Experimental Investigations Relevant to the Development of a Laser Interferometric Gravitational Wave Detector

The direct detection of gravitational radiation is one of the greatest challenges facing modern experimental physics. Successful detection of the minute changes in the curvature of spacetime caused by violent astrophysical phenomena could open up an entirely new branch of astronomy, furthering our understanding of the nature of the surrounding Universe. Over the past few years much progress has been made in finding possible methods of detecting these gravitational waves. In particular, current investigations into the use of laser interferometric sensing techniques are showing great promise, indicating that ground-based laser interferometric detectors could potentially reach the sensitivities required. In this thesis some of the aspects of the development of a 10 m prototype interferometeric gravitational wave detector are discussed. In addition, some aspects of the techniques necessary for the successful operation of a full scale detector are investigated. A general discussion of feedback control systems used in laser interferometeric detectors is given, and some of the implications of the various noise sources and their effects on the potential sensitivity of the detector are pointed out. With these considerations in mind, a description of an electronic damping system for controlling the high Q pendulum resonances of the suspended test masses in a full scale laser interferometric gravitational wave detector is detailed and its noise performance analysed. In addition to this an experimental demonstration of a novel inertial damping control system for the suspended interferometer test masses is described and the performance of the system evaluated. An ultra high precision automatic alignment technique for use in optical interferometers is presented, followed by a detailed mathematical description of its operation and performance. It is expected that such a scheme, which can detect angular and lateral offsets of two interfering laser beams, along with mismatches in the beam size and phase front curvature, will be of particular importance in accurate alignment of a full scale detector. A description of the experimental testing of this alignment technique on one of the 10 m long suspended optical cavities forming part of the prototype detector in Glasgow is given. The current status of the 10 m prototype laser interferometric gravitational wave detector is described, outlining the present configuration of the detector and its method of operation. A detailed description of the method of calibrating the detector is given. Some of the optical and mechanical problems which previously set severe limits to the performance of the detector are examined and the steps taken to reduce these effects are discussed. In particular, the development of two double pendulum suspension systems, designed to reduce the noise imposed on the detector output signal due to electronic noise in the pendulum control system is described. Much of this work is based on the earlier theoretical discussions on control systems and noise. Finally, a summary of the work carried out is given and the prospects for detecting gravitational waves are discussed