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

Abstract

We present an experimental investigation on third-order nonlinear optical properties of RF-sputtered WSe2 thin films using a single-beam Z-scan technique around the optical communication window in a near-infrared spectral band. The nonlinear absorption coefficient was obtained from the open-aperture Z-scan transmission using ultrashort pulses centered at 1520nm excitation wavelength. The results show a reverse saturable absorption signature for all the WSe2 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 WSe2 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.