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Title: Laser vibrometry and the secret life of speckle patterns
Authors: Martin, Peter
Rothberg, Steve
Keywords: Laser vibrometry
Laser speckle
Speckle noise
Speckle motions
Vibration measurement
Issue Date: 2008
Publisher: © SPIE The International Society for Optical Engineering
Citation: MARTIN, P. and ROTHBERG, S., 2008. Laser vibrometry and the secret life of speckle patterns. IN: Proc. SPIE 7098, 709812, Eighth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications.
Series/Report no.: Proc. SPIE 7098;
Abstract: Speckle patterns are produced when coherent light scatters from optically rough surfaces. In typical applications, a Laser Vibrometer collects a region of a speckle pattern on its photodetector. However, noise can be generated in the Laser Vibrometer output when surface motions cause changes in the speckle pattern. This paper uses high resolution images to investigate typical intensity profiles in the partially- and fully-developed speckle patterns scattered from target surfaces with roughnesses in the range 11nm to 1μm Ra (≈1/60λ to 1.6λ) and from a surface treated with retro-reflective tape. In-plane and tilt target motions cause changes in the scattered speckle patterns and sequences of images are used to investigate how the speckle patterns behave in response to these motions. In the case of retro-reflective tape, incident beam diameter is also found to have an important effect on speckle pattern changes and different incident beam diameters are considered for other target surfaces and motions too. This qualitative analysis of the speckle pattern intensity profiles is compared with established theoretical understanding of speckle patterns and their motions and related directly to the instrument noise levels ultimately encountered. Such fundamental evaluation of speckle pattern motions provides a greater appreciation of speckle noise generation in the Laser Vibrometer outputs.
Description: This is a conference paper presented at the Eighth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications [© SPIE The International Society for Optical Engineering] and the definitive version is available at: http://dx.doi.org/10.1117/12.803156
Version: Accepted for publication
DOI: 10.1117/12.803156
URI: https://dspace.lboro.ac.uk/2134/8840
Publisher Link: http://dx.doi.org/10.1117/12.803156
Appears in Collections:Conference Papers (Mechanical and Manufacturing Engineering)

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