Near-zero thermal expansion diamagnetic as a magneto-optical material for Faraday isolators for high power laser radiation

Abstract

The optical transmission, the wavelength and temperature dependence of the Verdet constant as well as the thermally induced depolarization in a Zn₄B₆O₁₃ crystal were investigated. The analytical dependence of the Verdet constant on wavelength and temperature, which describes well the experimental data in the 240–1100 nm range, was obtained. The small coefficient of linear expansion and its isotropy significantly suppressed thermally induced depolarization associated with thermally induced linear birefringence caused by the photo-elastic effect, while the diamagnetic nature of the material ensured the absence of thermally induced depolarization associated with the temperature dependence of the Verdet constant. The results revealed that Zn₄B₆O₁₃ is highly suitable for the wavelength range of 248–350 nm and can be used as a magneto-optical material for an optical isolator for high-average-power UV lasers.