Interferometric determination of intrinsic nonlinear Kerr index in lead-halide perovskites

Abstract

Lead halide perovskites have recently been reported to demonstrate an exceptionally high nonlinear (Kerr) refractive index n${}_2$ of up to 10${}^{-8}$ cm${}^2$/W in CH${}_3$NH${}_3$PbBr${}_3$. Other researchers however observe different, substantially more conservative numbers. In order to resolve this disagreement the nonlinear Kerr index of a bulk sample of lead halide perovskite was measured directly by means of an interferometer. This approach has many advantages as compared to the more standard z-scan technique. In particular this method allows studying the induced changes to the refractive index in a time-resolved manner, thus enabling to separate the different contributions to $n_2$. The extracted n${}_2$ values for CsPbBr${}_3$ and MAPbBr${}_3$ at $\lambda \approx 1\mu m$ are $n_2=+2.1\times$ 10${}^{-14}$ cm${}^2$/W and $n_2=+6\times$ 10${}^{-15}$ cm${}^2$/W respectively hence substantially lower than what has been indicated in most of the previous reports implying the latter should be regarded with a great care.