Phasing Of Segmented Telescopes Research Articles

Fresnel phasing of segmented mirror telescopes

Shack-Hartmann (S-H) phasing of segmented telescopes is based upon a physical optics generalization of the geometrical optics Shack-Hartmann test, in which each S-H lenslet straddles an intersegment edge. For the extremely large segmented telescopes currently in the design stages, one is led naturally to very large pupil demagnifications for the S-H phasing cameras. This in turn implies rather small Fresnel numbers F for the lenslets; the nominal design for the Thirty Meter Telescope calls for F=0.6. For such small Fresnel numbers, it may be possible to eliminate the lenslets entirely, replacing them with a simple mask containing a sparse array of clear subapertures and thereby also eliminating a number of manufacturing problems and experimental complications associated with lenslets. We present laboratory results that demonstrate the validity of this approach.

Rolled edges and phasing of segmented telescopes

To achieve the diffraction limit, the segments in a segmented telescope must be correctly aligned to a fraction of a wavelength. This alignment is performed via optical measurements using starlight. We investigate the piston degree of freedom or phasing of the segments and the impact of rolled segment edges on the accuracy of the optical alignment. Three models for edge profiles are developed and fit to data from optic manufacturers. These profiles are then used, along with a simplified model of a Shack-Hartmann optical sensor, to determine their impact on phasing accuracy. The results can help estimate the residual phasing error and set requirements on segment polishing.

On-sky performance of the Zernike phase contrast sensor for the phasing of segmented telescopes

On-sky performance of the Zernike phase contrast sensor for the phasing of segmented telescopes

Zernike phase sensor for phasing of segmented telescopes

We study an adaptive dynamical feedback system for phasing of segmented mirrors. The system, which combines a Zernike wave front sensor with a feedback loop, is shown to be capable of separating (static) misalignment errors of segmented mirrors from (dynamical) atmospheric turbulence. Our numerical simulations establish that it can retrieve multi-wave segment misalignment error in the presence of large-amplitude atmospheric phase distortion.