Femtosecond self-diffraction as a measure of the nonlinear response spectrum

TL;DR

This paper demonstrates a method to measure the electronic third-order nonlinear susceptibility spectrum of materials using femtosecond self-diffraction, accounting for absorption and phase matching, applicable across various compounds.

Contribution

It introduces a novel experimental approach to directly evaluate the nonlinear susceptibility spectrum using femtosecond self-diffraction in dye solutions, with theoretical validation.

Findings

The method accurately reproduces the $ ext{| ext{χ}^{(3)}|}$ spectral profile in low absorption, thin samples.

Experimental results align with theoretical predictions across different dye concentrations.

The technique enables measurement of bound-electronic nonlinear responses over a wide spectral range.

Abstract

Self diffraction is a four-wave mixing process proportional to the square modulus of third-order nonlinearity susceptibility $\chi^{(3)}$, which is related to the material's electronic and thermal properties. In this study, we investigate the wavelength dependence of the self-diffracted signal generated by a femtosecond pulsed laser in a dye solution to directly evaluate the electronic third-order nonlinear susceptibility spectrum. By accounting for absorption effects and phase matching conditions, we determine the $\vert\chi^{(3)}\vert$ for different concentrations. Experimental results complemented with theoretical predictions, show that in the low absorption and thin sample limits, the signal reproduce the $\vert\chi^{(3)}\vert$ spectral profile. These findings demonstrate the feasibility of measuring nonlinear susceptibility spectra arising solely from the bound-electronic response across a wide spectral range and for various compounds.