TUNABLE LIQUID-CRYSTAL FILTER FOR SOLAR IMAGING AT THE HE-I 1083-NM LINE

A Lyot-Ohman filter for imaging near the solar He I 1083-nm line is de scribed. Fast and continuous spectral tunability is provided by nemati c liquid crystals. This solid-state filter has a free spectral range o f 2.35 nm and a spectral resolution of 0.135 nm at the operating wavel ength of 1083 nm. A wide-fielded design was used for both static and e lectro-optic retarder elements, facilitating use in fast imaging syste ms. A first-light He I image of the Sun is presented. (C) 1997 Optical Society of America