Enhanced Control of Transient Raman Scattering Using Buffered Hydrogen in Hollow-Core PCF

TL;DR

This paper demonstrates that adding a buffer gas to hollow-core photonic crystal fiber can enhance Raman gain through precise dispersion control, leading to efficient sideband generation at lower pressures.

Contribution

It reveals that buffer gases can counterintuitively increase Raman gain when dispersion is precisely managed, enabling lower-pressure operation and improved sideband conversion efficiencies.

Findings

Enhanced Raman gain with buffer gas addition under controlled dispersion.

Achieved up to 5% anti-Stokes conversion efficiency in visible spectrum.

High modal purity in emitted Raman sidebands.

Abstract

Many reports on stimulated Raman scattering in mixtures of Raman-active and noble gases indicate that the addition of a dispersive buffer gas increases the phase-mismatch to higher-order Stokes and antiStokes sidebands, resulting in preferential conversion to the first few Stokes lines, accompanied by a significant reduction in Raman gain due to collisions with buffer gas molecules. Here we report that, provided the dispersion can be precisely controlled, the effective Raman gain in gas-filled hollow-core photonic crystal fiber (PCF) can actually be significantly enhanced when a buffer gas is added. This counterintuitive behavior occurs when the nonlinear coupling between the interacting fields is strong, and can result in a performance similar to that of a pure Raman-active gas, but at much lower total gas pressure, allowing competing effects such as Raman backscattering to be suppressed. We report high modal purity in all the emitted sidebands, along with anti-Stokes conversion efficiencies as high as 5% in the visible and 2% in the ultraviolet. The results point to a new class of gas-based waveguide device in which the pressure-tunable nonlinear optical response is beneficially adjusted by the addition of other gases.