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We describe a diffraction-grating interferometer that enables us to obtain a high contrast ratio of 120 between the test wave and the reference wave by optimizing the groove shape of a blazed-type diffraction grating. The high contrast provides good visibility for the resulting interference fringes when testing aspheric mirrors using computer-generated holograms (CGHs). Generally CGHs perform wavefront nulling, but greatly attenuate the intensity of the test wave. We present experimental results for an aspheric concave mirror of 600 mm diameter obtained using a blazed diffraction grating with a 1/1200 mm groove spacing and a 17-deg blazed angle. The binary-type CGH used for the experiments provided low transmittance efficiency but was cost effective. © 2004 Society of Photo-Optical Instrumentation Engineers.

We present a new concept for a phase-shifting diffraction-grating interferometer, which is intended to test concave mirrors simply using a single reflective diffraction grating and fiber optic confocal microscope focusing optics. Our configuration allows generating a high-quality reference wave from a small active grating area that can be readily fabricated with good homogeneity of grating substrate and uniformity of groove spacing. The test and reference waves encounter no other optical components, so only a small active surface area of the grating affects the test result. The fiber optic confocal microscope design adopted to solve the alignment problem between the grating and the converging wave greatly reduces systematic errors of the interferometer. In addition, the phase-shifting capability provided by translating the grating using a microactuator enables one to attain nanometer accuracy in optical figure metrology. © 2003 Society of Photo-Optical Instrumentation Engineers.

We present a high-speed moire´ method of color grating projection, which performs phase-shifting 3-D contouring with only a single operation of fringe capturing. Three red, green, and blue pairs of projection and viewing gratings are fabricated on a single glass plate with predetermined lateral offsets. The glass plate is translated along with the color gratings during measurement at a fast speed, so that a color CCD camera simultaneously monitors three separate patterns of moire´ fringes with 2/3 phase offset. This time-integral fringe capturing enables us to obtain high-quality moire´ fringes with the line images of the original viewing gratings inherently removed, which leads to better measurement accuracy with less computational burden of fringe processing. © 2002 Society of Photo-Optical Instrumentation Engineers.

We perform computer simulation and experimental work to investigate how the surface topography of reflecting mirrors affects the optical performance of the thin-film micromirror array (TMA) designed for projection display. We reveal that the form accuracy of mirror surface specified by the peak to valley should be less than 0.3 m, so that the reflecting efficiency becomes more than 95. We also find that the micromirrors should be tilted in a diagonal mode so as to maximize the contrast ratio that is defined by the ratio of the maximum amount of through light to the minimum. © 2002 Society of Photo-Optical Instrumentation Engineers.

We present a new computational method of white light scanning interferometry for 3-D surface mapping. This method accomplishes the task of detecting the true peak of the interference fringe in two steps. The first step is global search locating the envelope peak by fitting sampled intensity data directly to a symmetric quadratic polynomial. The second step is fine-tuning to precisely determine the fringe peak by compensating for the phase shift on reflection using the absolute fringe order identified by the envelope peak obtained in the first step. This two-step method offers an efficient means of computation to provide a good measuring accuracy with high noise immunity owing to its inherent reliance on least squares principles. © 2000 Society of Photo-Optical Instrumentation Engineers.

With the intention of precision profile measurement of aspheric surfaces, the Ronchi test is revisited to devise a special scheme of multiple-beam lateral shearing interferometry. A holographic sinusoidal grating is used instead of conventional rule gratings so that only 0 and ±1lower order diffraction beams induce necessary lateral shear with high quality. In addition, relative fringe phases of wavefront slopes are automatically obtained by applying phase shifts along two orthogonal directions in sheared interferograms. Finally an elaborate in-line calibration scheme is incorporated to identify the system scale factors with which the 3-D profiles of test surfaces are accurately reconstructed from the measured wavefront slopes. Experimental results prove that the proposed technique is useful, especially for aspheric surfaces with a short focal length. © 1999 Society of Photo-Optical Instrumentation Engineers.

A lateral-shearing interferometer specially devised for production-line inspection of lenses is presented. The interferometer is configured with four square prisms whose relative sliding motions readily provide lateral shearing and phase shifting necessary for evaluating the beam wavefront collimated by the lens under test. The prisms are attached face-to-face using immersion oil so that undesirable disturbances from external mechanical vibration and atmospheric turbulence can be minimized in the measurement. Further, a special phase-measuring least-squares algorithm is adopted to compensate the phase-shifting error caused by the thickness variation in the immersion oil holding the prisms. © 1997 Society of Photo-Optical Instrumentation Engineers.Key words:lateral-shaped interferometry; optical testing; phase shifting; least-squares phase-measuring algorithms; immersion oil.

One important issue in phase-shifting interferometry is to eliminate or compensate for phase shift errors. One solution is to adopt a least-squares technique in that actual reference values of phase shifts are readily identified directly from interferograms. This however, requires a relatively long computation time since a considerable amount of intensity information must be processed in an iterative way. To cope with this problem, we present an accelerated version of a least-squares phase-measuring algorithm that can drastically reduce computation time. © 1997 Society of Photo-Optical Instrumentation Engineers.

A phase-shifting projection moire´ method particularly intended for high-speed three-dimensional inspection of fine objects is presented. Emphasis is on realization of phase-shifting fringe analysis in projection moire´ topography using a set of line grating pairs designed to provide different phase shifts in sequence. Further, a time-integral fringe capturing scheme is devised to remove undesirable high-frequency original grating patterns in real time without time-consuming software image processing. Finally, the performances of the proposed method are discussed with measurement results. © 1998 Society of Photo-Optical Instrumentation Engineers.

We present a new type of point diffraction interferometer that employs single-mode optical fibers instead of traditional pinholes. Two optical fibers with different exit endfaces are used; one is normally cut and the other obliquely cleaved. The normally cut fiber is used to generate a near-perfect spherical reference wave. The test wave is produced from the oblique fiber that performs two functions: generating a spherical wave to illuminate the test optics, and reflecting the test wave for common-path combination with the reference wave. The interferometer proposed in this investigation is found suitable for testing large size mirrors with a relatively simple overall hardware configuration.