Tunable liquid-crystal filter for solar imaging at the He I 1083-nm line

摘要

A Lyot-Ohman filter for imaging near the solar He I 1083-nm line is described. Fast and continuous spectral tunability is provided by nematic liquid crystals. This solid-state filter has a free spectral range of 2.35 nm and a spectral resolution of 0.135 nm at the operating wavelength of 1083 nm. A wide-fielded design was used for both static and electro-optic retarder elements, facilitating use in fast imaging systems. A first-light He I image of the Sun is presented. (C) 1997 Optical Society of America