Low absorption magneto-optical materials for near-future upgrades of gravitational-wave detectors.

The Laser Interferometer Gravitational-Wave Observatory (LIGO) uses high-power laser interferometry to detect gravitational waves. Faraday isolators are key devices in reducing the amount of light scatter from building up in the interferometer, as well as protecting lasers from inadvertent exposure to retro-reflected light. Current LIGO isolators are based on terbium gallium garnet (TGG), which shows high performance in terms Faraday rotation, as well as superior thermo-optical properties. Recently, newer materials with lower absorption losses are being explored to replace TGG, especially in those applications that involve higher average laser powers. In this presentation we are discussing potential applications to LIGO of potassium terbium fluoride (KTF), which has a similar Verdet constant with TGG, while much smaller bulk absorption. I will discuss similarities and differences between TGG and KTF, and how temperature affects the Faraday rotation, and its performance in LIGO.