’t act like that won’t work. Point it at them and make them get down on their belly. Then stick them with this.” She gave AnyKaat the longest blade she had collected. “Don’t hesitate. We got no friends around here.”

And you'll need some serious cooling. I'd go with liquid-metal microchannel heat pipes etched into all the hot surfaces, and leading to cooling fins around the "barrel". If you use the chemical-propellant option, regenerative cooling could also work.

en note: "regenerative cooling" is where the cold liquid chemical fuel is used as coolant for the reaction chamber, right before it is fed into the chamber to be burnt for power.

I recently asked this question to master game designer, and all around great human being Ken Burnside, who is creative director of Ad Astra Games:

Ken Burnside: "You'll also have the not-so-trivial task of not cooking the hands of the person using the weapon."

"When you fire a bullet from a rifle, about 80% of the chemical energy imparted to the projectile sends it downrange. The remaining 20% is waste heat, ejected in the form of hot brass. The waste heat rejection issue is also why caseless ammo never really took off. In round numbers, a typical .223 (5.56mm) round delivers (975²) * 0.0035 kgm/sec energy or about 3.3 kilojoules of energy to the target. It's dumping about .05 kilojoules in waste heat and hot gasses."

"Right now, lasers are about 7-15% efficient. For the sake of numbers, we'll call it 12.5%. That means that for every kilojoule you're delivering to the target, you'll need to get rid of 7 kilojoules of waste heat. Very roughly, cooking a 9oz New York Strip steak to medium-rare is about one kilojoule."

• 

With penetration, range, and repeatability dealt with, it is time to turn to accuracy. Lack of recoil, automatic fire capability, and line-of-sight accuracy are all major assets here, but there is one more improvement to be made. Both lasers and particle beams can be steered at least a degree or two off-axis, in the case of the laser via the adaptive-optic mirror, for particle beams with a transverse magnetic field at the muzzle.

If we can throw in a chip-mounted laser or acoustic gyro set, we can have a gyrostabilized handgun. The weapon shoots not at where the gun is pointed at the instant of firing, but at a weighted average of where it has been pointing over the past quarter of a second or so. Smoothes out a lot of the jitter inherent in human marksmanship.

You'd probably want to integrate this feature with the weapon's sights. A reflex-type optical sight could have an LED display linked to the gyrostabilizer, rather than a fixed reticule. The dot, or crosshairs, would then indicate the actual shot path and would remain similarly stable under jitter.

(ed note: "Reflex" in this context refers to the viewfinder on a reflex camera. A mirror allows the viewfinder to use the actual camera's optics. The user literally sees the exact image which will be captured on film. When the shutter is tripped, the mirror moves out of the way and allows the image to fall on the film. So in Dr. Schilling's concept, the shooter would aim through the laser pistol's optics, the same optics that will direct the weapon's beam.)

Another interesting thing is that you could use the beam optics for your scope. Just install a switchable mirror that flashes reflective for the millisecond the beam is on, and you could then direct the light from your target that comes into your weapon's optics straight into an eyepiece. You could see exactly where the beam would strike without having to make any allowances for parallax or beam deflection (since the incoming light would be deflected along exactly the same path as the outgoing beam). Thus, no separate lens for a scope, sitting on top of the gun.

While using the laser's optics as a scope is pretty clever, a quicker type of sight will be needed for close in shots. Iron sights or some type of collimating sight (e.g. red dot sight, holographic sight) strapped to the top will do well.

Another clever one would be to use the laser's optics to project a laser sight. Pull the trigger, and the harmless red dot suddenly explodes. BANG!

(ed note: this will be even more accurate than a laser dot sight for a conventional slugthrower firearm. Laser dot is guaranteed to be parallel to laser weapon beam since it is using the exact same optics. Unlike bullets, weapon laser beams are not subject to bullet drop and windage. Target mobility while the bullet travels is also not a factor since the target is unlikely to be moving at a high fraction of the speed of light. The weapon laser beam will hit exactly where the red dot is resting.)

Using the laser optics as a scope would be more useful for long range or high accuracy shots.

In combat, I would expect such a weapon to be used in automatic fire mode at ~10 Hz. With fifty to a hundred pulses to play with, you won't run out of ammunition too soon as is the case with current machine pistols. And recoilless, stabilized automatic fire should allow a moderately capable marksman to walk a burst on target in one or two reaction cycles (say, half a second) in most circumstances. Imperial Stormtroopers ^(tm) could no doubt still find a way to miss with such a weapon at ten meters, but not competent soldiers. Practical combat range, if you don't mind missing a good part of the time, would be on the order of 50 meters

As a point of detail: see that blue water line? That shows wavelengths to not use, because it means atmospheric water vapor is opaque at those wavelengths. Also, light that is transmitted through flesh or is scattered internally will still typically wind up being absorbed in the end.

Once you have a reasonably deep hole (fairly high aspect ratio) absorption will be essentially 100% regardless of wavelength — light that is scattered or reflected will often not bounce straight out of the hole, giving it a chance to be absorbed by the sides of the hole. This won't help with penetration, but will make the hole bigger.

In the past, I have advocated for using "cyan" (bluish-green) lasers for orbital bombardment of Earth, mainly because of graphs like this:

• 

This image basically plots how much light of a given frequency reaches the ground. E.g. 1m-wavelength radio waves aren't absorbed at all, visible light is absorbed a little bit, and 10nm UV is completely absorbed. We want a frequency that is not absorbed very much, and as high as possible so that we don't suffer diffraction losses.

Cyan is a sweet spot in this image: it's the furthest-left trough (i.e., highest-frequency, and therefore lowest-diffraction, band that doesn't get outright absorbed), and it's the bottom of that trough (i.e., the least-absorbed within that band).

Well, lately I got flustered with this graph for being too coarse. This graph looks like a cartoon sketch! I went looking for a better source and, well, it turns out not to exist. I mean, I can find tons of graphs that look like this, but none that have reasonable resolution (and preferably, data, so that I could reproduce it myself).

In-fact, the only detailed data that people seem to have even collected is in certain frequency ranges, notably the IR bands (ref. HITRAN, GEISA, etc. datasets, and the many projects that use them). In-particular, I played with HITRAN's buggy API for a while until I figured out they don't actually have data on the whole spectrum. However, I did find a graph:

• 

It's basically the interesting section of the previous graph (inverted since it is transmittance rather than absorbance). It goes to 150nm, shorter than which we can be fairly confident will be absorbed by the atmosphere (such are called "vacuum frequencies" for a reason. You can still get sunburned by UV, so I assume that's basically the 300nm-400nm section of the last image that's still UV, but also nonzero transmission).

Now let's consider diffraction. To first order:

(divergence half angle) = (wavelength) / (π (aperture radius))
(spot radius) = (distance) (divergence half angle)
(irradiance) = (transmittance) (laser power) / (π (spot radius)²)
(damage rate) ∝ (irradiance)
(damage rate) ∝ π (transmittance) (laser power) ( (aperture radius) / ( (distance) (wavelength) ) )²

Considering distance, aperture radius, and available power to be constants with respect to the wavelength we choose, we can see that:

(damage rate) ∝ (transmittance) / (wavelength)²

To maximize damage rate, we simply have to take that graph and divide it by the x-axis-squared. Since the data was not available, I digitized the chart using WebPlotDigitizer, copied the approximate data out, and plotted it myself. In the graph below, you can see the original data in blue, and the effect of the division in orange.

• 

The graph's peak says that a wavelength of about 400nm is optimal for orbital bombardment!

We can see that cyan (about 480nm) is close, at about 92% relative effectiveness. At least it's a better recommendation than green (which I also see bandied about: 532nm, 83% effectiveness).

400nm is pretty much the border between violet and ultraviolet, but in human perceptual terms it's not a binary cutoff. Under well-lit viewing conditions, the human eye sees best at about 555nm. At 400nm, a light source appears about 0.04% as bright—which might sound small, but the human visual system is logarithmic, and anyway a typical orbital-bombardment laser would use extremely high powers. As another reference: I've myself have 405nm lasers (expected 0.065% as bright) and they're plenty visible.

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How general is this? Technically, it applies to surface-to-orbit/orbit-to-surface bombardment at a 70° surface-to-horizon angle. The main optical variation in the atmosphere is moisture content, but it turns out that water's transmission (for liquid or vapor) is actually coincidentally near-maximum at 400nm, so if anything more moisture will make every other wavelength even worse.

One thing that doesn't generalize is firing lasers from points on the surface to other points on the surface. In the first case, the exact height of the orbit didn't matter (it's orbital bombardment; one assumes you're above nearly all the atmosphere), but here, the path length within the atmosphere varies, meaning that the amount of absorption that you suffer at a given wavelength does too.

Given a particular range, one could measure/compute a graph like the above and get the optimal wavelength. Longer ranges will absorb more, making having a higher transmission coefficient (lower absorption coefficient) more important. But, because the Beer-Lambert law is nonlinear, there's little we can say else generally about such a graph.

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Note: after the fact, I noticed that "MODTRAN", named on the source graph, is the name of a software package that computes such spectra. If it didn't cost $1800+, it'd be perfect. Of course, I could also wonder why no one hasn't just uploaded a reasonable-quality graph ever.

ABSTRACT

The US Navy is exploring the feasibility of using a high energy laser weapon as a ship-borne self-defense system against sea-skimming cruise missile attacks. Since the attenuation of laser energy by the atmosphere is the highest at low altitudes and varies with frequency, the selection of appropriate wavelengths becomes critical for a laser weapon to be effective. A high energy free electron laser (FEL) is suitable for employment in the envisaged role because it can be designed to operate at any desired frequency and, to a degree, is tunable in operation. This study aims to determine the optimal atmospheric windows for high energy, pico second, short pulse lasers.

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Suitable wavelength windows were selected from either the Jan 1 or July 1, 2004 spectra for the date with a narrower transmittance window by meeting the following two criteria:

1. Transmittance value of at least 90%, 95% and 99% respectively over a 10 km long, 10 m high horizontal path.
2. Absorption coefficient value of less than 0.02 per km.

Table 5 summarizes the suitable wavelengths. The first four bands from 0.95 μm to 2.5 μm were able to meet the criteria of at least 90% transmittance and absorption coefficient of not more than 0.02 per km. However, there are no wavelengths in the 3.45 to 4.16 μm band that can meet the two specified criteria. The best wavelength window for this band is chosen for 70% transmission and absorption coefficient less than 0.04 per km.

From Table 5, the optimal wavelength windows for molecular atmospheric absorption are between 1.03 μm and 1.06 μm, and around 1.241 and 1.624 μm. This band provides a transmittance of more than 99%. However, as noted earlier, the main drawback of operating in a lower wavelength band is the strong extinction of energy from aerosol scattering.

Table 5.

	Suitable wavelength windows for various values of T(z) in μm
Wavelength Bands	T(z) > 90% αabs < 0.01/km	T(z) > 95% αabs < 0.005/km	T(z) > 99% αabs < 0.001/km	T(z) > 70%
0.95 to 1.11 μm	0.990 - 1.075	0.992 - 0.998 1.002 - 1.006 1.01 - 1.067	1.030 - 1.060	N/A
1.11 to 1.33 μm	1.230 - 1.260 1.271 - 1.283	1.235 - 1.256	1.241	N/A
1.47 to 1.82 μm	1.530 - 1.680	1.535 - 1.565 1.58 - 1.595 1.610 - 1.660	1.624	N/A
2 to 2.5 μm	2.125 - 2.140 2.220 - 2.245	N/A	N/A	N/A
3.45 to 4.16 μm	N/A	N/A	N/A	3.91 - 3.94

Summary of suitable wavelength bands for FEL operation for a 10 km horizontal path, 10 m above the ocean with no aerosol extinction.

(ed note: 400 nm equals 0.4 μm)

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A. CONCLUSIONS

The possibility of using a laser beam as a ship-borne self-defense weapon has become more feasible with recent advancements in laser technology. The advantages of a high energy laser as a weapon are its key attributes of speed-of-light response, ability to handle fast maneuvering and crossing targets, deep magazine capacity, minimal collateral damage, target identification and adaptability for lethal to non-lethal employment. The attenuation of laser energy by the atmosphere is a result of molecular attenuation and scattering. Atmospheric scattering mainly disperses the energy of the laser beam but molecular absorption heats the atmosphere, reducing the index of refraction and thereby creating thermal blooming. The FEL has potential as a shipborne weapon system because it can be designed to operate at any desired frequency and, to a degree, is tunable in operation. The ability to select an operating frequency greatly enhances the successful propagation of the laser beam through the relatively dense air at low altitudes.

The objective of this thesis was to determine optimal operating wavelength bands for a high energy FEL weapon between 0.6 μm and 4.2 μm using the US Air Force PLEXUS Release 3 Version 2 program to set up MODTRAN 4 Version 2 and FASCODE 3 atmospheric transmission programs. Since PLEXUS and its user interface are export limited, this thesis was restricted to processing the MODTRAN and FASCODE output files. These codes allow for complex atmospheric transmittance and radiance calculations based on absorption and scattering phenomena for a variety of path geometries. The input parameters chosen for the simulation runs are meant to represent likely operational scenarios for ship self defense against a cruise missile attack. The main consideration was a 10 m altitude horizontal transmission path. Korea, Taiwan and the Persian Gulf were the three geographical areas chosen for the study. The effect of a short FEL laser pulse was modeled by convolving a normalized Gaussian frequency spectrum with the MODTRAN and FASCODE transmission and absorption coefficient spectra. The result of the convolution operation averages the transmittance values over a number of wavenumbers. The amount of averaging increases as the length of the FEL pulse decrease.

2. FASCODE Results

The higher resolution 0.1 cm^-1 FASCODE was used to conduct further analysis on five selected bands or “windows” found from the MODTRAN results. Using the FASCODE aerosol extinction output file results, absorption coefficients for each wavenumber (or spectral frequency) were calculated. The molecular absorption coefficient is a key parameter for thermal blooming calculations. Data for the absorption coefficient were also used to compute the transmission spectrum for molecular absorption only. Using the transmission spectrum and absorption coefficient graphs, the optimal wavelength bands for employment of FEL at low altitudes were identified and summarized in Table 5. The four main bands of 0.95 to 1.11 μm, 1.11 to 1.33 μm, 1.47 to 1.82 μm, and 2 to 2.5 μm contain quite a number of suitable wavelengths that allow transmittance of at least 90% for a 10 km path and have absorption coefficient values of 0.02 per km or less. For a more stringent requirement of at least 99% transmittance, the suitable wavelength windows are between 1.03 to 1.06 μm and around 1.241 and 1.624 μm. However, the main concern for laser transmission through the atmosphere in the 1 μm region is the strong aerosol extinction.

So lets take a hypothetical laser sidearm, assume a 10cm lens, 10kW output power, 1ms beam duration, and 0.5 duty cycle. Given these as constant, but varying the wavelength of the laser, we get the following penetration on a carbon target at the listed ranged:

7e-7 m (Near infrared)
Range	Penetration
25m	6.25mm
50m	0.78mm
100m	0.10mm
200m	0.01mm

5.5e-7 m (Green)
Range	Penetration
25m	12.88mm
50m	1.61mm
100m	0.20mm
200m	0.03mm

4.3e-7 m (Indigo)
Range	Penetration
25m	26.96mm
50m	3.37mm
100m	0.42mm
200m	0.05mm

3.2e-7 m (UVA)
Range	Penetration
25m	65.4mm
50m	8.18mm
100m	1.02mm
200m	0.13mm

It's obvious that as wavelength decreases, neglecting atmospheric effects, damage on the target increases. So the question is, how low can I push my wavelength, and what are the effects? If 90% of the UVA beam is scattered, then it is equivalent to the infrared beam. If only 50%, it is superior.

Seems like an important point to figure out. Does anyone have a good model? I've been digging on scholar.google.com to no avail.

Hm. Not sure how you're getting penetration.

Actually, it's penetration that increases, not damage. In any case, the practical limits for laser weapons are as follows: 1) We have very limited ability to generate high power short wave lasers. 2) Beyond a certain energy density, air breaks down and becomes opaque due to nonlinear effects. I'm not sure exactly how this scales with wavelength, but I'm pretty sure shorter wavelength is worse.

Factor (1) tends to produce lasers in the 800-1000 nm range. Factor (2) doesn't generally limit modern lasers, but is a real issue for small arms lasers.

Anthony Jackson: Hm. Not sure how you're getting penetration.

From the equations on the Atomic Rocket website. As I said, assuming a Carbon target.

(ed note: he even made an online calculator)

Anthony Jackson: Actually, it's penetration that increases, not damage.

Not sure how you figure that. At 7×10^-7m, we vaporize 2.23×10^-8m³ of carbon at 25m. At 4.3×10^-7m, we vaporize 3.61×10^-8m³ of carbon at 25m.

Both damage and penetration increase.

Anthony Jackson:

1) We have very limited ability to generate high power short wave lasers.

2) Beyond a certain energy density, air breaks down and becomes opaque due to nonlinear effects. I'm not sure exactly how this scales with wavelength, but I'm pretty sure shorter wavelength is worse.

Factor 1 disappears with less handwavium than it takes for an MFT (magic fusion torch spacecraft), so I'm not terribly concerned with it. While X-rays have some inherent problems, we can and do make cheap UV lasers right now, and there seems to be no reason why we can't up their power significantly.

Factor 2 is definitely an issue for small arms lasers, but at what point does it become a problem? What is the wave length at which we get the most bang for the buck? How bad is it at various wave lengths? Surely a model exists somewhere.

A lower limit on wavelength in oxygen atmospheres is somewhere around 150 to 200 nanometers. Below this you get single photon absorption by an electronic transition — this means your beam gets absorbed very fast.

For femptosecond pulses when you get self-focusing, you can get so called supercontinuum light, where the monochromatic light of the laser gets scattered into white light across a range of wavelengths. Self focused filaments can propagate for ten meters at least, and the primary absorption is in the plasma core of abut 0.1 mm across, indicating that air can handle gigawatt power levels across most of the visible spectrum across areas of more than 0.01 mm².

Another data point is that 0.193 micron light (193 nanometers) at 50 GW/m² will fall off with distance R as approximately exp(-R/100 m) due to two photon absorption.

If I'm not concerned about civilian eye safety and I don't care if the bad guys can see where I am, visible green is probably a pretty good wavelength to use for long distance lasing — it focuses well compared to longer wavelengths but doesn't suffer much from atmospheric Rayleigh scattering like shorter wavelengths. Details on calculating Rayleigh scattering can be found here

http://panoptesv.com/SciFi/LaserDeathRay/LinAbs.html

Since you are describing a pistol, however, you probably don't care about long range targets. In this case you might consider using nanosecond to femptosecond pulses, causing damage by producing power levels high enough to explode a small part of the target, thus causing mechanical damage through the shock wave rather than direct heating. Now the range depends more on your instantaneous intensity. Some rough details can be found at

http://panoptesv.com/SciFi/LaserDeathRay/Blaster.html

http://panoptesv.com/SciFi/LaserDeathRay/DamageInstant.html

In this regime, you can also use self focusing and filamentation to increase your depth of field so you can penetrate your target right through at close range

http://panoptesv.com/SciFi/LaserDeathRay/DepthOfField.html

http://panoptesv.com/SciFi/LaserDeathRay/SelfFocus.html

Winchel Chung

I'm a little fuzzy on what the muzzle of a laser pistol would look like

Dr. Schilling's laser has to focus the spot size to less than a millimeter. He says that at a guess, a pistol could not have a focusing mirror larger than, say, 5 centimeters in diameter, which would restrict the effective range to about 60 meters.

Question: how do you vary the focus with a mirror? Does the mirror have to have a variable geometry, or do you just alter the distance between the emitter and the mirror?

Would the laser pistol muzzle look like the ALP turret, or like the lens on a camcorder, or like something totally different?

• 

• 

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Isaac Kuo

You can just alter the distances of the optics.

For John Schilling's laser pistol, I'd guess that maybe the beam generator would have a diameter of 10mm, so the laser cavity optics suffer only 1/100 the intensity of the light on the target (1mm diameter spot). The highly reflective dielectric mirrors would only absorb maybe 1/1000 as much light as the target would absorb, so the intensity of the absorbed light would only by 1/100,000 as much as the target suffers.

It might look something like this:

• 

However, such an exposed mechanism would get dirty and would be difficult to keep clean. Thus, the muzzle would be protected by a shroud with a clear flat circular window. This window would be much easier to wipe clean.

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Luke Campbell

I always figured it would look like a camera lens. Maybe several camera lenses, for focusing at targets at long, medium, and short ranges, and the beam switched to the lens most appropriate to the target range.

• 

Question: how do you vary the focus with a mirror? Does the mirror have to have a variable geometry, or do you just alter the distance between the emitter and the mirror?

Either would work, though the latter is simpler (although maybe slower). Note that the "emitter" should be a diverging beam (so may in fact be the focal point of a mirror that diverges the beam that comes nearly parallel out of the laser).

Would the laser pistol muzzle look like the ALP turret, or like the lens on a camcorder, or like something totally different?

The airborn laser turret would be appropriate for something that aimed itself. This would probably not be called a pistol (but would be really scary). Something designed to be pointed with a human hand and arm would have a fixed lens or mirror. If using a mirror, I expect it would protect the mirror with a window. So either a lens or mirror ends up looking like a camcorder or camera lens or some such.

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David McMillan

If my experience is any guide, the field kit for such a weapon will require at least a few spare "window" glasses — even with the beam diffuse as it passes through the final optics, at these power levels a speck of dirt on the window can create a burn spot on the glass, which will absorb some of the beam energy and become larger, absorbing more of the beam, and so on. The performance drop is roughly asymptotic.

The field kit should probably also include at least one spare lens, just in case — some fumble-fingered grunt is sure to drop the weapon and crack the lens while they have the window unit detached for cleaning/replacement. On the systems I've built, the lenses usually ran ~$500 and the post-lens window glasses ~$30.

Whichever way you go, though, a near-optical laser weapon is going to raise the military mania for clean weapons to unprecedented heights.

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Stephen Rider

Can we slap an iris on the ends of these suckers? Means you'd need an aiming port, but I know first hand how much dust you can get on digital optics just from changing a camera lens in a dusty room that an extra level of protection would be VERY useful.

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Isaac Kuo

The iris can be made of clear plastic so it can be used for optics or to fire an "aiming dot". Its acceptable for the iris to get a little dirty. Upon firing, the iris slides out of the way to reveal the clean window underneath.

Perhaps the window behind the iris could have a number of layers. If the outer layer gets too dirty to wipe clean, you peel it off.

What would it sound like?

The actual mechanism of producing the laser beam could sound like anything, from complete silence, to the click of an electrical contact, to a sharp, electric snap, to a gunshot-like thunderclap.

The beam, when incident upon its target, will make a nice bang.

The pistol won't make a "zap" sound, will it?

If the beam is repeated rapidly it might, however, make a buzz. It might end up sounding quite electrical at a few hundred Hertz.

Will it be too quiet to hear or will be loud enough to cause hearing loss? Will it sound like an extended explosion as the series of steam detonations bore a hole?

Remember that the temporary cavity caused by the explosions only lasts a few milliseconds, so the beam has to have completed its work of piercing the target at this time. The individual explosions will be too closely spaced (microseconds apart) to be individually audible. Since shocks are always supersonic to the air in their path, and subsonic to the moving air left behind them, multiple subsequent shocks from the same source tend to merge into one stronger shock. Thus, each pulse probably makes one bang. The bang comes from a series of explosions whose total energy is about the same as that of the gunpowder detonating in a firing rifle, so it will probably be about as loud.

What would the beam look like?

This depends on a number of things. If the beam is in the visible part of the spectrum, you get a noticeable path through clean air at indoor lighting intensities. I am not sure if it will be visible out of doors under full sunlight, but you could see it at night. The beam will be widest at the aperture of the gun, probably a few centimeters across to keep the optics from being damaged by the intense light. The beam will converge to a spot a millimeter or so across at the target. In unclean air, the beam will be a lot more visible. This Rayleigh scattering is linear, so the total integrated brightness across the cross section of the beam should be constant, if we neglect the gradual attenuation of the beam due to the light being scattered out of it. Higher frequency light scatters much more than lower frequency light, so a blue beam would be much more visible than a red one.

When a visible beam is incident on the target, it creates a very bright flash of the same color as the beam. This may temporarily dazzle those looking at it, and the beam itself may be overlooked because of the bright flash obscuring it.

If the weapon lases in the UV, the intense pulse may cause multi-photon ionization of atoms in the air, causing a fluorescent glow along the path of the beam (possibly red, green, or violet, I'm not quite sure what sparsely ionized air at atmospheric pressure looks like). Since this process is non-linear, it will be dimmest near the aperture where the beam is widest, and most intense nearer the target. Weapon designers will probably try to minimize this effect, since it leads to attenuation of the beam and subsequent loss of effectiveness.

Near IR beams are likely to only be visible if there are relatively large pieces of dust, lint, or pollen floating around, which will glow incandescent as they burn under the irradiation of your beam. I doubt beams in the "thermal" IR range would be used, even though the air is fairly transparent to these wavelengths, because with short, intense pulses you tend to get cascade ionization with these lower frequencies, and this will completely absorb the beam.

Beams at non-visible frequencies will also make a flash and a bang where incident on the target from the expanding plasma of their explosion, but nowhere near as bright as that of a visible beam.

In vacuum, of course, the beam itself is always invisible, but you can still see the flashes at the target.

What would the Asteroid Pirate look like after they got hit?

The method of subsequent explosions on the back of an expanding cavity driving the cavity through the target will leave a wound much like that of a gunshot, except without fun stuff like the bullet fragmenting or breaking up. A variant where nearly parallel beams a few cm apart literally rip the tissue between them could leave a wound looking more like an ugly gash - add on a few more of these beams on the same plane and you could literally cut someone in half with one millisecond pulse, using only about as much energy as goes into accelerating the bullet of a modern day battle rifle. (ed note: in some SF novels by E.E."Doc" Smith and Robert Heinlein, this is referred to as setting your sidearm to "fan beam".)

Will there be a large splash of blood and gore on the wall behind the unlucky pirate?

Quite likely, Note that since you do not have the momentum associated with a projectile, it will be more spread out than you would get from a gunshot wound, and you would get blood and gore coming out the front, too.

I assume that since the beam is one millimeter in diameter but the hole in the pirate is four centimeters, little or no wound cauterization will occur.

Nope, the wound would be ragged and messy. It is created by mechanical, not thermal effects.

• 

• 

• 

(ed note: in this future society, duels are legal. Everybody uses energy weapons, bullet-firing slugthrowers are ancient history)

      "Me? Shucks, no. I'm one long joke on myself. Remind me to tell you about it sometime. But look—the other thing I came to see you about. Notice my new sidearm?"
     Monroe-Alpha glanced at Hamilton's holster. In fact, he had not noticed that his friend was bearing anything new in the way of weapons—had he arrived unarmed Monroe-Alpha would have noticed it, naturally, but he was not particularly observant about such matters, and could easily have spent two hours with a man and never noticed whether he was wearing a Stokes coagulator or a common needlebeam.
     But, now that his attention was directed to the matter, he saw at once that Hamilton was armed with something novel…and deucedly odd and uncouth. "What is it?" he asked.
     "Ah!" Hamilton drew the sidearm clear and handed it to his host. "Woops! Wait a moment. You don't know how to handle it—you'll blow your head off. " He pressed a stud on the side of the grip, and let a long flat container slide out into his palm. "There—I've pulled its teeth (no, you haven't. You also have to check that there is no round in the chamber). Ever see anything like it?"
     Monroe-Alpha examined the machine. "Why, yes, I believe so. It's a museum piece, isn't it? An explosive-type hand weapon?"
     "Right and wrong. It's mill new, but it's a facsimile of one in the Smithsonian Institution collection. It's called a point forty-five Colt automatic pistol."
     "Point forty-five what?"
     "Inches."
     "Inches…let me see, what is that in centimeters?"
     "Huh? Let's see—three inches make a yard and a yard is about one meter. No, that can't be right. Never mind, it means the size of the slug it throws. Here…look at one." He slid one free of the clip. "Damn near as big as my thumb, isn't it?"
     "Explodes on impact, I suppose."
     "No. It just drills its way in."
     "That doesn't sound very efficient."
     "Brother, you'd be amazed. It'll blast a hole in a man big enough to throw a dog through."

     Monroe-Alpha handed it back. "And in the meantime your opponent has ended your troubles with a beam that acts a thousand times as fast. Chemical processes are slow, Felix."
     "Not that slow. The real loss of time is in the operator. Half the gunfighters running around loose chop into their target with the beam already hot (continuous beam laser). They haven't the skill to make a fast sight. You can stop 'em with this, if you've a fast wrist. I'll show you. Got something around here we can shoot at?"
     "Mmm…this is hardly the place for target practice."
     "Relax. I want something I can knock out of the way with the slug, while you try to burn it. How about this?" Hamilton picked up a large ornamental plastic paperweight from Monroe-Alpha's desk.
     "Well…I guess so."
     "Fine." Hamilton took it, removed a vase of flowers from a stand on the far side of the room, and set the target in its place. "We'll face it, standing about the same distance away. I'll watch for you to start to draw, as if we really meant action. Then I'll try to knock it off the stand before you can burn it."
     Monroe-Alpha took his place with lively interest. He fancied himself as a gunman, although he realized that his friend was faster. This might be, he thought, the split second advantage he needed. "I'm ready."
     "Okay."
     Monroe-Alpha started his draw.

     There followed a single CRACK! so violent that it could be felt through the skin and in the nostrils, as well as heard. Piled on top of it came the burbling Sring-ow-ow! as the bullet ricocheted around the room, and then a ringing silence.
     "Hell and breakfast, " remarked Hamilton. "Sorry, Cliff—I never fired it indoors before." He stepped forward to where the target had been. "Let's see how we made out. "
     The plastic was all over the room. It was difficult to find a shard large enough to show the outer polish. "It's going to be hard to tell whether you burned it, or not."
     "I didn't."
     "Huh?"
     "That noise—it startled me. I never fired."
     "Really? Say, that's great. I see I hadn't half realized the advantages of this gadget. It's a psychological weapon, Cliff."
     "It's noisy."
     "It's more than that. It's a terror weapon. You wouldn't even have to hit with your first shot. Your man would be so startled you'd have time to get him with the second shot. And that isn't all. Think…the braves around town are used to putting a man to sleep (killing him) with a bolt that doesn't even muss his hair. This thing's bloody. You saw what happened to that piece of vitrolith. Think what a man's face will look like after it stops one of those slugs. Why a necrocosmetician would have to use a stereosculp to produce a reasonable facsimile for his friends to admire. Who wants to stand up to that kind of fire?"

---

• 

(ed note: Monroe-Alpha and Hamilton go to eat at a fancy restaurant. Some stupid bravo insults Hamilton, trying to start a duel.)

     Monroe-Alpha touched Hamilton's arm. "He's drunk, " he whispered. "Take it easy."
     "I know, " his friend answered in a barely audible aside, "but he gives me no choice."
     "Perhaps his friends will take care of him."
     "We'll see."
     Indeed his friends were attempting to. One of them placed a restraining hand on his weapon arm, but he shook him off. He was playing to a gallery—the entire restaurant was quiet now, the diners ostentatiously paying no attention, a pose contrary to fact. "Answer me!" he demanded.
     "I will, " Hamilton stated quietly. "You have been drinking and are not responsible. Your friends should disarm you and place a brassard on you. Else some short-tempered gentleman may fail to note that your manners were poured from a bottle."
     There was a stir and a whispered consultation in the party behind the other man, as if some agreed with Hamilton's estimate of the situation. One of them spoke urgently to the belligerent one, but he ignored it.
     "What's that about my manners, you misplanned mistake?"
     "Your manners, " Hamilton stated, "are as thick as your tongue. You are a disgrace to the gun you wear."
     The other man drew too fast, but he drew high, apparently with the intention of chopping down.

     The terrific explosion of the Colt forty-five brought every armed man in the place to his feet, sidearm clear, eyes wary, ready for action. But the action was all over. A woman laughed, shortly and shrilly. The sound broke the tension for everyone. Men relaxed, weapons went back to belts, seats were resumed with apologetic shrugs. The diners went back to their own affairs with the careful indifference to other people's business of the urbane sophisticate.
     Hamilton's antagonist was half supported by the arms of his friends. He seemed utterly surprised and completely sobered. There was a hole in his chemise near his right shoulder from which a wet dark stain was spreading. One of the men holding him up waved to Hamilton with his free arm, palm out. Hamilton acknowledged the capitulation with the same gesture.

---

     Hamilton chewed his lip. "I say…you'll pardon me…but isn't it indiscreet for a man who does no fighting to appear in public armed?"
     Mordan smiled. "You misconstrue. Watch." He indicated the far wall. It was partly covered with a geometrical pattern, consisting of small circles, all the same size and set close together. Each circle had a small dot exactly in the center.
     Mordan drew his weapon with easy swiftness, coming up, not down, on his target. His gun seemed simply to check itself at the top of its swing, before he returned it to his holster.
     A light puff of smoke drifted up the face of the wall. There were three new circles, arranged in tangent trefoil. In the center of each was a small dot.

• 

      The girl laughed harshly. “Lord, I sure do get the live ones, don’t I? I just can’t believe it,” she repeated. “If I hadn’t seen you in action … What are those things, anyway?” she said, pointing to Jalandra’s pistols.
     He took one out, thumbed on the safety, and showed it to her. “Rhorrvo-Jenkins’n 11-mm. automatics. A chemical explosion set off inside each cartridge propels a small pellet, called a bullet, out the barrel.” He slipped out the clip. “Each one of these holds nine cartridges. Some sets are explosive bullets; others are non-explosive slugs of lead or steel. Or some other things. Depends on what I want to use them for.”

     “Sounds weird, but I guess they work pretty good. Loud, though.”
     He smiled. “You get used to it.“ He replaced the clip and returned the automatic to its holster. “The advantage over a blaster is primarily impact. A blaster beam is primarily heat energy. Hit a man in the arm, say, and while you’re burning the arm off, he can put a beam in your guts. A man gets hit with one slug from these automatics, he’s not going to be returning fire very accurately. At short range, it’s as accurate as a blaster, and at longer ranges a blaster beam’s not that effective, anyway. The heat’s not intense enough. The speed difference is negligible. I more than make up for that.”

---

     “So my uncle became my guardian, and he trained me. For my thirteenth birthday he made those automatics and gave them to me.”
     “Made them?”
     “Yes. He was a gunsmith. Benson didn’t have a lot of off-world trade, probably because it didn’t have much worth exporting, so we were pretty self-sufficient. He had seen the design somewhere and made copies. He wouldn’t let me wear them in public, and he wouldn’t let me register. But he practiced with me every day, drawing and shooting.

     “Take shooting. Most blaster-men aren’t really good marksmen, because they don’t have to be. Most of them shoot first and aim afterward. Oh, they shoot in the right general direction, but, since the beam is visible and lasts as long as the charge holds out, most of them use the beam itself to adjust their aim. In itself, that visible beam is handy; you can adjust your fire quickly and precisely. The trouble is, everybody’s lazy. They get to depend on being able to take that split-second to direct the beam precisely on target.

     “You can’t do that with those guns of mine.

     “I got to know those guns better than my own hands. I could take them apart and put them together in the dark. l could hold one in my hand and tell you how many shells were left in the clip, just from judging the weight.

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(ed note: Jalandra the professional duelist takes his lady fair Julane to a fancy restaurant. A stupid bravo from Vega sends a fancy drink to Julane, tring to pick her up.)

     Jalandra shook his head. Incredible. He looked at Julane and saw, with surprise, fear in her eyes. He sensed rather than saw the Vegan approach.
     “Let me buy you a drink,” the man said to Julane, “even if he won’t.”
     Jalandra was too shocked for a moment even to speak. When he did, his voice went high with disbelief. “Are you out of your Bog-bedamned mind?” he cried. “l’ll blow you apart!”
     The Vegan swung toward Jalandra, backed away a step. The room had gone suddenly still at Jalandra’s outburst. “Challenge,” he said in the silence. (dueling is legal in this society)

     For an instant, Jalandra looked at him, unable fully to believe anyone quite capable of such conduct. “Accepted,” he said. Without moving from his chair, he drew his right-hand automatic and fired.
     The Vegan was fast. For the briefest of moments the astonishment on Jalandra’s face was mirrored on his own. Then he reached for the blaster at his side. He did not quite make it.
     By the time the Vegan’s body hit the floor, there were five gaping holes in it. Let them patch that up, Jalandra thought savagely.

     As Jalandra’s automatic went off thunderously, nearly everyone in the room jumped. Half a dozen men were standing. A few even had guns out. Those hastily holstered and sat down. A loud murmur replaced the silence that had again fallen as the echoes of the automatic died away. Abruptly, everyone was babbling to his neighbor.

Will the beam be invisible or bright enough to be blinding?

It is quite likely to be both. The beam itself may be invisible or minimally visible, but if even a tiny fraction of the beam is specularly scattered into your eye, near IR and visible and some near UV will be focused to a diffraction limited spot on your retina, causing burns and permanent scarring. This can lead to degradation of vision or total blindness. Interestingly, the brain compensates for blind spots on the retina, so that you might have lost up to 60% of your vision from multiple exposures to beams and you still think you can see just fine. Also interestingly, the fluid in our eyes can cause a small amount of non-linear upconversion of intense coherent light that passes through it, so when directly exposed to a near IR beam, you may actually see it as two IR photons are combined into one visible photon with twice the frequency. Some people who have been blinded by pulsed neodymium lasers (which lase at around 1 micron near IR) have reported that the last thing they ever saw was a green flash (green, at 0.5 micron, has half the wavelength and twice the frequency of the 1 micron neodymium line).

Anyone likely to be using a laser will probably wear protective goggles or contacts. With today's technology, you would probably make them out of an optical band gap material that excludes a very narrow window of light centered on the laser's frequency. This means that the people who fired the lasers would not be able to see the beams or flashes of their own weapons (assuming they used visible light lasers). They would still see the flashes from the plasma explosions, though, plus incandescence of suspended atmospheric particles and fluorescence from multi-photon absorption.

Article 1: It is prohibited to employ laser weapons specifically designed, as their sole combat function or as one of their combat functions, to cause permanent blindness to unenhanced vision, that is to the naked eye or to the eye with corrective eyesight devices. The High Contracting Parties shall not transfer such weapons to any State or non-State entity.

Article 2: In the employment of laser systems, the High Contracting Parties shall take all feasible precautions to avoid the incidence of permanent blindness to unenhanced vision. Such precautions shall include training of their armed forces and other practical measures.

Article 3: Blinding as an incidental or collateral effect of the legitimate military employment of laser systems, including laser systems used against optical equipment, is not covered by the prohibition of this Protocol.

Article 4: For the purpose of this protocol "permanent blindness" means irreversible and uncorrectable loss of vision which is seriously disabling with no prospect of recovery. Serious disability is equivalent to visual acuity of less than 20/200 Snellen measured using both eyes.

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(ed note: Warning: Spoilers for the story follow. The protagonist is a native of the fictional African nation of Umbala, which on the equator has a fictional Zambue crater. The nation has been taken over by a power-mad dictator named Chaka who has instituted a reign of terror. The protagonist is only a humble astronomer, but realizes Chaka must be stopped. The fact that Chaka put to death several of the astronomer's relatives only makes it personal.

The radio telescope will be opening soon. The astronomer knows that Chaka won't be able to resist taking the elevator to the top of the telescope and overlooking his domain.

Meanwhile, the narrator is waiting on the other side of the hills.)

It seems strange that my country, one of the most backward in the world, should play a central role in the conquest of space. That is an accident of geography, not at all to the liking of the Russians and the Americans. But there is nothing that they could do about it; Umbala lies on the equator, directly beneath the paths of all the planets. And it possesses a unique and priceless natural feature: the extinct volcano known as the Zambue Crater.

When Zambue died, more than a million years ago, the lava retreated step by step, congealing in a series of terraces to form a bowl a mile wide and a thousand feet deep. It had taken the minimum of earth-moving and cable-stringing to convert this into the largest radio telescope on Earth. Because the gigantic reflector is fixed, it scans any given portion of the sky for only a few minutes every twenty-four hours, as the Earth turns on its axis. This was a price the scientists were willing to pay for the ability to receive signals from probes and ships right out to the very limits of the solar system.

Chaka was a problem they had not anticipated. He had come to power when the work was almost completed, and they had had to make the best of him. Luckily, he had a superstitious respect for science, and he needed all the rubles and dollars he could get. The Equatorial Deep Space Facility was safe from his megalomania; indeed, it helped to reinforce it.

The Big Dish had just been completed when I made my first trip up the tower that sprang from its centre. A vertical mast, more than fifteen hundred feet high, it supported the collecting antennas at the focus of the immense bowl. A small elevator, which could carry three men, made a slow ascent to its top.

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As soon as the NASA technicians had installed their equipment and handed over the Hughes Mark X Infrared Communications System, I began to make my plans.

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Colonel Mtanga, his Chief of Security, would object, but his protests would be overruled. Knowing Chaka, one could predict with complete assurance that on the official opening day he would stand here, alone, for many minutes, as he surveyed his empire. His bodyguard would remain in the room below, having already checked it for booby traps. They could do nothing to save him when I struck from three miles away and through the range of hills that lay between the radio telescope and my observatory. I was glad of those hills; though they complicated the problem, they would shield me from all suspicion. Colonel Mtanga was a very intelligent man, but he was not likely to conceive of a gun that could fire around corners. And he would be looking for a gun, even though he could find no bullets….

I went back to the laboratory and started my calculations. It was not long before I discovered my first mistake. Because I had seen the concentrated light of its laser beam punch a hole through solid steel in a thousandth of a second, I had assumed that my Mark X could kill a man. But it is not as simple as that. In some ways, a man is a tougher proposition than a piece of steel. He is mostly water, which has ten times the heat capacity of any metal. A beam of light that will drill a hole through armour plate, or carry a message as far as Pluto—which was the job the Mark X had been designed for—would give a man only a painful but quite superficial burn. About the worst I could do to Chaka, from three miles away, was to drill a hole in the colourful tribal blanket he wore so ostentatiously, to prove that he was still one of the People.

For a while, I almost abandoned the project. But it would not die; instinctively, I knew that the answer was there, if only I could see it. Perhaps I could use my invisible bullets of heat to cut one of the cables guying the tower, so that it would come crashing down when Chaka was at the summit. Calculations showed that this was just possible if the Mark X operated continuously for fifteen seconds. A cable, unlike a man, would not move, so there was no need to stake everything on a single pulse of energy. I could take my time.

But damaging the telescope would have been treason to science, and it was almost a relief when I discovered that this scheme would not work. The mast had so many built-in safety factors that I would have to cut three separate cables to bring it down. This was out of the question; it would require hours of delicate adjustment to set and aim the apparatus for each precision shot. I had to think of something else; and because it takes men a long time to see the obvious, it was not until a week before the official opening of the telescope that I knew how to deal with Chaka, the All-Seeing, the Omnipotent, the Father of his People.

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It took me three days to install the carefully silvered, optically perfect mirror in its hidden alcove (at the top of the hills). The tedious micrometer adjustments to give the exact orientation took so long that I feared I would not be ready in time. But at last the angle was correct, to a fraction of a second of arc. When I aimed the telescope of the Mark X at the secret spot on the mountain, I could see over the hills behind me. The field of view was tiny, but it was sufficient; the target area was only a yard across, and I could sight on any part of it to within an inch.

Along the path I had arranged, light could travel in either direction. Whatever I saw through the viewing telescope (at his observatory on one side of the hills) was automatically in the line of fire of the transmitter.

It was strange, three days later, to sit in the quiet observatory, with the power-packs humming around me, and to watch Chaka move into the field of the telescope (standing at the top of the radio telescope on the other side of the hills). I felt a brief glow of triumph, like an astronomer who has calculated the orbit of a new planet and then finds it in the predicted spot among the stars. The cruel face was in profile when I saw it first, apparently only thirty feet away at the extreme magnification I was using. I waited patiently, in serene confidence, for the moment that I knew must come—the moment when Chaka seemed to be looking directly toward me. Then with my left hand I held the image of an ancient god who must be nameless, and with my right I tripped the capacitor banks that fired the laser, launching my silent, invisible thunderbolt across the mountains.

Yes, it was so much better this way. Chaka deserved to be killed, but death would have turned him into a martyr and strengthened the hold of his regime. What I had visited upon him was worse than death, and would throw his supporters into superstitious terror.

Chaka still lived; but the All-Seeing would see no more. In the space of a few microseconds, I had made him less than the humblest beggar in the streets.

And I had not even hurt him. There is no pain when the delicate film of the retina is fused by the heat of a thousand suns.

I’ve always liked the phasers of Star Trek more than the blasters/turbolasers of Star Wars. Ship to ship: phasers are computer controlled and seem to always hit the target (even if they don’t necessarily damage the target), while turbolasers are manually targeted and can’t seem to hit a damn thing. Same with hand-held weapons… phasers are zero time of flight weapons that non-professional soldiers can wield accurately, while blasters seem to travel slower than bullets and the biggest, most expensive and advanced military out there has troops so poorly trained that they can’t seem to hit the broad side of a barn.

But there’s one area where blasters are better than phasers: total energy usage per shot. If you get shot with a blaster, it’s like getting shot with a firearm. Perhaps an extra powerful firearm… a 12-gauge filled with buckshot, perhaps, but still roughly equivalent to a conventional gun. But phasers have a top setting that will vaporize a human. That’s not just overkill, that’s an insane level of overkill. It’s like using a TOW anti-tank missile to target an individual.

And this is one of the things that Star Trek got wrong. Not that it’s necessarily impossible for a weapon the size of a keychain to vaporize a human, but that the process of vaporizing the human wouldn’t utterly trash the surroundings. Face it: you’re converting, oh, 180 pounds of water to steam, and converting the calcium in the bones, the metal and plastic in his clothes, tools, weapons, etc. into plasma. And if the target is also holding a phaser, you’re converting that into vapor, which means that its battery (or whatever the power source is) is going to explode.

Phaser-vaporizing someone on board a spaceship is going to be a disaster, because by converting 180 pounds of water into steam, you’re increasing the volume by a factor of around 1,000. Imagine if the room the target was in suddenly found itself loaded with 1,000 more people. The pressure will blow the hull apart. While a blaster will simply poke a hole in the target, maybe burning their clothes.

Star Trek always made the result of someone getting vaporized pretty… well, sterile. Zap, bright light, gone. But it wouldn’t be like that. If you want to know what someone getting phasered at full power would look like, YouTube provides. Behold the phenomenon of the “Arc Flash,” where enough electrical energy can be dumped into a human to convert said human into a steam explosion. Obviously, this might be considered slightly grisly, so gather the kids around (occurs at 1:14; you can adjust settings to .25 speed to watch the guy go from “normal” to “Hey, he’s a glowing blob, just like in Star Trek” to “Where’d he go?” in three frames):

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It’s kinda unclear just what the hell happened here, but it sure looks like the guy was converted into mostly a cloud and a bit of a spray. In any event, there’s no missing the fact that something really quite energetic happened to the guy. The captain of the Klingon scout vessel vaporizes one of his crew on the bridge, they’re going to be scrubbing it down for days, assuming that the steam and overpressure doesn’t kill everyone else on the bridge.

In the later Star Trek series, the “vaporize” setting seemed to fall out of fashion. More often than not energy weapons were used as “simple blasters” of roughly firearm-power. And that’s all you need. Firearms are as powerful as they are because that’s Good Enough. You don’t need a weapon that essentially turns the target into a suicide bomber.

It might be interesting to actually show accurate phasering on some future Star Trek movie or episode. In one scene, out heroes board a wrecked space station. They go in a room where someone was shot with a phaser set to Blaster Mode: the doctor rushes over, applies hand to carotid artery, looks up sadly and says “He’s dead.” Then they go to the next room, where someone was vaporized. All the furniture is smashed up against the walls; the floor, ceiling, walls, furniture are all covered in gore. Blood sprayed everywhere, teeth embedded in the ceiling, small bits of burnt, semi-burnt and unburnt eviscera scattered about, bits dripping from the ceiling. Doc stands there in the door, slack jawed; Ensign Redshirt looks in and promptly doubles over and upchucks the Tribble Surprise he had for lunch. Captain Hero looks looks in, turns a shade of green and asks “So, Doc, who was it?”

Doc looks at Captain Hero like he’s a freakin’ mo-ron and replies with something like “How the hell would I know?”

What will the laser pistol look like?

The laser weapon will probably end up looking something like a camcorder, with a big lens that the beam goes through, and a fairly compact design. Since mirrors and internal optics can bend the beam inside the weapon, there is no need for the long barrels you see on modern firearms. Cooling, if necessary, would probably not involve fins - I would expect something more like the radiator on modern automobiles. Remember, shedding your heat through contact with the air is much more efficient than radiation.

(ed note: keeping in mind that using contact with the air doesn't work if there is no air, i.e., in vacuum. C. James Huff notes that there is one kind of fin for radiant cooling and another for air cooling. He mentions that the fins on a CPU hot sink is a good example of the latter. For a vacuum rated laser he recommends a compressed or liquified gas cartridge since a radiant cooler would be inconveniently huge.)

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Also, lasers are getting surprisingly efficient. When each beam pulse contains no more energy than imparted to a rifle bullet, lasers might need cooling no more than a modern rifle.