Experiment with a laser (U.S. Air Force)

A laser is an electronic-optical device that emits coherent light radiation. In Physics, coherence is a property of waves that enables stationary (i Radiation, as in Physics, is Energy in the form of waves or moving Subatomic particles emitted by an atom or other body as it changes from a higher energy The term "laser" is an acronym for Light Amplification by Stimulated Emission of Radiation. Acronyms, initialisms, and alphabetisms are Abbreviations that are formed using the initial components in a phrase or name ^[1][2] A typical laser emits light in a narrow, low-divergence beam, with a narrow wavelength spectrum ("monochromatic" light). The beam divergence of an electromagnetic beam is an angular measure of the increase in Beam diameter with distance from the optical aperture or Antenna aperture In Physics wavelength is the distance between repeating units of a propagating Wave of a given Frequency. The electromagnetic (EM spectrum is the range of all possible Electromagnetic radiation frequencies In this respect, laser light is in sharp contrast with such light sources as the incandescent light bulb, which emits light over a wide area and over a wide spectrum of wavelengths. Light, or visible light, is Electromagnetic radiation of a Wavelength that is visible to the Human eye (about 400–700 The incandescent light bulb, incandescent lamp or incandescent light globe is a source of electric Light that works by Incandescence, (a general

The first working laser was demonstrated on May 16, 1960 by Theodore Maiman at Hughes Research Laboratories. Events 1204 - Baldwin IX Count of Flanders is crowned as the first Emperor of the Latin Empire. Year 1960 ( MCMLX) was a Leap year starting on Friday (link will display full calendar of the Gregorian calendar. Theodore Harold "Ted" Maiman ( July 11, 1927 - May 5, 2007) was an American Physicist who made the first working HRL redirects here For the US airport see Valley International Airport. ^[3] Since then, lasers have become a multi-billion dollar industry. The most widespread use of lasers is in optical storage devices such as compact disc and DVD players, in which the laser (a few millimeters in size) scans the surface of the disc. Optical storage is a term from Engineering referring to the storage of data on an optically readable medium A Compact Disc (also known as a CD) is an Optical disc used to store digital data, originally developed for storing digital audio DVD (also known as " Digital Versatile Disc " or " Digital Video Disc " - see Etymology)is Other common applications of lasers are bar code readers, laser printers and laser pointers. A bar code (also barcode) is an optical Machine-readable representation of data A laser printer is a common type of Computer printer that rapidly produces high quality text and graphics on plain paper A laser pointer is a portable pen-sized Laser designed to be held in the hand and most commonly used to project a point of light to highlight items of interest during a

In industry, lasers are used for cutting steel and other metals and for inscribing patterns (such as the letters on computer keyboards). Laser cutting is a technology that uses a Laser to cut materials and is typically used for industrial manufacturing applications Lasers are also commonly used in various fields in science, especially spectroscopy, typically because of their well-defined wavelength or short pulse duration in the case of pulsed lasers. Science (from the Latin scientia, meaning " Knowledge " or "knowing" is the effort to discover, and increase human understanding Spectroscopy was originally the study of the interaction between Radiation and Matter as a function of Wavelength (λ Lasers are used by the military for rangefinding, target identification and illumination for weapons delivery. Lasers used in medicine are used for internal surgery and cosmetic applications.

Design

Principal components:
1. Gain medium
2. Laser pumping energy
3. High reflector
4. Output coupler
5. An output coupler ( OC) is a partially reflective Mirror used in Lasers to extract a portion of the laser beam from the Optical resonator. Laser beam

Main article: Laser construction

A laser consists of a gain medium inside a highly reflective optical cavity, as well as a means to supply energy to the gain medium. A laser is constructed from three principal parts An energy source (usually referred to as the pump or pump source) A The active laser medium or gain medium is the source of optical Gain within a Laser. An optical cavity or optical resonator is an arrangement of Mirrors that forms a Standing wave Cavity resonator for Light waves Optical The gain medium is a material with properties that allow it to amplify light by stimulated emission. In Optics, stimulated emission is the process by which an electron perturbed by a Photon having the correct energy may drop to a lower Energy level resulting In its simplest form, a cavity consists of two mirrors arranged such that light bounces back and forth, each time passing through the gain medium. Typically one of the two mirrors, the output coupler, is partially transparent. An output coupler ( OC) is a partially reflective Mirror used in Lasers to extract a portion of the laser beam from the Optical resonator. The output laser beam is emitted through this mirror.

Light of a specific wavelength that passes through the gain medium is amplified (increases in power); the surrounding mirrors ensure that most of the light makes many passes through the gain medium, being amplified repeatedly. An optical amplifier is a device that amplifies an Optical signal directly without the need to first convert it to an electrical signal Part of the light that is between the mirrors (that is, within the cavity) passes through the partially transparent mirror and escapes as a beam of light.

The process of supplying the energy required for the amplification is called pumping. Laser pumping is the act of energy transfer from an external source into the Gain medium of a Laser. The energy is typically supplied as an electrical current or as light at a different wavelength. Such light may be provided by a flash lamp or perhaps another laser. A xenon flash lamp is an Electric glow discharge lamp designed to produce extremely intense incoherent, full-spectrum white light for very short durations Most practical lasers contain additional elements that affect properties such as the wavelength of the emitted light and the shape of the beam.

Terminology

From left to right: gamma rays, X-rays, ultraviolet rays, visible spectrum, infrared, microwaves, radio waves

The word light in the acronym Light Amplification by Stimulated Emission of Radiation is typically used in the broader sense, as including photons of any electromagnetic energy, not just those in the visible spectrum. Gamma rays (denoted as &gamma) are a form of Electromagnetic radiation or light emission of frequencies produced by sub-atomic particle interactions X-radiation (composed of X-rays) is a form of Electromagnetic radiation. Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays Infrared ( IR) radiation is Electromagnetic radiation whose Wavelength is longer than that of Visible light, but shorter than that of Microwaves are electromagnetic waves with Wavelengths ranging from 1 mm to 1 m or frequencies between 0 Radio waves are electromagnetic waves occurring on the Radio frequency portion of the Electromagnetic spectrum. In Physics, the photon is the Elementary particle responsible for electromagnetic phenomena Hence there are infrared lasers, ultraviolet lasers, X-ray lasers, etc. Infrared ( IR) radiation is Electromagnetic radiation whose Wavelength is longer than that of Visible light, but shorter than that of Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays X-radiation (composed of X-rays) is a form of Electromagnetic radiation. Because the microwave equivalent of the laser, the maser, was developed first, devices that emit microwave and radio frequencies are usually called masers. Microwaves are electromagnetic waves with Wavelengths ranging from 1 mm to 1 m or frequencies between 0 A maser is a device that produces coherent Electromagnetic waves through amplification due to Stimulated emission. Radio frequency ( RF) is a Frequency or rate of Oscillation within the range of about 3 Hz to 300 GHz In early literature, particularly from researchers at Bell Telephone Laboratories, the laser was often called the optical maser. Bell Laboratories (also known as Bell Labs and formerly known as AT&T Bell Laboratories and Bell Telephone Laboratories) is the Research organization This usage has since become uncommon, and as of 1998 even Bell Labs uses the term laser. ^[4]

The back-formed verb to lase means "to produce laser light" or "to apply laser light to". In Etymology, back-formation refers to the process of creating a new Lexeme (less precisely a new "word" by removing actual or supposed Affixes ^[5] The word "laser" is sometimes used to describe other non-light technologies. For example, a source of atoms in a coherent state is called an "atom laser". An atom laser is a Coherent state of propagating atoms They are created out of a Bose-Einstein condensate of atoms that are output coupled using various techniques

Laser physics

A helium-neon laser demonstration at the Kastler-Brossel Laboratory at Univ. Paris 6. A helium-neon laser, usually called a HeNe laser, is a type of small Gas laser. Pierre and Marie Curie University ( Université Pierre et Marie Curie or UPMC - Paris Universitas or Paris 6) is a French University The glowing ray in the middle is an electric discharge producing light in much the same way as a neon light. It is the gain medium through which the laser passes, not the laser beam itself, which is visible there. The active laser medium or gain medium is the source of optical Gain within a Laser. The laser beam crosses the air and marks a red point on the screen to the right.

Spectrum of a helium neon laser showing the very high spectral purity intrinsic to nearly all lasers. Compare with the relatively broad spectral emittance of a light emitting diode.

See also: Laser science

The gain medium of a laser is a material of controlled purity, size, concentration, and shape, which amplifies the beam by the process of stimulated emission. Laser science or laser physics is a branch of Optics that describes the theory and practice of Lasers Laser science is principally concerned with It can be of any state: gas, liquid, solid or plasma. A state of matter (or physical state, or form of matter) has physical properties which are qualitatively different from other states of matter This page is about the physical properties of gas as a state of matter Liquid is one of the principal States of matter. A liquid is a Fluid that has the particles loose and can freely form a distinct surface at the boundaries of A solid' object is in the States of matter characterized by resistance to Deformation and changes of Volume. In Physics and Chemistry, plasma is an Ionized Gas, in which a certain proportion of Electrons are free rather than being bound The gain medium absorbs pump energy, which raises some electrons into higher-energy ("excited") quantum states. Excitation is an elevation in energy level above an arbitrary baseline energy state In Quantum physics, a quantum state is a mathematical object that fully describes a quantum system. Particles can interact with light both by absorbing photons or by emitting photons. Emission can be spontaneous or stimulated. In 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 and the amount of stimulated emission due to light that passes through is larger than the amount of absorption. In Physics, specifically Statistical mechanics, a population inversion occurs when a system (such as a group of Atoms or Molecules exists in state Hence, the light is amplified. By itself, this makes an optical amplifier. An optical amplifier is a device that amplifies an Optical signal directly without the need to first convert it to an electrical signal When an optical amplifier is placed inside a resonant optical cavity, one obtains a laser.

The light generated by stimulated emission is very similar to the input signal in terms of wavelength, phase, and polarization. The phase of an oscillation or wave is the fraction of a complete cycle corresponding to an offset in the displacement from a specified reference point at time t = 0 This gives laser light its characteristic coherence, and allows it to maintain the uniform polarization and often monochromaticity established by the optical cavity design.

The optical cavity, a type of cavity resonator, contains a coherent beam of light between reflective surfaces so that the light passes through the gain medium more than once before it is emitted from the output aperture or lost to diffraction or absorption. A resonator is a device or system that exhibits Resonance or resonant behavior that is it naturally oscillates at some frequencies, called its resonance As light circulates through the cavity, passing through the gain medium, if the gain (amplification) in the medium is stronger than the resonator losses, the power of the circulating light can rise exponentially. Exponential growth (including Exponential decay) occurs when the growth rate of a mathematical function is proportional to the function's current value But each stimulated emission event returns a particle from its excited state to the ground state, reducing the capacity of the gain medium for further amplification. When this effect becomes strong, the gain is said to be saturated. The balance of pump power against gain saturation and cavity losses produces an equilibrium value of the laser power inside the cavity; this equilibrium determines the operating point of the laser. If the chosen pump power is too small, the gain is not sufficient to overcome the resonator losses, and the laser will emit only very small light powers. The minimum pump power needed to begin laser action is called the lasing threshold. The lasing threshold is the lowest excitation level at which a laser's output is dominated by Stimulated emission rather than by Spontaneous emission. The gain medium will amplify any photons passing through it, regardless of direction; but only the photons aligned with the cavity manage to pass more than once through the medium and so have significant amplification.

The beam in the cavity and the output beam of the laser, if they occur in free space rather than waveguides (as in an optical fiber laser), are, at best, low order Gaussian beams. An optical fiber (or fibre) is a Glass or Plastic fiber that carries Light along its length In Optics, a Gaussian beam is a Beam of Electromagnetic radiation whose transverse Electric field and Intensity ( Irradiance However this is rarely the case with powerful lasers. If the beam is not a low-order Gaussian shape, the transverse modes of the beam can be described as a superposition of Hermite-Gaussian or Laguerre-Gaussian beams (for stable-cavity lasers). In Mathematics, the Hermite polynomials are a classical orthogonal Polynomial sequence that arise in Probability, such as the Edgeworth In Mathematics, a Gaussian function (named after Carl Friedrich Gauss) is a function of the form f(x = a e^{- { (x-b^2 \over 2 In Mathematics, the Laguerre polynomials, named after Edmond Laguerre (1834 &ndash 1886 are the Canonical solutions of Laguerre's equation Unstable laser resonators on the other hand, have been shown to produce fractal shaped beams. ^[6] The beam may be highly collimated, that is being parallel without diverging. Collimated light is Light whose rays are nearly parallel and therefore will spread slowly as it propagates The beam divergence of an electromagnetic beam is an angular measure of the increase in Beam diameter with distance from the optical aperture or Antenna aperture However, a perfectly collimated beam cannot be created, due to diffraction. Diffraction is normally taken to refer to various phenomena which occur when a wave encounters an obstacle The beam remains collimated over a distance which varies with the square of the beam diameter, and eventually diverges at an angle which varies inversely with the beam diameter. Thus, a beam generated by a small laboratory laser such as a helium-neon laser spreads to about 1. A helium-neon laser, usually called a HeNe laser, is a type of small Gas laser. 6 kilometers (1 mile) diameter if shone from the Earth to the Moon. EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 By comparison, the output of a typical semiconductor laser, due to its small diameter, diverges almost as soon as it leaves the aperture, at an angle of anything up to 50°. However, such a divergent beam can be transformed into a collimated beam by means of a lens. A lens is an optical device with perfect or approximate Axial symmetry which transmits and refracts Light, converging or diverging In contrast, the light from non-laser light sources cannot be collimated by optics as well.

Although the laser phenomenon was discovered with the help of quantum physics, it is not essentially more quantum mechanical than other light sources. Quantum mechanics is the study of mechanical systems whose dimensions are close to the Atomic scale such as Molecules Atoms Electrons The operation of a free electron laser can be explained without reference to quantum mechanics. A free-electron laser, or FEL is a Laser that shares the same optical properties as conventional lasers such as emitting a Beam consisting of coherent Quantum mechanics is the study of mechanical systems whose dimensions are close to the Atomic scale such as Molecules Atoms Electrons

Modes of operation

The output of a laser may be a continuous constant-amplitude output (known as CW or continuous wave); or pulsed, by using the techniques of Q-switching, modelocking, or gain-switching. A continuous wave or continuous waveform ( CW) is an Electromagnetic wave of constant Amplitude and Frequency; and in Mathematical Q-switching, sometimes known as giant pulse formation, is a technique by which a Laser can be made to produce a pulsed output beam Mode-locking is a technique in Optics by which a Laser can be made to produce pulses of Light of extremely short duration on the order of picoseconds (10-12s Gain-switching is a technique in Optics by which a Laser can be made to produce pulses of Light of extremely short duration of the order of picoseconds In pulsed operation, much higher peak powers can be achieved.

Some types of lasers, such as dye lasers and vibronic solid-state lasers can produce light over a broad range of wavelengths; this property makes them suitable for generating extremely short pulses of light, on the order of a few femtoseconds (10^-15 s). To help compare Orders of magnitude of different Times this page lists times between 10&minus15 second and 10&minus12 second (1 Femto

Continuous wave operation

In the continuous wave (CW) mode of operation, the output of a laser is relatively consistent with respect to time. A continuous wave or continuous waveform ( CW) is an Electromagnetic wave of constant Amplitude and Frequency; and in Mathematical The population inversion required for lasing is continually maintained by a steady pump source.

Pulsed operation

In the pulsed mode of operation, the output of a laser varies with respect to time, typically taking the form of alternating 'on' and 'off' periods. In many applications one aims to deposit as much energy as possible at a given place in as short time as possible. In laser ablation for example, a small volume of material at the surface of a work piece might evaporate if it gets the energy required to heat it up far enough in very short time. Laser ablation is the process of removing material from a solid (or occasionally liquid surface by irradiating it with a Laser beam If, however, the same energy is spread over a longer time, the heat may have time to disperse into the bulk of the piece, and less material evaporates. Disperse is a Christian Rock band from Southern Indiana. History The band consist of Guitarists Chris Billings and Andy Higham his brother There are a number of methods to achieve this.

Q-switching

Main article: Q-switching

In a Q-switched laser, the population inversion (usually produced in the same way as CW operation) is allowed to build up by making the cavity conditions (the 'Q') unfavorable for lasing. Q-switching, sometimes known as giant pulse formation, is a technique by which a Laser can be made to produce a pulsed output beam Then, when the pump energy stored in the laser medium is at the desired level, the 'Q' is adjusted (electro- or acousto-optically) to favorable conditions, releasing the pulse. This results in high peak powers as the average power of the laser (were it running in CW mode) is packed into a shorter time frame.

Modelocking

Main article: Modelocking

A modelocked laser emits extremely short pulses on the order of tens of picoseconds down to less than 10 femtoseconds. Mode-locking is a technique in Optics by which a Laser can be made to produce pulses of Light of extremely short duration on the order of picoseconds (10-12s To help compare Orders of magnitude of different Times this page lists times between 10&minus12 seconds and 10&minus11 seconds (1 Pico To help compare Orders of magnitude of different Times this page lists times between 10&minus15 second and 10&minus12 second (1 Femto These pulses are typically separated by the time that a pulse takes to complete one round trip in the resonator cavity. Due to the Fourier limit (also known as energy-time uncertainty), a pulse of such short temporal length has a spectrum which contains a wide range of wavelengths. This article specifically discusses Fourier transformation of functions on the Real line; for other kinds of Fourier transformation see Fourier analysis and In Quantum physics, the Heisenberg uncertainty principle states that locating a particle in a small region of space makes the Momentum of the particle uncertain Because of this, the laser medium must have a broad enough gain profile to amplify them all. An example of a suitable material is titanium-doped, artificially grown sapphire (Ti:sapphire). Titanium (taɪˈteɪniəm is a Chemical element with the symbol Ti and Atomic number 22 Sapphire (antique greek hyacinthos refers to gem varieties of the mineral Corundum, an Aluminium oxide (Al2O3 when it is a color other than Tisapphire lasers (also known as TiAl2O3 lasers, titanium-sapphire lasers, or simply Tisapphs) are Tunable lasers which

The modelocked laser is a most versatile tool for researching processes happening at extremely fast time scales also known as femtosecond physics, femtosecond chemistry and ultrafast science, for maximizing the effect of nonlinearity in optical materials (e. Femtochemistry is the Science that studies Chemical reactions on extremely short timescales approximately 10–15 seconds (one Femtosecond In Optics, an ultrashort pulse of light is an Electromagnetic pulse whose time duration is on the order of the femtosecond (10^{-15} second Nonlinear optics (NLO is the branch of Optics that describes the behaviour of Light in nonlinear media, that is media in which the dielectric polarization g. in second-harmonic generation, parametric down-conversion, optical parametric oscillators and the like), and in ablation applications. Second harmonic generation ( SHG; also called frequency doubling) is a nonlinear optical process in which Photons interacting with a nonlinear An optical parametric oscillator (OPO is a Parametric oscillator which oscillates at optical frequencies Again, because of the short timescales involved, these lasers can achieve extremely high powers.

Pulsed pumping

Another method of achieving pulsed laser operation is to pump the laser material with a source that is itself pulsed, either through electronic charging in the case of flashlamps, or another laser which 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 a broad spectrum pump flash. Pulsed pumping is also required for lasers which disrupt the gain medium so much during the laser process that lasing has to cease for a short period. These lasers, such as the excimer laser and the copper vapour laser, can never be operated in CW mode.

History

Foundations

In 1917 Albert Einstein, in his paper Zur Quantentheorie der Strahlung (On the Quantum Theory of Radiation), laid the foundation for the invention of the laser and its predecessor, the maser, in a ground-breaking rederivation of Max Planck's law of radiation based on the concepts of probability coefficients (later to be termed 'Einstein coefficients') for the absorption, spontaneous, and stimulated emission. Albert Einstein ( German: ˈalbɐt ˈaɪ̯nʃtaɪ̯n; English: ˈælbɝt ˈaɪnstaɪn (14 March 1879 – 18 April 1955 was a German -born theoretical A maser is a device that produces coherent Electromagnetic waves through amplification due to Stimulated emission.

In 1928, Rudolph W. Landenburg confirmed the existence of stimulated emission and negative absorption. ^[7] In 1939, Valentin A. Fabrikant (USSR) predicted the use of stimulated emission to amplify "short" waves. ^[8]

In 1947, Willis E. Lamb and R. Willis Eugene Lamb Jr ( July 12, 1913 &ndash May 15, 2008) was a Physicist who won the Nobel Prize in Physics in C. Retherford found apparent stimulated emission in hydrogen spectra and made the first demonstration of stimulated emission. ^[9]

In 1950, Alfred Kastler (Nobel Prize for Physics 1966) proposed the method of optical pumping, which was experimentally confirmed by Brossel, Kastler and Winter two years later. Alfred Kastler ( May 3, 1902 &ndash January 7, 1984) was a French Physicist, and Nobel Prize laureate. ^[10]

Maser

In 1953, Charles H. Townes and graduate students James P. Charles Hard Townes (born July 28, 1915) is an American Nobel Prize-winning Physicist and educator Gordon and Herbert J. Zeiger produced the first microwave amplifier, a device operating on similar principles to the laser, but amplifying microwave rather than infrared or visible radiation. Microwaves are electromagnetic waves with Wavelengths ranging from 1 mm to 1 m or frequencies between 0 Infrared ( IR) radiation is Electromagnetic radiation whose Wavelength is longer than that of Visible light, but shorter than that of Townes's maser was incapable of continuous output. A maser is a device that produces coherent Electromagnetic waves through amplification due to Stimulated emission. Nikolay Basov and Aleksandr Prokhorov of the Soviet Union worked independently on the quantum oscillator and solved the problem of continuous output systems by using more than two energy levels and produced the first maser. Nikolay Gennadiyevich Basov (Николай Геннадиевич Басов ( December 14, 1922 &ndash July 1, 2001) was a Soviet Aleksandr Mikhailovich Prokhorov (Александр Михайлович Прохоров (11 July 1916 &ndash 8 January 2002 was a Soviet / Russian physicist The Union of Soviet Socialist Republics (USSR was a constitutionally Socialist state that existed in Eurasia from 1922 to 1991 Oscillation is the repetitive variation typically in Time, of some measure about a central value (often a point of Equilibrium) or between two or more different states These systems could release stimulated emission without falling to the ground state, thus maintaining a population inversion. In Optics, stimulated emission is the process by which an electron perturbed by a Photon having the correct energy may drop to a lower Energy level resulting In Physics, specifically Statistical mechanics, a population inversion occurs when a system (such as a group of Atoms or Molecules exists in state In 1955 Prokhorov and Basov suggested an optical pumping of multilevel system as a method for obtaining the population inversion, which later became one of the main methods of laser pumping.

Townes reports that he encountered opposition from a number of eminent colleagues who thought the maser was theoretically impossible -- including Niels Bohr, John von Neumann, Isidor Rabi, Polykarp Kusch, and Llewellyn H. Niels Henrik David Bohr (nels ˈb̥oɐ̯ˀ in Danish 7 October 1885 – 18 November 1962 was a Danish Physicist who made fundamental contributions to understanding Isidor Isaac Rabi ( July 29, 1898 &ndash January 11, 1988) Galician born Physicist, and Nobel laureate. Polykarp Kusch ( January 26, 1911 &ndash March 20, 1993) was a German-American physicist Thomas[1].

Townes, Basov, and Prokhorov shared the Nobel Prize in Physics in 1964 "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". The Nobel Prize in Physics (Nobelpriset i fysik is awarded once a year by the Royal Swedish Academy of Sciences.

Laser

In 1957, Charles Hard Townes and Arthur Leonard Schawlow, then at Bell Labs, began a serious study of the infrared laser. Arthur Leonard Schawlow ( May 5, 1921 – April 28, 1999) was an American physicist. Bell Laboratories (also known as Bell Labs and formerly known as AT&T Bell Laboratories and Bell Telephone Laboratories) is the Research organization As ideas were developed, infrared frequencies were abandoned with focus on visible light instead. Infrared ( IR) radiation is Electromagnetic radiation whose Wavelength is longer than that of Visible light, but shorter than that of The concept was originally known as an "optical maser". Bell Labs filed a patent application for their proposed optical maser a year later. A patent is a set of Exclusive rights granted by a State to an inventor or his assignee for a fixed period of time in exchange for a disclosure of an Schawlow and Townes sent a manuscript of their theoretical calculations to Physical Review, which published their paper that year (Volume 112, Issue 6). Physical Review (frequently abbreviated as Phys Rev) is one of the oldest and most-respected Scientific journals publishing research on all aspects of

The first page of Gordon Gould's laser notebook in which he coined the acronym LASER and described the essential elements for constructing one.

At the same time Gordon Gould, a graduate student at Columbia University, was working on a doctoral thesis on the energy levels of excited thallium. Gordon Gould (July 17 1920–September 16 2005 was an American Physicist who is widely but not universally credited with the invention of the Laser Columbia University is a private University in the United States and a member of the Ivy League. A dissertation (also called thesis or disquisition) is a document that presents the author's Research and findings and is submitted in support of candidature Thallium (ˈθæliəm is a Chemical element with the symbol Tl and Atomic number 81 Gould and Townes met and had conversations on the general subject of radiation emission. In Physics, emission is the process by which the Energy of a Photon is released by another entity for example by an Atom whose Electrons Afterwards Gould made notes about his ideas for a "laser" in November 1957, including suggesting using an open resonator, which became an important ingredient of future lasers. A resonator is a device or system that exhibits Resonance or resonant behavior that is it naturally oscillates at some frequencies, called its resonance

In 1958, Prokhorov independently proposed using an open resonator, the first published appearance of this idea. Schawlow and Townes also settled on an open resonator design, apparently unaware of both the published work of Prokhorov and the unpublished work of Gould.

The term "laser" was first introduced to the public in Gould's 1959 conference paper "The LASER, Light Amplification by Stimulated Emission of Radiation". ^[1][11] Gould intended "-aser" to be a suffix, to be used with an appropriate prefix for the spectra of light emitted by the device (x-ray laser = xaser, ultraviolet laser = uvaser, etc. ). None of the other terms became popular, although "raser" was used for a short time to describe radio-frequency emitting devices.

Gould's notes included possible applications for a laser, such as spectrometry, interferometry, radar, and nuclear fusion. Spectroscopy was originally the study of the interaction between Radiation and Matter as a function of Wavelength (λ Interferometry is the technique of using the pattern of Interference created by the superposition of two or more Waves to diagnose the properties of Radar is a system that uses electromagnetic waves to identify the range altitude direction or speed of both moving and fixed objects such as Aircraft, ships In Physics and Nuclear chemistry, nuclear fusion is the process by which multiple- like charged atomic nuclei join together to form a heavier nucleus He continued working on his idea and filed a patent application in April 1959. A patent application is a request pending at a Patent office for the grant of a Patent for the Invention described and claimed by that application The U.S. Patent Office denied his application and awarded a patent to Bell Labs in 1960. The United States Patent and Trademark Office ( PTO or USPTO) is an agency in the United States Department of Commerce that issues Patents to Bell Laboratories (also known as Bell Labs and formerly known as AT&T Bell Laboratories and Bell Telephone Laboratories) is the Research organization This sparked a legal battle that ran 28 years, with scientific prestige and much money at stake. Gould won his first minor patent in 1977, but it was not until 1987 that he could claim his first significant patent victory when a federal judge ordered the government to issue patents to him for the optically pumped laser and the gas discharge laser. Gas discharge lamps are a family of artificial light sources that generate light by sending an Electrical discharge through an ionized gas i

The first working laser was made by Theodore H. Maiman in 1960^[12] at Hughes Research Laboratories in Malibu, California, beating several research teams including those of Townes at Columbia University, Arthur L. Theodore Harold "Ted" Maiman ( July 11, 1927 - May 5, 2007) was an American Physicist who made the first working HRL redirects here For the US airport see Valley International Airport. Malibu is an incorporated city in western Los Angeles County, California, United States. Charles Hard Townes (born July 28, 1915) is an American Nobel Prize-winning Physicist and educator Columbia University is a private University in the United States and a member of the Ivy League. Schawlow at Bell Labs,^[13] and Gould at a company called TRG (Technical Research Group). Maiman used a solid-state flashlamp-pumped synthetic ruby crystal to produce red laser light at 694 nanometres wavelength. A xenon flash lamp is an Electric glow discharge lamp designed to produce extremely intense incoherent, full-spectrum white light for very short durations A Ruby is a pink to blood-red Gemstone, a variety of the Mineral Corundum ( Aluminium oxide) In Materials science, a crystal is a Solid in which the constituent Atoms Molecules or Ions are packed in a regularly ordered repeating Maiman's laser, however, was only capable of pulsed operation due to its three energy level pumping scheme.

Later in 1960 the Iranian physicist Ali Javan, working with William R. Bennett and Donald Herriot, made the first gas laser using helium and neon. For a topic outline on this subject see List of basic Iran topics. Ali Javan ( Persian: علی جوان, born December 26, 1926 in Tehran, Iran) is an Iranian inventor and Physicist William R Bennett ( January 30, 1930 - June 29, 2008) was an American Physicist known for his pioneering work on gas A gas laser is a Laser in which an Electric current is discharged through a Gas to produce light Helium ( He) is a colorless odorless tasteless non-toxic Inert Monatomic Chemical Neon (ˈniːɒn is the Chemical element that has the symbol Ne and Atomic number 10 Javan later received the Albert Einstein Award in 1993. The Albert Einstein Award (sometimes called the Albert Einstein Medal because it is accompanied with a gold medal is an award in Theoretical physics, that was established

The concept of the semiconductor laser diode was proposed by Basov and Javan. A laser diode is a Laser where the active medium is a Semiconductor similar to that found in a Light-emitting diode. The first laser diode was demonstrated by Robert N. Hall in 1962. Robert N Hall (b December 25, 1919) is an American engineer He demonstrated the first semiconductor laser, and invented a type of Magnetron Hall's device was made of gallium arsenide and emitted at 850 nm in the near-infrared region of the spectrum. Gallium arsenide ( GaAs) is a compound of two elements Gallium and Arsenic. Infrared ( IR) radiation is Electromagnetic radiation whose Wavelength is longer than that of Visible light, but shorter than that of The first semiconductor laser with visible emission was demonstrated later the same year by Nick Holonyak, Jr. Nick Holonyak Jr (born in Zeigler Illinois on November 3, 1928) invented the first visible LED in 1962 while working as a consulting As with the first gas lasers, these early semiconductor lasers could be used only in pulsed operation, and indeed only when cooled to liquid nitrogen temperatures (77 K). Liquid nitrogen (liquid density at the Triple point is 0707 g/mL is the liquid produced industrially in large quantities by Fractional distillation of

In 1970, Zhores Alferov in the Soviet Union and Izuo Hayashi and Morton Panish of Bell Telephone Laboratories independently developed laser diodes continuously operating at room temperature, using the heterojunction structure. Zhores Ivanovich Alferov (Жоре́с Ива́нович Алфёров ʐɐˈrʲɛs ɪˈvanəvʲɪtɕ ɐlˈfʲorəf (born March 15 1930) is a Russian Bell Laboratories (also known as Bell Labs and formerly known as AT&T Bell Laboratories and Bell Telephone Laboratories) is the Research organization A heterojunction is the interface that occurs between two layers or regions of dissimilar Crystalline Semiconductors These semiconducting materials have unequal

Recent innovations

Graph showing the history of maximum laser pulse intensity throughout the past 40 years.

Since the early period of laser history, laser research has produced a variety of improved and specialized laser types, optimized for different performance goals, including:

• new wavelength bands
• maximum average output power
• maximum peak output power
• minimum output pulse duration
• maximum power efficiency
• maximum charging
• maximum firing

and this research continues to this day.

Lasing without maintaining the medium excited into a population inversion, was discovered in 1992 in sodium gas and again in 1995 in rubidium gas by various international teams. Sodium (ˈsoʊdiəm is an element which has the symbol Na( Latin natrium, from Arabic natrun) atomic number 11 atomic mass 22 Rubidium (ruːˈbɪdiəm /rəˈbɪdiəm/ is a Chemical element with the symbol Rb and Atomic number 37 This was accomplished by using an external maser to induce "optical transparency" in the medium by introducing and destructively interfering the ground electron transitions between two paths, so that the likelihood for the ground electrons to absorb any energy has been cancelled.

In 1985 at the University of Rochester's Laboratory for Laser Energetics a breakthrough in creating ultrashort-pulse, very high-intensity (terawatts) laser pulses became available using a technique called chirped pulse amplification, or CPA, discovered by Gérard Mourou. The University of Rochester ( U of R UR) is a private, nonsectarian Coeducational Research University located in Rochester The watt (symbol W) is the SI derived unit of power, equal to one Joule of energy per Second. Chirped pulse amplification ( CPA) or optical parametric chirped pulse amplification ( OPCPA) is a technique for amplifying an ultrashort Gérard Mourou is a French pioneer in the field of electrical engineering and Lasers. These high intensity pulses can produce filament propagation in the atmosphere. In Nonlinear optics, filament propagation is propagation of a beam of Light through a medium without Diffraction.

Types and operating principles

For a more complete list of laser types see this list of laser types. This is a list of laser types, their operational Wavelengths and their applications.

Spectral output of several types of lasers.

Gas lasers

Gas lasers using many gases have been built and used for many purposes. A gas laser is a Laser in which an Electric current is discharged through a Gas to produce light This page is about the physical properties of gas as a state of matter

The helium-neon laser (HeNe) emits at a variety of wavelengths and units operating at 633 nm are very common in education because of its low cost. A helium-neon laser, usually called a HeNe laser, is a type of small Gas laser.

Carbon dioxide lasers can emit hundreds of kilowatts^[14] at 9. The carbon dioxide laser ( CO2 laser) was one of the earliest Gas lasers to be developed (invented by Kumar Patel of Bell Labs in 1964 6 µm and 10. A micrometre ( American spelling: micrometer; symbol µm) is one millionth of a Metre, or equivalently one thousandth of a Millimetre 6 µm, and are often used in industry for cutting and welding. The efficiency of a CO₂ laser is over 10%.

Argon-ion lasers emit light in the range 351-528. An ion laser is a Gas laser which uses an Ionized gas as its lasing medium 7 nm. Depending on the optics and the laser tube a different number of lines is usable but the most commonly used lines are 458 nm, 488 nm and 514. 5 nm.

A nitrogen transverse electrical discharge in gas at atmospheric pressure (TEA) laser is an inexpensive gas laser producing UV Light at 337. The CO2 TEA Laser was invented in the late 1960s by Dr Jacques Beaulieu working at the Defence Research Establishment Valcartier in Quebec, Canada 1 nm. ^[15]

Metal ion lasers are gas lasers that generate deep ultraviolet wavelengths. Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays Helium-silver (HeAg) 224 nm and neon-copper (NeCu) 248 nm are two examples. Helium ( He) is a colorless odorless tasteless non-toxic Inert Monatomic Chemical Silver (ˈsɪlvɚ is a Chemical element with the symbol " Ag " (argentum from the Ancient Greek: ἀργήντος - argēntos gen Neon (ˈniːɒn is the Chemical element that has the symbol Ne and Atomic number 10 Copper (ˈkɒpɚ is a Chemical element with the symbol Cu (cuprum and Atomic number 29 These lasers have particularly narrow oscillation linewidths of less than 3 GHz (0. The spectral linewidth characterizes the width of a Spectral line, such as in the electromagnetic emission spectrum of an atom or the Frequency spectrum The hertz (symbol Hz) is a measure of Frequency, informally defined as the number of events occurring per Second. 5 picometers),^[16] making them candidates for use in fluorescence suppressed Raman spectroscopy. A picometre ( American spelling: picometer, symbol pm) is a unit of Length in the Metric system, equal to one trillionth Fluorescence is a Luminescence that is mostly found as an Raman spectroscopy (pronounced S— is a spectroscopic technique used in Condensed matter physics and Chemistry to study vibrational rotational and

Chemical lasers

Chemical lasers are powered by a chemical reaction, and can achieve high powers in continuous operation. A chemical laser is a Laser that obtains its energy from a Chemical reaction. For example, in the Hydrogen fluoride laser (2700-2900 nm) and the Deuterium fluoride laser (3800 nm) the reaction is the combination of hydrogen or deuterium gas with combustion products of ethylene in nitrogen trifluoride. The hydrogen fluoride laser is an Infrared Chemical laser. It is capable of delivering continuous output power in the Megawatt range The hydrogen fluoride laser is an Infrared Chemical laser. It is capable of delivering continuous output power in the Megawatt range Structure This Hydrocarbon has four Hydrogen Atoms bound to a pair of Carbon atoms that are connected by a Double bond. Nitrogen trifluoride is the Inorganic compound with the formula NF3 They were invented by George C. Pimentel. George Claude Pimentel (1922 &ndash 1989 was the inventor of the Chemical laser.

Excimer lasers

Excimer lasers are powered by a chemical reaction involving an excited dimer, or excimer, which is a short-lived dimeric or heterodimeric molecule formed from two species (atoms), at least one of which is in an excited electronic state. An excimer laser (sometimes and more correctly called an exciplex laser) is a form of ultraviolet laser which is commonly used in Eye surgery and Semiconductor An excimer (originally short for excited dimer) is a short-lived dimeric or heterodimeric Molecule formed from two species at least one of which is in Excitation is an elevation in energy level above an arbitrary baseline energy state They typically produce ultraviolet light, and are used in semiconductor photolithography and in LASIK eye surgery. Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays Photolithography (also called optical lithography) is a process used in Microfabrication to selectively remove parts of a thin film (or the bulk of a substrate LASIK or Lasik ( Laser -assisted In situ Keratomileusis) is a type Commonly used excimer molecules include F₂ (fluorine, emitting at 157 nm), and noble gas compounds (ArF [193 nm], KrCl [222 nm], KrF [248 nm], XeCl [308 nm], and XeF [351 nm]). Fluorine, fluorum meaning "to flow" is the Chemical element with the symbol F and Atomic number 9 ^[17]

Solid-state lasers

A 50 W FASOR, based on a Nd:YAG laser, used at the Starfire Optical Range

Solid state laser materials are commonly made by doping a crystalline solid host with ions that provide the required energy states. In Physics, a FASOR is an acronym for Frequency Addition Source of Optical Radiation. Starfire Optical Range is a United States Air Force research laboratory on the Kirtland Air Force Base in Albuquerque New Mexico. A solid-state laser is a Laser that uses a gain medium that is a Solid, rather than a Liquid such as in Dye lasers or a Gas For example, the first working laser was a ruby laser, made from ruby (chromium-doped corundum). A ruby laser is a Solid-state laser that uses a synthetic Ruby crystal as its gain medium. A Ruby is a pink to blood-red Gemstone, a variety of the Mineral Corundum ( Aluminium oxide) Chromium (ˈkroʊmiəm is a Chemical element which has the symbol Cr and Atomic number 24 Corundum (from Tamil kurundam குருந்தம் or kuruvindam குருவிந்தம் is a Crystalline form of Formally, the class of solid-state lasers includes also fiber laser, as the active medium (fiber) is in the solid state. A fiber laser or fibre laser is a Laser in which the Active gain medium is an Optical fiber doped with Rare-earth elements such as Practically, in the scientific literature, solid-state laser usually means a laser with bulk active medium; while wave-guide lasers are caller fiber lasers. A solid-state laser is a Laser that uses a gain medium that is a Solid, rather than a Liquid such as in Dye lasers or a Gas A fiber laser or fibre laser is a Laser in which the Active gain medium is an Optical fiber doped with Rare-earth elements such as

Neodymium is a common dopant in various solid state laser crystals, including yttrium orthovanadate (Nd:YVO₄), yttrium lithium fluoride (Nd:YLF) and yttrium aluminium garnet (Nd:YAG). Neodymium (ˌniːoʊˈdɪmiəm is a Chemical element with the symbol Nd and Atomic number 60 Yttrium orthovanadate ( YVO4) is a transparent crystal It is commonly doped with Neodymium to form NdYVO4, an Active laser medium Neodymium-doped yttrium orthovanadate ( NdYVO4) is a Crystalline material formed by adding Neodymium ions to Yttrium orthovanadate. Yttrium lithium fluoride (LiYF4 sometimes abbreviated YLF) is a birefringent crystal typically doped with Neodymium and used as a gain Neodymium-doped yttrium lithium fluoride ( NdYLF) is a lasing medium for Arclamp - pumped and diode-pumped Solid-state lasers YAG redirects here For the IATA airport code see Fort Frances Municipal Airport. NdYAG ( neodymium-doped yttrium aluminium garnet; NdY3Al5O12) is a Crystal that is used as a lasing medium All these lasers can produce high powers in the infrared spectrum at 1064 nm. Infrared ( IR) radiation is Electromagnetic radiation whose Wavelength is longer than that of Visible light, but shorter than that of They are used for cutting, welding and marking of metals and other materials, and also in spectroscopy and for pumping dye lasers. Spectroscopy was originally the study of the interaction between Radiation and Matter as a function of Wavelength (λ A dye laser is a Laser which uses an organic Dye as the Lasing medium, usually as a Liquid Solution. These lasers are also commonly frequency doubled, tripled or quadrupled to produce 532 nm (green, visible), 355 nm (UV) and 266 nm (UV) light when those wavelengths are needed. Nonlinear optics (NLO is the branch of Optics that describes the behaviour of Light in nonlinear media, that is media in which the dielectric polarization Nonlinear optics (NLO is the branch of Optics that describes the behaviour of Light in nonlinear media, that is media in which the dielectric polarization Nonlinear optics (NLO is the branch of Optics that describes the behaviour of Light in nonlinear media, that is media in which the dielectric polarization Green is a Color, the perception of which is evoked by light having a spectrum dominated by energy with a Wavelength of roughly 520–570- nm. Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays

Ytterbium, holmium, thulium, and erbium are other common dopants in solid state lasers. Holmium (ˈhoʊlmiəm is a Chemical element with the symbol Ho and Atomic number 67 Thulium (ˈθjuːliəm is a Chemical element that has the symbol Tm and Atomic number 69 Erbium (ˈɝbiəm is a Chemical element with the symbol Er and Atomic number 68 Ytterbium is used in crystals such as Yb:YAG, Yb:KGW, Yb:KYW, Yb:SYS, Yb:BOYS, Yb:CaF2, typically operating around 1020-1050 nm. They are potentially very efficient and high powered due to a small quantum defect. Extremely high powers in ultrashort pulses can be achieved with Yb:YAG. Holmium-doped YAG crystals emit at 2097 nm and form an efficient laser operating at infrared wavelengths strongly absorbed by water-bearing tissues. Holmium (ˈhoʊlmiəm is a Chemical element with the symbol Ho and Atomic number 67 Infrared ( IR) radiation is Electromagnetic radiation whose Wavelength is longer than that of Visible light, but shorter than that of The Ho-YAG is usually operated in a pulsed mode, and passed through optical fiber surgical devices to resurface joints, remove rot from teeth, vaporize cancers, and pulverize kidney and gall stones.

Titanium-doped sapphire (Ti:sapphire) produces a highly tunable infrared laser, commonly used for spectroscopy as well as the most common ultrashort pulse laser. Titanium (taɪˈteɪniəm is a Chemical element with the symbol Ti and Atomic number 22 Tisapphire lasers (also known as TiAl2O3 lasers, titanium-sapphire lasers, or simply Tisapphs) are Tunable lasers which A tunable laser is a Laser whose Wavelength of operation can be altered in a controlled manner Infrared ( IR) radiation is Electromagnetic radiation whose Wavelength is longer than that of Visible light, but shorter than that of Spectroscopy was originally the study of the interaction between Radiation and Matter as a function of Wavelength (λ In Optics, an ultrashort pulse of light is an Electromagnetic pulse whose time duration is on the order of the femtosecond (10^{-15} second

Thermal limitations in solid-state lasers arise from unconverted pump power that manifests itself as heat and phonon energy. In Physics, a phonon is a quantized mode of vibration occurring in a rigid crystal lattice, such as the Atomic lattice of a Solid This heat, when coupled with a high thermo-optic coefficient (dn/dT) can give rise to thermal lensing as well as reduced quantum efficiency. These types of issues can be overcome by another novel diode-pumped solid state laser, the diode-pumped thin disk laser. A disk laser or active mirror (Fig1 is a type of Solid-state laser characterized by a heat sink and laser output that are realized on opposite sides of The thermal limitations in this laser type are mitigated by utilizing a laser medium geometry in which the thickness is much smaller than the diameter of the pump beam. This allows for a more even thermal gradient in the material. Thin disk lasers have been shown to produce up to kilowatt levels of power. A disk laser or active mirror (Fig1 is a type of Solid-state laser characterized by a heat sink and laser output that are realized on opposite sides of ^[18]

Fiber-hosted lasers

Solid-state lasers where the light is guided due to the total internal reflection in an optical fiber are called fiber lasers. An optical fiber (or fibre) is a Glass or Plastic fiber that carries Light along its length A fiber laser or fibre laser is a Laser in which the Active gain medium is an Optical fiber doped with Rare-earth elements such as Guiding of light allows extremely long gain regions providing good cooling conditions; fibers have high surface area to volume ratio which allows efficient cooling. In addition, the fiber's waveguiding properties tend to reduce thermal distortion of the beam. Erbium and ytterbium ions are common active species in such lasers. Erbium (ˈɝbiəm is a Chemical element with the symbol Er and Atomic number 68

Quite often, the fiber laser is designed as a double-clad fiber. In Fiber optics, a double-clad fiber (or doubly clad fiber or DCF is an Optical fiber that has a relatively small-diameter core and two layers This type of fiber consists of a fiber core, an inner cladding and an outer cladding. The index of the three concentric layers is chosen so that the fiber core acts as a single-mode fiber for the laser emission while the outer cladding acts as a highly multimode core for the pump laser. This lets the pump propagate a large amount of power into and through the active inner core region, while still having a high numerical aperture (NA) to have easy launching conditions.

Pump light can be used more efficiently by creating a fiber disk laser, or a stack of such lasers. A fiber disk laser is a Fiber laser with transverse delivery of the pump light

Fiber lasers have a fundamental limit in that the intensity of the light in the fiber cannot be so high that optical nonlinearities induced by the local electric field strength can become dominant and prevent laser operation and/or lead to the material destruction of the fiber. This effect is called photodarkening. Photodarkening is Optical effect observed in interaction of laser radiation with amorphous media (glasses in Optical fibers. In bulk laser materials, the cooling is not so efficient, and it is difficult to separate the effects of photodarkening from the thermal effects, but the experiments in fibers show that the photodarkening can be attributed to the formation of long-living color centers. The color center is a region in the human Brain responsible for processing colour

Photonic crystal lasers

Photonic crystal lasers are lasers based on nano-structures that provide the mode confinement and the density of optical states (DOS) structure required for the feedback to take place. In statistical and Condensed matter physics, the density of states ( DOS) of a system describes the number of states at each energy level that are available They are typical micron-sized and tunable on the bands of the photonic crystals. [2]

Semiconductor lasers

Commercial laser diodes emit at wavelengths from 375 nm to 1800 nm, and wavelengths of over 3 µm have been demonstrated. A laser diode is a Laser where the active medium is a Semiconductor similar to that found in a Light-emitting diode. Low power laser diodes are used in laser printers and CD/DVD players. A laser printer is a common type of Computer printer that rapidly produces high quality text and graphics on plain paper More powerful laser diodes are frequently used to optically pump other lasers with high efficiency. Laser pumping is the act of energy transfer from an external source into the Gain medium of a Laser. The highest power industrial laser diodes, with power up to 10 kW (70dBm), are used in industry for cutting and welding. External-cavity semiconductor lasers have a semiconductor active medium in a larger cavity. These devices can generate high power outputs with good beam quality, wavelength-tunable narrow-linewidth radiation, or ultrashort laser pulses. The spectral linewidth characterizes the width of a Spectral line, such as in the electromagnetic emission spectrum of an atom or the Frequency spectrum

A small laser diode, most likely from a CD player or a DVD player. A Compact Disc (also known as a CD) is an Optical disc used to store digital data, originally developed for storing digital audio DVD (also known as " Digital Versatile Disc " or " Digital Video Disc " - see Etymology)is

Vertical cavity surface-emitting lasers (VCSELs) are semiconductor lasers whose emission direction is perpendicular to the surface of the wafer. The vertical-cavity surface-emitting laser ( VCSEL;) is a type of semiconductor Laser diode with Laser beam emission perpendicular from the top surface VCSEL devices typically have a more circular output beam than conventional laser diodes, and potentially could be much cheaper to manufacture. As of 2005, only 850 nm VCSELs are widely available, with 1300 nm VCSELs beginning to be commercialized,^[19] and 1550 nm devices an area of research. VECSELs are external-cavity VCSELs. A vertical-external-cavity surface-emitting-laser ( VECSEL) is a small Semiconductor laser similar to a Vertical-cavity surface-emitting laser (VCSEL Quantum cascade lasers are semiconductor lasers that have an active transition between energy sub-bands of an electron in a structure containing several quantum wells. Quantum cascade lasers (QCLs are Semiconductor lasers that emit in the mid- to far- Infrared portion of the Electromagnetic spectrum and were first demonstrated A quantum well is a Potential well that confines particles which were originally free to move in three dimensions to two dimensions forcing them to occupy a planar region

The development of a silicon laser is important in the field of optical computing, since it means that if silicon, the chief ingredient of computer chips, were able to produce lasers, it would allow the light to be manipulated like electrons are in normal integrated circuits. Silicon (ˈsɪlɪkən or /ˈsɪlɪkɒn/ silicium is the Chemical element that has the symbol Si and Atomic number 14 An optical computer is a computer that uses light instead of electricity (i Microchipsjpg|right|thumb|200px|Microchips ( EPROM memory with a transparent window showing the integrated circuit inside Thus, photons would replace electrons in the circuits, which dramatically increases the speed of the computer. Unfortunately, silicon is a difficult lasing material to deal with, since it has certain properties which block lasing. However, recently teams have produced silicon lasers through methods such as fabricating the lasing material from silicon and other semiconductor materials, such as indium(III) phosphide or gallium(III) arsenide, materials which allow coherent light to be produced from silicon. Indium phosphide ( is a binary Semiconductor composed of Indium and Phosphorus. Gallium arsenide ( GaAs) is a compound of two elements Gallium and Arsenic. These are called hybrid silicon laser. A hybrid silicon laser is a semiconductor Laser fabricated from both Silicon and group III-V Semiconductor materials The hybrid silicon laser was developed Another type is a Raman laser, which takes advantage of Raman scattering to produce a laser from materials such as silicon. The Raman laser is a byproduct of Raman scattering, discovered in 1928 by Nobel laureate Chandrasekhara Venkata Raman and Kariamanickam Srinivasa Krishnan Raman scattering or the Raman effect (pronounced — is the inelastic scattering of a Photon.

Dye lasers

Dye lasers use an organic dye as the gain medium. A dye laser is a Laser which uses an organic Dye as the Lasing medium, usually as a Liquid Solution. The wide gain spectrum of available dyes allows these lasers to be highly tunable, or to produce very short-duration pulses (on the order of a few femtoseconds)

Free electron lasers

Free electron lasers, or FELs, generate coherent, high power radiation, that is widely tunable, currently ranging in wavelength from microwaves, through terahertz radiation and infrared, to the visible spectrum, to soft X-rays. To help compare Orders of magnitude of different Times this page lists times between 10&minus15 second and 10&minus12 second (1 Femto A free-electron laser, or FEL is a Laser that shares the same optical properties as conventional lasers such as emitting a Beam consisting of coherent Electromagnetic waves sent at terahertz frequencies, known as terahertz radiation, submillimeter radiation, terahertz waves, terahertz They have the widest frequency range of any laser type. While FEL beams share the same optical traits as other lasers, such as coherent radiation, FEL operation is quite different. Unlike gas, liquid, or solid-state lasers, which rely on bound atomic or molecular states, FELs use a relativistic electron beam as the lasing medium, hence the term free electron.

Exotic laser media

In September 2007, the BBC News reported that there was speculation about the possibility of using positronium annihilation to drive a very powerful gamma ray laser. Positronium ( Ps) is a system consisting of an Electron and its anti-particle, a Positron, bound together into an " Exotic atom Annihilation is defined as "total destruction" or "complete obliteration" of an object having its root in the Latin nihil (nothing Gamma rays (denoted as &gamma) are a form of Electromagnetic radiation or light emission of frequencies produced by sub-atomic particle interactions ^[20] Dr. David Cassidy of the University of California, Riverside proposed that a single such laser could be used to ignite a nuclear fusion reaction, replacing the hundreds of lasers used in typical inertial confinement fusion experiments. The University of California Riverside, commonly known as UCR or UC Riverside, is a public Research university and one of the 10 general In Physics and Nuclear chemistry, nuclear fusion is the process by which multiple- like charged atomic nuclei join together to form a heavier nucleus Inertial confinement fusion ( ICF) is a process where Nuclear fusion reactions are initiated by heating and compressing a fuel target typically in the form of ^[20]

Space-based X-ray lasers pumped by a nuclear explosion have also been proposed as antimissile weapons. ^[21][22] Such devices would be one-shot weapons.

Uses

Lasers range in size from microscopic diode lasers (top) with numerous applications, to football field sized neodymium glass lasers (bottom) used for inertial confinement fusion, nuclear weapons research and other high energy density physics experiments

Main article: Laser applications

When lasers were invented in 1960, they were called "a solution looking for a problem". A laser diode is a Laser where the active medium is a Semiconductor similar to that found in a Light-emitting diode. Neodymium (ˌniːoʊˈdɪmiəm is a Chemical element with the symbol Nd and Atomic number 60 Glass in the common sense refers to a Hard, Brittle, transparent Solid, such as that used for Windows many Inertial confinement fusion ( ICF) is a process where Nuclear fusion reactions are initiated by heating and compressing a fuel target typically in the form of A nuclear weapon is an explosive device that derives its destructive force from Nuclear reactions either fission or a combination of fission and fusion. There are many scientific military medical and commercial laser applications which have been developed since the invention of the laser in the 1958 ^[23] Since then, they have become ubiquitous, finding utility in thousands of highly varied applications in every section of modern society, including consumer electronics, information technology, science, medicine, industry, law enforcement, entertainment, and the military. Consumer electronics include electronic equipment intended for everyday use Information technology ( IT) as defined by the Information Technology Association of America (ITAA is "the study design development implementation support Science (from the Latin scientia, meaning " Knowledge " or "knowing" is the effort to discover, and increase human understanding Medicine is the art and science of healing It encompasses a range of Health care practices evolved to maintain and restore Human Health by the For other uses of this term see Industry (disambiguation An industry (from Latin industrius, "diligent industrious" See also Entertainment (disambiguation and The Entertainer (disambiguation Entertainment is an activity designed to give people A military is an Organization authorized by its Nation to use force usually including use of Weapons in defending its Country (or by attacking

The first application of lasers visible in the daily lives of the general population was the supermarket barcode scanner, introduced in 1974. A bar code (also barcode) is an optical Machine-readable representation of data The laserdisc player, introduced in 1978, was the first successful consumer product to include a laser, but the compact disc player was the first laser-equipped device to become truly common in consumers' homes, beginning in 1982, followed shortly by laser printers. The Laserdisc (LD is an obsolete Home video disc format and was the first commercial Optical disc storage medium A Compact Disc (also known as a CD) is an Optical disc used to store digital data, originally developed for storing digital audio A laser printer is a common type of Computer printer that rapidly produces high quality text and graphics on plain paper

Some of the other applications include:

• Medicine: Bloodless surgery, laser healing, surgical treatment, kidney stone treatment, eye treatment, dentistry
• Industry: Cutting, welding, material heat treatment, marking parts
• Defense: Marking targets, guiding munitions, missile defence, electro-optical countermeasures (EOCM), alternative to radar
• Research: Spectroscopy, laser ablation, Laser annealing, laser scattering, laser interferometry, LIDAR
• Product development/commercial: laser printers, CDs, barcode scanners, thermometers, laser pointers, holograms, bubblegrams. Medicine is the art and science of healing It encompasses a range of Health care practices evolved to maintain and restore Human Health by the Surgery (from the χειρουργική cheirourgikē, via chirurgiae meaning "hand work" is a medical specialty that uses operative manual and instrumental Kidney stones, also called renal calculi, are solid concretions (crystal aggregations of dissolved minerals in Urine; calculi typically form Eye surgery, also known as orogolomistician surgery or ocular surgery, is Surgery performed on the Eye or its Adnexa, typically by Dentistry' is the "evaluation diagnosis prevention and/or treatment (nonsurgical surgical or related procedures of diseases disorders and/or conditions of the oral cavity For other uses of this term see Industry (disambiguation An industry (from Latin industrius, "diligent industrious" Welding is a fabrication process that joins materials usually Metals or Thermoplastics by causing coalescence. Defence Ammunition, often referred to as ammo, is a generic term derived from the French language la munition which WikipediaWikiProject Aircraft. Please see WikipediaWikiProject Aircraft/page content for recommended layout Directional Infrared Counter Measures ( DIRCM) is a system produced by Northrop Grumman and BAE Systems to protect Aircraft from Infrared Radar is a system that uses electromagnetic waves to identify the range altitude direction or speed of both moving and fixed objects such as Aircraft, ships Research is defined as Human activity based on Intellectual application in the investigation of Matter. Spectroscopy was originally the study of the interaction between Radiation and Matter as a function of Wavelength (λ Laser ablation is the process of removing material from a solid (or occasionally liquid surface by irradiating it with a Laser beam Scattering is a general physical process whereby some forms of Radiation, such as Light, Sound or moving particles for example are forced to deviate from Interferometry is the technique of using the pattern of Interference created by the superposition of two or more Waves to diagnose the properties of LIDAR ( Li ght D etection a nd R anging is an optical remote sensing technology that measures properties of scattered light to find range and/or A laser printer is a common type of Computer printer that rapidly produces high quality text and graphics on plain paper A Compact Disc (also known as a CD) is an Optical disc used to store digital data, originally developed for storing digital audio A bar code (also barcode) is an optical Machine-readable representation of data The thermometer is a device that measures Temperature or Temperature gradient using a variety of different principles it comes from the Greek roots A laser pointer is a portable pen-sized Laser designed to be held in the hand and most commonly used to project a point of light to highlight items of interest during a Holography (from the Greek, ὅλος - hólos whole + γραφή - grafē writing drawing is a technique that allows the A bubblegram is a 3D image composed of points suspended in a medium typically a plastic block

In 2004, excluding diode lasers, approximately 131,000 lasers were sold world-wide, with a value of US$2. 19 billion. ^[24] In the same year, approximately 733 million diode lasers, valued at $3. 20 billion, were sold. ^[25]

Examples by power

Different uses need lasers with different output powers. Lasers that produce a continuous beam or a series of short pulses can be compared on the basis of their average power. Lasers that produce pulses can also be characterized based on the peak power of each pulse. The peak power of a pulsed laser is many orders of magnitude greater than its average power. An order of magnitude is the class of scale or magnitude of any amount where each class contains values of a fixed ratio to the class preceding it The average output power is always less than the power consumed.

The continuous or average power required for some uses:

• 5 mW – CD-ROM drive
• 5–10 mW – DVD player or DVD-ROM drive
• 100 mW – CD-RW drive
• 250 mW – High-speed CD-R burner^[26]
• 500 mW – Consumer DVD-R burner^[27]
• 1 W – green laser in current Holographic Versatile Disc prototype development
• 1–20 W – output of the majority of commercially available solid-state lasers used for micro machining
• 30–100 W – typical sealed CO₂ surgical lasers^[28]
• 100–3000 W (peak output 1. CD-ROM (an initialism of "Compact Disc Read-Only Memory " is a pre-pressed Compact Disc that contains data accessible to but not writable This page relates to a Hardware device used to play DVDs For the Apple Software program, see DVD Player (Apple. DVD (also known as " Digital Versatile Disc " or " Digital Video Disc " - see Etymology)is Compact Disc ReWritable (CD-RW is a rewritable Optical disc format A CD-R ( C ompact D isc- R ecordable is a variation of the Compact Disc invented by Philips and Sony. DVD-R is a DVD recordable format A DVD-R typically has a storage capacity of 4 The Holographic Versatile Disc ( HVD) is an optical disc technology that would hold up to 3 5 kW) – typical sealed CO₂ lasers used in industrial laser cutting
• 1 kW – Output power expected to be achieved by a prototype 1 cm diode laser bar^[29]

Examples of pulsed systems with high peak power:

• 700 TW (700×10¹² W) – The National Ignition Facility is working on a system that, when complete, will contain a 192-beam, 1. Laser cutting is a technology that uses a Laser to cut materials and is typically used for industrial manufacturing applications The watt (symbol W) is the SI derived unit of power, equal to one Joule of energy per Second. The National Ignition Facility, or NIF, is a Laser -based Inertial confinement fusion (ICF research device under construction at the Lawrence 8-megajoule laser system adjoining a 10-meter-diameter target chamber. ^[30] The system is expected to be completed in April of 2009.
• 1. 3 PW (1. This page lists examples of the power in Watts produced by various different sources of energy 3×10¹⁵ W) – world's most powerful laser as of 1998, located at the Lawrence Livermore Laboratory^[31]

Hobby uses

In recent years, some hobbyists have taken interests in lasers. Year 1998 ( MCMXCVIII) was a Common year starting on Thursday (link will display full 1998 Gregorian calendar) The Lawrence Livermore National Laboratory ( LLNL) in Livermore California is a scientific research laboratory founded by the University of California in 1952 Lasers used by hobbyists are generally of class IIIa or IIIb, although some have made their own class IV types. ^[32] However, compared to other hobbyists, laser hobbyists are far less common, due to the cost and potential dangers involved. Due to the cost of lasers, some hobbyists use inexpensive means to obtain lasers, such as extracting diodes from DVD burners. A DVD recorder (also known as a DVDR mainly outside of the UK and Ireland is an Optical disc recorder that records video onto blank writeable DVD media ^[33]

Hobbyists also have been taking surplus pulsed lasers from retired military applications and modifying them for pulsed holography. Pulsed Ruby and Pulsed YAG lasers have been used.

Laser safety

Warning symbol for lasers

Main articles: Laser safety and Lasers and aviation safety

Even the first laser was recognized as being potentially dangerous. Laser safety is the avoidance of Laser accidents especially those involving eye injuries Under certain conditions Laser light or other bright lights (spotlights Searchlights) directed at aircraft can be a hazard Theodore Maiman characterized the first laser as having a power of one "Gillette"; as it could burn through one Gillette razor blade. Theodore Harold "Ted" Maiman ( July 11, 1927 - May 5, 2007) was an American Physicist who made the first working This article describes unusual units of measurement that are sometimes used by Anglophone Scientists, especially Physicists and Mathematicians, and other The Aston Martin Razor Blade team car was built in 1923 to break the one hour light car record of held by AC Cars. Today, it is accepted that even low-power lasers with only a few milliwatts of output power can be hazardous to human eyesight.

At wavelengths which the cornea and the lens can focus well, the coherence and low divergence of laser light means that it can be focused by the eye into an extremely small spot on the retina, resulting in localized burning and permanent damage in seconds or even less time. The cornea is the transparent front part of the Eye that covers the iris, Pupil, and Anterior chamber. Eyes are organs that detect Light, and send signals along the Optic nerve to the visual areas of the brain The vertebrate retina is a light sensitive part inside the inner layer of the Eye. Lasers are classified into safety classes numbered I (inherently safe) to IV (even scattered light can cause eye and/or skin damage). Laser products available for consumers, such as CD players and laser pointers are usually in class I, II, or III. Certain infrared lasers with wavelengths beyond about 1. 4 micrometres are often referred to as being "eye-safe". This is because the intrinsic molecular vibrations of water molecules very strongly absorb light in this part of the spectrum, and thus a laser beam at these wavelengths is attenuated so completely as it passes through the eye's cornea that no light remains to be focused by the lens onto the retina. Water is a common Chemical substance that is essential for the survival of all known forms of Life. The cornea is the transparent front part of the Eye that covers the iris, Pupil, and Anterior chamber. The vertebrate retina is a light sensitive part inside the inner layer of the Eye. The label "eye-safe" can be misleading, however, as it only applies to relatively low power continuous wave beams and any high power or q-switched laser at these wavelengths can burn the cornea, causing severe eye damage. Q-switching, sometimes known as giant pulse formation, is a technique by which a Laser can be made to produce a pulsed output beam

'High Powered' green handheld 125milliwatt lasers (considered 'High Power' compared to a normal laser pointer) have recently been used in attacks on aircraft pilots landing at Australian airports. The risk is that if the laser hit the pilots eyes it could cause temporary blindness at a critical point in the flight. In 2007 penalties under the Australian Civil Aviation Act for shining laser beams at aircraft were increased to two years' jail and fines of up to $30,000.

Fictional predictions

For lasers in fiction, see also the raygun. This article is about fictional weapons For other meanings see Raygun (disambiguation.

Before stimulated emission was discovered, novelists used to describe machines that we can identify as "lasers". In Optics, stimulated emission is the process by which an electron perturbed by a Photon having the correct energy may drop to a lower Energy level resulting A novel (from Italian novella, Spanish novela, French nouvelle for "new" "news" or "short story

• The first fictional device similar to a military CO₂ laser (see Heat-Ray) appears in the sci-fi novel The War of the Worlds by H. G. Wells in 1898. The Heat-Ray is the primary offensive weapon used by the Martians in the H The War of the Worlds (1898 by H G Wells, is an early Science fiction Novel which describes an invasion of England by Herbert George Wells (21 September 1866 &ndash 13 August 1946 He was an outspoken socialist and a pacifist, his later works becoming increasingly political
• A laser-like device was described in Alexey Tolstoy's sci-fi novel The Hyperboloid of Engineer Garin in 1927. Aleksei Nikolaevich Tolstoi (Алексей Николаевич Толстой ( January 10, 1883 ( December 29, 1882 ( O The Garin Death Ray also known as The Death Box and The Hyperboloid of Engineer Garin (Гиперболоид инженера
• Mikhail Bulgakov exaggerated the biological effect (laser biostimulation) of intensive red light in his sci-fi novel Fatal Eggs (1925), without any reasonable description of the source of this red light. Mikhail Afanasievich Bulgakov (Михаил Афанасьевич Булгаков, Kiev &ndash March 10, 1940, Moscow) was a Russian The Fatal Eggs ( Russian: Роковые яйца, rɔkovyi jajʦa is a Novella by Mikhail Bulgakov, a Soviet novelist (In that novel, the red light first appears occasionally from the illuminating system of an advanced microscope; then the protagonist Prof. Persikov arranges the special set-up for generation of the red light. )

See also

Notes and references

Further reading

Books

• Bertolotti, Mario (1999, trans. 2004). The History of the Laser, Institute of Physics. ISBN 0-750-30911-3
• Csele, Mark (2004). Fundamentals of Light Sources and Lasers, Wiley. ISBN 0-471-47660-9
• Koechner, Walter (1992). Solid-State Laser Engineering, 3rd ed. , Springer-Verlag. ISBN 0-387-53756-2
• Siegman, Anthony E. (1986). Lasers, University Science Books. ISBN 0-935702-11-3
• Silfvast, William T. (1996). Laser Fundamentals, Cambridge University Press. ISBN 0-521-55617-1
• Svelto, Orazio (1998). Principles of Lasers, 4th ed. (trans. David Hanna), Springer. ISBN 0-306-45748-2
• Taylor, Nick (2000). LASER: The inventor, the Nobel laureate, and the thirty-year patent war. New York: Simon & Schuster. ISBN 0-684-83515-0.  
• Wilson, J. & Hawkes, J. F. B. (1987). Lasers: Principles and Applications, Prentice Hall International Series in Optoelectronics, Prentice Hall. Prentice Hall is a leading educational publisher It is an Imprint of Pearson Education Inc ISBN 0-13-523697-5
• Yariv, Amnon (1989). Quantum Electronics, 3rd ed. , Wiley. ISBN 0-471-60997-8

Periodicals

• Applied Physics B: Lasers and Optics (ISSN 0946-2171)
• IEEE Journal of Lightwave Technology (ISSN 0733-8724)
• IEEE Journal of Quantum Electronics (ISSN 0018-9197)
• IEEE Journal of Selected Topics in Quantum Electronics (ISSN 1077-260X)
• IEEE Photonics Technology Letters
• Journal of the Optical Society of America B: Optical Physics (ISSN 0740-3224)
• Laser Focus World (ISSN 0740-2511)
• Optics Letters (ISSN 0146-9592)
• Photonics Spectra (ISSN 0731-1230)

External links

• Encyclopedia of laser physics and technology by Dr. Laser Focus World is a monthly magazine covering Laser, Photonics and Optoelectronics technologies applications and markets Optics Letters is a peer-reviewed rapid-publication Scientific journal published by the Optical Society of America. Rüdiger Paschotta
• A Practical Guide to Lasers for Experimenters and Hobbyists by Samuel M. Goldwasser
• Homebuilt Lasers Page by Professor Mark Csele
• Powerful laser is 'brightest light in the universe' - The world's most powerful laser as of 2008 might create supernova-like shock waves and possibly even antimatter (New Scientist, 9 April 2008)
• How Lasers Work at HowStuffWorks
• Homemade laser project by Kip Kedersha
• "The Laser: basic principles" an online course by Prof. F. Balembois and Dr. S. Forget. Instrumentation for Optics, 2008