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.     

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.     

The BIPM laser standards at 633 nm and 532 nm simultaneously linked to the SI second using a femtosecond laser in an optical clock configuration

A femtosecond laser comb was used in an optical clock configuration to measure simultaneously the optical frequency of an iodine-stabilized Nd:YAG laser at 532 nm and an iodine-stabilized He-Ne laser at 633 nm at the International Bureau of Weights and Measures (BIPM). The noise characteristics of the data corresponds well to those of the reference standards and the lasers under study. In a second series of measurements during which the comb was phase-locked to a hydrogen maser, laser standards at 532 nm and at 633 nm were measured. A standard deviation of 6/spl times/10/sup -15/ during 2 h of measurements for the Nd:YAG laser illustrates well the excellent stability of these standards and, at the same time, the capabilities of the comb techniques.     

Comparison of 127I2-stabilized frequency-doubled Nd:YAG lasers at the Bureau International des Poids et Mesures

A frequency comparison was carried out between iodine-stabilized Nd:YAG lasers at 532 nm from the Bureau International des Poids et Mesures, the Centre for Metrology and Accreditation, the Czech Metrology Institute, and the Bureau National de Métrologie-Institut National de Métrologie. The frequency differences between lasers, as well as the frequency reproducibility of each system,were investigated. Pressure-, modulation-, and power-induced shifts were studied. A frequency dispersion (1 sigma) of 3.5 kHz (6.2 x 10(-12) in relative terms) with an average reproducibility for each laser of the order of 0.4 kHz (7.1 x 10(-13) in relative terms) was observed over the duration of the comparison. Relative stabilities better than 1 x 10(13) at 1 s were demonstrated for the third-harmonic systems.     

Frequency stabilization of a diode-pumped Nd:Yag laser at 532 nm to iodine by using third-harmonic technique

A compact frequency standard was constructed by stabilizing the frequency of a diode-pumped Nd:YAG laser to the Doppler-free spectrum of iodine at 532 nm. The performance of the laser and the stability and repeatability of the stabilization scheme were investigated. The dependence of the laser frequency on such parameters as pressure of the iodine cell, modulation amplitude, and pressure were also studied. The results show that by using standard third-harmonic locking technique stability and repeatability comparable to more elaborate iodine-stabilized Nd:YAG laser systems can be achieved in a portable, and relatively simple and inexpensive, setup.     

Absolute frequency of the molecular iodine transition R(56)32-0near 532 nm

The absolute frequency of the hyperfine component a₁₀ in the transition R(56)32-0 of iodine has been measured using the D₂ line in Rb at 780 mm and an iodine-stabilized 633-nm He-Ne laser as references. This measurement provides a secondary frequency standard within the tuning range of a doubled Nd:YAG laser. The measured frequency of the a₁₀ component is 563 260 223.480 MHz ±70 kHz     

Study on a Thermal-diffusivity Standard for Laser Flash Method Measurements

The National Metrology Institute of Japan (NMIJ) of AIST has been studying the laser flash method in order to establish an SI traceable thermal- diffusivity standard. Key technologies have been developed to reduce the uncertainty in laser flash measurements. In the present study, an uncertainty evaluation has been carried out on the laser flash measurement method in order to determine the thermal diffusivity value of IG-110, a grade of isotropic high-density graphite, as a candidate reference material. The thermal diffusivity measured by the laser flash method is derived from a specimen thickness and a heat diffusion time. And a laser flash measurement is carried out at a given temperature. The measurement system is composed of three sections corresponding to each measured quantity: length, time, and temperature. Therefore, we checked and calibrated our measurement system, and estimated the uncertainty of measurement results for the case of a grade of isotropic graphite.Paper presented at the Seventeenth European Conference on Thermophysical Properties, September 5–8, 2005, Bratislava, Slovak Republic.     

Realization of the 3He Vapor-Pressure Temperature Scale and Development of a Liquid-He-Free Calibration Apparatus

The ³He vapor-pressure temperature scale was realized using an apparatus based on a continuously operating ³He cryostat at the National Metrology Institute of Japan (NMIJ), National Institute of Advanced Industrial Science and Technology (AIST). The cryostat has two operational modes: a ³He circulation mode and a 1 K pot mode. The ³He circulation mode can be used for ³He vapor-pressure measurements below 1.6 K, and the 1 K pot mode can be used for measurements above 1.3 K. Either mode can be selected for measurements from 1.3 K to 1.6 K. The realization of the ³He vapor-pressure temperature scale in this study fully covers its defined temperature range from 0.65 K to 3.2 K in the International Temperature Scale of 1990. The latest realization results are presented in this article. In addition, a liquid-He-free calibration apparatus was developed. It does not require liquid helium as a cryogen, which usually entails cumbersome handling and periodic refilling. The apparatus was designed for the calibration of capsule-type resistance thermometers from 0.65 K to 24.5561 K (the triple point of neon). The cooling system of the apparatus consists of a commercially available pulse-tube refrigerator and a ³He Joule?CThomson (JT) cooling circuit developed at NMIJ/AIST. The pulse-tube refrigerator is used in a pre-cooling stage and cools the apparatus to approximately 5 K. The ³He JT cooling circuit is used to cool the apparatus from 5 K to below 0.65 K. Since the ³He JT cooling circuit is a closed circuit, the apparatus can run continuously with only simple maintenance required. The basic characteristics of the apparatus are described.     

Thermal Diffusivity Measurements of Candidate Reference Materials by the Laser Flash Method

The National Metrology Institute of Japan (NMIJ) in AIST has investigated the laser flash method in order to establish a thermal diffusivity standard for solid materials above room temperature. A uniform pulse-heating technique, fast infrared thermometry, and a new data analysis method were developed in order to reduce the uncertainty in thermal diffusivity measurements. The homogeneity and stability of candidate reference materials such as isotropic graphite were tested to confirm their qualification as thermal diffusivity reference materials. Since graphite is not transparent to both the heating laser beam and infrared light for thermometry, the laser flash method can be applied to graphite without black coatings. Thermal diffusivity values of these specimens with different thicknesses, were measured with changing heating laser pulse energies. A unique thermal diffusivity value can be determined for homogeneous materials independent of the specimen thickness, by extrapolating to zero heating laser pulse energy on the plot of apparent thermal diffusivity values measured with the laser flash method as a function of heating laser pulse energy.Paper presented at the Fifteenth Symposium on Thermophysical Properties, June 22--27, 2003, Boulder, Colorado, U.S.A.     

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.     

Measurements with the new GABL-M field ballistic gravimeter under tundra conditions

A new version of the Russian absolute field gravimeter GABL-M with a green Nd:YAG laser developed at the Institute of Automation and Electrometry of the Siberian Branch of the Russian Academy of Sciences is discussed. The gravimeter is described briefly and its technical characteristics are given, along with some results from the first measurements under various conditions. (Field measurements were made in a tundra region.)     

Performance of diode-end-pumped Cr, Nd:YAG self-Q-switched and Nd:YAG/Cr:YAG diffusion bonded lasers

Self-passively Q-switching of a diode-pumped Cr,Nd:YAG, where the Cr⁴⁺ is used as a saturable absorber for the 1064 nm laser emission is reported. The maximum average output power was obtained using an output coupler of R=86%. The self-Q-switched diode pumped laser yielded 1.86-W average output power with low threshold pumping power (≈1.7-W), average slope efficiency of ≈34%, pulse duration of about 14–16 ns, and modulation frequency ranging from 2.4 to 73 kHz, depending on the input pumping power. These results are the highest reported for self-Q-switched lasers. Higher slope efficiency (42%) and shorter Q-switched pulses were obtained for a Q-switched Nd:YAG/Cr⁴⁺:YAG diffusion bonded laser. A comparison of the codoped Cr,Nd:YAG laser performance, with that of a diffusion bonded laser is reported and analyzed.     

Three-color optical range finding

In the known three-wavelength distance-measuring systems two optical wavelengths are used and a microwave is added for air-humidity influence consideration. In our research, which proceeds from results obtained at the National Research Laboratory of Metrology (Japan), the possibility of constructing a three-optical-wavelength ranging system is discussed. We investigate different versions by using a CO(2) laser as the source of the third wavelength. Analysis shows that the three-wavelength system with two lasers (YAG:Nd(3+) laser, which yields first- and second-harmonic radiation, and a CO(2) laser) seems to be optimum. A possible schematic structure of the three-wavelength YAG-CO(2) laser system is given.     

Absolute frequency stability of a diode-laser-pumped Nd:YAG laser stabilized to a high-finesse optical cavity

We report the frequency stabilization of a diode-laser-pumped monolithic ring Nd:YAG laser locked to a high-finesse optical cavity. With an independent cavity as a frequency discriminator, the absolute frequency noise was measured to be as low as 2 × 10(-2) Hz/Hz(1/2) at the Fourier frequency of approximately 3 kHz. We also measured the heterodyne beat note between two lasers locked to the independent cavities. The beat linewidth is narrower than 30 Hz and the minimum root Allan variance is approximately 6 × 10(-14).     

An AC Josephson Voltage Standard for AC–DC Transfer-Standard Measurements

We describe the traceability chain of length measurements at Centre for Metrology and Accreditation (MIKES) from atomic clocks to the lasers of primary interferometers. Crucial part of the traceability chain, an optical frequency comb generator linking optical frequencies to atomic clocks, is described in detail. The frequency comb generator is used in frequency calibrations of iodine-stabilized lasers, which are operated in compliance with the recommendations of the practical realization of the definition of the meter. Measured absolute frequencies of iodine-stabilized lasers, time records of the measurements, and the respective Allan deviations demonstrate the solid performance of the MIKES laser frequency standards. The results are in good agreement with the recommended values, as well as with the independent characterizations of the measured lasers     

One-Dimensional, Time-Resolved Raman Measurements in a Sooting Flame made with 355-nm Excitation

Single-shot vibrational Raman measurements were performed along an 11-mm-long line crossing the reaction zone in a premixed, fuel-rich (phi = 10), laminar methane-air flame by use of a frequency-tripled Nd:YAG laser with a 355-nm emission wavelength. This laser source seems to have advantages relative to KrF excimer lasers as well as to Nd:YAG lasers at 532 nm for hydrocarbon combustion diagnostics. The Raman emissions of all major species (N(2), O(2), CH(4), H(2), CO(2), H(2)O) were detected simultaneously with a spatial resolution of 0.4 mm. By integration over selected spectral intervals, the mole fractions of all species and subsequently the local gas temperatures have been obtained. A comparison of the temperatures that were found with results from filtered Rayleigh experiments showed good agreement, indicating the success of what are to the best of our knowledge the first one-dimensional single-shot Raman measurements in a sooting hydrocarbon flame.     

Optical frequency measurements with the global positioning system: tests with an iodine-stabilized He-Ne laser

Global positioning system- (GPS-) referenced optical frequency combs based on mode-locked lasers offer calibrations for length metrology traceable to international length standards through the SI second and the speed of light. The absolute frequency of an iodine-stabilized He-Ne laser [127I2 R(127) 11-5 f component] was measured with a femtosecond comb referenced to a multichannel GPS timing receiver. The expected performance and limitations of GPS-referenced comb measurements are discussed.     

Nd∶YAG激光透明陶瓷的研究进展

作为新一代固体激光增益介质,Nd∶YAG透明陶瓷以容易制造、成本低、易于实现大尺寸生产等优势,正逐步取代单晶和玻璃材料,应用前景十分广阔。从Nd∶YAG透明陶瓷光学质量的提升、激光输出特性以及实现Nd∶YAG透明陶瓷高功率激光输出3个方面,分别回顾并总结了我国、日本、美国、欧洲和俄罗斯关于Nd∶YAG激光透明陶瓷的研究进展,并概述了我国及日本关于复合结构及共掺杂Nd∶YAG透明陶瓷的发展情况。最后总结并展望了当前Nd∶YAG激光透明陶瓷的发展趋势和存在的主要问题。     

NMIJ Constant-Volume Gas Thermometer for Realization of the ITS-90 and Thermodynamic Temperature Measurement

The constant-volume gas thermometer (CVGT) of the National Metrology Institute of Japan (NMIJ), AIST with ³He as the working gas is used as an interpolating gas thermometer to realize the International Temperature Scale of 1990 (ITS-90) from 3 K to 24.5561 K and as a relative gas thermometer for thermodynamic temperature measurement calibrated at the triple point (TP) of Ne. The standard uncertainties of the realization and measurement are estimated to be 0.58 mK and 0.86 mK at a maximum in the mentioned temperature range, respectively. The maximum difference between both temperatures is about 1 mK. In the calibration of the CVGT, the TP of equilibrium hydrogen (e-H₂) is corrected for isotopic composition as specified in the Technical Annex for the ITS-90. The ambiguity of the TP of Ne due to the variability in isotopic composition is included in the uncertainty. Although the CVGT was also used in 2004 to realize the ITS-90, it was modified for the present experiment to reduce some measurement uncertainty components and the working gas was replaced with a higher-isotopic-purity gas. The results from 2004 were recalculated by correcting for the isotopic composition of e-H₂ and differ insignificantly from the present results, except for a wider scatter.     

Experimental Verification to Obtain Intrinsic Thermal Diffusivity by Laser-Flash Method

There is a need to obtain highly reliable values of thermophysical properties. The thermal conductivity of solids is often calculated from the thermal diffusivity, specific heat, and density, respectively, measured by the laser-flash method, differential scanning calorimetry, and Archimedes’ method. The laser-flash method is one of the most well-known methods for measuring the thermal diffusivity of solids above room temperature. This method is very convenient to measure the thermal diffusivity without contact in a short time. On the other hand, it is considered as an absolute reference measurement method, in particular, because only measurements of basic quantities such as time, temperature, length, and electrical quantities are required, and because the uncertainty of measurement can be analytically evaluated. However, it could be difficult in some cases to obtain reliable thermal-diffusivity values. The measurement results can indeed depend on experimental conditions; in particular, the pulse heating energy. A procedure to obtain the intrinsic thermal-diffusivity value was proposed by National Metrology Institute of Japan (NMIJ). Here, “intrinsic” means unique for the material, independent of measurement conditions. In this method, apparent thermal-diffusivity values are first measured by changing the pulse heating energy at the same test temperature. Then, the intrinsic thermal diffusivity is determined by extrapolating these apparent thermal diffusivities to a zero energy pulse. In order to verify and examine the applicability of the procedure for intrinsic thermal-diffusivity measurements, we have measured the thermal diffusivity of some materials (metals, ceramics) using the laser-flash method with this extrapolation procedure. NMIJ and Laboratoire National de Metrologie et d’essais (LNE) have laser-flash thermal-diffusivity measurement systems that are traceable to SI units. The thermal diffusivity measured by NMIJ and LNE on four materials shows good agreement, although they used different measurement systems and different analysis methods of the temperature-rise curve. Experimental verification on the procedure was carried out using the measured results. Some problems and considered solutions for laser-flash thermal-diffusivity measurements are discussed.