Saturable absorption and two-photon absorption in graphene

Abstract

Graphene, as a two-dimensional carbon material, exhibits unique linear and nonlinear optical absorption properties that have attracted a great deal of research interests. The saturation absorption of graphene has been studied in the infrared range. However, there is a large discrepancy in the reports of saturation intensity due to the different experimental conditions such as the graphene samples synthesized with different methods and the operating wavelength.

In the first part, we systematically studied the saturable absorption in graphene by carrying out Z-scan experiments at 780 nm with 1 kHz and 400-fs laser pulses on the monolayer, bilayer and multilayer epitaxial graphene, which have been demonstrated to be high quality graphene samples. Subsequently, we studied the spectral dependence of saturable absorption of graphene by carrying out the Z-scan experiments in the spectrum range from 900 nm to 1100 nm with femtosecond laser pulses. At last, we compared our experimental results with the reports from other groups and the saturable absorption of vertical aligned CNTs thin film.

In the second part, we explored the two-photon absorption properties of monolayer and bilayer graphene by carrying out pump-probe and Z-scan experiments with femtosecond laser pulses at 780 nm and 1100 nm. Subsequently, the two-photon absorption coefficient of graphene was theoretically studied by the second-order quantum perturbation theory.

The study of saturable absorption and two-photon absorption properties of graphene will facilitate the application of graphene in generating ultrashort laser pulses and other electro-optical devices.