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Optical Testing of Retroreflectors for Cryogenic ApplicationsA laser tracker (LT) is an important coordinate metrology tool that uses laser interferometry to determine precise distances to objects, points, or surfaces defined by an optical reference, such as a retroreflector. A retroreflector is a precision optic consisting of three orthogonal faces that returns an incident laser beam nearly exactly parallel to the incident beam. Commercial retroreflectors are designed for operation at room temperature and are specified by the divergence, or beam deviation, of the returning laser beam, usually a few arcseconds or less. When a retroreflector goes to extreme cold (.35 K), however, it could be anticipated that the precision alignment between the three faces and the surface figure of each face would be compromised, resulting in wavefront errors and beam divergence, degrading the accuracy of the LT position determination. Controlled tests must be done beforehand to determine survivability and these LT coordinate errors. Since conventional interferometer systems and laser trackers do not operate in vacuum or at cold temperatures, measurements must be done through a vacuum window, and care must be taken to ensure window-induced errors are negligible, or can be subtracted out. Retroreflector holders must be carefully designed to minimize thermally induced stresses. Changes in the path length and refractive index of the retroreflector have to be considered. Cryogenic vacuum testing was done on commercial solid glass retroreflectors for use on cryogenic metrology tasks. The capabilities to measure wavefront errors, measure beam deviations, and acquire laser tracker coordinate data were demonstrated. Measurable but relatively small increases in beam deviation were shown, and further tests are planned to make an accurate determination of coordinate errors.
Document ID
20100005271
Acquisition Source
Goddard Space Flight Center
Document Type
Other - NASA Tech Brief
External Source(s)
http://www.techbriefs.com/component/content/article/7157
Authors
Ohl, Raymond G. (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Frey, Bradley J. (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Stock, Joseph M. (SGT, Inc. Greenbelt , MD, United States)
McMann, Joseph C. (QinetiQ North America Cleveland, OH, United States)
Zukowiski, Tmitri J. (Research Support Instruments, Inc. United States)
Date Acquired
August 25, 2013
Publication Date
February 1, 2010
Publication Information
Publication: NASA Tech Briefs, February 2010
Subject Category
Man/System Technology And Life Support
Report/Patent Number
GSC-15702-1
Distribution Limits
Public
Copyright
Public Use Permitted.

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IDRelationTitle20100005249Collected WorksNASA Tech Briefs, February 2010
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