Optical and Magneto-Optic Properties of Polycrystalline CdCr2S4

Abstract

The optical absorption spectrum of hot‐pressed polycrystalline CdCr₂S₄ has been measured between 700 nm and 50 μ, with particular emphasis on the region of weak absorption between 700 and 1200 nm, in which Faraday rotation spectra were also obtained. In this region, two series of phonon‐assisted transitions have been observed, involving phonon energies of 0.041 and 0.046 eV. These energies are similar to the optical phonon energies obtained from infrared measurements on the same crystals. At 4.2°K, and with an applied magnetic field of 3000 Oe, the Faraday rotation reaches a value of about 1.6×10⁴ deg per cm near 750 nm. At 80°K, the rotation is decreased by about a factor of two. These crystals have very low optical scatter or impurity absorption, resulting in high transparency in the near infrared. At 4.2°K, the figure of merit is about 60 deg dB⁻¹ in this spectral region, and decreases to about 30 deg dB⁻¹ at 80°K.