Laboratory experiment of a coronagraph based on step-transmission filters

摘要

This paper presents the first results of a step-transmission-filter based coronagraph in the visible wavelengths. The primary goal of this work is to demonstrate the feasibility of the coronagraph that employs step-transmission filters, with a required contrast in the order of better than 10~(-5) at an angular distance larger than 4λ/D. Two 13-step-transmission filters were manufactured with 5% transmission accuracy. The precision of the transmitted wave distortion and the coating surface quality were not strictly controlled at this time. Although in perfect case the coronagraph can achieve theoretical contrast of 10~(-10), it only delivers 10~(-5) contrast because of the transmission error, poor surface quality and wave-front aberration stated above, which is in our estimation. Based on current techniques, step-transmission filters with better coating surface quality and high-precision transmission can be made. As a follow-up effort, high-quality step-transmission filters are being manufactured, which should deliver better performance. The step-transmission-filter based coronagraph has the potential applications for future high-contrast direct imaging of earth-like planets.