Show simple item record

dc.contributor.advisorAngel, J. Roger P.en_US
dc.contributor.authorLloyd-Hart, Michael
dc.creatorLloyd-Hart, Michaelen_US
dc.date.accessioned2011-10-31T17:47:14Z
dc.date.available2011-10-31T17:47:14Z
dc.date.issued1992en_US
dc.identifier.urihttp://hdl.handle.net/10150/185749
dc.description.abstractAtmospheric turbulence causes severe degradation of the resolving and signal-to-noise properties of present optical telescopes. Diffraction-limited resolution can be recovered through the use of a deformable ('adaptive') optical element to correct the atmospheric wavefront error. An adaptive optics system operating in the near infrared (1.7 - 3.5 μm) has been developed for use at the Multiple Mirror Telescope (MMT), an array of six co-mounted 1.8 m telescopes, in which six flat mirrors are used to correct the wavefront tilt across each aperture, and the phase differences between apertures. This can reduce the error sufficiently to achieve a diffraction-limited image with a central peak of 0.06 arcseconds full width at half maximum at 2.2 μm wavelength. A number of algorithms are used to drive the adaptive mirror in a closed servo loop, including a trained artificial neural network which deduces the wavefront aberration from a pair of simultaneous in- and out-of-focus images of a star, taken at the combined focal plane of the telescope. Computer simulations have shown that the net is capable of deriving the wavefront for the full six-mirror aperture, and in practice, the net has been demonstrated in the lab to maintain two- and three-aperture diffraction-limited beam profiles in the presence of distorting effects. On the sky, with a real star, the net has successfully restored the diffraction limit for two adjacent MMT segments. High resolution images have been obtained of various objects with a wide-field camera looking in the field around the wavefront reference star. Work has also been carried out to characterise the wavefront aberration at the MMT, which confirms the Kolmogorov model of turbulence. Finally, a new algorithm is discussed which shows great promise for correction of phase errors in array telescopes.
dc.language.isoenen_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.subjectOptics.en_US
dc.subjectAtmospheric waves.en_US
dc.subjectOptical instruments.en_US
dc.titleNovel techniques of wavefront sensing for adaptive optics with array telescopes using an artificial neural network.en_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
dc.identifier.oclc704432568en_US
thesis.degree.grantorUniversity of Arizonaen_US
thesis.degree.leveldoctoralen_US
dc.contributor.committeememberMcCarthy, Donald W.en_US
dc.contributor.committeememberWoolf, Neville J.en_US
dc.contributor.committeememberLow, Frank J.en_US
dc.identifier.proquest9220676en_US
thesis.degree.disciplineAstronomyen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.namePh.D.en_US
refterms.dateFOA2018-08-23T06:05:23Z
html.description.abstractAtmospheric turbulence causes severe degradation of the resolving and signal-to-noise properties of present optical telescopes. Diffraction-limited resolution can be recovered through the use of a deformable ('adaptive') optical element to correct the atmospheric wavefront error. An adaptive optics system operating in the near infrared (1.7 - 3.5 μm) has been developed for use at the Multiple Mirror Telescope (MMT), an array of six co-mounted 1.8 m telescopes, in which six flat mirrors are used to correct the wavefront tilt across each aperture, and the phase differences between apertures. This can reduce the error sufficiently to achieve a diffraction-limited image with a central peak of 0.06 arcseconds full width at half maximum at 2.2 μm wavelength. A number of algorithms are used to drive the adaptive mirror in a closed servo loop, including a trained artificial neural network which deduces the wavefront aberration from a pair of simultaneous in- and out-of-focus images of a star, taken at the combined focal plane of the telescope. Computer simulations have shown that the net is capable of deriving the wavefront for the full six-mirror aperture, and in practice, the net has been demonstrated in the lab to maintain two- and three-aperture diffraction-limited beam profiles in the presence of distorting effects. On the sky, with a real star, the net has successfully restored the diffraction limit for two adjacent MMT segments. High resolution images have been obtained of various objects with a wide-field camera looking in the field around the wavefront reference star. Work has also been carried out to characterise the wavefront aberration at the MMT, which confirms the Kolmogorov model of turbulence. Finally, a new algorithm is discussed which shows great promise for correction of phase errors in array telescopes.


Files in this item

Thumbnail
Name:
azu_td_9220676_sip1_m.pdf
Size:
4.639Mb
Format:
PDF
Description:
azu_td_9220676_sip1_m.pdf

This item appears in the following Collection(s)

Show simple item record