Yttrium aluminum garnet (_Y3Al5O12 or YAG) is a synthetically produced crystalline compound with good transmission properties in the wavelength range between 0.25 µm and 5 µm. The material is suitable for use in IR and UV optics. Its mechanical and chemical stability is similar to that of sapphire. However, unlike sapphire, YAG does not exhibit birefringence and is easier to process than sapphire. YAG has no absorption lines in the 2-3 µm range, where glasses typically tend to have high absorption due to the strong bonding of water molecules.

YAG is often used in high-temperature industrial, medical and scientific applications due to its high strength and other properties such as a high laser damage threshold (LDT), a high refractive index, good thermal conductivity and no absorption in the 2-3 µm range. Yttrium aluminum garnets are grown using the Czochralski method or horizontally.

Undoped YAG single crystals can be polished to laser quality and are therefore suitable as substrates for optical components such as light guides, prisms, mirrors and windows for endoscopes. In addition, doped YAG laser crystals are bonded to undoped YAG substrates in high-power lasers to improve heat transport.