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Recently, there have been increasing demands not only for the conventional profile surface roughness measurements using atomic force microscopes (AFM) but also for areal surface roughness measurements. In this study, a technique using Sal, one of the areal surface roughness parameters, instead of RSm, one of the profile roughness parameters, is proposed in order to extend the conventional method of profile roughness measurements specified in ISO 19606:2017 to areal roughness measurements. Areal surface roughness measurements performed using a metrological AFM and evaluation of their expanded uncertainties are also reported.

The refractive index of air is accurately measured using a vacuum cell and a tandem low-coherence interferometer with a communication optical fiber of 30 km length with standard uncertainties of 0.20 ppm for the phase refractive index and 0.29 ppm for the group refractive index. Experimental results are compared with the value calculated from the equation for the refractive index of air using data obtained from measurements of the surrounding air, with a standard uncertainty of 0.22 ppm, and the difference between the average values is within 0.1 ppm. This method is applicable to the in situ high-precision measurement of optical length.

A new remote-measurement technique of length is developed, in which a low-coherence tandem interferometer and a single-mode optical fiber are used. The optical path difference provided in the first low-coherence interferometer, which corresponds to the length being measured, is transmitted through the optical fiber to the second low-coherence interferometer. Interference fringes are generated when the optical path difference in the second interferometer compensates that of the first interferometer. End standards up to 10 mm have been calibrated remotely through the single-mode optical fiber of 10 m length with a standard deviation of 0.14 μm.

A new two-color heterodyne interferometer using an optical grating was proposed for measuring the refractive index of air. The heterodyne modulation is realized by moving the diffraction grating. The method allows us to measure the refractive index with high accuracy by using a 1:06 lm YAG laser and its second-harmonic wave because two beams (the fundamental and the second-harmonic wave) are in common path completely. Moreover, good signal-to-noise ratio (SNR) can be obtained by the heterodyne interference. Using the refractive index calculated by Edl e equation as a reference, that measured by present method was experimentally evaluated having an accuracy of about 1 � 10 � 6 within a distance of 100 mm. 2002 Elsevier Science B.V. All rights reserved.

A prism-pair interferometer for a spectrum lamp was developed for precise measurement of the refractive index of a prism of optical glass. Previously we reported the prism-pair interferometer with a He-Ne laser light source, resulting in a measurement uncertainty of 1.1×10⁻⁶. However, most of the refractive-index values managed by optical glass manufacturers are conventionally measured with spectrum lamps. We have optimized the prism-pair interferometer for spectrum lamps and implemented a signal-processing technique from Fourier-transform spectroscopy. When the refractive index is measured, the wavelength of the spectrum lamp is simultaneously calibrated by part of the interferometer, so that the resulting refractive index is traceable to a national standard of length. The combined standard uncertainty for a refractive index measured with the e-line (546 nm) of a Hg lamp is 6.9×10⁻⁶.

We developed a white-light interferometer that uses pseudo random-modulation for high-sensitivity, high-selectivity measurements of the surface profile of three-dimensional objects. The pseudo random-modulation is achieved by using a multi-segment mirror, where each segment has a different height in a maximum shift-register sequence (M-sequence). Preliminary experiments, where the white-light source was a halogen lamp and the test object was a plane mirror, show that our M-sequence modulated white-light interferometer (MMWI) had a four-time improvement in the signal-to-noise (SNR) ratio compared with that of a conventional interferometer.

For remote and in-situ calibration of translation stage, system comparing optical-path-differences of two distantly-located low-coherence-interferometers through a single-mode-optical-fiber has been developed. Results of 52 nm-deviation and 30 nm-standard deviation for 39 mm-displacement is achieved.

Practical lengths are remotely measured by excess fraction method using a tandem low-coherence interferometer through optical fiber networks. Interference fringes of high S/N are generated when the path difference between two interferometers is equal.

A low-coherence tandem interferometer with a single-mode optical fiber is developed for remote-measurement of length. The optical path difference provided in the first low-coherence interferometer is transmitted through the optical fiber to the second low-coherence interferometer. Low-coherence interference fringes are generated when the optical path difference in the second interferometer, which correspond to the length being measured, compensates that of the first interferometer. A gauge block of 50 mm long has been calibrated remotely through the single-mode optical fiber of 3 km length with a stnadard deviation of 0.12 μm.

A new remote-measurement technique of length is developed, by using a low-coherence tandem interferometer and a single-mode optical fiber. The optical path length with a gauge block in the first low-coherence interferometer is transmitted through the optical fiber to the second interferometer. And then the interference fringes containing the length information are generated and detected with high accuracy.

A Novel setup for two-dimensional (2-D) parallel measurements of low-coherence heterodyne signal by using a tandem interferometer and a 2-D sensor has been developed. Generally speaking, it is difficult to obtain heterodyne signals whose frequencies are much higher than the frame rate of the coventional 2-D sensor. A mode-locked femtosecond laser (MLFL) is used as a light source.

A new low-coherence interferometric technique is proposed for measuring the group refractive indices of dispersive samples with high accuracy. A tandem configuration of interferometers is used to compensate for the asymmetrical distortion of interferograms that results from the broad spectrum of the light source. The group refractive index can be measured without knowledge of the geometrical thickness of the sample under test. The proposed technique can successfully measure even a thick sample. Computer calculations have shown the effectiveness of the proposed technique, which was verified by preliminary experiments; the difference between the experimental result and the catalog data was 7 x 10(-4).

We have developed a gauge block measurement system that uses three frequency-stabilized lasers. The stabilized lasersare as follows: an 12-stabilized offset locked He-Ne laser (633 nm), an 12-stabilized Nd:YAG laser (532 nm), and a Rb-stabilized diode laser (780 nm). The 12-stabilized offset locked He-Ne laser is commercially available (NihonkagakuEngineering Co., Ltd.) and its relative wavelength uncertainty is 2.5 X 10' ' . An 12-stabilized Nd:YAG laser and a Rb-stabilized diode laser was developed in our institute and their relative wavelength uncertainties are 5 X 1 O12 and 1 X 1 O, respectively. In the measurement system, laser beams were introduced to the interferometer using an optical multimodefiber. An interferometric fringe pattern was taken using a CCD camera and the excess fraction parts were calculated from the fringe pattern using the Fourier transform method. The excess fraction part obtained from the Rb-stabilized semiconductor laser was used only to determine the integer part of the fringe order, because the accuracy and stability ofthe wavelength were not sufficient for the long gauge block measurements. This interferometer can measure gauge blocksofup to 1000 mm long and the standard uncertainty ofthe interferometer is about 75

The low-coherence interferometric technique is proposed for the in-situ measurement of the refractive index of dispersive samples with high accuracy. A tandem configuration of a Michelson interferometer and a triangular interferometer is used to compensate for the chirping effect which results from the broad spectrum of the light source. Thick samples can be successfully measured with the low- coherence interferometer, therefore the relative accuracy of the refractive index can be improved.

Heterodyne white-light interferometer that uses an optical grating to shift the optical frequency of the white light is proposed. By moving the optical grating, the diffracted lights undergo the frequency shift. The dependency of diffraction angle on wavelength can be resolved by using a spherical mirror, and then heterodyne detection of white-light can be realized with the combination of the optical grating and the spherical mirrors. In practical uses, a tandem-configuration interferometer is useful. The principle was demonstrated and the effect was confirmed experimentally for the first time The surface profile of a step-like object was measured. The signal-to-noise ratio of heterodyne signal is increased by thousand times from that of homodyne signal.

A novel low-coherence interferometer has been developed, based on the heterodyne technique for highly accurate and sensitive positioning of a three-dimensional (3-D) object, which uses two acousto-optic modulators (AOM's) and two spherical reflecting mirrors in a Michelson interferometer. By using this technique in a tandem interferometer, the profiles of diffusing and mirror-likes surfaces of the 3-D objects are measured with a high accuracy of 50 nm from the heterodyne signals of 200 kHz.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The results of the APMP key comparison on calibration of gauge blocks by interferometry (APMP.L-K1) are reported. The comparison involved the measurement, by ten participating institutes, of eight steel gauge blocks and ten ceramic gauge blocks ranging from 0.5 mm to 100 mm in length using techniques based on interferometry. The results are analysed using En values with weighted mean values as the reference values. Some measurement results had to be excluded by application of the En-criterion for the steel and ceramic gauges. Investigations of the reasons for the deviations have already been started by the respective institutes, including follow-up gauge block comparison, APMP.L-K1.1 with the same pilot laboratory as APMP.L-K1. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCL, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

The length information of end standards is transmitted through a 103-km-long optical fiber in the experimental room. The system uses a low-coherence tandem interferometer and a single-mode optical fiber in the wavelength range of 1500 nm. Interference fringes are generated when the optical path difference of the first interferometer compensates that of the second interferometer. The end standards of up to 50 mm in length have been calibrated remotely with a standard deviation of about 34 nm.

The information of practical length standards is transmitted through 47-km-long optical fiber network between Tsuchiura city and Kashiwa city in Japan. Interference fringes are generated when the optical path difference of a low-coherence interferometer in the Tsuchiura relay station compensates that in the Kashiwa station. End standards of 100 mm length in the Kashiwa station are calibrated remotely within a standard deviation of 118 nm with the reference standards in the Tsuchiura station.

A novel technique for the transmission of optical length information using a low-coherence tandem interferometer and a single-mode optical fiber is developed. The optical path length with a step gauge in the first low- coherence interferometer is transmitted through the optical fiber to the second interferometer. The interference fringes containing the length information of the gauge are generated with high accuracy by compensating the optical path difference in the second interferometer.

A tandem white-light interferometer has been developed, based on the heterodyne technique, for highly accurate and sensitive surface profiling of a three-dimensional (3-D) object. Two acousto-optic modulators (AOMs) and two spherical reflecting mirrors are used in a Michelson interferometer to provide the optical frequency shift for white light. By using this technique in the tandem interferometer, the profiles of mirrorlike and diffusing surfaces of 3-D objects are measured with heterodyne signals of 200 kHz. The optical path difference of the interferometer can be stabilized by simultaneously using coherent and incoherent light. The experimental results show a 27-fold improvement in the stability of the interferometer and the possibility of achieving high accuracy of several tens of nanometers.

We developed a prism-pair interferometer which measures precise refractive index of glasses while ensuring the SI-traceability of a lamp wavelength. The measurement result agrees with manufacture's value within 1×10−5.