ULTRAHIGH Q PENDULUM SUSPENSIONS FOR GRAVITATIONAL-WAVE DETECTORS

Pendulum suspensions for laser interferometer gravitational wave detec tors need to have an extremely high Q factor to minimize Brownian moti on noise. In this paper we analyze the limits to the Q factor of the c ompound pendulum. We show that the observed acoustic loss of niobium c an allow pendulum Q factors of 10(10) to be achieved. This should enab le a 3 km terrestrial laser interferometer detector to achieve strain sensitivity of 10(-22)/square-root Hz at frequencies as low as 10 Hz. At cryogenic temperatures Q factors up to 10(12) should be achievable.