  An adaptive optics (AO) system based on stochastic parallel gradient descent
(SPGD) algorithm is proposed to reduce the speckle noises in the optical system
of stellar coronagraph in order to further improve the contrast. The principle
of SPGD algorithm is described briefly and a metric suitable for point source
imaging optimization is given. The feasibility and good performance of SPGD
algorithm is demonstrated by experimental system featured with a 140-actuators
deformable mirror (DM) and a Hartmann- Shark wavefront sensor. Then the SPGD
based AO is applied to a liquid crystal array (LCA) based coronagraph. The LCA
can modulate the incoming light to generate a pupil apodization mask in any
pattern. A circular stepped pattern is used in our preliminary experiment and
the image contrast shows improvement from 10^-3 to 10^-4.5 at angular distance
of 2{\lambda}/D after corrected by SPGD based AO.
