The Virgo data acquisition system

International audienc

The gravitational wave detector VIRGO

International audienc

Search for non-Gaussian events in the data of the VIRGO E4 engineering run

International audienc

Description and accuracy tests of an improved lambdameter

An interferometric wavemeter with digital display is described. Fringes of an unknown and a reference wavelength are simultaneously generated through the motion of a moving double comer cube reflector in a Michelson-type interferometer. An electronic device compares the two wavelengths to within one hundredth of a fringe and numerically displays the result. Most of the systematic errors are eliminated by the total superposition of the optical paths of the reference and the measured beams, ensuring a high potential accuracy. As an illustration, we have remeasured with this device the wavelength of the λ = 612 nm radiation generated by a He-Ne laser stabilized on a saturated absorption peak of iodine. The results exhibit a statistical dispersion of ± 6 x 10-9 about a mean value which agrees to within 1.6 x 10 -9 with the more exact result obtained at BIPM.Nous décrivons un ondemètre interférométrique à lecture numérique. Il s'agit d'un interféromètre de type Michelson dans lequel la translation d'un réflecteur mobile (double coin de cube) engendre simultanément deux systèmes de franges sur les voies référence (longueur d'onde étalon) et mesure (longueur d'onde inconnue). Un dispositif électronique compare les deux longueurs d'onde au centième de frange et affiche numériquement le résultat. La plupart des erreurs systématiques sont éliminées grâce à la superposition totale des chemins optiques sur les deux voies, assurant ainsi une exactitude potentielle élevée. A titre d'exemple, nous avons remesuré avec ce dispositif la longueur d'onde de la raie λ = 612 nm émise par un laser à hélium néon asservi à un pic d'absorption saturée de l'iode. Les résultats présentent une dispersion statistique de ± 6 x 10-9 autour d'une valeur moyenne qui s'accorde à 1,6 x 10-9 près avec celle, plus exacte, obtenue au BIPM

The Inertial Damping of the VIRGO superattenuator and the residual motion of the mirror

The VIRGO superattenuator (SA) is effective in suppressing seismic noise below the expected thermal noise level above 4 Hz. However, the residual mirror motion associated with the SA normal modes can saturate the interferometer control system. This motion is reduced by implementing a wideband (DC–5 Hz) multidimensional active control (the so-called inertial damping) which makes use of both accelerometers and position sensors and of a digital signal processing (DSP) system. Feedback forces are exerted by coil–magnet actuators on the top of an inverted pendulum pre-isolator stage. The residual root mean square motion of the mirror in 10 s is less than 0.1 μm

The Virgo Suspensions

The VIRGO suspensions are chains of passive mechanical filters designed to isolate the interferometer mirrors from seismic noise starting from a few Hz. In order to reduce the low-frequency swing of the mirror along the beam, an active control system, acting at the level of the suspension point, damps the main resonant modes of the system (all below 2.5 Hz). Another control loop, at the level of the optical payload, makes use of a digital camera monitoring the mirror position in all six degrees of freedom. Its main goal is to decrease the rms angular displacements of the mirror, on a time scale of several minutes, down to less than 1 μrad. All the seven suspensions of the VIRGO central interferometer are presently in operation, while the assembly of the last two, for the terminal mirrors, is in progress. The design andperformance of the system are described in this paper

The present status of the VIRGO Central Interferometer

The VIRGO Central Interferometer (CITF) is a short suspended interferometer operated with the central area elements of the VIRGO detector. The main motivation behind the CITF is to allow the integration and debugging of a large part of the subsystems of VIRGO while the construction of the long arms of the antenna is being completed. This will permit a faster commissioning of the full-size antenna. In fact, almost all the main components of the CITF, with the exception of the large mirrors and a few other details, are the same as those to be used for the full-size detector. In this paper the present status of the VIRGO CITF is reported