Well, its quite simple to figure out why a handheld laser weapon would not fly:
A shout from a military handgun from 100 yards away has a kinetic energy of roughly 324 ft-lbs (from http://medlib.med.utah.edu/WebPath/TUTORIAL/GUNS/G UNBLST.html ). Converted, this means 440 Ws. So if you have a 4W Laser, you would need to point it on your target for 110s to even deliver the same ammount of energy (not considering your target moves, energy is lost due to reflection, cooling, etc.)
But now your gun does not deliver that energy in 110s, but in lets say 0,1s (guessing). So you need about 1000 times more energy. (so you need to point only 0,1s). This means you need 440000 Ws. A Li-Ion battery has a energy density of 160 Wh/kg. http://en.wikipedia.org/wiki/Lithium_ion_battery So this means you'd have to lug around 1kg of Li-Ion battery only for a single shot.
This is all not taking various other points into account where you loose energy. So, you see where the problem lies.
Slashdot Mirror
Well, its quite simple to figure out why a handheld laser weapon would not fly: A shout from a military handgun from 100 yards away has a kinetic energy of roughly 324 ft-lbs (from http://medlib.med.utah.edu/WebPath/TUTORIAL/GUNS/G UNBLST.html ). Converted, this means 440 Ws. So if you have a 4W Laser, you would need to point it on your target for 110s to even deliver the same ammount of energy (not considering your target moves, energy is lost due to reflection, cooling, etc.)
But now your gun does not deliver that energy in 110s, but in lets say 0,1s (guessing). So you need about 1000 times more energy. (so you need to point only 0,1s). This means you need 440000 Ws. A Li-Ion battery has a energy density of 160 Wh/kg. http://en.wikipedia.org/wiki/Lithium_ion_battery So this means you'd have to lug around 1kg of Li-Ion battery only for a single shot.
This is all not taking various other points into account where you loose energy. So, you see where the problem lies.