Vertically standing PtSe₂ film: A saturable absorber for a passively mode-locked Nd:LuVO₄ laser

The novel vertically standing PtSe₂ film on transparent quartz was prepared by selenization of platinum film deposited by the magnetron sputtering method, and an Nd:LuVO₄ passively mode-locked solid-state laser was realized by using the fabricated PtSe₂ film as a saturable absorber. The X-ray diffraction pattern and Raman spectrum of the film indicate its good crystallinity with a layered structure. The thickness of PtSe₂ film is measured to be 24 nm according to the cross-section height profile of the atomic force microscope image. High-resolution transmission electron microscopy images clearly demonstrate its vertically standing structure with an interlayer distance of 0.54 nm along the c-axis direction. The modulation depth (ΔT) and saturation fluence (Φ_s) of PtSe₂ film are measured to be 12.6% and 17.1 μJ∕cm², respectively. The obtained mode-locked laser spectrum has a central wavelength of 1066.573 nm, with a 3 dB bandwidth of 0.106 nm. The transform limited pulse width of the mode-locked laser was calculated to be 15.8 ps. A maximum average output power of 180 mW with a working repetition rate of 61.3 MHz is obtained. To the best of our knowledge, this is the first report of the generation of ultrafast mode-locked laser pulses by using layered PtSe₂ as a saturable absorber.