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4 May 2012 Real-time 3D vibration measurements in microstructures
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The real-time measurement of three-dimensional vibrations is currently a major interest of academic research and industrial device characterization. The most common and practical solution used so far consists of three single-point laser-Doppler vibrometers which measure vibrations of a scattering surface from three directions. The resulting three velocity vectors are transformed into a Cartesian coordinate system. This technique does also work for microstructures but has some drawbacks: (1) The surface needs to scatter light, (2) the three laser beams can generate optical crosstalk if at least two laser frequencies match within the demodulation bandwidth, and (3) the laser beams have to be separated on the surface under test to minimize optical crosstalk such that reliable measurements are possible. We present a novel optical approach, based on the direction-dependent Doppler effect, which overcomes all the drawbacks of the current technology. We have realized a demonstrator with a measurement spot of < 3.5 μm diameter that does not suffer from optical crosstalk because only one laser beam impinges the specimen surface while the light is collected from three different directions.
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Robert Kowarsch, Wanja Ochs, Moritz Giesen, Alexander Dräbenstedt, Marcus Winter, and Christian Rembe "Real-time 3D vibration measurements in microstructures", Proc. SPIE 8430, Optical Micro- and Nanometrology IV, 84300C (4 May 2012); doi: 10.1117/12.922184;

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