Direct ultrafast carrier imaging in a perovskite microlaser with optical coherence microscopy

Abstract

Nanophotonics is an actively developing field of optics that finds application in various areas, from biosensing to quantum computing. The study of ultrafast modulation of the refractive index Δn is an important task in nanophotonics, since it reveals the features of light–matter interaction inside devices. With the development of active photonic devices such as emitters and modulators, there is a growing need for Δn imaging techniques with both high spatial and high temporal resolutions. Here, we report on an all-optical ultrafast Δn imaging method based on phase-sensitive optical coherence microscopy with a resolution of 1 ps in time and 0.5 µm in space and a sensitivity to Δn down to 10−3RIU. The advantages of the method are demonstrated on emerging nanophotonic devices—perovskite microlasers, in which the ultrafast spatiotemporal dynamics of the refractive index during lasing is quantitatively visualized, illustrating the features of relaxation and diffusion of carriers in perovskites. The developed method allows us to estimate the ultrafast carrier diffusion and relaxation constants simultaneously and to show that the CsPbBr3 perovskite carrier diffusion coefficient is low compared to other semiconductors even during lasing at high carrier densities, which leads to high localization of the generated carrier cloud, and, consequently, to high fluorescence and lasing efficiency. The resulting technique is a versatile method for studying ultrafast carrier transport via Δn imaging, paving an avenue for the applications of optical coherence tomography and microscopy in the research of nanophotonic devices and materials.