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

TL;DR

This study investigates how the thickness and defect-induced bandstructure changes in WSe2 thin films influence their third-order nonlinear optical properties and optical limiting behavior, highlighting the role of Pauli-blocking effects.

Contribution

It provides new insights into the thickness-dependent nonlinear optical responses of WSe2 films and links defect-induced bandstructure modifications to optical limiting performance.

Findings

Pauli-blocking induces saturable absorption and optical limiting.

WSe2 films exhibit self-focusing with positive nonlinear refractive index.

Bandgap and defect states significantly affect nonlinear susceptibility.

Abstract

We present a detailed investigation on thickness-dependent third-order (\c{hi}^(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 the prominent role of Pauli-blocking towards inducing saturable absorption or optical limiting in WSe2 thin-films of various thicknesses. The study also explores the dispersion in third-order nonlinear susceptibility (\c{hi}^(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 (\b{eta}) 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.