Theoretical Performance Evaluation of Wide-band Diffraction-limited Coronagraph for the Next-generation Segmented Large Telescopes

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Abstract We investigate the raw-contrast mitigation ability of the spectroscopic coronagraph. We consider a mis-modulation of the complex amplitude by the transmissive focal-plane mask that is an intrinsic problem dependent on the spectral resolving power of a grating in a spectroscopic coronagraph, stellar angular radius, and non-common path error (NCP) that is due to chromaticity in the active wavefront control (WFC) as limitation factors to the performance of the spectroscopic coronagraph. Concerning the impact of the mis-modulation and stellar angular radius under the assumption with the an achromatic WFC, we found that the spectroscopic coronagraph potentially archives the raw-contrast of 1.25 × 10−10 at the spectral resolving power R greater than or equal to 2000 at 2 λ / D with the 10 pc distant solar radius 0.93 mas. It corresponds to approximately 0.03λ/D where the wavelength λ is 800 nm and telescope diameter D is 6 m. The inner working angle (defined as the minimal angular distance where planetary throughput is the maximal throughput) of the spectroscopic coronagraph is 2 λ / D . In addition, we found that the NCP limits the raw-contrast mitigation ability to 7.3 × 10−11 and 5.5 × 10−10 at 2 λ / D for 3% and 8% spectral bandwidths, respectively. We conclude that the spectroscopic coronagraph may serve as a promising method of broadband direct imaging of potentially habitable exoplanets located at small inner working angles with the next-generation segmented large telescopes.

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