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An optical interferometer is described which has the ease of alignment of a four-pass interferometer, but has the added convenience of having a remote reference surface.
English (United States)
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Two Pass Remote Reference Interferometer
An optical interferometer is described which has the ease of alignment of a
four-pass interferometer, but has the added convenience of having a remote
A four-pass interferometer normally compares a four-pass measurement path
to a two-pass reference path. Because of the difference in path sensitivity, the
reference in a four-pass interferometer normally cannot be made remote. If two
positions are to be compared using a four-pass interferometer, the interferometer
position itself normally must represent one of the compared positions. With a
two-pass interferometer, both the reference and measurement paths have two
passes, so that the reference can be remote. However, a two-pass
interferometer is much more sensitive to alignment than a four-pass
interferometer, and since a two-pass interferometer has only one optical axis
rather than two, it adversely affects laser performance due to optical feedback
much more than a four-pass interferometer.
The illustrated interferometer combines the advantages of both by fixing the
path length of two passes in the four-pass path of a four-pass interferometer.
Since the measurement path and the reference path now both have the same
sensitivity (effectively two-pass sensitivity), the reference can be remote.
The illustrated system works as follows: Light from source 1 (a Zeeman
laser, for example) is reflected by interferometer light splitter 3 through quarter-