Take the Advanced Tactical Laser (ATL) that U.S. Special Forces have begun to test-fire. Intended for 'covert strikes,' the ATL has been sold on its ability to blast away with pinpoint accuracy. A very rough estimate shows, however, that the effects when you target an individual are not quite what you might expect.
.... Bullets are lethal when they damage a vital organ (like the heart or the brain) or when they cause rapid blood loss. Most likely, a laser of this type would not easily be able to go deep enough to affect a vital organ. Plus, the laser would will be self-cauterizing, with the heat sealing off blood vessels. It's not going to kill you quickly.
While research in this area tends to be classified. But from what we know, the Air Force considers laser effects on eyes and skin, for the most part. Skin damage is very much easier to achieve than penetration; simply raising skin temperature to (say) 80C/ 180 f to a depth of a couple of millimeters will cause serious blistering (second-third degree burns). If 40% of the body is burned in this way, then the target will be disabled and may die.
A rough calculation suggests that exposed skin would be blistered/burned in under a twentieth of a second, so the beam could play over the target at quite a high rate. It's unclear whether clothing would have much protective effect or whether it would simply ignite and cause secondary burns.
So instead of 'zap-and-you're-dead' in normal science fiction style, with a hundred kilowatt laser, it's more a matter of spraying the target all over to ensure they're done. The description of the ATL as a 'long range blow torch' is probably quite accurate. ....
