Laser diode

semiconductor laserdiode laserlaser diodessemiconductor lasersdiode lasersdiodesemiconductor diode laserInjection Laser Diodelasercollimated diode
A laser diode, (LD), injection laser diode (ILD), or diode laser is a semiconductor device similar to a light-emitting diode in which the laser beam is created at the diode's junction.wikipedia
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Laser pointer

laser pointerslaser lightgreen laser lights
Laser diodes are the most common type of lasers produced, with a wide range of uses that include fiber optic communications, barcode readers, laser pointers, CD/DVD/Blu-ray disc reading/recording, laser printing, laser scanning and light beam illumination. Visible lasers, typically red but later also green, are common as laser pointers.
A laser pointer or laser pen is a small handheld device with a power source (usually a battery) and a laser diode emitting a very narrow coherent low-powered laser beam of visible light, intended to be used to highlight something of interest by illuminating it with a small bright spot of colored light.

Active laser medium

gain mediumlasing mediumlaser gain medium
A laser diode, (LD), injection laser diode (ILD), or diode laser is a semiconductor device similar to a light-emitting diode in which the laser beam is created at the diode's junction.
Pumping may be achieved with electrical currents (e.g. semiconductors, or gases via high-voltage discharges) or with light, generated by discharge lamps or by other lasers (semiconductor lasers).

Solid-state laser

solid state lasersolid statesolid-state
Either designation distinguishes diode lasers from solid-state lasers.
Semiconductor-based lasers are also in the solid state, but are generally considered as a separate class from solid-state lasers (see Laser diode).

Quantum well

multiple quantum wellquantum-wellwells
The active layer most often consists of quantum wells, which provide lower threshold current and higher efficiency.
As a result quantum wells are in wide use in diode lasers, including red lasers for DVDs and laser pointers, infra-red lasers in fiber optic transmitters, or in blue lasers.

Carrier generation and recombination

recombinationelectron-hole pairelectron–hole pair
When an electron and a hole are present in the same region, they may recombine or "annihilate" producing a spontaneous emission — i.e., the electron may re-occupy the energy state of the hole, emitting a photon with energy equal to the difference between the electron's original state and hole's state.
Carrier generation and recombination processes are fundamental to the operation of many optoelectronic semiconductor devices, such as photodiodes, LEDs and laser diodes.

Quantum well laser

quantum well laser diodesmultiple quantum well laserquantum-well laser
The efficiency of a quantum well laser is greater than that of a bulk laser because the density of states function of electrons in the quantum well system has an abrupt edge that concentrates electrons in energy states that contribute to laser action.
A quantum well laser is a laser diode in which the active region of the device is so narrow that quantum confinement occurs.

Quantum cascade laser

quantum cascade lasersquantum cascadequantum-cascade laser
In a quantum cascade laser, the difference between quantum well energy levels is used for the laser transition instead of the bandgap.
Quantum cascade lasers (QCLs) are semiconductor lasers that emit in the mid- to far-infrared portion of the electromagnetic spectrum and were first demonstrated by Jerome Faist, Federico Capasso, Deborah Sivco, Carlo Sirtori, Albert Hutchinson, and Alfred Cho at Bell Laboratories in 1994.

Interband cascade laser

A Interband cascade laser (ICL) is a type of laser diode that can produce coherent radiation over a large part of the mid-infrared region of the electromagnetic spectrum.
Interband cascade lasers (ICLs) are a type of laser diode that can produce coherent radiation over a large part of the mid-infrared region of the electromagnetic spectrum.

Quantum dot

quantum dotsartificial atomquantum-dot
Further improvements in the laser efficiency have also been demonstrated by reducing the quantum well layer to a quantum wire or to a "sea" of quantum dots.
Potential applications include transistors, solar cells, LED s, diode lasers and second-harmonic generation, quantum computing, and medical imaging.

Vertical-cavity surface-emitting laser

VCSELvertical cavity surface emitting laserVCSELs
DBR lasers can be edge emitting lasers or VCSELs.
The vertical-cavity surface-emitting laser, or VCSEL, is a type of semiconductor laser diode with laser beam emission perpendicular from the top surface, contrary to conventional edge-emitting semiconductor lasers (also in-plane lasers) which emit from surfaces formed by cleaving the individual chip out of a wafer.

DVD

DVD-ROMDVDsvideo album
Laser diodes are the most common type of lasers produced, with a wide range of uses that include fiber optic communications, barcode readers, laser pointers, CD/DVD/Blu-ray disc reading/recording, laser printing, laser scanning and light beam illumination.
All three common optical disc media (Compact disc, DVD, and Blu-ray) use light from laser diodes, for its spectral purity and ability to be focused precisely.

Catastrophic optical damage

optical damage threshold
In addition they are subject to catastrophic optical damage (COD) when operated at higher power.
Catastrophic optical damage (COD), or catastrophic optical mirror damage (COMD), is a failure mode of high-power semiconductor lasers.

Distributed feedback laser

distributed feedbackDFBdistributed feed back laser diode
A distributed feedback laser (DFB) is a type of single frequency laser diode.
A distributed feedback laser (DFB) is a type of laser diode, quantum cascade laser or optical fiber laser where the active region of the device contains a periodically structured element or diffraction grating.

Vertical-external-cavity surface-emitting-laser

vertical external cavity surface-emitting laser
Vertical external-cavity surface-emitting lasers, or VECSELs, are similar to VCSELs.
A vertical-external-cavity surface-emitting-laser (VECSEL) is a small semiconductor laser similar to a vertical-cavity surface-emitting laser (VCSEL).

Optical cavity

optical resonatorcavitylaser cavity
As in other lasers, the gain region is surrounded with an optical cavity to form a laser.
Plane-parallel resonators are therefore commonly used in microchip and microcavity lasers and semiconductor lasers.

Fabry–Pérot interferometer

Fabry–PérotetalonFabry-Perrot optical resonance cavity
The two ends of the crystal are cleaved to form perfectly smooth, parallel edges, forming a Fabry–Pérot resonator.
Laser resonators are often described as Fabry–Pérot resonators, although for many types of laser the reflectivity of one mirror is close to 100%, making it more similar to a Gires–Tournois interferometer. Semiconductor diode lasers sometimes use a true Fabry–Pérot geometry, due to the difficulty of coating the end facets of the chip. Quantum cascade lasers often employ Fabry-Pérot cavities to sustain lasing without the need for any facet coatings, due to the high gain of the active region.

Direct and indirect band gaps

direct bandgapdirect band gapindirect bandgap
Thus, laser diodes are fabricated using direct band-gap semiconductors.
This is why light-emitting and laser diodes are almost always made of direct band gap materials, and not indirect band gap ones like silicon.

Heterojunction

heterostructureheterostructuresheterotransistor
Each of the junctions between different bandgap materials is called a heterostructure, hence the name "double heterostructure laser" or DH laser.
Lasers: Using heterojunctions in lasers was first proposed in 1963 when Herbert Kroemer, a prominent scientist in this field, suggested that population inversion could be greatly enhanced by heterostructures. By incorporating a smaller direct band gap material like GaAs between two larger band gap layers like AlAs, carriers can be confined so that lasing can occur at room temperature with low threshold currents. It took many years for the material science of heterostructure fabrication to catch up with Kroemer's ideas but now it is the industry standard. It was later discovered that the band gap could be controlled by taking advantage of the quantum size effects in quantum well heterostructures. Furthermore, heterostructures can be used as waveguides to the index step which occurs at the interface, another major advantage to their use in semiconductor lasers. Semiconductor diode lasers used in CD and DVD players and fiber optic transceivers are manufactured using alternating layers of various III-V and II-VI compound semiconductors to form lasing heterostructures.

Gallium arsenide

GaAsgallium-arsenidegallium(III) arsenide
Gallium arsenide, indium phosphide, gallium antimonide, and gallium nitride are all examples of compound semiconductor materials that can be used to create junction diodes that emit light.
Gallium arsenide is used in the manufacture of devices such as microwave frequency integrated circuits, monolithic microwave integrated circuits, infrared light-emitting diodes, laser diodes, solar cells and optical windows.

Tunable laser

tunabletuned lasersTunable continuous-wave laser
External-cavity diode lasers are tunable lasers which use mainly double heterostructures diodes of the
Among the types of tunable lasers are excimer lasers, gas lasers (such as CO 2 and He-Ne lasers), dye lasers (liquid and solid state), transition metal solid-state lasers, semiconductor crystal and diode lasers, and free electron lasers.

Light-emitting diode

LEDLEDslight emitting diodes
A laser diode, (LD), injection laser diode (ILD), or diode laser is a semiconductor device similar to a light-emitting diode in which the laser beam is created at the diode's junction.
Today, magnesium-doping of gallium nitride remains the basis for all commercial blue LEDs and laser diodes.

Charge carrier

charge carrierscarriersminority carrier
Forward electrical bias across the laser diode causes the two species of charge carrier – holes and electrons – to be "injected" from opposite sides of the p-n junction into the depletion region.
The energy released can be either thermal, heating up the semiconductor (thermal recombination, one of the sources of waste heat in semiconductors), or released as photons (optical recombination, used in LEDs and semiconductor lasers).

Red

Redscolor redScarlet
Visible lasers, typically red but later also green, are common as laser pointers.
The use of red laser diodes became widespread with the commercial success of modern DVD players, which use a 660 nm laser diode technology.

Gallium nitride

GaNgallium nitride (GaN)gallium(III) nitride
Gallium arsenide, indium phosphide, gallium antimonide, and gallium nitride are all examples of compound semiconductor materials that can be used to create junction diodes that emit light.
GaN-based violet laser diodes are used to read Blu-ray Discs.

Blu-ray

BDBlu-ray DiscRegion A
Laser diodes are the most common type of lasers produced, with a wide range of uses that include fiber optic communications, barcode readers, laser pointers, CD/DVD/Blu-ray disc reading/recording, laser printing, laser scanning and light beam illumination.
The information density of the DVD format was limited by the wavelength of the laser diodes used.