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| Paper: |
Active Optical Control of Quasi-Static Aberrations for ATST |
| Volume: |
463, 2nd ATST-EAST Workshop in Solar Physics: Magnetic Fields from the Photosphere to the Corona |
| Page: |
315 |
| Authors: |
Johnson, L. C.; Upton, R.; Rimmele, T. R.; Hubbard, R.; Barden, S. C. |
| Abstract: |
The Advanced Technology Solar Telescope (ATST) requires active control
of quasi-static telescope aberrations in order to achieve the image
quality set by its science requirements. Four active mirrors will be
used to compensate for optical misalignments induced by changing
gravitational forces and thermal gradients. These misalignments
manifest themselves primarily as low-order wavefront aberrations that
will be measured by a Shack-Hartmann wavefront sensor. When operating
in closed-loop with the wavefront sensor, the active optics control
algorithm uses a linear least-squares reconstructor incorporating
force constraints to limit force applied to the primary mirror while
also incorporating a neutral-point constraint on the secondary mirror
to limit pointing errors. The resulting system compensates for
astigmatism and defocus with rigid-body motion of the secondary mirror
and higher-order aberrations with primary mirror bending modes. We
demonstrate this reconstruction method and present simulation results
that apply the active optics correction to aberrations generated by
finite-element modeling of thermal and gravitational effects over a
typical day of ATST operation. Quasi-static wavefront errors are
corrected to within limits set by wavefront sensor noise in all cases
with very little force applied to the primary mirror surface and
minimal pointing correction needed. |
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