From: Ronald C. Blue (ron_at_u2ai.us)
Date: Wed Nov 23 2005 - 08:21:52 PST
> PHYSICS NEWS UPDATE
> The American Institute of Physics Bulletin of Physics News
> Number 755 November 23, 2005 by Phillip F. Schewe, Ben Stein, and
> Davide Castelvecchi
>
> OPTICAL VORTEX---TRYING TO LOOK AT EXTRASOLAR PLANETS DIRECTLY. A
> new optical device might allow astronomers to view extrasolar
> planets directly without the annoying glare of the parent star. It
> would do this by "nulling" out the light of the parent star by
> exploiting its wave nature, leaving the reflected light from the
> nearby planet to be observed in space-based detectors. About ten
> years ago the presence of planets around stars other than our sun
> was first deduced by the very tiny wobble in the star's spectrum of
> light imposed by the mutual tug between the star and its satellite.
> Since then more than 100 extrasolar planets have been detected in
> this way. Also, in a few cases the slight diminution in the star's
> radiation caused by the transit of the planet across in front of the
> star has been observed.
> Many astronomers would, however, like to view the planet directly, a
> difficult thing to do. Seeing the planet next to its bright star
> has been compared to trying to discern, from a hundred meters away,
> the light of a match held up next to the glare of an automobile's
> headlight. The approach taken by Grover Swartzlander and his
> colleagues at the University of Arizona is to eliminate the star's
> light by sending it through a special helical-shaped mask, a sort of
> lens whose geometry resembles that of a spiral staircase turned on
> its side. The process works in the following way: light passing
> through the thicker and central part of the mask is slowed down.
> Because of the graduated shape of the glass, an "optical vortex" is
> created: the light coming along the axis of the mask is, in effect,
> spun out of the image. It is nulled, as if an opaque mask had been
> placed across the image of the star, but leaving the light from the
> nearby planet unaffected.
> The idea of an optical vortex has been around for many years, but it
> has never been applied to astronomy before. In lab trials of the
> optical vortex mask, light from mock stars has been reduced by
> factors of 100 to 1000, while light from a nearby "planet" was
> unaffected (see (see figure at http://www.aip.org/png/2005/241.htm
> ). Attaching their device to a telescope on Mt. Lemon outside
> Tucson, Arizona, the researchers took pictures of Saturn and its
> nearby rings to demonstrate the ease of integrating the mask into
> telescopic imaging system. This is, according to Swartzlander
> (520-626-3723, grovers_at_optics.arizona.edu), a more practical
> technique than merely attempting to cover the star's image, as is
> done in coronagraphs, devices for observing our sun's corona by
> masking out the disk of the sun. It could fully come into its own
> on a project like the Terrestrial Planet Finder, or TPF, a proposed
> orbiting telescope to be developed over the coming decade and
> designed to image exoplanets. (Foo et al., Optics Letters, 15
> December 2005; summary of articles related to optical vortex at
> http://www.u.arizona.edu/~grovers)
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