Effect of ponderomotive forces on wave dispersion and second-harmonic light emissions in laser-produced plasmas

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Abstract
In this paper we analyze the basic characteristics of experimentally observed second-harmonic light spectra generated during long-duration high-intensity laser-plasma interactions. It is shown that the observed spectrum characteristics of threshold, red-shift, and target material dependence can be explained by a two-step mechanism of parametric coupling affected by a strong "imposed" ponderomotive force. The imposed ponderomotive force, generated by the laser light's standing-wave pattern, affects the parametric coupling through increased linear wave dispersion. Experimental results agree with the theoretical prediction and suggest the existence of additional parametric instabilities in the ponderomotive-force-dominated regime.