Robust optical configurations for reducing the impact of spatial laser beam effects in gravitational wave detectors

Rowlinson, Samuel ORCID: 0000-0002-6269-447X (2021). Robust optical configurations for reducing the impact of spatial laser beam effects in gravitational wave detectors. University of Birmingham. Ph.D.

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Abstract

The gravitational wave detections of the past five years were a culmination of decades worth of research. To increase the detection rates and horizon of detectability going forwards, much more work is yet required for identifying the sources of noise in ground-based, laser interferometer observatories, understanding how these can couple into the differential arm motion and, hence, developing strategies by which such noise can be reduced; for both current and future detectors. One of the principle subjects in this regard is the impact of the transverse, spatial properties of laser beams on the sensitivity of gravitational wave detectors.

In this thesis I will highlight my contributions to the detector instrumentation field on this subject. A central theme underlying this work is the impact that larger beams, planned for future detectors, will have on the optical design of such facilities and, thus, the overall sensitivity of these new observatories. With regards to this, a novel design for mode matching telescopes in the arms of each Einstein Telescope interferometer is analysed for feasibility and adaptive mode matching potential. The results of this work indicate that such a design could be viable, and initial design values are provided as a good starting point for future trade-off studies. The effect that larger beams may have on the alignment to longitudinal coupling noise is also studied, in the context of third-generation gravitational wave detectors. Conclusions from these analyses indicate that the negative impact this has can be counteracted through careful tuning of the optical design.

Due to the complicated nature of the physics involved with these, and other closely related, topics, it is vital to be able to computationally model such phenomena in a fast and reliable way. As a result of this, running parallel to the aforementioned studies, in this thesis I will also address the task of building essential modelling tools in this regard. My contributions to a new open-source package, Finesse 3, designed to tackle complex interferometer modelling, are detailed; with particular attention paid to my work on implementing the tools for simulating spatial beam effects in interferometers. The uses of these newly developed tools are given throughout the research tasks within this document. The final chapter of this thesis is dedicated to the overall design of Finesse 3, highlighting how these features address the need, in the instrumentation community, for such a tool going forwards.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):