Second Harmonic Generation of Stimulated Raman Scattered Light in Underdense Plasmas

Experiments examining nonlinear scattering mechanisms of high intensity (2 × ${10}^{18}$ W/${\mathrm{cm}}^2$) laser light in underdense plasmas were performed. Redshifted second harmonic emission at 45° from the directly backscatterd direction was observed from field ionized plasmas having electron densities ranging up to ${10}^{19}$ ${\mathrm{cm}}^{-3\mathrm{}}$. This result is consistent with the doubling of stimulated Raman scattered light from large plasma electron density gradients produced by ponderomotive cavitation.