First-order performance evaluation of adaptive-optics systems for atmospheric-turbulence compensation in extended-field-of-view astronomical telescopes

Abstract

An approach is presented for evaluating the performance achieved by a closed-loop adaptive-optics system that is employed with an astronomical telescope. This method applies to systems incorporating one or several guide stars, a wave-front reconstruction algorithm that is equivalent to a matrix multiply, and one or several deformable mirrors that are optically conjugate to different ranges. System performance is evaluated in terms of residual mean-square phase distortion and the associated optical transfer function. This evaluation accounts for the effects of the atmospheric turbulence C"2(h) and wind profiles, the wave-front sensor and deformablemirror fitting error, the sensor noise, the control-system bandwidth, and the net anisoplanatism for a given constellation of natural and/or laser guide stars. Optimal wave-front reconstruction algorithms are derived that minimize the telescope's field-of-view-averaged residual mean-square phase distortion. Numerical results are presented for adaptive-optics configurations incorporating a single guide star and a single deformable mirror, multiple guide stars and a single deformable mirror, or multiple guide stars and two deformable mirrors.

Reconstruction Strategies for GeMS

“…In continuation of this work, we are currently investigating a full MV reconstructor and a constrained reconstructor as introduced by [11]. On the other hand, we are investigating different temporal filters, like predictive controllers, to evaluate the gain of such control laws.…”

Image quality with current adaptive optics instruments

“…Consequently, B. Ellerbroek has kindly generated a set of theoretical optical transfer functions (OTF) with a WFS geometry of D/d = 8 for the cases d/r 0 = 1 and 2 to compare with the COP experimental data. These predictions are based on analytical and covariance calculations in Ellerbroek (1994) which incorporate all the details of the AO system including the modal optimization Gendron & Léna 1994). Different corrections have been obtained by varying the rms WFS noise (from 0 to about 0.5 waves per subaperture) or the servo lag (translation from 0 to about one subaperture per time constant of the servo in a single turbulent layer We now define the scalar fcut as the spatial frequency cutoff at 40dB of the power spectrum.…”

“…One can find in the literature (Ellerbroek 1994;Wilson & Jenkins 1996 for recent examples) calculations of the mean correction achieved by an AO system running in some given turbulence conditions. The atmospheric coherence time t 0 and the atmospheric coherence length r 0 are two parameters used to describe these conditions.…”

Clearwidens the field for observations of the Sun with multi-conjugate adaptive optics

“…Supplemental wavefront sensors must be deployed to probe the optical aberrations over the targeted field of view in order to steer the DMs. This concept is known as multiconjugate adaptive optics (MCAO;Dicke 1975;Beckers 1987Beckers , 1988Ellerbroek 1994;Rigaut et al 2000;Fusco et al 2001;Tokovinin et al 2001). Stellar observations with MCAO were first carried out by the MCAO Demonstrator MAD at the Unit Telescope 3 of the Very Large Telescope (Marchetti et al 2007).…”