Compact and accurate concept of laser wavemeters based on ellipsometry

Common laser wavemeters are based on a scanning Michelson interferometer. Displacements of the moving mirror as long as tens of centimeters are needed to reach a relative accuracy of 1 × 10−6 (1σ) on the unknown laser wavelengths. Such a long displacement range makes the system very sensitive to mechanical vibrations and to misalignments of the laser beams. The purpose of this paper is to demonstrate a new concept of laser wavemeter based on the measurements of the ellipsometric parameters ψ and of the laser beams. Experimental results show that a 10−6 (1σ) accuracy level could be reach with a displacement range of only 4 μm. Implementations of the device are described. Comparisons between our polarimetric wavemeter and a calibrated wavemeter are presented for two lasers, an extended cavity laser diode at 656 nm and a 532 nm green line Nd:YAG laser

Polarimetric interferometer for nanoscale positioning applications

International audienceWe propose and demonstrate a displacement control method at the subnanometric scale based on a Michelson interferometer combined with a polarimeter and a phase-locked loop electronic board. Step by step displacements with a step value of 5 nm are presented. A repeatability of 0.47 nm is obtained from back and forth displacements over 1 m range. We show that a residual ellipticity of less than 10° on the polarization state leads to a positioning error of less than 1 nm. Such system could be used over millimeter range displacements in a controlled surrounding environment leading to numerous applications in nanometrology

Surgical management of patients with von Willebrand disease: summary of 2 systematic reviews of the literature

von Willebrand disease (VWD) is the most common inherited bleeding disorder. The management of patients with VWD who are undergoing surgeries is crucial to prevent bleeding complications. We systematically summarized the evidence on the management of patients with VWD who are undergoing major and minor surgeries to support the development of practice guidelines. We searched Medline and EMBASE from inception through October 2019 for randomized clinical trials (RCTs), comparative observational studies, and case series that compared maintaining factor VIII (FVIII) levels or von Willebrand factor (VWF) levels at >0.50 IU/mL for at least 3 days in patients undergoing major surgery, and those with options for perioperative management of patients undergoing minor surgery. Two authors screened and abstracted data and assessed the risk of bias. We conducted meta-analyses when possible. We evaluated the certainty of the evidence using the Grading of Recommendations, Assessment, Development and Evaluations (GRADE) approach. We included 7 case series for major surgeries and 2 RCTs and 12 case series for minor surgeries. Very-low-certainty evidence showed that maintaining FVIII levels or VWF levels of >0.50 IU/mL for at least 3 consecutive days showed excellent hemostatic efficacy (as labeled by the researchers) after 74% to 100% of major surgeries. Low- to very-low-certainty evidence showed that prescribing tranexamic acid and increasing VWF levels to 0.50 IU/mL resulted in fewer bleeding complications after minor procedures compared with increasing VWF levels to 0.50 IU/mL alone. Given the low-quality evidence for guiding management decisions, a shared-decision model leading to individualized therapy plans will be important in patients with VWD who are undergoing surgical and invasive procedures

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Sensibilité à la température d'un capteur de pression partielle de gaz carbonique à fibres optiques

An optical fibre sensor to measure weak partial pressures of carbon dioxide has been designed and realized. This sensor is based on direct molecular absorption in the near infrared at 4.3 μm. It is an extrinsic and amplitude modulation type sensor. In the linear region between 0 and 2000 μbar, the calibration curve that represents the transmitted power versus the carbon dioxide partial pressure in air shows a sensitivity of 20 nW/mbar with a minimum detectable pressure of 25 μbar. This article describes a temperature sensitivity analysis for all optoelectronic components and proposes a calculation method to distinguish two successive levels of partial pressure in a surrounding atmosphere where the temperature can vary. The experimental results show that without using a reference signal, the maximum variation of temperature is ±1.4 °C. The use of a reference signal combined with thermoelectric cooling of the photodetector tolerates a temperature variation of ±25 °C

Capteur de CO2_{2} à fibres optiques par absorption moléculaire à 4,3 μ\mathsf{\mu}m

This paper describes a remote optical fibre sensor for the carbon dioxide detection by molecular absorption in the near infrared (4.3 $\mu$m) corresponding to fundamental mode $\nu_{3}$. To overcome the problem of the strong attenuation signal of optical fibre in the near infrared, we have used the opto-suppling technique which changes the working wavelength from 4.3 $\mu$m to 860 nm and permits the use of standard optical fibre 50/125. The simulation of absorption has been obtained by original modelisation of the absorption spectrum and the establishment of the calibration curves takes to the sensor to detect a partial pressures greater than 100 $\mu$bar with a minimal error margin of 100 $\mu$bar, which is acceptable considering the future use of the device. The sensor has been designed to monitor the CO$_{2}$ rate in enriched greenhouses.Cet article décrit un capteur à fibres optiques de gaz carbonique par absorption moléculaire dans l'infrarouge moyen (4,3 $\mu$m) correspondant au mode fondamental $\nu_{3}$. La liaison entre le site de mesure et le site de contrôle est assurée par un fibre optique standard 50/125 après une transposition de longueur d'onde de 4,3 $\mu$m à 860 nm par opto-alimentation. La simulation de l'absorption a été obtenue par modélisation originale du spectre d'absorption et l'établissement des courbes d'étalonnage prévoit une marge d'erreur minimale de 100 $\mu$bar, ce qui est suffisant pour l'application du dispositif à la régulation de taux CO$_{2}$ dans les serres agricoles enrichies par de gaz

A new type of fiber-optic-based interferometric ellipsometer for in situ and real-time measurements

International audienceIt is shown that it is possible to improve interferometric ellipsometers by using a Pockels cell or a Bragg cell hence avoiding the use of any moving components. Furthermore, these methods allow one to increase the beat frequency signal permitting a better insensitiveness to mechanical disturbances. It is also shown how to incorporate an optical fiber between the neutral beam splitter and the sample without losing any information concerning the ellipsometric angles of the sample. Several configurations are described and theoretically analyzed. The last ones do not contain any active component around the sample. They offer a new measurement technique for real-time and in situ measurements

A transfer standard of the Mètre: an air wavelength reference

This paper presents the principle of an air wavelength standard for high accuracy length metrology. According to the definition of the Mètre, 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. The sensitivity of our air wavelength standard to some characteristics (such as temperature, pressure, ageing behaviour...) has been measured. Results show that the relative uncertainty level of the wavelength of our source is below 10−8