{getToc} $title={Table of Contents}
Summary
A simplified theory of occulter performance is developed for multi-vane linear or corral-baffle occulters and multi-disk circular occulters, explaining quasi-achromatic fringes and identifying ideal envelopes and limits to performance.
Highlights
- Developed a successive plane wave (SPW) approximation for calculating diffraction scattering around multiple-edge occulters.
- Identified the ideal envelope for a multi-edge occulter as a circular-cross-section cylinder or ogive.
- Explained the quasi-achromatic fringes observed around multi-edge external occulters.
- Identified a fundamental limit to occulter performance within a prescribed instrument size and angular offset.
- Developed a formula indicating the highest number of edges useful for a given occulter geometry.
- Discussed the surprisingly good performance of conical-profile multi-disk coronagraph occulters.
- Explored the brightness and overall flux of the Arago spot formed by coherent interference around an occulter.
Key Insights
- The SPW approximation represents a "middle ground" solution for calculating diffraction scattering around multiple-edge occulters, suitable for understanding the behavior of multi-vane linear or corral-baffle occulters and multi-disk circular occulters.
- The ideal envelope for a multi-edge occulter is a circular-cross-section cylinder or ogive, which explains the quasi-achromatic fringes observed around multi-edge external occulters.
- The SPW approach identifies a fundamental limit to occulter performance within a prescribed instrument size and angular offset, explaining why high-n solutions and smooth occulters do not perform as well as predicted.
- A formula indicating the highest number of edges useful for a given occulter geometry is developed, which can inform future instrument designs in both linear and circular geometry.
- The surprisingly good performance of conical-profile multi-disk coronagraph occulters is due to the intermediate disks interacting with the extended wave field of diffracted light near the occulter.
- The Arago spot formed by coherent interference around an occulter is important for single-disk designs but negligible for multi-disk designs, where it is attenuated by the action of the n-1 disks preceding the last one.
- The incoherent concentration of diffracted light by the circular geometry of the occulter, even outside the Arago spot, is identified analytically, and conservative design estimation formulae are generated to estimate occulter performance.
Mindmap
If MindMap doesn't load, go to the Homepage and visit blog again or Switch to Android App (Under Development).
Citation
DeForest, C. E., Erickson, N. F., Beasley, M. N., Osterman, S. N., Smith, T. J., & Hanson, M. H. (2024). A Simplified Theory of External Occulters for Solar Coronagraphs (Version 1). arXiv. https://doi.org/10.48550/ARXIV.2412.21047