Your search for "Youichi Bitou" returned 11 results

A simple method of evaluating the measurement capability of a practical Fizeau-type flatness measurement machine is proposed. In this method, by measuring only the peak-to-valley (PV) value of a calibrated test flat, the measurement capability of the flatness measurement machine for the PV value is evaluated while maintaining the traceability of the measurement. A simple approximate equation for estimating the measurement capability of the flatness measurement machine is presented.

A high-precision, low-coherence Fizeau interferometer system using a pulsed laser diode has been developed for the measurement of the flatness of transparent plates. A pulsed laser diode with a wavelength of around 633 nm was used as the low-coherence light source. A Twyman–Green interferometer with the pulsed laser diode was connected to the Fizeau interferometer. By adjusting the optical path differences in both interferometers, the interference fringe pattern due only to the reference and measurement surfaces could be observed. The accuracy of the measurements was found to be similar to that of a conventional Fizeau interferometer.

The lateral resolution of the angle-based deflectometric surface profiler using a commercially available autocollimator has been improved by introducing a novel null instrument. The proposed null instrument is simple, inexpensive, and has a short response time. High-accuracy flatness measurements of low-reflective surfaces have been successfully demonstrated using a laser beam with a spot size of 1 mm. The repeatability of the surface profile measurement is better than ±0.6 nm.

A gauge block measurement system that uses a wavelength scanning interferometer was developed. By using a wavelength scanning technique, we determined the integer part of the interference fringe order. From that integer part, we determined the absolute length of a gauge block using only a single light source (wavelength scanning laser diode), even when no information on the nominal length of the gauge block was available. Using the Fourier transform technique to analyze the interference fringe, we measured the excess fraction parts of the interference fringe order with a resolution of over 0.003, and then we determined the integer part of the fringe order in the test measurement of a 10 mm gauge block. It was estimated that we could determine the integer part when the nominal length was shorter than approximately 100 mm, which can be expanded by improving the frequency stability of the light source. The final uncertainty was similar to that obtained with a conventional system based on a multiple wavelength interferometer.

A wavelength scanning gauge block interferometer that uses a spatial light modulator for fringe counting was developed. We measured the integer part of the interference fringe order with respect to the synthetic wavelength using a spatial light modulator with no miscounts, and measured the excess fraction part from the interference fringe pattern. Consequently, we could determine the absolute length of a gauge block using only a wavelength scanning laser diode, even when no information on the nominal length of the gauge block was available. The degree of uncertainty was similar to that of a conventional system based on a multiple-wavelength interferometer.

A compact I₂-stabilized frequency-doubled Nd:YAG laser has been developed for a long gauge block interferometer. The laser frequency stabilization is realized by the third-harmonic technique, where a fast frequency modulation (20 kHz) is applied to the piezoelectric transducer attached on the laser crystal. The relative uncertainty of the laser frequency has reached 3.6×10^-12 for a 0.01-s averaging time. It is theoretically indicated that the phase error in the interferometric measurement due to the optical frequency modulation is sufficiently small to measure the long gauge block up to 1000 mm. Long gauge block measurement up to 1000 mm was successfully demonstrated with the developed I₂-stabilized frequency-doubled Nd:YAG laser.

The flatness of an optical surface can be evaluated using a Fizeau interferometer. There is strong demand for ensuring that the measurement uncertainty of flatness is of nanometer order over a measurement range of 300 mm or more; however, the measurement range and measurement uncertainty of flatness at the National Metrology Institute of Japan (NMIJ) are 300 mm and 10 nm, respectively. In a Fizeau flatness interferometer, the gap distance between the reference flat and the specimen is measured. To obtain the absolute profile of the specimen, the absolute profile of the reference flat should be measured in advance. The three-flat test is one of the methods used to measure the absolute profile of a reference flat. The reference flat, however, deforms under the force of gravity, and its absolute deformation value cannot be determined by the three-flat test. The deformation value of the reference flat can be corrected by the finite element method (FEM) analysis; however, it is difficult to ensure the validity of the analysis and there is a large uncertainty component of the Fizeau flatness interferometer. To verify the FEM analysis, we developed a scanning deflectometric profiler (SDP) that does not require a reference flat and can directly measure a profile. We calibrated an optical flat using a Fizeau flatness interferometer and the SDP. Finally, the deformation value of the reference flat under the force of gravity was evaluated by comparing the measurement results.

The long-term stability of NEXCERA^™ ceramics having a low coefficient of thermal expansion was evaluated over a period of eight years. Several gauge blocks of differing lengths were prepared, using two types of NEXCERA. Each gauge block was kept wrung to a platen and its absolute length was periodically measured by gauge block interferometer during the eight years. Relative uncertainties of measurement of changes in gauge block length were estimated as 4.1  ×  10⁻⁸ and 2.9  ×  10⁻⁸ for 200 mm and 800 mm gauge blocks, respectively. The experimental results show the trend of expansion and a relative change of less than 0.1  ×  10⁻⁶/year for every gauge block.

The Length Standards Group at the National Metrology Institute of Japan has developed a double-sided interferometer (DSI) for non-contact thickness measurement, that is traceable to SI units. The measurement uncertainty of DSI was evaluated. The results of gauge block measurements were compared with those of a conventional gauge block interferometer and their equivalency within the claimed uncertainty was confirmed. The advantage of applying a DSI in measuring the thickness of silicon wafers is that it has absolute measurement traceable to SI units with high precision and independence from the refractive index of the sample material. The expanded uncertainty of silicon wafer thickness measurement was evaluated as 20 nm (the coverage factor k = 2). A bilateral comparison on silicon wafers' thicknesses was conducted with Korea Research Institute of Standards and Science, using a different measurement technique from the spectral-domain interferometer. Results of 100 μm, 300 μm, 600 μm, and 950 μm-thick silicon wafers agreed well with absolute values of E_n-numbers of 0.15 or less.

The National Metrology Institute of Japan (NMIJ) has developed a highly accurate two-point diameter measurement method of a sphere using a micro-coordinate measuring machine (µ-CMM) with a low-force two-dimensional touch probe. The measured sphere is used as a reference to calibrate the probe of other µ-CMM in industry. Our strategy for measuring sphere's diameter is that the probe radius of NMIJ's µ-CMM is calibrated using a reference gauge block, and the NMIJ's µ-CMM using the calibrated probe measures the mean two-point diameter of a sphere. To achieve the highly accurate calibration of the reference gauge block, we have adopted a double-sided interferometer (DSI) and an atomic force microscopy (AFM). The DSI measures the length of gauge block without wringing. The phase correction value of the gauge block is evaluated by measuring the surface roughness using the AFM. Using the DSI and AFM, the mechanical length of reference gauge block was obtained with the expanded uncertainty of 13 nm (k = 2). Then, the probe radius of NMIJ's µ-CMM was also calibrated using the reference gauge block calibrated by the DSI and the AFM. The µ-CMM's probe radius was obtained with the expanded uncertainty of 10 nm (k = 2). Finally, the µ-CMM measured the mean two-point diameter of a sphere with the expanded uncertainty 21 nm (k = 2) was demonstrated.