Generation of periodic accelerating structures in plasma by colliding laser pulses.

A mechanism for generating large (>1 GeV/m) accelerating wakes in a plasma is proposed. Two slightly detuned counterpropagating laser beams, an ultrashort timing pulse and a long pump, exchange photons and deposit the recoil momentum in plasma electrons. This produces a localized region of electron current, which acts as a virtual electron beam, inducing intense plasma wakes with phase velocity equal to the group velocity of the short pulse. Modulating the pumping beam generates periodic accelerating structures in the plasma ("plasma linac") which can be used for particle acceleration unlimited by the dephasing between the particles and the wake. An important difference between this type of plasma accelerator and the conventional wakefield accelerators is that this type can be achieved with laser intensities I<<10(18) W/cm(2).