Search

International audience; The Grasse Satellite Laser Ranging (SLR) station (ID7845), part of the International Laser Ranging Service (ILRS) network, participates to various laser applications including SLR, Lunar Laser Ranging (LLR), Time Transfer by Laser Link (T2L2), high-resolution imagery, and debris detection. Since 2014, in collaboration with the France Space Agency (CNES), the Grasse station has been upgrading in order to be able to take part in laser communication (lasercom) experiments. The main challenges of these experiments are the implementation of a complete laser communication chain from space to ground and the characterization of the turbulent atmosphere during the optical data transfer. Several campaigns have been successfully performed and planned since 2015 between Grasse station and lasercom terminal at low Earth orbit, SOTA onboard SOCRATES [5], OPALS integrated on ISS [6], and recently DLR's OSIRIS mission [7]. To prepare for possible higher data-rate lasercom campaigns in the near future (OSIRISv1 at 40 Mbps, OSIRISv2 and Optelµ at 1 Gbps, OSIRISv3 at 10 Gbps) Grasse SLR station is upgrading on lasercom optical bench, with a fine auto-tracking system and a high sensitivity telecom detector. In the proceeding, we will describe the architecture of our optical bench for high data-rate lasercom link and some primary results of the lasercom link between OSIRISv1 [14] (onboard FlyingLaptop satellite) and the station.

International audience; Based on a fully passive space segment, the lunar laser ranging experiment is the last of the Apollo Lunar Surface Experiments Package to operate. Observations from the Grasse lunar laser ranging station have been made on a daily basis since the first echoes obtained in 1981. In this paper, first, we review the principle and the technical aspects of lunar laser ranging. We then give a brief summary of the progress made at the Grasse laser ranging facility (Observatoire de la Côte d'Azur, Calern Plateau on the French Riviera) since the first echoes. The current performance, driven by the use of an infrared wavelength laser, is presented in the last section for the year 2018.

This work aimed to prepare the spinel phase Li4Ti5O12 by a combination of the low-temperature precipitation technique and assisted calcination step. X-ray diffraction (XRD) revealed that the intermediated phase was Li2TiO3, and the spinel phase could be evidently formed at 700°C for 12 to 20 hours. The morphology of spinel powder, determined by SEM and TEM, exhibited a good distribution at the submicrometric scale that promoted a fast kinetic of Li migration and an excellent performance at the high-rate cycling test. The stable performances were achieved in the charge-discharge test at different current densities: 80 mA/g (165 mAh/g), 320 mA (160 mAh/g), and 1600 mA (145 mAh/g) upon 100 cycles. Moreover, we observe a capacity retention of 48% (corresponding 80 mA/g) at a high rate of 5000 mAh/g. The cyclic voltammetry measurement displayed a reversible system and revealed the lithium diffusion coefficient of 1.15 × 10−11 cm2/s.

Optical systems performances can be affected by local optical turbulence created by its surrounding environment (telescope dome, clean room, atmospheric surface layer). We present recent measurements of the local turbulence inside the 1.5m M´eO telescope dome at Calern observatory (France) with the INTENSE (INdoor TurbulENce SEnsor) instrument. Relationships between the dome turbulence and the local meteorological measurements (temperature, pressure, wind speed and direction) are investigated. The impact of the local dome turbulence on the seeing at the focal plane of the 1.5 m telescope is highlighted.

ICSO 2016 conference, paper 163; International audience; Distributed feedback (DFB) diode lasers are convenient, small footprint and robust single mode laser sources. Control of the diode forward current allows for the control the frequency of the emitted laser beam. Locking the laser frequency to some optical frequency discriminator, such as an optical interferometer or an atomic or molecular line, can easily be achieved. Such a lock, with a moderate (< kHz) bandwidth can prevent long term drifts of the laser optical frequency. On the other hand, reaching high lock bandwidth (> MHz) can lead to laser line narrowing. DFB lasers have an emission linewidth in the MHz to several MHz range, which may be too large for some applications, such as cold atom physics, optical clocks, laser ranging, lidar or gas sensing...We have tried to achieve a high bandwidth in the lock of a DFB diode laser with a feedback loop using both the laser diode forward current and an optoelectronic external modulator. A lock bandwidth in the MHz range has been obtained, and the optical spectrum shows narrowing. But a significant fraction (15-20%) of the optical power remains broadband. By contrast, much more efficient and convenient operation has been found when the external electro-optical modulator is not in a feed-back loop but in a feed-forward configuration. The optical spectrum shows a half width at half maximum of 3 to 4 kHz, with about 1% of residual broadband optical power. The system allows implementation at any wavelength, if the frequency discriminator is obtained from a Michelson interferometer with gold-coated mirrors.

In collaboration between CNES, NICT, Geoazur, the first successful lasercom link between the micro-satellite SOCRATES and an OGS in Europe has been established. This paper presents some results of telecom and scintillation first data analysis for 4 successful links in June & July 2015 between SOTA terminal and MEO optical ground station (OGS) at Caussols France. The telecom and scintillation data have been continuously recorded during the passes by using a detector developed at the laboratory. An irradiance of 190 nW/m2 and 430 nW/m2 has been detected for 1549 nm and 976 nm downlinks at 35° elevation. Spectrums of power fluctuation measured at OGS are analyzed at different elevation angles and at different diameters of telescope aperture to determine fluctuations caused by pointing error (due to satellite & OGS telescope vibrations) and caused by atmospheric turbulence. Downlink & Uplink budgets are analyzed, the theoretical estimation matches well to measured power levels. Telecom signal forms and bit error rates (BER) of 1549 nm and 976 nm downlink are also shown at different diameters of telescope aperture. BER is 'Error Free' with full-aperture 1.5m telescope, and almost in ‘good channel’ with 0.4 m sub-aperture of telescope. We also show the comparison between the expected and measured BER distributions.

Research Center for Advanced Magnetic Materials, Chungnam National University, Daejeon 305-764, South Korea Received 7 May 2007, revised 30 October 2007, accepted 31 October 2007 Published online 18 December 2007 PACS 75.70.Ak, 85.70.Kh Influence of film thickness (t) on the electrical and magnetic properties of Co–Fe–Al–O films has been systematically investigated via means of vibrating sample magnetometry (VSM), permeability spectra and magneto-optical Kerr effect (MOKE). It is found that the electrical resistivity (ρ) decreases as the film thickness increases; ρ = 412.5 µΩcm for the t = 600 nm sample decreases to ρ = 368.2 µΩcm for the t = 1200 nm sample. The coercive force, measured along the easy-axis direction, decreases as the film thickness increases. Interestingly, along the hard-axis magnetization direction, the magnetic hysteresis loop is reversed and the coercive force is negative for the t = 600 and 800 nm samples. However, this pe-culiar feature disappears as t reaches 1200 nm, which is probably attributed to the microstructural change with respect to changes of film thickness. At a frequency of 1GHz, the hard-axis effective permeability decreases from 1252 to 1000 as the film thickness increases from 600 to 1200 nm, respectively. The VSM and MOKE results reveal an increase in magnetic anisotropy in the near-surface region of the film.

In collaboration between CNES, NICT, Geoazur, the first successful lasercom link between the micro-satellite SOCRATES and a non-Japanese OGS has been established. This paper presents some results of telecom and scintillation first data analysis for 4 successful links in June & July 2015 between SOTA terminal and Meo optical ground station (OGS) at Caussols France. The telecom and scintillation data have been continuously recorded during the passes by using a detector developed at the laboratory. An irradiance of 190 nW/m2 and 430 nW/m2 has been detected for 1549 nm and 976 nm downlinks at 35° elevation. Spectrums of power fluctuation measured at OGS are analyzed at different elevation angles and at different diameters of telescope aperture to determine fluctuations caused by pointing error (due to satellite & OGS telescope vibrations) and caused by atmospheric turbulence. Telecom signal forms and bit error rates (BER) of 1549 nm and 976 nm downlink are also shown at different diameters of telescope aperture. BER is ‘Error Free’ with full-aperture 1.5m telescope, and almost in ‘good channel’ with 0.4 m sub-aperture of telescope.

International audience; For satellite to ground laser links, atmospheric turbulence is a major cause of impairments. The induced phase perturbations along the propagation path cause beam scintillation in the receiver plane and they can also severely compromise the coupling of the flux into a receiver of limited size. To address these impairments, dedicated mitigation strategies must be developed. This requires accurate understanding of the perturbation origin. Beam propagation models have demonstrated their ability to reproduce statistical characteristics of optical perturbations on a satellite to ground laser link for elevations as low as 20°. For smaller elevations, measurements performed on stars illustrated the limits of analytical approaches and the interest for end-to-end models. We report here the first propagation channel measurements performed on a LEO microsatellite with a Shack-Hartmann wavefront sensor (WFS). The laser beam at 976 nm provided by SOTA optical terminal have been analyzed with a Shack- Hartmann wavefront sensor located at Coudé focus of the French ground station (1,55 m MéO telescope) in July 2015. Wavefront characteristics and scintillation patterns recorded with the WFS are analyzed and compared to atmospheric turbulence perturbations model fed with in situ measurements of atmospheric parameters retrieved from GDIMM.; La turbulence atmosphérique est la principale cause de dégradation des liens laser sol satellite. Les perturbations de phase induites le long du cana de propagation conduisent à de la scintillation dans le plan du récepteur et peuvent sévèrement compromettre le couplage du flux dans un récepteur de petite dimension. Pour résoudre ces problèmes, différentes stratégies dédiées doivent être développées. Cela nécessite une compréhension précise de l'origine des perturbations. Les modèles de propagation de faisceau ont démontré leur capacité à reproduire les caractéristiques statistiques des perturbations optiques affectant un lien laser satellite sol pour des élévations descendant à 20°. Pour des élévations plus petites des mesures réalisées sur étoiles ont démontrées toutefois les limites de ces approches analytiques et l'intérêt de modèles de type Monte-Carlo. Nous faisons état ici des premières mesures sur un canal de propagation établi avec un microsatellite LEO grâce à un analyseur de Shack Hartmann. Le faisceau laser à 976nm est fourni par le terminal optique SOTA et analysé grâce à un Shack Hartmann situé au foyer coudé d'une station française (télescope MéO de 1.55m) en juillet 2015. Les caractéristiques du front d'onde et les structures de scintillation enregistrées avec l'analyseur sont analysées et comparées aux modèles de perturbation de la turbulence atmosphérique alimentés par les mesures in situ des paramètres atmosphériques tels que fournis par un GDIMM.

In this report, we demonstrate a comprehensive analysis of the effects of Au addition on the microstructure and magnetic properties of Fe 73.5 Si 13.5 B 9 Nb₃Au₁ Finemet-type alloy. It was found that the as-quenched alloys were the amorphous state and turned into nanocrystalline state under heat treatments. The DSC analysis indicates that the sharply exothermal peak corresponding to the crystallization of the α-Fe(Si) was observed at 547- 579℃ depending on the heating rates, which is little higher than that of original Finemet (542-570℃, respectively). Besides, the thermomagnetic result confirmed that the full substitution of Cu by Au with the single phase structure in the M(T) curve along cooling cycle. Ultrasoft magnetic properties of the nanocrystallized samples were significantly enhanced by the proper annealing such as the increase of permeability and the decrease of the coercivity. The optimum annealing condition was found at the annealing temperature of 540℃ and the increase of the annealing time up to 90 min.

Magnetization, resistivity, and electron spin resonance (ESR) measurements were carried out to investigate spin dynamics, electrical and magnetic properties of (La 0.5 Pr 0.5 ) 0.7 Pb 0.3 Mn 1− x Cu x O 3 ( x = 0 , 0.02) perovskites. It was found that with Cu addition the Curie temperature decreased from 326 K for x =0 to 300 K for x = 0.0 2 composition. The x = 0 sample underwent a metallic–insulator transition at ∼130 K, whereas the x = 0.0 2 sample with higher resistivity exhibited an insulating behavior as a whole. It was furthermore found that asymmetrical ESR signals at low temperatures became Lorentzian at high temperatures above T min . The temperature dependence of the linewidth, Δ H ( T ) , at T > T min fits well to the one-phonon model, Δ H ( T ) = AT + B . The activation energy E a , determined from the ESR intensity with respect to temperature, are 0.16 and 0.14 eV for x = 0 and 0.02 compositions, respectively. In terms of our experimental results, it is reasonable to conclude that the Cu addition led to a suppression of the ferromagnetism and conductivity of the parent compound ( x = 0 ).

International audience; We have achieved DFB laser diode line narrowing by simultaneously acting on the diode current via a feedback loop and on an external electrooptic phase modulator in feed-forward actuator. This configuration turns out to be very efficient in reaching large bandwidth in the phase correction: up to 15 MHz with commercial laser control units. About 98% of the laser power undergoes narrowing. The full width at half maximum of the narrowed optical spectrum is of less than 4 kHz. This configuration appears to be very convenient as the delay in the feed-forward control electronics is easily compensated for by a 20 m optical fiber roll.

En attente de publication papier; Lien vers l'éditeur: http://ieeexplore.ieee.org/xpl/articleDetails.jsp? arnumber=6775285&sortType%3Dasc_p_Sequence% 26filter%3DAND%28p_IS_Number%3A4357488%29; International audience; High accuracy and low noise measurement of the phase of a microwave signal requires that spurious contributions are adequately dealt with. In this paper we investigate the power-to-phase coupling in two commercial high bandwidth P-I-N, near-IR photodetectors. We observe that a sudden change of the optical power induces a transient of the phase of the 20 GHz signal, at different time scales. The temperature rise of the photodetector junction is likely to be involved in this dynamical behaviour. The value of the bias voltage applied to the photodetector appears to control the size of the phase transients, as well as the optical power for which the slope of the amplitude-to-phase coupling cancels. The most efficient way to reduce amplitude to phase couplings consists in implementing optical demodulation, instead of electrical demodulation, of the microwave signal.

International audience; We present a laser ranging system, under development, that uses a high frequency modulated beam to achieve sub-nm resolution by the combined use of interferometric and time-of-flight measurements. We first describe how the absolute distance is extracted from a two-mode interference signal. In particular we show that the signal, which presents both optical and synthetic wavelength scales, is essential to achieve nm-scale accuracy, despite the significant long-term phase drifts in the 20 GHz detection chains. Then we present results obtained with the telemeter implemented on an optical table, for a distance of about four meters, implemented by folding the laser beam path to the target. The challenge here is to achieve a phase and amplitude measurement of two 20 GHz signals with a resolution well below 10-4 cycle and 10-4, respectively, despite the fact that the signal undergoes very strong (×3 ) amplitude changes.

— It is shown that the results presented in the article by Wu et al. (IEEE Photon. Technol. Lett. 23 (n° 8) 2011, pp. 468-470), and attributed by the authors to amplitude-to-phase conversion in the photodetector, do not originate in the photodetector under test, due to the power dependence observed. More recent results show that conversion effects with the same size and frequency dependence are observed in passively mode-locked NPR (non-linear polarization rotation) mode-locked lasers. Index Terms — Phase measurement, Phase noise, Photodetectors, mode-locked lasers. n their article, K. Wu et al. [1] address the problem of the amplitude-to-phase conversion in photodetectors, already observed in earlier publications. They present a particularly simple set-up, that may provide a convenient means to characterize the AM-to-PM conversion in high bandwidth photodetectors. They use a 2.4 mW free-running passively mode-locked laser at 147 MHz repetition rate, and modulate the power of the laser at audio frequencies by modulating the power of the pump diode. They subsequently detect the pulse train emitted by the mode-locked laser using a 2GHz photodiode. The signal of the photodiode is analyzed by a signal analyzer FSUP26, which can deliver - the relative intensity noise power spectrum and the phase noise of the 147 MHz signal, separately, (Fig. 2 a- and b-, respectively) as a function of the offset frequency - or the spectrum, in dBm of the signal around 147 MHz, Fig. 4. Both figures show that the 147 MHz signal is phase-modulated at the frequency of the power modulation and at its harmonics. In Fig. 4, the phase modulation appears as a an asymmetry in the side bands: the asymmetry