Effect of ultraviolet radiation exposure on optical nonlinearity and switching traits of SnO2 thin films deposited by thermal evaporation

Abstract

Highly transparent amorphous SnO2 thin films were deposited using the thermal evaporation method and characterized. The influence of the UV radiation exposure (for approximately 2 h) on the morphology, linear and nonlinear optical properties of the films was evaluated for the first time. The optical switching performance of the as-deposited thin films was examined using the pump–probe technique. A continuous wave (CW) diode-pumped solid-state laser (532 nm with maximum power of 100 mW) and He-Ne laser (633 nm with maximum power of 35 mW) was used for the pump and probe beam, respectively. The band gap energies of the films were calculated using the Mott and Davis model fitting procedure. The films transmittance was increased and band gap was decreased upon the UV exposure. The signal modulations in the films were observed with the increase in the pump power. The signal intensities of both as-deposited and UV radiation exposed films were correspondingly dropped from 7.58 to 7.47 mW and from 8.16 to 8.05 mW, when the pump power was raised beyond 20 mW. The achieved SnO2 films displayed unaltered dynamic range under the UV radiation exposure. In addition, the nonlinear absorption coefficients of the UV radiation exposed films were increased from 0.10139 to 0.36435 cm W-1. This indicated the stabilization of the films upon the UV exposure and subsequent removal of the excess oxygen. The higher value of the nonlinear absorption by the films satisfied their figure of merit. The proposed SnO2 thin films may be effective for the development of the nonlinear optical devices working in the UV region.