Spatial frequency domain model for adaptive optics compensation of segmented mirror misalignments and figure errors

Abstract

In addition to their essential function of providing atmospheric turbulence compensation, astronomical Adaptive Optical (AO) systems also supplement the role of active optics (aO) by providing some additional correction of the wavefront aberrations introduced by mirror mounting, alignment, thermal distortion and/or fabrication errors. This feature is particularly desirable for segmented mirror telescopes such as the Thirty Meter Telescope (TMT), but wavefront discontinuities across segment boundaries are challenging to properly sense and correct. In this paper we describe a fast, analytical, frequency domain model which may be used to study and quantify the above effects, and discuss a range of sample results obtained to support the development of the top-level requirements for the TMT primary mirror. In general, AO compensation of mirror segment piston errors is not particulary useful unless the deformable mirror (DM) interactuator spacing is equivalent to no more than one-half of a mirror segment diameter (when both of these dimensions are expressed in the same pupil plane). Effective AO compensation of mirror segment tip/tilt errors, or low order segment figure errors such as astigmatism, typically requires 3-4 DM actuators per mirror segment. These results illustrate the importance of quantifying and minimizing uncorrectable telescope wavefront errors when developing performance predictions for adaptive optical systems.

A conceptual design for the Thirty Meter Telescope adaptive optics systems

“…11 Extensive analysis and simulation work on ExAO systems is also proceeding, including detailed wave-optics end-to-end simulations of the AO architecture described in Section 4.4, as well as studies of the impact of M1 segment alignment, figure and reflectivity errors upon high-contrast imaging. 14,15 These simulations include the front-end AO system with a Pyramid WFS and a 128 by 128 DM, the diffraction suppression system (nuller) and the back-end interferometric WFS with a second 128 by 128 DM located in the nuller. The atmosphere model uses a 7 layer diffractive model to correctly account for the impact from scintillation with a time step of 0.5 msec.…”

“…Further details may be found in the related papers presented at this conference. [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]…”

The Simulation Platform of Adaptive Optics for the Extremely Large Telescope

“…Due to the complex and cost of the adaptive optics, it is very important to simulate the performance before construction [9]. Typically, the adaptive optics system is composed of at least one deformable mirror, possibly a tip/tilt mirror, a wavefront sensor, and a controller including a wavefront reconstructor.…”