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Proceedings Paper

Heterodyne interferometry for high sensitivity absolute amplitude vibrational measurements
Author(s): Hanne Martinussen; Astrid Aksnes; Helge E. Engan
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Paper Abstract

A heterodyne interferometer has been built in order to characterize vibrations on Micro-Electro-Mechanical Systems (MEMS). The interferometer offers the possibility of both phase and high resolution absolute amplitude vibrational measurements, which is of great importance. A frequency shift is achieved by introducing acoustooptic (AO) modulation in one of the interferometer arms. By using a lock-in amplifier a narrow bandwidth detection regime is achieved. This factor improves the amplitude resolution. By using two AO-modulators and varying the frequency inputs of both, the setup is designed to measure vibrations in the entire frequency range 0 - 1.2GHz. The absolute amplitude is obtained by performing two measurements at each sample point. The first step is to measure the first harmonic of the object vibration. The second step is to measure the frequency components of the light reflected from the test device corresponding to the frequency without object modulation. This is obtained by mixing the detector signal with an external signal generator, and adjusting the frequency of the latter. By combining these two measurements we are able to determine the absolute amplitude of the vibration. The interferometric setup can be used to characterize various kinds of micro- and nanostructures. The system is here demonstrated on a Surface Acoustic Wave (SAW) device and on Capacitor Micromachined Ultrasonic Transducers (CMUTs). We have measured absolute amplitudes with picometer resolution.

Paper Details

Date Published: 14 August 2006
PDF: 11 pages
Proc. SPIE 6292, Interferometry XIII: Techniques and Analysis, 62920Z (14 August 2006); doi: 10.1117/12.679376
Show Author Affiliations
Hanne Martinussen, Norwegian Univ. of Science and Technology (Norway)
Astrid Aksnes, Norwegian Univ. of Science and Technology (Norway)
Helge E. Engan, Norwegian Univ. of Science and Technology (Norway)

Published in SPIE Proceedings Vol. 6292:
Interferometry XIII: Techniques and Analysis
Katherine Creath; Joanna Schmit, Editor(s)

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