Advanced experimental systems for gravitational wave detectors and dark matter searches

This thesis outlines the work I undertook at Cardiff University as part of my degree for doctor of philosophy. The document is split into two distinct parts. The first section covers the development of new photodetector electronics that successfully reduced the dark noise of the LIGO experiment by a factor of 6.5 at 2 kHz. This reduction in the dark noise is mainly achieved by filtering the majority of the DC photocurrent from the audio readout path and increasing the transimpedance resistor by a factor of 100. The new readouts are projected to improve the overall DARM sensitivity of LIGO by 10% at 2 kHz in the next observing run. The second section covers the implementation of a laser auto-alignment system using differential wavefront sensing for the ALPS II dark matter search. The autoalignment system is currently undergoing further commissioning but has already shown an improvement in low frequency cavity noise of roughly an order of magnitude which will help the ALPS II detector reach the target design sensitivity in its search for axion-like particles in the upcoming science run at the end of 2022. Both projects involved the development of advanced techniques for ultra-precise interferometry experiments but the goals and techniques implemented were vastly different. This document outlines the approach in tackling these projects and will hopefully prove a useful guide for others in the future.