LIGO Document T1900391-v1

Measuring mechanical loss in cryogenic gentle nodal suspension resonator

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T - Technical notes
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This experiment is a cryogenic version of the Gentle Nodal Suspension system for measuring Q-factors of mechanical resonators. In order to increase the Q-factor of this system, we will focus initially and substantially on the intrinsic loss in the silicon near the zero crossing point of its thermal expansion coefficient. At this zero point, some dominant losses and noise contributions drop to zero. A better understanding of the losses in the silicon could prove invaluable, as this thin film is used to coat highly reflective surfaces in the LIGO cryogenics. These silicon coatings store a small fraction of the energy in the acoustic modes, so the additional mechanical losses must be even smaller. To accurately measure the silicon coating losses, other losses must be subdominant.
We will calculate a loss budget for the silicon wafers, looking at surface and bulk losses and what happens at the contact point of the suspension system.
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