Yttrium aluminium garnet is a synthetic crystalline material of the garnet group. It is a cubic yttrium aluminium oxide phase, with other examples being YAlO₃ in a hexagonal or an orthorhombic, perovskite-like form, and the monoclinic Y₄Al₂O₉.
An Er: YAG laser (erbium-doped yttrium aluminium garnet laser, erbium YAG laser) is a solid-state laser whose active laser medium is erbium-doped yttrium aluminium garnet (Er:Y3Al5O12). Er: YAG lasers typically emit light with a wavelength of 2940 nm, which is infrared light.