Improved mid-infrared polarizers using yttrium vanadate

Pure yttrium vanadate crystals (YVO4) have optical properties ideal for polarizers in the mid-infrared spectrum. YVO4 is highly transmissive from 400 to 3800 nm and is optically useful to 5 mum. YVO4 is a positive uniaxial crystal with a birefringence (n(e)-n(o)) larger than the negative uniaxial crystal calcite (+0.209 vs. -0.163 at 1064 nm). The positive birefringence Of YVO4 gives ordinary polarization to the beam transmitted by the polarizer, producing a desirable symmetric field-of-view for all standard designs. Glan, Wollaston, and Rochon polarizers were fabricated from YVO4 and tested. The preferred Glan design for YVO4 is Glan-Foucault and not Glan-Taylor as for calcite. YVO4 has advantages in large aperture size, excellent optical quality, high laser-damage threshold, and excellent optical working ability (480 Knoop hardness) with only a slight tendency to cleave. New monolithic crystal polarizer designs will be described. It is also believed than YVO4 would be an excellent synthetic substitute for calcite in the visible spectrum (>400 nm).