Phase sensor for solar adaptive-optics

Big Bear Solar Observatory, 40386 North Shore Lane, Big Bear City, CA 92314-9672, USA
e-mail: kellerer@bbso.njit.edu

Received: 5 March 2011
Accepted: 13 April 2011

Abstract

Context. Wavefront sensing in solar adaptive-optics is currently done with correlating Shack-Hartmann sensors, although the spatial- and temporal-resolutions of the phase measurements are then limited by the extremely fast computing required to correlate the sensor signals at the frequencies of daytime atmospheric-fluctuations.

Aims. To avoid this limitation, a new wavefront-sensing technique is presented, that makes use of the solar brightness and is applicable to extended sources.

Methods. The wavefront is sent through a modified Mach-Zehnder interferometer. A small, central part of the wavefront is used as reference and is made to interfere with the rest of the wavefront.

Results. The contrast of two simultaneously measured interference-patterns provides a direct estimate of the wavefront phase, no additional computation being required. The proposed optical layout shows precise initial alignment to be the critical point in implementing the new wavefront-sensing scheme.