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

Abstract

We present a detailed investigation on thickness-dependent third-order (χ (3) ) nonlinear optical properties of RF-sputtered W Se2 thin-films using ultrashort pulses centered at different excitation wavelengths. The single-beam Z-scan based investigation in the visible spectrum reveals the prominent role of Pauli-blocking towards inducing saturable absorption or optical limiting in W Se2 thin-films of various thicknesses. The study also explores the dispersion in third-order nonlinear susceptibility (χ (3) ) in W Se2 thin films. Interestingly, W Se2 thin-films of any thickness exhibit a self-focusing effect depicting a positive nonlinear refractive index (n2 > 0). The frequencydependent 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 W Se2 thin-films which has discernible impact on the optical limiting characteristics.