Cool Stars 14 - Submitted Abstract # 306
This version created on 05 October 2006

Coronagraph experiments with dynamic range absorption by pre-optics


Jun Nishikawa, NAOJ
Naoshi Murakami, NAOJ
Lyu Abe, NAOJ
Takayuki Kotani, MPIR
Motohide Tamura, NAOJ
Yokochi Kaito, Tokyo University of Agricalture and Technology 
Takashi Kurokwa, Tokyo University of Agricalture and Technology 
Alexander Tavrov, NAOJ
Mitsuo Takeda, The University of Electro-Communications

A novel method to absorb a part of the required dynamic range is
developed.  It works as pre-optics infront of any coronagraph.  It
consists of an unbalanced nulling interferometer and an adaptive
optics with two defromable mirrors.  It reduces the speckle level from
1E-8 caused by a lambda/1000  wavefront to 1E-10  by kambda/10000  and
the central star intensity by 1/100.  Because the quantity of
wavefront errors at the AO and the coronagraph is converted by a
reduction factor of the unbalanced nulling interferometer, the
required wavefront error level of lambda/10000  can be achieved by
lambda/1000  optics with the reduction factor of 10.  A downstream
coronagraph is required to achieve the rest of the dynamic range of
1E-8 which can be achieved by lambda/1000  level optics.  A
common-path AIC is a candidate of the downstream coronagraph which
consists of a 3D Sagnac nulling interferometer using achromatic
geometric phase shift by mirror reflections.  

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