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

Abstract

The effects of group- and phase-velocity mismatch are well known in optical harmonic generation, but the nondegenerate cases remain unexplored. In this work we develop an analytic model which predicts velocity mismatch effects in nondegenerate 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-$\ensuremath{\mu}\mathrm{m}$-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.