Compensation for thermal effects in mirrors of Gravitational Wave Interferometers

In this paper we study several means of compensating for thermal lensing which, otherwise, should be a source of concern for future upgrades of interferometric detectors of gravitational waves. The methods we develop are based on the principle of heating the cold parts of the mirrors. We find that thermal compensation can help a lot but can not do miracles. It seems finally that the best strategy for future upgrades (``advanced configurations'') is maybe to use thermal compensation together with another substrate materials than Silica, for example Sapphire.Comment: 20 pages, 12 figure

Detection of gravitational wave bursts by interferometric detectors

We study in this paper some filters for the detection of burst-like signals in the data of interferometric gravitational-wave detectors. We present first two general (non-linear) filters with no {\it a priori} assumption on the waveforms to detect. A third filter, a peak correlator, is also introduced and permits to estimate the gain, when some prior information is known about the waveforms. We use the catalogue of supernova gravitational-wave signals built by Zwerger and M\"uller in order to have a benchmark of the performance of each filter and to compare to the performance of the optimal filter. The three filters could be a part of an on-line triggering in interferometric gravitational-wave detectors, specialised in the selection of burst events.Comment: 15 pages, 8 figure

Radiation Pressure Induced Instabilities in Laser Interferometric Detectors of Gravitational Waves

The large scale interferometric gravitational wave detectors consist of Fabry-Perot cavities operating at very high powers ranging from tens of kW to MW for next generations. The high powers may result in several nonlinear effects which would affect the performance of the detector. In this paper, we investigate the effects of radiation pressure, which tend to displace the mirrors from their resonant position resulting in the detuning of the cavity. We observe a remarkable effect, namely, that the freely hanging mirrors gain energy continuously and swing with increasing amplitude. It is found that the `time delay', that is, the time taken for the field to adjust to its instantaneous equilibrium value, when the mirrors are in motion, is responsible for this effect. This effect is likely to be important in the optimal operation of the full-scale interferometers such as VIRGO and LIGO.Comment: 27 pages, 11 figures, RevTex styl

Virgo and the quest for gravitational waves

In the past ten years,several giant interferometers have been built around the world with the goal ofa first direct detection ofgravitational waves.The most sensitive detectors,2 interferometers for the US LIGO collaboration and the detector built by the Italo-French collaboration Virgo (fig.1) are approaching their design sensitivity. Scientific exploitation ofthese instruments is now starting ..

Utilização da ferramenta ?Socialização do Levantamento de Expectativas? (SLE) no desenvolvimento de Projetos, Programas e Cursos.

By contextualizing the ramifications of government public policies on planning, development and evaluation of capacity-building programs and projects and on technology transfer and dissemination, under Embrapa Strategic Studies and Training?s scope of action, and under the expansion of South-South dialogue, this article aims to explore the connection between the different contingencies to which such programs, projects and courses are subjected, and the development of educational solutions or even innovating educational technologies to increase effectiveness and efficiency of these capacity-building actions and thus of their impacts. Herein we specifically analyze the use of the tool "Socialization of the Survey of Expectations" (SSE) with stakeholders (participants, instructors and organizers) in one of these projects, treated here as a case study: the International Course "Sustainable Coconut Production System and Fruit and Vegetables Quality Classification", jointly held by the Ministry of Agriculture, the Brazilian Cooperation Agency of the Ministry of Foreign Affairs, Embrapa Coastal Tablelands and Embrapa Strategic Studies and Training

A high accuracy method for the simulation of non-ideal optical cavities

We present an algorithm able to represent with a high accuracy any kind of stable cavity, even when many static or dynamical defects are present, like misalignments, curvature errors, surface irregularities, substrate inhomogeneities... We first present the theory, giving ideas on its validity domain, and a discussion of its accuracy in terms of a RMS phase error, which is found to be negligible compared to the phase noise due to roughness of optical surfaces. Then we show that the well-known features of ideal resonant cavities are found by the algorithm with a good accuracy. This tool can help for designing laser cavities, mode cleaners, or passive Fabry-Perot standards ; as an example, some results are presented concerning the design of a very long cavity planned for interferometric purposes

Compensation of Strong Thermal Lensing in High Optical Power Cavities

In an experiment to simulate the conditions in high optical power advanced gravitational wave detectors such as Advanced LIGO, we show that strong thermal lenses form in accordance with predictions and that they can be compensated using an intra-cavity compensation plate heated on its cylindrical surface. We show that high finesse ~1400 can be achieved in cavities with internal compensation plates, and that the cavity mode structure can be maintained by thermal compensation. It is also shown that the measurements allow a direct measurement of substrate optical absorption in the test mass and the compensation plate.Comment: 8 page

About the detection of gravitational wave bursts

Several filtering methods for the detection of gravitational wave bursts in interferometric detectors are presented. These are simple and fast methods which can act as online triggers. All methods are compared to matched filtering with the help of a figure of merit based on the detection of supernovae signals simulated by Zwerger and Muller.Comment: 5 pages, proceedings of GWDAW99 (Roma, Dec. 1999), to appear in Int. J. Mod. Phys.

An efficient filter for detecting gravitational wave bursts in interferometric detectors

Typical sources of gravitational wave bursts are supernovae, for which no accurate models exist. This calls for search methods with high efficiency and robustness to be used in the data analysis of foreseen interferometric detectors. A set of such filters is designed to detect gravitational wave burst signals. We first present filters based on the linear fit of whitened data to short straight lines in a given time window and combine them in a non linear filter named ALF. We study the performances and efficiencies of these filters, with the help of a catalogue of simulated supernova signals. The ALF filter is the most performant and most efficient of all filters. Its performance reaches about 80% of the Optimal Filter performance designed for the same signals. Such a filter could be implemented as an online trigger (dedicated to detect bursts of unknown waveform) in interferometric detectors of gravitational waves