Phase-resolved imaging of coherent phonon-magnon coupling

We use a direct phase-resolved optical technique to study the coherence of spin waves (SWs) thatare driven by surface acoustic waves (SAWs) via resonant magnetoelastic coupling. For this, weemploy a piezoelectric lithium tantalate (LiTaO3) substrate, equipped with micropatterned inter-digital transducers for SAW excitation, which interact with SWs in a 5 nm thin and 20 μm wideCo40Fe40B20-waveguide. We detect the SAW and the SW using a phase-locked micro-focused opti-cal polarization detection experiment and use the characteristic polarization dependence to separatethe SAW and SW signals. Our measurements directly image the resonant and coherent excitationof the SW by the SAW.