birefringent filter(bÿ-ri-frin -jĕnt) A type of narrow-band filter that uses a birefringent (double-refracting) medium between polarizers to produce selective absorption of polarized light. The earliest design is the Lyot (or Lyot–Öhman) filter devised independently by the French astronomer Bernard Lyot in 1933 and the Swedish astronomer Yngve Öhman in 1938. Its action depends on the extinction of polarized light occurring in birefringent crystalline laminae precisely orientated between Polaroid sheets: a stack of these elements, each of suitable thickness, transmits well-separated and very narrow wavebands of about 0.07 nanometer.
birefringent filter[‚bī·ri′frin·jənt ′fil·tər]
A filter consisting of alternate layers of polarizing films and plates cut from a birefringent crystal; transmits light in a series of sharp, widely spaced wavelength bands. Also known as Lyot filter; monochromatic filter.