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

Abstract

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.

Material anisotropy unveiled by random scattering of surface acoustic waves

“…The scanning heterodyne optical probe is sensitive to the vertical displacement of the surface. 9,11 The amplitude and phase of the measured speckle field are shown in Fig. 2, together with the FT result.…”

Extraction of lateral eigenmode properties in thin film bulk acoustic wave resonator from interferometric measurements

“…Interferometric measurements of the resonator were carried out with a scanning heterodyne laser interferometer. 5 The heterodyne concept enables acquisition of the absolute amplitude of the surface vibration independently of the local optical surface reflectance. The heterodyne signal also carries phase information of the acoustic wave field, measured simultaneously with the amplitude data at each measurement point.…”

Imaging gigahertz surface acoustic waves through the photoelastic effect

“…A variety of optical techniques have been used to image electrically excited [1][2][3][4][5][6][7] or laser-excited [8][9][10][11] surface acoustic waves (SAWs) on solids and microstructures. When point-focused laser pulses are used for the SAW generation, the resulting omnidirectional twodimensional wave field can be mapped in the time domain and then Fourier-analyzed to obtain the in-plane acoustic dispersion relation [9,[12][13][14].…”