Introduction to LIGO and an Experiment Regarding the Quality Factor of Crystalline Silicon

Third generation LIGO detectors will be limited by thermal noise at a low frequency band where gravitational wave signals are expected to exist. A large contribution to thermal noise is caused by internal friction of the mirror and suspension elements. In order to meet the quantum mechanical sensitivity limits of the detector, it will be necessary to further push down the contribution of thermal noise. Future detectors will require new materials with extremely high mechanical quality. Silicon at cryogenic temperatures shows the promise to provide the required mechanical quality due to its vanishing expansion coefficient at 120 K. The fluctuation dissipation theorem links thermal noise to mechanical dissipation which, in turn, motivates us to study the quality factor of silicon cantilevers. An experiment is designed to measure the mechanical quality of silicon flexures at cryogenic temperatures. Utilizing a ring-down method in vacuum, we determine the quality factor of a silicon cantilever at room temperatures. Q-factors of up to 2.84 • 10 5 were measured. Further experiments should be performed at cryogenic temperatures with etched samples to determine how the quality factor is impacted. In addition, an introduction to LIGO and the respective sources of noise is presented. 2 Figure 1: A picture of the LIGO Livingston site with the two perpendicular arms that extend for 4 kilometers.