LIGO Document P1400148-v1

Techniques for Resonant Optical Interferometry with Applications to the Advanced LIGO Gravitaional Wave Detectors.

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P - Publications
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My Ph.D. Thesis.

A worldwide effort to detect gravitational radiation directly with large scale laser interferometers has been underway for the past several decades. In the United States the Laser Interferometer Gravitational-Wave Observatories (LIGO) have been operating since the early 2000s. These detectors use multiply resonant optical interferometers operating at a wavelength of 1064 nm to read out the strain induced by passing gravitational waves. This dissertation discusses a number of techniques and applications related to the operation of these interferometers at there designed sensitivity.

Part I introduces the reader to the concept of gravitational wave detection. We start by showing how the Einstein equations lead to the concept of propagating gravitational radiation and discuss some astrophysical events which are expected to emit enough radiation to be seen here on Earth. The reader is then introduced to the topology of modern terrestrial gravitational wave detectors and the limiting noise sources for such devices.

In Part II mathematical techniques for understanding and modeling these complex instruments are discussed; with a focus on the interaction of monochromatic radiation with resonant optical interferometers. Part II also contains a discussion of the effects of heating in high power resonant optical interferometers such as the Advanced LIGO (aLIGO) gravitational wave detectors.

Part III focuses on the design and testing of a particular subsystem of the aLIGO interferometers; the input optics. In particular it begins by examining the electro-optic modulator whose task it is to add radio frequency sidebands to the main laser beam for sensing and detection of the various degrees of freedom of the interferometer. It discusses the in-vacuum, high power Faraday isolator which is responsible for deflecting the reflected light from the interferometer for sensing and control and for isolating the reflected light from returning to the rest of the input chain. Finally, it describes the input mode cleaner which is used to stabilize and prepare the laser beam before injection into the main interferometer.

Finally, Part IV of this dissertation describes a technique for characterizing these resonant optical interferometers through measurement of their eigenspectra. This technique and some of the nuanced details are explained before moving on to a description of the ways in which it has been used to characterize the Advanced LIGO interferometers. The key results obtained with this technique are described in which the eigenspectra measurement is used to monitor the thermal state of the input mode cleaner and of the power recycling cavity.

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