[en] A sinusoidally vibrating interference pattern (SVIP) is used as an exact spatial scale in order to measure a cross-sectional profile of a thread gauge. The SVIP is projected on the thread gauge surface, and lights diffracted and reflected from the end points of the thread gauge surface are extracted by spatial frequency filtering in an imaging system to make an image of the end points whose positions are decided by the peak positions of amplitude distributions in the image. The coordinates of the end points or the cross-sectional profile of the thread gauge is obtained from the phases measured at the positions of the end points, phase distribution of the SVIP on a CCD image sensor, and the pixel positions of the CCD image sensor.

[en] A feedback-control-equipped phase-shifting laser diode interferometer that eliminates external disturbance is proposed. The feedback loop is stabilized by adaptive control of the polarity of the interference signal. Conventional phase-shifting interferometry can be used with the feedback control, resulting in simplified signal processing and accurate measurement. Several experiments confirm the stability of the feedback control with a measurement repeatability of 1.8 nm.

[en] A grating-based shearing interferometeric setup for slope measurement of bent plates has been proposed. The specimen under test is illuminated by a collimated beam from the laser. Light reflected from the specimen passes through two identical holographic gratings placed in tandem. The grating frequency has been so chosen that the diffracted orders from each grating are separated out distinctly. Two first-order beams diffracted from each of the gratings superpose in space. In the resulting interferogram, the fringes due to slope information of the object are visualized. Mathematical formulation for experimental determination of slope values has been undertaken. Validation of the experimental results with theoretical predictions in case of cantilever beam provides good correlation. The main advantage of the technique has been the realization of very compact geometry without the need for spatial filtering arrangement commonly associated with the grating-based techniques used to date.

[en] We demonstrate a simple method for obtaining slope contours of bent plates using Talbot interferometry. The technique has been used to map slope contours of polymethyl methacrylate specimens of different shapes. The Talbot image of a coarse grating is projected onto a specimen such that the self-image is backreflected onto the same grating again. As a Talbot interferometer is basically a grating shearing interferometer, it results in the generation of characteristic slope maps of the specimen under test. Results of the investigation match well with other slope-mapping techniques. Validation of experimental results with theoretical predictions in the case of a cantilever beam specimen has been undertaken. Accuracy of about 4.7% with respect to theoretical predictions is obtained.

[en] We propose a new method to measure the thickness of very thin single layers in helical computed tomography images. This method involves using the density profile of a longitudinal image to obtain the image width. First, we examined the images of the step density distribution of block phantoms to clarify the step spread function and to decide the spread width (L) of longitudinal images. It was found that the spread width is half of a sum of the X-ray beam collimation and the table feed distance when 180 degrees linear interpolation is used. Next, we derived the density profile of a single layer by taking the density distributions of a single layer to be the composite of step density distributions of different step heights. An important relation is made clear that the image width of the longitudinal image for a single layer of thickness (D) is equal to D+2L whether the shape is symmetrical or not. From this relation the thickness can be measured by detecting the image width with a known value of the spread width of longitudinal images. In conditions of beam collimation of 1.0 mm, table feed distance of 1.0 mm, and reconstruction interval of 0.5 mm, measurement accuracy of this method using the density profile of a longitudinal image is estimated to be within 0.05 mm. This method is much more effective than the conventional method using a gray level image for measuring thicknesses less than 0.6 mm. In addition, this method appears to be more consistent than the conventional method, as indicated by a lower standard deviation for figures obtained with this method than for those obtained with the conventional method. We applied this method to the measurement of the thickness of thin cortical bones. (author)

[en] We describe a double-grating interferometer for the measurement of cylinder diameters. The unique characteristic of this interferometer is that one can freely change the period of the interference fringes by turning the grating, which permits the measurement range of the interferometer also to be changed freely according to the cylinder diameter to be measured. A clear image of the cylinder can be obtained because the aperture diaphragm blocks the beams diffracted from the edge of the cylinder. The outside and inside diameters of the M4 x 0.7 mm hand tap are measured with this double-grating interferometer

[en] A previously proposed double sinusoidal phase-modulating (DSPM) laser-diode interferometer measures distances larger than a half-wavelength by detecting modulation depth. Although it requires a vibrating mirror to provide the second modulation to the interference signal, such vibrations naturally affect measurement accuracy. We propose a static-type DSPM laser-diode interferometer that uses no mechanical modulation. Our experimental results indicate a measurement error of ±1.6 μm

[en] Conventional scanning white-light interferometers (SWLIs) cannot measure the exact shape of a thick glass plate because of the large dispersion effect. In this paper, a novel dual SWLI is proposed where the thicknesses of both an object and a compensation glass plate can be measured exactly in four-step measurements by decreasing the dispersion effect in both arms of the dual SWLI. The compensation glass plate is made of the same material as the object and has a similar thickness. The peak positions of the interference signals in the SWLI can be exactly measured using a piezoelectric transducer stage and an additional interference signal which detects the time-varying optical path difference in the SWLI. Experimental results show that the measurement error is less than 60 nm for a glass plate of thickness 1 mm. (paper)