In adaptive optics (AO) applications, point spread function (PSF) is defined as the impulse response of the system, and the PSF reconstruction is used in calibrating image analysis techniques for astrometry and in the deconvolution of images to enhance their contrast. The partial correction provided by the AO systems is due to the finite sampling of the wavefront sensor (WFS), the deformable mirror (DM) and the finite bandwidth of the overall system. This partial correction is mainly due to the high spatial frequencies introduced by the atmospheric turbulence, which translates into a halo artifact on the PSF. Furthermore, the correction provided by the AO system in direction of target objects degrades at greater angular distances from the guide star. This is called anisoplanatism. Consequently, the dimmer details of the AO images may not be detectable. One possible way to counteract this halo effect is through PSF reconstruction. In order to achieve accurate results, the analysis of the AO corrected images must account for the PSF temporal variation. The most promising and reliable technique to achieve PSF reconstruction is to use the wavefront sensor data measured synchronously with the observation (AO exposure).
With the off-axis PSF reconstruction from a dual DM AO system as a general objective, a model based experimental evaluation of PSF reconstruction from classical AO systems has been performed. Building on the success from on-axis classical AO systems, the complexity of the model and the experimental set-up has been gradually increased to a multi DM AO system and a methodology has been proposed. The good agreements between the numerical and experimental evaluation of the reconstructed PSF comparisons ensured the successful implementation of the methodology. Last, the complexity of the analysis and of the model is further extended from a single light source to a multi-light source scheme, and the off-axis PSF reconstruction is achieved from a dual DM AO scheme in order to accommodate for the anisoplanatic errors.
One of the challenges in interpreting PSF over wide fields arises from the temporal and field-dependent evolution of the adaptive optics PSF. The methodologies described in this thesis allow a quantitative analysis of wide-field observations that can account for these effects. The outcome of this research is important for post-processing of images obtained by next generation AO systems. Although the results are unique to the UVic experimental AO bench, the proposed PSF reconstruction methodologies will be applicable to other dual DM systems and to multi DM AO systems. More precisely, the importance of this thesis is to offer a PSF reconstruction technique for the adaptive optics instruments for the Thirty Meter Telescope (TMT). Once operational in 2016, TMT will be the first extremely large ground based optical telescope. It will have a primary mirror diameter of 30 m.
| Identifer | oai:union.ndltd.org:uvic.ca/oai:dspace.library.uvic.ca:1828/3210 |
| Date | 01 February 2011 |
| Creators | Keskin, Onur |
| Contributors | Bradley, Colin |
| Source Sets | University of Victoria |
| Language | English, English |
| Detected Language | English |
| Type | Thesis |
| Rights | Available to the World Wide Web |
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