If, power source and size restrictions cast aside, I managed to mass-produce a hand held laser weapon (pistol or rifle) and used it on a person or object. Is there any way to trace that a specific laser weapon did the damage? Is there some kind of signature to the burn mark that would be unique to a given weapon?
I think it would depend on the specifics of the weapon and the specifics of the weapons you are trying to distinguish it from. In general, two laser beams of the same frequency and intensity are indistinguishable no matter their source. Studying the burn pattern produced by a laser could probably give you a good idea of the beam’s intensity and duration, but I don’t think you could determine its frequency.
The burn pattern might be a unique signature, but a handheld weapon would have a significant amount of jitter, making a lot harder to isolate.
Interesting idea – are you doing some sort of futuristic murder mystery where they try to find the laser that did it (like looking at the grooves in a bullet with a conventional gun)?
I doubt if it would work in most cases, but I feel compelled to point out that:
1.) Similar Lasers don’t operate on exactly the same frequency. The exact frequency is determined by the cavity length (as long as it’s within the gain region of the laser), so there will always be a slight difference between lasers.
2.) Depending upon what you’re firing at, you can record information about the laser frequency. For instance, at one of my jobs we fired a carbon dioxide laser at plastic. There were bits of metal in the plastic, and a bit of this protruded from the plastic. The wave reflected from the metal interfered with the direct wave from the laser, and the result was a “bullseye” pattern surrounding the metal, the dimensions of which were determined by the wavelength of the laser.
3.) Of course, even in this case, your ability to discriminate between similar CO2 lasers would be negligible – the frequency difference would be pretty small. But it is conceivable that the laser could be fired into something (a laser wavemeter, holographic medium) that would provide you with enough information to accurately measure the wavelength/frequency.
4.) Bear in mind that cavity length can be changed by heating of the laser, index of refraction changes, etc. I think if you had a worldful of similar lasers, this would be a hopeless enterprise. I could see you distinguishing among a handful of possible candidates, however.
Well, it’s very difficult to get a perfect single mode, flat wavefront laser beam. Lots of money is spent on industrial lasers to achieve these qualities so that the beam will cut cleanly and predictably.
In a hypothetical laser pistol, I suppose these qualities wouldn’t be nearly as important as power throughput, manufacturability, and reliability.
Also, in order to deliver maximum punch, a laser weapon would probably be a pulse laser, emitting short pulses of extremely high power and then resting. This cycle would repeat many times per second, and the pulses would last only a few milliseconds.
Human aiming accuracy being what it is, this would probably leave a pattern of burn spots, rather than one spot or a smeared spot. Some spots may overlap, sure, but you’re bound to get one good one if the trigger was held down for more than a tiny fraction of a second.
Variations in the manufacturing process would probably result in item-specific spot patterns due to higher mode intrusion and wavefront errors. This “beamprint” would make good forensic evidence provided you could recover the weapon and burn test spots with it for comparison, just like they do with bullets and rifle patterns.
Actually I was fantasizing more along the lines of mounting one on my car instead of a machine gun for dealing with inconsiderate drivers. Was just curious if there was a signature of some sort from laser burn. Punching a hole silently and invisibly in a tailgaters radiator, etc, etc. A bit of musing that resulted in a semi serious point to ponder.