Mechanical loss in state-of-the-art amorphous optical coatings

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 figure

Measurements of mechanical thermal noise and energy dissipation in optical dielectric coatings

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.

Estimation of losses in a 300 m filter cavity and quantum noise reduction in the KAGRA gravitational-wave detector

International audienceThe sensitivity of the gravitational-wave detector KAGRA, presently under construction, will be limited by quantum noise in a large fraction of its spectrum. The most promising technique to increase the detector sensitivity is the injection of squeezed states of light, where the squeezing angle is dynamically rotated by a Fabry-Pérot filter cavity. One of the main issues in the filter cavity design and realization is the optical losses due to the mirror surface imperfections. In this work we present a study of the specifications for the mirrors to be used in a 300 m filter cavity for the KAGRA detector. A prototype of the cavity will be constructed at the National Astronomical Observatory of Japan, inside the infrastructure of the former TAMA interferometer. We also discuss the potential improvement of the KAGRA sensitivity, based on a model of various realistic sources of losses and their influence on the squeezing amplitude

Analyse expérimentale et modélisation de couplages multiphysiques dans un contact frottant / acier-matériau de friction modèle

VILLENEUVE D'ASCQ-ECLI (590092307) / SudocSudocFranceF

GPU implementation of FSR simulations: performance improvements and limitations

International audienceNumerical simulation to calculate the free spectral range scans (FSR scans) of laser resonators is a computationally intensive task. OSCAR is a well-established Matlab toolbox that enables for such simulations based on Fourier optics. Any arbitrary discrete complex electromagnetic input fields as well as misalignment or mismatching of resonators can be considered in the FSR simulation. Unfortunately, it currently only features CPU based calculations on one or more CPU cores. However, the computational cost increases exponentially with increasing lateral resolution of the complex electromagnetic fields. In addition, only a limited number of roundtrips can be carried out in an acceptable computation time, which limits the applicability only to low finesse resonators. Due to good parallelizability of the FSR scan calculation, this numerical computation is very well suited for modern graphics cards, which are outstanding in performing many calculations in parallel. This paper introduces the extension of FSR scan simulations on modern graphics cards (GPUs) within the OSCAR Toolbox. First, a statistical analysis is provided, that presents the massive performance improvement compared to CPU computations. Subsequently, the disadvantages in the form of memory limitations of GPUs are outlined. Therefore, generally valid data is presented, from which a trade-off between lateral resolution of the complex electromagnetic fields and the number of roundtrips to be performed can be derived. In conclusion, the great potentials of new applications are highlighted, which were previously not feasible. Any code of this GPU implementation discussed in this paper has been integrated into the OSCAR Matlab Toolbox and is made available open source on GitHub

Calibration and performances of the integrated Mach-Zehnder (iMZ) wavefront sensor for extreme adaptive optics

International audienceWe describe new results obtained with the integrated Mach-Zehnder (iMZ) self referenced wavefront sensor (WFS) allowing to extract independently phase and amplitude from intensity variations in the pupil images produced by the interferometer. This kind of wavefront sensor meets extreme adaptive optics requirements, high speed (1 kHz) and high accuracy (< 10 nm at 5-10 cm spatial scale), as well as the reconstruction of phasing errors on segmented telescopes and scintillation measurements. In this paper we present the calibration method we have developed and validated experimentally to accurately extract the phase and the amplitude of the wavefront from the Mach-Zehnder signal, using several diversities in the phase patterns. We also present a new phase modulation method which combined with an unwrapping algorithm increases the dynamical range of the wavefront sensor up to several microns, otherwise limited to ± lambda/4 without these new strategies. Numerical simulations of the Mach-Zehnder performances for various turbulence phase will be presented to address the ultimate sensor accuracy. We will also report on our latest laboratory calibration results, using a deformable mirror and a spatial light modulator to introduce the required phase modulations

Point defects in IBS coating for very low loss mirrors

International audienceHigh 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

Large and extremely low loss: the unique challenges of gravitational wave mirrors

International audienceThis 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

Prior-damage dynamics in a high-finesse optical enhancement cavity

International audienceAn 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 phenomeno