Multi-conjugate Adaptive Optics for the Swedish ELT Investigation of the Effects of Laser Guide Stars at a finite Distance.

• 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.

Subject headings

NATURVETENSKAP  -- Fysik -- Astronomi, astrofysik och kosmologi (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences -- Astronomy, Astrophysics and Cosmology (hsv//eng)

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