Nd:YAG（Neodymium-doped Yttrium-Aluminum Garnet）crystal is the best of the rare earth garnet materials that are characterized by four-level system which permits low threshold operation both in pulsed and CW mode. It is the most mature and widely used solid-state laser material adopted by R&D, medical, industrial and military customers. Its properties are a good compromise between the strengths and weaknesses of its competition.