Nonlinear Infrared Photodetection Based on Strong Nondegenerate Two‐Photon Absorption of Perovskite Single Crystal

Abstract Halide perovskites have been recently shown to exhibit strong nonlinear optical properties such as two‐photon absorption, second harmonic generation, etc. In this work, the nondegenerate two‐photon absorption, i.e., when the energies of two photons absorbed are not the same, of methylammonium lead bromide single crystal is studied. It is found that the nondegenerate two‐photon absorption is much stronger than the degenerate two‐photon absorption. For the photon pair ℏω 1 = 2.96 eV, ℏω 2 = 0.73 eV, the nondegenerate two‐photon absorption coefficient reaches 51.3 cm GW −1 , which is around 6 times that of degenerate two‐photon absorption. Taking advantage of the strong nondegenerate two‐photon absorption, a nonlinear infrared pulse photodetector based on the combination of a methylammonium lead bromide single crystal and a silicon photodiode is developed. The infrared femtosecond laser pulses at 1700 nm can be well measured with a resolution on the order of 1 nJ and responsivity of 68 V W −1 . These findings provide novel insight for the understanding of nondegenerate nonlinear optical properties in halide perovskites and may open a new avenue for the development of high‐sensitivity infrared photon detection.