Large Third-Order Optical Kerr Nonlinearity in Nanometer-Thick PdSe₂ 2D Dichalcogenide Films: Implications for Nonlinear Photonic Devices

We report a large third-order nonlinear-optical response of palladium diselenide (PdSe2) films, a two-dimensional (2D) noble-metal dichalcogenide material. Both open-aperture (OA) and closed-aperture (CA) Z-scan measurements are performed with a femtosecond pulsed laser at 800 nm to investigate the nonlinear absorption and nonlinear refraction, respectively. In the OA experiment, we observe optical limiting behavior originating from large two-photon absorption (TPA) in the PdSe2 film of β = 3.26 × 10–8 m/W. In the CA experiment, we measure a peak–valley response corresponding to a large and negative Kerr nonlinearity of n2 = −1.33 × 10–15 m2/W, 2 orders of magnitude larger than that of bulk Si. We also characterize the variation of n2 as a function of the laser intensity, observing that n2 decreases in magnitude with incident laser intensity, becoming saturated at n2 = −9.96 × 10–16 m2/W at high intensities. These results verify the large third-order nonlinear-optical response of 2D PdSe2 as well as its strong potential for high-performance nonlinear photonic devices.