Zygo Corporation

Earl W Ebert

Gary E Sommargren

A linear displacement interferometer system employs glass wedge prisms (71, 73, 75, 76) diposed about the interferometer axis of symmetry to refract the beams (51A, 55A) produced by the interferometer onto a single area (72, 86) approximately the size of the interferometer beam. If only one spot is produced on each of the stage and reference mirrors (72, 86), then any ambiguity concerning the beams (51B, 55B) is eliminated. In the preferred system, the stage (72) and standard (86) mirrors are located where the refracted beam crosses an interferometer axis of symmetry (80).

Differential displacement measuring interferometer

An angular displacement interferometer system capable of measuring accurately changes in angular displacement comprises a source (10) of a frequency stabilized input beam with two linear orthogonally polarized components; a tilted parallel plate or shear place (16) with regions of reflection, antireflection, and polarizing coatings for converting the input beam (12) into two separated, parallel, orthogonally polarized beams (30, 31); a half-wave retardation plate (29) located in one of the separated beams (31) for converting the two separated, parallel, orthogonally polarized beams (30, 31); into first and second beams which are spatially separated parallel, and have the same polarization (30, 33); a polarizing beamsplitter (40) and quarter-wave retardation plate (44) for transmitting the first and second beams (34, 35) to a fixed plano mirror (70) nominally perpendicular to the first and second beams for reflecting the first and second beams back into the quarter-wave retardation plate (44), polarizing beamsplitter (40), and retroreflector (48) for producing third and fourth beams (56, 67); a rotatable angle prism (72, 93) attached to the mechanical apparatus whose angular displacement is to be measured, located such that the third and fourth beams enter adjacent polygon faces of prism (72) or legs of prism (93) and are refracted to produce fifth and sixth beams which are reflected from the fixed plano mirror (70) back through the angle prism (72, 93) back through the quarter-wave retardation plate (44), beamsplitter (40), retardation plate (29) and shear plate (16) where the fifth and sixth beams are recombined into a single output beam (80) having two orthogonally polarized components in which the phase difference between the two components of the output beam (80) is related to the angular displacement; a polarizer (81) for mixing the orthogonal components of the output beam (80); a photoelectric detector (83) for producing an electrical measurement signal (85); and a phase meter/accumulator (90) for indicating the measured phase (92), the measured phase being related to the angular displacement.

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Middletown, CT, United States of America

Earl W Ebert