The Ultrafast Kerr Effect in Anisotropic and Dispersive Media

TL;DR

This paper investigates the ultrafast optical Kerr effect in anisotropic and dispersive media, revealing how group index and birefringence influence the nonlinear response and providing methods to extract material properties from time-resolved measurements.

Contribution

It introduces a detailed description of phase-mismatched ultrafast OKE and demonstrates how to quantify birefringence and group index from experimental data.

Findings

Group index and birefringence significantly affect OKE signals.

Birefringence can alter the character of the nonlinear response.

Methods to extract spectrally resolved birefringence and group index are developed.

Abstract

The ultrafast optical Kerr effect (OKE) is widely used to investigate the structural dynamics and interactions of liquids, solutions and solids by observing their intrinsic nonlinear temporal responses through nearly-collinear four-wave mixing (FWM). Non-degenerate mixing schemes allow for background free detection and can provide information on the interplay between a material's internal degrees of freedom. Here we show a source of temporal dynamics in the OKE signal that is not reflective of the intrinsic nonlinear response but arises from group index and momentum mismatch. It is observed in two-color experiments on condensed media with sizable spectral dispersion, a common property near an optical resonance. In particular birefringence in crystalline solids is able to entirely change the character of the OKE signal via the off-diagonal tensor elements of the nonlinear susceptibility. We develop a detailed description of the phase-mismatched ultrafast OKE and show how to extract quantitative information on the spectrally resolved birefringence and group index from time-resolved experiments in one and two dimensions.