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International audience; We have measured the three-dimensional coordinates of retroreflecting glass spheres using a multilateration technique. To this end, the distances between each target and our measurement heads have been determined by an in-house prototype of electro-optical absolute distance meter. The used targets are spheres of glass refractive index n=2 and of diameter 14.2 mm. They offer a much larger aperture than corner cubes and a lower cost, but they present a low reflectivity. However, this paper shows that with a proper collimation of the laser beams it is possible to reach a range of operation of 20 m. The standard uncertainty on such distances is better than 11 µm, including the mechanical errors of the gimbal mechanisms of our aiming systems. This uncertainty has been validated thanks to a comparison with an interferometric bench. In addition, the measurement of the coordinates of 16 glass spheres using a self-calibration multilateration algorithm has also confirmed the performances of the developed system: the standard deviation on the position errors has been estimated to about 10 µm.

International audience; Large Volume Metrology is essential to many high value industries to go towards the factory of the future, but also to many science facilities for fine alignment of large structures. In this context, we have developed a multilateration coordinate measurement system, traceable to SI metre, and suitable for outdoor measurements or industrial environments. It is based on a high accuracy absolute distance meter developed in-house and shared between several measurement heads by fibre-optic links. Thus, from these measurement stations, multiple distance measurements of several positions of a target can be performed. At the end, coordinates of the heads and of the different target locations are determined using a multilateration algorithm with self-calibration.In this paper, the uncertainty of this multilateration coordinate measurement system is determined with a consistent metrological approach. First, 13 different sources of errors are listed and quantified. Then, thanks to Monte Carlo simulations, the standard uncertainty on a single absolute distance measurement is assessed to 4.7 µm. This includes the uncertainty contribution of the telemetric system itself, but also the contributions of the mechanical designs of the measurement heads and the target. Lastly, measurements of three-dimensional coordinates of target positions are performed in a control environment, then in a large workshop without temperature control: these measurements validate the uncertainty assessment of the system.

We are developing a multilateration system at a reasonable cost that aims at an accuracy better than 50 µm determined with a consistent metrological approach. In this context, an absolute distance meter, developed in-house, is used as a unique telemetric system to feed the different measurement heads of the multilateration system through a network of optical fibers. The uncertainty contribution for a distance measurement of the telemetric system itself, in a controlled environment, is from 2 µm up to 100 m (k = 1). In this paper, the uncertainty contribution due to mechanical designs of the measurement heads and the target is estimated: the gimbal mechanisms we have designed are presented and their sources of error are identified, experimentally quantified, and minimized. At the end, we demonstrate that the current design of the measurement head does not induce errors higher than 2 µm on the measured distances and the design of the target does not induce errors higher than 9 µm.

This paper describes a quantum realization of the pascal based a helium absolute refractometer at 532 nm. The short-term stability in pressure is ± 2 mPa with a resolution in pressure of this new optical pressure standard is better than 1 mPa with temperature stability about 1 mK. A new design of the refractometer is presented to have better temperature stability and accurate temperature measurements to reach uncertainties in pressure better than current conventional methods.

We have developed a transportable distance meter based on a 1550-nm laser diode, that is, intensity modulated at 5 GHz. This fiber-based prototype is realized using telecommunication components that are reliable, largely available, and affordable. We have identified and quantified the different sources of error when measuring with this technique a distance between two positions of the same reflector. Minimizing these errors and evaluating their uncertainties lead to a global uncertainty of $4~\mu \text{m}$ ( $k = 1$ ) up to 1 km. This value does not include the additional errors caused by the evaluation of the atmospheric parameters. This uncertainty has then been verified over 100 m by comparison with an optical interferometer. The prototype was also tested outdoors over 5.4 km and has shown a resolution of 25 $\mu \text{m}$ for an integration time of 10 ms. Distance measurements for long distances with this prototype are still limited by the air refractive index effect. Nevertheless, we have demonstrated that the uncertainty on optical distances reached with this simple technique is compatible with the future development of a two-wavelength system with air index compensation.

This paper describes a transportable system based on synthetic wavelength interferometry for absolute distance measurement. The synthetic wavelength is generated by means of two frequency-doubled Nd:YAG lasers. A superheterodyne technique has been implemented to detect the synthetic phase, enabling a fringe interpolation of ∼2π/5 600. A ∼5 μm accuracy (1σ) is demonstrated over 25 m, based on an indoor comparison with a classical fringe counting interferometer. An outdoor comparison has been carried out on a 864 m-long standard baseline located in Finland (Nummela), yielding an uncertainty of 700 μm (1σ). This work was carried out within the framework of the “Long distance” EMRP project that ended on June 2011.

We have validated the laser-induced fluorescence technique to measure the quality of iodine cells whose transitions are used as a reference in laser standards for the realization of the definition of the metre. In this technique, the change in induced fluorescence is measured for different values of iodine pressure in the cell: for an iodine cell contaminated with foreign gases the fluorescence is more sensitive to iodine pressure changes than for a pure one due to collisional quenching of the excited states. We have measured the fluorescence parameter Ko for a total of 96 iodine cells, and for each cell we correlated Ko with the measured absolute frequency when the cell is inserted into laser standards at wavelengths 515?nm, 532?nm and 633?nm. We observed that the distribution of the quality of the produced iodine cells has a large dispersion and we believe that this also significantly affects the frequency distribution of the iodine-based laser standards that are used to realize the definition of the metre.

Following various works on second harmonic process using periodically poled Lithium Niobate crystals (PPLN), we report on the performances comparison between commercial bulk and proton-exchanged waveguide crystals operating at 1029 nm. We use a continuous wave (CW) amplified Yb doped single fiber laser delivering up to 500 mW in single mode regime. In case of bulk crystal we generate 4 mW using 400 mW IR power. The use of waveguide crystal leads to an increase of the harmonic power up to 33 mW with input IR power limited to 200 mW. Nevertheless, this impressive efficiency was affected by the long term degradation of the non-linear waveguide crystal. A decrease of about 40% of the conversion efficiency was observed after 2 years of use, neither associated to the degradation of the coupling efficiency nor to that of the AR coating. This behavior could be attributed to a slow diffusion of protons in the guide.

International audience; We have developed an optical Absolute Distance Meter (ADM) based on the measurement of the phase accumulated by a Radio Frequency (RF) wave during its propagation in the air by a laser beam. In this article, the ADM principle will be described and the main results presented. In particular, we will emphasize how the choice of an appropriate photodetector can significantly improve the telemeter performances by minimizing the amplitude to phase conversion. Our prototype, tested in the field, has proven its efficiency with a resolution better than 15 µm for a measurement time of 10 ms and distances up to 1.2 km.

International audience; We are developing a telemeter based on the measurement of the phase accumulated by a RF sine wave during its propagation in air. This wave is carried by a laser beam thanks to an intensity modulation. The main limitation of this technique lies in amplitude-to-phase conversion occurring in the detection of this modulation. Therefore, we characterized in this paper this phenomenon for a given telemetric system and discuss on how to reduce its effects on the resolution and the accuracy of the distance measurement. Finally, a solution is implemented and tested outdoor, in real conditions of use.

The frequency of several hyperfine components of 127I2 has been measured at 514.67 nm using an optical frequency comb. Among them, the a3 component of the P(13)43-0 transition is recommended by the CIPM for the practical realization of the definition of the metre. The result is consistent with other measurements of the same line within 1.5 kHz of uncertainty, when the collisional shift is taken into account. A frequency-doubled distributed feedback fibre laser has been developed to carry out these measurements.

A spectrometer for ultrahigh-resolution spectroscopy of molecular iodine at wavelength of 501.7 nm, near the dissociation limit is described. Line shapes about 30 kHz wide half-width half-maximum (HWHM) were obtained using saturation spectroscopy in a pumped cell. The frequency of an Ar/sup +/ laser was locked to a hyperfine component of the R(26)62-0 transition and the first absolute frequency measurement of this line is reported.

This paper presents new developments of the BNM-INM heterodyne compact refractometer. Air refractive index measurements have been made at 633 nm with a relative uncertainty of 10 −8 and the realization of a new type of wavelength stabilized laser source has been demonstrated at 633 nm. We now have adapted this source to a commercial interferometric system working at 633 nm. Length variation measurements in air have been made. Results show that the wavelength of our source is insensitive to slow variations of the refractive index of air at a level of 10 −8 , demonstrating the possibility to make distance measurements in air without the need to make any index correction.

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.

Based on the current state of technology, distance measurements over a few hundred metres in air with relative uncertainties significantly better than 10_6 are still an almost impossible challenge. In the European Joint Research Project (JRP) “Metrology for long distance surveying” measurement uncertainties in GNSS-based and optical distance metrology are going to be thoroughly investigated, novel technologies and primary standards developed and guidelines to improve surveying practice in the field worked out. A better understanding and a decrease of measurement uncertainty is also targeted for the critical local tie measurement at geodetic fundamental stations.

The frequency of an I2 stabilized Nd:YAG optical frequency standard, developed at the BNM-INM as a national standard for the `mise en pratique' of the definition of the metre, has been measured with a frequency measurement chain based on a femtosecond laser. A frequency (in-)stability of 2.5×10-13τ-1/2 has been measured in the optical domain against a hydrogen maser. The measured (in-)stability decreases to 1×10-14 without evidence of flicker floor.

We present our first results in the realization of a laser diodes based telemeter. We aim at developing an air index compensated distance meter taking advantage of the dependence of the chromatic dispersion of the refractive index with air temperature. This will be realized by two simultaneous distance measurements at two different wavelengths: each measurement is based on the measurement of the phase accumulated by a radio wave propagated in air by an intensity modulated laser beam.

We show that the lineshape and size of the detected signal in ultra-high-resolution stimulated Raman spectroscopy computed from a general expression of the modulated signal are in good agreement with the experimental results. Using the theoretical expression of the signal, we analyze the resolving power and the sensitivity of our Raman spectrometer. We show that a second harmonic detection in high-frequency transfer modulation generates a lineshape without modulation broadening. A 2.6-kHz-wide resonance has been obtained with iodine, mainly limited by both the transit time and collisions.

Linewidths only limited by the transit time and by collisions are obtained in stimulated Raman and Rayleigh spectroscopy by a second-harmonic detection in high-frequency modulation transfer. The distortion of the line shape due to a residual amplitude modulation is shown to vanish for a third- or a fourth-harmonic detection with a proper choice of the modulation index and the detection phase.

An international comparison of eight 127I2-stabilized semiconductor laser systems (DLs) has been carried out. Five of the DLs were extended-cavity lasers (ECLs) using extra-cavity saturation spectroscopy; another was a microlens-mounted diode modified to have weak optical feedback, stabilized using the same technique; the seventh ECL was stabilized using frequency-modulated spectroscopy. The final DL was a simple laser diode at 635 nm locked with a digital system on a linear absorption of iodine. The P(33) 6-3 transition of iodine was first used to compare the first seven DLs with a He-Ne laser stabilized on the R(127) 11-5 transition of iodine. The relative frequency stability of these lasers was between 5 parts in 1011 and 7 parts in 1012 for a sampling time of 1 s, with the best results less than 2 parts in 1013 over 1000 s. The frequency repeatability measured during one week was of the order of a few tens of kilohertz. This large fluctuation was caused by poor adjustment of the electronic offset of two of the lasers. For the well-corrected lasers, the repeatability was within a few kilohertz. A study of stabilization on the strong absorption group of transitions R(60) 8-4, R(125) 9-4 and P(54) 8-4, located about -12 GHz from the R(127) 11-5 transition, was also carried out. For the first time, a short-term frequency stability better than that of the classical He-Ne laser around 633 nm has been achieved with a relative frequency stability of 4 parts in 1012 for 1 s.

Measurements of hyperne splittings in the ground electronic state of I2 have been performed by stimulated Raman spectroscopy. An argon laser emitting at 514.5 nm, drives the coherence between hyperne levels of the J 00 =1 3 orJ 00 = 15 rotational levels of the ground vibronic state, via resonant excitation of the hyperne transitions of the optical resonances (43-0) P(13) or R(15). We study the influence of the various experimental parameters on the line shape: the beam geometry, the laser modulation spectrum, the laser power, the molecular frequency shifts. We show that only beam aberrations can give rise to a signicant asymmetry of the line shape, which contributes to an error in the determination of the resonance frequency. From a theoretical expression of the line shape taking into account the beam geometry, a detailed study of this error is performed. The theoretical predictions and the experimental results are in very good agreement. From the measurements, improved sets of hyperne interaction constants for the I2 molecule have been calculated for J 00 =1 3 andJ 00 = 15. These constants are identical for both levels, except for quadrupole coupling constant eqQ which exhibits a J-dependence, which we attribute to the centrifugal distortion of the molecule. PACS. 33.15.Pw Fine and hyperne structure { 33.70.Jg Line and band widths, shapes, and shifts

We describe a transportable distance measurement system based on synthetic wavelength interferometry. Two frequency-doubled Nd:yttrium aluminum garnet lasers at 532 nm are used to generate a synthetic wavelength of approximately 2.5 cm. A nonpolarizing interferometric system has been set up to eliminate polarization cross-talk issue. A superheterodyne detection was performed to measure the synthetic phase and to determine absolute distances. The capability to achieve fringe interpolation of 2pi/5600 has been demonstrated and an agreement in distance measurement at the 4 microm level has been achieved, compared to an optical interferometric 3 m long displacement bench.

This paper describes our project of an optical refractometer. The targeted accuracy for air index measurement is below 10−8. It is based on an optical resonator whose mechanical distortion as a function of pressure will be calibrated using helium gas.

One of the most promising projects for the new definition of the kilogram is the watt balance. It uses a two-mode procedure: static mode and dynamic mode. One of the key points is to control the velocity, the yaw and the pitch of a moving coil during the dynamic mode. We have developed a specific method based on the use of a homemade double pass heterodyne interferometer, a two-level translation stage, and a home-made high frequency phase shifting electronic circuit. This system will replace the commercial heterodyne system (laser head and interferometer) used at present time which is limited in power and has polarization limitations. In this paper, we propose a novel and specific heterodyne interferometer able to ensure all previous demands to control the displacements of the moving coil in order to reduce the velocity noise. The laser source is powerful enough to ensure multiple measurements axis. The laser is frequency stabilized on iodine atomic transition around l=532 nm to ensure traceability. All the polarization defaults of the classical heterodyne interferometer have been minimized in order to reduce non-linearity effects. The most original point is that the reference beam is locked on an external electronic reference, which allows to be less sensitive to vibration and polarization defects of optical components from the laser head to the vacuum enclosure where the interferometer is placed.

We demonstrate and investigate (theory, experiment) a peculiar mode of cw Yb3+:doped crystal laser operation when two emissions, at two independently tunable wavelengths, are simultaneously produced. Both emissions are generated from a single pumped volume and take place either in a single beam or in spatially separated beams. The laser employs original two-channel cavities that use a Passively Self-Injection Locking (PSIL) control to reduce the intracavity losses or a very simple for practical realization two near collinear channels cavity. A two-wavelength, single, longitudinal mode generation is also obtained. The results reported are based on the example of Yb3+:GGG laser and Yb3+:YAH laser. The lasers operate in the range 1023-1033 nm and 1030-1040 nm, respectively with a total output power of ~0.4 W.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We report recent progress in optical frequency measurements at the BNM-SYRTE. The work presented is centered around the development of a frequency measurement chain based on a femtosecond laser (Diddams, 2001) and the construction of an optical frequency standard (OFS) using cold Sr atoms. The Kerr lens mode-locked femtosecond laser is centered at 800 nm with a repetition rate at 840 MHz, locked to a cryogenic oscillator referenced to a primary Cs standard. The frequency comb from the laser is broadened to more than an optical octave in a photonic crystal fiber. The infrared part of the frequency comb is frequency doubled in KTP and heterodyned with the green part of the spectrum to yield the carrier envelope offset frequency. For absolute frequency measurements, the CW laser from an OFS is superimposed with the frequency comb, and the beat signal with an adjacent line is measured. We present recent developments in our setup, as well as recent experiments on high stability transfer between various OFS in the lab

We have developed a source of 515 nm light by frequency doubling the amplified ouput of an ytterbium-doped fiber laser with a periodically poled lithium niobate (PPLN) crystal. We present here the main characteristics of the laser and the frequency doubling system, permitting to obtain 22 mW of green radiation in single pass

We report here experimental results obtained in saturated absorption spectroscopy of iodine in a low pressure cell at 501.7 nm. We obtained lines of 30 kHz wide (HWHM) for the R(26)62-0 transition, which are, to our knowledge, the narrowest resonances ever observed in iodine spectroscopy in cell

We present new solutions of a diode-pumped, cw Yb:YAG laser that is of interest for applications in spectroscopy and metrology. The proposed schemes permit producing of the emission in a single pumped volume at two independently tunable wavelengths, including single-mode regime. A passively self-injection (PSIL) controlled operation that ensures low threshold and high output is presented. The peculiarities of the two-wavelength operation of the considered laser are carried out. The laser operates in the range 1028 - 1035 nmw with a total output power of 0.4 - 0.7 W.

We demonstrate and investigate a peculiar mode of cw Yb3+-doped crystal laser operation when two emissions, at two independently tunable wavelengths, are simultaneously produced. Both emissions are generated from a single pumped volume and take place in either a single beam or spatially separated beams. The laser employs original two-channel cavities that use a passive self-injection-locking (PSIL) control to reduce intracavity loss. The advantages of the application of the PSIL technique and some limitations are shown. The conditions for two-wavelength multimode operation of the cw quasi-three-level diode-pumped Yb3+ lasers and the peculiarity of such an operation are carried out both theoretically and experimentally. The results reported are based on the example of a Yb3+:GGG laser but similar results are also obtained with a Yb3+:YAG laser. The laser operates in the 1023–1033-nm (1030–1040-nm) range with a total output power of 0.4 W. A two-wavelength, single longitudinal mode generation is also obtained.

We present the results obtained with a compact heterodyne refractometer at 633 nm based on the measurement of the frequency of a laser diode locked to a Fabry Perot cavity, by comparison with a He-Ne laser. An agreement with Edlen's formulas has been obtained at the level of 4/spl times/10/sup -8/, limited by the accuracy of these formulas. The principle of this instrument is similar to the refractometer already developed in our laboratory and working at 780 nm (N. Khelifa et al, Appl. Opt., vol. 37, pp. 156-161, 1998). This apparatus may be also used as an air wavelength reference as described in ref. (R. Thibout et al, Eur. Phys. J. AP., vol. 16, pp. 239-245, 2001).

We report recent results obtained at the BNM-LPTF with the new frequency measurement chain based on a femtosecond laser. An I/sub 2/ stabilized Nd:YAG optical frequency standard, developed at the BNM-INM as a national standard for the "mise en pratique" of the definition of the meter has been measured for the first time.

This paper presents the principle of an air wavelength standard for high accuracy length metrology. According to the definition of the metre, nanometric accuracy by interferometric measurement techniques can be reached only for measurements made under vacuum or by taking into account the fluctuations of the refractive index of air. We have developed a new type of laser source whose wavelength is insensitive to slow fluctuations of the refractive index of air. We now have adapted this source to a commercial interferometric system working at 633 nm. Length variation measurements in air have been made. Results show that the wavelength of our source is insensitive to slow variations of the refractive index of air at a level of 10/sup -8/, giving the possibility of making distance measurements in air without the need to make any index correction.

Very narrow resonances (3.3 kHz HWHM) have been obtained by stimulated resonance Raman spectroscopy of iodine with a continuously pumped cell. This technique is used to measure frequency differences between hyperfine levels of the rovibronic ground state. Experimental and theoretical line shapes are compared and the accuracy of the measurements is discussed.

We have performed measurements of frequency splittings of the different hyperfine components of the P(33) 6-3 transition of /sup 127/I/sub 2/ by beat frequency measurements using a laser diode emitting around 633 nm. The four principal hyperfine constants of the rovibrational level v"=6, J"=33 of the ground electronic state have been deduced.

Lines without frequency broadening are obtained by an original technique of second harmonic detection in high frequency modulation transfer. We apply this technique to Raman and degenerated Raman interactions.

We describe and analyze an original technique for all-optical and high gain (approximately 10 3 - 10 6 ) amplification of a periodically modulated (PM) intensity low-power (approximately (mu) W) laser radiation. The amplification is based on the injection locking control in linear laser schemes with homogeneously broadened active medium. The main problem of the injection locking amplifiers is to obtain a linear response to the PM injection. We propose to solve this problem by injecting a second laser beam with a constant power and a slightly different wavelength or orthogonal polarization compared to the injected PM beam.

This paper presents a comparison between interferometric heterodyne measurements of a commercial system (Axiom 2/20, Zygo) with its frequency stabilized He-Ne laser source and the same apparatus whose laser source has been replaced by our wavelength stabilized laser diode. The aim of this paper is only to demonstrate the feasibility of length measurements by interferometric techniques using new type of laser source which is insensitive to fluctuations of the refractive index of air.

Dimensional metrology applications require performing measurements of profile and form/shape of parts at a nanometer-level of accuracy. Therefore, the metrological characteristics of a miniature optical micro-probe based on a Michelson interferometer are evaluated. The optical micro-probe is designed to perform dimensional measurements with a target uncertainty in the order of few nanometers. Two microprobe designs having reflection-transmission ratios of 75-25% and 25-75%, are characterized. Two optical setups have been implemented as well: firstly, using a single laser diode with a 1550.3 nm wavelength and secondly using a tunable laser source in the C-L bands. The characterization of the two micro-probes is performed using a new ultra-precise test bench, with respect to both dissociated metrology structure and Abbe principles. The experiments allow the evaluation of the error sources such as: stability, axial motion errors (residual errors), material dependence, tilt angle and roughness of the tested object. The experimental results revealed that dimensional measurements could be achieved with nanometer-scale errors, ranging from 2 nm to 15 nm, depending on the probe design and the reflectance of the device under test. (C) 2015 Elsevier B.V. All rights reserved.

The experimental set-up for high-resolution spectroscopy of iodine at 501.7 nm, near the dissociation limit, is described. Line shapes of about 30 kHz wide are obtained with hyperfine components of the R(26)62-0 transition. Preliminary results on the absolute frequency measurements of the Ar + laser locked onto these transitions are given.