The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in Durham E-Theses • the full-text is not changed in any wayThe full-text must not be sold in any format or medium without the formal permission of the copyright holders. Please consult the full Durham E-Theses policy for further details. Abstract For the next generation of extremely large telescopes, Focal Anisoplanatism (FA) renders single Laser Guide Star AO useless. Here we analyze a novel LGS alternative configuration with corresponding wavefront sensing and reconstruction method, termed Projected Pupil Plane Pattern, to solve the problem of Focal Anisoplanatism. With PPPP, turbulence is sensed during uplink by a laser beam projected as a collimated beam from the whole telescope primary mirror. Phase changes due to the turbulence introduce intensity variations that then increase in amplitude with propagation distance. By observing the distribution of intensity at two distant planes, the Transport-of-Intensity equation can be used to determine the phase aberration encountered during the uplink path. A simple imaging camera can then be used to measure the wavefront by imaging the backscattered light patterns. We have successfully demonstrated PPPP works both by simulation and laboratory experiment, where we find that PPPP can achieve equivalent performance to a SH WFS associated with a NGS. However it is shown that the main problem of PPPP is its low Signal-to-Noise Ratio if a 20 W laser is used. To reduce the requirement for high laser power, an alternative reconstructor based upon nonlinear Artificial Neural Networks has been developed, and provides a wavefront with measurement error around 160 nm RMS with a single 200 W laser on a 4-m diameter telescope. PPPP is therefore ready for a practical onsky test, which we are currently undertaking at Electro Optical Systems (EOS) Debris Laser Ranging (DLR) system, Australia. Supervisors: Nazim Bharmal and Richard Myers ii Acknowledgements I acknowledge financial support from China Scholarship Council (CSC) for covering the living expenses during my first three years of study, and from Durham University for my last year, as well as the funding of STFC for my PhD project.

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A new LGS configuration termed Projected Pupil Plane Pattern (P 4), together with the corresponding wavefront sensing and reconstruction method, is presented. A theoretical analysis and Monto Carlo simulation show the feasibility of this novel method for a 4m-class telescope and great promise for the next generation of ELTs. Also we carry out a simple laboratory test with only defocus aberration and compare the reconstructed phase with the corresponding result from a Shack-Hartmann WFS. A further high-order experiment will follow, as well as plans for an on-sky test at William Herschel Telescope (WHT), La Palma.

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