title: Laser Doppler vibrometer employing active frequency feedback.
abstract: We present a heterodyne Michelson interferometer for vibration measurement in which feedback is used to obviate the need to unwrap phase data. The Doppler shift of a vibrating target mirror is sensed interferometrically and compensated by means of a voltage-controlled oscillator driving an acousto-optic modulator. For frequencies within the servo bandwidth, the oscillator control voltage provides a direct measurement of the target velocity. Outside the servo bandwidth, phase-sensitive detection is used to evaluate high-frequency displacements. This approach is of great interest for the frequently-occurring situation where vibration amplitudes at low frequency exceed an optical wavelength, but knowledge of the vibration spectrum at high frequency is important as well.
authors.affiliation: National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, Maryland 20899, USA.
authors.forename: Akobuije
authors.initials: A
authors.lastname: Chijioke
authors.forename: John
authors.initials: J
authors.lastname: Lawall