LIGO Document T1800077-v4
- We apply the optimal control techniques (H-infinity and mu-syntheses) to align the aLIGO arm cavity. For the soft mode, it can be further combined with the digital subtraction of the Sidles-Sigg torque so only one set of filters is needed for different input power levels.
We show that our scheme can simultaneously improve the low-frequency rms motion and the high-frequency sensing noise. Moreover, the controller is robust under typical fluctuations in the arm power and/or sensing gain.
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