Impact of pauli-blocking effect on optical limiting properties of WSe2 thin films

We present a detailed investigation on thickness-dependent third-order (χ(3)) nonlinear optical properties of RF-sputtered WSe2 thin-films using ultrashort pulses centered at different excitation wavelengths. The single-beam Z-scan based investigation in the visible spectrum reveals a predominant Pauli-blocking effect led saturable absorption or optical limiting in WSe2 thin-films. The study also explores the dispersion in third-order nonlinear susceptibility (χ(3)) in WSe2 thin films. Interestingly, WSe2 thin-films of any thickness exhibit a self-focusing effect depicting a positive nonlinear refractive index (n2 > 0). The frequency-dependent nonlinear absorption (β) bear distinct correlations with the bandgap of the films which is also investigated through density-functional-theory (DFT) based simulations. The alteration in bandstructure is primarily due to the Se-deficiency induced defect bands in WSe2 thin-films which has discernible impact on the optical limiting characteristics. •The third-order nonlinear optical properties of RF sputtered WSe2 thin films are investigated.•The thin films exhibit strong Pauli-blocking induced saturable absorption effect which is strongy affected by the defect states/bands emanating from Se-deficiency in the films.•The density-functional-theory (DFT) simulations predict the defect state(s) which closely match with the experimental observations.