J. Hough

Photon-pressure-induced test mass deformation in gravitational-wave detectors

A widely used assumption within the gravitational-wave community has so far been that a test mass acts like a rigid body for frequencies in the detection band, i.e. for frequencies far below the first internal resonance. In this paper, we demonstrate that localized forces, applied for example by a photon pressure actuator, can result in a non-negligible elastic deformation of the test masses. For a photon pressure actuator setup used in the gravitational-wave detector GEO 600, we measured that this effect modifies the standard response function by 10% at 1 kHz and about 100% at 2.5 kHz.

The optics of an interferometric gravitational-wave antenna

The basic concept of an interferometric gravitational wave detector, the realization of the long light path with optical delay lines or with Fabry-Perot cavities, and the need for high light power are described. The techniques for improving the sensitivity, recycling and squeezed states of light, are considered and the consequences on the specifications of the optical components are shown. The specifications are explicitly given and particularly the influence of thermal effects is treated quantitatively.

Mechanical aspects in interferometric gravity wave detectors

In order to measure the tiny effects of gravitational waves, strains in space (i.e. relative changes in distance) of as little as 10-21 or even less have to be detected, at frequencies ranging from 10011z to several kHz. Large laser interferometers are the most promising approach to reach such extreme sensitivities. This ‘straightforward’ road is, however, obstructed by a multitude of effects that cause (or fake) such fluctuations in distance. Among these are seismic motions, thermal vibrations of optical components, pressure fluctuations of the residual gas in the vacuum tubes, and fundamental effects such as Heisenbergs uncertainty relation.

Development of Ultra-low Optical and Mechanical Loss aSi Coatings Using Novel ECR Ion Beam Deposition

One of the significant limiting factors in gravitational wave detectors is the Brownian noise associated with the optical coatings [1], which are required to form the highly-reflective laser mirrors. UWS has a unique range of capabilities being used to help develop novel coating technology that can address this challenge, targeted for aLIGO+ and beyond.

DEVELOPMENTS TOWARD MONOLITHIC SUSPENSIONS FOR ADVANCED GRAVITATIONAL WAVE DETECTORS

The proposed upgrades to both the LIGO and Virgo gravitational wave observatories will seek to improve detector sensitivity by reducing thermal noise. Based on technologies first implemented at the GEO600 detector, the test mass mirrors will be suspended using fused silica fibres of either circular or rectangular cross section to form monolithic suspensions. In GEO600 cylindrical fused silica fibres were produced using a hydrogen-oxygen flame based machine. Here we report on a new CO2 laser based fibre pulling system under development in Glasgow designed to achieve higher tolerances and reduce contamination of fibres. Preliminary testing of a laser welding process suitable for constructing full scale monolithic suspensions for advanced detectors is described.