Optical nonlinear refractive index measurements of Cr₂Te₃ with an immense photothermal effect

In this work, the optical nonlinearity of PVD-grown Cr₂Te₃ thin films of 33- and 100-nm thickness with an immense thermal optical effect was investigated. By removing the thermally induced background signal, the n₂ value without accumulated heat could then be estimated to be of the order of magnitude of around 10⁻⁸ cm² W⁻¹. A decrease in the n₂ value with the pump power was observed, leading to increased absorption. In addition, the changing sign for the 100-nm-thick thin film as the pump power exceeded 450 mW was investigated, exhibiting good agreement with the observed additional increasing temperature resulting from the anomalous increasing absorption. This work paves the way to not only characterize the optical nonlinearity of samples with initiable thermal effects but also to evaluate materials with potential for real applications through the methodology provided.