137 research outputs found
Kalman Filter Estimation for Focal Plane Wavefront Correction
Space-based coronagraphs for future earth-like planet detection will require
focal plane wavefront control techniques to achieve the necessary contrast
levels. These correction algorithms are iterative and the control methods
require an estimate of the electric field at the science camera, which requires
nearly all of the images taken for the correction. We demonstrate a Kalman
filter estimator that uses prior knowledge to create the estimate of the
electric field, dramatically reducing the number of exposures required to
estimate the image plane electric field. In addition to a significant reduction
in exposures, we discuss the relative merit of this algorithm to other
estimation schemes, particularly in regard to estimate error and covariance. As
part of the reduction in exposures we also discuss a novel approach to
generating the diversity required for estimating the field in the image plane.
This uses the stroke minimization control algorithm to choose the probe shapes
on the deformable mirrors, adding a degree of optimality to the problem and
once again reducing the total number of exposures required for correction.
Choosing probe shapes has been largely unexplored up to this point and is
critical to producing a well posed set of measurements for the estimate.
Ultimately the filter will lead to an adaptive algorithm which can estimate
physical parameters in the laboratory and optimize estimation.Comment: 14 pages, 9 figures, SPIE Astronomical Telescopes and Instrumentation
2012 conference proceedings. Journal version at arXiv:1301.382
Rectangular-Mask Coronagraphs for High-Contrast Imaging
We present yet another new family of masks for high-contrast imaging as
required for the to-be-built terrestrial planet finder space telescope. The
``best'' design involves a square entrance pupil having a 4-vane spider, a
square image-plane mask containing a plus-sign shaped occulter to block the
starlight inside 0.6 lambda/D, and a Lyot-plane mask consisting of a
rectangular array of rectangular opennings. Using Fraunhofer analysis, we show
that the optical system can image a planet 10^{-10} times as bright as an
on-axis star in four rectangular regions given by {(xi,zeta): 1.4 < | xi | <
20, 1.4 < | zeta | < 20}.
Since the design involves an image plane mask, pointing error is an issue. We
show that the design can tolerate pointing errors of about 0.05 lambda/D.
The inclusion of a 4-vane spider in the entrance pupil provides the
possibility to build a mirror-only on-axis system thereby greatly reducing the
negative effects of polarization.
Each of the masks can be realized as two masks consisting of stripes of
opaque material with the stripes oriented at right angles to each other. We
call these striped masks barcode masks. We show that it is sufficient for the
barcode masks by themselves to provide 10^{-5} contrast. This then guarantees
that the full system will provide the required 10^{-10} contrast.Comment: 12 pages, 5 figure
Shaped pupil design for the Gemini Planet Imager
The Gemini Planet Imager (GPI) is an instrument designed for the Gemini South
telescope to image young Jupiter-mass planets in the infrared. To achieve the
high contrast needed for this, it employs an apodized pupil Lyot coronagraph
(APLC) to remove most of the starlight. Current designs use a
partially-transmitting apodizer in the pupil; we examine the use of binary
apodizations in the form of starshaped shaped pupils, and present a design that
could achieve comparable performance, along with a series of design guidelines
for creating shaped pupil versions of APLCs in other systems.Comment: 20 pages, 7 figures, accepted for publication in Ap
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