Ground-based interferometers for the detection of gravitational waves

Abstract

The ground-based interferometers currently under construction share their goal and principle of operation with the space project LISA: the detection and measurement of gravitational waves by laser interferometry. There are, however, differences in the frequency ranges (and thus the detectable sources) and in the noise requirements. A lower frequency limit for ground-based detection is, in practice, dictated by seismic noise, and yet more fundamentally by ‘gravity gradient noise’: geophysical, meteorological, and man-made motions of large masses. Ground-based detectors are expected to cover the range from a few Hz to a few kHz. It is only in space that detection of signals below, say, 1 Hz is possible, opening a wide window to a different class of interesting sources of gravitational waves. Actually, many requirements in the ground-based detectors turn out to be more stringent than the ones in space. Thus LISA can profit from a wealth of long-time experience gathered in the prototypes for ground-based interferometers. The recent years have brought a great break-through in the quest for earth-bound detection: on five sites the world over, detectors of armlengths from 0.3 to 4 km are being built. A review of these projects will be given, stressing the similarities, but also the differences, in their respective concepts. First operation of all of the ground-based interferometers is expected around the years 2000/2001, leading to an era of world-wide collaboration in gravitational wave astronomy.