| Summary: | In this paper, we propose an optically controlling broadband terahertz modulator of a layer-dependent PtSe<sub>2</sub> nanofilm based on a high-resistance silicon substrate. Through optical pump and terahertz probe system, the results show that compared with 6-, 10-, and 20-layer films, a 3-layer PtSe<sub>2</sub> nanofilm has better surface photoconductivity in the terahertz band and has a higher plasma frequency <i>ω<sub>p</sub></i> of 0.23 THz and a lower scattering time <i>τ<sub>s</sub></i> of 70 fs by Drude–Smith fitting. By the terahertz time-domain spectroscopy system, the broadband amplitude modulation of a 3-layer PtSe<sub>2</sub> film in the range of 0.1–1.6 THz was obtained, and the modulation depth reached 50.9% at a pump density of 2.5 W/cm<sup>2</sup>. This work proves that PtSe<sub>2</sub> nanofilm devices are suitable for terahertz modulators.
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