Highly-efficient perturbative Raman shifting by engineering the nonlinear temporal response

TL;DR

This paper introduces a time-domain theoretical framework for Raman scattering that captures all temporal regimes, revealing new insights and enabling more efficient frequency shifting in various media.

Contribution

The authors develop a unified time-domain approach to Raman interactions, surpassing traditional frequency-domain models and demonstrating enhanced quantum efficiency through experimental gas mixture tuning.

Findings

Up to four-fold increase in quantum efficiency using gas mixtures.

Time-domain analysis reveals distortions affecting frequency shifting.

Unity-efficiency Raman shifting is achievable.

Abstract

Raman scattering underlies a broad range of spectroscopic and light-generation techniques, yet its conventional description, based on the Raman gain spectrum, accurately describes only long-pulse, steady-state dynamics. We present a time-domain theoretical approach that provides a unified and physically-transparent description of Raman interactions across all temporal regimes. It enables direct visualization of Raman temporal dynamics and accounts for spectrotemporal aspects of Raman phenomena, which cannot be addressed by prior theories. In particular, molecules with strong Raman responses do not produce an efficient soliton self-frequency shift in gas-filled hollow-core fibers. The time-domain analysis exposes temporal and spectral distortions from the Raman response that impact frequency-shifting detrimentally, and identifies how these distortions can be suppressed by reducing the Raman interaction to a perturbation on the electronic response. Experiments that employ gas mixtures with tunable Raman fractions of the nonlinear response demonstrate up to a four-fold increase in quantum efficiency (from 20 to 80%) compared to the pure molecular gas, and unity-efficiency Raman shifting will be possible. The new time-domain framework uncovers phenomena that are inaccessible through the decades-old frequency-domain treatment of Raman scattering, and it applies to Raman interactions in solids, liquids, and gases on various timescales.