Abstract:
The tilted relationship between the reference and test mirrors (24,26) of a Fizeau interferometer is used to spatially separate the reflections (R,T) from the two surfaces. The separate beams (R, T) are filtered through a spatial polarization element (32) that provides different states of polarization to the beams. The beams (R,T) are subsequently recombined to form a substantially collinear beam that is processed using a spatial-phase-shift interferometer (44) that permits quantitative phase measurement in a single video frame. Alternatively, two beams (104,106) with orthogonal polarization are injected into the Fizeau cavity (20) at different angles, such that after reflection from the reference and test optics (24,26) they are substantially collinear. Unwanted reflections are blocked at the focal plane through the use of a circular aperture (112). Short coherence length light and a delay line (84) may be used to mitigate stray reflections, reduce measurement integration times, and implement temporal phase averaging.
Abstract:
An optical device for characterizing a test surface (26) combines a Fizeau interferometer with a polarization frequency-shifting element (10). Two substantially collinear, orthogonally polarized beams (12,13) having respective frequencies differing by a predetermined frequency shift are generated by the polarization frequency-shifting element (10) and projected into the Fizeau optical cavity (24) to produce a pair of test beams (33,34) and a pair of reference beams (31,32), wherein the beams in each pair have orthogonal polarization states and have frequencies differing by the predetermined frequency shift. A second, substantially equal frequency shift is introduced in the Fizeau cavity (24) on either one of the pairs of test and reference beams, thereby generating a four-beam collinear output that produces an interf erogram without tilt or short-coherence light. The invention may also be implemented by reversing the order of the Fizeau cavity (24) and the polarization frequency-shifting element (10) in the optical train.
Abstract:
A phase-difference sensor (10) measures the spatially resolved difference in phase between orthogonally polarized reference (R) and test (T) wavefronts. The sensor (10) is constructed as a pixelated phase-mask (14) aligned to and imaged on a pixelated detector array (16). Each adjacent pixel of the phase-mask (14) measures a predetermined relative phase shift between the orthogonally polarized reference and test beams (R,T). Thus, multiple phase-shifted interferograms can be synthesized at the same time by combining pixels with identical phase-shifts. The multiple phase-shifted interferograms can be combined to calculate standard parameters such as modulation index or average phase step. Any configuration of interferometer that produces orthogonally polarized reference and object beams (R,T) may be combined with the phase-difference sensor (10) of the invention to provide, single-shot, simultaneous phase-shifting measurements.
Abstract:
An interferometer includes a short-coherence source and an internal path-matching assembly contained within its housing. Because path matching occurs within the housing of the interferometer, it is removed from external environmental factors that affect measurements. Therefore, a single cateye measurement of an exemplary surface can be performed in advance and stored as a calibration for subsequent radius-of-curvature measurements. In one embodiment, a path-matching stage is incorporated into a dynamic interferometer where orthogonally polarized test and reference beams are fed to a dynamic imaging system. In another embodiment, orthogonal linearly polarized test and reference beams are injected into a remote dynamic interferometer by means of one single-mode polarization-maintaining optical fiber.