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.