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| 2. |
- Andersen, Torben, et al.
(författare)
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Euro50
- 2003
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Ingår i: Proceedings of the SPIE - The International Society for Optical Engineering. - : SPIE. - 1996-756X .- 0277-786X. ; 5382:1, s. 169-182
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Konferensbidrag (refereegranskat)abstract
- The Euro50 is a telescope for optical and infrared wavelengths. It has an aspherical primary mirror with a size of 50 meters and 618 segments. The optical configuration is of Gregorian type and the secondary mirror is deformable for adaptive optics. Observations can take place in prime focus, Gregorian foci, and Nasmyth foci using additional relay mirrors. The telescope provides seeing limited observations, partial adaptive optics with ground layer correction, single conjugate adaptive optics and dual-conjugate adaptive optics. For prime focus observations, a clam-shell corrector with a doublet lens is used. The primary mirror segments can be polished using the precessions polishing technique. "Live Optics" denotes the joint segment alignment system, secondary mirror control system, adaptive optics and main axes servos. An overview is given of the live optics architecture, including feedback from wavefront sensors for natural and laser guide stars, and from primary mirror segment edge sensors. A straw man concept of the laser guide star system using sum-frequency YAG lasers is presented together with a solution to the laser guide star perspective elongation problem. The structural design involves a large steel structure and a tripod of carbon fiber reinforced polymer to support the secondary mirror. Integrated models have been set up to simulate telescope performance. Results show that an enclosure is needed to protect the telescope against wind during observations. The enclosure is very large box-shaped steel structure
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| 3. |
- Andersen, Torben, et al.
(författare)
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The Euro50 Extremely Large Telescope
- 2003
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Ingår i: Future Giant Telescopes. Proceedings of the SPIE.. - 081944619X ; 4840, s. 214-225
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Konferensbidrag (refereegranskat)abstract
- Euro50 is a proposed optical telescope with an equivalent primary mirrordiameter of 50 m. Partners of the collaboration are institutes inSweden, Spain, Ireland, Finland, and the UK. The telescope will have asegmented primary mirror and an aplanatic Gregorian configuration withtwo elliptical mirrors. For a 50 m telescope there would be noeconomical advantage in going to a spherical primary. The size of theprimary mirror segments (2 m) has been selected on the basis of aminimization of cost. An adaptive optics system will be integrated intothe telescope. The telescope will have three operational modes: Seeinglimited observations, single conjugate adaptive observations in theK-band, and dual conjugate observations also in the K-band. An upgradeto adaptive optics also in the visible down to 500 nm is foreseen. Therewill be an enclosure to protect the telescope against adverse weatherand wind disturbances. Integrated simulation models are underdevelopment. The project time will be 10 years and the cost some 591MEuros.
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| 4. |
- 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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| 5. |
- 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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| 6. |
- Gontcharov, Alexander, et al.
(författare)
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Adaptive optics schemes for future extremely large telescopes
- 2002
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Ingår i: Optical Engineering. - : SPIE-Intl Soc Optical Eng. - 0091-3286. ; 41:5, s. 1065-1072
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Tidskriftsartikel (refereegranskat)abstract
- The adaptive optics for any telescope in the 25- to 100-m class will be complex. It is believed that adaptive optics should, to the maximum extent, be designed as an integrated part of a telescope. The proposed Swedish 50-m Extremely Large Telescope is considered here to illustrate the principle of integrated adaptive optics. Two alternative designs both using the Ritchey-Chretien telescope system and laser guide star (LGS) reference sources are presented. The first design employs trombone optics, which bring the laser guide star images back to the normal Ritchey-Chretien focal surface (referred to as the RC-focus) from the LGS focal surface (referred to as the LRC-focus), and a layer-oriented wavefront sensor system optically performing the averaging "shift and add" in the final focus. According to this procedure, sensed wavefronts are overlapped with a certain mutual shift and added for estimation of wavefront average slope values, resulting in actuator commands for driving the shape of the cleformable mirrors. The second design employs a numerical "shift and add" procedure and has two wavefront sensors. The first one performs LGS sensing in an intermediate focus (LRC-focus), giving the input data for an analytical algorithm for deriving the mirror deformations to correct for atmospheric turbulence. By using an artificial laser source at the intermediate focus, the shape of the second cleformable mirror is controlled by a second wavefront sensor in the final focus. The capability of the analytical algorithm to derive the mirror corrections from the measured wavefronts ensures proper functioning of the adaptive optics system. This system has a simpler optical design compared to the first design. (C) 2002 Society of Photo-Optical Instrumentation Engineers.
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| 7. |
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| 8. |
- Gontcharov, Alexander
(författare)
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Extremely Large Telescopes Optical Design and Wavefront Correction
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- An overview of the state of art within optical design of large astronomical telescopes is given. Recent advances within the field are presented. The importance of new computer-controlled mirror-polishing methods is emphasized. Some important aspects of atmospheric optics are presented together with current compensation methods using adaptive optics, with or without laser guide stars. An overview of wavefront sensing, wave-front reconstruction and techniques for compensation is given. Methods for optical design of large, optical telescopes with fast primary mirrors are presented in a systematic way. Three different approaches are outlined and commented. They include an algebraic method, a method based on optimization through ray tracing and an analytical method based on Fermat’s principle and the Abbe sine condition. Studies of optical designs for large telescopes with fast, spherical primary mirrors are examined and discussed. For two-mirror designs, an analytical method has been derived, using aberration control based on Fermat’s principle. Intrinsic apodization for design of extremely fast primary mirrors is analyzed. For four-mirror designs with spherical primary mirrors, a ray tracing approach has been chosen. A total of fifteen different four-mirror designs have been analyzed and discussed. For the 50 m optical telescope, Euro50, a two-mirror design was chosen. This optical design is presented in detail, together with the optical layout of an adaptive optical system that forms an integrated part of the telescope. An analysis of essential components of the Euro50 is given. Finally, an analytical approach is presented for control of two or more deformable mirrors for adaptive optics in extremely large telescopes for optical wavelengths. The same algorithms are used to evaluate and predict the performance of the adaptive optics for the Euro50.
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| 9. |
- Gontcharov, Alexander, et al.
(författare)
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Intrinsic apodization effect in a compact two-mirror system with a spherical primary mirror
- 2002
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Ingår i: Optical Engineering. - : SPIE-Intl Soc Optical Eng. - 0091-3286. ; 41:12, s. 3111-3115
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Tidskriftsartikel (refereegranskat)abstract
- In so-called compact two-mirror focusing and afocal systems the secondary mirror is situated at the paraxial focus of the spherical primary mirror. The peculiar conelike shape of the secondary is chosen to eliminate the spherical aberration. Thus the systems are stigmatic, but they have a great offence against the sine condition (OSC), creating uneven distribution of energy on the surface of the outgoing wavefront. There is a substantial concentration of energy toward the optical axis, similar to apodization of the pupil. Calculations of the point spread function (PSF) show that in such systems, the Airy disk is slightly enlarged (at most 20%) and the second maximum (the first bright ring) can be completely suppressed. The most effective suppression of the second and higher maxima in the diffraction pattern is obtained with an imposed central obscuration ratio of 0.5 and a primary mirror focal ratio of 2. Compact two-mirror afocal and focusing systems have intrinsic apodization, enabling modification of the diffraction pattern without the use of a variable transmission filter or coating at the pupil. (C) 2002 Society of Photo-Optical Instrumentation Engineers.
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