Filamentation and second-harmonic emission in laser-plasma interactions

Abstract

Interferograms of an underdense, preformed plasma which is irradiated with a line-focused laser beam show pronounced density perturbations. The interferograms are compared to simultaneous, gated images of second-harmonic emission. We observe a correlation between the spatial positions of the density perturbations and the peak of the second-harmonic emission. We interpret these phenomena as being emission from a local, nonlinear focus in the underdense plasma, rather than from the entire length of a filament.