Full-wave and ray-based modeling of cross-beam energy transfer between laser beams with distributed phase plates and polarization smoothing

Abstract

Radiation-hydrodynamic simulations of inertial confinement fusion (ICF) experiments rely on ray-based cross-beam energy transfer (CBET) models to calculate laser-energy deposition. The ray-based models assume locally plane-wave laser beams and polarization-averaged incoherence between laser speckles for beams with polarization smoothing. The impact of beam speckle and polarization smoothing on CBET are studied using the 3-D wave-based laser–plasma interaction code LPSE. The results indicate that ray-based models underpredict CBET when the assumption of spatially averaged longitudinal incoherence across the CBET interaction region is violated. A model for CBET between linearly polarized speckled beams is presented that uses ray tracing to solve for the real speckle pattern of the unperturbed laser beams within the eikonal approximation and gives excellent agreement with the wave-based calculations. OMEGA-scale 2-D LPSE calculations using ICF-relevant plasma conditions suggest that the impact of beam speckle on laser absorption calculations in ICF implosions is small (<1%).