Neodymium-doped ytt rium aluminium garnet (Nd-YAG) crystal is a common lasing medium used in solid state lasers. It has been used and researched since 1964. The laser is designed by replacing a few yttrium irons in the crystal structure of the garnet with neodymium irons. The ions of YAG and yttrium are similarly sized, which is why the replacement is effective. The neodymium ion acts as a lasing medium.