Consequences of being out of shape: the effects of beam distortions in advanced interferometric gravitational wave detectors

Töyrä, Daniel Axel Wilhelm (2019). Consequences of being out of shape: the effects of beam distortions in advanced interferometric gravitational wave detectors. University of Birmingham. Ph.D.

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The era of gravitational wave astronomy has begun, which enables us to collect complementary information on events that can be seen by other means, and to study events that previously were invisible. The gravitational wave detectors that have made this possible, use laser interferometry to measure the gravitational-wave induced differential length change in two perpendicular arms. These laser interferometers are optical systems with high complexity, and can therefore be challenging to understand, diagnose and design. Numerical modelling softwares provide a bridge in the gap between theory and experiment, which allows for studying the realistic effects of isolated variables or perturbations, and exploring the large parameter space of the detectors. This can be used to contribute to design improvements, or identifying the cause of a certain symptom seen in the experiment.

The aim of the work presented in this thesis is to contribute to the commissioning and design processes of gravitational wave detectors by building and simulating realistic models, as well as developing tools that enable and/or facilitate the same for others. In particular, this work focus on the effects of beam distortions and misalignments in the LIGO and Virgo gravitational wave detectors. These beam distortions can be modelled by adding spatial higher-order Hermite-Gaussian modes to the ideal Gaussian beam.

We have quantified the effects of spatial mode mismatches on the performance of frequency dependent squeezed light, which is planned to be used in the near-future. A way of mitigating this negative effect is proposed, which includes the use of squeezed higher-order spatial modes. In addition, this work includes commissioning modelling for Virgo, related to the length control of the near-unstable power recycling cavity during lock acquisition, and creating a LIGO model designed for alignment sensing modelling.

Type of Work: Thesis (Doctorates > Ph.D.)
Award Type: Doctorates > Ph.D.
Licence: All rights reserved
College/Faculty: Colleges (2008 onwards) > College of Engineering & Physical Sciences
School or Department: School of Physics and Astronomy
Funders: European Commission
Subjects: Q Science > QC Physics


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