title: Phasing the mirror segments of the Keck telescopes: the broadband phasing algorithm.
abstract: To achieve its full diffraction limit in the infrared, the primary mirror of the Keck telescope (now telescopes) must be properly phased: The steps or piston errors between the individual mirror segments must be reduced to less than 100 nm. We accomplish this with a wave optics variation of the Shack-Hartmann test, in which the signal is not the centroid but rather the degree of coherence of the individual subimages. Using filters with a variety of coherence lengths, we can capture segments with initial piston errors as large as +/-30 microm and reduce these to 30 nm--a dynamic range of 3 orders of magnitude. Segment aberrations contribute substantially to the residual errors of approximately 75 nm.
authors.affiliation: Department of Physics and Astronomy, University of California, Irvine, California 92697, USA.
authors.forename: G
authors.initials: G
authors.lastname: Chanan
authors.forename: M
authors.initials: M
authors.lastname: Troy
authors.forename: F
authors.initials: F
authors.lastname: Dekens
authors.forename: S
authors.initials: S
authors.lastname: Michaels
authors.forename: J
authors.initials: J
authors.lastname: Nelson
authors.forename: T
authors.initials: T
authors.lastname: Mast
authors.forename: D
authors.initials: D
authors.lastname: Kirkman