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Dimpled scalar vortex coronagraph laboratory demonstration

Niyati Desai, Garreth Ruane, Susan Redmond, Dimitri Mawet, Eugene Serabyn, Bertrand Mennesson

Abstract

Achieving the Habitable Worlds Observatory (HWO) goal of 10^-10 contrast at a separation of 3 $λ$/D across a 20% bandwidth requires coronagraph focal plane masks with both broadband high contrast performance and high planet throughput. Scalar vortex coronagraphs (SVCs) offer a promising alternative to polarization-sensitive vector vortex designs but face chromatic limitations. This work presents the latest laboratory demonstrations of second-generation scalar vortex prototypes that incorporate radial phase dimples to improve broadband starlight suppression. We compare these new "dimpled" sawtooth masks to previous-generation scalar designs through high-contrast imaging experiments on the In-Air Coronagraph Testbed. Using electric field conjugation, we achieve near testbed-limited contrasts across both narrow (2%) and broadband (10%) spectral ranges. We report the best in-air contrasts achieved to date for scalar vortex masks across narrow and broadband spectral ranges and we also show that the dimpled vortex predicted bench-limited contrast performances for 2%, 10% and 18% bandwidths agree with the measured lab contrasts within a factor of two. These results highlight the potential of topographically achromatized scalar vortex masks as candidates for future space-based high-contrast imaging missions and mark a significant step toward polarization-independent coronagraphs capable of meeting HWO performance requirements.

Dimpled scalar vortex coronagraph laboratory demonstration

Abstract

Achieving the Habitable Worlds Observatory (HWO) goal of 10^-10 contrast at a separation of 3 /D across a 20% bandwidth requires coronagraph focal plane masks with both broadband high contrast performance and high planet throughput. Scalar vortex coronagraphs (SVCs) offer a promising alternative to polarization-sensitive vector vortex designs but face chromatic limitations. This work presents the latest laboratory demonstrations of second-generation scalar vortex prototypes that incorporate radial phase dimples to improve broadband starlight suppression. We compare these new "dimpled" sawtooth masks to previous-generation scalar designs through high-contrast imaging experiments on the In-Air Coronagraph Testbed. Using electric field conjugation, we achieve near testbed-limited contrasts across both narrow (2%) and broadband (10%) spectral ranges. We report the best in-air contrasts achieved to date for scalar vortex masks across narrow and broadband spectral ranges and we also show that the dimpled vortex predicted bench-limited contrast performances for 2%, 10% and 18% bandwidths agree with the measured lab contrasts within a factor of two. These results highlight the potential of topographically achromatized scalar vortex masks as candidates for future space-based high-contrast imaging missions and mark a significant step toward polarization-independent coronagraphs capable of meeting HWO performance requirements.
Paper Structure (8 sections, 4 figures, 1 table)

This paper contains 8 sections, 4 figures, 1 table.

Table of Contents

  1. Introduction
  2. A Review of Scalar Vortex Coronagraphs
  3. Dimpled Vortex Design, Manufacturing and Testing
  4. Results
  5. Discussion and Conclusion
  6. Acknowledgments
  7. Disclosures
  8. Code and Data Availability

Figures (4)

  • Figure 1: (left) Two-dimensional map of the desired spatially-varying phase shift showing central $\pi$ shifted region. (middle) Three-dimensional schematic of dimpled scalar vortex design. (right) A microscope image of the mask manufactured in fused silica.
  • Figure 2: Electric field conjugation (EFC) was performed across a 10% band with 5 subbands shown here. The estimated and measured intensity match closely and the residual speckles are more visible at offset wavelengths.
  • Figure 3: In-air coronagraphic testbed dark holes (from left to right): narrowband (2%), broadband (10%), and broadband (18%). Dark holes were dug from 3 - 18 $\lambda/D$ and scored between 3 - 10 $\lambda/D$.
  • Figure 4: In-air coronagraphic testbed V-curve demonstrating contrast as a function of wavelength offset.