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-In2Se3 thin film and investigate the broadband nonlinear absorption (β) and refraction (n2) characteristics. The β-In2Se3 semiconductor shows an excellent optical nonlinearity with large β in 10^2 cm/GW scale and n2 in 10^-12 cm2/W scale from visible to near-infrared wavelengths, which are superior to those of metal carbides and nitrides (MXenes) and metal-organic frameworks (MOFs). This excellent optical nonlinearity makes β-In2Se3 a promising candidate for advanced nanophotonic devices and beyond.