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Title: Introducing speckle noise maps for laser vibrometry
Authors: Martin, Peter
Rothberg, Steve
Keywords: Laser vibrometry
Speckle noise
Speckle pattern
Vibration measurement
Issue Date: 2009
Publisher: © Elsevier
Citation: MARTIN, P. and ROTHBERG, S., 2009. Introducing speckle noise maps for laser vibrometry. Optics and Lasers in Engineering, 47, (3-4), pp. 431-442.
Abstract: When coherent light scatters from a surface, which is rough on the scale of the wavelength of the light, a speckle pattern is produced. The Laser Vibrometer measures target vibration velocity in the direction of the incident laser beam and typically samples a region of a speckle pattern on its photodetector. Target motions can cause the speckle pattern to change on the photodetector surface, particularly when target motions are non-normal to the direction of the laser beam. This speckle motion modulates the Doppler signal and adds noise to the demodulated output signal. Periodic target motions can cause the speckle noise to become pseudo-random and produce harmonic peaks, with the same fundamental frequency as the genuine target vibrations, which can be indistinguishable from the genuine target vibrations. Typical speckle noise levels are generally considered to be low-level, but they have not so far been adequately quantified. This paper reports preliminary results quantifying speckle noise levels using controlled experimental configurations incorporating periodic in-plane and tilt target motions. Working with commercial Laser Vibrometers, various target surface finishes and treatments are considered and speckle noise maps are produced for each configuration. For a tilting surface, speckle noise has been quantified at approximately 1 μm s−1/deg s−1 while, for surfaces with in-plane motion, the sensitivity to speckle noise has been estimated pessimistically at 0.1% of the in-plane velocity. Ultimately, these speckle noise maps will form a valuable practical resource for the Laser Vibrometer user.
Description: This article was published in the journal, Optics and Lasers in Engineering [© Elsevier] and the definitive version is available at: http://dx.doi.org/10.1016/j.optlaseng.2008.06.010
Version: Accepted for publication
DOI: 10.1016/j.optlaseng.2008.06.010
URI: https://dspace.lboro.ac.uk/2134/8878
Publisher Link: http://dx.doi.org/10.1016/j.optlaseng.2008.06.010
ISSN: 0143-8166
Appears in Collections:Published Articles (Mechanical, Electrical and Manufacturing Engineering)

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