CW frequency doubling of 1029 nm radiation Using single pass bulk and waveguide PPLN crystals

Following various works on second harmonic process using periodically poled Lithium Niobate crystals (PPLN), we report on the performances comparison between commercial bulk and waveguide crystals at 1029 nm. We use a continuous wave (CW) amplified Yb doped single fibre laser delivering up to 500mW 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 33mW with input IR power limited to 200mW. Nevertheless, this impressive efficiency was affected by the long term degradation of the non-linear waveguide crystal

Frequency Measurement of an Ar+ Laser Stabilized on Narrow Lines of Molecular Iodine at 501.7 nm

A spectrometer for ultra high-resolution spectroscopy of molecular iodine at wave length 501.7 nm, near the dissociation limit is described. Line shapes about 30 kHz wide (HWHM) were obtained using saturation spectroscopy in a pumped cell. The frequency of an Ar+ 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

Arpent : un prototype de haute exactitude pour les mesures de grande distance

International audienc

Helium-Based Refractometry for Pressure Measurements in the Range 1–100 kPa

International audienceThis paper describes an alternative of pressure measurements based on a helium absolute refractometer at 532 nm. The Fabry-Perot cavity has been characterized from relevant parameters and the resolution in pressure of this new optical pressure sensor is lower than 0.2 Pa

Uncertainty assessment of a prototype of multilateration coordinate measurement system

International audienceLarge 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

Optical distance measurements at two wavelengths with air refractive index compensation

[EN] We present our first results in the realization of an absolute distance meter that will bring well-defined and metrologically traceable measurements for distances of several kilometers. The purpose is to achieve an accuracy of 1 mm up to 5 km and beyond. To this end, the developed prototype operates at two different wavelengths, 780 nm and 1560 nm. For each of these wavelengths, the measured distance is determined from the phase accumulated by a radio-frequency carrier propagated in air by a laser beam modulated in intensity. Thus, using the dispersion relation between these two measurements, a compensation of the refractive index of air can be applied, i.e. no measurement of temperature, pressure and CO2 content of the air is required. In this paper, the principle of the two-wavelength absolute distance meter is explained, and preliminary results are presented, for each wavelength and with air refractive index compensation.Guillory, J.; Truong, D.; Wallerand, J. (2023). Optical distance measurements at two wavelengths with air refractive index compensation. Editorial Universitat Politècnica de València. 151-157. https://doi.org/10.4995/JISDM2022.2022.1378615115

Multilateration with Self-Calibration: Uncertainty Assessment, Experimental Measurements and Monte-Carlo Simulations

International audienceLarge-volume metrology is essential to many high-value industries and contributes to the factories of the future. In this context, we have developed a tri-dimensional coordinate measurement system based on a multilateration technique with self-calibration. In practice, an absolute distance meter, traceable to the SI metre, is shared between four measurement heads by fibre-optic links. From these stations, multiple distance measurements of several target positions are then performed to, at the end, determine the coordinates of these targets. The uncertainty on these distance measurements has been determined with a consistent metrological approach and it is better than 5 µm. However, the propagation of this uncertainty into the measured positions is not a trivial task. In this paper, an analytical solution for the uncertainty assessment of the positions of both targets and heads under a multilateration scenario with self-calibration is provided. The proposed solution is then compared to Monte-Carlo simulations and to experimental measurements: it follows that all three approaches are well agreed, which suggests that the proposed analytical model is accurate. The confidence ellipsoids provided by the analytical solution described well the geometry of the errors

Absolute multilateration-based coordinate measurement system using retroreflecting glass spheres

International audienceWe 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

Laser diodes based absolute distance meter

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

Low frequency acoustic pressure meaurements based on a Fabry-Perot refractometer

International audienceThis paper presents the development, the operating principle, and the experimental results of an innovative technique for the measurement of acoustic pressures in the range of 40 mHz up to 5 Hz. This new measurement technique is based on the use of a Fabry Perot refractometer in which the air density variations related to an acoustic wave can be tracked and determined by measuring the optical frequency variations of a laser locked on a longitudinal mode of the Fabry Perot cavity. This approach covers a wider range in the low and infrasonic frequencies compared to conventional sensors