Special CMSM Seminar No.303

Direct visualization of the spatiotemporal dynamics of magnons and phonons provides valuable insights into their coupling in magnetic materials. In this seminar, I introduce ultrafast optical measurement techniques that enable multidimensional observations resolved in both time and space. The key technology is the optical frequency comb, which synchronizes two pulsed lasers with extremely low timing jitter. By introducing a slight difference in their repetition rates, we employ asynchronous optical sampling, where the relative delay between pulses automatically expands in time, enabling rapid delay scanning without mechanical delay lines. Because the timing jitter remains well below 100 fs over several hours, this method enables high-speed time-resolved measurements at multiple spatial points, allowing spatiotemporal imaging of phonons and magnons. Rapid delay scanning also enables many repeated measurements, allowing statistical analysis of the acquired waveforms. This opens a route to non-equilibrium noise spectroscopy and provides insights into the relaxation dynamics of electronic spin systems after ultrashort laser excitation. Such measurements reveal rich information on quasiparticle generation and relaxation, offering a powerful approach to studying nonequilibrium phenomena in materials science.

Yuta Sasaki
Research Center for Magnetic and Spintronic Materials
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