weight of power pack
Looks like with modern ultracapacitors you could get about .5mW for 1 second from an 84 kg bank (according to some wikipedia numbers). You could have several of those so you can pulse the laser several times, realistically 2 banks should be all you need (if the charge time is equal to the discharge time) in order to maintain more or less continuous operation using an adequate generator that you could draw that much power from continuously. More banks needed if you have less continuous power from your generator. Of course the heat these components would produce is certainly significant, so again, that's even more cooling overhead required.