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.

中文翻译：

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具有半导体和半金属相的 PtSe2 薄膜的厚度相关超快非线性吸收特性

PtSe2 的带隙、电学和光学特性在很大程度上取决于垂直堆叠和制造方法。在这里，我们研究了由单个薄膜中的半导体和半金属相组成的 PtSe2 薄膜的非线性吸收特性。这些 PtSe2 薄膜对 400 nm 和 800 nm 的飞秒脉冲表现出显着的依赖于厚度的饱和吸收。由于伴随着半金属成分的增加，饱和强度随着薄膜厚度的增加而降低，并且远小于通过热辅助转化合成的 PtSe2 的报道值。可饱和吸收特性由时间分辨光谱证实。这些 PtSe2 薄膜的非线性折射率应小于 1 × 10–12 cm2/W。