Nd:YAG lasers - terminology and functionality

One type of solid-state laser is an Nd:YAG laser. These discharge at 1064nm, close to infrared. The main source is the crystal yttrium aluminum garnet. Neodymium-doping replaces roughly 0.5% - 3% of the yttrium atoms. Bell Laboratories produced this type of laser in 1964. YAG lasers, along with CO₂ and fiber, are popular for processing industrial applications and materials.

Diode-pumped lasers are excited through diode lasers with an 808nm wavelength. These lasers typically have an output power of 100 watts on average. The electrons of the neodymium atoms absorb the electric pump light to reach a greater energy level. Stimulated emission then releases the energy that is housed in the excited atoms.

One of the greatest technical challenges with a solid-state laser is the need for the structure to be composed of a single crystal throughout as well as high-purity and selective doping of the medium. It needs to have minimal heat loss with the greatest achievable efficiency. The solid-state laser can damage itself with excessive pumping power, meaning that it needs to be able to endure tremendous energy density.

Nd:YAG refers to a yttrium-aluminum-garnet crystal where the yttrium ions have been substituted by neodymium. The chemical symbol of yttrium = Y and the chemical symbol of neodymium = Nd, thus Nd:YAG. With these lasers, the neodymium-doping is roughly 0.5% - 3%. As the level of doping increases, the laser power also increases. However, the quality of the beam decreases as the power goes up. This is the same for all lasers.

Various types of lamps, including krypton arc, halogen, and xenon flash, or light or laser diodes may be used as pump sources. With power optically supplied and neodymium ions electrically stimulated, the Nd:YAG crystal is illuminated.

These systems are proper light-emitting diodes with mirrored interfaces building a resonator. Laser diodes are electrically pumped and remarkably compact semiconductor lasers (these are a subgroup of the solid-state lasers). The great capability of the diodes, the accurate controllability, and the more prolonged service life related to lamps, have considerably enhanced the prevalence of the Nd:YAG laser, uprooting the older lamp pump source technology, especially in the lower wattage spectrum.

The ratio between laser power and light power will determine the efficiency of the system. Lamp-pumped YAG systems are typically at 2-4% efficiency. However, diode-pumped YAG lasers can range between 30-50% efficiency. Diode-pumped systems also have reduced heat loss, therefore, less cooling is needed, which can extend the lifetime of the laser. Additionally, they have a greater number of pulses per second in pulse mode and pulse peak powers.

Disc and slab lasers are becoming increasingly popular, often replacing traditional cylindrical Nd:YAG laser rods. The cylindrical rods have an incredibly small diameter in relation to their length, making the surface area of the rods quite smaller than disks of the same volume. Due to this, it is more difficult to cool the cylindrical rods. Disc lasers are also capable of higher pump power and, therefore, higher laser power. Some Nd:YAG lasers have an output power greater than 10kW. These systems are typically reserved for industrial applications.

The Nd:YAG lasers have a wavelength that is roughly ten times less than CO2 lasers. This smaller wavelength creates a smaller area of focus and a higher intensity. This is incredibly beneficial when working with metals.