GEO600 is a gravitational-wave detector and a key technology development center of the international gravitational-wave research community. Technologies developed and tested in the GEO project are now used in all large gravitational-wave detectors.
GEO600 is a ground-based interferometric gravitational-wave detector located near Hannover, Germany. It is designed and operated by scientists from the Max Planck Institute for Gravitational Physics and the Leibniz Universität Hannover, along with partners in the United Kingdom, and is funded by the Max Planck Society and the Science and Technology Facilities Council (STFC).
GEO600 is part of a worldwide network of gravitational-wave detectors. Two detectors have been constructed in the USA (LIGO), and one each in Italy (Virgo) and Japan (KAGRA). In India LIGO India will be built. Scientists from GEO600 and LIGO collaborate within the LIGO Scientific Collaboration (LSC). GEO600 scientists together with the Laser Zentrum Hannover (LZH) built the lasers for Advanced LIGO.
GEO scientists were the first to tame unwanted quantum mechanical background noise in gravitational-wave detectors by manipulating the fluctuations so as to produce what is called “squeezed light”. GEO600 was upgraded with a squeezed-light source in mid-2010 and has since kept the world record for the use of strongest squeezing in a gravitational-wave detector. GEO600 therefore uses two lasers: the standard laser with a power of about 10 watts and the squeezed-light laser, which adds only a few entangled photons per second, but significantly improves the sensitivity of GEO600.
The central elements in all gravitational-wave detectors are mirrors weighing up to dozens of kilograms, which are used to direct the laser beams. These mirrors are suspended as pendulums, so that they are isolated from various disturbances. The mirror suspensions must meet several special requirements: they have to hold the heavy mirrors securely and must not cause disturbances of their own. The Institute for Gravitational Research (IGR) of the University of Glasgow has developed suspensions meeting these requirements: thin threads made of quartz glass – fused silica fibres.
A highly stable laser
In close cooperation of AEI and LZH a new type of high-performance laser has been developed for use in the next generation of gravitational-wave detectors. These new lasers have been installed in the Advanced LIGO project. A special feature is that it provides 200 Watt of power at a wavelength of 1064 nanometers. Its unsurpassed stability in both output power and frequency is what makes the high sensitivity of the new generation of gravitational-wave detectors possible.
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