Analysis and control of Raman phonon dynamics for enhanced optical frequency conversion

TL;DR

This paper clarifies the physical role of Raman phonons in optical frequency conversion, introduces a phonon-controlled approach for efficient Stokes conversion, and confirms it through numerical simulations.

Contribution

It presents a new time-domain framework that incorporates phonon dynamics into Raman scattering analysis, enabling better control of frequency conversion processes.

Findings

Raman phonons correspond to oscillatory index modulation components.

A linear phonon-mediated interaction within Raman scattering is identified.

Numerical simulations confirm the effectiveness of phonon-controlled frequency conversion.

Abstract

Raman phonons are quantized molecular motions that arise from the inelastic scattering of light and mediate a wide range of spectroscopic and nonlinear optical phenomena. These can play a major role in frequency-conversion processes, but commonly-used theoretical treatments based on the Raman gain spectrum largely neglect the phonons and their dynamical interaction with the field. In this work, we clarify the physical role of Raman phonons within a recently-developed time-domain framework based on the Raman-induced index modulation, and show that phonons correspond to the oscillatory component of the Raman-induced index modulation. The analysis further reveals a linear phonon-mediated interaction embedded within Raman scattering, in which optical fields couple through wave-vector matching with existing phonons. This mechanism underlies, but has been neglected in, coherent Stokes and anti-Stokes scattering, as well as molecular modulation. Building on this insight, we introduce a phonon-controlled approach that enables efficient conversion into a selected Stokes order by tuning the wave-vector-matching relation between the driven phonons and the targeted Raman process, and we confirm the approach by numerical simulations that consider realistic Raman dynamics. These results provide a clearer physical interpretation of Raman phonons and their dynamics, and offer new strategies for controlling Raman interactions.