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Accadia T.,University of Savoy | Swinkels B.L.,European Gravitational Observatory EGO
Classical and Quantum Gravity | Year: 2010

The Virgo interferometer is one of the big observatories aimed at detecting gravitational waves. This paper will describe the Virgo + upgrades and the commissioning work performed between the first Virgo science run (VSR1) and the second Virgo science run (VSR2). Some first results of VSR2 will be discussed, which was recently started with a good duty cycle and an inspiral range for the detection of binary neutron-star inspirals of 10 Mpc. To conclude, an outlook will be given on some future upgrades of the detector. © 2010 IOP Publishing Ltd.

Schreiber E.,Leibniz University of Hanover | Dooley K.L.,Leibniz University of Hanover | Dooley K.L.,University of Mississippi | Vahlbruch H.,Leibniz University of Hanover | And 10 more authors.
Optics Express | Year: 2016

Beam alignment is an important practical aspect of the application of squeezed states of light. Misalignments in the detection of squeezed light result in a reduction of the observable squeezing level. In the case of squeezed vacuum fields that contain only very few photons, special measures must be taken in order to sense and control the alignment of the essentially dark beam. The GEO 600 gravitational wave detector employs a squeezed vacuum source to improve its detection sensitivity beyond the limits set by classical quantum shot noise. Here, we present our design and implementation of an alignment sensing and control scheme that ensures continuous optimal alignment of the squeezed vacuum field at GEO 600 on long time scales in the presence of free-swinging optics. This first demonstration of a squeezed light automatic alignment system will be of particular interest for future long-term applications of squeezed vacuum states of light. © 2016 Optical Society of America.

Affeldt C.,Leibniz University of Hanover | Danzmann K.,Leibniz University of Hanover | Dooley K.L.,Leibniz University of Hanover | Grote H.,Leibniz University of Hanover | And 17 more authors.
Classical and Quantum Gravity | Year: 2014

For almost 20 years, advanced techniques have been developed and tested at the GEO 600 laser-interferometric gravitational wave detector. Many of these innovations have improved the sensitivity of GEO 600 and could be shown to be consistent with stable and reliable operation of gravitational wave detectors. We review the performance of these techniques and show how they have influenced the upgrades of other detectors worldwide. In the second half of the paper, we consider how GEO 600 continues to pioneer new techniques for future gravitational wave detectors. We describe some of the new methods in detail and present new results on how they improve the sensitivity and/or the stability of GEO 600 and possibly of future detectors. © 2014 IOP Publishing Ltd.

Day R.A.,European Gravitational Observatory EGO | Vajente G.,National Institute of Nuclear Physics, Italy | Vajente G.,California Institute of Technology | Du Mezeray M.P.,RTEMIS Observatoire de la Cote DAzur
Journal of the Optical Society of America A: Optics and Image Science, and Vision | Year: 2014

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. © 2014 Optical Society of America.

Allocca A.,National Institute of Nuclear Physics, Italy | Allocca A.,University of Siena | Gatto A.,University Paris Diderot | Tacca M.,University Paris Diderot | And 5 more authors.
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2015

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 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. © 2015 American Physical Society.

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