Study of Coronagraphic Techniques

Abstract

Abstract. SAO has set up a testbed to study coronagraphic techniques, starting with Labeyrie's multi-step speckle reduction technique. This technique expands the general concept of a coronagraph by incorporating a speckle corrector (phase and/or amplitude) in combination with a second occulter for speckle light suppression. The correction function is derived applying the phase diversity method on images taken in focus and slightly out-of-focus. The occulter masks for the testbed will initially be produced lithographically. However, in a parallel program we are studying a new manufacturing method. This method utilizes focussed ion beams and will directly mill the mask shape into absorbing material deposited on a transparent substrate.

Precise wavefront correction with an unbalanced nulling interferometer for exo-planet imaging coronagraphs

“…Similarities can be found with previous studies, i.e. pre-optics by a balanced nulling interferometer (Nishikawa et al 2005;, coronagraphic pre-optics with non-zero amplitude distribution in the pupil after an interference and complex amplitude correction (Abe et al 2006), and a multiple-stage wavefront correction by commercial quality AO systems (Tolls et al 2005).…”

“…Wavefront phase control by an adaptive optics (AO) system can reduce the halo intensity of a limited area, called "dark hole" (Malbet et al 1995). Multiple-stage coronagraphs (Aime & Soummer 2004;Tolls et al 2005), and combinations of these methods, or pre-optics schemes have been proposed to achieve a higher dynamic range (Nishikawa et al 2005;Abe et al 2006). …”

“…In addition, the wavefront stability of the entire telescope system must be guaranteed during this time lapse. A multiplestage coronagraph that reduces speckles with AO at every stage (Tolls et al 2005) faces the same problem. In the case of multiple stages for approaches using nulling coronagraphs or nulling interferometers, no wavefront sensing was previously considered (e.g.…”