Propagation in a plasma of a laser beam smoothed by longitudinal spectral dispersion

The paraxial propagation of a large-bandwidth laser beam focused by a grating onto a plasma is examined. Plasma nonlinearity inducing filamentation is modeled by ion-acoustic waves via three-dimensional simulations. The resulting longitudinal spectral dispersion (LD) smoothing is compared to the standard transverse dispersion (TD) smoothing. The coherence time and size, the peak intensity and the propagation angle of the speckles are addressed. The influence of a transverse plasma flow is discussed. No special advantage of one of the smoothing techniques is observed for controlling filamentation. Only beam bending appears to be reduced when LD is used instead of TD. (C) 2003 American Institute of Physics.