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Modal phase correction for large-aperture ground-based telescope with multi-guide stars

Abstract 135

Submitted by Vladimir LUKIN


L.A. Bolbasova, V.P. Lukin


Institute of Atmospheric Optics SB RAS, 1 Akademicheskii Av., Tomsk, Russia Tomsk State University, 36, Lenin Av., Russia, Tomsk


Simple analytical expressions for parameter Strehl of ground-based astronomical telescope: (i) without adaptive correction, (ii) phase correction with use single laser guide star, (iii) phase correction with use multi-guide stars (square matrix system of guide stars with variable number of elements) are obtained. Models of the vertical dependence of the structure parameter of refractive index of the turbulent atmosphere for various sites are used in the calculations. Requirements on bandwidth of adaptive optical system for effective correction are formulated. It leads to , where is a height of LGS formation, is a speed of light in the atmosphere, is the effective wind velocity, is time delay of adaptive optical system, is the isoplanatic angle for highest corrected mode. For the full phase correction it expressed as . If isoplanatic angle for the full phase correction at the observation in zenith be approximated as , where is coherence radius for plane wave, is the effective altitude of turbulent atmosphere. For the best conditions of an observation site it estimate to . In practice we are producing the partial or modal correction of image in large aperture ground-based telescope. Isoplanatic angles for several modes of the phase distortion with use various models of turbulence profile are calculation. The lowest modes of the phase distortion of wavefront (tilt and defocus) are sensitive to the outer scale of turbulence values. Isoplanatic angles decrease with increase number of mode. Finally, the chose a position of separate stars for multi-guide stars techniques for correction image in large-aperture telescopes are shown.