Single-beam reflection technique for determination of nonlinear-refractive index of thin-film semiconductors using an electrically focus tunable lens

In this paper, we propose a technique named reflection F-scan or RF-scan, that can be used to measure the nonlinear-refractive index n_2 of thin-film semiconductors. In this technique, a p-polarized Gaussian beam is focused using an electrically focus-tunable lens onto a sample, which is positioned at a fixed distance from the lens and makes an angle with respect to the optical axis. Due to EFTL has the capability to vary its focal distance over a specific range when an electric current is applied to it. The electrically focus-tunable lens varies its focal distance as a function of an applied electric current over a specific range thus, when light is focused on the surface of the sample the beam intensity is high enough to generate nonlinear optical effects such as changes in the refractive index of the material. This changes are then register as variations in reflectance, measured by an intensity detector. Results for three-dimensional CH3NH3PbBr3 hybrid perovskite thin films are presented.