Optical Properties of Cobalt-Doped Lithium Niobate

Abstract

The optical absorption spectrum for Co-doped LiNbO₃ was measured below 25,000 cm⁻¹ at 77 K and room temperature. The data was analyzed by the crystal field theory. Level splitting of the excited ⁴T_1g state of Co²⁺ due to spin-orbit coupling and the trigonal field was identified. The results give B=850 cm⁻¹, Dq=900 cm⁻¹, ζ=628 cm⁻¹, and Δ_e=−768 cm⁻¹ for Co²⁺, and Dq=1600 cm⁻¹ for Co³⁺. The circular dichroism (CD) for the ⁴T_1g→⁴T_1g band of Co²⁺ was measured in the k⊥c configuration. It is shown that CD off-resonance in this configuration is directly proportional to the difference in absorption for the ordinary and extraordinary waves and to the off-diagonal element of the dielectric tensor Im ε₂′(k, ω) for the medium with |ε₂′(k, ω)⁄(ε_e−ε₀)|<<1. The observed CD shows frequency dispersion in good agreement with the phenomenological theory.