Misplaced Pages

#900099

112-600: The US based company ROFIN-SINAR Technologies Inc. develops, manufactures and sells laser sources and laser-based solutions for industrial material processing. On 7 November 2016, the company was acquired by Coherent Inc . From 1996 to November 2016, ROFIN-SINAR Technologies’ shares have been traded on the NASDAQ Stock Exchange. In addition, in July 2001, RSTI was listed on the German "Prime Standard" segment of

224-464: A Swiss manufacturer of cameras . By taking over the British enterprise Rofin, the company changed its name to ROFIN-SINAR Laser GmbH. In 2015, Rofin came under significant pressure by an investor, SilverArrow Capital, to exchange the companies independent directors based on questions on compliance and below average management performance. SilverArrow, a London-based activist investment firm and one of

336-519: A gain medium , a mechanism to energize it, and something to provide optical feedback . The gain medium is a material with properties that allow it to amplify light by way of stimulated emission. Light of a specific wavelength that passes through the gain medium is amplified (power increases). Feedback enables stimulated emission to amplify predominantly the optical frequency at the peak of the gain-frequency curve. As stimulated emission grows, eventually one frequency dominates over all others, meaning that

448-471: A lens system, as is always included, for instance, in a laser pointer whose light originates from a laser diode . That is possible due to the light being of a single spatial mode. This unique property of laser light, spatial coherence , cannot be replicated using standard light sources (except by discarding most of the light) as can be appreciated by comparing the beam from a flashlight (torch) or spotlight to that of almost any laser. A laser beam profiler

560-563: A GaAs p-n junction light emitter and an electrically isolated semiconductor photodetector. On August 8, 1962, Biard and Pittman filed a patent titled "Semiconductor Radiant Diode" based on their findings, which described a zinc-diffused p–n junction LED with a spaced cathode contact to allow for efficient emission of infrared light under forward bias . After establishing the priority of their work based on engineering notebooks predating submissions from G.E. Labs, RCA Research Labs, IBM Research Labs, Bell Labs , and Lincoln Lab at MIT ,

672-464: A broad spectrum of light or emit different wavelengths of light simultaneously. Certain lasers are not single spatial mode and have light beams that diverge more than is required by the diffraction limit . All such devices are classified as "lasers" based on the method of producing light by stimulated emission. Lasers are employed where light of the required spatial or temporal coherence can not be produced using simpler technologies. A laser consists of

784-504: A chain reaction. The materials chosen for lasers are the ones that have metastable states , which stay excited for a relatively long time. In laser physics , such a material is called an active laser medium . Combined with an energy source that continues to "pump" energy into the material, it is possible to have enough atoms or molecules in an excited state for a chain reaction to develop. Lasers are distinguished from other light sources by their coherence . Spatial (or transverse) coherence

896-436: A coherent beam has been formed. The process of stimulated emission is analogous to that of an audio oscillator with positive feedback which can occur, for example, when the speaker in a public-address system is placed in proximity to the microphone. The screech one hears is audio oscillation at the peak of the gain-frequency curve for the amplifier. For the gain medium to amplify light, it needs to be supplied with energy in

1008-671: A current source of a battery or a pulse generator and with a comparison to a variant, pure, crystal in 1953. Rubin Braunstein of the Radio Corporation of America reported on infrared emission from gallium arsenide (GaAs) and other semiconductor alloys in 1955. Braunstein observed infrared emission generated by simple diode structures using gallium antimonide (GaSb), GaAs, indium phosphide (InP), and silicon-germanium (SiGe) alloys at room temperature and at 77  kelvins . In 1957, Braunstein further demonstrated that

1120-419: A device lacks the spatial and temporal coherence achievable with lasers. Such a device cannot be described as an oscillator but rather as a high-gain optical amplifier that amplifies its spontaneous emission. The same mechanism describes so-called astrophysical masers /lasers. The optical resonator is sometimes referred to as an "optical cavity", but this is a misnomer: lasers use open resonators as opposed to

1232-508: A gain medium must have a gain bandwidth sufficiently broad to amplify those frequencies. An example of a suitable material is titanium -doped, artificially grown sapphire ( Ti:sapphire ), which has a very wide gain bandwidth and can thus produce pulses of only a few femtoseconds duration. Such mode-locked lasers are a most versatile tool for researching processes occurring on extremely short time scales (known as femtosecond physics, femtosecond chemistry and ultrafast science ), for maximizing

SECTION 10

#1732793545901

1344-480: A given pulse energy, this requires creating pulses of the shortest possible duration utilizing techniques such as Q-switching . The optical bandwidth of a pulse cannot be narrower than the reciprocal of the pulse width. In the case of extremely short pulses, that implies lasing over a considerable bandwidth, quite contrary to the very narrow bandwidths typical of CW lasers. The lasing medium in some dye lasers and vibronic solid-state lasers produces optical gain over

1456-554: A glass window or lens to let the light out. Modern indicator LEDs are packed in transparent molded plastic cases, tubular or rectangular in shape, and often tinted to match the device color. Infrared devices may be dyed, to block visible light. More complex packages have been adapted for efficient heat dissipation in high-power LEDs . Surface-mounted LEDs further reduce the package size. LEDs intended for use with fiber optics cables may be provided with an optical connector. The first blue -violet LED, using magnesium-doped gallium nitride

1568-399: A higher energy level with energy difference ΔE, it will not stay that way forever. Eventually, a photon will be spontaneously created from the vacuum having energy ΔE. Conserving energy, the electron transitions to a lower energy level that is not occupied, with transitions to different levels having different time constants. This process is called spontaneous emission . Spontaneous emission is

1680-476: A laser beam, it is highly collimated : the wavefronts are planar, normal to the direction of propagation, with no beam divergence at that point. However, due to diffraction , that can only remain true well within the Rayleigh range . The beam of a single transverse mode (gaussian beam) laser eventually diverges at an angle that varies inversely with the beam diameter, as required by diffraction theory. Thus,

1792-471: A laser is normally a material of controlled purity, size, concentration, and shape, which amplifies the beam by the process of stimulated emission described above. This material can be of any state : gas, liquid, solid, or plasma . The gain medium absorbs pump energy, which raises some electrons into higher energy (" excited ") quantum states . Particles can interact with light by either absorbing or emitting photons. Emission can be spontaneous or stimulated. In

1904-568: A longer lifetime, improved physical robustness, smaller sizes, and faster switching. In exchange for these generally favorable attributes, disadvantages of LEDs include electrical limitations to low voltage and generally to DC (not AC) power, the inability to provide steady illumination from a pulsing DC or an AC electrical supply source, and a lesser maximum operating temperature and storage temperature. LEDs are transducers of electricity into light. They operate in reverse of photodiodes , which convert light into electricity. Electroluminescence as

2016-485: A loudspeaker. Intercepting the beam stopped the music. We had a great deal of fun playing with this setup." In September 1961, while working at Texas Instruments in Dallas , Texas , James R. Biard and Gary Pittman discovered near-infrared (900 nm) light emission from a tunnel diode they had constructed on a GaAs substrate. By October 1961, they had demonstrated efficient light emission and signal coupling between

2128-557: A method for producing high-brightness blue LEDs using a new two-step process in 1991. In 2015, a US court ruled that three Taiwanese companies had infringed Moustakas's prior patent, and ordered them to pay licensing fees of not less than US$ 13 million. Two years later, in 1993, high-brightness blue LEDs were demonstrated by Shuji Nakamura of Nichia Corporation using a gallium nitride (GaN) growth process. These LEDs had efficiencies of 10%. In parallel, Isamu Akasaki and Hiroshi Amano of Nagoya University were working on developing

2240-418: A multi-level system as a method for obtaining the population inversion, later a main method of laser pumping. Townes reports that several eminent physicists—among them Niels Bohr , John von Neumann , and Llewellyn Thomas —argued the maser violated Heisenberg's uncertainty principle and hence could not work. Others such as Isidor Rabi and Polykarp Kusch expected that it would be impractical and not worth

2352-523: A phenomenon was discovered in 1907 by the English experimenter Henry Joseph Round of Marconi Labs , using a crystal of silicon carbide and a cat's-whisker detector . Russian inventor Oleg Losev reported the creation of the first LED in 1927. His research was distributed in Soviet, German and British scientific journals, but no practical use was made of the discovery for several decades, partly due to

SECTION 20

#1732793545901

2464-574: A phosphor-silicon mixture on the LED using techniques such as jet dispensing, and allowing the solvents to evaporate, the LEDs are often tested, and placed on tapes for SMT placement equipment for use in LED light bulb production. Some "remote phosphor" LED light bulbs use a single plastic cover with YAG phosphor for one or several blue LEDs, instead of using phosphor coatings on single-chip white LEDs. Ce:YAG phosphors and epoxy in LEDs can degrade with use, and

2576-441: A process called pumping . The energy is typically supplied as an electric current or as light at a different wavelength. Pump light may be provided by a flash lamp or by another laser. The most common type of laser uses feedback from an optical cavity —a pair of mirrors on either end of the gain medium. Light bounces back and forth between the mirrors, passing through the gain medium and being amplified each time. Typically one of

2688-483: A process of optical amplification based on the stimulated emission of electromagnetic radiation . The word laser is an anacronym that originated as an acronym for light amplification by stimulated emission of radiation . The first laser was built in 1960 by Theodore Maiman at Hughes Research Laboratories , based on theoretical work by Charles H. Townes and Arthur Leonard Schawlow . A laser differs from other sources of light in that it emits light that

2800-468: A quantum-mechanical effect and a direct physical manifestation of the Heisenberg uncertainty principle . The emitted photon has a random direction, but its wavelength matches the absorption wavelength of the transition. This is the mechanism of fluorescence and thermal emission . A photon with the correct wavelength to be absorbed by a transition can also cause an electron to drop from the higher to

2912-508: A red light-emitting diode. GaAsP was the basis for the first wave of commercial LEDs emitting visible light. It was mass produced by the Monsanto and Hewlett-Packard companies and used widely for displays in calculators and wrist watches. M. George Craford , a former graduate student of Holonyak, invented the first yellow LED and improved the brightness of red and red-orange LEDs by a factor of ten in 1972. In 1976, T. P. Pearsall designed

3024-432: A seminar on this idea, and Charles H. Townes asked him for a copy of the paper. In 1953, Charles H. Townes and graduate students James P. Gordon and Herbert J. Zeiger produced the first microwave amplifier, a device operating on similar principles to the laser, but amplifying microwave radiation rather than infrared or visible radiation. Townes's maser was incapable of continuous output. Meanwhile, in

3136-431: A small volume of material at the surface of a workpiece can be evaporated if it is heated in a very short time, while supplying the energy gradually would allow for the heat to be absorbed into the bulk of the piece, never attaining a sufficiently high temperature at a particular point. Other applications rely on the peak pulse power (rather than the energy in the pulse), especially to obtain nonlinear optical effects. For

3248-646: A very narrow frequency spectrum . Temporal coherence can also be used to produce ultrashort pulses of light with a broad spectrum but durations as short as an attosecond . Lasers are used in optical disc drives , laser printers , barcode scanners , DNA sequencing instruments , fiber-optic and free-space optical communications, semiconductor chip manufacturing ( photolithography , etching ), laser surgery and skin treatments, cutting and welding materials, military and law enforcement devices for marking targets and measuring range and speed, and in laser lighting displays for entertainment. Semiconductor lasers in

3360-430: A wide bandwidth, making a laser possible that can thus generate pulses of light as short as a few femtoseconds (10 s). In a Q-switched laser, the population inversion is allowed to build up by introducing loss inside the resonator which exceeds the gain of the medium; this can also be described as a reduction of the quality factor or 'Q' of the cavity. Then, after the pump energy stored in the laser medium has approached

3472-492: A wide range of technologies addressing many different motivations. Some lasers are pulsed simply because they cannot be run in continuous mode. In other cases, the application requires the production of pulses having as large an energy as possible. Since the pulse energy is equal to the average power divided by the repetition rate, this goal can sometimes be satisfied by lowering the rate of pulses so that more energy can be built up between pulses. In laser ablation , for example,

Rofin-Sinar - Misplaced Pages Continue

3584-934: A wide variety of consumer electronics. The first visible-light LEDs were of low intensity and limited to red. Early LEDs were often used as indicator lamps, replacing small incandescent bulbs , and in seven-segment displays . Later developments produced LEDs available in visible , ultraviolet (UV), and infrared wavelengths with high, low, or intermediate light output, for instance, white LEDs suitable for room and outdoor lighting. LEDs have also given rise to new types of displays and sensors, while their high switching rates are useful in advanced communications technology with applications as diverse as aviation lighting , fairy lights , strip lights , automotive headlamps , advertising, general lighting , traffic signals , camera flashes, lighted wallpaper , horticultural grow lights , and medical devices. LEDs have many advantages over incandescent light sources, including lower power consumption,

3696-445: Is coherent . Spatial coherence allows a laser to be focused to a tight spot, enabling applications such as optical communication, laser cutting , and lithography . It also allows a laser beam to stay narrow over great distances ( collimation ), a feature used in applications such as laser pointers , lidar , and free-space optical communication . Lasers can also have high temporal coherence , which permits them to emit light with

3808-404: Is a transition between energy levels that match the energy carried by the photon or phonon. For light, this means that any given transition will only absorb one particular wavelength of light. Photons with the correct wavelength can cause an electron to jump from the lower to the higher energy level. The photon is consumed in this process. When an electron is excited from one state to that at

3920-480: Is also required for three-level lasers in which the lower energy level rapidly becomes highly populated, preventing further lasing until those atoms relax to the ground state. These lasers, such as the excimer laser and the copper vapor laser, can never be operated in CW mode. In 1917, Albert Einstein established the theoretical foundations for the laser and the maser in the paper " Zur Quantentheorie der Strahlung " ("On

4032-413: Is called an optical amplifier . When an optical amplifier is placed inside a resonant optical cavity, one obtains a laser. For lasing media with extremely high gain, so-called superluminescence , light can be sufficiently amplified in a single pass through the gain medium without requiring a resonator. Although often referred to as a laser (see, for example, nitrogen laser ), the light output from such

4144-550: Is difficult but desirable since it takes advantage of existing semiconductor manufacturing infrastructure. It allows for the wafer-level packaging of LED dies resulting in extremely small LED packages. GaN is often deposited using metalorganic vapour-phase epitaxy (MOCVD), and it also uses lift-off . Even though white light can be created using individual red, green and blue LEDs, this results in poor color rendering , since only three narrow bands of wavelengths of light are being emitted. The attainment of high efficiency blue LEDs

4256-492: Is difficult on silicon , while others, like the University of Cambridge, choose a multi-layer structure, in order to reduce (crystal) lattice mismatch and different thermal expansion ratios, to avoid cracking of the LED chip at high temperatures (e.g. during manufacturing), reduce heat generation and increase luminous efficiency. Sapphire substrate patterning can be carried out with nanoimprint lithography . GaN-on-Si

4368-462: Is emitted by stimulated emission is identical to the photon that triggered its emission, and both photons can go on to trigger stimulated emission in other atoms, creating the possibility of a chain reaction . For this to happen, many of the atoms or molecules must be in the proper excited state so that the photons can trigger them. In most materials, atoms or molecules drop out of excited states fairly rapidly, making it difficult or impossible to produce

4480-421: Is formed by single-frequency quantum photon states distributed according to a Poisson distribution . As a result, the arrival rate of photons in a laser beam is described by Poisson statistics. Many lasers produce a beam that can be approximated as a Gaussian beam ; such beams have the minimum divergence possible for a given beam diameter. Some lasers, particularly high-power ones, produce multimode beams, with

4592-443: Is frequently used in the field, meaning "to give off coherent light," especially about the gain medium of a laser; when a laser is operating, it is said to be " lasing ". The terms laser and maser are also used for naturally occurring coherent emissions, as in astrophysical maser and atom laser . A laser that produces light by itself is technically an optical oscillator rather than an optical amplifier as suggested by

Rofin-Sinar - Misplaced Pages Continue

4704-421: Is impossible. In some other lasers, it would require pumping the laser at a very high continuous power level, which would be impractical, or destroying the laser by producing excessive heat. Such lasers cannot be run in CW mode. The pulsed operation of lasers refers to any laser not classified as a continuous wave so that the optical power appears in pulses of some duration at some repetition rate. This encompasses

4816-794: Is more apparent with higher concentrations of Ce:YAG in phosphor-silicone mixtures, because the Ce:YAG decomposes with use. The output of LEDs can shift to yellow over time due to degradation of the silicone. There are several variants of Ce:YAG, and manufacturers in many cases do not reveal the exact composition of their Ce:YAG offerings. Several other phosphors are available for phosphor-converted LEDs to produce several colors such as red, which uses nitrosilicate phosphors, and many other kinds of phosphor materials exist for LEDs such as phosphors based on oxides, oxynitrides, oxyhalides, halides, nitrides, sulfides, quantum dots, and inorganic-organic hybrid semiconductors. A single LED can have several phosphors at

4928-405: Is not the result of random thermal processes. Instead, the release of a photon is triggered by the nearby passage of another photon. This is called stimulated emission . For this process to work, the passing photon must be similar in energy, and thus wavelength, to the one that could be released by the atom or molecule, and the atom or molecule must be in the suitable excited state. The photon that

5040-599: Is perceived as white light, with improved color rendering compared to wavelengths from the blue LED/YAG phosphor combination. The first white LEDs were expensive and inefficient. The light output then increased exponentially . The latest research and development has been propagated by Japanese manufacturers such as Panasonic and Nichia , and by Korean and Chinese manufacturers such as Samsung , Solstice, Kingsun, Hoyol and others. This trend in increased output has been called Haitz's law after Roland Haitz. Light output and efficiency of blue and near-ultraviolet LEDs rose and

5152-489: Is to heat an object; some of the thermal energy being applied to the object will cause the molecules and electrons within the object to gain energy, which is then lost through thermal radiation , that we see as light. This is the process that causes a candle flame to give off light. Thermal radiation is a random process, and thus the photons emitted have a range of different wavelengths , travel in different directions, and are released at different times. The energy within

5264-504: Is to pump the laser material with a source that is itself pulsed, either through electronic charging in the case of flash lamps, or another laser that is already pulsed. Pulsed pumping was historically used with dye lasers where the inverted population lifetime of a dye molecule was so short that a high-energy, fast pump was needed. The way to overcome this problem was to charge up large capacitors which are then switched to discharge through flashlamps, producing an intense flash. Pulsed pumping

5376-451: Is to use individual LEDs that emit three primary colors —red, green and blue—and then mix all the colors to form white light. The other is to use a phosphor material to convert monochromatic light from a blue or UV LED to broad-spectrum white light, similar to a fluorescent lamp . The yellow phosphor is cerium -doped YAG crystals suspended in the package or coated on the LED. This YAG phosphor causes white LEDs to appear yellow when off, and

5488-441: Is typically expressed through the output being a narrow beam, which is diffraction-limited . Laser beams can be focused to very tiny spots, achieving a very high irradiance , or they can have a very low divergence to concentrate their power at a great distance. Temporal (or longitudinal) coherence implies a polarized wave at a single frequency, whose phase is correlated over a relatively great distance (the coherence length ) along

5600-430: Is used to measure the intensity profile, width, and divergence of laser beams. Diffuse reflection of a laser beam from a matte surface produces a speckle pattern with interesting properties. The mechanism of producing radiation in a laser relies on stimulated emission , where energy is extracted from a transition in an atom or molecule. This is a quantum phenomenon that was predicted by Albert Einstein , who derived

5712-662: The Frankfurt Stock Exchange under the ISIN US7750431022. The companies wide range of laser sources, including CO 2 lasers , fiber lasers , solid-state, diode and various q-switch lasers are now available at Coherent. The company was founded 1975 in Hamburg , Germany as "SINAR Laser Systeme Verkaufsgesellschaft mbH". Sinar is the Sanskrit for "beam of light", but this name was already used by

SECTION 50

#1732793545901

5824-934: The Nobel Prize in Physics in 2014 for "the invention of efficient blue light-emitting diodes, which has enabled bright and energy-saving white light sources." In 1995, Alberto Barbieri at the Cardiff University Laboratory (GB) investigated the efficiency and reliability of high-brightness LEDs and demonstrated a "transparent contact" LED using indium tin oxide (ITO) on (AlGaInP/GaAs). In 2001 and 2002, processes for growing gallium nitride (GaN) LEDs on silicon were successfully demonstrated. In January 2012, Osram demonstrated high-power InGaN LEDs grown on silicon substrates commercially, and GaN-on-silicon LEDs are in production at Plessey Semiconductors . As of 2017, some manufacturers are using SiC as

5936-553: The U.S. patent office issued the two inventors the patent for the GaAs infrared light-emitting diode (U.S. Patent US3293513 ), the first practical LED. Immediately after filing the patent, Texas Instruments (TI) began a project to manufacture infrared diodes. In October 1962, TI announced the first commercial LED product (the SNX-100), which employed a pure GaAs crystal to emit an 890 nm light output. In October 1963, TI announced

6048-457: The human eye as a pure ( saturated ) color. Also unlike most lasers, its radiation is not spatially coherent , so it cannot approach the very high intensity characteristic of lasers . By selection of different semiconductor materials , single-color LEDs can be made that emit light in a narrow band of wavelengths from near-infrared through the visible spectrum and into the ultraviolet range. The required operating voltages of LEDs increase as

6160-410: The phase of the emitted light is 90 degrees in lead of the stimulating light. This, combined with the filtering effect of the optical resonator gives laser light its characteristic coherence, and may give it uniform polarization and monochromaticity, depending on the resonator's design. The fundamental laser linewidth of light emitted from the lasing resonator can be orders of magnitude narrower than

6272-421: The transverse modes often approximated using Hermite – Gaussian or Laguerre -Gaussian functions. Some high-power lasers use a flat-topped profile known as a " tophat beam ". Unstable laser resonators (not used in most lasers) produce fractal-shaped beams. Specialized optical systems can produce more complex beam geometries, such as Bessel beams and optical vortexes . Near the "waist" (or focal region ) of

6384-505: The "pencil beam" directly generated by a common helium–neon laser would spread out to a size of perhaps 500 kilometers when shone on the Moon (from the distance of the Earth). On the other hand, the light from a semiconductor laser typically exits the tiny crystal with a large divergence: up to 50°. However even such a divergent beam can be transformed into a similarly collimated beam employing

6496-451: The 3-subpixel model for digital displays. The technology uses a gallium nitride semiconductor that emits light of different frequencies modulated by voltage changes. A prototype display achieved a resolution of 6,800 PPI or 3k x 1.5k pixels. In a light-emitting diode, the recombination of electrons and electron holes in a semiconductor produces light (be it infrared, visible or UV), a process called " electroluminescence ". The wavelength of

6608-677: The Quantum Theory of Radiation") via a re-derivation of Max Planck 's law of radiation, conceptually based upon probability coefficients ( Einstein coefficients ) for the absorption, spontaneous emission, and stimulated emission of electromagnetic radiation. In 1928, Rudolf W. Ladenburg confirmed the existence of the phenomena of stimulated emission and negative absorption. In 1939, Valentin A. Fabrikant predicted using stimulated emission to amplify "short" waves. In 1947, Willis E. Lamb and R.   C.   Retherford found apparent stimulated emission in hydrogen spectra and effected

6720-509: The Soviet Union, Nikolay Basov and Aleksandr Prokhorov were independently working on the quantum oscillator and solved the problem of continuous-output systems by using more than two energy levels. These gain media could release stimulated emissions between an excited state and a lower excited state, not the ground state, facilitating the maintenance of a population inversion . In 1955, Prokhorov and Basov suggested optical pumping of

6832-614: The acronym. It has been humorously noted that the acronym LOSER, for "light oscillation by stimulated emission of radiation", would have been more correct. With the widespread use of the original acronym as a common noun, optical amplifiers have come to be referred to as laser amplifiers . Modern physics describes light and other forms of electromagnetic radiation as the group behavior of fundamental particles known as photons . Photons are released and absorbed through electromagnetic interactions with other fundamental particles that carry electric charge . A common way to release photons

SECTION 60

#1732793545901

6944-476: The beam. A beam produced by a thermal or other incoherent light source has an instantaneous amplitude and phase that vary randomly with respect to time and position, thus having a short coherence length. Lasers are characterized according to their wavelength in a vacuum . Most "single wavelength" lasers produce radiation in several modes with slightly different wavelengths. Although temporal coherence implies some degree of monochromaticity , some lasers emit

7056-800: The blending of the colors. Since LEDs have slightly different emission patterns, the color balance may change depending on the angle of view, even if the RGB sources are in a single package, so RGB diodes are seldom used to produce white lighting. Nonetheless, this method has many applications because of the flexibility of mixing different colors, and in principle, this mechanism also has higher quantum efficiency in producing white light. There are several types of multicolor white LEDs: di- , tri- , and tetrachromatic white LEDs. Several key factors that play among these different methods include color stability, color rendering capability, and luminous efficacy. Often, higher efficiency means lower color rendering, presenting

7168-425: The blue to near-UV have also been used in place of light-emitting diodes (LEDs) to excite fluorescence as a white light source; this permits a much smaller emitting area due to the much greater radiance of a laser and avoids the droop suffered by LEDs; such devices are already used in some car headlamps . The first device using amplification by stimulated emission operated at microwave frequencies, and

7280-1088: The cladding and quantum well layers for ultraviolet LEDs, but these devices have not yet reached the level of efficiency and technological maturity of InGaN/GaN blue/green devices. If unalloyed GaN is used in this case to form the active quantum well layers, the device emits near-ultraviolet light with a peak wavelength centred around 365 nm. Green LEDs manufactured from the InGaN/GaN system are far more efficient and brighter than green LEDs produced with non-nitride material systems, but practical devices still exhibit efficiency too low for high-brightness applications. With AlGaN and AlGaInN , even shorter wavelengths are achievable. Near-UV emitters at wavelengths around 360–395 nm are already cheap and often encountered, for example, as black light lamp replacements for inspection of anti- counterfeiting UV watermarks in documents and bank notes, and for UV curing . Substantially more expensive, shorter-wavelength diodes are commercially available for wavelengths down to 240 nm. As

7392-417: The cost of reliable devices fell. This led to relatively high-power white-light LEDs for illumination, which are replacing incandescent and fluorescent lighting. Experimental white LEDs were demonstrated in 2014 to produce 303 lumens per watt of electricity (lm/W); some can last up to 100,000 hours. Commercially available LEDs have an efficiency of up to 223 lm/W as of 2018. A previous record of 135 lm/W

7504-561: The effect of nonlinearity in optical materials (e.g. in second-harmonic generation , parametric down-conversion , optical parametric oscillators and the like). Unlike the giant pulse of a Q-switched laser, consecutive pulses from a mode-locked laser are phase-coherent; that is, the pulses (and not just their envelopes ) are identical and perfectly periodic. For this reason, and the extremely large peak powers attained by such short pulses, such lasers are invaluable in certain areas of research. Another method of achieving pulsed laser operation

7616-503: The effort. In 1964, Charles H. Townes, Nikolay Basov, and Aleksandr Prokhorov shared the Nobel Prize in Physics , "for fundamental work in the field of quantum electronics, which has led to the construction of oscillators and amplifiers based on the maser–laser principle". Light-emitting diode Appearing as practical electronic components in 1962, the earliest LEDs emitted low-intensity infrared (IR) light. Infrared LEDs are used in remote-control circuits, such as those used with

7728-543: The emitted wavelengths become shorter (higher energy, red to blue), because of their increasing semiconductor band gap. Blue LEDs have an active region consisting of one or more InGaN quantum wells sandwiched between thicker layers of GaN, called cladding layers. By varying the relative In/Ga fraction in the InGaN quantum wells, the light emission can in theory be varied from violet to amber. Aluminium gallium nitride (AlGaN) of varying Al/Ga fraction can be used to manufacture

7840-496: The field of luminescence with research on radium . Hungarian Zoltán Bay together with György Szigeti patenting a lighting device in Hungary in 1939 based on silicon carbide, with an option on boron carbide, that emitted white, yellowish white, or greenish white depending on impurities present. Kurt Lehovec , Carl Accardo, and Edward Jamgochian explained these first LEDs in 1951 using an apparatus employing SiC crystals with

7952-612: The first commercial hemispherical LED, the SNX-110. In the 1960s, several laboratories focused on LEDs that would emit visible light. A particularly important device was demonstrated by Nick Holonyak on October 9, 1962, while he was working for General Electric in Syracuse, New York . The device used the semiconducting alloy gallium phosphide arsenide (GaAsP). It was the first semiconductor laser to emit visible light, albeit at low temperatures. At room temperature it still functioned as

8064-521: The first commercially available blue LED, based on the indirect bandgap semiconductor, silicon carbide (SiC). SiC LEDs had very low efficiency, no more than about 0.03%, but did emit in the blue portion of the visible light spectrum. In the late 1980s, key breakthroughs in GaN epitaxial growth and p-type doping ushered in the modern era of GaN-based optoelectronic devices. Building upon this foundation, Theodore Moustakas at Boston University patented

8176-603: The first demonstration of stimulated emission. In 1950, Alfred Kastler (Nobel Prize for Physics 1966) proposed the method of optical pumping , which was experimentally demonstrated two years later by Brossel, Kastler, and Winter. In 1951, Joseph Weber submitted a paper on using stimulated emissions to make a microwave amplifier to the June 1952 Institute of Radio Engineers Vacuum Tube Research Conference in Ottawa , Ontario, Canada. After this presentation, RCA asked Weber to give

8288-721: The first high-brightness, high-efficiency LEDs for optical fiber telecommunications by inventing new semiconductor materials specifically adapted to optical fiber transmission wavelengths. Until 1968, visible and infrared LEDs were extremely costly, on the order of US$ 200 per unit, and so had little practical use. The first commercial visible-wavelength LEDs used GaAsP semiconductors and were commonly used as replacements for incandescent and neon indicator lamps , and in seven-segment displays , first in expensive equipment such as laboratory and electronics test equipment, then later in such appliances as calculators, TVs, radios, telephones, as well as watches. The Hewlett-Packard company (HP)

8400-407: The important GaN deposition on sapphire substrates and the demonstration of p-type doping of GaN. This new development revolutionized LED lighting, making high-power blue light sources practical, leading to the development of technologies like Blu-ray . Nakamura was awarded the 2006 Millennium Technology Prize for his invention. Nakamura, Hiroshi Amano , and Isamu Akasaki were awarded

8512-428: The largest shareholders of the company, claimed in various public letters that the company was lacking an adequate growth strategy and had missed market opportunities for years. Before the shareholders could have a final vote on the claim in the upcoming Annual General Meeting the company announced it was being acquired by a competitor company, Coherent Inc. Laser A laser is a device that emits light through

8624-422: The laser power inside the cavity; this equilibrium determines the operating point of the laser. If the applied pump power is too small, the gain will never be sufficient to overcome the cavity losses, and laser light will not be produced. The minimum pump power needed to begin laser action is called the lasing threshold . The gain medium will amplify any photons passing through it, regardless of direction; but only

8736-501: The lasing medium or pumping mechanism, then it is still classified as a "modulated" or "pulsed" continuous wave laser. Most laser diodes used in communication systems fall into that category. Some applications of lasers depend on a beam whose output power is constant over time. Such a laser is known as a continuous-wave ( CW ) laser. Many types of lasers can be made to operate in continuous-wave mode to satisfy such an application. Many of these lasers lase in several longitudinal modes at

8848-414: The latter case, the photon is emitted in the same direction as the light that is passing by. When the number of particles in one excited state exceeds the number of particles in some lower-energy state, population inversion is achieved. In this state, the rate of stimulated emission is larger than the rate of absorption of light in the medium, and therefore the light is amplified. A system with this property

8960-417: The light depends on the energy band gap of the semiconductors used. Since these materials have a high index of refraction, design features of the devices such as special optical coatings and die shape are required to efficiently emit light. Unlike a laser , the light emitted from an LED is neither spectrally coherent nor even highly monochromatic . Its spectrum is sufficiently narrow that it appears to

9072-420: The light produced is engineered to suit the human eye. Because of metamerism , it is possible to have quite different spectra that appear white. The appearance of objects illuminated by that light may vary as the spectrum varies. This is the issue of color rendition, quite separate from color temperature. An orange or cyan object could appear with the wrong color and much darker as the LED or phosphor does not emit

9184-450: The linewidth of light emitted from the passive resonator. Some lasers use a separate injection seeder to start the process off with a beam that is already highly coherent. This can produce beams with a narrower spectrum than would otherwise be possible. In 1963, Roy J. Glauber showed that coherent states are formed from combinations of photon number states, for which he was awarded the Nobel Prize in physics . A coherent beam of light

9296-402: The literal cavity that would be employed at microwave frequencies in a maser . The resonator typically consists of two mirrors between which a coherent beam of light travels in both directions, reflecting on itself so that an average photon will pass through the gain medium repeatedly before it is emitted from the output aperture or lost to diffraction or absorption. If the gain (amplification) in

9408-522: The lower level, emitting a new photon. The emitted photon exactly matches the original photon in wavelength, phase, and direction. This process is called stimulated emission. The gain medium is put into an excited state by an external source of energy. In most lasers, this medium consists of a population of atoms that have been excited into such a state using an outside light source, or an electrical field that supplies energy for atoms to absorb and be transformed into their excited states. The gain medium of

9520-412: The maximum possible level, the introduced loss mechanism (often an electro- or acousto-optical element) is rapidly removed (or that occurs by itself in a passive device), allowing lasing to begin which rapidly obtains the stored energy in the gain medium. This results in a short pulse incorporating that energy, and thus a high peak power. A mode-locked laser is capable of emitting extremely short pulses on

9632-498: The medium is larger than the resonator losses, then the power of the recirculating light can rise exponentially . But each stimulated emission event returns an atom from its excited state to the ground state, reducing the gain of the medium. With increasing beam power, the net gain (gain minus loss) reduces to unity and the gain medium is said to be saturated. In a continuous wave (CW) laser, the balance of pump power against gain saturation and cavity losses produces an equilibrium value of

9744-404: The object is not random, however: it is stored by atoms and molecules in " excited states ", which release photons with distinct wavelengths. This gives rise to the science of spectroscopy , which allows materials to be determined through the specific wavelengths that they emit. The underlying physical process creating photons in a laser is the same as in thermal radiation, but the actual emission

9856-456: The order of tens of picoseconds down to less than 10  femtoseconds . These pulses repeat at the round-trip time, that is, the time that it takes light to complete one round trip between the mirrors comprising the resonator. Due to the Fourier limit (also known as energy–time uncertainty ), a pulse of such short temporal length has a spectrum spread over a considerable bandwidth. Thus such

9968-448: The phosphors, the Ce:YAG phosphor converts blue light to green and red (yellow) light, and the PFS phosphor converts blue light to red light. The color, emission spectrum or color temperature of white phosphor converted and other phosphor converted LEDs can be controlled by changing the concentration of several phosphors that form a phosphor blend used in an LED package. The 'whiteness' of

10080-418: The photons in a spatial mode supported by the resonator will pass more than once through the medium and receive substantial amplification. In most lasers, lasing begins with spontaneous emission into the lasing mode. This initial light is then amplified by stimulated emission in the gain medium. Stimulated emission produces light that matches the input signal in direction, wavelength, and polarization, whereas

10192-599: The photosensitivity of microorganisms approximately matches the absorption spectrum of DNA , with a peak at about 260 nm, UV LED emitting at 250–270 nm are expected in prospective disinfection and sterilization devices. Recent research has shown that commercially available UVA LEDs (365 nm) are already effective disinfection and sterilization devices. UV-C wavelengths were obtained in laboratories using aluminium nitride (210 nm), boron nitride (215 nm) and diamond (235 nm). There are two primary ways of producing white light-emitting diodes. One

10304-409: The power output is essentially continuous over time or whether its output takes the form of pulses of light on one or another time scale. Of course, even a laser whose output is normally continuous can be intentionally turned on and off at some rate to create pulses of light. When the modulation rate is on time scales much slower than the cavity lifetime and the period over which energy can be stored in

10416-662: The properties of the emitted light, such as the polarization, wavelength, and shape of the beam. Electrons and how they interact with electromagnetic fields are important in our understanding of chemistry and physics . In the classical view , the energy of an electron orbiting an atomic nucleus is larger for orbits further from the nucleus of an atom . However, quantum mechanical effects force electrons to take on discrete positions in orbitals . Thus, electrons are found in specific energy levels of an atom, two of which are shown below: An electron in an atom can absorb energy from light ( photons ) or heat ( phonons ) only if there

10528-457: The relationship between the A coefficient , describing spontaneous emission, and the B coefficient which applies to absorption and stimulated emission. In the case of the free electron laser , atomic energy levels are not involved; it appears that the operation of this rather exotic device can be explained without reference to quantum mechanics . A laser can be classified as operating in either continuous or pulsed mode, depending on whether

10640-421: The rudimentary devices could be used for non-radio communication across a short distance. As noted by Kroemer Braunstein "…had set up a simple optical communications link: Music emerging from a record player was used via suitable electronics to modulate the forward current of a GaAs diode. The emitted light was detected by a PbS diode some distance away. This signal was fed into an audio amplifier and played back by

10752-410: The same time, and beats between the slightly different optical frequencies of those oscillations will produce amplitude variations on time scales shorter than the round-trip time (the reciprocal of the frequency spacing between modes), typically a few nanoseconds or less. In most cases, these lasers are still termed "continuous-wave" as their output power is steady when averaged over longer periods, with

10864-480: The same time. Some LEDs use phosphors made of glass-ceramic or composite phosphor/glass materials. Alternatively, the LED chips themselves can be coated with a thin coating of phosphor-containing material, called a conformal coating. The temperature of the phosphor during operation and how it is applied limits the size of an LED die. Wafer-level packaged white LEDs allow for extremely small LEDs. In 2024, QPixel introduced as polychromatic LED that could replace

10976-408: The space between the crystals allow some blue light to pass through in LEDs with partial phosphor conversion. Alternatively, white LEDs may use other phosphors like manganese(IV)-doped potassium fluorosilicate (PFS) or other engineered phosphors. PFS assists in red light generation, and is used in conjunction with conventional Ce:YAG phosphor. In LEDs with PFS phosphor, some blue light passes through

11088-547: The subsequent device Pankove and Miller built, the first actual gallium nitride light-emitting diode, emitted green light. In 1974 the U.S. Patent Office awarded Maruska, Rhines, and Stanford professor David Stevenson a patent for their work in 1972 (U.S. Patent US3819974 A ). Today, magnesium-doping of gallium nitride remains the basis for all commercial blue LEDs and laser diodes . In the early 1970s, these devices were too dim for practical use, and research into gallium nitride devices slowed. In August 1989, Cree introduced

11200-480: The substrate for LED production, but sapphire is more common, as it has the most similar properties to that of gallium nitride, reducing the need for patterning the sapphire wafer (patterned wafers are known as epi wafers). Samsung , the University of Cambridge , and Toshiba are performing research into GaN on Si LEDs. Toshiba has stopped research, possibly due to low yields. Some opt for epitaxy , which

11312-569: The team at Fairchild led by optoelectronics pioneer Thomas Brandt to achieve the needed cost reductions. LED producers have continued to use these methods as of about 2009. The early red LEDs were bright enough for use as indicators, as the light output was not enough to illuminate an area. Readouts in calculators were so small that plastic lenses were built over each digit to make them legible. Later, other colors became widely available and appeared in appliances and equipment. Early LEDs were packaged in metal cases similar to those of transistors, with

11424-425: The two mirrors, the output coupler , is partially transparent. Some of the light escapes through this mirror. Depending on the design of the cavity (whether the mirrors are flat or curved ), the light coming out of the laser may spread out or form a narrow beam . In analogy to electronic oscillators , this device is sometimes called a laser oscillator . Most practical lasers contain additional elements that affect

11536-410: The very high-frequency power variations having little or no impact on the intended application. (However, the term is not applied to mode-locked lasers, where the intention is to create very short pulses at the rate of the round-trip time.) For continuous-wave operation, the population inversion of the gain medium needs to be continually replenished by a steady pump source. In some lasing media, this

11648-461: The very inefficient light-producing properties of silicon carbide, the semiconductor Losev used. In 1936, Georges Destriau observed that electroluminescence could be produced when zinc sulphide (ZnS) powder is suspended in an insulator and an alternating electrical field is applied to it. In his publications, Destriau often referred to luminescence as Losev-Light. Destriau worked in the laboratories of Madame Marie Curie , also an early pioneer in

11760-538: The wavelength it reflects. The best color rendition LEDs use a mix of phosphors, resulting in less efficiency and better color rendering. The first white light-emitting diodes (LEDs) were offered for sale in the autumn of 1996. Nichia made some of the first white LEDs which were based on blue LEDs with Ce:YAG phosphor. Ce:YAG is often grown using the Czochralski method . Mixing red, green, and blue sources to produce white light needs electronic circuits to control

11872-618: Was achieved by Nichia in 2010. Compared to incandescent bulbs, this is a huge increase in electrical efficiency, and even though LEDs are more expensive to purchase, overall lifetime cost is significantly cheaper than that of incandescent bulbs. The LED chip is encapsulated inside a small, plastic, white mold although sometimes an LED package can incorporate a reflector. It can be encapsulated using resin ( polyurethane -based), silicone, or epoxy containing (powdered) Cerium-doped YAG phosphor particles. The viscosity of phosphor-silicon mixtures must be carefully controlled. After application of

11984-598: Was called a maser , for "microwave amplification by stimulated emission of radiation". When similar optical devices were developed they were first called optical masers , until "microwave" was replaced by "light" in the acronym, to become laser . Today, all such devices operating at frequencies higher than microwaves (approximately above 300 GHz ) are called lasers (e.g. infrared lasers , ultraviolet lasers , X-ray lasers , gamma-ray lasers ), whereas devices operating at microwave or lower radio frequencies are called masers. The back-formed verb " to lase "

12096-415: Was engaged in research and development (R&D) on practical LEDs between 1962 and 1968, by a research team under Howard C. Borden, Gerald P. Pighini at HP Associates and HP Labs . During this time HP collaborated with Monsanto Company on developing the first usable LED products. The first usable LED products were HP's LED display and Monsanto's LED indicator lamp , both launched in 1968. Monsanto

12208-433: Was made at Stanford University in 1972 by Herb Maruska and Wally Rhines , doctoral students in materials science and engineering. At the time Maruska was on leave from RCA Laboratories , where he collaborated with Jacques Pankove on related work. In 1971, the year after Maruska left for Stanford, his RCA colleagues Pankove and Ed Miller demonstrated the first blue electroluminescence from zinc-doped gallium nitride, though

12320-443: Was quickly followed by the development of the first white LED . In this device a Y 3 Al 5 O 12 :Ce (known as " YAG " or Ce:YAG phosphor) cerium -doped phosphor coating produces yellow light through fluorescence . The combination of that yellow with remaining blue light appears white to the eye. Using different phosphors produces green and red light through fluorescence. The resulting mixture of red, green and blue

12432-571: Was the first intelligent LED display, and was a revolution in digital display technology, replacing the Nixie tube and becoming the basis for later LED displays. In the 1970s, commercially successful LED devices at less than five cents each were produced by Fairchild Optoelectronics. These devices employed compound semiconductor chips fabricated with the planar process (developed by Jean Hoerni , ). The combination of planar processing for chip fabrication and innovative packaging methods enabled

12544-484: Was the first organization to mass-produce visible LEDs, using Gallium arsenide phosphide (GaAsP) in 1968 to produce red LEDs suitable for indicators. Monsanto had previously offered to supply HP with GaAsP, but HP decided to grow its own GaAsP. In February 1969, Hewlett-Packard introduced the HP Model 5082-7000 Numeric Indicator, the first LED device to use integrated circuit (integrated LED circuit ) technology. It

#900099