Noise and dynamics in forward Brillouin interactions

TL;DR

This paper presents a comprehensive theoretical framework for understanding noise and dynamics in forward Brillouin scattering, highlighting differences from backward scattering and exploring mechanisms for amplification in micro- and nano-scale systems.

Contribution

It introduces a fully coupled nonlinear Hamiltonian model for forward Brillouin interactions, incorporating optomechanical effects and analyzing noise and amplification mechanisms.

Findings

Noise-initiated stimulated forward Brillouin scattering is generally suppressed.

The single-pass gain for forward Brillouin is often negative, preventing energy transfer.

Dispersive symmetry breaking can enable amplification similar to backward Brillouin scattering.

Abstract

In this paper, we explore the spatio-temporal dynamics of spontaneous and stimulated forward Brillouin scattering. This general treatment incorporates the optomechanical coupling produced by boundary-induced radiation pressures (boundary motion) and material-induced electrostrictive forces (photo-elastic effects), permitting straightforward application to a range of emerging micro- and nano-scale optomechanical systems. Through a self-consistent fully coupled nonlinear treatment, developed within a general Hamiltonian framework, we establish the connection between the power spectral density of spontaneously scattered light in forward Brillouin interactions and the nonlinear coupling strength. We show that, in sharp contrast to backward Brillouin scattering, noise-initiated stimulated forward Brillouin scattering is forbidden in the majority of experimental systems. In fact, the single-pass gain, which characterizes the threshold for energy transfer in back-scattering processes, is negative for a large class of forward Brillouin devices. Beyond this frequent experimental case, we explore mechanisms for dispersive symmetry breaking that lead to amplification and dynamics reminiscent of backward Brillouin scattering.