Second-harmonic generation of Raman scattered light in a plasma channel

The experimental results of Krushelnick et al. on second-harmonic generation of Raman scattered light at 45° to the backscatter direction may be understood as follows. The intense short pulse laser produces a plasma wave via Raman backscattering. In the region of the wake, the plasma shrinks in size, and forms a narrow plasma channel, of a few plasma periods width. The channel breaks into bubbles via oscillating two-stream instability on a picosecond time scale. The Raman backscattered light propagating through the channel of bubbles generates a second harmonic, observed at oblique angles. © 1996 The American Physical Society.