Studying ultrafast carrier diffusion with transient holographic microscopy.

Transient absorption microscopy enables the observation of ultrafast excited-state dynamics with spatial resolution. Conventional implementations are technologically limited to small fields of view around a single diffraction-limited spot, offering no statistical information on the photophysics of the sample. We recently used off-axis holography to demonstrate an all-optical lock-in camera enabling widefield transient imaging at arbitrary repetition rate. Here, we propose a structured excitation pattern comprised of hundreds of diffraction-limited spots as an effective way to study diffusion of carriers in semiconductors whilst probing the sample's heterogeneity over areas more than 100 times larger than current techniques. We validate the technique studying exciton diffusion in metal-halide perovskites thin films and we show how the signal-to-noise ratio can be increased by averaging the signal of individual spots, allowing us to measure at low excitation densities to avoid many-body effects. We envision that this technique can be used to provide a much more complete picture of photophysical processes in heterogeneous samples.