Large nonlinear optical absorption and refraction of β-In₂Se₃ thin film from above to below bandgap excitation

Nonlinear optical materials, especially two-dimensional materials, are anticipated to reveal broadband optical nonlinearity for future miniaturized photonic applications. Herein, we report a physical vapor deposition method to produce β-In 2 Se 3 thin film and investigate the broadband nonlinear absorption ( β ) and refraction (n 2 ) characteristics. The β-In 2 Se 3 semiconductor shows an excellent optical nonlinearity with large β in 10 2 cm GW −1 scale and n 2 in 10 −12 cm 2 W −1 scale from visible to NIR wavelengths, which are superior to those of metal carbides and nitrides (MXenes) and metal-organic frameworks. This excellent optical nonlinearity makes β-In 2 Se 3 a promising candidate for advanced nanophotonic devices and beyond.