Second Harmonic Emission from Laser-Preformed Plasmas as a Diagnostic for Filamentation in Various Interaction Conditions

Second harmonic emission from underdense laser-preformed plasmas has been investigated in forward direction with respect to the interaction beam axis. Two series of measurements have been performed using two focusing conditions and changing the intensity of the interaction beam. Effects of beam smoothing by random phase plates on second harmonic emission were also tested. Novel information on density and intensity gradients driven by filamentation instability was obtained.