Optical Testing of Retroreflectors for Cryogenic Applications
Goddard Space Flight Center, Greenbelt, Maryland
Monday, February 01 2010
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Commercial uses include cryogenic metrology on aerospace
structures and optical metrology instrumentation.
A 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.
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