Wavefront reconstruction algorithms and simulation results for multiconjugate adaptive optics on giant telescopes

Abstract

The very high-order multi-conjugate adaptive optics (MCAO) systems proposed for future giant telescopes will require new, computationally efficient, concepts for wavefront reconstruction. Advanced methods from computational linear algebra have recently been applied to this problem, and explicit simulations of MCAO wavefront reconstruction problems for 30-meter class telescopes are now possible using desktop personal computers. In this paper, we present sample simulation results obtained using these techniques to illustrate the trends in MCAO performance as the telescope aperture diameter increases from 8 to 32 meters. We consider systems based upon natural guidestars, sodium laser guidestars, and Rayleigh laser guidestars. The performance achieved by the first two classes of guidestars is similar, and the variation in their performance with respect to telescope size is very gradual over this range of aperture diameters. Next, we describe work in progress to adapt the minimum variance reconstruction algorithm, which is optimized for open-loop wavefront estimation, to the more realistic and meaningful case of closed-loop wavefront control. Finally, we summarize the current status of efforts to quantify the impact of sodium laser guide star (LGS) elongation on guidestar signal requirements for LGS AU systems on 30 meter class telescopes.

Solar tomography adaptive optics

“…For a MCAO system, wide-field atmospheric turbulence compensation is accomplished by means of multiple DMs that apply phase/wavefront adjustments in two or more planes optically conjugate to the distinct ranges along the propagation path. The information to drive these DMs is obtained from WFS measurements of multiple guide stars via a tomographic wave-front reconstruction algorithm [28].…”

Shack-Hartmann wavefront sensing with elongated sodium laser beacons: centroiding versus matched filtering

“…The LGS angular spot size along the elongation direction at the edge of the TMT exceeds three times the angular size of the seeing-limited transverse laser beacon intensity at the laser focus on the sodium layer. Possible approaches to defeat this effect include (i) radial-format CCDs 8 combined with a noise-optimal spot position estimation algorithm 4,5 and (ii) dynamic refocusing. We discussed the first approach.…”

“…4,5 The continuous subaperture average spot will be denoted i͑ x , y ͒, where x and y denote the angular position coordinates in the subaperture focal plane along the horizontal and vertical directions. In the angular frequency domain, the subaperture spot spectrum will be denoted î͑u x , u y ͒, where u x and u y denote the angular frequency coordinates along the horizontal and vertical directions.…”

Adaptive optics requirements definition for TMT

“…Following a multi-year feasibility study phase 1,2,3,4,5 , TMT is poised to begin formal development of observatory and subsystem level requirements. The TMT adaptive optics subsystem functional requirement are proposed to be developed using an industry standard process 6,7 depicted in the functional cascade shown in the left-hand side of Figure 1.…”