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How to stay in shape: overcoming beam and mirror distortions in advanced gravitational wave interferometers

Bond, Charlotte Zoë (2014)
Ph.D. thesis, University of Birmingham.

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The Laser Interferometer Gravitational-wave Observatory (LIGO) aims to detect gravitational waves using laser interferometry. A direct observation has so far eluded scientists, and LIGO is currently being upgraded to Advanced LIGO, aiming for 10 times the current sensitivity. This upgrade will increase the complexity of the instrument and it is crucial that the behaviour of the interferometer is understood in advance, particularly the impact of distortions of the laser beam through interactions with mirrors which deviate from a perfect sphere. Many features of advanced detectors can influence the beam shape: thermal aberrations of the mirrors; high finesse cavities; and signal recycling. This thesis reports the modelling of beam and mirror distortions in such interferometers.

The model developed throughout my PhD is detailed: beam distortions are described by the addition of higher order Gaussian modes. This model is used for Advanced LIGO commissioning tasks, required to reach design sensitivity. In particular I identify additional losses at the beam-splitter. I also report a feasibility study into using a completely different beam shape, an LG33 mode, as a future input beam. I show that advanced detectors are not yet compatible with the LG33 mode and derive the mirror requirements for a possible upgrade.

Type of Work:Ph.D. thesis.
Supervisor(s):Freise, Andreas
School/Faculty:Colleges (2008 onwards) > College of Engineering & Physical Sciences
Department:School of Physics and Astronomy
Subjects:QC Physics
Institution:University of Birmingham
ID Code:5223
This unpublished thesis/dissertation is copyright of the author and/or third parties. The intellectual property rights of the author or third parties in respect of this work are as defined by The Copyright Designs and Patents Act 1988 or as modified by any successor legislation. Any use made of information contained in this thesis/dissertation must be in accordance with that legislation and must be properly acknowledged. Further distribution or reproduction in any format is prohibited without the permission of the copyright holder.
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