Impact of defects on the χ(3) optical nonlinearity of sputtered WSe2 thin films in the optical communication band

We present an experimental investigation on third-order nonlinear optical properties of RF-sputtered WSe[Formula: see text] thin films using a single-beam [Formula: see text]-scan technique around the optical communication window in a near-infrared spectral band. The nonlinear absorption coefficient was obtained from the open-aperture [Formula: see text]-scan transmission using ultrashort pulses centered at [Formula: see text] excitation wavelength. The results show a reverse saturable absorption signature for all the WSe[Formula: see text] films due to two-photon absorption (TPA) mediated electronic transitions. The dependency of the TPA coefficient on film thickness is analyzed through the modification in an electronic band structure essentially caused due to defects induced in the samples. In addition, we also explored the impact of high laser intensity on the TPA process, which essentially pointed toward a significant contribution of free-carrier absorption at small laser intensities in WSe[Formula: see text] thin films. This investigation provides a basis for optimally tailoring the nonlinear optical properties of transition-metal-dichalcogenides via bandgap engineering for improving photonic device functionality.