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Optics Express

Optics Express

  • Editor: Andrew M. Weiner
  • Vol. 22, Iss. 11 — Jun. 2, 2014
  • pp: 12924–12934

Fizeau interferometric cophasing of segmented mirrors: experimental validation

Anthony Cheetham, Nick Cvetojevic, Barnaby Norris, Anand Sivaramakrishnan, and Peter Tuthill  »View Author Affiliations

Optics Express, Vol. 22, Issue 11, pp. 12924-12934 (2014)

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We present an optical testbed demonstration of the Fizeau Interferometric Cophasing of Segmented Mirrors (FICSM) algorithm. FICSM allows a segmented mirror to be phased with a science imaging detector and three filters (selected among the normal science complement). It requires no specialised, dedicated wavefront sensing hardware. Applying random piston and tip/tilt aberrations of more than 5 wavelengths to a small segmented mirror array produced an initial unphased point spread function with an estimated Strehl ratio of 9% that served as the starting point for our phasing algorithm. After using the FICSM algorithm to cophase the pupil, we estimated a Strehl ratio of 94% based on a comparison between our data and simulated encircled energy metrics. Our final image quality is limited by the accuracy of our segment actuation, which yields a root mean square (RMS) wavefront error of 25 nm. This is the first hardware demonstration of coarse and fine phasing an 18-segment pupil with the James Webb Space Telescope (JWST) geometry using a single algorithm. FICSM can be implemented on JWST using any of its scientic imaging cameras making it useful as a fall-back in the event that accepted phasing strategies encounter problems. We present an operational sequence that would co-phase such an 18-segment primary in 3 sequential iterations of the FICSM algorithm. Similar sequences can be readily devised for any segmented mirror.

© 2014 Optical Society of America

OCIS Codes
(120.3180) Instrumentation, measurement, and metrology : Interferometry
(120.6085) Instrumentation, measurement, and metrology : Space instrumentation
(110.1080) Imaging systems : Active or adaptive optics

ToC Category:
Instrumentation, Measurement, and Metrology

Original Manuscript: February 5, 2014
Revised Manuscript: April 4, 2014
Manuscript Accepted: April 10, 2014
Published: May 21, 2014

Anthony Cheetham, Nick Cvetojevic, Barnaby Norris, Anand Sivaramakrishnan, and Peter Tuthill, "Fizeau interferometric cophasing of segmented mirrors: experimental validation," Opt. Express 22, 12924-12934 (2014)

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