A laser powerful enough to be a weapon has a major shortcoming in that any dirt or debris on the output optics will heat up and transfer energy to the optic itself, probably destroying it.
How clean is combat?
You can "somewhat" get around this by designing a laser that will have relatively low energy (density --TAT) at the output optics but will put the beam waist at the target - focus, if you will. But this is a rather difficult approach to take in a personal weapon.
Well, don't we pretty much have that technology right now? I'm thinking of autofocus cameras, which have been around for many decades. Find range, move the lens system so the beam "waist" is on the target automatically.
Power supply? Heck, I'm constantly being stunned at the increases in power density for small batteries --my son has a model chopper whose battery is amazing, though I can't quote specs right now. And supercapacitors have incredibly reduced the bulk required to store charges. I guess right now, they're somewhat limited in discharge rate, but tomorrow? I can envision a capacitor with a two-atom thick diamond dieletric and vacuum-deposited plates, repeated one on top of the other.(Bear in mind that distance between plates is a term in the capacitance formula.)
A hundred years? Don't forget that even though we are now at the "just discovered gunpowder" phase, technical communications are many orders of magnitude faster and better now (since journal articles aren't in Latin anymore :) ) and there's m/billions of dollars of profit involved nowadays.
"Invent a better way for these Europeans to kill each other, and you'll make a fortune." Or something like that by Maxim or someone. Maybe one of his friends, I don't remember perzackly, so don't let's get off on exactifying the quote.
Terry, 230RN