Nd:YAG Laser

Nd:YAG lasers are used in many different fields such as medicine, cosmetics, and manufacturing. In fluid mechanics for example, Nd:YAG lasers are commonly used to perform imaging based measurements of flow field variables such as in Particle Image Velocimetry (PIV) and Laser Induced Fluorescence (LIF). The name Nd:YAG is given after the laser’s gain medium: Neodymium-doped Yttrium Aluminum Garnet (Nd:Y₃Al₅O₁₂). The gain medium host material, Yttrium Aluminum Garnet or YAG (Y₃⁺³Al₅⁺³O₁₂^2-), is doped with triply ionized neodymium (Nd⁺³). The doping process results in a crystal defect where Y₃⁺³ ions substitute a small percentage of Nd⁺³ ions. The resultant crystal is pink in color, as can be seen below.

The absorption of Nd:YAG is broad near 800 nm wavelength; therefore, these lasers are typically pumped with laser diode arrays or flash lamps. Here is a picture of a laser diode array pump system. Note that the purple light seen in the picture was not visible to the human eye, but was captured by the CCD digital camera. Coolant tubes are used to keep the laser diode array operating at an appropriate temperature.  

Nd:YAG lasers are capable of several emission lines. However, the four level transition with an emission line of 1064 is the most common arrangement. The line width of the 1064 nm transition at 300K is approximately 0.45 nm or 120 GHz. Often times, the 1064 nm infrared line is frequency doubled to generate visible green light at 532 nm. This type of laser can be operated in both continuous and pulsed lasing modes. Here is a picture of a continuous Nd:YAG laser that is frequency doubled to generate green light at 532 nm.