This work deals with the application of parallel robots for the correction of defocus and coma optical aberrations in
the case study of the VST (VLT Survey Telescope) telescope, to be installed at the ESO observatory of Cerro
Paranal (Chile). The parallel robots are used to change position and orientation of the secondary mirror. The
secondary mirror positioning capability is a fundamental part in an active optics system, i.e. a closed loop control
system for the minimization of the telescope optical aberrations, where the outer optical feedback coming from the
wavefront sensor is used to generate references for the inner motion control loop of the secondary mirror
positioning robots. Two devices are presented: a 6-6 Stewart platform where both fixed and mobile platforms are
regular and similar hexagons whose vertexes belong to the same plane and are on a circle, and a two stages device
composed by a XY table plus a tilt platform. The basic theory of active optics corrections is presented. The
kinematics of both devices is solved in connection with the active optics application; first test data are presented.
Proc. SPIE. 6342, International Optical Design Conference 2006
KEYWORDS: Actuators, Astronomy, Digital signal processing, Interferometers, High power lasers, Interference (communication), Wavefronts, Adaptive optics, Deformable mirrors, Transmission electron microscopy
We present the results of an Adaptive Optics prototype system used to test the feasibility of active control for corrections of geometrical aberrations of gravitational wave interferometers input laser beam. It is shown that the efficiency of the system in correcting fluctuations extends up to 80 Hz unity gain frequency and that the upper limit of reintroduced noise is within gravitational wave interferometers requirements.
In this paper we briefly discuss the possibility to use Adaptive Optics in long baseline interferometric gravitational wave detectors. Analisys is carried out to demonstrate the usefulness of Adaptive Optics as a method to integrate double-mode-cleaner systems, presently used or foreseen in the next generation detectors as systems for the reduction of geometrical fluctuations of input laser beam. Finally a prototype of (AO) system for the control of geometrical fluctuations in a laser beam, based on the interferometric detection of phase front, is presented. By comparison with the usual Shack-Hartmann based AO system, we show that this technique is of particular interest when high sensitivity and high band-pass are required for correction of small perturbations like, for instance, the control of the input beam of gravitational waves interferometric detectors.
The French-Italian interferometric gravitational wave detector VIRGO is currently being commissioned. Its principal instrument is a Michelson interferometer with 3 km long optical cavities in the arms and a power-recycling mirror. This paper gives an overview of the present status of the system. We report on the presently attained sensitivity and the system’s performance during the recent commissioning runs.
In this paper we discuss an Adaptive Optics (AO) system for the control of geometrical fluctuations in a laser beam based on the interferometric detection of phase front. By comparison with the usual Shack-Hartmann based AO system, we show that this technique is of particular interest when high sensitivity and high band-pass are required for correction of small perturbations like, for instance, the control of the input beam of gravitational waves interferometric detectors. The good results obtained allow us to decide for its application within the mode cleaner system of the 3m prototype optical interferometer on gravitational wave detection (IDGW-3P) developed for R&D and operational in Napoli.
We present an Adaptive Optics (AO) system for the control of geometrical fluctuations in a laser beam based on the interferometric detection of phase front. By comparison with the usual Shack-Hartmann based AO system, we show that this technique is of particular interest when high sensitivity and high band-pass are required for correction of small perturbations like, for instance, the control of the input beam of gravitational waves interferometric detectors.
The goal of the VIRGO program is to build a giant Michelson type interferometer (3 kilometer long arms) to detect gravitational waves. Large optical components (350 mm in diameter), having extremely low loss at 1064 nm, are needed. Today, the Ion beam Sputtering is the only deposition technique able to produce optical components with such performances.
Consequently, a large ion beam sputtering deposition system was built to coat large optics up to 700 mm in diameter. The performances of this coater are described in term of layer uniformity on large scale and optical losses (absorption and scattering characterization).
The VIRGO interferometer needs six main mirrors. The first set was ready in June 2002 and its installation is in progress on the VIRGO site (Italy). The optical performances of this first set are discussed. The requirements at 1064 nm are all satisfied. Indeed, the absorption level is close to 1 ppm (part per million), the scattering is lower than 5 ppm and the R.M.S. wavefront of these optics is lower than 8 nm on 150 mm in diameter. Finally, some solutions are proposed to further improve these performance, especially the absorption level (lower than 0.1 ppm) and the mechanical quality factor Q of the mirrors (thermal noise reduction).
We present a study and preliminary experimental results on the possibility of using an adaptive optics system for reduction of geometrical fluctuations of input laser beam in long baseline interferometric detectors of gravitational waves. Presently used completely passive systems are expected to reduce fluctuations only at a level that, due to coupling of geometrical fluctuations with interferometer asymmetries, impose requirements on interferometer operation which are at the limit of present technology. Active pre-stabilization could reduce fluctuations and relax these requirements, allowing a safer and more robust interferometer operation on the planned time-scale of years of continue data acquisition.
In this paper we describe the non linear error signal extraction, which is an efficient and robust technique for the automatic control of optical interferometers. It represents a global solution to the problem of the longitudinal error signal extraction also when the uncontrolled optical system spans hundreds of fringes. This technique basically uses classic modulation techniques (phase modulation, mechanical modulation, etc.), but extends their range of validity using also the information available at the output photodiode. We have digitally implemented such technique following modular hardware and software architectures. In fact, the hardware consists of commercial VME boards for A/D and D/A conversion and processing, housed in standard VME crates, while the software algorithm is written in standard C language for portability and easy integration within digital control architectures.
Fiberoptic sensors are employed for the measurement of many physical quantities. 1,2 Fiberoptic sensors
using glass or lead glass optical fibers have been shown in radiation detectors3,4 or dosimeters.5,6 It has been
shown7-9 that the main effect of the interaction of ionizing radiation (typically, ? -rays from a Co60 source)
with optical fibers is the increase in the specific optical attenuation (dB/m) of the fiber waveguide due to the
radio-induced additional formation of color centers.
In a previous paper (SPIE Conf. 1584, 1991, 304-307) we proposed an optical fiber interferometric sensor for X-ray dosimetry. Basically, on absorption of a modulated X-ray beam, a temperature rise is produced in a silica fiber, which is detected with a Mach-Zehnder interferometric scheme. In this paper we report on the test measurements performed with our prototype detector using a X-ray rube. A possible application for X-ray synchrotron radiation monitor is discussed.
Virgo is an experiment carried out by INFN (Italy) and CNRS (France) to detect gravitational waves using a long baseline (3 X 3 km) interferometer, that requires a strong integration process among the various subsystems, for the functional coupling of the real-time control, database, communication, and visualization aspects of the project. In this paper we present the system architecture and illustrate some of the subsystems with particular emphasis on the data retrieval and processing, used in the monitoring and data storage subsystems.