1,146 research outputs found
Higher-order Laguerre-Gauss interferometry for gravitational-wave detectors with in situ mirror defects compensation HIGHER-ORDER LAGUERRE-GAUSS INTERFEROMETRY ... A. ALLOCCA et al
No full textThe 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 LG3,3 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
Optical detector topology for third-generation gravitational wave observatories
No full textThe third generation of gravitational wave observatories, with the aim of providing 100 times better sensitivity than currently operating interferometers, is expected to establish the evolving field of gravitational wave astronomy. A key element, required to achieve this ambitious sensitivity goal, is the exploration of new interferometer geometries, topologies and configurations. In this article we review the current status of the ongoing design work for third-generation gravitational wave observatories. The main focus is the evaluation of the detector geometry and detector topology. In addition we discuss some promising detector configurations and potential noise reduction schemes
Control of the double pendulum optics suspension system of a 30 m triangular Fabry-Pérot cavity
No full textSci. Instrum., vol. 71, n. 7, pp. , 2000, 2000International audienceWe present a technique for the control of a double pendulum suspension system used to carry the optical elements of a 30 m long Fabry-Pérot cavity, a prototype for the mode cleaner of the VIRGO experiment. The movement of the payload is sensed with a charge coupled device camera, and the feedback forces are applied to the intermediate stage of the suspension via coil-magnet systems. The control strategy is explained and the application of the system for the longitudinal locking of the cavity is demonstrated
Multi-modal/multi-resolution 3d data acquisition and processing for a new understanding of the historical city of Siena (Italy)
No full textThe paper presents the acquisition and data processing approach for the Ground Penetrating Radar (GPR) and laser scanner surveys carried out within the SOS project (the acronym comes from ‘SOtto Siena’, in English ‘Beneath Siena’). SOS is a program aimed to overcome some of the problems and limitations currently present in the study of cities with long-term continuity of life, responding in particular to the need for a better understanding of the city’s ancient fabric and hence to improvements in its conservation by: GPR city survey full coverage (of all the public spaces, streets, squares, courtyards, gardens, etc.), GIS data entry of the historical-archaeological and geoarchaeological knowledge and the development of a 3D Archaeological WEBGIS.
The paper discusses the procedure for the creation of a 3D viewer within an already active WEBGIS platform, specifically created for the visualisation and management of archaeological data. The GPR data, once acquired, were exported in 3D in the form of point clouds and subjected to a procedure of cleaning and filtering from noise, so as to eliminate geometries not referable to anomalies and therefore to the presence of buried structures or cavities, and then transformed into mesh to meet the needs of the subsequent process of semantic enrichment. The GPR survey of the underground was flanked by laser scanning of some of the most significant structures in the historic centre (e.g. the cathedral). All 3D geometries were then inserted into the new visualiser via a pipeline using open-source tools and libraries
Joint tests of cosmology and modified gravity in light of GW170817
No full textInternational audienceIn this Letter we constrain for the first time both cosmology and modified gravity theories conjointly, by combining the GW and electromagnetic observations of GW170817. We provide joint posterior distributions for the Hubble constant , and two physical effects typical of modified gravity: the gravitational wave (GW) friction, encoded by the parameter , and several GW dispersion relations. Among the results of this analysis, we can improve by 15\% the bound of the graviton mass with respect to measurement using the same event, but fixing . We obtain a value of at 99.7\% confidence level (CL), when marginalising over the Hubble constant and GW friction term . We find poor constraints on , but demonstrate that for all the GW dispersions relations considered, including massive gravity, the GW must be emitted 1.74s before the Gamma-ray burst (GRB). Furthermore, at the GW merger peak frequency, we show that the fractional difference between the GW group velocity and is
Optical losses as a function of beam position on the mirrors in a 285-m suspended Fabry-Perot cavity
No full textInternational audienceReducing optical losses is crucial for reducing quantum noise in gravitational-wave detectors. In fact, with equal input power, a lower level of round-trip losses in the arm cavities allows more power to be stored. Moreover, losses are the main source of degradation of the squeezed vacuum, which, along with increasing the power, is the most effective strategy to reduce quantum noise. Frequency-dependent squeezing obtained via a filter cavity is currently used to reduce quantum noise over the whole detector bandwidth. Such filter cavities are required to have high finesse in order to produce optimal squeezing angle rotation, and the presence of losses is particularly detrimental for the squeezed beam, as it does multiple round trips within the cavity. Characterizing such losses is crucial to assess the achievable quantum noise reduction. Here we present an in situ measurement of the optical losses, for different positions of the beam on the mirrors of the Virgo filter cavity. We implemented an automatic system to map the losses with respect to the beam position on the mirrors, finding that optical losses depend clearly on the position at which the beam hits the input mirror, varying from 42 to 87 ppm (parts per million), while they are much more uniform when we scan the end mirror (53 to 61 ppm). We repeated the measurements on several days, finding a statistical error less than ±4 ppm. The lowest measured losses are not much different from those estimated by individual mirror characterization performed before installation (30.3–39.3 ppm). This means that no major loss mechanism has been neglected in the estimation presented here. The larger discrepancy found for some beam positions is likely to be due to contamination. In addition to a thorough characterization of the losses, the methodology described herein allowed an optimal cavity axis position to be found for which the cavity round-trip losses are among the lowest ever measured. This work can contribute to achieving the very challenging loss goals for the optical cavities of future gravitational-wave detectors, such as the Einstein Telescope and Cosmic Explorer
Thermal detuning of a bichromatic narrow linewidth optical cavity
No full textn the Advanced Virgo+ interferometric gravitational-wave detector, the length control of the Fabry-Pérot cavities in the arms and of the detuned filter cavity, used for generating frequency-dependent squeezing, uses an auxiliary green beam at half of the operation laser wavelength (1064 nm). While operating the filter cavity with such a bichromatic control scheme for tens of hours, we observed that the mirror reflection phase shift of the fields at the two wavelengths responds differently to temperature changes in the mirrors, causing a change in the relative resonance condition of the two beams. In this paper we show that this thermal detuning effect can be explained by considering the thermomechanical properties of the mirror coating. Our experimental measurements are in good agreement with the theoretical predictions and allow us to drive requirements on the bicolor coating design and mirror temperature stability for long-term stable cavity control
Higher-Order Laguerre-Gauss Mode Generation and Interferometry for Gravitational Wave Detectors
No full textWe report on the first experimental demonstration of higher-order Laguerre-Gauss (LGpℓ) mode generation and interferometry using a method scalable to the requirements of gravitational wave (GW) detection. GW detectors which use higher-order LGpℓ modes will be less susceptible to mirror thermal noise, which is expected to limit the sensitivity of all currently planned terrestrial detectors. We used a diffractive optic and a mode-cleaner cavity to convert a fundamental LG00 Gaussian beam into an LG33 mode with a purity of 98%. The ratio between the power of the LG00 mode of our laser and the power of the LG33 transmitted by the cavity was 36%. By measuring the transmission of our setup using the LG00, we inferred that the conversion efficiency specific to the LG33 mode was 49%. We illuminated a Michelson interferometer with the LG33 beam and achieved a visibility of 97%
Probing modified gravity theories and cosmology using gravitational-waves and associated electromagnetic counterparts
No full textInternational audienceThe direct detection of gravitational waves by the LIGO/Virgo Collaboration has opened a new window with which to measure cosmological parameters such as the Hubble constant H0, and also probe general relativity on large scales. In this paper we present a new phenomenological approach, together with its inferential implementation, for measuring deviations from general relativity (GR) on cosmological scales concurrently with a determination of H0. We consider gravitational waves (GWs) propagating in an expanding homogeneous and isotropic background, but with a modified friction term and dispersion relation relative to that of GR. We find that a single binary neutron star GW detection will poorly constrain the GW friction term. However, a joint analysis including the GW phase and GW-GRB detection delay could improve constraints on some GW dispersion relations provided the delay is measured with millisecond precision. We also show that, for massive gravity, by combining 100 binary neutron stars detections with observed electromagnetic counterparts and host galaxy identification, we will be able to constrain the Hubble constant, the GW damping term and the GW dispersion relation with 2%, 15% and 2% accuracy, respectively. We emphasize that these three parameters should be measured together in order to avoid biases. Finally we apply the method to GW170817, and demonstrate that for all of the GW dispersions relations we consider, including massive gravity, the GW must be emitted ∼1.74 s before the gamma-ray burst. Furthermore, at the GW merger peak frequency, we show that the fractional difference between the GW group velocity and c is ≲10-17
Design of a high-magnification and low-aberration compact catadioptric telescope for the Advanced Virgo gravitational-wave interferometric detector
No full textInternational audienceAdvanced Virgo is a major upgrade of the Virgo gravitational-wave detector, aiming to increase its sensitivity by an order of magnitude. Among the main modifications of the instrument, the size of the laser beam inside the central area has been roughly doubled. Consequently, the input/output optics systems have been re-designed. Due to the overall Advanced Virgo optical scheme, high-magnification and compact telescopes are needed. These telescopes also have to fulfill stringent requirements in terms of aberrations, separation of secondary beams and scattered light. In this paper we describe the design of the Advanced Virgo telescopes and their estimated performances in terms of tuning capability and optical properties
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