Phase sensitive imaging of 10 GHz vibrations in an AlN microdisk resonator.

We demonstrate a high frequency phase-sensitive heterodyne vibrometer, operating up to 10 GHz. Using this heterodyne vibrometer, the amplitude and phase fields of the fundamental thickness mode, the radial fundamental, and the 2nd-order modes of an AlN optomechanical microdisk resonator are mapped with a displacement sensitivity of around 0.36pm/Hz. The simultaneous amplitude and phase measurement allow precise mode identification and characterization. The recorded modal frequencies and profiles are consistent with numerical simulations. This vibrometer will be of great significance for the development of high frequency mechanical devices.