title: Iceland spar and birefringent filter (BF) development
abstract: Birefringent crystals for BF are required to provide the necessary linear aperture, wavefront quality, and filter transmission in a given spectral region. Based on the review of foreign and domestic BF developments, the difficulties in using crystals from known deposits are examined. The Institute of Solar-Terrestrial Physics has developed BFs with extreme characteristics, using an innovative method for enriching crystals from East Siberian deposits and new methods for optical treatment and cont
journal: Solar-Terrestrial Physics