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Encyclopedia > Laser diode
A packaged laser diode with penny for scale.
A packaged laser diode with penny for scale.
Image of the actual laser diode chip (shown on the eye of a needle for scale) contained within the package shown in the above image.
Image of the actual laser diode chip (shown on the eye of a needle for scale) contained within the package shown in the above image.

A laser diode is a laser where the active medium is a semiconductor similar to that found in a light-emitting diode. The most common and practical type of laser diode is formed from a p-n junction and powered by injected electrical current. These devices are sometimes referred to as injection laser diodes to distinguish them from optically pumped laser diodes, which are more easily produced in the laboratory. Image File history File links Download high resolution version (3060x2036, 1070 KB)original caption: This technology is known as a Tunable Diode Laser (TDL) gas sensor. ... Image File history File links Download high resolution version (3060x2036, 1070 KB)original caption: This technology is known as a Tunable Diode Laser (TDL) gas sensor. ... For the NBA basketball player with the nickname see Penny Hardaway A variety of low value coins, including an Irish 2p piece and many U.S. pennies. ... Image File history File links Download high resolution version (2720x1925, 1216 KB)Original caption: Tunable Diode Laser Chip in the Eye of a Needle Tunable Diode Lasers (TDL) can be tuned like a radio to frequencies that allow them to look for specific gases. ... Image File history File links Download high resolution version (2720x1925, 1216 KB)Original caption: Tunable Diode Laser Chip in the Eye of a Needle Tunable Diode Lasers (TDL) can be tuned like a radio to frequencies that allow them to look for specific gases. ... For other uses, see Laser (disambiguation). ... A semiconductor is a solid whose electrical conductivity is in between that of a conductor and that of an insulator, and can be controlled over a wide range, either permanently or dynamically. ... “LED” redirects here. ... A p-n junction is formed by combining N-type and P-type semiconductors together in very close contact. ... In electricity, current is the rate of flow of charges, usually through a metal wire or some other electrical conductor. ...

Contents

Principle of operation

A laser diode, like many other semiconductor devices, is formed by doping a very thin layer on the surface of a crystal wafer. The crystal is doped to produce an n-type region and a p-type region, one above the other, resulting in a p-n junction, or diode. In semiconductor production, doping refers to the process of intentionally introducing impurities into an intrinsic semiconductor in order to change its electrical properties. ... An N-type semiconductor is obtained by carrying out a process of doping, that is adding a certain type of atoms to the semiconductor in order to increase the number of free (in this case negative) charge carriers. ... A P-type semiconductor is obtained by carrying out a process of doping, that is adding a certain type of atoms to the semiconductor in order to increase the number of free (in this case positive) charges. ... Closeup of the image below, showing the square shaped semiconductor crystal various semiconductor diodes, below a bridge rectifier Structure of a vacuum tube diode In electronics, a diode is a two-terminal component, almost always one that has electrical properties which vary depending on the direction of flow of charge...


The many, many types of diode lasers known today collectively form a subset of the larger classification of semiconductor p-n junction diodes. Just as in any semiconductor p-n junction diode, forward electrical bias 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, situated at its heart. Holes are injected from the p-doped, and electrons from the n-doped, semiconductor. (A depletion region, devoid of any charge carriers, forms automatically and unavoidably as a result of the difference in chemical potential between n- and p-type semiconductors where ever they are in physical contact.) As charge injection is a distinguishing feature of diode lasers as compared to all other lasers, diode lasers are traditionally and more formally called "injection lasers." (This terminology differentiates diode lasers, e.g., from flashlamp-pumped solid state lasers, such as the ruby laser. Interestingly, whereas the term "solid-state" was extremely apt in differentiating 1950s-era semiconductor electronics from earlier generations of vacuum electronics, it would not have been adequate to convey unambiguously the unique characteristics defining 1960s-era semiconductor lasers.) When an electron and a hole are present in the same region, they may recombine or "annihilate" with the result being 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 and hole states involved. (In a conventional semiconductor junction diode, the energy released from the recombination of electrons and holes is carried away as phonons, i.e., lattice vibrations, rather than as photons.) Spontaneous emission gives the laser diode below lasing threshold similar properties to an LED. Spontaneous emission is necessary to initiate laser oscillation, but it is one among several sources of inefficiency once the laser is oscillating. A solid-state laser is a laser that uses a gain medium that is a solid, rather than a liquid such as dye lasers or a gas such as gas lasers. ... In solid state physics, recombination is the process by which the broken semiconductor crystal bonds are restored, via a mutual elimination of an electron and a hole, the complementary charge carriers. ... Spontaneous emission is the process by which a molecule in an excited state drops to the ground state, resulting in the creation of a photon. ... In optics, the lasing threshold is the lowest excitation level at which laser output is dominated by stimulated emission rather than by spontaneous emission. ... External links LEd Category: TeX ...


The difference between the photon-emitting semiconductor laser or LED (on one hand) and conventional phonon-emitting (non-light-emitting) semiconductor junction diodes (on the other hand) lies in the use of a different type of semiconductor, one whose physical and atomic structure confers the possibility for photon emission. These photon-emitting semiconductors are the so-called "direct bandgap" semiconductors. It is the nature of silicon and germanium, which are single-element semiconductors, that the bandgap does not align in such as way as to be considered "direct." However, the so-called compound semiconductors, which have virtually the identical crystal structure as silicon or germanium but use alternating arrangements of two different atomic species in a checkerboard-like pattern break the symmetry and in doing so create the critical direct bandgap. Examples of compound semiconductors are gallium arsenide, indium phosphide, gallium antimonide, gallium nitride and so forth, and junction diodes fabricated from these materials emit light

Diagram (not to scale) of a simple laser diode.
Diagram (not to scale) of a simple laser diode.

In the absence of stimulated emission (e.g., lasing) conditions, electrons and holes may coexist in proximity to one another, without recombining, for a certain time (termed the "upper-state lifetime" or "recombination time," about a nanosecond for typical diode laser materials) before they recombine. Then a nearby photon with energy equal to the recombination energy can cause recombination by stimulated emission. This generates another photon of the same frequency, travelling in the same direction, with the same polarization and phase as the first photon. This means that stimulated emission causes gain in an optical wave (of the correct wavelength) in the injection region, and the gain increases as the number of electrons and holes injected across the junction increases. The spontaneous and stimulated emission processes are vastly more efficient in direct bandgap semiconductors than in indirect bandgap semiconductors, thus silicon is not a common material for laser diodes. Image File history File links Simple_laser_diode. ... In optics, stimulated emission is the process by which, when perturbed by a photon, matter may lose energy resulting in the creation of another photon. ... In electrodynamics, polarization (also spelled polarisation) is the property of electromagnetic waves, such as light, that describes the direction of their transverse electric field. ... This article is about a portion of a periodic process. ... In semiconductor physics, a direct bandgap means that the minimum of the conduction band lies directly above the maximum of the valence band in momentum space. ... In semiconductor physics, an indirect bandgap is a bandgap in which the minimum energy in the conduction band is shifted by a k-vector, which is determined by the materials crystal structure. ... Not to be confused with Silicone. ...


As in other lasers, the gain region is surrounded with an optical cavity to form a laser. In the simplest form of laser diode, an optical waveguide is made on that crystal surface, such that the light is confined to a relatively narrow line. The two ends of the crystal are cleaved to form perfectly smooth, parallel edges, forming a Fabry-Perot resonator. Photons emitted into a mode of the waveguide will travel along the waveguide and be reflected several times from each end face before they are emitted. As a light wave passes through the cavity, it is amplified by stimulated emission, but light is also lost due to absorption and by incomplete reflection from the end facets. Finally, if there is more amplification than loss, the diode begins to "lase". A cavity resonator uses resonance to amplify a wave. ... In optics, a Fabry-Perot interferometer or etalon is typically made of a transparent plate with two reflecting surfaces, or two parallel highly-reflecting mirrors. ... Look up waveguide in Wiktionary, the free dictionary. ... In optics, stimulated emission is the process by which, when perturbed by a photon, matter may lose energy resulting in the creation of another photon. ... In optics, the lasing threshold is the lowest excitation level at which laser output is dominated by stimulated emission rather than by spontaneous emission. ...


Some important properties of laser diodes are determined by the geometry of the optical cavity. Generally, in the vertical direction, the light is contained in a very thin layer, and the structure supports only a single optical mode in the direction perpendicular to the layers. In the lateral direction, if the waveguide is wide compared to the wavelength of light, then the waveguide can support multiple lateral optical modes, and the laser is known as "multi-mode". These laterally multi-mode lasers are adequate in cases where one needs a very large amount of power, but not a small diffraction-limited beam; for example in printing, activating chemicals, or pumping other types of lasers. Laser pumping is the act of energy transfer from an external source into the laser gain medium. ...


In applications where a small focused beam is needed, the waveguide must be made narrow, on the order of the optical wavelength. This way, only a single lateral mode is supported and one ends up with a diffraction limited beam. Such single spatial mode devices are used for optical storage, laser pointers, and fiber optics. Note that these lasers may still support multiple longitudinal modes, and thus can lase at multiple wavelengths simultaneously.


The wavelength emitted is a function of the band-gap of the semiconductor and the modes of the optical cavity. In general, the maximum gain will occur for photons with energy slightly above the band-gap energy, and the modes nearest the gain peak will lase most strongly. If the diode is driven strongly enough, additional side modes may also lase. Some laser diodes, such as most visible lasers, operate at a single wavelength, but that wavelength is unstable and changes due to fluctuations in current or temperature.


Due to diffraction, the beam diverges (expands) rapidly after leaving the chip, typically at 30 degrees vertically by 10 degrees laterally. A lens must be used in order to form a collimated beam like that produced by a laser pointer. If a circular beam is required, cylindrical lenses and other optics are used. For single spatial mode lasers, using symmetrical lenses, the collimated beam ends up being elliptical in shape, due to the difference in the vertical and lateral divergences. This is easily observable with a red laser pointer. The intensity pattern formed on a screen by diffraction from a square aperture Diffraction refers to various phenomena associated with wave propagation, such as the bending, spreading and interference of waves passing by an object or aperture that disrupts the wave. ... This article is about the optical device. ... A keychain laser pointer. ...


The simple diode described above has been heavily modified in recent years to accommodate modern technology, resulting in a variety of types of laser diodes, as described below.


Laser diode types

The simple laser diode structure, described above, is extremely inefficient. Such devices require so much power that they can only achieve pulsed operation without damage. Although historically important and easy to explain, such devices are not practical.


Double heterostructure lasers

Diagram of front view of a double heterostructure laser diode (not to scale).

In these devices, a layer of low bandgap material is sandwiched between two high bandgap layers. One commonly-used pair of materials is gallium arsenide (GaAs) with aluminium gallium arsenide (AlxGa(1-x)As). Each of the junctions between different bandgap materials is called a heterostructure, hence the name "double heterostructure laser" or DH laser. The kind of laser diode described in the first part of the article may be referred to as a homojunction laser, for contrast with these more popular devices. Image File history File links Simple_dh_laser_diode. ... Image File history File links Simple_dh_laser_diode. ... In solid state physics and related applied fields, the band gap is the energy difference between the top of the valence band and the bottom of the conduction band in insulators and semiconductors. ... This article is about the chemical compound. ... Aluminium gallium arsenide (also Aluminum gallium arsenide) (AlxGa1-xAs) is a semiconductor with very nearly the same lattice constant as GaAs, but a larger bandgap. ... An area location represented by a point, or a line segment that is bound or unbound, or a plane surface bound or unbound, or a structure that can be represented by multi-plane surfaces that bounds the contained area. ...


The advantage of a DH laser is that the region where free electrons and holes exist simultaneously—the active region—is confined to the thin middle layer. This means that many more of the electron-hole pairs can contribute to amplification—not so many are left out in the poorly amplifying periphery. In addition, light is reflected from the heterojunction; hence, the light is confined to the region where the amplification takes place. Within a laser, the active laser medium or gain medium is the material that exhibits optical gain. ...


Quantum well lasers

Diagram of front view of a simple quantum well laser diode (not to scale).
Diagram of front view of a simple quantum well laser diode (not to scale).

If the middle layer is made thin enough, it acts as a quantum well. This means that the vertical variation of the electron's wavefunction, and thus a component of its energy, is quantised. 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. Image File history File links Simple_qw_laser_diode. ... Image File history File links Simple_qw_laser_diode. ... A quantum well is a potential well that confines particles in one dimension, forcing them to occupy a planar region. ... This article discusses the concept of a wavefunction as it relates to quantum mechanics. ... Density of states (DOS) is a property in statistical and condensed matter physics that quantifies how closely packed energy levels are in some physical system. ...


Lasers containing more than one quantum well layer are known as multiple quantum well lasers. Multiple quantum wells improve the overlap of the gain region with the optical waveguide mode. Look up waveguide in Wiktionary, the free dictionary. ... For other types of mode, see mode. ...


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. In condensed matter physics, a quantum wire is an electrically conducting wire, in which quantum effects are affecting transport properties. ... A quantum dot is a semiconductor nanostructure that confines the motion of conduction band electrons, valence band holes, or excitons (bound pairs of conduction band electrons and valence band holes) in all three spatial directions. ...


In a quantum cascade laser, the difference between quantum well energy levels is used for the laser transition instead of the bandgap. This enables laser action at relatively long wavelengths, which can be tuned simply by altering the thickness of the layer. As of 2005, quantum cascade lasers have not yet been widely commercialized. The quantum cascade laser or QC laser is a unipolar laser which uses electrons as its only charge carrier. ... For other uses, see Wavelength (disambiguation). ...


Separate confinement heterostructure lasers

Diagram of front view of a separate confinement heterostructure quantum well laser diode.

The problem with the simple quantum well diode described above is that the thin layer is simply too small to effectively confine the light. To compensate, another two layers are added on, outside the first three. These layers have a lower refractive index than the centre layers, and hence confine the light effectively. Such a design is called a separate confinement heterostructure (SCH) laser diode. Image File history File links Simple_sch_laser_diode. ... Image File history File links Simple_sch_laser_diode. ... The refractive index (or index of refraction) of a medium is a measure for how much the speed of light (or other waves such as sound waves) is reduced inside the medium. ...


Almost all commercial laser diodes since the 1990s have been SCH quantum well diodes.


Distributed feedback lasers

Distributed feedback lasers (DFB) are the most common transmitter type in DWDM-systems. To stabilize the lasing wavelength, a diffraction grating is etched close to the p-n junction of the diode. This grating acts like an optical filter, causing a single wavelength to be fed back to the gain region and lase. Since the grating provides the feedback that is required for lasing, reflection from the facets is not required. Thus, at least one facet of a DFB is anti-reflection coated. The DFB laser has a stable wavelength that is set during manufacturing by the pitch of the grating, and can only be tuned slightly with temperature. Such lasers are the workhorse of demanding optical communication. A distributed feedback laser (DFB) is a type of laser diode where the active region of the device is structured as a diffraction grating. ... The original version of this article was based on FOLDOC, with permission In telecommunications wavelength division multiplexing (WDM) is a technology which multiplexes several optical carrier signals on a single optical fibre by using different wavelengths (colours) of laser light to carry different signals. ... Uncoated glasses lens (top) versus lens with anti-reflective coating. ...


VCSELs

Diagram of a simple VCSEL structure.

Vertical-cavity surface-emitting lasers (VCSELs) have the optical cavity axis along the direction of current flow rather than perpendicular to the current flow as in conventional laser diodes. The active region length is very short compared with the lateral dimensions so that the radiation emerges from the surface of the cavity rather than from its edge as shown in Fig. 2. The reflectors at the ends of the cavity are dielectric mirrors made from alternating high and low refractive index quarter-wave thick multilayer. Image File history File links Simple_vcsel. ... Image File history File links Simple_vcsel. ... Diagram of a simple VCSEL structure. ... A dielectric mirror is a special kind of a mirror. ...


There are several advantages to producing VCSELs when compared with the production process of edge-emitting lasers. Edge-emitters cannot be tested until the end of the production process. If the edge-emitter does not work, whether due to bad contacts or poor material growth quality, the production time and the processing materials have been wasted. Additionally, because VCSELs emit the beam perpendicular to the active region of the laser as opposed to parallel as with an edge emitter, tens of thousands of VCSELs can be processed simultaneously on a three inch Gallium Arsenide wafer. Furthermore, even though the VCSEL production process is more labor and material intensive, the yield can be controlled to a more predictable outcome.


Such dielectric mirrors provide a high degree of wavelength-selective reflectance at the required free surface wavelength λ if the thicknesses of alternating layers d1 and d2 with refractive indices n1 and n2 are such that n1d1 + n2d2 = ½λ which then leads to the constructive interference of all partially reflected waves at the interfaces. But there is a disadvantage because of the high mirror reflectivities, VCSELs have lower output powers when compared to edge emitting lasers.


VECSELs

Vertical external-cavity surface-emitting lasers, or VECSELs, are similar to VCSELs. In VCSELs, the mirrors are typically grown epitaxially as part of the diode structure, or grown separately and bonded directly to the semiconductor containing the active region. VECSELs are distinguished by a construction in which one of the two mirrors is external to the diode structure. As a result, the cavity includes a free-space region. A typical distance from the diode to the external mirror would be 1 cm. A Vertical-External-Cavity Surface-Emitting-Laser (VECSEL) is a small, tunable semiconductor laser similar to a VCSEL. VECSELs are used primarily as near infrared devices in laser cooling and spectroscopy. ... Epitaxy is the growth of crystals of one material on the crystal face of another (heteroepitaxy) or the same (homoepitaxy) material, such that the two materials have a defined relative structural orientation. ...


One of the most interesting features of any VECSEL is the thin-ness of the semiconductor gain region in the direction of propagation, less than 100 nm. In contrast, a conventional in-plane semiconductor laser entails light propagation over distances of from 250 µm upward to 2 mm or longer. The significance of the short propagation distance is that it causes the effect of "antiguiding" nonlinearities in the diode laser gain region to be minimized. The result is a large-cross-section single-mode optical beam which is not attainable from in-plane ("edge-emitting") diode lasers.


Several workers demonstrated optically pumped VECSELs, and they continue to be developed for many applications including high power sources for use in industrial machining (cutting, punching, etc.) because of their unusually high power and efficiency when pumped by multi-mode diode laser bars.


Electrically pumped VECSELs have also been demonstrated. Applications for electrically pumped VECSELs include projection displays, served by frequency doubling of near-IR VECSEL emitters to produce blue and green light. Second harmonic generation (SHG; also called frequency doubling) is a nonlinear optical process, in which photons interacting with a nonlinear material are effectively combined to form new photons with twice the energy, and therefore twice the frequency and half the wavelength of the initial photons. ...


Failure modes

Laser diodes have similar reliability and failure issues as light emitting diodes. In addition, they are subject to catastrophic optical damage (COD) when operated at higher power. Reliability engineering is the discipline of ensuring that a system (or a device in general) will perform its intended function(s) when operated in a specified manner for a specified length of time. ... External links LEd Category: TeX ... Catastrophic optical damage (COD) is a failure mode of high-power semiconductor lasers. ...


Many of the advances in reliability of diode lasers in the last 20 years remain proprietary to their developers. The reliability of a laser diode can make or break a product line. Moreover, "reverse engineering" is not always able to uncover the differences between more-reliable and less-reliable diode laser products. Reverse engineering (RE) is the process of taking something (a device, an electrical component, a software program, etc. ...


At the edge of a diode laser, where light is emitted, a mirror is traditionally formed by cleaving the semiconductor wafer to form a specularly reflecting plane. This approach is facilitated by the weakness of the [110] crystallographic plane in III-V semiconductor crystals (such as GaAs, InP, GaSb, etc.) compared to other planes. A scratch made at the edge of the wafer and a slight bending force causes a nearly atomically perfect mirror-like cleavage plane to form and propagate in a straight line across the wafer. Cleavage, in mineralogy, is the tendency of crystalline materials to split along definite planes, creating smooth surfaces, of which there are several named types: Basal cleavage: cleavage parallel to the base of a crystal, or to the plane of the lateral axes. ... Crystallography (from the Greek words crystallon = cold drop / frozen drop, with its meaning extending to all solids with some degree of transparency, and graphein = write) is the experimental science of determining the arrangement of atoms in solids. ... Gallium arsenide (GaAs) is a chemical compound composed of gallium and arsenic. ... Flash point Non-flmmable. ... Gallium antimonide (GaSb) is a semiconducting compound of gallium and antimony of the III-V family. ...


But it so happens that the atomic states at the cleavage plane are altered (compared to their bulk properties within the crystal) by the termination of the perfectly periodic lattice at that plane. Surface states at the cleaved plane, have energy levels within the (otherwise forbidden) bandgap of the semiconductor. Surface states are electronic states found at the surface of materials and are part of condensed matter physics. ...


Essentially as a result, when light propagates through the cleavage plane and transits to free space from within the semiconductor crystal, a fraction of that light energy is absorbed by the surface states whence it is converted to heat by phonon-electron interactions. This heats the cleaved mirror. In addition, the mirror may heat simply because the edge of the diode laser—which is electrically pumped—is in less-perfect contact with the mount that provides a path for heat removal. The heating of the mirror causes the bandgap of the semiconductor to shrink in the warmer areas. The bandgap shrinkage brings more electronic band-to-band transitions into alignment with the photon energy causing yet more absorption. This is thermal runaway, a form of positive feedback, and the result can be melting of the facet, known as catastrophic optical damage, or COD. Normal modes of vibration progression through a crystal. ... For other uses, see Electron (disambiguation). ... This article is about Thermal runaway. ... Positive feedback is a feedback system in which the system responds to the perturbation in the same direction as the perturbation (It is sometimes referred to as cumulative causation). ...


In the 1970's, this problem, which is particularly nettlesome for GaAs-based lasers emitting between 1 µm and 0.630 µm wavelengths (less so for InP based lasers used for long-haul telecommunications which emit between 1.3 µm and 2 µm), was identified. Michael Ettenberg, a researcher and later Vice President at RCA Laboratories' David Sarnoff Research Center in Princeton, New Jersey, devised a solution. A thin layer of aluminum oxide was deposited on the facet. If the aluminum oxide thickness is chosen correctly it functions as an anti-reflective coating, reducing reflection at the surface. This alleviated the heating and COD at the facet. RCA, formerly an acronym for the Radio Corporation of America, is now a trademark owned by Thomson SA through RCA Trademark Management S.A., a company owned by Thomson. ... Sarnoff Corporation, with headquarters on the southeast side (northbound lane) of U.S. Route 1 in Princeton, New Jersey, is the former RCA Laboratories. ... Nassau Street, Princetons main street. ... Aluminium oxide (or aluminum oxide) (Al2O3) is a chemical compound of aluminium and oxygen. ... Anti-reflective coatings are a type of optical coating applied to lenses and other devices to reduce reflection from optical surfaces. ...


Since then, various other refinements have been employed. One approach is to create a so-called non-absorbing mirror (NAM) such that the final 10 µm or so before the light emits from the cleaved facet are rendered non-absorbing at the wavelength of interest.


In the very early 1990s, SDL, Inc. began supplying high power diode lasers with good reliability characteristics. CEO Donald Scifres and CTO David Welch presented new reliability performance data at, e.g., SPIE Photonics West conferences of the era. The methods used by SDL to defeat COD were considered to be highly proprietary and have still not been disclosed publicly as of June, 2006. SPIE - The International Society for Optical Engineering (or SPIE) is a not-for-profit society that has become the largest international force for the exchange, collection and dissemination of knowledge in optics, photonics, and imaging engineering. ...


In the mid-1990s, IBM Research (Ruschlikon, Switzerland) announced that it had devised its so-called "E2 process" which conferred extraordinary resistance to COD in GaAs-based lasers. This process, too, has never been disclosed as of June, 2006.


Reliability of high-power diode laser pump bars (employed to pump solid state lasers) remains a difficult problem in a variety of applications, in spite of these proprietary advances. Indeed, the physics of diode laser failure is still in the process of being worked out and research on this subject remains active, if proprietary.


Extension of the lifetime of laser diodes is critical to their continued adaptation to a wide variety of applications.


Applications of laser diodes

Laser diodes can be arrayed to produce very high power (continuous wave or pulsed) outputs. Such arrays may be used to efficiently pump solid state lasers for inertial confinement fusion or high average power drilling or burning applications.
Laser diodes can be arrayed to produce very high power (continuous wave or pulsed) outputs. Such arrays may be used to efficiently pump solid state lasers for inertial confinement fusion or high average power drilling or burning applications.

Laser diodes are numerically the most common type of laser, with 2004 sales of approximately 733 million diode lasers,[1] as compared to 131,000 of other types of lasers.[2] Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... Inertial confinement fusion using lasers rapidly progressed in the late 1970s and early 1980s from being able to deliver only a few joules of laser energy (per pulse) to a fusion target to being able to deliver tens of kilojoules to a target. ... Year 2004 (MMIV) was a leap year starting on Thursday of the Gregorian calendar. ...


Laser diodes find wide use in telecommunication as easily modulated and easily coupled light sources for fiber optics communication. They are used in various measuring instruments, eg. rangefinders. Another common use is in barcode readers. Visible lasers, typically red but later also green, are common as laser pointers. Both low and high-power diodes are used extensively in the printing industry both as light sources for scanning (input) of images and for very high-speed and high-resolution printing plate (output) manufacturing. Infrared and red laser diodes are common in CD players, CD-ROMs and DVD technology. Violet lasers are used in HD-DVD and Blu-Ray technology. High-power laser diodes are used in industrial applications such as heat treating, cladding, seam welding and for pumping other lasers, such as diode pumped solid state lasers. The use of diode lasers for high-speed, low-cost, combustion spectroscopy is being explored. Copy of the original phone of Alexander Graham Bell at the Musée des Arts et Métiers in Paris Telecommunication is the assisted transmission of signals over a distance for the purpose of communication. ... Optical fibers An optical fiber (or fibre) is a glass or plastic fiber designed to guide light along its length. ... A rangefinder is an optical device that allows distance to be estimated or measured using triangulation, laser, radar, or other method. ... A typical barcode scanner. ... The optical spectrum (light or visible spectrum) is the portion of the electromagnetic spectrum that is visible to the human eye. ... For other uses, see Red (disambiguation). ... For other uses, see Green (disambiguation). ... A keychain laser pointer. ... For other uses, see Infrared (disambiguation). ... CD, DVD and SACD player A Compact Disc player (often written as compact disc player), or CD player, is an electronic device which plays audio Compact Discs. ... The CD-ROM (an abbreviation for Compact Disc Read-Only Memory (ROM)) is a non-volatile optical data storage medium using the same physical format as audio compact discs, readable by a computer with a CD-ROM drive. ... DVD (also known as Digital Versatile Disc or Digital Video Disc) is a popular optical disc storage media format. ... Violet (named after the flower violet) is used in two senses: first, referring to the color of light at the short-wavelength end of the visible spectrum, approximately 380–420 nanometres (this is a spectral color). ... HD DVD or High-Definition DVD is a high-density optical disc format designed for the storage of data and high-definition video. ... A Blu-ray Disc (also called BDray) is a high-density optical disc format for the storage of digital information, including high-definition video. ... Diode pumped solid state (DPSS) lasers are solid-state lasers made by pumping a solid gain medium, for example, a ruby or a neodymium-doped YAG crystal, with a laser diode. ...


In general, applications of laser diodes can be categorized in various ways. Most applications of diode lasers can be served by larger solid state lasers or optical parametric oscillators but it is the ability to mass-produce diode lasers at low cost that makes them essential for mass-market applications. Diode lasers have application to virtually every field of endeavor that attracts wide attention today. Since light has many different properties (power, wavelength & spectral quality, beam quality, polarization, etc.) it is interesting to classify applications by these basic properties.


Many applications of diode lasers primarily make use of the "directed energy" property of an optical beam. In this category one might include the laser printers, bar-code readers, image scanning, illuminators, designators, optical data recording, combustion ignition, laser surgery, industrial sorting, industrial machining, and directed energy weaponry. Some of these applications are emerging whereas many are familiar to the wider society. 1993 Apple LaserWriter Pro 630 laser printer A laser printer is a common type of computer printer that rapidly produces high quality text and graphics on plain paper. ... A typical barcode scanner. ... Image scanning is the action or process of producing images from text documents, photographic film, photographic paper or other physical objects. ... Lasers were used in the 2005 Classical Spectacular concert Soon after the invention of the laser in 1960, it was described as a solution in search of a problem. However, since that time, the laser has found a place as a useful tool in many scientific, military, medical and industrial...


Applications which may today or in the future make use of the "coherent" properties of diode-laser-generated light include interferometric distance measurement, holography, coherent communications, and coherent control of chemical reactions.


Applications which may make use of "narrow spectral" properties of diode lasers include range-finding, telecommunications, infra-red countermeasures, spectroscopic sensing, generation of radio-frequency or terahertz waves, atomic clock state preparation, quantum key cryptography, frequency doubling and conversion, water purification (in the UV), and photodynamic therapy (where a particular wavelength of light would cause a substance such as porphyrin to become chemically active as an anti-cancer agent only where the tissue is illuminated by light). Structure of porphine, the simplest porphyrin. ...


Applications where the ability to "generate ultra-short pulses of light" by the technique known as "mode-locking" include clock distribution for high-performance integrated circuits, high-peak-power sources for laser-induced breakdown spectroscopy sensing, arbitrary waveform generation for radio-frequency waves, photonic sampling for analog-to-digital conversion, and optical code-division-multiple-access systems for secure communication.


History

The first to demonstrate coherent light emission from a semiconductor diode (the first laser diode), is widely acknowledged to have been Robert N. Hall and his team at the General Electric research center in 1962.[3] Coherence is the property of wave-like states that enables them to exhibit interference. ... American inventor Robert N. Hall (December 25, 1919-) demonstrated the first semiconductor laser, and invented a type of magnetron commonly used in microwave ovens. ...


The first visible wavelength laser diode was demonstrated by Nick Holonyak, Jr., later in 1962[4] Nick Holonyak Jr. ...


Other teams at IBM, MIT Lincoln Laboratory, Texas Instruments, and RCA Laboratories were also involved in and receive credit for historic initial demonstrations of efficient light emission and lasing in semiconductor diodes in 1962 and thereafter.


In the early 1960s liquid phase epitaxy (LPE) was invented by Herbert Nelson of RCA Laboratories. By layering the highest quality crystals of varying compositions, it enabled the demonstration of the highest quality heterojunction semiconductor laser materials for many years. LPE was adopted by all the leading laboratories, worldwide and used for many years. It was finally supplanted in the 1970s by molecular beam epitaxy and organometallic chemical vapor deposition.


Diode lasers of that era operated with threshold current densities of 1000 Amperes per square centimeter at 77°K temperatures. This is a rather modest current density considering that the contact area of diode lasers is a tiny fraction of a square centimeter. Such performance enabled continuous-lasing to be demonstrated in the earliest days. However, when operated at room temperature, 300°K or thereabouts, the threshold current densities were two orders of magnitude greater, or 100,000 Amperes per square centimeter in the best devices. The dominant challenge for the remainder of the 1960s was to obtain low threshold current density at 300°K and thereby to demonstrate continuous-wave lasing at room temperature from a diode laser.


The first diode lasers were homojunction diodes. That is, the bandgaps of the waveguide core layer and that of the surrounding clad layers, were identical. It was recognized that there was an opportunity, particularly afforded by the use of liquid phase epitaxy using aluminum gallium arsenide, to introduce heterojunctions. Heterostructures consist of layers of semiconductor crystal having varying bandgap and refractive index. Heterojunctions (formed from heterostructures) had been recognized by Herbert Kroemer, while working at RCA Laboratories in the mid-1950s, as having unique advantages for several types of electronic and optoelectronic devices including diode lasers. LPE afforded the technology of making heterojunction diode lasers. Herbert Kroemer (born August 25, 1928) is a Professor of Electrical and Computer Engineering at University of California, Santa Barbara, received a Ph. ...


The first heterojunction diode lasers were single-heterojunction lasers. These lasers utilized aluminum gallium arsenide p-type injectors situated over n-type gallium arsenide layers grown on the substrate by LPE. An admixture of aluminum replaced gallium in the semiconductor crystal and raised the bandgap of the p-type injector over that of the n-type layers beneath. It worked; the 300°K threshold currents went down by 10× to 10,000 amperes per square centimeter. Unfortunately, this was still not in the needed range and these single-heterostructure diode lasers did not function in continuous wave operation at room temperature.


The innovation that broke the room temperature challenge was the double heterostructure laser. The trick was to quickly move the wafer in the LPE apparatus between different "melts" of aluminum gallium arsenide (p- and n-type) and a third melt of gallium arsenide. It had to be done rapidly since the gallium arsenide core region needed to be significantly under 1 µm in thickness. This may have been the earliest true example of "nanotechnology." The first laser diode to achieve continuous wave operation was a double heterostructure demonstrated in 1970 essentially simultaneously by Zhores Alferov and collaborators (including Dmitri Z. Garbuzov) of the Soviet Union, and Morton Panish and Izuo Hayashi working in the United States. However, it is widely accepted that Zhores I. Alferov and team reached the milestone first. A continuous wave (CW) is an electromagnetic wave of constant amplitude and frequency. ... A double heterostructure is formed when two semiconductor materials, one with an energy gap, less than the other are joined together. ... Zhores Ivanovich Alferov (also Alfyorov) (Russian: Жоре́с Ива́нович Алфёров) (born March 15, 1930) is a Soviet/Russian physicist with a Belarusian origin. ... Dmitri Z. Garbuzov (1940, Sverdlovsk, Russia - August 2006, Princeton, New Jersey) is one of the pioneers and inventors of room temperature continuous-wave-operating diode lasers and high-power diode lasers which were successfully invented, developed, and almost simultaneously demonstrated at the Ioffe Physico-Technical Institute in Leningrad, Russia by... Izuo Hayashi ) (May 1, 1922-September 26, 2005) was a Japanese physicist. ...


For their accomplishment and that of their co-workers, Alferov and Kroemer shared the 2000 Nobel Prize in Physics.


See also

The semiconductor laser multimode rate equations relate photon and carrier (electron) numbers or densities, to device parameters such as carrier and photon lifetime, optical gain, injection current and other material parameters. ... A collimating lens is a lens used to gather together a parallel beam of light. ... Superluminescent diode (SLD) is an edge-emitting semiconductor light source based on superluminescence, combines high power and brightness of laser diodes with low coherence of ELED. Emission band (on 2005): 20-100 nm. ... Millstone River Photonickers is an informal affinity association of those individuals associated with the development of semiconductor diode laser technology at RCA Laboratories and its successor organization Sarnoff Corporation, as well as companies and government or university groups which have grown out of the RCA Laboratories optoelectronics tradition. ...

References

  1. ^ Steele, Robert V. (2005). "Diode-laser market grows at a slower rate". Laser Focus World 41 (2). 
  2. ^ Kincade, Kathy; Stephen Anderson (2005). "Laser Marketplace 2005: Consumer applications boost laser sales 10%". Laser Focus World 41 (1). 
  3. ^ Hall, Robert N.; G. E. Fenner, J. D. Kingsley, T. J. Soltys, and R. O. Carlson (Nov. 1962). "Coherent Light Emission From GaAs Junctions". Physical Review Letters 9 (9): 366–369. doi:10.1103/PhysRevLett.9.366. 
  4. ^ "After Glow", Illinois Alumni Magazine, May-June 2007. Retrieved on 2007-08-03. 
  • Zheludev, N. (2007). The life and times of the LED - a 100-year history. Nature Photonics 1(4), 189-192 ( For LED )
  • B. Van Zeghbroeck's Principles of Semiconductor Devices( for direct and indirect band gaps)
  • Saleh, Bahaa E. A. and Teich, Malvin Carl (1991). Fundamentals of Photonics. New York: John Wiley & Sons. ISBN 0-471-83965-5. ( For Stimulated Emission )
  • Koyama et al, Fumio (1988), "Room temperature cw operation of GaAs vertical cavity surface emitting laser", Trans. IEICE, E71(11): 1089-1090( for VCSELS)
  • Iga, Kenichi (2000), "Surface-emitting laser—Its birth and generation of new optoelectronics field", IEEE Journal of Selected Topics in Quantum Electronics 6(6): 1201–1215(for VECSELS)

American inventor Robert N. Hall (December 25, 1919-) demonstrated the first semiconductor laser, and invented a type of magnetron commonly used in microwave ovens. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... is the 215th day of the year (216th in leap years) in the Gregorian calendar. ...

External links


  Results from FactBites:
 
Laser diode - Wikipedia, the free encyclopedia (1920 words)
A laser diode is a laser where the active medium is a semiconductor similar to that found in a light-emitting diode.
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.
Laser diodes are numerically the most common type of laser, with 2004 sales of approximately 733 million diode lasers (Steele 2005), as compared to 131,000 of other types of lasers (Kincade and Anderson 2005).
  More results at FactBites »

 
 

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