Check out this article on laser weapons in USA Today: link
From the article:
So what do y’all think? Are 1920’s Style Death Rays finally coming? Can I get my blast pistol now? 
A blaster would need a compact power source. Get hack to me when room-temperature superconductors become stable and cheap.
Spoilsport! 
Ok, so maybe a hand-held weapon is a little further off. But, we seem to be making progress in that direction. How about a tank with a laser weapon? Probably not quite useful yet, but more likely than a hand-held laser.
Directed energy weapons will be front line stuff in less than 20 years, at least assuming the DoD’s budget doesn’t get gutted to pay off the war debt. Lasers will be on ships and aircraft and tank or APC-sized vehicles.
Man-portable hand-held stuff is doable today, but the power supply for it isn’t.
This, for example, is just over 3 years old http://www.raytheon.com/newsroom/technology/rtn07_sslad/ .
This recent article http://www.army.mil/-news/2010/02/19/34737-100kw-solid-state-laser-to-be-transferred-to-helstf-for-field-tests/ gives you some terms to Google for more info.
So I’m guessing the next big breakthrough needs to be in terms of power sources. Battery technology just does not seem to be anywhere near what we need for all our energy hungry devices. You take the iPad and everyone is “Wow! 10 hrs of battery!”. But let’s face it – what we really want is something like a week of battery power. I think once the compact energy storage device (call it a battery or whatever) is solved, a host of other problems can then be solved such as true electric cars, hand held energy weapons, hand held energy tools (hey, I want a laser post hole digger :D), portable computing devices which will last for days, weeks or more.
So, it seems that we should be pouring more into research on compact energy storage as it will open up a lot more fields and possibilities.
Power sources are a problem, not to mention that lasers are also very delicate, compared to say, a 155mm howitzer.
I’d be curious to see how directed energy weapons change warfare. For one, it would probably be nothing like what you see in Star Wars. I imagine a powerful laser weapon would render conventional aircraft, missles and artillery obsolete. Any object that appeared above the horizon could be instantly targetted and destroyed by an invisible beam. It would probably mean a return to WWI style trench warfare since anything that can be seen could be killed.
That would be 2020’s Style Death Rays.
Ask** Richard Pearse.**
A lot of the effort on batteries today is for storing a lot of power & letting it go very slowly. If your latest Apple IGizmo is going to run for hours or days, it’ll do so by sipping power at a low and mostly steady rate.
A laser blaster needs to dump a great whackin’ pile of power in there for a millisecond or less, then wait a few seconds or minutes or hours, then do it again.
Those are very very different requirements.
Batteries might be part of the solution, but they won’t be the whole solution; they just aren’t the right technical base for delivering large pulses of power.
If not for that annoying “No weaponization of space treaty” we could solve all those problems with a “Spies like us” scenario. Remote industrial power battery, Satellite bounce aiming, and you don’t even need to care about the horizon.
America fuck yeah! 
Everything you ever wanted to know about Death Rays!
And, of course, The Original!
True, very true. It is more on the order of a large capacitor which can let loose all at once. But you have to have more than one charge for it to be at all useful. This is undoubtedly the most serious obstacle to overcome for a hand-held energy weapon or tool. Power where you need it, when you need it and in sufficient quantity. Solve that one, and the rest is a piece of cake.
Oh yeah! Tesla was a frackin’ genius! Imagine if he were around today and up on the latest technology. Hoo boy would be have some badass weaponry!