Role of copper dopant in two-photon absorption and nonlinear optical properties of sprayed ZnS thin films for optical limiting applications

This letter reports on the effect of copper dopant (3,5, and 10 at%) on nonlinear optical (NLO) properties of spray deposited ZnS (CZS) thin films. The standard Z-scan technique with diode-pumped solid-state (DPSS) laser was used to determine third order NLO properties at 532 nm. Maximum nonlinear absorption coefficient, β (31.9×10⁻² cm/W) was observed for 5 at% doped ZnS corresponding to reverse saturable absorption (RSA) which is useful for optical limiting applications. Two-photon absorption (TPA) and self-defocusing effect was confirmed using theoretical fit. Nonlinear figure of merit was found to be less than unity confirming their usefulness in optical switching. Optical limiting studies showed threshold value in the range of 2.8–8.7 kJ/cm². The NLO results showed that the cost effective and industrially beneficial spray deposited CZS films are suitable for optical limiting applications.