| 1. |
- Beckers, Jacques M, et al.
(författare)
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Rapid refocusing system for the Euro50 telescope aimed at removing the perspective elongation of laser beacons
- 2003
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Ingår i: Society of Photo-Optical Instrumentation Engineers. Proceedings. - : SPIE. - 0361-0748. ; 5169, s. 123-136
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Tidskriftsartikel (refereegranskat)abstract
- To obtain full sky coverage, astronomical adaptive optics systemsrequire Na Sodium Beacons (SBs) (also referred to as Laser Guide Starsor LGSs) located at heights extending from 85 to 100 km. When viewed atthe edge of large telescopes these SBs appear elongated. For the Euro5050 meter aperture telescopes this elongation amounts to 6 to 9arcseconds when the laser is launched from a point on the telescopeaxis. This is substantially larger than the ~0.6 arcsec FWHM SB whenviewed near the telescope center. This so-called "perspectiveelongation" substantially decreases the sensitivity of SB aided adaptiveoptics. We describe a way of removing this elongation when using pulsedlasers. It uses rapid (microsecond) refocusing of the telescope with theaid of birefringent lenses and polarization modulators. We present anoutline of the SB wavefront sensor for the Euro50.
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| 2. |
- Beckers, Jacques M., et al.
(författare)
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Sodium beacon wavefront sensing for the Euro50 telescope in the presence of perspective elongation
- 2004
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Ingår i: Proceedings of the SPIE. - : SPIE. - 0819452998 ; 5382, s. 510-519
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Konferensbidrag (refereegranskat)abstract
- To obtain full sky coverage, astronomical adaptive optics systemsrequire Na Sodium Beacons (SBs) (also referred to as Laser Guide Starsor LGSs) located at heights extending from 85 to 100 km. When viewed atthe edge of large telescopes these SBs appear elongated. For the Euro5050 meter aperture telecopes this elongation amounts to 6 to 9 arcsecondswhen the laser is launched from a point on the telescope axis. This issubstantially larger than the -0.6 arcsec FWHM SB when viewed near thetelescope center. This so-called "perspective elongation" substantiallydecreases the sensitivity of SB aided adaptive optics. We describe a wayof removing this elongation when using pulsed lasers. It uses rapid(microsecond) refocusing of the telescope with the aid of birefringentlenses and polarization modulators. We present an outline of the SBwavefront sensor for the Euro50.
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| 3. |
- Beckers, Jacques M., et al.
(författare)
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Very high-resolution spectroscopy for extremely large telescopes using pupil slicing and adaptive optics
- 2007
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Ingår i: Optics Express. - 1094-4087. ; 15:5, s. 1983-1994
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Tidskriftsartikel (refereegranskat)abstract
- Under seeing limited conditions very high resolution spectroscopy becomes very difficult for extremely large telescopes (ELTs). Using adaptive optics (AO) the stellar image size decreases proportional with the telescope diameter. This makes the spectrograph optics and hence its resolution independent of the telescope diameter. However AO for use with ELTs at visible wavelengths require deformable mirrors with many elements. Those are not likely to be available for quite some time. We propose to use the pupil slicing technique to create a number of sub-pupils each of which having its own deformable mirror. The images from all subpupils are combined incoherently with a diameter corresponding to the diffraction limit of the sub-pupil. The technique is referred to as "Pupil Slicing Adaptive Optics" or PSAO. (c) 2007 Optical Society of America.
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| 4. |
- Gontcharov, Alexander, et al.
(författare)
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Adaptive optics for the Euro50: design and performance
- 2003
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Ingår i: Future Giant Telescopes. Proceedings of the SPIE. - : SPIE. - 081944619X ; 4840, s. 36-46
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Konferensbidrag (refereegranskat)abstract
- The optical design for the proposed Euro50 extremely large telescopewith integrated adaptive optics (AO) is presented. For atmosphericturbulence correction, we propose using single and dual-conjugate AOsystems working with natural and laser guide stars. The corrective shapeof the deformable mirrors (DMs) is derived from an analytical algorithmbased on minimization of the sum of the residual power spectra of thephase fluctuations seen by guide stars after correction. Predictions forperformance of the Euro50 ELT with Dual-conjugate AO are given for the Kband using a seven layer atmospheric model for the atmosphere at theObservatorio del Roque de los Muchachos (ORM) on La Palma. The averageStrehl ratio is used to quantify the system performance for differentvalues of actuator pitch and DM conjugation altitudes. The influence ofthe outer scale and telescope pointing on the RMS stroke of the DMs ispresented. It is concluded that construction of such a system isfeasible and that there is a need for development of a simulation toolto verify the analytical calculations. Precise knowledge of the outerscale of the atmosphere at the ORM is needed to establish the dynamicalrange of the mirrors.
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| 5. |
- Owner-Petersen, Mette, et al.
(författare)
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Control strategy for the adaptive optics of the Euro50
- 2003
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Ingår i: Future Giant Telescopes. Proceedings of the SPIE. - : SPIE. - 081944619X ; 4840, s. 427-435
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Konferensbidrag (refereegranskat)abstract
- The scheme presently envisaged for the EURO50 adaptive optics ispresented. The Euro50 adaptive optics will primarily work with laserguide stars (LGSs) and control of either one or two deformable mirrors(SCAO and DCAO respectively), but operation using a natural guide star(NGS) is also foreseen. The point spread function (PSF) for SCAOoperation using a single NGS is evaluated. An algorithm for optimalcontrol of the deformable mirrors (DMs) using LGSs and Shack-Hartmanwavefront sensors is presented and commented upon. It is an extension ofa recently developed algorithm for optimal control using NGSs andworking in the spatial Fourier domain. In addition the concept of avirtual wavefront sensor is introduced to overcome the difficulty intransmitting a large number (37) of LGSs to the final DCAO focus withboth adequate field and adequate aberrations. The expected performanceis estimated in form of maps of the Strehl ratio versus field angleusing a standard seven layer atmospheric model for the Observatorio delRoque de los Muchachos (ORM) site on la Palma for the case of the outerscale being either 20 m (nominal for ORM) or infinity (Kolmogorov - mostpessimistic case).
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