Supra-bubble regime for laser acceleration of coldelectron beams in tenuous plasma

Relativistic electrons can be accelerated by an ultraintense laser pulse in the "supra-bubble" regime, that is, in the blow-out regime ahead of the plasma bubble (as opposed to the conventional method, when particles remain inside the bubble). The acceleration is caused by the ponderomotive force of the pulse, via the so-called snow-plow mechanism. The maximum energy gain, Δγ ~ γg a, is attained when the particle Lorentz factor γ is initially about γg/a, where γg is the pulse group speed Lorentz factor, and a is the laser parameter, proportional to the laser field amplitude. The scheme operates at a ≤ γg, yielding Δγ of up to that via wakefield acceleration for the same plasma and laser parameters, Δγ ~ γ2g. The interaction length is shorter than that for the wake field mechanism but grows with the particle energy, hindering acceleration in multiple stages