Fine-scale spatial and temporal structures of second-harmonic emission from an underdense plasma

Second-harmonic emission during the interaction between a laser beam and an underdense preformed plasma has been studied simultaneously using time-resolved images as well as two-dimensional time-integrated images. The emission appeared with very localized structures in space and pulsed in time. These structures are consistent with the presence of filamentary structures whose presence has been confirmed by Schlieren diagnostic. The spatial dimensions of the observed second-harmonic emission is in agreement with the scale length of the filamentation instability. The characterization of second-harmonic emission appears to be a potential diagnostic for filamentation.