Acceleration and compression of charged particle bunches using counterpropagating laser beams

The nonlinear interaction between counterpropagating laser beams in a plasma results in the generation of large (enhanced) plasma wakes. The two beams need to be slightly detuned in frequency, and one of them has to be ultrashort (shorter than a plasma period). Thus produced wakes have a phase velocity close to the speed of light and can be used for acceleration and compression of charged bunches. The physical mechanism responsible for the enhanced wake generation is qualitatively described and compared with the conventional laser wakefield mechanism. We also demonstrate that depending on the sign of the frequency difference between the lasers, the enhanced wake can be used as a 'snow-plow' to accelerate and compress either positively or negatively charged bunches. This ability can be used in an electron-positron injector.