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Parametric instabilities and their control in advanced interferometer GW detectors

C. Zhao·L. Ju·J. Degallaix·S. Gras·D. G. Blair
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Abstract

A detailed simulation of Advanced LIGO test mass optical cavities shows that parametric instabilities will excite acoustic modes in the test masses in the frequency range 28-35 kHz and 64-72 kHz. Using nominal Advanced LIGO optical cavity parameters with fused silica test masses, parametric instability excites 7 acoustic modes in each test mass, with parametric gain R up to 7. For the alternative sapphire test masses only 1 acoustic mode is excited in each test mass with R ~ 2. Fine tuning of the test mass radii of curvature cause the instabilities to sweep through various modes with R as high as ~2000. Sapphire test mass cavities can be tuned to completely eliminate instabilities using thermal g-factor tuning with negligible degradation of the noise performance. In the case of fused silica test mass, instabilities can be minimized but not eliminated.

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C. Zhao, L. Ju, J. Degallaix, S. Gras, D. G. Blair. 2005-02-18. Parametric instabilities and their control in advanced interferometer GW detectors. https://doi.org/10.1103/physrevlett.94.121102

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