Filamentation of spatiotemporal smoothed focal spot in plasma by Beam Smoothing scheme

Abstract

Abstract An intense laser would suffer nonlinear effects during its propagation in plasma, which greatly affects the illumination uniformities of laser beams in a hohlraum for ignition. Based on the theory of the relativistic and ponderomotive effects, and taking the beam smoothing technologies into consideration, the propagation model of spatiotemporal smoothed focal spot has been built up. The filamentation characteristics of the focal spots with different beam smoothing techniques, including smoothing by spectral dispersion and radial smoothing have been analyzed. In turn, the beam smoothing technique is optimized based on the filament characteristics of the focal spot. The results show that the filamentation of the laser in plasma is a complex nonlinear phenomenon affected by the relativistic and ponderomotive effects simultaneously. Radial smoothing performs better on the mitigation of the filamentation due to its uniform speed of spatial sweep. In addition, the temporal shape of the pump laser should be reasonable to ensure the radial smoothing performance while suppressing the filamentation instability.