Straightness of travel interferometer

Abstract

An interferometer system capable of measuring accurately the deviations from straightness of travel comprises a source (10) of a frequency stabilized input beam (12) with two linear orthogonally polarized components which may or may not be of the same frequency; a tilted parallel plate or shear plate (16) with regions of reflection, antireflection, and polarizing coatings, for converting the input beam into two separated, parallel, orthogonally polarized beams (30, 31); a half-wave retardation plate (24), located in one of the separated beams (31), for converting the two separated, orthogonally polarized beams 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 prism assembly (45), attached to the mechanical apparatus whose straightness of travel is to be measured, for refracting the parallel first and second beams (36, 37) into diverging third and fourth beams (38, 39); a mirror assembly (70) with its surfaces (70 A, 70B) perpendicular to the third and fourth beams (38, 39) for producing converging fifth and sixth beams (38A, 39A) which are refracted by the prism assembly (45A, 45B) to produce parallel seventh and eighth beams (36A, 37A); the quarter-wave retardation plate (44), the polarizing beamsplitter (40), a split retroreflector (47) for producing parallel ninth and tenth beams which are converted into eleventh and twelfth diverging beams by the prism assembly (45); the mirror assembly (70) producing converging thirteenth and fourteenth beams which are refracted by the prism assembly (45) to produce parallel fifteenth and sixteenth beams which are transmitted by the quarter-wave retardation plate (44) and the polarizing beamsplitter (40); a beam switch (72), for transposing the fifteenth and sixteenth beams (60, 61) so that one (62) passes through the half-wave retardation plate (29) and both (62, 63) pass through the tilted parallel or shear plate (16) where the fifteenth and sixteenth beams (63, 64) 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 deviation from straightness of travel; 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, the measured phase being related to the deviation from straightness of travel.

Dependencies are inferred from the claim text.