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This is more technology than strictly physical science, but I’m professionally interested in laser physics. My own area is mainly attosecond pulses at modest average power, still, the applications of broader laser technology are always instructive.

Boeing has been working on laser weapons technology for a while now. I’ve written about it before, mainly from the perspective of battlefield anti-missile and anti-mortar defense. Anti-personnel use is possible but generally impractical. A bullet is just as effective and several orders of magnitude cheaper. There’s possible advantages with using one from the air, but again a guided missile is usually equally or more effective. Usually, but not always.

Lasers have an advantage that explosive or projectile weapons don’t. Light goes in perfectly straight lines (if you aren’t fighting near a black hole) and it stays in a small, tightly controlled beam over a very long distance. That means if you have Osama bin Laden standing in the middle of the Pakistan Cute Children and Puppies Convention, he can’t be hit with a missile without causing innocent lives to be lost. But if you have a C-130 with a chemical laser in the nose, you can turn him into charcoal in a flash of light, without any damage other than some shocked and awed little kids.

Boeing also claims this provides plausible deniability. Well, I can’t blame them for hamming up the press release but this seems unlikely. The symptoms of death by high intensity laser are unlikely to be mistaken for anything else. It’s not exactly subtle.

Anyway, notice that the laser involved is a chemical one. The problem with lasers as weapons has always been the power density. Even being briefly hit with an industrial steel-cutting laser probably won’t kill you, though it will hurt and do lots of damage. Actually delivering enough power to be an effective battlefield weapon is very difficult. The old optically-pumped lasers just don’t have the power density. Chemically pumped lasers have been the main thrust of weapons research because the chemical reaction is fast and delivers tremendous beam energy. I believe this particular Boeing weapon claims around 100kW, with plans to end up in the megawatt range. Semiconductor lasers have been catching up, and they’re easier to built, power, and maintain. But heat dissipation and power density still aren’t quite there for weaponized semiconductor lasers. In both chemical and semiconductor lasers only a fraction of the chemical or electrical energy actually ends up as part of the beam. The remaining energy is released mostly as heat, which in such large quantities tends to wreck whatever delicate lasing apparatus is being designed. Gradually that problem is being overcome. The remaining work is more of an engineering challenge than a basic physics one.

I don’t think any scientist likes to see the triumphs of physics and engineering to find their first application in killing people. Lasers used in surgical medicine, communications, and instrumentation and someday maybe even power transmission are certainly better uses of laser technology. Still, at least in this case it has the potential to replace much less discriminating weapons as bombs in urban areas. Prior to lasers the US military has long tried to find ways to kill enemies from the air without killing nearby civilians, with some but limited success. They’ve even dropped precision-guided lumps of concrete. While target specificity has been much more successful in Iraq and Afghanistan than, say, in Tokyo 1945, there have been plenty of instances where bombs have killed civilians in the current US wars. If lasers are going to be used in combat, at least they can be used to lessen the danger to civilians.

Comments

  1. #1 Dunc
    August 19, 2008

    But if you have a C-130 with a chemical laser in the nose, you can turn him into charcoal in a flash of light, without any damage other than some shocked and awed little kids.

    Wouldn’t his explosive vaporisation present some risks to nearby bystanders? And isn’t there also a risk that the pulse length is going to be long enough to not only vaporise Osama, but also whatever he’s standing in front of?

    It’s possibly worth remarking here that in terms of accuracy (ie going off where you intend it to) a car bomb or IED is still far more accurate than a laser- or GPS-guided munition. It’s the secondary effects that cause the problems.

  2. #2 Uncle Al
    August 19, 2008

    The worst kind of war decouples price from cost. Guerilla action offers no target for reprisal. Aseptic targetting justifies profligate use. The stabilizing effect of 60 years of nuclear weaponry is that one must be MAD (the acronym)to use it.

    If the enemy is blithe about suicide, inhibiting effects of reciprocal great loss are voided. War must be horrible and intolerable or it becomes a global industry feeding local folk art (including a perpetual hunt for Emmanuel Goldstein re 1984).

  3. #3 Zifnab
    August 19, 2008

    If lasers are going to be used in combat, at least they can be used to lessen the danger to civilians.

    They’ve been promising us weapons that don’t kill the wrong people for ages, but someone we still end up with another Hadditha or five every time we put boots on the ground in a foreign country.

    Want to save civilian lives? Stop using deadly force in their places of residence.

    Besides, all the precision in the world won’t save an innocent civilian’s life if the soldier pointing the laser is aiming at the wrong dude. That has happened as often as not in Iraq – with “alleged” hideouts getting raided or bombed because 100 dead Iraqis are worth one dead guy from the Iraqi playing card deck.

  4. #4 Matt Springer
    August 19, 2008

    Want to save civilian lives? Stop using deadly force in their places of residence.

    As long as there have been cities, wars have been fought in them. Unless a nation is willing to commit to absolute pacifism, urban warfare will always remain something that must be planned for. Even if your country doesn’t want to fight in cities, the other army might. Thus in my opinion, precision weapons development is a great improvement from (say) WWII style incendiary bombing.

  5. #5 phisrow
    August 19, 2008

    Would lasers of high enough power to be weapon usable reflect and scatter the way smaller ones do, or do they destroy imperfect reflectors before too much reflecting goes on?

    If high powered lasers do scatter and reflect, wouldn’t there be a substantial(if very unpredictably distributed) risk to anybody within line of sight? I’d imagine that the distribution would be a lot more erratic than the more prosaic compression and shrapnel of explosives; but quite likely to damage those nearby.

  6. #6 Pierce R. Butler
    August 19, 2008

    If lasers are going to be used in combat, at least they can be used to lessen the danger to civilians.

    Yah sure, the same way tasers were supposed to reduce police violence.

    Bought any good bridges lately?

  7. #7 Odysseus
    August 19, 2008

    Thus in my opinion, precision weapons development is a great improvement from (say) WWII style incendiary bombing.

    Developing precision weapons is one thing, employing them another. As long as the US refuse to ban cluster bombs, I doubt that these developments will result in a significant improvement for civil victims.

  8. #8 Matt Springer
    August 19, 2008

    Yah sure, the same way tasers were supposed to reduce police violence.

    Military combat is a pretty different animal than police work. But even so, I’d rather be bit with a taser than a bullet – and I am the last person to defend excessive force by police.

  9. #9 Nomen Nescio
    August 19, 2008

    Matt, your last comment more or less assumes police are in fact using tasers as replacements for firearms, such that it’s a choice between one or the other. the counterargument is that this isn’t so, and that tasers are being used when firearms would not be warranted.

    i haven’t personally studied any really good statistics on this, but i’ve heard tell of data out of the Houston P.D. indicating that firearms use did not go down as tasers were introduced. that would seem to support the counterargument, at least for that one police department around that point in time.

  10. #10 Mark P
    August 19, 2008

    My guess is that the deployment of such precision weapons (if it ever happens) will result in an increase in the number of total casualties for the entire conflict equal to approximately the number of times the weapon is used.

  11. #11 Andres Villarreal
    August 19, 2008

    Sorry, but there is no “ethical” or “kind” or “humane” or “defensive” weapons.

    Super smart weapons terrorize the opponent, since they permit the obliteration of an opponent’s capacity to organize itself. Whether the opponent deserves such treatment, that is another matter. The need to win a war with simpler weapons coerces both sides into a need to find a negotiated solution.

    Israel had the closest thing to a surgical war machine, but it used it to kill both the guilty and the innocent until the international uproar ended the killing spree.

  12. #12 Nomen Nescio
    August 19, 2008

    The need to win a war with simpler weapons coerces both sides into a need to find a negotiated solution.

    this makes rather a great deal of assumptions about the combatants, assumptions that would be better stated outright. the Punic Wars were surely fought with very simple weapons indeed, yet the sides involved apparently felt little need to negotiate a solution.

  13. #13 Matt Springer
    August 19, 2008

    the Punic Wars were surely fought with very simple weapons indeed, yet the sides involved apparently felt little need to negotiate a solution

    I have to agree with you and disagree with #11. Israel has fought preposterously clean wars given its circumstances, and even the simple weapons of the Battle of the Somme caused a million and a half casualties (one for every centimeter of ground gained by the Allies) – and the negotiated solution that eventually ended the war two years later provided the perfect propaganda point for Hitler to start an even bloodier war.

    I’ll take the laser any day.

  14. #14 Brian
    August 19, 2008

    I think the purpose of the laser weapon is already to destroy incoming ballistic missile weapons, particularly nuclear ones. I can’t think of a more noble use of a weapon.

    Zapping individuals is not remotely practical in any way, now or in the foreseeable future. But, lasers are already used everyday for that purpose. They are used to guide precision bombs and missiles. They’ve saved countless numbers of collateral casualties. In fact, the US has developed smaller and smaller weapons for this purpose. Boeing itself is producing a weapon called the SDB–small diameter bomb, that contains the blast in as limited an area as possible.

  15. #15 Zifnab
    August 19, 2008

    As long as there have been cities, wars have been fought in them. Unless a nation is willing to commit to absolute pacifism, urban warfare will always remain something that must be planned for. Even if your country doesn’t want to fight in cities, the other army might. Thus in my opinion, precision weapons development is a great improvement from (say) WWII style incendiary bombing.

    Why did we invade Iraq and Afghanistan? Because our government got us jazzed up over the 9/11 attacks to start slaughtering brown people. Why did we suffer the 9/11 attacks? Because Osama Bin Have’n Too Much Time On His Hands decided to jazz up a bunch of religious wackos over military bases in Saudi Arabia. Why do we have military bases in Saudi Arabia (and why do we plan to build more in Iraq, Kuwait, and any other nation we can cram our troops into)? Because we need to control the oil supply. Why do we need to control the oil supply? Because our entire economy is keyed to the price of gasoline. Why? Because we refuse to invest in alternative energies.

    So we’re going to spend tens of billions on a defense budget to build a giant plane-mounted death ray to kill the guys who bombed us for occupying their turf in a resource war dating back to British Colonialism, all to get the opportunity to drill for a gallon of gasoline that we could just as easily have replaced with a wind turbine for a few more pennies on the dollar.

    Billions in defense, not a penny for interior development! Now that’s smart.

  16. #16 Chris P
    August 19, 2008

    “Even being briefly hit with an industrial steel-cutting laser probably won’t kill you, though it will hurt and do lots of damage.”

    I think you need to redo the laser safety class. Even a small burst of a small semiconductor laser to the eye causes huge damage and pain for a long time.

    If it has enough power to cut steel it WILL kill you.

  17. #17 Matt Springer
    August 19, 2008

    It CAN kill you, but it probably won’t. It will at minimum blind you if it hits your eye however briefly.

    A steel-cutting laser basically functions along the same lines as welding equipment. Tremendous heat, small area. While the resulting burn will be hideous, dangerous, and possibly cost you a limb, brief exposure will probably not be fatal. Probably.

    Obviously this is no reason to cut corners in a laser lab. They are very dangerous and “you might not die” is not a reason to take risks.

  18. #18 Nomen Nescio
    August 19, 2008

    seen on a warning sign in a laser lab: “do not look into laser with remaining good eye”.

    then of course there’s these warning sign fridge magnets

  19. #19 Clark@lextek.com
    August 19, 2008

    Would lasers of high enough power to be weapon usable reflect and scatter the way smaller ones do, or do they destroy imperfect reflectors before too much reflecting goes on?

    They destroy mirrors pretty fast. Getting good mirrors for high powered lasers is very expensive. I worked with some giant lasers as Los Alamos while working on inertial confinement fusion in college. They would burn out mirrors worth thousands of dollars fairly regularly.

    Even for smaller lasers – say the kind used for laser hair removal – you have to buy good mirrors and you can still run into problems.

  20. #20 Rich
    August 20, 2008

    The defensive (in a military sense) applications of lasers are interesting. With modern tracking systems, I think I’m right in saying they could be used to shoot down shells and RPGs as well as missiles (great for stopping someone randomly firing such things into your town).

  21. #21 Pierce R. Butler
    August 20, 2008

    “The Stun Gun Fallacy” (2005):

    In one recent year alone, there were 77 post-Taser fatalities around the nation.

  22. #22 Tercel
    August 20, 2008

    High power lasers do damage mirrors, but that doesn’t mean a significant amount of reflection/scattering won’t take place. The truth is that a laser weapon would indeed pose a serious risk to the vision of those near the target. Of course, if you asked those people if they’d rather be blind or dead…

  23. #23 schrecken licht
    August 20, 2008

    It’s true these lasers weren’t initially designed with anti-personnel uses in mind, but you gotta admit that it would be one hell of a way for a terrorist to go….!

    Also, lasers ARE destructive by nature (unless you’re talking about applications like communications, entertainment and anything else where the beam isn’t required to cut or burn) – if you have had LASIK surgery the beam vaporized a microscopic portion of your cornea.

    Industrial lasers of at least several kilowatts could kill a person…a focused beam to a vital area would surely kill. Even the “puny” beam of a 20 watt CO2 laser (about the lowest power you can get for that type of laser) can cause some serious damage to various targets:

    However, in factory settings generally only the eyes, hands and fingers are vulnerable, so death there would be highly unlikely (unless you come into contact with the power supply….that’s a whole ‘nother story!) But not long ago I talked with a man who witnessed a horrible industrial laser accident – the victim got his eye burned clean out of the socket when he took a direct hit from a multi-kilowatt CO2 beam (unfocused, if it had been focused he surely would have died). The witness said it was the most gruesome thing he’d ever seen (and smelled) and that he had nightmares for weeks later…
    But seriously, laser weapons do have a couple of advantages over kinetic munitions – striking distance is one – to kill someone from, say, 6 miles away, a gun won’t do – bullets lose their momentum way before that. Other choices are self-propelled explosives (or dropped, say from a drone) – i.e., bombs. But that’s where the collateral damage is the problem. Worse yet for the enemy is the psychological issue – imagine being a terrorist cohort and seeing Bin Laden just burst into flames for no apparent reason – like something out of a horror movie! Would be like that old Stephen King movie Firestarter – but hundreds of times worse! That’s one area I think that laser weapons will shine (pardon the pun), as well as the obvious rocket and missile defense aspect.

  24. #24 CCPhysicist
    August 21, 2008

    Applied physics error:

    Light goes in perfectly straight lines (if you aren’t fighting near a black hole) and it stays in a small, tightly controlled beam over a very long distance.

    Light refracts in air due to density gradients due to temperature or pressure, and it is scattered by particles in the air. The contractor who thought the laser in his alignment device always went straight ended up with a pipe curving up out of the ground. Been there, seen that.

    Political science:

    Comment #15 points to the geopolitics behind our involvement in the middle east, and the “clean war” approach the US pursued after WW II and Korea and Vietnam, trying to use technology to reduce the need for boots on the ground. The flaw in this approach could not have been clearer in Georgia. We did not know Russia was ready to move in because our satellites were busy elsewhere. Similarly, we learned that the general the President fired had a better idea of what would be required for a peace-keeping role in Iraq than he and his civilian advisers did. It turns out that troops really are needed and we don’t have enough on active duty to meet our current demands.

    If our political choice is to favor a military “I know how to win wars” approach to Russia in Georgia, Poland, and the Ukraine, we will need a return of the draft to man all of those new bases in addition to our existing deployments.

  25. #25 Scott Simmons
    August 21, 2008

    Light goes in perfectly straight lines (if you aren’t fighting near a black hole) and it stays in a small, tightly controlled beam over a very long distance.
    Light refracts in air due to density gradients due to temperature or pressure, and it is scattered by particles in the air.”

    The more accurate initial statement might have been that a laser aimed optically will always hit the target–the light rays coming from the target allowing us to see it and the light rays going back to the target will follow the same path. (Of course, that’s still not quite true, as refractive indices vary by wavelength …)

    And I can’t believe we’ve gotten this far without being smitten by movie quotes. “All you’d need is a targeting system with a big rotating mirror, and you’d have everything you need to vaporize a human target from space.”

  26. #26 Jonathan
    August 21, 2008

    Lasers may be expensive as a means of killing soldiers but they would be very effective as a mass blinding weapon. A number of countries are working on such systems, although their deployment is banned by international agreement. Such weapons should be regarded the same way we view poison gas — as cruel, inhumane and immoral. More info here:

    http://www.icltd.org/laser_weapons.htm

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