BROWNIAN-MOTION OF A TORSION PENDULUM WITH INTERNAL-FRICTION

We constructed a torsion pendulum in which the dissipation is dominate d by internal friction in the fiber. We compare the measured thermal n oise spectrum with the prediction from the fluctuation-dissipation the orem. The agreement is excellent. The spectrum exhibits an approximate ly 1/f slope below resonance, We discuss the implications for interfer ometric gravitational wave detectors.