Promising Materials for High Power Laser Isolators

Northrop Grumman Synoptics is developing the growth of large singlecrystal fluoride materials for Faraday rotator / isolator applications. These materials exhibit smaller nonlinear refractive index and thermo-optic coefficients, while maintaining Verdet constants near those of the commonly used terbium gallium garnet (TGG) crystals. In particular, the cubic potassium terbium fluoride, KTF (KTb₃F₁₀) crystal has low absorption and thermo-optic coefficients. The crystal growth and performance of these single-crystal fluoride materials will be discussed as well as recent improvements to the performance of TGG crystals.