Researchers at SLAC have developed a very elegant solid state electron accelerator, an "accelerator on a chip": http://news.stanford.edu/news/2013/september/slac-chip-accelerator-09271... Nice explanation: https://www.youtube.com/watch?v=V89qvy8whxY Original paper at: http://arxiv.org/abs/1308.0464 So if one can accelerate electrons to 50 GeV in 100 feet, that means a one meter chip would presumably get you 500 MeV (linear increase in energy by length). The paper merely claims 25 MeV/m, but 25 MeV is still a pretty penetrating beam. Likely not perfect for a weapon (hard to get all the energy of the laser into the electrons; might be better to send the laser at the target instead) but useful for a lot of things like the starter step for an X-ray free electron laser. It might be possible to boost electrons using plasma discharges into the TeV range http://arxiv.org/pdf/1306.6516v1.pdf If the model here is right, one could get 2.3 TeV/m.