Nd: YAG laser is a solid-state laser that uses an 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 lasers operate in both pulsed and continuous wave modes. The pulsed wave output is generated using Q-switching where a power output of up to 250 MW and pulse duration of 10 to 25 ns can be achieved.

As seen in the illustration above, an 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.

How does an Nd-YAG Laser Work?

An 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.

Applications of Nd: YAG lasers

Since Nd: YAG lasers are high-power lasers, they can be used in a wide range of applications in the Military, Medical and Industrial Sectors.

Medical

Nd: YAG lasers are widely used lasers for laser-induced thermotherapy, in which benign or malignant lesions in various organs are ablated by the beam. They can be used to remove skin cancers and are also used to reduce benign thyroid nodules and to destroy primary and secondary malignant liver lesions. These lasers are also used extensively in the field of cosmetic medicine for laser hair removal and the treatment of minor vascular defects such as spider veins on the face and legs. They are also used to treat Venous Lake lip lesions and recently Nd: YAG lasers have been used for treating dissecting cellulitis of the scalp, a rare skin disease. Using hysteroscopy this laser has been used for the removal of uterine septa within the inside of the uterus. In podiatry, the Nd: YAG laser is being used to treat onychomycosis, which is a fungus infection of the toenail.

Military

Nd: YAG laser is the most common laser used in laser designators and laser rangefinders.

Industry

Nd: YAG lasers are used in industries for engraving, etching, or marking a variety of metals and plastics, or for metal surface enhancement processes. They are extensively used in manufacturing for cutting and welding steel, semiconductors, and various alloys. Super alloy drilling (for gas turbine parts) typically uses pulsed Nd: YAG lasers. These lasers are also employed to make subsurface markings in transparent materials such as glass or acrylic glass, for selective laser melting of metals in additive layered manufacturing. In aerospace applications, they can be used to drill cooling holes for enhanced airflow/heat exhaust efficiency. Nd: YAG lasers are also used in the non-conventional rapid prototyping process of laser-engineered net shaping (LENS).