Detuned Raman amplification of short laser pulses in plasma

The recently proposed scheme of so-called "fast compression" of laser pulse s in plasma can increase peal; laser intensities by 10(5) [Phys. Rev. Lett. 82, 4448 (1999)]. The compression mechanism is the transient stimulated Ra man backscattering, which outruns the fastest filamentation instabilities o f the pumped pulse even at highly overcritical powers. This Letter proposes a novel nonlinear filtering effect that suppresses premature backscatterin g of the pump in a noisy plasma layer, while the desired amplification of a sufficiently intense seed persists with a high efficiency. The effect is o f basic interest and also makes it robust to noise the simplest technologic ally fast compression scheme.