Terbium Gallium Garnet (TGG) is a type of garnet crystal that is made of terbium, gallium, and oxygen. It is a non-linear optical crystal that has a high electro-optic coefficient, making it useful for applications in electro-optic modulators and switches. TGG is a high-refractive index crystal, which makes it ideal for use as a substrate in optical components, such as laser resonators, waveguides, and polarizers. TGG has a high thermal stability and is resistant to radiation damage, making it suitable for use in high-power laser systems and other demanding applications.