Gravitational wave detectors LIGO[2, 34], Virgo[78, 4, 503] shown in Figure 16.1, GEO[147, 601] and TAMA[15] are broad band detectors, sensitive in a frequency range of about 20–2000 Hz. The laser interferometric detectors are based on Michelson interferometry, and have a characteristic right angle between their two arms for optimal sensitivity for spin-2 waves[476]. At low frequencies (approximately less than 50 Hz), observation is limited by unfiltered seismic noise. In a middle band of up to about 150 Hz, it is limited by thermal noise and, at high frequencies above a few hundred Hz, by shot noise[495]. The design bandwidth of these detectors is chosen largely by the expected gravitational wave frequencies emitted in the final stages of binary neutron star coalescence, i.e. frequencies up to a few hundred Hz produced by compact stellar mass objects. At these frequencies, the detectors operate in the short wavelength limit, wherein the signal increases linearly with the length of the arms. It is therefore advantageous to build detectors with arm lengths as long as is practically feasible, given that many noise sources are independent of the arm length.