The Theoretical Study Of The Six-region Phase Mask Coronagraph

In the field of detecting extrasolar planets and stars, the phase mask coronagraph drawsmuch attention because of its simple structure, high image quality. The paper simply introducesseveral common phase mask coronagraph, and then mentions the wide-band coronagraphs’advantages which include rich graphics information and the shorter imaging time of detectingextrasolar planets. We propose a new achromatic six-region phase mask coronagraph, and wesuggest a formula that can check whether the general phase mask can be a wide band phase mask.Through certification, we find that the sinusoidal phase mask coronagraph satisfy this formula.And we can say that this formula is useful to select phase mask coronagraph.In this paper, all our work is based on scalar diffraction theory. Through theoretical analysisand arithmetical operation, we find that the six-region phase mask has double periods in theangular direction. Then, by designing a reasonable structure, we can increase the coronagraph’swork band. At the same time, we explain why we choose six-region phase mask rather than fiveor seven. Furthermore, a six-level phase mask, as an example of the six-region phase mask, istheoretically investigated. According to2-D FFT, we find that the six-level phase mask has adeep elimination of starlight, good performance of achromatism and small inner working angle.As a single phase mask, the ratio of the remaining starlight of the six-level phase mask to thetotal incident starlight is less than10-3when the wavelength is between500nm and600nm.