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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 calibration service of profile surface roughness by using a metrological atomic force microscope is now available at National Metrology Institute of Japan (NMIJ), AIST. The calibration method is designed by referring to ISO 19606: 2017 (JIS R 1683: 2014). The scope of the ISO 19606: 2017, however, is limited to roughness measurements of surfaces with an arithmetical mean roughness, Ra, in the range of about 1 nm–30 nm. Currently there is strong demand for the measurement of surface roughness of more than 30 nm in the precision machining industry and for the measurement of surface roughness of sub-nanometer order in the semiconductor industry. In order to meet such demand, it is necessary to extend the range of surface roughness measurements in the NMIJ's calibration service. In this study, authors performed surface roughness measurements using a metrological AFM and evaluated their uncertainties. As a result of a series of measurements and evaluation of their uncertainties, it has been found that the calibration range can be extended to surfaces with an arithmetical mean roughness, Ra, in the range of about 0.2 nm–100 nm. The measurement results and the future challenges are reported in this paper.

In this study, we developed a methodology to evaluate scanning electron microscopy (SEM)-based line edge roughness (LER) metrology. In particular, we used a metrological tilting atomic force microscopy (tilting-mAFM) as LER reference metrology. We analyzed the height-height correlation function (HHCF) of SEM line-edge profiles combining averaging and unbiased correction methods. The direct comparison of our method with tilting-mAFM enabled a precise evaluation of the SEM-based LER metrology. We demonstrated that a combination of unbiased HHCF and averaging methods with appropriate condition enabled relatively precise measurement of three roughness parameters. We observed that, for precise roughness evaluation, reducing noise in the line-edge profiles is important before performing the HHCF analysis and unbiased correction.

High blood glucose is associated with increased risk of various diseases. Red clover (RC; Trifolium pratense L.) is an edible legume whose sprout is rich in isoflavones such as formononetin and biochanin A. We examined the effects of RC extract on postprandial and fasting blood glucose level, using a randomized, double-blind, placebo-controlled trial with 36 participants, aged 25 to 64 years, who were randomly assigned to receive either 1.91 g of RC extract (containing 8 mg formononetin and 1.8 mg biochanin A) or placebo. Each participant ingested the assigned test food daily for 8 weeks, and at the oral maltose tolerance test (OMTT). Initially, the two groups did not significantly differ in OMTT results. However, fasting insulin levels at 8 weeks were significantly lower in the RC group (4.76 μIU/ml at Week 0 to 4.01 μIU/ml at Week 8) with a significant interaction (P = 0.046). Subgroup analysis showed that change in blood glucose level (blood glucose ΔC) tended to decrease late in the trial period during OMTT in the ≤50-year-old RC group, as did fasting blood glucose and insulin levels at 8 weeks; hemoglobin A1c was also significantly reduced in this subgroup (5.36% at Week 0 to 5.28% at Week 8) with a significant interaction (P = 0.040). These results suggest that the daily intake of RC could reduce blood glucose, particularly for those ≤50 years old. Formononetin-an α-glucosidase inhibitor-is considered to be the major functional molecule for these effects. Therefore, intake of RC that contains formononetin might help blood glucose control.

Background: Conventional scanning electron microscopy (SEM) that is used for 2D top-view metrology, a classical line edge roughness (LER) measurement technique, is incapable of measuring 3D structures of a nanoscale line pattern. For LER measurements, SEM measurement generates a single line-edge profile for the 3D sidewall roughness, although the line-edge profile differs at each height in the 3D sidewall. Aim: To develop an evaluation method of SEM-based LER measurement techniques and to verify how the 3D sidewall shape is reflected in the SEM’s 2D result. Approach: Direct comparison by measuring an identical location of a line pattern by SEM and an atomic force microscopy (AFM) with the tip-tilting technique that is capable of measuring the 3D sidewall. The line pattern has vertical stripes on the sidewall due to its fabrication process. Measured line edge profiles were analyzed using power spectral density, height-height correlation function, and autocorrelation function. Results: Line edge profiles measured by SEM and AFM were well matched except for noise level. Frequency and scaling analyses showed that SEM profile contained high noise and had lost a property of self-affine fractals in contrast to AFM. Conclusions: In the case of the line pattern with vertical stripes on the sidewall, SEM profile is generally consistent with 3D sidewall shape. The AFM-based LER measurement technique is useful as LER reference metrology to evaluate other LER measurement techniques.

Line edge roughness (LER) measurement of a nanoscale line pattern is a metrology challenge in the inspection of semiconductor devices. Conventional scanning electron microscopy (SEM), a classical LER measurement technique, is a top-view (2D) metrology and incapable of accurately measuring 3D structures. For LER measurements, SEM measurement generates a single line edge profile for the 3D sidewall roughness, although the line edge profile differs at each height in the 3D sidewall. In this study, we used atomic force microscopy (AFM) with the tip-tilting technique to measure the 3D sidewall roughness, as an LER reference metrology. An identical location of a line pattern measured by SEM and AFM was compared to evaluate the SEM’s performance. The line edge profile from the AFM measurement exhibited lower noise than that from SEM. The measured line edge profiles were analyzed using the power spectral density (PSD), height-height correlation function (HHCF), and autocorrelation function. The results demonstrate that the standard deviation (σ) and correlation length (ξ) are overestimated while the roughness exponent (α) is underestimated by SEM, considering the AFM results as reference values.

It is known that the periodic error of heterodyne interferometers limits the accuracy of measurement to nanometre order. It is mainly derived from frequency mixing in the interferometer optics and this can be resolved using the configuration with two spatially separated beams. However, there remains a periodic error associated with parasitic reflections. Recently, we have developed a differential single-path heterodyne interferometer with two spatially separated beams, which was constructed within a single small quasi-cubic optical unit to minimize the parasitic reflections. In this work, the residual periodic error of this interferometer was evaluated with two evaluation methods, ‘the amplitude method’ and ‘the subtraction method’, and their results were compared. By applying uncertainty estimation procedures to the results, these two methods were shown to be highly consistent, confirming the reliability of our evaluation results. The error in λ/2 period of this interferometer was 7.6 pm.

One-dimensional grating is one of the most important standards that are used to calibrate magnification of critical-dimension scanning electron microscopes (CD-SEMs) in the semiconductor industry. Long-term stability of pitch calibration systems is required for the competence of testing and calibration laboratories determined in ISO/IEC 17025:2005. In this study, calibration and measurement capabilities of two types of pitch calibration systems owned by a calibration laboratory are re-evaluated through comparison to a reference value and its expanded uncertainty given by a metrological atomic force microscope (metrological AFM) at National Metrology Institute of Japan (NMIJ), AIST. The calibration laboratory’s pitch calibration systems are designed by using the diffraction method (optical and X-ray).

Line edge roughness (LER) measurement is one of the metrology challenges for 3D device structures, and LER reference metrology is important for reliable LER measurements. We developed an LER measurement technique, which is able to analyze LER distribution along height of a line pattern, with high accuracy, resolution, and reproducibility. Highly accurate atomic force microscopy (AFM) image of a vertical sidewall of a line pattern was obtained using a metrological tilting- AFM, which offers SI-traceable dimensional measurements. The tilting-tip was controlled with an inclined servo axis and scans the vertical sidewall along a line pattern with a high sampling density to enable an analysis of the LER height distribution at the sidewall. A horizontal cross-section of the sidewall shows sidewall roughness with sub-nm resolution. Power spectral density (PSD) analysis of the sidewall profile showed that the PSD noise in the high-frequency region was several orders of magnitude lower than the noise of typical scanning electron microscopy methods. AFM measurements were sequentially repeated three times to evaluate the reproducibility of the sidewall measurement and LER analysis; results indicated a high reproducibility of 0.07 nm evaluated as a standard deviation of LER at each height.

Line edge roughness (LER) measurement is one of the metrology challenges for three-dimensional device structures, and LER reference metrology is important for reliable LER measurements. For the purpose of LER reference metrology, we developed an LER measurement technique that can analyze LER distribution along the height of a line pattern, with high resolution and repeatability. A high-resolution atomic force microscopy (AFM) image of a vertical sidewall of a line pattern was obtained using a metrological tilting-AFM, which offers SI-traceable dimensional measurements. The tilting-tip was controlled with an inclined servo axis, and it scans the vertical sidewall along a line pattern with a high sampling density to enable an analysis of the LER height distribution at the sidewall. A horizontal cross-section of the sidewall shows sidewall roughness with sub-nm resolution. Power spectral density (PSD) analysis of the sidewall profile showed that the PSD noise in the high-frequency region was several orders of magnitude lower than the noise of typical scanning electron microscopy methods. AFM measurements were sequentially repeated three times to evaluate the repeatability of the LER measurement; results indicated a high repeatability of 0.07 nm evaluated as a standard deviation of LER at each height.

A signal-processing method is proposed in the fully interferometric three-dimensional (3D) imaging spectrometry. This processing computes a 3D interferogram, in which recorded fringe patterns do not directly reflect wavefront forms propagated from a polychromatic light source under measurement. This paper presents a procedure for signal processing including a synthesis of the 3D interferogram and retrieval of a set of spectral components of 3D images. We demonstrate retrieving 3D images for spectral components of two planar light sources by means of the proposed method. The procedure to synthesize the 3D interferogram in this method suggests the possibility of direct measurement of the 3D interferogram.

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.

The group refractive index of BK-7 glass material is accurately measured using a tandem low-coherence interferometer, which is composed of a Mychelson interferometer and a Fizeau interferometer, within a combined standard uncertainty of 8.4 ppm. The experimental results are compared with the value calculated from the conventional data base on the phase refractive index, within a difference of about 4.7 ppm. This new method is applicable to in situ measurement due to the principle of its common optical path.

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.

A multichannel spectral imaging system consisting of dichroic mirrors is proposed. The system is expected to have the highest signal-to-noise ratio (SNR) because of the largest optical throughput realized by the multichannel configurations for both imaging and spectrometry. A multichannel spectral imaging system with eight spectral bands was designed by the evolutionary algorithms and then fabricated. The SNR is studied and compared experimentally with those of other fast spectral imaging techniques. A time-sequence of spectral images of a super-continuum light beam is measured using the present system. The number of spectral channels of the system is limited chiefly by the difficulty in designing the arrangement of dichroic mirrors and the optical performance of those mirrors. These limitations restrict the number of spectral channels to approximately 16 at present.

Editors:Prathan Buranasiri,Sarun Sumriddetchkajorn, We have studied a method to obtain both three-dimensional (3-D) spatial information and spectral information of a usual polychromatic object by a fully passive interferometric technique that is strongly coupled with digital signal processing. Our method can be used for a vast range of wavelengths, because no special imaging devices, such as lenses, are required. In addition, coherent light sources are not necessary. A hyperbolic-type volume interferogram is one type of the volume interferogram, which is used for retrieve the object information, and an interferometer to measure directly this volume interferogram has been introduced. This paper introduces a method to measure the hyperbolic-type volume interferogram with high sensitivity in fully interferometric 3-D imaging spectrometry. This is accomplished by coupling of interferometer to measure directly the hyperbolic-type volume interferogram and heterodyne detection system for broadband light. We also report a preliminary experimental result based on the interferometer to measure directly the hyperbolic-type volume interferogram.

A multichannel spectral imaging system consisting of dichroic mirrors is applied to spectral imaging of the ultrafast super-continuum light. The mechanism of ultrafast supercontinuum light has not yet been elucidated completely. The spectral images of the supercontinuum light are expected to give us a deeper insight. The multichannel spectral imaging system can capture a spectral image instantaneously and is expected to have a high signal-to-noise ratio. The spectral image of the single pulse of the super-continuum shows that the spectrum varies according to the distance from the optical axis.

A Fourier transform spectrometer with heterodyne modulation achieved by a moving diffraction grating has been developed for the near-infrared (NIR) region. The grating simultaneously acts as a beam splitter and a modulator, which realizes the optical frequency shift of incident light for increasing the sensitivity of measurements by the heterodyne detection technique. The differences in diffraction angle among broad spectra are compensated by a collimating mirror and plane mirrors. The proposed spectrometer is used for the measurements of spectra in the NIR region. The signal-to-noise ratio of measurements is improved sevenfold with a heterodyne modulation of 410 Hz. As examples, this spectrometer is applied for quantitative calibration and discrimination of organic solutions. The measurement of transmission spectra of a grape is also demonstrated.

We propose a variable-path interferometric technique for the measurement of the absolute refractive index of optical glasses. We use two interferometers to decide the ratio between changes in the optical path in a prism-shaped sample glass and in air resulting from displacement of the sample. The method allows precise measurements to be made without prior knowledge of the properties of the sample. The combined standard uncertainty of the proposed method is 1.6x10(-6).

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.

Deep, stable starlight suppression is needed for the direct interferometric detection of Earth-like planets and requires careful control of the intensity and phase of the beams that are being combined. We have developed a novel compensator for the Terrestrial Planet Finder Interferometer based on a deformable mirror to correct the intensity and phase at each wavelength across the bandwidth of 8 to 12 microns wavelength. This paper will discuss the results of using the adaptive nuller to achieve deep broadband nulling in the mid-IR.

Technique of transferring length-information between two distantly-located low-coherence-interferometers through a single-mode-optical-fiber for remote and in-situ calibration of linear scale is developed. Results of 200 nm-deviation and 100 nm-standard deviation for 50 mm-length is preliminary achieved.

Deep, stable starlight nulls are needed for the direct detection of Earth-like planets and require careful control of the intensity and phase of the beams that are being combined. We have tested a novel compensator based on a deformable mirror to correct the intensity and phase at each wavelength across the bandwidth of 8 to 12 microns wavelength. This paper will cover the results of the adaptive nuller tests performed in the mid-IR.

PARKINSON'S disease (PD) is a relatively common neurologic disorder. Manuy drugs currently used for the treatment of PD may have significant interactions with anesthetic and cardiovascular drugs. 1 Even brief interruption of anti-PD drugs during surgery may result in exacerbation of Parkinson's symptoms. 2 However, safe and effective ways to administer anti-PD drugs during surgery are not widely known. 3 We used the enteral administration of levodopa (LD) in a patient with PD who had experienced exacerbation of PD during emergence from general anesthesia in two previous operations. This method of LD administration successfully prevented the exacerbation of the symptoms in this patient.

Deep, stable starlight nulls are needed for the direct detection of Earth-like planets and require careful control of the intensity and phases of the beams that are being combined. We are testing a novel compensator based on a deformable mirror to correct the intensity and phase at each wavelength and polarization across the nulling bandwidth. We have successfully demonstrated intensity and phase control using a deformable mirror across a 100nm wide band in the near-IR, and are in the process of conducting experiments in the mid-IR wavelengths. This paper covers the current results and in the mid-IR.

A technique for the group refractive index dispersion measurement of transparent materials using a low-coherence tandem interferometer without knowledge of the sample thickness is proposed. The experimental result of BK7 show an accuracy of 10-5.

Deep, stable starlight nulls are needed for the direct detection of Earth-like planets and require careful control of the intensity and phases of the beams that are being combined. We are testing a novel compensator based on a deformable mirror to correct the intensity and phase at each wavelength and polarization across the nulling bandwidth. We have successfully demonstrated intensity and phase control using a deformable mirror across a 100nm wide band in the near-IR, and are in the process of building the phase 2 experiment operating at mid-IR wavelengths. This paper covers the results of our demonstration in the near-IR, as well as our current progress in the mid-IR.

Deep, stable nulling of starlight requires careful control of the amplitudes and phases of the beams that are being combined. The detection of earth-like planets using the interferometer architectures currently being considered require that the electric field amplitudes are balanced at the level of ~ 0.1% and the phases are controlled at the level of 1 mrad (corresponding to ~ 1.5 nm for a wavelength of 10 microns). These conditions must be met simultaneously at all wavelengths across the science band and for both polarization states, imposing unrealistic tolerances on the symmetry between the optical beamtrains. Lay et. al. proposed the concept of a compensator that is inserted into the beamtrain, which can adaptively correct for the mismatches across the spectrum enabling deep nulls with realistic, imperfect optics. This proposed design uses a deformable mirror to adjust the amplitude and phase of the electric field that couples into the single-mode spatial filter. We have demonstrated amplitude and phase control at a single wavelength in the near-IR. We are preparing to demonstrate control with our deformable mirror actuator in the near-IR and in parallel are preparing a demonstration in the mid-IR where the compensator will be required to operate.

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 Fourier transform spectrometer with heterodyne modulation using a moving diffraction grating has been developed for the NIR region. The grating simultaneously acts as a beam splitter and a modulator, which realizes optical frequency shift of incident light for increasing the sensitivity of measurement by heterodyne modulation technique. The difference of diffraction angle is compensated by a collimating lens or a mirror and plane mirrors.

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).

Two types of heterodyne broad-spectrum interferometers for highly-sensitive measurements are described. One uses two acoustooptic modulators and the other a diffraction grating to provide the optical frequency shift of a broad spectrum of light. The principle and some experimental results arc shown.

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.

A multichannel spectral imaging system consisting of dichroic mirrors is proposed and evaluated. The system is expected to have the highest signal-to-noise ratio because of the largest optical throughput. The signal-to-noise ratio is studied and compared with that of another fast spectral imaging technique.

A bilateral comparison of refractive index measurements between the National Metrology Institute of Japan (NMIJ) and the Istituto Nazionale di Ricerca Metrologica (INRiM) was carried out in 2008. Each laboratory developed a measurement system based on different principles. NMIJ's system was based on the interferometric technique and INRiM's system was based on a modified method of the traditional refractive technique. A comparison using a prism-shaped glass made of OHARA BSL7Y was carried out in order to evaluate the newly developed methods and confirm the consistency of the results. The details of the comparison artefacts, measurement conditions and uncertainty factors and their degrees of freedom of each laboratory are described here. The measurement results for the glass at 633 nm at 20 °C and 23 °C are within each laboratory's claimed expanded uncertainty (coverage factor k = 2) which was of the order of 10−6. The agreement between the two different measurement approaches shows that both systems can be used to obtain accurate measurements.