Kavli Affiliate: David Charbonneau
| First 5 Authors: Matthew C. H. Leung, Colby A. Jurgenson, Andrew Szentgyorgyi, Brian McLeod, Cem Onyuksel
| Summary:
The Hartmann test is a method used to measure the wavefront error in a focal
optical system, wherein a mask with a pattern of small holes is placed at the
system’s aperture stop. By taking an image at a defocused plane, the
differences between the ideal and real positions of the reimaged holes (called
the transverse ray aberrations) can be measured, which can then be used to
estimate the wavefront error. However, the Hartmann test is usually used with
an on-axis field. In this paper, we present a wavefront sensing method which
generalizes the classical Hartmann test for off-axis field angles and arbitrary
reference wavefronts. Our method involves taking images at two defocused
planes, and then using the real reimaged hole positions on both planes to
estimate the trajectories of rays from the system’s exit pupil, at which the
reference wavefront is situated. We then propagate the rays forward from the
reference wavefront to one of the two defocused planes, in order to find the
ideal reimaged hole positions, from which we can compute transverse ray
aberrations. We derive and solve a pair of nonlinear partial differential
equations relating transverse ray aberrations to wavefront error, using Zernike
decomposition and nonlinear least squares. Our method has been verified on
simulated data from the 7-lens f/2.25 red camera system of the GMT-Consortium
Large Earth Finder (G-CLEF), a high resolution optical echelle spectrograph
which will be a first light instrument for the Giant Magellan Telescope (GMT).
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