A reflective Gaussian coronagraph for ExAO: laboratory performance

Ryeojin Park; Laird M. Close; Nick Siegler; Eric L. Nielsen; Thomas Stalcup

doi:10.1117/12.670802

Abstract

We report laboratory results of a coronagraphic testbed to assess the intensity reduction differences between a "Gaussian" tapered focal plane coronagraphic mask and a classical hard-edged "Top Hat" function mask at Extreme Adaptive Optics (ExAO) Strehl ratios of ~94%. However, unlike a traditional coronagraph design, we insert a reflective focal plane mask at 45^o to the optical axis and used a "spot of Arago blocker" (axicon stop) before a final image in order to block additional mask edge-diffracted light. The testbed simulates the optical train of ground-based telescopes (in particular the 8.1m Gemini North telescope) and includes one spider vane and different mask radii (r= 1.9λ/D, 3.7λ/D, 7.4λ/D) and two types of reflective focal plane masks (hard-edged "Top Hat" and "Gaussian" tapered profiles). In order to investigate the performance of these competing coronagraphic designs with regard to extra-solar planet detection sensitivity, we utilize the simulation of realistic extra-solar planet populations (Nielsen et al. 2006). With an appropriate translation of our laboratory results to expected telescope performance, a "Gaussian" tapered mask radius of 3.7λ/D with an axicon stop performs best (highest planet detection sensitivity). For a full survey with this optimal design, the simulation predicts ~30% more planets detected compared to a similar sized "Top Hat" function mask with an axicon stop. Using the best design, the "point contrast ratio" between the stellar PSF peak and the coronagraphic PSF at 10λ/D (0.4" in H band if D = 8.1m) is 1.4 x 10⁶. This is ~10 times higher than a classical Lyot "Top Hat" coronagraph.

Citation Download Citation

Ryeojin Park, Ryeojin Park, Laird M. Close, Laird M. Close, Nick Siegler, Nick Siegler, Eric L. Nielsen, Eric L. Nielsen, Thomas Stalcup, Thomas Stalcup, "A reflective Gaussian coronagraph for ExAO: laboratory performance", Proc. SPIE 6272, Advances in Adaptive Optics II, 62724V (28 June 2006); doi: 10.1117/12.670802; https://doi.org/10.1117/12.670802

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