Laser diodes have many uses in today’s world, from military applications to telecommunications, meteorology and medicine. There are several common modes of operation and a wide variety of structures to suit proposed industrial uses.
Operation of Laser Diodes
A laser diode is similar to a light-emitting diode (LED) in that it has as its active medium a semiconductor. The most usual type of diode is found at a p-n junction (the boundary between p-type and n-type semiconductors) that is created by a process called doping. These junctions are then powered by injected electric current and are called injection laser diodes to differentiate them from optically pumped laser diodes.
Many diodes emit in continuous wave (cw) mode from anywhere from several watts down to just milliwatts of power. These industrial diodes lack the ability to be overdriven and even small periods of exceeding the maximum power can cause damage to laser resonators and effectively shut down the laser. For industrial applications that require a lot of peak power usage time, pulsed laser diodes are able to be overdriven effectively and easily for short time periods. To achieve this, short pulses are followed by pauses, keeping the pulse lengths in the 200ns range. These pulses of light are generated by laser currents that lessen inductive loss through the use of fast switching transistors and very short electrical connections.
Laser Structures Over the Years
Laser diode technology has changed rapidly from the early 60s, when it was demonstrated at the IBM T.J. Watson Research Center. Since then, we have seen diodes move from liquid phase epitaxy (LPE), or layering of crystals, to molecular beam epitaxy and organometallic chemical vapor deposition in the 1970s. These forms have been added to and expanded with the addition of Vertical Extended Cavity Surface Emitting Lasers (VECSELs), Vertical Cavity Surface Emitting Lasers (VSELs), external cavity Switching Diodes and others, including subcategories.
Common Industrial Uses
Some of the smaller varieties of Switching Diodes are used in laser printers, bar code scanners, laser pointers and CD planners. But the larger diodes are used in many important defense applications, such as the pulsed laser rangefinders in military tanks and directed energy strike systems that produce powerful light to destroy land mines, rockets, mortar rounds and other ordinances. The medical community benefits through the use of this technology through cosmetic applications such as Intense Pulsed Light (IPL) for hair, age spot, and wrinkle removal, other lasers for soft tissue surgery, and even in dentistry for procedures as diverse as cavity removal and tooth whitening. Vertical extended cavity surface emitting lasers (VECSELs) are important for big screen televisions and other commercial uses. Other various applications for laser diodes include welding and cutting of metals and other industrial materials, fiber optics for telecommunications systems, laser levels for surveying, and the taking of accurate 3D measurements.