Evidence of parametric instabilities in second harmonic spectra from 1054 nm laser-produced plasmas

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Abstract
Second harmonic spectra emitted from 1054 nm laser‐produced plasmas have been observed in side‐ and backscattering and are shown to have angularly dependent, complex structures. Sidescattered spectra show regularly spaced (∼20 Å) Stokes components at intensities above 5×1013 W/cm2. The Stokes components are polarized and stronger in the plane of the polarization of the incident laser. These Stokes components are interpreted to be caused by a combination of electron plasma waves generated by the parametric decay instability and the subsequent electron decay instability. Backscattered spectra show additional finely spaced red‐shifted satellites above 4×1014 W/cm2, indicative of the electron decay instability of plasmons generated from resonance absorption.