Ultralong pump-probe movies of magnon and phonon dynamics from ultrafast generation to microsecond relaxation

Abstract

The long lifetimes of magnons and phonons make them attractive for information-processing devices, highlighting the importance of visualizing their spatiotemporal dynamics from generation through relaxation. Ultrafast pump-probe spectroscopy is a powerful tool for investigating their early-stage dynamics after impulsive excitation; however, their long-lived nature makes it challenging to comprehensively track their evolution across all relevant time scales while maintaining sufficient temporal resolution. Here, we demonstrate spatiotemporal tracking of magnon and phonon dynamics over more than seven orders of magnitude in time, from 500 femtoseconds to 20 microseconds, using $4 \times 10^7$ sampled time points enabled by the highly precise time base of optical frequency combs. The resulting spatiotemporal movie, consisting of $4.5 \times 10^{5}$ frames, captures their generation, coherent motion, propagation, and relaxation, providing a powerful platform for exploring their full dynamical evolution.