Thickness-dependent ultrafast nonlinear absorption properties of PtSe2 films with both semiconducting and semimetallic phases

Abstract

The bandgap, electrical, and optical properties of PtSe2 depend dramatically on the vertical stacking and fabrication method. Here, we study the nonlinear absorption properties of the PtSe2 films composed of both semiconducting and semimetallic phases in a single film. These PtSe2 films exhibit remarkable thickness-dependent saturable absorption for femtosecond pulses at 400 nm and 800 nm. The saturation intensities decrease with the increase in the film thickness due to the accompanied increase in the semimetallic component and are much smaller than the reported values of PtSe2 synthesized by thermally assisted conversion. The saturable absorption characteristics are confirmed by time-resolved spectroscopies. The nonlinear refractive indexes of these PtSe2 films should be smaller than 1 × 10–12 cm2/W. Our results imply that the optical nonlinearities of PtSe2 could be flexibly tuned by the synthesis method and thickness.