Machine-learning nonstationary noise out of gravitational-wave detectors

Signal extraction out of background noise is a common challenge in high-precision physics experiments, where the measurement output is often a continuous data stream. To improve the signal-to-noise ratio of the detection, witness sensors are often used to independently measure background noises and subtract them from the main signal. If the noise coupling is linear and stationary, optimal techniques already exist and are routinely implemented in many experiments. However, when the noise coupling is nonstationary, linear techniques often fail or are suboptimal. Inspired by the properties of the background noise in gravitational wave detectors, this work develops a novel algorithm to efficiently characterize and remove nonstationary noise couplings, provided there exist witnesses of the noise source and of the modulation. In this work, the algorithm is described in its most general formulation, and its efficiency is demonstrated with examples from the data of the Advanced LIGO gravitational-wave observatory, where we could obtain an improvement of the detector gravitational-wave reach without introducing any bias on the source parameter estimation

In situ correction of mirror surface to reduce round-trip losses in Fabry–Perot cavities

High-finesse resonant cavities play an important role in many metrology applications such as gravitational wave detectors. The performance of these cavities can be limited by round-trip losses (RTP) generated by light that is scattered by the mirror surface defects into higher-order modes that are close to resonance. In this paper we develop a detailed model of this effect and we study possible strategies to correct the mirror surface. We show that it is possible to restrict the correction to the combination of a reduced set of surface deformations that can be reproduced on the mirror using projected heating patterns. We show with an optical simulation that by acting on the cavity mirrors it is possible to reduce RTP to the large angle scattering limit. We also show that the optimal correction can be computed without any a priori knowledge of the mirror surface, but based only on measurements of the power stored inside the cavity, thus opening up the possibility of a simple implementation of the proposed algorithm

Accelerated convergence method for fast Fourier transform simulation of coupled cavities

Fast Fourier transform (FFT) simulation was used to calculate the power and spatial distribution of resonant fields in optical cavities. This is an important tool when characterizing the effect of imperfect geometry and mirror aberrations. This method is, however, intrinsically slow when the cavities are of relatively high finesse. When this is the case, an accelerated convergence scheme may be used to calculate the steady-state cavity field with a speed that is orders of magnitude faster. The rate of convergence of this method, however, is unpredictable, as many different factors may detrimentally affect its performance. In addition, its use in multiple cavity configurations is not well understood. An in-depth study of the limitations and optimization of this method is presented, together with a formulation of its use in multiple cavity configurations. This work has not only resulted in consistent improvement in performance and stability of the accelerated convergence method but also allows the simulation of optical configurations, which would not previously have been possible

Etude d'un réseau à très faible teneur en matière organique biodégradable : le réseau de la ville de Nice

La Ville de Nice bénéficie de deux ressources en eau d'excellente qualité, la Vésubie et la nappe alluviale du Var, qui se caractérisent par leur très faible teneur en matière organique biodégradable. La Compagnie Générale des Eaux, gestionnaire de son alimentation en eau potable, applique depuis sa mise au point au début du siècle le procédé de désinfection par l'ozone et distribue une eau sans ajouter de chlore.Un diagnostic complet de la qualité microbiologique et sanitaire de ce réseau non chloré et sans Carbone Organique Dissous Biodégradable (CODB) a été entrepris.Le suivi de la qualité de l'eau dans le réseau a consisté en des campagnes de prélèvements à partir de plusieurs points d'observation répartis sur l'ensemble du réseau. Ce suivi a permis de confirmer la bonne qualité de l'eau distribuée et le maintien de cette qualité tout au long de son transport dans les canalisations. Le CODB est absent sur l'ensemble des points confirmant l'absence de relargage et de contamination pendant le transport.La récupération des dépôts présents dans les canalisations n'a pas révélé de colonisation du réseau par des micro-organismes supérieurs. La quantité de biofilm présente sur les parois des canalisations a été évaluée en suivant la colonisation de pastilles de matériau immergées dans les réservoirs.Ce diagnostic complet de l'état microbiologique et sanitaire du réseau de Nice montre que l'absence de chloration n'entraîne pas de dégradation de la qualité bactériologique de l'eau et que c'est essentiellement l'absence de matière organique biodégradable qui limite la croissance bactérienne et qui contribue au maintien de la qualité de l'eau dans le réseau de distribution.Within the more general scope of studies aiming at a better knowledge of the mechanisms responsible for biological biodegradation in water systems, it was interesting to learn the microbiological behaviour of a drinking water network supplied with water free of biodegradable organics. The case in point is the town of Nice which enjoys excellent quality water ressources, to the extent that the Compagnie Générale des Eaux, managers of the municipal water utility, were able to apply ozonation as a disinfectant when the technique first appeared at the beginning of the century, and supply chlorine free water.The Municipal Services of the Town of Nice, the Nice Health Laboratory and the Compagnie Générale des Eaux bave therefore combined forces to carry out a study on the development of water quality in the supply network in such an animal environment. The objective is to make a complete diagnosis of the microbiological and hygienic quality of a chlorine-free network which would confirm the excellent quality of the distributed water and serve as a reference within the scope of general research on the removal of biodegradable organics for the supply of non chlorinated water.The study consisted of monitoring three supply systems fed by three different water works :- the Super Rimiez plant treating water from the river Vésubie in the following stages : flocculation, primary clarification, sand filtration and virucidal ozonation;-the Jean Moreno plant : water pumped from the alluvion layers of the Var and ozonated;-the Prairies plant : pumping and temporary chlorination of the Var aquifer with chlorine dioxyde.In order to take seasonal variations info account, our study lasted for a whole year, with sampling campaigns every two weeks on 20 observation points along the network, and on the raw water treated in three production plants. The physico-chemical and microbiological characteristics of the water samples were analyzed.Samples were collected at a high flow rate from fire hydrants near the observation points. The sediments were gathered in a plankton net and analyzed to detect the presence of possible animalcules.The immersion of PVC coupons in two reservoirs, fed respectively with the two types of water, enabled the growth kinetics of fixed bacteria to be followed, and the quantifies of fixed biomass at steady state to be compared.It was possible, by monitoring the chloride content (on average 25 mg Cl¯/l in Var water compared with 5 mg Cl¯/l in Vésubie water), to identify the precise influence of the two water resources.Total bacteria measured by epilluorescence are not very high compared with networks in other large towns. It will be noted, however, that the figure is higher in the network supplied from the Vésubie than in those treating water from the Var aquifer. Bacterial regrowth in circulating water is minor, showing that the influence of bacteria released by the biofilm installed on the pipe walls is minimized. This biofilm is present just the same, as is shown by the results of colonization an the immersed coupons in reservoirs.The quantity of fixed bacteria at steady state is different according to the type of water but, in both cases, it was lower than the figure obtained with water loaded with biodegradable organics. The total plate count remains low on the whole, even at end sections of the network. The presence at fecal bacteria was only observed at a few points during some of the studies and the Nice network, on the whole, is of excellent quality judged by the very few fecal contamination indicators found.The presence of Aeromonas hydrophila was detected in very small quantities and at a few of the sampling points only.Analyses of Dissolved Organic Carbon (on average 0.3 mgC/l) and Biodegradable Dissolved Organic Carbon (less than 0.1 mgC/l, by the minimum detection threshold method) reveal a very low concentration in organics and a total absence of BDOC on all sampling points, thus confirming the good quality of the water supplied and the tact that these is very little bacteria) remise and contamination while the water is in transit.Examination of the sediments in water mains and at the bottom of reservoirs did not reveal the existence of higher forma of microorganisms.This complete diagnosis of the mirobiological and health condition of the Nice water system has brought confirmation of the good quality of the water supplied throughout its transit in the water mains. The lack of chlorination dues not cause a deterioration of the bacteriological quality of the water, the sustainable quality of which is essentially linked with the absence of BDOC which restricting the growth of bacteria.The importance of these findings on such a distinctive network as that of the Nice utility will enable this study to be used as reference for future research on the means of maintaining the quality of water in supply networks without using chlorine

Higher-order Laguerre-Gauss interferometry for gravitational-wave detectors with in situ mirror defects compensation

The use of higher-order Laguerre-Gauss modes has been proposed to decrease the influence of thermal noise in future generation gravitational-wave interferometric detectors. The main obstacle for their implementation is the degeneracy of modes with same order, which highly increases the requirements on the mirror defects, beyond the state-of-the-art polishing and coating techniques. In order to increase the mirror surface quality, it is also possible to act in situ, using a thermal source, sent on the mirrors after a proper shaping. In this paper we present the results obtained on a tabletop Fabry-Pérot Michelson interferometer illuminated with a LG_(3,3) mode. We show how an incoherent light source can reduce the astigmatism of one of the mirrors, increasing the quality of the beam in one of the Fabry-Pérot cavities and then the contrast of the interferometer. The system has the potential to reduce more complex defects and also to be used in future gravitational-wave detectors using conventional Gaussian beams

Performance of a thermally deformable mirror for correction of low-order aberrations in laser beams

The thermally deformable mirror is a device aiming at correcting beam-wavefront distortions for applications where classical mechanical methods are precluded by noise considerations, as in advanced gravitational wave interferometric detectors. This moderately low-cost technology can be easily implemented and controlled thanks to the good reproducibility of the actuation. By using a flexible printed circuit board technology, we demonstrate experimentally that a device of 61 actuators in thermal contact with the back surface of a high-reflective mirror is able to correct the low-order aberrations of a laser beam at 1064 nm and could be used to optimize the mode matching into Fabry-Perot cavities

High Precision Detection of Change in Intermediate Range Order of Amorphous Zirconia-Doped Tantala Thin Films Due to Annealing

Understanding the local atomic order in amorphous thin film coatings and how it relates to macroscopic performance factors, such as mechanical loss, provides an important path towards enabling the accelerated discovery and development of improved coatings. High precision x-ray scattering measurements of thin films of amorphous zirconia-doped tantala (ZrO_2−Ta_2O_5) show systematic changes in intermediate range order (IRO) as a function of postdeposition heat treatment (annealing). Atomic modeling captures and explains these changes, and shows that the material has building blocks of metal-centered polyhedra and the effect of annealing is to alter the connections between the polyhedra. The observed changes in IRO are associated with a shift in the ratio of corner-sharing to edge-sharing polyhedra. These changes correlate with changes in mechanical loss upon annealing, and suggest that the mechanical loss can be reduced by developing a material with a designed ratio of corner-sharing to edge-sharing polyhedra

Machine-learning nonstationary noise out of gravitational-wave detectors

Signal extraction out of background noise is a common challenge in high-precision physics experiments, where the measurement output is often a continuous data stream. To improve the signal-to-noise ratio of the detection, witness sensors are often used to independently measure background noises and subtract them from the main signal. If the noise coupling is linear and stationary, optimal techniques already exist and are routinely implemented in many experiments. However, when the noise coupling is nonstationary, linear techniques often fail or are suboptimal. Inspired by the properties of the background noise in gravitational wave detectors, this work develops a novel algorithm to efficiently characterize and remove nonstationary noise couplings, provided there exist witnesses of the noise source and of the modulation. In this work, the algorithm is described in its most general formulation, and its efficiency is demonstrated with examples from the data of the Advanced LIGO gravitational-wave observatory, where we could obtain an improvement of the detector gravitational-wave reach without introducing any bias on the source parameter estimation

Displacement power spectrum measurement of a macroscopic optomechanical system at thermal equilibrium

The mirror relative motion of a suspended Fabry-Perot cavity is studied in the frequency range 3-10 Hz. The experimental measurements presented in this paper, have been performed at the Low Frequency Facility, a high finesse optical cavity 1 cm long suspended to a mechanical seismic isolation system identical to that one used in the VIRGO experiment. The measured relative displacement power spectrum is compatible with a system at thermal equilibrium within its environmental. In the frequency region above 3 Hz, where seismic noise contamination is negligible, the measurement distribution is stationary and Gaussian, as expected for a system at thermal equilibrium. Through a simple mechanical model it is shown that: applying the fluctuation dissipation theorem the measured power spectrum is reproduced below 90 Hz and noise induced by external sources are below the measurement.Comment: 11 pages, 9 figures, 2 tables, to be submitte