Collective stimulated Brillouin scattering modes of two crossing laser beams with shared ion acoustic wave

TL;DR

This paper presents an exact analytic solution for the convective amplification of collective stimulated Brillouin scattering with shared ion acoustic waves in overlapping laser beams, highlighting effects of crossing angle, polarization, and beam overlap.

Contribution

It provides a novel linear kinetic model analysis of shared ion acoustic wave modes stimulated by crossing laser beams, including effects of wavelength difference, crossing angle, polarization, and beam overlap.

Findings

Wavelength difference of several nanometers has negligible effect.

Crossing angle, polarization, and beam overlap significantly influence shared IAW modes.

Out-of-plane modes are important for certain polarization states and crossing angles.

Abstract

The overlapping of multiple beams is common in inertial confinement fusion (ICF), making the collective stimulated Brillouin scattering (SBS) with shared ion acoustic wave (IAW) potentially important because of the effectively larger laser intensities to drive the instability. In this work, based on a linear kinetic model, an exact analytic solution for the convective amplification of SBS with the shared IAW modes stimulated by two overlapped beams is presented. From this solution, effects of the wavelength difference, crossing angle, polarization states, and finite beam overlapping volume of the two laser beams on the shared IAW modes are studied. It is found that a wavelength difference of several nanometers between the laser beams has negligible effects, except for a very small crossing angle about one degree. However, the crossing angle, beam polarization states, and finite beam overlapping volume can have significant influences on the shared IAW modes. Furthermore, the out-of-plane modes, in which the wavevectors of daughter waves lie in the different planes from the two overlapped beams, are found to be important for certain polarization states and crossing angles of the laser beams with the finite beam overlapping volume. This work is helpful to comprehend and estimate the collective SBS with shared IAW in ICF experiments.