title: Fizeau interferometric cophasing of segmented mirrors.
abstract: Segmented mirror telescope designs address issues of mechanical rigidity, but introduce the problem of aligning, or cophasing, the separate segments to conform to the optimum mirror shape. While several solutions have been widely adopted, a few difficulties persist - the introduction of non-common path errors and an artificial division of the problem into coarse and fine regimes involving separate dedicated hardware solutions. Here we propose a novel method that addresses many of these issues. Fizeau Interferometric Cophasing of Segmented Mirrors (FICSM) uses non-redundant sparse aperture interferometry to phase mirror segments to interferometric precision using unexceptional science hardware. To show the potential of this technique we numerically simulate conditions on NASA's James Webb Space Telescope (JWST), showing that the FICSM method has the potential to phase the primary mirror from an initial state with segment-to-segment pistons as large as 150 microns and tilts as large as 0.5 arcseconds, to produce a final state with 0.75 nm rms segment-to-segment pistons and 3.7 mas rms segment tilts. The image undergoes monotonic improvement during this process. This results in a rms wavefront error of 3.65 nm, well below the 100 nm requirement of JWST's coarse phasing algorithm.
authors: Sydney Institute for Astronomy, School of Physics, University of Sydney, NSW 2006, Australia. a.cheetham@physics.usyd.edu.au
authors: Anthony C
authors: AC
authors: Cheetham
authors: Peter G
authors: PG
authors: Tuthill
authors: Anand
authors: A
authors: Sivaramakrishnan
authors: James P
authors: JP
authors: Lloyd