Smoothing of transverse nonuniformities at the critical density in laser interaction with nonuniform plasmas

Abstract This study addresses the smoothing of transverse inhomogeneities at the critical layer for S- and P-polarized laser pulses interacting with plasmas which are inhomogeneous in the pulse propagation direction. Numerical simulations, incorporating ion mobility, demonstrate the formation of low-density plasma channels, which serve as waveguides for the lower-frequency components of the laser pulse. These channels are enclosed by regions of higher plasma electron density that act as scattering mirrors for the higher-frequency components. The channels are inclined relative to the direction of laser propagation. At the critical layer, where the pulse amplitude intensifies, localized plasma electron cavities initially form before merging into a uniform transverse channel due to the ponderomotive force of the trapped electromagnetic field. These findings are relevant to inertial confinement fusion, as they suggest that the homogenization of plasma structures could facilitate more uniform energy deposition in the supercritical plasma region and the shock-wave formation area.