LIGO Document T2200172-v3

Actively Monitoring and Increasing Stability of the Auxiliary Laser Controls

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T - Technical notes
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Auxiliary (AUX) lasers in the Laser Interferometer Gravitational-wave Observatory (LIGO) interferometers are at the core of the arm length stabilization (ALS) system. This system is routinely used to lock the interferometer to its nominal operating point for gravitational wave (GW) detection. Furthermore, the possibility of using the AUX laser system as a future calibration scheme has been suggested. In order to better understand the viability of an AUX laser calibration scheme, measuring the systematics of the AUX laser control loop is necessary. I used a Red Pitaya as a small and inexpensive measurement device to measure the Unity Gain Frequency of the AUX control loop, in order to easily monitor the gain of the AUX controls over long periods of time. I also developed an inversion filter to cancel out the resonances of the AUX control loop actuator, in order to increase overall loop stability.
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Final report and presentation by Cici Hanna for LIGO SURF, summer 2022

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