Raman backscattering in laser wake-field and beat-wave accelerators

An intense short laser pulse propagating through a plasma undergoes stimulated Raman backscattering when oscillatory electron velocity v0≥4c/(2ω0τ0ωpτ0)1/2, where ω0 and τ0 are the frequency and pulse duration of the laser and ωp is the plasma frequency. In a laser wake-field accelerator employing short laser pulses with ωpτ0∼2π, this threshold is exceeded when v0/c approx-gt 0.1. The threshold is smaller in a beat-wave accelerator where longer pulses are used