Stroboscopic white-light interferometry of vibrating microstructures

Abstract

We describe a LED-based stroboscopic white-light interferometer and a data analysis method that allow mapping out-of-plane surface vibration fields in electrically excited microstructures with sub-nm amplitude resolution for vibration frequencies ranging up to tens of MHz. The data analysis, which is performed entirely in the frequency domain, makes use of the high resolution available in the measured interferometric phase data. For demonstration, we image the surface vibration fields in a square-plate silicon MEMS resonator for three vibration modes ranging in frequency between 3 and 14 MHz. The minimum detectable vibration amplitude in this case was less than 100 pm.

Imaging local acoustic pressure in microchannels

“…The setup is based on a white-light phase-shifting Michelson interferometer design as used by Shavrin et al [43] (see Fig. 2).…”

Characterization of surface acoustic waves by stroboscopic white-light interferometry

“…The SC light source is used in our Michelson-type white-light interferometer setup [13] as illustrated in Fig. 1.…”

“…The sample position is scanned along the optical z-axis by a piezoelectric translator stage to vary the optical path length difference between the two arms of the SWLI. To measure surface vibration fields, the phase θ between the excitation of the sample and the illumination pulses is varied in 20 degree steps over the vibration cycle at each z-position, such that a set of instantaneous deformation data can be obtained by high-resolution frequencydomain white-light interferometer data-analysis techniques [13]. To obtain the desired amplitude and phase data of the sinusoidal surface vibration, the set of measured instantaneous deformations is analyzed by utilizing Fourier transform techniques.…”

“…It has been shown that, by combining the fringe envelope location measurement with phase detection of the interferometric signal, a sub-100 pm amplitude limit can be obtained in a SWLI setup using a LED light source with 8 ns optical pulses [13]. Achieving significantly shorter pulses with high enough power from a LED source is technically challenging.…”

Transient vibration imaging with time-resolved synthetic holographic confocal microscopy

“…High-speed cameras were shown to enable imaging of out-of-plane vibration modes with kHz and MHz frame rates [5][6][7][8]. Alternatively, the speed limitation of conventional camera technology was mitigated by employing stroboscopic illumination schemes, and vibration imaging of microelectromechanical systems (MEMS), surface and bulk acoustic wave devices (SAW, BAW) at up to GHz frequencies was demonstrated [9][10][11][12][13][14][15][16][17]. However, the vertical sensitivity is typically found to be on the tens of picometer to nanometer scale owing to the inferior shot noise of cameras in comparison to photo detectors, although recent developments in camera technology promise improved vertical sensitivity [18].…”