| 1. |
- Andersen, Torben, et al.
(författare)
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The Swedish 50 m ELT
- 2002
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Ingår i: Beyond conventional adaptive optics; ESO Conference and Workshop Proceedings. - 3923524617 ; 58, s. 7-10
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Konferensbidrag (refereegranskat)
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| 2. |
- Flicker, Ralf, et al.
(författare)
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Tilt anisoplanatism and PSF retrieval in LGS MCAO using a predictive controller
- 2002
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Ingår i: Beyond conventional adaptive optics : ESO Conference and Workshop Proceedings. - 3923524617 ; 58, s. 377-377
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Konferensbidrag (refereegranskat)abstract
- It is shown how tilt anisoplanatism in laser-supported multi-conjugatedadaptive optics (MCAO) systems can be a) predicted from a prioriknowledge, b) compensated using additional natural guide stars (NGS),and c) estimated in real time from control loop data to allow PSFretrieval. As a consequence of the problems associated with retrievingatmospheric tip and tilt from laser guide star (LGS) measurements, anMCAO system without additional reference beacons will have a set of nullmodes that can not be measured by the LGS. These are the global tip andtilt modes, and three plate scale modes deriving principally fromtomographical combinations of quadratic modes (focus and astigmatisms).These modes can be compensated by introducing a NGS-supported null modecontrol loop totally decoupled from the LGS system. Invoking a prioriassumptions about the atmospheric turbulence, we compute the loss ofStrehl ratio from residual tilt anisoplanatism due to noise and servolag for some sample NGS configurations and magnitudes. PSF retrieval isdemonstrated in all cases. Results are obtained and compared using botha simple and a noise-weighted least squares estimator, and both anintegrating and a predictive linear controller. Finally, a method forreal time estimation is presented, and verification by monte carlogenerated loop data is work in progress.
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| 3. |
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| 4. |
- Owner-Petersen, Mette, et al.
(författare)
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Multi-conjugate Adaptive Optics for the Swedish ELT Investigation of the Effects of Laser Guide Stars at a finite Distance.
- 2002
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Ingår i: Beyond conventional adaptive optics : a conference devoted to the development of adaptive optics for extremely large telescopes. Proceedings of the Topical Meeting held May 7-10, 2001, Venice, Italy.. - 3923524617 ; 58, s. 299-299
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Konferensbidrag (refereegranskat)abstract
- In a recent paper we presented a procedure for optimal analyticalcontrol of several deformable mirrors based on only the measured guidestar wavefronts. The expected performance was evaluated for variousguide star configurations using up to three deformable mirrors. Forsimplicity the guide stars were assumed to be infinitely distant. Inthis paper we address the effect of using laser guide stars in 90 kmaltitude for the wavefront measurements. As a consequence of this, theimage of a distant science star will not be adequately corrected bycounteracting the wavefront error measured by a laser guide star in thesame direction as the science star. This problem will be more pronouncedthe larger is the telescope diameter. We present a modified version ofthe mirror control algorithm taking the finite distance of the laserguide stars into account and some preliminary performance evaluationswith special emphasis on the consequences for ELTs.
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