Okay, for the purposes of the question, say I have a laser pistol. It’s the general size and weight of an M1911 Colt .45. (It operates at a wavelength of…eh, 475 nm.) Now, say, the beam is roughly powerful enough to equal a the damage caused by a .45 ACP (so, I mean, I can’t shoot down satellites with it, but I don’t have to hold the beam on target for two minutes to burn through a phone book. You know what I mean.).
Now, my question is…if I pick up and fire my laser gun, do I feel any noticable recoil?
(If any further technical details are needed to make the question answerable, I can probably pull them out of—I mean, figure them out, as needed.)
Well, let’s see.[ol][li]The muzzle velocity for a 200-grain bullet (about 13 grams) coming out of a .45 ACP is approximately 300 m/s.[]Therefore, the momentum imparted to the bullet, and which will therefore be imparted to whatever’s holding the gun as “recoil” is about 3.9 kg m/s.[]The kinetic energy of a bullet coming out of a .45 ACP is, according to the link you gave, approximately 500 J.If we assume that our laser pistol imparts this same amount of energy to its beam, and we recall that the momentum of a photon is related to its energy by E = p c, where c is the speed of light, the total momentum of the beam will be about 1.7 x 10[sup]-6[/sup] kg m/s.[/ol][/li]So under these assumptions, the recoil of a laser pistol would be negligible.
Heh, this reminds me of the Rifts role-playing game. In the section describing laser pistols and rifles, it mentions that a true laser pistol has no sound or recoil, but due to years of popular culture showing them emit sound and force, manufacturers eventually made the guns have noises and sometimes a fake recoil because the people buying them wanted those features.
Your laser pistol might still jump some when you pump 500+ watt seconds through whatever coils, flashlamps or circuitry you use to create the beam. That wouldn’t strictly count as recoil, but it could be enough to mess with your aim.
Remember that blasters are a different story altogether, firing as they do an extremely high-energy gas compressed into a beam of intense energy particles that are propelled by or fused with (or somedamnthing) a beam of light.
Way back in high school I did a physics report on the whole “Star Wars” thing (as in SDI, not the movie). One bit I remember reading was that a laser would need to pump closer to 20,000J into a human target to vaporize a hole that would do the same kind of damage as a .45 bullet does by plowing through tissue. Much less efficient.
Not that it’d really change your answer - even 100x that tiny recoil is still…tiny.
Using a laser as a weapon would almost certainly rely on the thermal shock effect, i.e. you heat the affected area so rapidly that it explodes into a cloud of superheated steam, which then proceeds to do the majority of the damage. You would presumably do this with a pulsed laser, firing repeatedly at a rate of once every few tens of microseconds to increase penetration. This would still likely be more energy than the ~500 joules in a .230 grain 45 ACP, but less than that required strictly to evacuate a .451" hole.
However, this is all dependent upon a compact power source that could deliver sufficient energy to the lasing medium to power such a device, and of course a handgun-sized lasing apparatus that could generate sufficient throughput. Both of these are well and beyond any current technology. For the time being, we’ll have to stick with projectile weapons to cause serious damage to one another at range.
In any case, the amount of recoil would be negligable; in order to generate any measurable amount of recoil would require terawatts of power, vastly more than could conceivably be generated by any extant power source.
How about a current-tech supercapacitor for a few 2,000 joule pulses at a time, pumped by a compact diesel generator. You could fit that in a shopping cart. It would be like the minigun in Predator, where a user would actually have to drag around a car battery to power the rotary barrels, and a big box of ammo. The latest weapon tech semiconductor lasers can deliver about 20 kw continuously. Dunno how big they are but that could go in the cart too, with the beam directed down a hand-held optical fibre.
Blasters do no such thing. Blasters are nothing more than ‘lasers’ of a variety that emit in the microwave spectrum, thus causing aqueous-fluid-filled bodies that they strike to burst apart.
The beam’s not pushing against anything. The gun contains a fatass pulsed power supply of some sort. When that discharges it’ll generate a transient magnetic field. That field will exert force on the conductor and any nearby metal: Why Do Transformers Hum?
Since I can turn it off, it seems that it’s a customer expectation thing, not a safety feature. However, it’s pretty old, and I do think I read something about newer models needing to “click” or beep to alert others when it’s taking pics. But that wasn’t the initial reason digitals could make a wholly artificial digital click and whir noise. It was originally added because we expected it, and it’s an almost unconscious signal that the picture was indeed taken. (How many times have you stood there while your Aunt Edna peers into the wrong end of a camera saying, “Did it take? I don’t know? One more, just to be sure!”)
Likewise, one might find that experienced shooters unconsciously correct for recoil, and so a recoilless pistol might be *less *accurate in the hands of experienced shooters than in those only accustomed to “shooting” the remote at the television. It could be practiced, of course, but people who want to add a laser pistol to a collection of firearms might simply prefer an artificial recoil built in to make things more consistent.
