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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