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

Bond, Charlotte Zoë (2014). How to stay in shape: overcoming beam and mirror distortions in advanced gravitational wave interferometers. University of Birmingham. Ph.D.

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Abstract

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:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):