Department of Physics
is pleased to announce a Colloquium
with
(Report As Fulfillment Of the Requirement Of The Preliminary
Exam)
Weidong Yang
(Graduate student, Physics Department, Michigan
Technological Univ.)
Small
Phase Error Problems In Extra-Solar Planet Imaging And An Algorithm For Small Phase Retrieval Using Coronagraph
Abstract: Coronagraph technique has been regarded as one of the most
promising technique in the direct detection of the extra-solar planets or faint
light sources near a bright star. In coronagraph , the combination use of the
mask and Lyot_stop can reduce the intensity of the bright star’s halo
background to the order of magnitude of the targeted planet . However, we will
see in this talk that even the small phase errors over the aperture can degrade
the performance of coronagraph severely.
These small phase errors may come from the residual error after the Adaptive
Optics phase correction and will take some light energy away from the on-axis
beam and form the “sea” of speckles on the final imaged plane in a wide dynamic
range. So retrieval and correction of the small phase errors becomes important
in the coronagraph imaging.
Methods
using Inverse Fourier Transform in the phase retrieval problem are common and
fast like what Saxton and Gonsalvs did in their works, but these methods are
not applicable to the retrieval of the extreme small phase error that matters
to the coronagraph system with a Lyot-stop. In this talk , a possible
non-Fourier Transform method for the
small phase retrieval problem , that
should be suitable for the small phase retrieval using coronagraph , will be
discussed and some preliminary simulation results for the 1-D case will be
presented.
3:00 p.m., Fisher Hall 135
Monday, April 22, 2002