L. Milano

Effects of misalignments and beam jitters in interferometric gravitational wave detectors

Abstract We present a calculation of the phase noise in a recycled interferometer with Fabry-Perot cavities in the arms, induced by the coupling of the geometrical fluctuations of the input laser with geometrical asymmetries of the interferometer. By comparison with the shot-noise limit planned for long-baseline interferometric gravitational wave detectors, upper limits in interferometer misalignments are established.

Testing gravitational theories using Eccentric Eclipsing Detached Binaries

In this paper, we compare the effects of different theories of gravitation on the apsidal motion of a sample of eccentric eclipsing detached binary stars. The comparison is performed by using the formalism of the post-Newtonian parametrization to calculate the theoretical advance at periastron and compare it to the observed one, after having considered the effects of the structure and rotation of the involved stars. n n n nA variance analysis on the results of this comparison shows that no significant difference can be found due to the effect of the different theories under test with respect to the standard general relativity (GR). It will be possible to observe differences, as we would expect, by checking the observed period variation on a much larger lapse of time. It can also be noted from our results that f(R) theory is the nearest to GR with respect to the other tested theories.

Analysis of contact binary systems - AA Ursae Majoris, V752 Centauri, AO Camelopardalis, and V 677 Centauri

In this paper we present a methodology for the solution of binary systems that allows the simultaneous use of all the available information. We give a statistical criterion to judge about the quality of the results. This methodology, based mainly on the Wilson-Prince procedure devised by our group for the solution of binary systems (by Barone et al. in 1988 and 1990 and Milano et al. in 1989), has here been applied to the analysis of four W UMa binaries for which existing solutions were, for different reasons, unsatisfactory. We show the cases for which more observational data are necessary or those for which a better analysis would be sufficient to give final answers

Photon self-induced spin-to-orbital conversion in a terbium-gallium-garnet crystal at high laser power

In this paper, we present experimental evidence of a third-order nonlinear optical process, self-induced spinto-orbital conversion (SISTOC) of the photon angular momentum. This effect is the physical mechanism at the origin of the depolarization of very intense laser beams propagating in isotropic materials. The SISTOC process, like self-focusing, is triggered by laser heating leading to a radial temperature gradient in the medium. In this work we tested the occurrence of SISTOC in a terbium-gallium-garnet rod for an impinging laser power of about 100 W. To study the SISTOC process we used different techniques: polarization analysis, interferometry, and tomography of the photon orbital angular momentum. Our results confirm, in particular, that the apparent depolarization of the beam is due to the occurrence of maximal entanglement between the spin and orbital angular momentum of the photons undergoing the SISTOC process. This explanation of the true nature of the depolarization mechanism could be of some help in finding novel methods to reduce or to compensate for this usually unwanted depolarization effect in all cases where very high laser power and good beam quality are required.

Adaptive optics approach for prefiltering of geometrical fluctuations of the input laser beam of an interferometric gravitational waves detector

In this article we present a preliminary study and experimental results on the use of an adaptive optics (AO) system for the reduction of geometrical fluctuations in a laser beam. The AO system is based on a Shack–Hartmann wave front sensor and a micromachined deformable mirror as a corrective element. The aim of this work is to investigate the applicability of such technologies to improving wave front clean-up conditions in long baseline interferometric gravitational wave detection.

A Neural Network-based ARX Model of Virgo Noise.

In this paper a Neural Networks based approach is presented to identify the noise in the VIRGO context. VIRGO is an experiment to detect Gravitational Waves by means of a Laser Interferometer. Preliminary results appear to be very promising for data analysis of realistic Interferometer outputs.

An optical readout system for the drag-free control of LISA

In this paper, we analyse the application of an optical readout system to the gravitational reference sensor of LISA. The goal is not the replacement of the capacitive sensor with an optical one, but the integration of the optical sensor in the present design of LISA. The main motivation is the implementation of a back-up solution, so that there is a significant risk reduction for the mission in case the main sensor fails for some reason. Furthermore, an optical system is potentially more sensitive than the capacitive one for some degrees of freedom. In this paper, we report some preliminary experimental results on the sensitivity of the sensor and describe a possible set-up for the implementation according to the present design of the gravitational reference sensor.

A dedicated system for breast cancer study with combined SPECT–CT modalities

A prototype ofa combined CT–SPECT tomograph f or breast cancer study has been developed and evaluated. It allows to perform scintimammography and X-ray CT in the same geometrical conditions. The CT system is based on a quasi-monochromatic beam tuned at 28 keV and an array ofultra f ast ceramic scintillators coupled to photodiodes whilst the SPECT system is based on two scintillator matrices coupled to position sensitive photomultipliers. CT and SPECT sinograms ofa test phantom were recorded and reconstruted with both modalities. Image f ofCT and SPECT images was then performed. The developed CT–SPECT prototype is able to detect a region of interest of 1 cm 3 ,

A hierarchical Bayesian learning scheme for autoregressive neural networks: application to the CATS benchmark

In this paper, a hierarchical Bayesian learning scheme for autoregressive neural network models is shown, which overcomes the problem of identifying the separate linear and nonlinear parts modeled by the network. We show how the identification can be carried out by defining suitable priors on the parameter space, which help the learning algorithms to avoid undesired parameter configurations. An application to synthetic data is shown and we apply the method to the CATS times series prediction benchmark.

Effects of misalignment and beam jitter in Fabry-Perot laser stabilization

Abstract We present a first order calculation of the equivalent frequency noise in a Fabry-Perot interferometer, when used as frequency sample for laser stabilization, induced by the coupling of misalignments of the cavity with the various geometrical fluctuations of the input laser beam.