Scanning heterodyne laser interferometer for phase-sensitive absolute-amplitude measurements of surface vibrations

We describe a scanning heterodyne interferometer for imaging surface vibrations with a wide frequency range, with current electronics, up to 6GHz. The heterodyne operation facilitates measurement of absolute amplitude and phase of the surface vibration without calibration. Currently, the setup allows detection of vibration amplitudes down to ∼1pm with a lateral resolution of <1μm. The interferometer is designed to accommodate the different sample types, e.g., surface and bulk acoustic wave devices and micromechanical resonators. The absolute-amplitude and phase information allows for a thorough characterization of surface vibrations in such components and provides direct information of the vibration fields not obtainable via electrical measurements.