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Description:
The dawn of the 21st century marked a monumental milestone in scientific exploration with the groundbreaking detection of gravitational waves, a phenomenon long predicted by Einstein's theory of general relativity. After the first detection in 2015, the network of detectors located around the world has continued to improve its sensitivity, leading to the observation of more than 80 events in the first three observation runs. GEO600 is a gravitational wave detector designed to improve its high-frequency sensitivity. The frequency band around a few kHz is particularly important for signals from the post-merger of binary neutron stars. A more ambitious project for the detector, GEO-VHF (Very High Frequency), aims to explore previously uncharted territory in the frequency range of a few hundred kHz. Exotic signals, such as the emission of gravitational waves from the bosonic superradiance of black holes, are expected to occur in this frequency range. The new project will include the calibration of the detector up to 500 kHz, the possibility of changing the de-tuning of the Signal Recycling Cavity (SRC), the increase of circulating light power and the injection of squeezed states of light to reduce the shot noise of the detector. The current error signal for the SRC length control, based on the frontal modulation scheme, is sub-optimal for a detuned operation of the interferometer. The aim of this thesis is to test a new SRC locking technique that is more suitable for transitioning the detector to a detuned state. The new technique is based on detecting changes in the SRC length by injecting an auxiliary sub-carrier field from the dark port of the interferometer. A crucial aspect of the new scheme is to prove its compatibility with squeezing. In fact, the sub-carrier field shares the same path with the squeezed light. Furthermore, the thesis investigates methods to enhance squeezing performance by tackling two key challenges: mitigating backscattered light interference in the squeezed light generation process and ...