Group and phase velocity mismatch fringes in triple sum-frequency spectroscopy

TL;DR

This paper develops and experimentally verifies an analytic model predicting how group and phase velocity mismatches affect triple sum-frequency spectroscopy, revealing spectral fringes and strategies for mitigation.

Contribution

It introduces a novel analytic model for velocity mismatch effects in non-degenerate TSF and demonstrates experimental validation with ultrafast lasers.

Findings

Spectral fringes depend on velocity mismatches.

Velocity differences influence TSF spectral dependence.

Strategies can mitigate velocity mismatch effects.

Abstract

The effects of group and phase velocity mismatch are well-known in optical harmonic generation, but the non-degenerate cases remain unexplored. In this work we develop an analytic model which predicts velocity mismatch effects in non-degenerate triple sum-frequency mixing, TSF. We verify this model experimentally using two tunable, ultrafast, short-wave-IR lasers to demonstrate spectral fringes in the TSF output from a 500 $\mu$m thick sapphire plate. We find the spectral dependence of the TSF depends strongly on both the phase velocity and the group velocity differences between the input and output fields. We define practical strategies for mitigating the impact of velocity mismatches.