Jun NISHIKAWA^1,2* and Naoshi MURAKAMI^3,4

¹Division of Optical and Infrared Astronomy, National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588, Japan
²School of Physical Sciences, Graduate University for Advanced Studies, Mitaka, Tokyo 181-8588, Japan
³Division of Applied Physics, Faculty of Engineering, Hokkaido University, Sapporo 060-8628, Japan
⁴Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, U.S.A.

(Received May 13, 2013; Accepted September 25, 2013)

A nulling interferometer was proposed to achieve direct detection of extra-solar planets (exoplanets) by suppressing light from the central star using a pair of telescopes. Recently, the stellar coronagraph method has shown rapid progress, which uses an extended concept of the nulling interferometer within single telescope optics. A dynamic range larger than 1×10⁹ for the detection of Earth-like exoplanets can be attained by reducing diffraction patterns using the nulling coronagraph, and by suppressing speckle noise using an adaptive optics with an accuracy of λ/10000 rms. An unbalanced nulling interferometer (UNI), which is used as fore-optics, improves the wavefront sensing sensitivity and compensation level of the adaptive optics by a factor of 10. Consequently, the dynamic range of the coronagraph can also be improved by two orders of magnitude. The UNI is composed of a modified coronagraph or a traditional interferometer and magnifies the aberrations of incoming wavefronts.

Key words: interferometer, nulling, adaptive optics, coronagraph, wavefront, diffraction, exoplanet

^*E-mail address: jun.nishikawa@nao.ac.jp