Monitoring the thermal and nonthermal excitation of fibers

The vibrations of well-isolated tungsten and fused silica fibers under tension were examined with a highly optimized shadow sensor. We adapted event search and analysis techniques used with resonant gravitational wave detectors to search for burstlike excitation events in the fibers. The method is optimized to distinguish rapid excitations against a background of thermal driving. The level and statistics of thermal noise were consistent with the fluctuation-dissipation theorem. No excess noise fiber events were seen. The energy innovation threshold for events was 1.8 kT in the case of a fused silica fiber loaded at 518 MPa (54% of breaking strength) during a 24 h run and 27 kT in the case of a tungsten fiber loaded at 326 MPa (94% of breaking strength) during a 6 h run.