Observation of Interband Two-Photon Absorption Saturation in CdS Nanocrystals

TL;DR

This paper reports the first observation of interband two-photon absorption saturation in CdS nanocrystals, demonstrating significantly higher saturation intensity compared to bulk CdS, using femtosecond laser techniques.

Contribution

It provides experimental evidence of TPA saturation in CdS nanocrystals and compares it to bulk material, highlighting size-dependent nonlinear optical properties.

Findings

Saturation intensity for CdS NCs is 190 GW/cm^2.

Two orders of magnitude higher saturation intensity in NCs than bulk.

Results agree with an inhomogeneously-broadened TPA model.

Abstract

We report the observation of interband two-photon absorption (TPA) saturation in cadmium sulfide nanocrystals (CdS NCs) under intense femtosecond laser excitation with 1.6-eV photon energy. The observation has been compared to interband TPA saturation in bulk CdS under the same experimental conditions. By using both Z-scan technique and transient absorption measurement, the saturation intensity has been determined to be 190 GW/cm^2 for CdS NCs of 4-nm diameter, which shows two orders of magnitude greater than that for CdS bulk crystal. The results are in agreement with an inhomogeneously-broadened, saturated TPA model.