Different lasers use different materials as the active medium. The medium can be either solid, liquid, or gas, and there are advantages for each in the amount of energy that can be stored, ease of handling and storage, secondary safety hazards, cooling properties, and physical characteristics of the laser output.
Another group of applications is collectively known as materials processing. This includes the processes used in manufacturing. Production facilities use lasers to cut, weld, drill, mark, and heat-treat numerous materials such as metals, plastics, wood, ceramics, and even diamonds. Lasers are much more precise than other mechanical means used to process materials, and lasers make it possible to build devices with tiny, even microscopic, dimensions. A subgroup of this category, medical device manufacturing, relies on lasers to machine stents and other devices for implantation into the human body.
Military uses for lasers are abundant, from range finding to guided munitions to laser aiming devices on firearms. Warfare has been revolutionized by the laser. Law enforcement uses lasers to lift hard-to recover fingerprints and in laser radar speed guns.
Laser printers, bar code readers, unmanned freeway tollbooths, laser pointers—none of these very common devices would be possible without laser technology. This is just a minor sampling; the list of laser applications goes on and on.
Solid-State Lasers
The term “solid-state laser” refers to lasers that use solids as their active medium. However, two kinds of materials are required: a “host” crystal and an impurity “dopant.” The dopant is selected for its ability to form a laser population inversion. The Nd:YAG laser, for example, uses a small number of neodymium ions as a dopant in the solid YAG (yttrium-aluminum-garnet) crystal. Solid-state lasers are pumped with an outside source such as a flash lamp, arc lamp, or another laser. This energy is then absorbed by the dopant, raising the atoms to an excited state. Solid-state lasers are sought after because the active medium is relatively easy to handle and store. Also, because the wavelength they produce is within the transmission range of glass, they can be used with fiber optics.
Diode (Semiconductor) Lasers
Also using solids but considered separately because of their unique characteristics, diode lasers are the most common lasers in use. Compact size and reliability are the chief benefits of this kind of laser. The two common families of diode lasers contain active mediums composed of GaAlAs (gallium-aluminum arsenite) or InGaAsP (indium/phosphorus). These media emit radiation in the infrared range. Much like those working with radar in the 1940s and ‘50s, researchers in the 1980s and ‘90s found ways to shorten wavelengths of lasers produced by diode-pumped to reach into the range of blue visible light.
