Faraday Isolator Based On Ntf Crystal In Critical Orientation

The characteristics of a magneto-optical material promising for the development of Faraday isolators for high-power lasers-the Na0.37Tb0.63F2.26 (NTF) solid solution crystal with a negative value of optical anisotropy parameter-were investigated. The value of the optical anisotropy parameter xi(NTF) = -0.26 +/- 0.02 was refined in model experiments on samples with increased absorption, and the value of the thermo-optical constant Q characterizing thermally induced depolarization was measured to be Q(NTF) = (3.44 +/- 0.4)center dot 10(-6) K-1. The negative value of xi indicates that the depolarization resulting from stress-induced birefringence in this material is strongly dependent on orientation and ensures the presence of a critical orientation [C], with the use of which the magnitude of thermally induced depolarization in the Faraday isolator may be significantly reduced. The [C] orientation is determined by the parameter xi; therefore, its accurate measurement is of particular importance. The investigation of Faraday isolators based on NTF crystals cut in [001] and [C] orientations demonstrated a significant advantage of the critical orientation. According to the measurement result, with the use of crystals with normal absorption, it is possible to develop a traditional (single element) Faraday isolator operating at room temperature and ensuring the isolation ratio of about 30 dB at the laser radiation power of similar to 7 kW. This makes the NTF crystal one of the most prospective magneto-active media.