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We investigate optical frequency dissemination over a 1400 km long fiber link in looped configuration over a pair of underground fibers between Braunschweig and Strasbourg. This fiber link is the first to combine fiber Brillouin amplifiers with a repeater laser station. Phase-coherent operation over more than five days is demonstrated. We analyze the repeatability of the performance over four campaigns and present results of 65 days in total. The weighted mean of the fractional frequency offset of the transferred optical frequency over the complete data set is $(-1.1 \pm 0.4) \times 10^{-20}$. By analyzing the stabilization signals of the two individual fibers, the correlation of the phase noise on the two fibers is shown to be >98%., 12 pages, 6 figures

Forecasting mortality rates is a problem which involves the analysis of high-dimensional time series. Most of usual mortality models propose to decompose the mortality rates into several latent factors to reduce this complexity. These approaches, in particular those using cohort factors, have a good fit, but they are less reliable for forecasting purposes. One of the major challenges is to determine the spatial–temporal dependence structure between mortality rates given a relatively moderate sample size. This paper proposes a large vector autoregressive (VAR) model fitted on the differences in the log-mortality rates, ensuring the existence of long-run relationships between mortality rate improvements. Our contribution is threefold. First, sparsity, when fitting the model, is ensured by using high-dimensional variable selection techniques without imposing arbitrary constraints on the dependence structure. The main interest is that the structure of the model is directly driven by the data, in contrast to the main factor-based mortality forecasting models. Hence, this approach is more versatile and would provide good forecasting performance for any considered population. Additionally, our estimation allows a one-step procedure, as we do not need to estimate hyper-parameters. The variance–covariance matrix of residuals is then estimated through a parametric form. Secondly, our approach can be used to detect nonintuitive age dependence in the data, beyond the cohort and the period effects which are implicitly captured by our model. Third, our approach can be extended to model the several populations in long run perspectives, without raising issue in the estimation process. Finally, in an out-of-sample forecasting study for mortality rates, we obtain rather good performances and more relevant forecasts compared to classical mortality models using the French, US and UK data. We also show that our results enlighten the so-called cohort and period effects for these populations.

In non-life insurance, business sustainability requires accurate and robust predictions of reserves related to unpaid claims. To this aim, two different approaches have historically been developed: aggregated loss triangles and individual claim reserving. The former has reached operational great success in the past decades, whereas the use of the latter still remains limited. Through two illustrative examples and introducing an appropriate tree-based algorithm, we show that individual claim reserving can be really promising, especially in the context of long-term risks.

We search for transient variations of the fine structure constant using data from a European network of fiber-linked optical atomic clocks. By searching for coherent variations in the recorded clock frequency comparisons across the network, we significantly improve the constraints on transient variations of the fine structure constant. For example, we constrain the variation to |δα/α| < 5 × 10−17 for transients of duration 103 s. This analysis also presents a possibility to search for dark matter, the mysterious substance hypothesised to explain galaxy dynamics and other astrophysical phenomena that is thought to dominate the matter density of the universe. At the current sensitivity level, we find no evidence for dark matter in the form of topological defects (or, more generally, any macroscopic objects), and we thus place constraints on certain potential couplings between the dark matter and standard model particles, substantially improving upon the existing constraints, particularly for large (≳104 km) objects.

International audience; We present our work on realizing two-branch fiber links enabling multiple-partner clock comparisons in Europe. We report in detail on the setup connecting two long haul links, and report for the relative frequency stability and accuracy. We report on a combined uptime of 90% for our dual-branch link during almost one month. We finally discuss the combined uncertainty contribution of the ensemble of the link architecture to a clock comparison. We show that the frequency transfer uncertainty is 2 × 10 −19 .

International audience; There is an increasing demand for precise molecular spectroscopy, in particular in the mid-infrared fingerprint window that hosts a considerable number of vibrational signatures, whether it be for modeling our atmosphere, interpreting astrophysical spectra or testing fundamental physics. We present a high-resolution mid-infrared spectrometer traceable to primary frequency standards. It combines a widely tunable ultra-narrow Quantum Cascade Laser (QCL), an optical frequency comb and a compact multipass cell. The QCL frequency is stabilized onto a comb controlled with a remote near-infrared ultra-stable laser, transferred through a fiber link. The resulting QCL frequency stability is below 10-15 from 0.1 to 10s and its frequency uncertainty of 4×10-14 is given by the remote frequency standards. Continuous tuning over ~400 MHz is reported. We use the apparatus to perform saturated absorption spectroscopy of methanol in the low-pressure multipass cell and demonstrate a statistical uncertainty at the kHz level on transition center frequencies, confirming its potential for driving the next generation technology required for precise spectroscopic measurements.

We report on the progresses of REFIMEVE, the French fiber network for optical frequency dissemination and comparison. We present the originality and the strengths of the approach promoted by RENATER to allow the propagation of bi-directional signals in parallel to data traffic on an active and operational network. We show, for the first time to the best of our knowledge, simultaneous dissemination of optical frequency standard into 3 branches of a 2x1300 km telecom network. Performances are at the state of the art, and the availability of the signal is typically > 96% over 25 days of continuous operation.

International audience; We present a brief review of our progress towards measuring parity violation in heavy-metal chiral complexes using mid-infrared Ramsey interferometry. We discuss our progress addressing the main challenges, including the development of buffer-gas sources of slow, cold polyatomic molecules, and the frequency-stabilisation of quantum cascade lasers calibrated using primary frequency standards. We report investigations on achiral test species of which promising chiral derivatives have been synthesized.

Flow of supercritical CO2-bearing fluids through a rock is a fundamental phenomenon which acts upon a great many geological processes ranging from seismic activity to formation of ore deposits. Atomic Force Microscopy scanning experiments allowed us to infer movement of supercritical CO2-bearing fluids through calcite crystals and relate it to natural decrepitation of nanoscale fluid inclusions. Calculated velocities exceed the rate of diffusion predicated via current vacancy models by several orders of magnitude implying that CO2-rich fluid movement through micro and nano-pore space may presently be greatly underestimated.

We are stabilizing the frequency of a mid-infrared quantum cascade lasers (QCLs) to an optical frequency comb itself stabilized to an ultra-stable near-infrared reference signal at $\pmb{1.5\mu} \mathbf{m}$ transferred from SYRTE to LPL using an optical link. The reference stability is copied to the QCL and we benefit from the traceability to the primary standards of SYRTE. The stabilized QCL can be scanned by scanning the near-IR reference with an electro-optic modulator. We use this ultrastable spectrometer to carry out saturated absorption spectroscopy of methanol. A detailed analysis of the frequency measurement uncertainty will be presented.

We report on the progress of a metrological fiber network on the French territory, with extensiONS to Europe, which aims to provide an ultra-stable frequency signal to around 20 laboratories. We present a low sensitivity multi-branch Michelson interferometer serving as a node for the dissemination to several network branches. We show in addition reliable and robust operation over several months of operation of a 1400 km, which instability is in the - 10−20 range at long-term. This work is an important step towards the realization of an effective fiber network disseminating optical frequency standards to a wide variety of research laboratories.

Comparisons of clocks through fiber links at the continental scale have become a reality in Europe, opening the way to the realization of a clock network. We will show that we can improve the reliability of the frequency comparison by combining several dissemination techniques. We will report on the implemention of a two-branch fiber link, as part of a wider concatenation of links between NMIs in Europe. This is a key step towards a new definition of the SI second based on optical frequency standards and opens novel opportunities for stringent tests of fundamental physics.

We present a hybrid fiber link combining effective optical frequency transfer and evaluation of performances with a self-synchronized two-way comparison. It enables us to detect the round-trip fiber noise and each of the forward and backward one-way fiber noises simultaneously. The various signals acquired with this setup allow us to study quantitatively several properties of optical fiber links. We check the reciprocity of the accumulated noise forth and back over a bi-directional fiber to the level of 3.1(±3.9) × 10

International audience; We present an hybrid fiber link combining effective optical frequency transfer and evaluation of performances with a self-synchronized two-way comparison. It enables us to detect the round-trip fiber noise and each of the forward and backward one-way fiber noises simultaneously. The various signals acquired with this setup allow us to study quantitatively several properties of optical fiber links. We check the reciprocity of the accumulated noise forth and back over a bi-directional fiber to the level of 3.1(±3.9) × 10 −20. We also analyze the noise correlation between two adjacent fibers and show the first experimental evidence of interferometric noise at very low Fourier frequency. We estimate redundantly and consistently the stability and accuracy of the transferred optical frequency over 43 km at 4 × 10 −21 level after 16 days of integration and demonstrate that frequency comparison with resolution as low as 8 × 10 −18 would be achievable with uni-directional fibers in urban area.

National audience; En France, le programme Investissements dAvenir a permis de lancer la construction de « REFIMEVE+ », un équipement dexcellence qui vise à délivrer une référence de fréquence optique à une vingtaine de laboratoires répartis sur tout le territoire métropolitain, via le réseau Internet de RENATER.Cette nouvelle technologie dépasse de plusieurs ordres de grandeur les capacités offertes par le service GPS dans le domaine radiofréquence (RF). Une révolution est en marche, avec une finalité : ouvrir la voie à des applications inédites dans des domaines aussi variés que la métrologie, la physique ou la géodésie !

In this paper, we consider nonparametric copula inference under bivariate censoring. Based on an estimator of the joint cumulative distribution function, we define a discrete and two smooth estimators of the copula. The construction that we propose is valid for a large number of estimators of the distribution function, and therefore for a large number of bivariate censoring frameworks. Under some conditions on the tails of the distributions, the weak convergence of the corresponding copula processes is obtained in $l^{\infty}([0,1]^2).$ We derive the uniform convergence rates of the copula density estimators deduced from our smooth copula estimators. Investigation on the practical behavior of our estimators is done through a simulation study and two real data applications, corresponding to different censoring settings. We use our nonparametric estimators to define a goodness-of-fit procedure for parametric copula models. A new bootstrap scheme is proposed to compute the critical values.

International audience

We have demonstrated the feasibility of a free-space ultra-stable optical link on a 3 meters test bench, operating at 100 MHz. With this type of link, it is possible to transfer a 100 MHz signal with a relative frequency stability of a few 10−14 at one second integration time, 10−16 at one day and a phase stability of a few picoseconds per day in presence of moderate mechanical vibrations and thermal fluctuations. The comparisons of modern clocks of distant (

We present a hybrid fiber link to realize the local two-way optical frequency comparison with self-synchronization. It enables us to detect round-trip fiber noise and one-way fiber noise, and estimate the residuals. Moreover, we can check, to the best of our knowledge for the first time, the reciprocity of the accumulated noise forth and back over a bi-directional fiber, and also evaluate the noise correlation between two adjacent fibers with the hybrid setup.

We present a frequency comb-assisted experimental setup which enables us to both coherently transfer the stability and accuracy of a remote near-infrared (NIR) ultrastable laser to a mid-infrared (MIR) quantum cascade laser (QCL), and widely tune the QCL frequency for spectroscopic applications. The QCL is stabilized at the level of 2×10−15 from 1 to 100 s, with an accuracy of 10−14 after 100 s. The achievable frequency tuning paves the way for high-resolution saturated absorption spectroscopy of molecular transitions, in particular in spectral regions that were previously inaccessible with standard stabilized MIR lasers. Preliminary results show a sensitivity at the kHz level on transition center frequencies.

We report on the first comparison of distant caesium fountain primary frequency standards (PFSs) via an optical fiber link. The 1415 km long optical link connects two PFSs at LNE-SYRTE (Laboratoire National de m\'{e}trologie et d'Essais - SYst\`{e}me de R\'{e}f\'{e}rences Temps-Espace) in Paris (France) with two at PTB (Physikalisch-Technische Bundesanstalt) in Braunschweig (Germany). For a long time, these PFSs have been major contributors to accuracy of the International Atomic Time (TAI), with stated accuracies of around $3\times 10^{-16}$. They have also been the references for a number of absolute measurements of clock transition frequencies in various optical frequency standards in view of a future redefinition of the second. The phase coherent optical frequency transfer via a stabilized telecom fiber link enables far better resolution than any other means of frequency transfer based on satellite links. The agreement for each pair of distant fountains compared is well within the combined uncertainty of a few 10$^{-16}$ for all the comparisons, which fully supports the stated PFSs' uncertainties. The comparison also includes a rubidium fountain frequency standard participating in the steering of TAI and enables a new absolute determination of the $^{87}$Rb ground state hyperfine transition frequency with an uncertainty of $3.1\times 10^{-16}$. This paper is dedicated to the memory of Andr\'{e} Clairon, who passed away on the 24$^{th}$ of December 2015, for his pioneering and long-lasting efforts in atomic fountains. He also pioneered optical links from as early as 1997.

The injection of a gas phase through a water saturated porous medium can reduce the water saturation not only by displacement mechanisms but also by evaporation mechanisms. In the presence of brine, this process can induce salt crystallization and precipitation within the porous medium with a risk of permeability alteration. In the field of gas production and storage, the occurrence of such a phenomenon can have detrimental consequence on the well productivity or injectivity. In this work, we investigated experimentally and numerically the effect of dry gas injection on salt precipitation and permeability impairment. State of the art equipment designed for high throughput coreflood experimentation was used to capture the dynamic of salt migration using X-Ray radiography. A set of experiments have been conducted on a sample of Bentheimer sandstone (10mm in diameter and 20 mm in length) as well as a two layers composite sample with a significant permeability contrast. Experiments were conducted using Nitrogen and KBr brine with different boundary conditions (i.e. with and without capillary contact). Results showed that salt precipitation results from the interplay of different parameters, namely pressure gradient, brine salinity, capillary forces and vapor partial pressure. Experimental observations indicate that in the case of dry gas injection, salt systematically precipitates but permeability alteration is observed only if a capillary contact is maintained with the brine. We built a 2D flow model integrating two-phase Darcy flow, capillary forces, salt effect on vapor partial pressure, dissolved salt transport, as well as the different PVT equilibria needed to describe properly the systems. Once calibrated, the model showed good predictability of lab scale experiment and thus can be used for parametrical study and upscaled to the well bore scale.

We present the first experimental demonstration over a 43-km-long urban fiber network of a local two-way optical frequency comparison, which does not require any synchronization of the measurements. It was combined with a regular active-noise compensation on another parallel fiber leading to a very reliable and robust frequency transfer. This hybrid scheme enables us to investigate the major limiting factors of the local two-way comparison. We analyze the contribution to the phase noise of the recovered signal by the interferometers at local and remote places. By using the ability of this set up to be injected by a single laser or two independent lasers, we measure the contribution to the long-term instability by the demodulated laser instabilities. We show that a fractional frequency instability level of $1\times10^{-20}$ at 10 000 s can be obtained with this simple setup after 43-km-long propagation in an urban area.

In this paper we provide a new nonparametric estimator of the joint distribution of two lifetimes under random right censoring and left truncation which can be seen as a bivariate extension of the Kaplan–Meier estimator. We derive asymptotic results for this estimator, including uniform n 1 / 2 -consistency, and develop a general methodology for bivariate lifetime modeling, a critical issue in studying reversion conditions that are commonplace in defined benefit pensions and private annuity contracts. An application to goodness-of-fit for survival copula models is discussed. We show that the procedures that we use are consistent, and propose a bootstrap procedure based on our estimator to compute the critical values. The new technique that we propose is tested on the Canadian dataset initially studied by Frees et al. (1996) .

L’espace d’échange que constitue la Méditerranée invite naturellement à se pencher sur la question de la mobilité des hommes, notamment dans le cadre professionnel. Dans ce cadre, l’activité de la Compagnie royale d’Afrique et le trafic commercial réalisé entre les côtes de Barbarie et Marseille durant la seconde moitié du xviiie siècle, constituent un laboratoire de premier ordre pour étudier le travail chez l’autre, en raison de la pérennité et de l’importance des concessions qu’elle gère, notamment à La Calle. L’importante présence française, dans un cadre institutionnel original, implique des pratiques spécifiques tant dans le rapport à l’autre que dans la définition du travail avec l’autre. The space of exchange constituted by the Mediterranean Sea invites naturally to bend over the question of the mobility of men, and particularly of professional mobility. Within this frame, the activity of the royal Company of Africa and the commercial exchanges between the Barbary coasts and Marseille in the second half of the 18th century constitute an excellent laboratory to study how one worked with the other, because of the durability and the importance of the concessions which it manages, especially in La Calle. The important French presence, in an original institutional frame, implied specific practices both in the relationship that in the definition of the work with the other.

In a regression model with univariate censored responses, a new estimator of the joint distribution function of the covariates and response is proposed, under the assumption that the response and the censoring variable are independent conditionally to the covariates. This estimator is based on the conditional Kaplan-Meier estimator of Beran (1981), and happens to be an extension of the multivariate empirical distribution function used in the uncensored case. We derive asymptotic i.i.d. representations for the integrals with respect to the measure defined by this estimated distribution function. These representations hold even in the case where the covariates are multidimensional under some additional assumption on the censoring. Applications to censored regression and to density estimation are considered.

We report on a fully bi-directional 680~km fiber link connecting two cities for which the equipment, the set up and the characterization are managed for the first time by an industrial consortium. The link uses an active telecommunication fiber network with parallel data traffic and is equipped with three repeater laser stations and four remote double bi-directional Erbium-doped fiber amplifiers. We report a short term stability at 1~s integration time of $5.4\times 10^{-16}$ in 0.5~Hz bandwidth and a long term stability of $1.7\times10^{-20}$ at 65\,000 s of integration time. The accuracy of the frequency transfer is evaluated as $3\times 10^{-20}$. No shift is observed within the statistical uncertainty. We show a continuous operation over 5 days with an uptime of 99.93$\%$. This performance is comparable with the state of the art coherent links established between National Metrology Institutes in Europe. It is a first step in the construction of an optical fiber network for metrology in France, which will give access to an ultra-high performance frequency standard to a wide community of scientific users., 16 pages, 7 figures

In this article, we describe an experiment performed at the Laboratoire de physique des lasers and dedicated to an optical measurement of the Boltzmann constant k B . With the proposed innovative technique, determining k B comes down to an ordinary frequency measurement. The method consists in measuring as accurately as possible the Doppler absorption profile of a rovibrational line of ammonia in thermal equilibrium. This profile is related to the Maxwell–Boltzmann molecular velocity distribution along the laser beam. A fit of the absorption line shape leads to a determination of the Doppler width proportional to k B T and thus to a determination of the Boltzmann constant. The laser source is an ultra-stable CO2 laser with a wavelength λ ≈ 10 μm . The absorption cell is placed in a thermostat, keeping the temperature at 273.15 K within 1.4 mK. We were able to measure k B with a relative uncertainty as small as 3.8 × 10 − 5 , which represents an improvement of an order of magnitude for an integration time comparable to our previous measurement published in 2007. To cite this article: K. Djerroud et al., C. R. Physique 10 (2009).

An opto-electronic device for the stabilization of laser beam intensity in a narrow frequency band based on a numeric corrector driving the radio-frequency signal of an acousto-optic modulator is applied to improve the signal-to-noise ratio of the detected signal in saturation spectroscopy of iodine in a cell at 501.7?nm, both in the FM spectroscopy technique and in the transfer modulation technique. In the latter case, a 30?dB rejection of the amplitude noise of the probe beam is achieved and, when the laser frequency is locked to the saturation signal, the enhancement of the sensitivity of the frequency jitter detection is demonstrated in a frequency band extending up to 1?kHz. For the long term stabilization the laser is locked to a narrow line detected in a low pressure cell. A relative Allan deviation of about 10?13 is found for 1?s integration time and a deviation of 10?14 is reached for 500?s. Linewidths smaller than 40?kHz (FWHM) are also demonstrated at low saturating power for hyperfine components of the transition R(26)62-0 at 501.7?nm.

In this article, we propose some new generalizations of M-estimation procedures for single-index regression models in presence of randomly right-censored responses. We derive consistency and asymptotic normality of our estimates. The results are proved in order to be adapted to a wide range of techniques used in a censored regression framework (e.g. synthetic data or weighted least squares). As in the uncensored case, the estimator of the single-index parameter is seen to have the same asymptotic behavior as in a fully parametric scheme. We compare these new estimators with those based on the average derivative technique of Lu and Burke [2005. Censored multiple regression by the method of average derivatives. J. Multivariate Anal. 95, 182–205] through a simulation study.

The composition of carbonate minerals formed in past and present oceans is assumed to be significantly controlled by temperature and seawater composition. To determine if and how temperature is kinetically responsible for the amount of Mg incorporated in calcite, we quantified the influence of temperature and specific dissolved components on the complex mechanism of calcite precipitation in seawater. A kinetic study was carried out in artificial seawater and NaCl–CaCl 2 solutions, each having a total ionic strength of 0.7 M. The constant addition technique was used to maintain [Ca 2+ ] at 10.5 mmol kg −1 while [ CO 3 2 - ] was varied to isolate the role of this variable on the precipitation rate of calcite. Our results show that the overall reaction of calcite precipitation in both seawater and NaCl–CaCl 2 solutions is dominated by the following reaction: Ca 2 + + CO 3 2 - ↔ k b , k f Ca CO 3 where k f and k b are the forward and backward reaction rate constants, respectively, while the net precipitation rate R, can be described at any temperature by R = k f a Ca 2 + n 1 a CO 3 2 - n 2 - k b or in its logarithmic form Log (R + k b ) = Log K f + n 2 Log [ CO 3 2 - ] where n i are the partial reaction orders with respect to the participating ions, a the ion activity, γ the activity coefficients, and K f = k f ( a Ca 2 + ) n 1 ( γ CO 3 2 - ) n 2 is a constant at a given temperature. We find that, irrespective of the presence of Mg, SO 4 , and other specific seawater components known calcite reaction rate inhibitors, the partial reaction order with respect to carbonate ion concentration changes from 2 to 5 while the rate constant K f , increases by 3–4 orders of magnitude when temperature varies from 5 to 70 °C. The observed variations of the kinetic mechanism resulting from the temperature changes are correlated with the variable amount of Mg incorporated in the formed calcites. Moreover, at a given temperature, the increase in the saturation state enhances the rate of calcite precipitation without influencing the reaction mechanism and without changing the amount of Mg incorporated in the growing lattice. Thus, the results of this experimental study are consistent with present-day abiotic marine carbonates where low-Mg calcite cements are mainly associated with cool water while high-Mg carbonates are dominantly found in warm-water environments. This suggests that the apparent inverse relationship between the global average paleo-temperature and the Mg/Ca ratio in past formed marine carbonate may correspond to major changes in seawater saturation state or (Mg/Ca) ratios that in turn should reflect significant changes in the relative seawater geochemical cycles of these cations.

International audience; We report a laboratory demonstration of the dissemination of an ultrastable optical frequency signal to two distant users simultaneously using a branching network. The ultrastable signal is extracted along a main fibre link; it is optically tracked by a narrow linewidth laser diode, which light is injected in a secondary link. The propagation noise of both links is actively compensated. We implement this scheme with two links of 50-km fibre spools, the extraction being set up at the mid-point of the main link. We show that the extracted signal at the end of the secondary link exhibits a fractional frequency instability of 1.4 × 10−15 at 1-s measurement time, almost equal to the 1.3 × 10−15 instability of the main link output end. The long-term instabilities are also very similar, at a level of 3–5 × 10−20 at 3 × 104-s integration time. We also show that the setting up of this extraction device, or of a simpler one, at the main link input, can test the proper functioning of the noise rejection on this main link. This work is a significant step towards a robust and flexible ultrastable network for multi-users dissemination.

International audience; We propose a regression tree procedure to estimate the conditional distribution of a variable which is not directly observed due to censoring. The model that we consider is motivated by applications in insurance , including the analysis of guarantees that involve durations, and claim reserving. We derive consistency results for our procedure, and for the selection of an optimal subtree using a pruning strategy. These theoretical results are supported by a simulation study, and two applications involving insurance datasets. The first concerns income protection insurance, while the second deals with reserving in third-party liability insurance.

International audience

Leveraging the unrivaled performance of optical clocks in applications in fundamental physics beyond the standard model, in geo-sciences, and in astronomy requires comparing the frequency of distant optical clocks truthfully. Meeting this requirement, we report on the first comparison and agreement of fully independent optical clocks separated by 700 km being only limited by the uncertainties of the clocks themselves. This is achieved by a phase-coherent optical frequency transfer via a 1415 km long telecom fiber link that enables substantially better precision than classical means of frequency transfer. The fractional precision in comparing the optical clocks of three parts in $10^{17}$ was reached after only 1000 s averaging time, which is already 10 times better and more than four orders of magnitude faster than with any other existing frequency transfer method. The capability of performing high resolution international clock comparisons paves the way for a redefinition of the unit of time and an all-optical dissemination of the SI-second., Comment: 14 pages, 3 figures, 1 table

We present a new method for direct determination of the Boltzmann constant by laser spectroscopy. The principle consists in recording the linear absorption in a vapour of an atomic or molecular line at a controlled temperature around 273.15 K. By eliminating the pressure broadening, we deduced the pure Doppler width which gives a first optical measurement of the Boltzmann constant k B . The present determination should be significantly improved in the near future and contribute to a new definition of kelvin.

International audience; We report a cascaded optical link of 1100 km for ultra-stable frequency distribution over an Internet fiber network. The link is composed of four spans for which the propagation noise is actively compensated. The robustness and the performance of the link are ensured by five fully automated optoelectronic stations, two of them at the link ends, and three deployed on the field and connecting the spans. This device coherently regenerates the optical signal with the heterodyne optical phase locking of a low-noise laser diode. Optical detection of the beat-note signals for the laser lock and the link noise compensation are obtained with stable and low-noise fibered optical interferometer. We show 3.5 days of continuous operation of the noise-compensated 4-span cascaded link leading to fractional frequency instability of 4x10 −16 at 1-s measurement time and 1x10 −19 at 2000 s. This cascaded link was extended to 1480-km with the same performance. This work is a significant step towards a sustainable wide area ultra-stable optical frequency distribution and comparison network at a very high level of performance.

International audience; The distribution and the comparison of an ultra-stable optical frequency and accurate time using optical fibres have been greatly improved in the last ten years. The frequency stability and accuracy of optical links surpass well-established methods using the global navigation satellite system and geostationary satellites. In this paper, we present a review of the methods and the results obtained. We show that public telecommunication network carrying Internet data can be used to compare and distribute ultra-stable metrological signals over long distances. This novel technique paves the way for the deployment of a national and continental ultra-stable metrological optical network.; La distribution et la comparaison d'étalons de fréquence optique ultra-stables et d'échelle de temps ont été grandement améliorées depuis dix ans par l'emploi de fibres optiques. La stabilité de fréquence et l'exactitude des liens optiques fibrés surpassent les méthodes bien établies fondées sur les communications satellitaires. Dans cet article, nous présentons les méthodes et les résultats obtenus pendant cette décade. Nous montrons que les réseaux de télécommunication publics transportant des données internet peuvent être utilisés pour comparer et distribuer des signaux métrologiques sur de grandes distances. Ceci ouvre la voie au déploiement d'un réseau métrologique à l'échelle nationale et continentale.

International audience; Quantum Cascade Lasers (QCL) are increasingly being used to probe the mid-infrared “molecular fingerprint” region. This prompted efforts towards improving their spectral performance, in order to reach ever-higher resolution and precision. Here, we report the stabilisation of a QCL onto an optical frequency comb. We demonstrate a relative stability and accuracy of 2x10-15 and 10-14, respectively. The comb is stabilised to a remote near-infrared ultra-stable laser referenced to frequency primary standards, whose signal is transferred via an optical fibre link. The stability and frequency traceability of our QCL exceed those demonstrated so far by two orders of magnitude. As a demonstration of its capability, we then use it to perform high-resolution molecular spectroscopy. We measure absorption frequencies with an 8x10-13 relative uncertainty. This confirms the potential of this setup for ultra-high precision measurements with molecules, such as our ongoing effort towards testing the parity symmetry by probing chiral species.

International audience; We theoretically and experimentally investigate relevant noise processes arising in optical fiber links, which fundamentally limit their relative stability. We derive the unsuppressed delay noise for three configurations of optical links: two-way method, Sagnac interferometry, and actively compensated link, respectively designed for frequency comparison, rotation sensing, and frequency transfer. We also consider an alternative two-way setup allowing real-time frequency comparison and demonstrate its effectiveness on a proof-of-principle experiment with a 25-km fiber spool. For these three configurations, we analyze the noise arising from uncommon fiber paths in the interferometric ensemble and design optimized interferometers. We demonstrate interferometers with very low temperature sensitivity of respectively -2.2, -0.03 and 1 fs/K. We use one of these optimized interferometers on a long haul compensated fiber link of 540 km. We obtain a relative frequency stability of 3x10^-20 after 10,000 s of integration time.

A series of controlled abiotic syntheses of magnetite nanocrystals were carried out to explore the possibility of using morphological criteria, crystal size distributions, and shape ratio as tools for identifying nanocrystals that would be specifically produced by magnetotactic bacteria. High-quality magnetite crystals synthesized with various controlled total iron concentrations were shown to have cubo-octahedral shapes and sizes varying from 4 to 24 nm. The mean particle size of the population was found to be 10.5 ± 0.7 nm and no significant effect of the total iron concentration on the particle size was observed. Systematical analyses of size and morphology also allowed for the determination of crystal size and shape ratio distributions. Crystal sizes were observed to follow log-normal distributions. Shape factors are bounded by one, with maxima between 0.80 to 1.00. Their distributions are asymmetric, with a cut off toward the high values. Crystal morphologies and shape factors appear not to be a powerful diagnostic tool for the differentiation of abiotic vs. biotic particles. However, crystal size distributions of abiotic crystals are significantly different from those of biotic populations. Indeed, opposite asymmetry of the size distributions from biogenic and non biogenic crystals was observed, with cut off toward larger sizes for biogenic nanocrystals and with cut off toward smaller sizes for abiogenic nanocrystals. This therefore constitutes a potential diagnostic tool for deciphering magnetite origin.

es proprietes spectrales d'un laser femtoseconde ont ete exploitees pour realiser des mesures de frequences optiques de tres haute precision. Les mesures sont referencees a un etalon primaire situe a l'Observatoire de Paris et achemine au LPL par un lien optique. Plusieurs etalons de frequence, reposant sur des transitions electroniques ou rovibrationnelles de molecules, ont ete mesures avec des incertitudes relatives comprises entre 2x 10 -12 et 5 x 10 -14 La mesure de l'evolution de leurs frequences au cours du temps permettra de tester une eventuelle variation des constantes fondamentales.