On the influence of optical smoothing techniques on cross-beam energy transfer

TL;DR

This paper investigates how optical smoothing techniques, especially spectral dispersion, affect cross-beam energy transfer in inertial confinement fusion, highlighting their importance for accurate modeling and experimental design.

Contribution

It introduces a linear kinetic model and compares it with fluid and particle-in-cell simulations to show the significant impact of spectral dispersion and other factors on CBET.

Findings

Spectral dispersion significantly influences CBET.

Accounting for plasma velocity and beam modulation improves predictions.

Phase modulator synchronization strongly affects power transfer.

Abstract

In the context of inertial confinement fusion (ICF) experiments, spatial and temporal laser beam smoothing techniques are used to control the beams propagation in hohlraum plasmas. Currently, spatial and temporal smoothing are either neglected or not properly taken into account in the inline cross beam energy transfer (CBET) models included in the hydrodynamic codes dedicated to the design of these experiments. In some cases, which we will highlight in this study, this simplification leads to important errors in the power transfer of importance for the implosion symmetry of the capsule, either in the direct or indirect drive ICF configurations. In a recent study [A. Oudin et \textit{al}., Phys. Plasmas \textbf{32}, 042706 (2025)], we demonstrated the necessity of accounting for spatial smoothing when modeling CBET, provided that the beams do not have the same wavelength. This work presents a linear kinetic model compared with Hera paraxial fluid simulations and compared with the Smilei particle-in-cell code, demonstrating the important influence of smoothing by spectral dispersion on CBET. Moreover, we demonstrate the importance of accounting for the plasma velocity profile, the beam modulation bandwidth, and the spectral dispersion to better predict the power exchanged between the beams. Additionally, we reveal a strong sensitivity of this power transfer to the synchronization of the phase modulators.