Intense second-harmonic generation in two-dimensional PtSe.

Platinum diselenide (PtSe), classified as a noble metal dichalcogenide, has garnered substantial interest owing to its layer-dependent band structure, remarkable air-stability, and high charge-carrier mobilities. These properties make it highly promising for a wide array of applications in next-generation electronic and optoelectronic devices, as well as sensors. Additionally, two-dimensional (2D) PtSe demonstrates significant potential as a saturable absorber due to its exceptional nonlinear optical response across an ultrabroad spectra range, presenting exciting opportunities in ultrafast and nonlinear photonics. In this work, we explore the second-order nonlinear optical characteristics of 2D PtSe by analyzing its second-harmonic generation (SHG) excited by a pulsed laser at 1064 nm. Our investigation unveils a layer-dependent SHG response in PtSe, with prominent SHG intensity observed in few-layer PtSe. The distinct six-fold polarization dependence pattern observed in the SHG intensity reflects the inherent threefold rotational symmetry inherent to the PtSe crystal structure. Remarkably, the SHG intensity of 4-layer PtSe surpasses that of mechanically exfoliated monolayer molybdenum disulfide (MoS) by approximately two orders of magnitude (60-fold), underscoring its exceptional second-order nonlinear optical response. Combined with its ultrahigh air-stability, these distinctive nonlinear optical characteristics position two-dimensional PtSe as a promising candidate for ultrathin nonlinear nanophotonic devices.