| 摘要 |
An angular interferometer includes a laser (20) which generates a beam (22) of coherent light. A polarising beam splitter (24) and prism (26) split beam (22) into a pair orthogonally polarised, parallel extending beams (22S, 22P). The beams (22S, 22P) each pass through a glass block (30, 32), respectively of a refractive artefact mounted on a table under calibration, which in turn is rotatable about an axis (A). The beams (22S, 22P) are subsequently reflected back parallel to their incident path by a pair of rooftop retroreflectors (40, 42), displaced one relative to the other inthe direction of beam propagation by a distance equal to the separation between the beams; this reduces phase noise. The beams (22S, 22P) are recombined to generate an interference beam (50). Rotation of the artefact results in a change in relative path lengths of the beams (22S, 22P), and therefore a shift in the phase of the interference beam (50), which may be used to determine angular displacement of the table. The beams (22S, 22P) are axially spaced, enabling the use of an artefact having a relative low moment of inertia, and allowing a high range of angular displacement.
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