Abstract
This paper presents a simultaneous multi-segmented mirror orientation test system (SMOTS) using localized sheared images. A CMOS camera captures images of reflected 2D sinusoidal patterns from the test mirrors as their orientation changes. Surface orientation is measured to within 0.8 µrad (0.16 arcseconds) for a flat mirror. In addition, we measure the variation of seven mirror segments simultaneously. Furthermore, SMOTS is applied to measure the orientation of two concave mirrors with an accuracy of 2.7 µrad (0.56 arcseconds). The measurement time for seven segments is 0.07 s. This technique can monitor the mirror segment orientation in an open/closed-loop for various optical setups.
Highlights
To see deeper into our Universe, scientists need to build larger telescopes [1,2]
A point spread function (PSF) is a well-known metric to judge the image quality, and it can be an indicator for alignment [5]
This mathematical approach needs an influence parameter for each segment. This method does not have a one-to-one correspondence between image quality and segment orientation
Summary
To see deeper into our Universe, scientists need to build larger telescopes [1,2]. The use of a multi-segment primary mirror is very useful to achieve this for large aperture telescopes, and has fabrication advantages [3,4]. Once you measure the distance from the mirror to the pattern, the orientation angle is calculated from the phase shift of the sinusoidal pattern. From the amplitude of the Fourier transform of the sheared sinusoidal pattern, we calculate the amount of phase difference between the reference and the shifted fringe images. A short period has better sensitivity, but in this case, the phase difference could face 2π ambiguity for a smaller angle change To resolve this problem, a multiplexing method to include many frequency signals in one picture can be adopted. A few multiplexed sinusoidal patterns with different periods (not a factor of each other) will reduce such ambiguity as they are clearly distinguishable in the Fourier domain and can be independently processed using the same SMOTS data processing
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