Results from international comparisons at the BIPM providing a world-wide reference network of /sup 127/I/sub 2/ stabilized frequency-doubled Nd:YAG lasers

Frequency comparisons have been carried out between iodine-stabilized Nd:YAG lasers from the Bureau International des Poids et Mesures, the Bureau National de Metrologie-Institut National de Metrologie, the Czech Metrology Institute, the Centre for Metrology and Accreditation, and the National Metrology Institute of Japan/National Institute of Advanced Industrial Science and Technology. The comparison data of these lasers can now be linked to the results of recent absolute frequency measurements of lasers from different institutes.     

Comparison of independent optical frequency measurements using a portable iodine-stabilized Nd:YAG laser

A comparison of two independent absolute optical frequency measurements has been carried out between the National Metrology Institute of Japan/National Institute of Advanced Industrial Science and Technology (NMIJ/AIST), Tsukuba, Japan and the JILA (formerly the Joint Institute for Laboratory Astrophysics), Boulder, CO, using a portable iodine-stabilized Nd:YAG laser. The agreement between the two absolute measurements is better than the measurement uncertainty of 6.7/spl times/10/sup -13/ that can be attributed to the reproducibility limitations of the portable laser. This comparison is used to confirm the measured absolute frequency of an iodine-stabilized Nd:YAG laser at NMIJ/AIST (Y3), which is reported to the Consultative Committee for Length (CCL) for the determination of the absolute frequency value of iodine-stabilized Nd:YAG lasers.     

The BNM-LPTF software for the frequency comparison of atomic clocks by the carrier phase of the GPS signal

This paper describes the software and equipment used at the Laboratoire Primaire du Temps et des Frequences du Bureau National de Metrologie (BNM-LPTF), Paris, France. Two H-masers in short baseline, one located at the BNM-LPTF and the other at the Laboratoire de l'Horloge Atomique du Centre National de la Recherche Scientifique (CNRS-LHA), Orsay, France, were computed in parallel with the BNM-LPTF software and with the BERNESE V 4.1 software. The comparison of the results issued from both computations shows an agreement within 100 ps (1 sigma). In addition, comparisons with the BNM-LPTF software were made over 10 days with the H-masers located at the Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, Germany, and another at the National Physical Laboratory (NPL), Teddington, United Kingdom. The data collected show that a modulation with an amplitude of 50 ps and a period of 700-800 ps affects the equipment of the NPL. In addition, these comparisons show that the noise of the instruments together with the environmental conditions at the PTB was higher than that of the NPL and the BNM-LPTF during the observation period. The best relative frequency stability obtained, in the BNM-LPTF/NPL comparison, is about 3x10(-15) for averaging periods between 6x10(4) s and 3x10(5) s. This result is in good agreement with the expected stability of H-masers. It demonstrates that the noise brought by the GPS carrier phase measurements can be averaged out at this level.     

Bilateral comparison of power measurement standards for KrF excimer lasers between PTB and NIST

We report results of the first bilateral laser power comparison for 248 nm KrF excimer lasers accomplished by the National Metrology Institutes of Germany (Physikalisch-Technische Bundesanstalt, PTB) and of the United States of America (National Institute of Standards and Technology, NIST). Laser transfer standards for average power were calibrated at both laboratories. The average powers were approximately 0.5 W, 1 W and 2 W. At 248 nm, the relative agreement was between 1×10⁻³ and 6×10⁻³, which is well within the expanded uncertainty of the bilateral degree of equivalence of approximately 2×10⁻². Thus, this comparison confirms that the measurement procedures of both laboratories are consistent and the uncertainty budgets contain all significant contributions.     

Comparison of four QHR systems within one month using a temperatureand pressure stabilized 100-Ω resistor

We have carried out a resistance comparison of four QHR systems using a 100-Ω resistor in a temperature-controlled and hermetically sealed enclosure, the comparison was performed in November and December 1998, the participants were Bureau International des Poids et Mesures (BIPM), Bureau National de Metrology-Laboratoire Central des Industries Electroniques (BNM-LCIE) France, Physikalisch-Technische Bundesanstalt (PTB) Germany, and Valtion Teknillinen Tutkimuskeskus (VTT Automation) Finland, acting as a pilot laboratory. The comparison results agree within 3 parts in 10⁹ with a relative combined standard uncertainty of ±1×10^-8     

12.7mm电容传声器耦合腔互易法校准

中国计量科学研究院于８０年代末开始了对１２７ｍ ｍ 电容传声器互易法校准技术的研究。本文介绍了计量院 １２７ｍ ｍ 电 容传 声器 耦合 腔互 易 法校 准技 术,其 不 确定 度在 ６３ Ｈｚ—１０ｋ Ｈｚ 小 于００７ｄ Ｂ（包 含因 子 ｋ ＝ ３）, 在２０ｋ Ｈｚ 时小于０１２ｄ Ｂ（包含因子 ｋ＝ ３）。     

Frequency Stability at the Kilohertz Level of a Rubidium-Locked Diode Laser at 192.114 THz

The frequency stability of a 1560-nm diode laser, whose second harmonic was locked to (87)Rb sub-Doppler lines, was characterized by measuring the beat frequency relative to a 780-nm reference laser that was locked to sub-Doppler lines of another rubidium cell. The square root of the Allan variance reached a minimum value of 7.5 x 10(-12) in 1 s, which corresponded to frequency variations of 1.44 kHz for the 1560-nm laser. The frequency reproducibility of the system was approximately 1 x 10(-9). These values are better than those that can be achieved by locking to Doppler-broadened transitions at the 1550-nm wavelength band.     

Compact inductance standard

A portable Maxwell-Wien bridge as a part of the Korea Research Institute of Standards and Science (KRISS) inductance standard has been developed. Two auxiliary resistive-capacitive networks (analogous to a "Wagner ground") provide excellent stability of the bridge balance and impose less strict requirements on the components of the networks. Removable capacitance and ac/dc resistance standards used in the bridge arms make it possible to realize the inductance unit in terms of capacitance and resistance in the frequency range 500 Hz to 3 kHz. Investigations of the standard and results of preliminary (trial) comparison with the Mendeleyev Institute for Metrology demonstrate that the bridge can be used for measurement of 10 and 100 mH inductance standards with an uncertainty within (1-3) /spl mu/H/H at frequencies of 1 and 1.6 kHz. The use of this bridge as a constituent part of a transportable standard gives an opportunity to eliminate any uncertainty arising from instability of the standard inductors.     

Recent developments in BIPM voltage standard comparisons

The Bureau International des Poids et Measures (BIPM) carries out a number of comparisons of dc voltage standards with National Metrology Institutes (NMIs). These take the form of on-site comparisons of Josephson standards or bilateral comparisons using traveling standards based on Zener diodes. This paper describes some of the new procedures used in both types of comparison and presents some results of five recent BIPM key comparisons     

NIST gravimetrically prepared atmospheric level methane in dry air standards suite

The Gas Metrology Group at the National Institute of Standards and Technology was tasked, by a congressional climate change act, to support the atmospheric measurement community through standards development of key greenhouse gases. This paper discusses the development of a methane (CH(4)) primary standard gas mixture (PSM) suite to support CH(4) measurement needs over a large amount-of-substance fraction range 0.3-20,000 μmol mol(-1), but with emphasis at the atmospheric level 300-4000 nmol mol(-1). Thirty-six CH(4) in dry air PSMs were prepared in 5.9 L high-pressure aluminum cylinders with use of a time-tested gravimetric technique. Ultimately 14 of these 36 PSMs define a CH(4) standard suite covering the nominal ambient atmospheric range of 300-4000 nmol mol(-1). Starting materials of pure CH(4) and cylinders of dry air were exhaustively analyzed to determine the purity and air composition. Gas chromatography with flame-ionization detection (GC-FID) was used to determine a CH(4) response for each of the 14 PSMs where the reproducibility of average measurement ratios as a standard error was typically (0.04-0.26) %. An ISO 6134-compliant generalized least-squares regression (GenLine) program was used to analyze the consistency of the CH(4) suite. All 14 PSMs passed the u-test with residuals between the gravimetric and the GenLine solution values being between -0.74 and 1.31 nmol mol(-1); (0.00-0.16)% relative absolute. One of the 14 PSMs, FF4288 at 1836.16 ± 0.75 nmol mol(-1) (k = 1) amount-of-substance fraction, was sent to the Korea Research Institute of Standards and Science (KRISS), the Republic of Korea's National Metrology Institute, for comparison. The same PSM was subsequently sent to the National Oceanic and Atmospheric Administration (NOAA) for analysis to their standards. Results show agreement between KRISS-NIST of +0.13% relative (+2.3 nmol mol(-1)) and NOAA-NIST of -0.14% relative (-2.54 nmol mol(-1)).     

绝对重力仪国际比对新动态

全球绝对重力仪国际比对活动从1981年起每隔4年在法国国际计量局举办。近两年来,该比对活动发生了一些变化,同时,区域性绝对重力仪国际比对活动日益兴起。中国计量科学研究院代表我国参与了这方面的工作,并介绍了中国计量科学研究自主研制的NIM-II型绝对重力仪参加2009年第8届全球绝对重力仪国际比对的情况和结果     

低能X射线空气比释动能国际关键比对

为促进我国在低能X射线空气比释动能计量领域内的量值统一并达到国际等效,中国计量科学研究院(NIM)于2018年采用平板自由空气基准电离室复现低能X射线空气比释动能,并通过传递电离室Radcal-RC6M在国际计量局(BIPM)低能X射线辐射场中开展了间接比对,其比对结果在合成标准不确定度为0.37%范围内与国际计量局等效一致,该比对结果已纳入国际计量局的关键比对数据库(KCDB)。     

高精密自动绝热量热计

介绍了中国计量科学研究院用新近开发的高精密自动绝热量热计的测量控制系统对美国国家标准技术研究院（NIST）的标准物质α-Al2O3进行的比热测量,并对测量结果和不确定度作了分析。该自动绝热量热计是中国计量科学研究院原有的绝热量热计的发展,它继承了原有量热计的本体,又开发了高精度量热和温度自动测量控制系统。进行了与NIST的数据和其它数据对比以及不确定度分析。测量结果与NIST的数据相比,其相对均方根偏差为0．447％,一致性为0．167％。合成相对标准不确定度为0．333％。结果表明,该自动绝热量热计具有高精密量热和比热测量的能力。     

Stability of short, single-mode erbium-doped fiber lasers

We conducted a detailed study of the stability of short, erbium-doped fiber lasers fabricated with two UV-induced Bragg gratings written into the doped fiber. We find that the relative intensity noise of single-longitudinal-mode fiber grating lasers is approximately 3 orders of magnitude lower than that of a single-frequency 1.523-mum helium-neon laser. The frequency noise spectrum contains few resonances, none of which exceeds 0.6 kHz/Hz(1/2) rms; the integrated rms frequency noise from 50 Hz to 63 kHz is 36 kHz. We also demonstrate a simple method for monitoring the laser power and number of oscillating modes during laser fabrication.     

Set Up and Characterization of a System for the Generation of Reference Magnetic Fields From 1 to 100 kHz

This paper describes the design process, the specific features, and the characterization procedures of the Istituto Nazionale di Ricerca Metrologica (I.N.RI.M.) set up for the generation of reference magnetic fields in the frequency range from 1 to 100 kHz. Numerical techniques, validated by comparison with experimental data, make it possible to choose the best solutions for obtaining magnetic flux densities up to 100 muT at 1 kHz and 25 muT at 100 kHz with relative uncertainty from a few parts in 10³ up to the percent     

Measurement of the refractive index of distilled water from the near-infrared region to the ultraviolet region

By the minimum deviation method using a prism shaped cell, the absolute refractive indices of high-performance liquid chromatography distilled water were measured at the wavelengths from 1129 to 182 nm, at the temperature of 19 degrees C, 21.5 degrees C, and 24 degrees C, and then dn/dt at 21.5 degrees C was calculated. The coefficients of the four-term Sellmeier dispersion formula were determined by using the refractive indices at each temperature. As a result of the comparison of our refractive index data in the visible wavelength region with the formula by Tilton et al. at the National Bureau of Standards in 1938, both the refractive index data corresponded within 6 x 10(-6). In the UV region, the absolute refractive index at 193.39 nm calculated by the data measured nearby the wavelengths from 200 to 190 nm was 1.436517 (21.5 degrees C). The value was lower by 9 x 10(-5) or 10 x 10(-5) than the data measured by Burnett et al. at the National Institute of Standards and Technology.     

Interlaboratory Comparison in Measuring Low Levels of AC Voltage between Italy and Egypt

The paper describes an interlaboratory comparison program between the National Institute for Standards (NIS), Egypt and the Istituto Nazionale di Ricerca Metrological (I.N.Ri.M.), Italy for measuring low ac voltages. The aim of this program is to demonstrate the technical competence of both institutes. The interlaboratory comparison has been carried out under the framework of the executive program of scientific and technological cooperation between Italy and Egypt. A Fluke model 792A has been used as a travelling standard, which was calibrated against the reference standard of NIS and I.N.Ri.M. at 10, 20, 50, 100 and 200 mV at 40 Hz, 1 kHz, 10 kHz and 20 kHz. The standards of the two institutes, NIS and I.N.Ri.M., have been used to calibrate the traveling standard at 10, 20, 50, 100 and 200 mV at frequencies of 40 Hz, 1 kHz, 10 kHz  and 20 kHz. The ac–dc transfer difference results of the traveling standard are evaluated then compared at the intended frequencies. In this paper, the comparison results are discussed in detail. The performance of this test is also judged by calculating the relative error normalized with respect to the uncertainty of the measurement. The comparison results and the efficiency test E _n values show a good agreement between the NIS and the I.N.Ri.M. systems in assigning ac–dc transfer difference.     

Bilateral Comparison of Blackbodies for Clinical Infrared Ear Thermometers between NIMT and NMIJ

This article describes the results of the bilateral comparison of blackbodies for infrared ear thermometers (IRETs) between the National Institute of Metrology (Thailand), NIMT, and the National Metrology Institute of Japan (NMIJ). The purpose of this comparison was to ensure consistency of the national radiance temperature scales for IRETs maintained by NIMT and NMIJ. Results of the measurements indicate differences in radiance temperature within 10 mK with a maximum measurement uncertainty of 64 mK. The equivalence of the radiance temperature scales realized by both NIMT and NMIJ in the range of 35  \(^{\circ }\) C to 42  \(^{\circ }\) C for IRET calibration is indicated. The results of this bilateral comparison can be used in terms of quality assurance and validation of calibration.     

Trilateral optical powermeter comparison between NIST, NMIJ/AIST, and METAS

We describe the results of a comparison of reference standards between three National Metrology Institutes: the National Institute of Standards and Technology (NIST, USA), the National Metrology Institute of Japan/National Institute of Advanced Industrial Science and Technology (NMIJ/AIST, Japan), and the Federal Office of Metrology (METAS, Switzerland). Open-beam- (free field) and optical-fiber-based measurements at wavelengths of 1302 and 1546 nm are reported. Three laboratories' reference standards are compared by means of two temperature-controlled, optical trap detectors. Measurement results show the largest differences of less than 4.2 parts in 10(3), which is within the expanded (k=2) uncertainty for the laboratories' reference standards.