LIGO Document T2200173-v1

Frequency Stabilization for Auxilliary Lasers in the 40m

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T - Technical notes
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The auxiliary lasers in the 40m LIGO Observatory are used to stabilize the main laser. The auxiliary laser is controlled by the mechanical resonances of a piezoelectric transducer, which controls the laser intensity as a function of its voltage, temperature and orientation. At some points in the control loop formed by the auxiliary laser and PZT, the mechanical resonances of the PZT are so loud that they add excess noise to the system. The aim of this project is to accurately measure the open-loop transfer function of the PZT and laser output, and analytically find the poles and zeroes of the system. With this done, the inverse of the transfer function can be found and applied to the system using digital filters, effectively cancelling out any noise from the PZT and thus increasing the bandwidth of the system. It will add a digital aspect to the laser control systems that were previously entirely analog.
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Deeksha Sabhari SURF 2022 project reports.

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