The GEO600 project

GE0600, an interferometric graitvitational-wave detector with an arm length of 600 m, is currently being built in northern Germany close to Hannover. GE0600 incorporates an externally modulated fourfold delay-line Michelson interferometer giving a round-trip optical length of 2400 m. A master-slave combination of a monolithic diode-pumped Nd:YAG ring laser and an injection-locked amplifier will give a light power of about 10 W at a wavelength of 1064 nm. Power recycling increases the light power inside the interferometer to a level of about 10 kW. The use of both power and signal recycling will yield a sensitivity of the same order of magnitude as the first stages of the other large-scale gravitational-wave detectors LIGO and VIRGO currently under construction. High signal recycling factors allow the sensitivity to be increased at a chosen frequency while reducing the bandwidth of the detector. This gives an advantage over broad-band detectors in detecting narrow-band periodic sources such as pulsars. The 25 cm diameter mirrors will be suspended as double pendulums from a platform supported by vibration-reduction systems. The passive filtering properties of this system sufficiently reduce the seismic noise in the frequency range of interest, i.e. 50-1000 Hz. The detector will start taking data in the year 2000.