| Titre : |
Group delay tracking with the Sydney University Stellar Interferometer |
| Type de document : |
texte imprimé |
| Auteurs : |
Peter Roderick Lawson (1963-....), Auteur ; University of Sydney, Organisme de soutenance |
| Editeur : |
s.l. : [s.n.] |
| Année de publication : |
1993 |
| Importance : |
1 vol. (xi-227 p.) : ill. en coul. ; 30 cm |
| Présentation : |
ill. en coul. |
| Format : |
30 cm |
| Note générale : |
Thesis : Astronomy : University of Sydney. School of Physics : 1993 . - PPN 283290196. - Résumé paru dans Publications of the Astronomical Society of the Pacific vol. 106, pp. 917-917, 1994 August. Il est accessible en ligne sur le site de l'IOP à l'adresse : https://iopscience.iop.org/article/10.1086/133461 |
| Langues : |
Anglais (eng) |
| Tags : |
Interférométrie -- Thèses et écrits académiques Sydney University Stellar Interferometer (SUSI) Interferometry -- Thesis |
| Index. décimale : |
522 Astronomie - Techniques, procédés, appareils, équipement, matériel |
| Résumé : |
"The Sydney University Stellar Interferometer (SUSI) is a long-baseline optical interferometer, located at the Paul Wild Observatory near Narrabri, in northern New South Wales, Australia. It is designed to measure stellar angular diameters using light collected from a pair of siderostats, with eleven fixed siderostats giving separations between 5 and 640 m. Apertures smaller than Fried’s coherence length, r0, are used and active tilt-compensation is employed. This ensures that when the beams are combined in the pupil plane the wavefronts are parallel. Fringes are detected when the optical path-difference between the arriving wavefronts is less than the coherence length of light used for the observation. While observing a star it is necessary to compensate for the changes in pathlength due to the earth’s rotation, and moreover to compensate for changes due to the effects of atmospheric turbulence. Tracking the path-difference permits an accurate calibration of the fringe visibility, allows
larger bandwidths to be used, and therefore improves the sensitivity of the instrument. I describe a fringe tracking system which I developed for SUSI, based on group delay tracking with a PAPA (Precision Analog Photon Address) detector. The method uses short exposure images of fringes, 1-10 ms, detected in the dispersed spectrum of the combined starlight. The number of fringes across a fixed bandwidth of channeled spectrum is directly proportional to the path-difference between the arriving wavefronts. A Fast Fourier Transform, implemented in hardware, is used to calculate the spatial power spectrum of the fringes, thereby locating the delay. The visibility loss due to a non-constant fringe spacing on the detector is investigated, and the improvements obtained from rebinning the photon data are shown. The low light level limitations of group delay tracking are determined theoretically with emphasis on the probability of tracking error, rather than the signal-to-noise ratio. Experimental results from both laboratory studies and stellar observations are presented. These show the first closed-loop operation of a fringe tracking system based on observations of group delay with a stellar interferometer. The Sydney University PAPA camera, a photon-counting array detector developed for use in this work, is also described. The design principles of the PAPA camera are outlined and the potential sources of image artifacts are identified. The artifacts arise from the use of optical encoding with Gray coded masks, and the new camera is distinguished by its mask-plate, which was designed to overcome artifacts due to vignetting. New lens mounts are also presented which permit a simplified optical alignment without the need for tilt-plates. The performance of the camera is described" |
| Note de contenu : |
Bibliogr. p. 221-228 |
Group delay tracking with the Sydney University Stellar Interferometer [texte imprimé] / Peter Roderick Lawson (1963-....), Auteur ; University of Sydney, Organisme de soutenance . - s.l. : [s.n.], 1993 . - 1 vol. (xi-227 p.) : ill. en coul. ; 30 cm : ill. en coul. ; 30 cm. Thesis : Astronomy : University of Sydney. School of Physics : 1993 . - PPN 283290196. - Résumé paru dans Publications of the Astronomical Society of the Pacific vol. 106, pp. 917-917, 1994 August. Il est accessible en ligne sur le site de l'IOP à l'adresse : https://iopscience.iop.org/article/10.1086/133461 Langues : Anglais ( eng)
| Tags : |
Interférométrie -- Thèses et écrits académiques Sydney University Stellar Interferometer (SUSI) Interferometry -- Thesis |
| Index. décimale : |
522 Astronomie - Techniques, procédés, appareils, équipement, matériel |
| Résumé : |
"The Sydney University Stellar Interferometer (SUSI) is a long-baseline optical interferometer, located at the Paul Wild Observatory near Narrabri, in northern New South Wales, Australia. It is designed to measure stellar angular diameters using light collected from a pair of siderostats, with eleven fixed siderostats giving separations between 5 and 640 m. Apertures smaller than Fried’s coherence length, r0, are used and active tilt-compensation is employed. This ensures that when the beams are combined in the pupil plane the wavefronts are parallel. Fringes are detected when the optical path-difference between the arriving wavefronts is less than the coherence length of light used for the observation. While observing a star it is necessary to compensate for the changes in pathlength due to the earth’s rotation, and moreover to compensate for changes due to the effects of atmospheric turbulence. Tracking the path-difference permits an accurate calibration of the fringe visibility, allows
larger bandwidths to be used, and therefore improves the sensitivity of the instrument. I describe a fringe tracking system which I developed for SUSI, based on group delay tracking with a PAPA (Precision Analog Photon Address) detector. The method uses short exposure images of fringes, 1-10 ms, detected in the dispersed spectrum of the combined starlight. The number of fringes across a fixed bandwidth of channeled spectrum is directly proportional to the path-difference between the arriving wavefronts. A Fast Fourier Transform, implemented in hardware, is used to calculate the spatial power spectrum of the fringes, thereby locating the delay. The visibility loss due to a non-constant fringe spacing on the detector is investigated, and the improvements obtained from rebinning the photon data are shown. The low light level limitations of group delay tracking are determined theoretically with emphasis on the probability of tracking error, rather than the signal-to-noise ratio. Experimental results from both laboratory studies and stellar observations are presented. These show the first closed-loop operation of a fringe tracking system based on observations of group delay with a stellar interferometer. The Sydney University PAPA camera, a photon-counting array detector developed for use in this work, is also described. The design principles of the PAPA camera are outlined and the potential sources of image artifacts are identified. The artifacts arise from the use of optical encoding with Gray coded masks, and the new camera is distinguished by its mask-plate, which was designed to overcome artifacts due to vignetting. New lens mounts are also presented which permit a simplified optical alignment without the need for tilt-plates. The performance of the camera is described" |
| Note de contenu : |
Bibliogr. p. 221-228 |
|
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