Noise behavior of the Garching 30-meter prototype gravitational-wave detector

The prototype gravitational-wave detector at Garching is described: in a laser-illuminated Michelson interferometer having arms 30 m in length, a folded optical path of 3 km is realized. The origin, action, and magnitude of possible noise sources are given. The agreement between the expected and measured noise is good. For a band of astrophysical interest, extending from 1 to 6 kHz, the quantum shot noise corresponding to a light power of P=0.23 W is dominant. In terms of the dimensionless strain h the best sensitivity in a 1-kHz bandwidth is h=3\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}18}$, comparable to the most sensitive Weber-bar-type antennas.