Search

International audience; The severe acute respiratory syndrome novel coronavirus-2 pandemic is affecting almost every country in the world. Even if the major symptoms of coronavirus disease-2019 are respiratory, different symptoms at presentation are now recognized. Venous thromboembolism has been reported in infected patients and few but increasing cases of arterial thrombosis have been described. We report a case of acute aortoiliac and lower limb artery occlusions in a patient presenting with severe coronavirus disease-2019 infection. The mechanism of the occlusion seemed to be distal embolization from a floating thrombus in the aortic arch caused by a major inflammatory state and virus infection. The patient underwent aortoiliac and lower limb artery mechanical thrombectomy, but required unilateral major amputation.

International audience; Due to the increasing number of astronomical projects and of their associated instruments, the request of large optics with higher optical performances does not stop growing. An important step in the manufacture of these optics is the deposition of high-precision optical coatings. To answer to this request, we developed dichroic coatings, with sharp transition for large optics, working at different angles of incidence and spectral ranges. The work done for the dichroic optics of the HRS and LRS instruments for the 4MOST project will be presented.

International audience; We report the characterization of superlow-loss optics used in the second-generation gravitational-wave detectors currently in operation. The sapphire test-mass mirrors in the KAGRA detector are introduced as an example, but the techniques here are common to all detectors. In this work, we discuss mainly the surface topography obtained by interferometric techniques and the optical properties obtained with special setups.

An observation of prior-damage behavior inside a high-finesse optical resonator is reported. Intra-cavity average power drops appeared with magnitude and time scale depending on the power level. Increasing further the incident laser beam power led to irreversible damage of the cavity coupling mirror surface. The origin of this phenomenon is investigated with post mortem mirror surface imaging and analysis of the signals reflected and transmitted by the enhancement cavity. Scattering losses induced by surface deformation due to a hot-spot surface contaminant is found to be most likely the dominant physics process behind this phenomenon.

The interferometer mirrors of gravitational-wave detectors (GWDs) are Bragg reflectors made of alternate amorphous silica ( SiO 2) and titania-doped tantala ( TiO 2 : Ta 2 O 5) layers as low- and high-refractive index materials, respectively. A thermal treatment is usually performed to reduce both mechanical losses and near-infrared (NIR) optical absorptions of the coatings. The authors present a spectroscopic ellipsometry (SE) investigation of the effect of annealing and Ti:Ta mixing on Ta 2 O 5 coatings deposited under conditions similar to those adopted for building up mirrors of GWDs. The broadband analysis covers both the NIR and the fundamental absorption threshold region. The data show an evident annealing-induced reduction of the fundamental optical absorption broadening. Modeling the data through the Cody-Lorentz formula confirms that NIR absorptions are below the SE sensitivity and shows a notable annealing-induced reduction of so-called Urbach tails. Titania-doping of tantala slightly reduces the Urbach energy. After the heating treatment, the resulting Urbach energy of the doped material is lower than that of annealed pure tantala. The observed reduction of Urbach tails is important because it parallels the reduction of the so-called internal friction observed in mechanical measurements so that SE emerges as a convenient tool for an agile diagnostic of both the optical and the mechanical quality of amorphous oxide coatings.The interferometer mirrors of gravitational-wave detectors (GWDs) are Bragg reflectors made of alternate amorphous silica ( SiO 2) and titania-doped tantala ( TiO 2 : Ta 2 O 5) layers as low- and high-refractive index materials, respectively. A thermal treatment is usually performed to reduce both mechanical losses and near-infrared (NIR) optical absorptions of the coatings. The authors present a spectroscopic ellipsometry (SE) investigation of the effect of annealing and Ti:Ta mixing on Ta 2 O 5 coatings deposited under conditions similar to those adopted for building up mirrors of GWDs. The broadband analysis covers both the NIR and the fundamental absorption threshold region. The data show an evident annealing-induced reduction of the fundamental optical absorption broadening. Modeling the data through the Cody-Lorentz formula confirms that NIR absorptions are below the SE sensitivity and shows a notable annealing-induced reduction of so-called Urbach tails. Titania-doping of tantala sl...

Coating thermal noise is a fundamental limit for precision experiments based on optical and quantum transducers. In this review, after a brief overview of the techniques for coating thermal noise measurements, we present the latest world-wide research activity on low-noise coatings, with a focus on the results obtained at the Laboratoire des Mat\'{e}riaux Avanc\'{e}s. We report new updated values for the Ta$_2$O$_5$, Ta$_2$O$_5$-TiO$_2$ and SiO$_2$ coatings of the Advanced LIGO, Advanced Virgo and KAGRA detectors, and new results from sputtered Nb$_2$O$_5$, TiO$_2$-Nb$_2$O$_5$, Ta$_2$O$_5$-ZrO$_2$, MgF$_2$, AlF$_3$ and silicon nitride coatings. Amorphous silicon, crystalline coatings, high-temperature deposition, multi-material coatings and composite layers are also briefly discussed, together with the latest developments of structural analyses and models., Comment: arXiv admin note: text overlap with arXiv:1909.03737

High reflective coatings are used in many physics experiments. Despite the high quality of the opticalcoating, the performances of the mirrors is altered by the scattered light induced by micrometers sizedefects in the coating layers. The topic of this paper is the study of the point-like scatterers present in thespecific coating of the mirrors used in state of the art, high sensitivity optical experiments. We studied thebehavior of the materials according to different thicknesses, and how the defects change after annealing.To our knowledge, this is a first insight into the formation of such defects for different materials andthickness and how this is reduced when samples are annealed., Comment: 9 pages, 4 figures, submitted to Applied Optics - OSA

High-reflection interference mirrors for current gravitational wave detectors (aLIGO, Advanced Virgo, KAGRA) are made of high-quality oxide multi-layers deposited by ion beam sputtering (IBS) at the Laboratoire des Matériaux Avancés (LMA). For this task, LMA uses a large IBS custom-made machine (the grand coater GC) able to deposit very uniform coatings over very large surfaces, with diameter of some tens of cm. We report for the first time about the optical characterization by spectroscopic ellipsometry of oxide coatings deposited by the GC under strictly the same conditions used for the production of interference mirrors. We have investigated oxide materials like silica (SiO2), tantala (Ta2O5) and titania-doped tantala (Ti:Ta2O5), providing for each material a broad-band (190–1700 nm) accurate determination of the complex index of refraction, with particular attention to wavelengths used in interferometers. Particular focus has been dedicated to the influence of Ti-doping on tantala coating. The doping induces a red-shift of the optical gap and an increase of the NIR refractive index. Furthermore, doping induces a decrease of the so-called Urbach energy, consistent with the well-known reduction of the internal friction in these kind of systems.

International audience; This paper describes the making of large mirrors for laser interferometer gravitational wave detectors. These optics, working in the near infrared, are among the best optics ever created and played a crucial role in the first direct detection of gravitational waves from black holes or neutron star fusions.

International audience; In this paper, we present, to the best of our knowledge, the first low-loss vacuum-compatible thermally controlled Faraday isolator able to retain a good isolation factor under high-vacuum working conditions. The throughput that can be obtained with the developed device is as high as 99%, retaining an isolation factor higher than 40 dB. That very high isolation ratio can be kept over long time periods independently from external temperature conditions with a few Celsius degrees of variation due to thermal active control. The mechanical and optical configuration is detailed, and the performances achieved with this device are presented.

We present the results of mechanical characterizations of many different high-quality optical coatings made of ion-beam-sputtered titania-doped tantala and silica, developed originally for interferometric gravitational-wave detectors. Our data show that in multi-layer stacks (like high-reflection Bragg mirrors, for example) the measured coating dissipation is systematically higher than the expectation and is correlated with the stress condition in the sample. This has a particular relevance for the noise budget of current advanced gravitational-wave interferometers, and, more generally, for any experiment involving thermal-noise limited optical cavities., Comment: 31 pages, 14 figures

Masking technique and planetary motion are two techniques to improve the coating thickness uniformity. However their combination generates a characteristic pattern like a spiral that can limit the sensitivity of gravitational wave interferometers.

A real-time optical monitoring of coated thin films is being installed in a large coating machine. An optical system and a coating simulation software were developped, predicting the success rate of the deposition.

International audience; We estimate the loss angles of the materials currently used in the highly reflective test-mass coatings of interferometric detectors of gravitational waves, namely Silica, Tantala, and Ti-doped Tantala, from direct measurement of coating thermal noise in an optical interferometer testbench, the Caltech TNI. We also present a simple predictive theory for the material properties of amorphous glassy oxide mixtures, which gives results in good agreement with our measurements on Ti-doped Tantala. Alternative measurement methods and results are reviewed, and some critical issues are discussed.

International audience; To improve the in situ monitoring of thin films at the Laboratoire des Matériaux Avancés, a broadband optical monitoring of the coated thin films was developed and installed in the biggest ion-beam sputtering machine in the world. Due to the configuration of the coating machine and the chamber strain under vacuum, a standard calibration procedure is impossible and a double-beam optical system is not suitable. A novel theoretical and practical solution to calibrate the measurements was found and is described in this paper. Some relevant results achieved thanks to this technique are discussed as well.

International audience; We report in this article on the measurement of the optical absorption of moderately doped crystalline silicon samples at 1550 nm, which is a candidate material for the main optics of the low temperature interferometer of the Einstein Telescope (ET). We observe a nearly constant absorption from room temperature down to cryogenic temperatures for two silicon samples presenting an optical absorption of 0.029 cm −1 and 780 ppm cm −1 , both crystals doped with boron. This is in contradiction to what was assumed previously—a negligible optical absorption at low temperature due to the carrier freezeout. As the main consequence, if the silicon intrinsic absorption can not be lowered , the cross section of the mirror suspension of the ET must be increased to be able to carry away the excess heat generated by the partially absorbed laser beam during the operation of the interferometer.

In recent years an increasing number of devices and experiments are shown to be limited by mechanical thermal noise. In particular sub-Hertz laser frequency stabilization and gravitational wave detectors, that are able to measure fluctuations of 1E-18 m/rtHz or less, are being limited by thermal noise in the dielectric coatings deposited on mirrors. In this paper we present a new measurement of thermal noise in low absorption dielectric coatings deposited on micro-cantilevers and we compare it with the results obtained from the mechanical loss measurements. The coating thermal noise is measured on the widest range of frequencies with the highest signal to noise ratio ever achieved. In addition we present a novel technique to deduce the coating mechanical losses from the measurement of the mechanical quality factor which does not rely on the knowledge of the coating and substrate Young moduli. The dielectric coatings are deposited by ion beam sputtering. The results presented here give a frequency independent loss angle of (4.70 $\pm$ 0.2)x1E-4 with a Young's modulus of 118 GPa for annealed tantala from 10 Hz to 20 kHz. For as-deposited silica, a weak frequency dependence (~ f^{-0.025}) is observed in this frequency range, with a Young's modulus of 70 GPa and an internal damping of (6.0 $\pm$ 0.3)x1E-4 at 16 kHz, but this value decreases by one order of magnitude after annealing and the frequency dependence disappears., Comment: Accepted for publication in Phys. Rev. D

From 28nm technology node and below, Optical Proximity Correction (OPC) needs to take into account light scattering effects from prior layers when bottom anti-reflective coating (BARC) is not used, which is typical for implant layers. In this paper, we implement a sub-layer aware simulation method into a verification tool for Optical Rule Check (ORC) that is used on full 28nm test chip. The sub-layer aware verification can predict defects that are missed by standard ORC. SEM-CD review and defectivity analysis were used to confirm the validity of the sub-layer aware model on wafer.

Reflection by wafer topography and underlying layers during optical lithography can cause unwanted overexposure in the resist [1]. In most cases, the use of bottom anti reflective coating limits this effect. However, this solution is not always suitable because of process complexity, cost and cycle time penalty, as for ionic implantation lithography process in 28nm bulk technology. As a consequence, computational lithography solutions are currently under development to simulate and correct wafer topographical effects [2], [3]. For ionic implantation source drain (SD) photolithography step, wafer topography influences resulting in implant pattern variation are various: active silicon areas, Poly patterns, Shallow Trench Isolation (STI) and topographical transitions between these areas. In 28nm bulk SD process step, the large number of wafer stack variations involved in implant pattern modulation implies a complex modeling of optical proximity effects. Furthermore, those topography effects are expected to increase with wafer stack complexity through technology node downscaling evolution. In this context, rigorous simulation can bring significant value for wafer topography modeling evolution in R and D process development environment. Unfortunately, classical rigorous simulation engines are rapidly run time and memory limited with pattern complexity for multiple under layer wafer topography simulation. A presentation of a fast rigorous Maxwell’s equation solving algorithm integrated into a photolithography proximity effects simulation flow is detailed in this paper. Accuracy, run time and memory consumption of this fast rigorous modeling engine is presented through the simulation of wafer topography effects during ionic implantation SD lithography step in 28nm bulk technology. Also, run time and memory consumption comparison is shown between presented fast rigorous modeling and classical rigorous RCWA method through simulation of design of interest. Finally, integration opportunity of such fast rigorous modeling method into OPC flow is discussed in this paper.

Demonstrating the quantum ground state of a macroscopic mechanical object is a major experimental challenge in physics, at the origin of the rapid emergence of cavity optomechanics. We have developed a new generation of optomechanical devices, based on a microgram quartz micropillar with a very high mechanical quality factor. The structure is used as end mirror in a Fabry-Perot cavity with a high optical finesse, leading to ultra-sensitive interferometric measurement of the resonator displacement. We expect to reach the ground state of this optomechanical resonator by combining cryogenic cooling in a dilution fridge at 30 mK and radiation-pressure cooling. We have already carried out a quantum-limited measurement of the micropillar thermal noise at low temperature.

International audience; We report on the first demonstration, to the best of our knowledge, of the locking of a Fabry–Perot cavity with a finesse of 28,000 in the pulsed regime. The system is based on a stable picosecond oscillator, an ultrastable cavity with high-reflection mirrors, and an all-numerical feedback system that allows efficient and independent control of the repetition rate and the pulse to pulse carrier-to-envelop phase drift (CEP). We show that the carrier to envelop phase can have a dramatic effect even for pulses with hundreds of cycles. Moreover, we have succeeded in unambiguously measuring the CEP of a 2 ps pulse train. Finally, we discuss the potential of our findings to reach the MW average power level stored in an external cavity enhancement architecture.

We report on the measurement of the optical absorption of bulk crystalline silicon at 1550 nm. Using the photodeflection technique, absorption as low as 5 ppm/cm has been measured on a sample with a resistivity of 10 kΩ⋅cm . The absorption as a function of the resistivity has been derived for n-type silicon.

The LSST design foresees the use of six wide-band large optical filters that can alternatively be moved in front of the CCD camera. Each of the six filters has a different band-pass covering all the wavelengths from 300 nm to 1200 nm. The way to achieve this is to coat an optimized optical thin films stack on a filter substrate. Each filter requires a specific design using specific appropriate materials. The main characteristics of these filters, that constitute a real technological challenge, are: their relatively large size - their radii of curvature (about 5.6 m) that represent a sagitta of 12,5 mm that increases the uniformity complexity, the large rejection band requirements with transmission lower than 0.01 % out of the band and a transmission of 95 % over the band-pass. This paper proposes to show the problematic and the results obtained at LMA (Laboratoire des Materiaux Avances-FRANCE) to the purpose of realizing these filters using the IBS (Ion Beam Sputtering) deposition technique. The results obtained with High-Pass/Low-Pass structures will be presented. Experimental results will be shown concerning the R-band filter (552-691 nm). An overview of the work to be done to realize transmittance map over large filters will be given.

In recent years an increasing number of devices and experiments are shown to be limited by mechanical thermal noise. In particular sub-Hertz laser frequency stabilization and gravitational wave detectors, that are able to measure fluctuations of 10-18 m/√(Hz) or less, are being limited by thermal noise in the dielectric coatings deposited on mirrors. We present a novel technique of structural relaxation analysis based on the direct thermal noise measurements on micro-cantilevers and we compare it with the results obtained from the mechanical loss measurements. The dielectric coatings are deposited by ion beam sputtering. The results presented here give a loss angle of annealed tantala and as-deposited silica coatings of (3.9 ± 0.4)·10-4 and (5.8 ± 1.0)·10-4 respectively, from 10 Hz to 20 kHz.

Reflection by wafer topography and underlying layers during optical lithography can cause unwanted exposure in the resist [1]. This wafer stack effect phenomenon which is neglected for larger nodes than 45nm, is becoming problematic for 32nm technology node and below at the ionic implantation process. This phenomenon is expected to be attenuated by the use of anti-reflecting coating but increases process complexity and adds cost and cycle time penalty. As a consequence, an OPC based solution is today under evaluation to cope with stack effects involved in ionic implantation patterning [2] [3]. For the source drain (SD) ionic implantation process step on 28nm Fully Depleted Silicon-on-Insulator (FDSOI) technology, active silicon areas, poly silicon patterns, Shallow Trench Isolation (STI), Silicon-on-Insulator (SOI) areas and the transitions between these different regions result in significant SD implant pattern critical dimension variations. The large number of stack variations involved in these effects implies a complex modeling to simulate pattern degradations. This paper deals with the characterization of stack effects on 28nm node using SOI substrates. The large number of measurements allows to highlight all individual and combined stack effects. A new modeling flow has been developed in order to generate wafer stack aware OPC model. The accuracy and the prediction of the model is presented in this paper.

We report on low-frequency measurements of the mechanical loss of a high-quality (transmissivity T

LSST is a new kind of telescope with ambitious scientific objectives. Its optical design includes large bandpass filters with high optical requirements: in-band transmission higher than 95%, out-of-band transmission less than 0.01% and steep edges.

Milligram-scale resonators have been shown to be suitable for the creation of 3-mode optoacoustic parametric amplifiers, based on a phenomena first predicted for advanced gravitational-wave detectors. To achieve practical optoacoustic parametric amplification, high quality factor resonators are required. We present millimetre-scale silicon resonators designed to exhibit a torsional vibration mode with a frequency in the 10^5 - 10^6 Hz range, for observation of 3-mode optoacoustic interactions in a compact table-top system. Our design incorporates an isolation stage and minimizes the acoustic loss from optical coating. We observe a quality factor of 7.5 x 10^5 for a mode frequency of 401.5 kHz, at room temperature and pressure of 10^-3 Pa. We confirmed the mode shape by mapping the amplitude response across the resonator and comparing to finite element modelling. This study contributes towards the development of 3-mode optoacoustic parametric amplifiers for use in novel high-sensitivity signal transducers and quantum measurement experiments., Comment: 6 pages, 4 figures, 2 tables

This report describes techniques and protocols implemented at the Geneva Canton University Hospitals (HUG) for the combination of various biomedical imaging modalities and sensors including electromagnetic tomography, to study, assess, and localize neurological (dys) function. The interest for this combination stems from the broad variety of information brought out by (functional) magnetic resonance imaging, magnetic resonance spectroscopy, computed tomography, single-photon emission tomography, positron emission tomography, and electromagnetic tomography. Combining these data allows morphology, metabolism, and function to be studied simultaneously, the complementary nature of the information from these modalities becoming evident when studying pathologies reflected by metabolic or electrophysiologic dysfunctions. Compared with other current multimodality approaches, the one at the HUG is totally compatible with both clinical and research protocols, and efficiently addresses the multidimensional registration and visualization issues. It also smoothly integrates electrophysiology and related data as fully featured modalities.

The Large Synoptic Survey Telescope (LSST) uses a novel, three-mirror, telescope design feeding a camera system that includes a set of broad-band filters and three refractive corrector lenses to produce a flat field at the focal plane with a wide field of view. Optical design of the camera lenses and filters is integrated in with the optical design of telescope mirrors to optimize performance. We discuss the rationale for the LSST camera optics design, describe the methodology for fabricating, coating, mounting and testing the lenses and filters, and present the results of detailed analyses demonstrating that the camera optics will meet their performance goals.

Quantum radiation pressure noise has never been experimentally demonstrated, though it has been predicted for more than thirty years. It is, however, expected to limit the low-frequency sensitivity of second generation gravitational-wave interferometers. We have demonstrated classical radiation-pressure-induced correlations between two optical beams sent into the same high-finesse cavity with a moving mirror. Our two-beam scheme can be used to retrieve quantum noise embedded in an overwhelming classical noise, and has applications both in high-sensitivity measurements and in quantum optics.

This paper investigates the electric power extractable from an helicopter conical nozzle equipped with thermoelectrical modules. The thermoelectric nozzle is heated by the final exhaust gas from helicopter turbine and cooled by oil. A computer model has been developed to simulate the performance of the thermoelectric system. Results were obtained for various operating conditions showing that the electrical power produced in real operating conditions is significant but currently insufficient if we consider the weight-to-power ratio. The numerical model is also used to optimize the electric power showing a good potential for the future.

Gravitational-wave detectors such as Virgo and the laser interferometric gravitational-wave observatory (LIGO) use a long-baseline Michelson interferometer with Fabry–Perot cavities in the arms to search for gravitational waves. The symmetry between the two Fabry–Perot cavities is crucial to reduce the interferometer’s sensitivity to the laser amplitude and frequency noise. To this purpose, the transmittance of the mirrors in both cavities should be as close as possible. This paper describes the realization and the characterization of the first twin large low-loss mirrors with transmissions differing by less than 0.01%.

A standard quarter-wavelength multilayer optical coating will produce the highest reflectivity for a given number of coating layers, but in general it will not yield the lowest thermal noise for a prescribed reflectivity. Coatings with the layer thicknesses optimized to minimize thermal noise could be useful in future generation interferometric gravitational wave detectors where coating thermal noise is expected to limit the sensitivity of the instrument. We present the results of direct measurements of the thermal noise of a standard quarter-wavelength coating and a low noise optimized coating. The measurements indicate a reduction in thermal noise in line with modeling predictions., 8 pages, 14 figures

New generation of advanced interferometer needs fused silica mirrors having better optical and mechanical properties. This paper describes the way to reduce the IBS coating absorption (1064 nm) and to improve the layer thickness uniformity.

We present a new micromechanical resonator designed for the observation of its quantum ground state (QGS). To reach QGS, a high frequency resonator with the lowest possible mass and the highest possible quality factor, coupled with an extremely sensitive measurement technique, has to be implemented. Using a high-finesse Fabry-Perot cavity with a mirror coated on the resonator, we expect benefits from the unique sensitivity of optical interferometry (10−38 m2/Hz) and from the optomechanical coupling between the light and the micro-resonator both to laser cool the resonator down to its ground state and to observe its residual quantum position fluctuations. We present the resonator we have developed for that purpose, which takes advantage from the high intrinsic quality factor of single crystal quartz and is designed to obtain a high resonance frequency (a few MHz) as well as a low mass (a few tens of µg). A length extension mode is used in order to avoid any deformation of the mirror surface and so to preserve the intrinsic quality factor of the resonator. A dedicated crystallographic orientation and a beam equilateral cross-section have been defined with respect to the quartz trigonal symmetry, allowing the micromachining of the resonator by wet etching. A beam cross-section area of 10−2 mm2 has been chosen to ease the deposit of the multilayered mirror. First mechanical characterizations of the resonator give a resonance frequency of 3.6 MHz, with a 25 µg mass and a quality factor of 390 000. Next steps will be the coating of the low-loss mirror on the resonator and its implementation in the Fabry-Perot cavity.

Through its participation to European programs, SAGEM has worked on the design and manufacturing of normal incidence collectors for EUV sources. By opposition to grazing incidence, normal incidence collectors are expected to collect more light with a simpler and cheaper design. Designs are presented for the two current types of existing sources: Discharge Produced Plasma (DPP) and Laser Produced Plasma (LPP). Collection efficiency is calculated in both cases. It is shown that these collectors can achieve about 10 % efficiency for DPP sources and 40 % for LPP sources. SAGEM works on the collectors manufacturability are also presented, including polishing, coating and cooling. The feasibility of polishing has been demonstrated with a roughness better than 2 angstroms obtained on several materials (glass, silicon, Silicon Carbide, metals...). SAGEM is currently working with the Institut d'Optique and the Laboratoire des Materiaux Avances on the design and the process of EUV coatings for large mirrors. Lastly, SAGEM has studied the design and feasibility of an efficient thermal control, based on a liquid cooling through slim channels machined close to the optical surface.

In this paper, we describe in detail the BMV (Bir\'efringence Magn\'etique du Vide) experiment, a novel apparatus to study the propagation of light in a transverse magnetic field. It is based on a very high finesse Fabry-Perot cavity and on pulsed magnets specially designed for this purpose. We justify our technical choices and we present the current status and perspectives., Comment: To be published in the European Physical Journal D

We experimentally demonstrate the high-sensitivity optical monitoring of moving micromirrors, made of low-loss dielectric coatings upon silicon resonators of various shapes and sizes. The very high optical finesses obtained (\mathcal{F}\simeq 30\,000 ) have allowed us to measure the thermal noise of the micromirrors at room temperature with a shot-noise limited sensitivity at the 10^{-19}\,{\rm m}/\sqrt{\rm Hz} level and to completely characterize their mechanical behavior, in excellent agreement with the results of a finite-element computation. Applications of such optomechanical systems range from quantum optics experiments to the experimental demonstration of the quantum ground state of a macroscopic mechanical resonator.

Reducing thermal noise from optical coatings is crucial to reaching the required sensitivity in next generation interferometric gravitational-waves detectors. Here we show that adding TiO$_2$ to Ta$_2$O$_5$ in Ta$_2$O$_5$/SiO$_2$ coatings reduces the internal friction and in addition present data confirming it reduces thermal noise. We also show that TiO$_2$-doped Ta$_2$O$_5$/SiO$_2$ coatings are close to satisfying the optical absorption requirements of second generation gravitational-wave detectors.

Background A battery of tests has been developed to better define the variety of defects which can occur in the process of visual perception of motion. Methods The tests assessed the perception of 1) coherent motion, in each of the four cardinal directions; (2) form from motion; (3) flow in depth; and (4) motion of a target moving in depth, within or without an optic flow surround. A normative study was conducted with 34 subjects, 21 to 69 years of age. Results Recognition of form from motion was better with upwards than with downwards motion. Perception of motion in depth was better with backward than forwards motion. The presence of an optic flow altered the perception of a motion in depth. Conclusion The recognition of form from motion demonstrated an asymmetry in threshold between the upward and downward movements. This asymmetry did not occur with global coherent motion, thus reflecting the variety of mechanisms involved in the visual process of motion. Moreover, alteration of perception of motion in depth within an optic flow reflected background effect.

présentée par A. Remillieux; The coating deposition on large optical components (diameter 350 mm) has required the development of new metrology tools at 1064 nm. To give realistic values of the optical performances, the whole surface of the component needs to be scanned. Our scatterometer (commercial system) has been upgraded to support large and heavy samples. The other metrology tools are prototypes we have developed. We can mention the absorption (photothermal effect) and birefringence bench, a control interferometer equipped with an original stitching option, the optical profilometer (RMS roughness and small defect measurements). A detailed description of these metrology benches will be exposed. Their sensitivity, accuracy and capability to map the optical properties of substrates or mirrors will be discussed. We will describe the recent developments: the stitching option adapted to the Micromap profilometer to measure the RMS roughness on larger area (exploration of a new spatial frequency domain), the accurate bulk absorption calibration.

présenté par A. Remillieux; Large mirrors (350 mm), having extremely low optical loss (absorption, scattering, wavefront) were coated for the VIRGO interferometer. The new mirror generation needs better wavefront and lower mechanical loss. The first results are discussed.

The Advanced Virgo gravitational wave detector aims at a sensitivity ten times better than the initial LIGO and Virgo detectors. This implies very stringent requirement on the optical losses in the interferometer arm cavities. In this paper we focus on the mirrors which form the interferometer arm cavities and that require a surface figure error to be well below one nanometre on a diameter of 150 mm. This 'sub-nanometric flatness' is not achievable by classical polishing on such a large diameter. Therefore we present the corrective coating technique which has been developed to reach this requirement. Its principle is to add a non-uniform thin film on top of the substrate in order to flatten its surface. In this paper we will introduce the Advanced Virgo requirements and present the basic principle of the corrective coating technique. Then we show the results obtained experimentally on an initial Virgo substrate. Finally we provide an evaluation of the round-trip losses in the Fabry-Perot arm cavities once the corrected surface is used.

To support the research effort for the third generation of gravitational wave interferometers, the Laboratoire des Materiaux Avances (LMA) at Lyon, France has developed a new cryogenic facility to characterize optics at low temperature. The new cryostat is installed in a clean room and allows samples to be cooled down to 10 Kelvin in around 12 hours. Currently, two independent experiments have been installed in the cryostat: the measure of the optical absorption of silicon and the measurement of the coating mechanical loss. After a short presentation of the cryogenic and optical setup, preliminary results from the optical absorption experiment will be presented.

Large mirrors (∅350 mm) having extremely low optical loss (absorption, scattering, wavefront) were coated for the VIRGO interferometer. The new generation of mirrors needs to have a better wavefront and lower mechanical loss. To improve the component wavefront, the corrective coating technique was used. By doping the tantalum pentoxide layers, we improved, for the first time to our knowledge, the multilayer mechanical loss. The first results are discussed.