Quantitative Evaluation of Continuous Diffractive Baffles for Heliospheric Imagers

Wide-angle heliospheric imagers such as those carried on the SMEI and STEREO spacecraft require highly effective baffle systems to exclude diffracted light from the solar disk as well as other sources of stray light. Buffington (2000, Appl. Opt. 39, 2683-2686) has proposed replacing multi-vane baffle systems with a curved surface that can be thought of as the limiting case of closely spaced vanes. Buffington's experimental data showed that the diffractive performance of a continuous baffle is consistent with the limiting form expected from multi-vane diffraction on heuristic grounds, but a detailed prediction was not possible because multi-vane diffraction calculations assume that the diffractive edges act independently, an assumption that breaks down for a continuous surface. I present analytic calculations of diffraction from a curved surface and use them to evaluate the effectiveness of continuous-surface baffles for heliospheric imagers.