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Schematic of the experimental setup for the PPLV laser microphone. B.S. denotes beam splitter.
Surface vibration spectra of a speckle-inducing aluminum surface detected by the PPLV. The surface displacement of the aluminum surface was 75 pm, and the frequency was 600 (upper trace) and 500 Hz (lower trace). The spectra have been displaced by 30 dB for visual clarity. The inset shows a typical optical speckle pattern reaching the sensor’s front surface.
Vibration spectra detected by the three-bounce (dotted), five-bounce (dashed), and six-bounce (solid) PPLV laser microphone. The target mirror was vibrating sinusoidally at 500 Hz and with the displacement value of 400 pm.
Vibration spectra detected by the 23-bounce PPLV laser microphone. The target mirror was vibrating sinusoidally at 500 Hz and with the displacement value of 40 pm. The dotted trace was taken with a 4096-point data window ( time window width), while the solid curve was obtained over a point data window (, assuming the laser pulse repetition rate of roughly 2.3 kHz), leading to finer frequency resolution. The minor peak in the solid trace was caused by the sudden shift in laser repetition rate during the longer data acquisition time period. The inset shows the same spectra in logarithm scales.
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