Experimental studies of the high and low frequency electromagnetic radiation produced from nonlinear laser-plasma interactions

We present the results of experiments on the generation of both high and low frequency electromagnetic radiation from the nonlinear interaction of intense laser beams with underdense plasmas. High frequency radiation is generated as a result of the reflection of a near-infrared laser beam by breaking plasma waves. In the proof-of-principle experiment, a 2 TW, 76 fs Ti:sapphire laser pulse was focused to generate wake waves, and a ~0.1 TW laser pulse was focused to collide with the electron density modulations. Frequencies of the reflected light were 56–110 times higher than that of the initial laser. The estimated number of photons per solid angle was 3×107 photons/sr. Low frequency radiation is emitted by the plasma as well. We found that the polarization of the radiation was similar to that of the driver laser. These properties are in accordance with the generation mechanism by relativistic solitons.