Nd: YAG laser is a solid-state laser that uses Nd: YAG (Neodymium-doped Yttrium Aluminium Garnet) crystal as the active medium. This laser typically emits light in the infrared region of the electromagnetic spectrum with a wavelength of 1064 nm, however; other wavelength emissions such as 946, 1120, 1320, and 1440 nm are also possible. Nd: YAG laser operates in both pulsed and continuous wave modes. The pulsed wave output is generated using Q-switching where a power output of 250 MW and pulse duration of 10 to 25 ns can be achieved.
Nd: YAG laser has a rod-like structure. The active medium material here is formed by doping triply ionized neodymium ion (Nd3+) with the host crystal yttrium aluminium garnet (YAG – Y3Al5O12). Due to doping, the yttrium ions get replaced by Nd3+ ions since both ions are of similar size. The Nd3+ ions in the crystal are responsible for the lasing action. Nd: YAG lasers are optically pumped using a flash tube or laser diodes. The Nd: YAG rod and the flash tube are placed inside an elliptical cavity so that maximum light from the optical pumping source can reach the rod. The two ends of this rod are coated with silver, one end is completely coated, while the other end is partially coated to form the active medium.
Nd: YAG laser is a four-level laser. The Nd3+ ions in the active medium are responsible for the lasing action. The ions in the ground state E0 are optically pumped using a flashlamp or a laser diode to the upper excited levels of E3. This is a short-lived energy level and thus these ions make a non-radiative decay to the metastable state E2. This is a long-lived state and thus ions accumulate in this level and thus a population inversion condition is achieved between E2 and the lower energy level E1. This stimulated transition between E2 and E1 results in a laser emission of 1064 nm. The atoms reaching E1 then non-radiatively decay to the ground state.
Since Nd: YAG lasers are high-power lasers, they are used in military applications to find the desired target. This type of laser also finds its application in the medical field for surgical purposes. These are also used in welding and cutting and in communication systems also.
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