Dynamic visualization of subangstrom high-frequency surface vibrations

An optical scanning interferometer for accurate imaging of high-frequency surface vibrations is described. Vertical-displacement (out-of-plane) resolution of the interferometer is ∼0.003 Å, while lateral resolution is diffraction limited, typically ∼0.5 μm. The high-frequency response is limited by the detector to ∼6 GHz. Both the magnitude and phase are recorded at each point of the scan, so that an accurate measurement of the instantaneous surface shape is obtained. Furthermore, the phase information allows one to make a slow-motion movie of the vibrating surface. Data are presented for three examples in the frequency range 4 MHz–2 GHz.