Quality Factor of Crystalline Silicon at Cryogenic Temperatures (SURF Report)

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Abstract:: 3rd 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 up to
were measured. Further experiments should be performed at
cryogenic temperatures with etched samples to determine how the quality factor is impacted.

Files in Document:

Final Report (Quality Factor of Crystalline Silicon at Cryogenic Tem...pdf, 1.1 MB)

LIGO Document P1300172-v1