G. Newton

The GEO 600 gravitational wave detector

The GEO 600 laser interferometer with 600 m armlength is part of a worldwide network of gravitational wave detectors. Due to the use of advanced technologies like multiple pendulum suspensions with a monolithic last stage and signal recycling, the anticipated sensitivity of GEO 600 is close to the initial sensitivity of detectors with several kilometres armlength. This paper describes the subsystems of GEO 600, the status of the detector by September 2001 and the plans towards the first science run.

Status of the GEO600 detector

Of all the large interferometric gravitational-wave detectors, the German/British project GEO600 is the only one which uses dual recycling. During the four weeks of the international S4 data-taking run it reached an instrumental duty cycle of 97% with a peak sensitivity of 7 × 10−22 Hz−1/2 at 1 kHz. This paper describes the status during S4 and improvements thereafter.

The status of GEO 600

The GEO 600 laser interferometer with 600m armlength is part of a worldwide network of gravitational wave detectors. GEO 600 is unique in having advanced multiple pendulum suspensions with a monolithic last stage and in employing a signal recycled optical design. This paper describes the recent commissioning of the interferometer and its operation in signal recycled mode.

Gravitational Wave Detectors Using Laser Interferometers and Optical Cavities: Ideas, Principles and Prospects

In these two lectures we will discuss principles underlying the development of some laser interferometer gravitational radiation detectors, some of the techniques being devised to overcome the many experimental problems, and results obtained so far in experimental work at the University of Glasgow and the California Institute of Technology. We also hope to give some indication about possible long-term prospects, as well as presenting some new ideas bearing on these problems.

Silica research in Glasgow

The Glasgow group is involved in the construction of the GEO600 interferometer as well as in R&D activity on technology for advanced gravitational wave detectors. GEO600 will be the first GW detector using quasimonolithic silica suspensions in order to decrease thermal noise significantly with respect to steel wire suspensions. The results concerning GEO600 suspension mounting and performance will be shown in the first section. Section 2 is devoted to the present results from the direct measurement of thermal noise in mirrors mounted in the 10 m interferometer in Glasgow which has a sensitivity limit of 4 × 10 −19 mH z −1/2 above 1 kHz. Section 3 presents results on the measurements of coating losses. R&D activity has been carried out to understand better how thermal noise in the suspensions affects the detector sensitivity, and in section 4 a discussion on the non-linear thermoelastic effect is presented.

Calibration of the Glasgow 10 m prototype laser interferometric gravitational wave detector using photon pressure

We show that the radiation pressure from an amplitude modulated, low power, Nd:YAG laser can be used to calibrate the displacement sensitivity of the Glasgow 10 m prototype gravitational wave detector. This demonstrates the possibility of radiation pressure being used as a standard method of calibrating long base line gravitational wave detectors. Further, this technique has the very important additional advantage that the test mass acted upon by the radiation pressure is not altered in any way, by, for example, the attachment of magnets, etc. The high Q-factor of the internal modes, required for good detector sensitivity, is therefore preserved.

Commissioning, characterization and operation of the dual-recycled GEO 600

The German-British laser-interferometric gravitational-wave detector GEO 600 is currently being commissioned as part of a worldwide network of gravitational-wave detectors. GEO 600 recently became the first kilometre-scale interferometer to employ dual recycling-an optical configuration that combines power recycling and signal recycling. We present a brief overview of the commissioning of this dual-recycled interferometer, the performance results achieved during a subsequent extended data-taking period, and the plans intended to bring GEO 600 to its final configuration.

The Status of GEO600

The GEO 600 laser interferometer with 600m armlength is part of a worldwide network of gravitational wave detectors. GEO 600 is unique in having advanced multiple pendulum suspensions with a monolithic last stage and in employing a signal recycled optical design. This paper describes the recent commissioning of the interferometer and its operation in signal recycled mode.

A report on the status of the GEO 600 gravitational wave detector

GEO 600 is an interferometric gravitational wave detector with 600 m arms, which will employ a novel, dual-recycled optical scheme allowing its optical response to be tuned over a range of frequencies (from ~100 Hz to a few kHz). Additional advanced technologies, such as multiple pendulum suspensions with monolithic bottom stages, make the anticipated sensitivity of GEO 600 comparable to initial detectors with kilometre arm lengths. This paper discusses briefly the design of GEO, reports on the status of the detector up to the end of 2002 with particular focus on participation in coincident engineering and science runs with LIGO detectors. The plans leading to a fully optimized detector and participation in future coincident science runs are briefly outlined.

Optical Cavity Laser Interferometers for Gravitational Wave Detection

Most of the techniques being developed for detection of gravitational radiation involve sensing the small strains in space associated with the gravitational waves by looking for changes in the apparent distance between two (or more) test masses. In many of the experimental searches performed so far the detectors consisted of massive aluminium bars, the metal near the ends of the bars acting as the test masses, and impulsive strains induced in the bars were searched for. Thetrain sensitivity of such experiments has been in the range 10−16 to 10−18 for pulses of duration of order 1 millisecond, the limits usually being set by thermal noise in the bar, and transducer and amplifier sensitivity. Current predictions of gravitational waves to be expected from various types of astrophysical sources suggest that strain sensitivities some three orders of magnitude better than these are likely to be required for detection of gravitational wave bursts from known types of sources at a useful rate, although indecd signals may be present over a wide frequency range — from 10 kHz to 10−4 Hz or lower. (A good summary is given in the proceedings of a conference on “Sources of Gravitational Radiation” [1]). Work on bar gravity wave detectors is continuing; but an alternative approach is to use widely separated and nearly free test masses, and monitor changes in their separation by optical interferometry techniques. This method shows considerable promise for both high sensitivity and wide bandwidth and frequency coverage. At the sensitivity levels required absolute length measurements would be difficult, but a comparison of two baselines perpendicular to one another, which may be affected in opposite senses by a gravitational wave travelling in a suitable direction, provides a practical alternative. Early experiments of this type were carried out at Hughes Laboratories [2] using a simple Michelson interferometer to monitor separations between ree test masses suspended in vacuum. The displace- ment sensitivity of such an arrangement may be improved by causing the light in each arm of the interferometer to travel back and forth many times between mirrors attached to the test masses, and a multireflection system of this type using Herriott delay lines was proposed by R. Weiss [3]. Experimental work on multireflection Michelson interferometers for gravity wave detection has been carried out at MIT, the Max-Planck Institute at Munich, and the University of Glasgow.