Originally Posted by Valgard
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.
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.