The nonlinear optical properties of nickel nano-films in the cw regime: Proposed model

In this research, the nonlinear optical properties of Ni nano-films were investigated in the cw regime. Metallic films with thicknesses of 4, 8 and 16 nm were fabricated at room temperature by thermal evaporation. The film's nonlinear optical properties were determined using the z-scan technique pumped at 650 nm. The films showed saturable absorber behavior which became stronger with the film's thickness. However, this behavior was not observed when the films were irradiated at 405 nm. A model based on the allowed density of states in the fabricated films is adopted to explain the dependence of the saturable absorber on the irradiation wavelength. Through the mechanistic discernments of the model, capability of controlling nonlinear optical limiting by light is discussed. •Nickel nano-films were prepared using thermal evaporation.•The thermal optical nonlinearity was investigated using z-scan technique.•Dependence of saturable absorber on the irradiation wavelength was observed.•The optical nonlinearity was explained using density of states model.