Three photon absorption in ZnO and ZnS crystals

TL;DR

This study investigates three-photon absorption and nonlinear refraction in ZnO and ZnS crystals, revealing their potential for optical switching at telecommunication wavelengths through systematic experiments and modeling.

Contribution

It provides the first detailed analysis of 3PA spectra and nonlinear refraction dispersions in ZnO and ZnS, including higher-order effects and practical implications.

Findings

3PA spectra follow a specific wavelength dependence model

Higher-order nonlinear effects are negligible below 40 GW/cm2

ZnO and ZnS are promising for optical switching applications

Abstract

We report a systematic investigation of both three-photon absorption (3PA)spectra and wavelength dispersions of Kerr-type nonlinear refraction in wide-gap semiconductors. The Z-scan measurements are recorded for both ZnO and ZnS with femtosecond laser pulses. While the wavelength dispersions of the Kerr nonlinearity are in agreement with a two-band model, the wavelength dependences of the 3PA are found to be given by (3Ephoton/Eg-1)5/2(3Ephoton/Eg)-9. We also evaluate higher-order nonlinear optical effects including the fifth-order instantaneous nonlinear refraction associated with virtual three-photon transitions, and effectively seventh-order nonlinear processes induced by three-photon-excited free charge carriers. These higher-order nonlinear effects are insignificant with laser excitation irradiances up to 40 GW/cm2. Both pump-probe measurements and three-photon figures of merits demonstrate that ZnO and ZnS should be a promising candidate for optical switching applications at telecommunication wavelengths.