In physicsPhysics (Greek: (phúsis), "nature" and (phusiké), "knowledge of nature") is the branch of science concerned with discovering and characterizing universal laws that govern matter, energy, space, and time. Discoveries in physics resonate throughout the natural sciences, and physics has been described as the "fundamental science" because ...physics, a laser is a device that emits light through a specific mechanism for which the term laser is an acronymAcronyms and initialisms are abbreviations, such as NATO, laser, and IBM, that are formed using the initial letters of words or word parts in a phrase or name. Acronyms and initialisms are usually pronounced in a way that is distinct from that of the full forms for which they stand: as the names of the individual ...acronym: Light Amplification by Stimulated Emission of Radiation. This is a combined quantum-mechanicalQuantum mechanics is a fundamental branch of physics with wide applications in both experimental and theoretical physics. The effects of quantum mechanics are typically not observable on macroscopic scales, but become evident at the atomic and subatomic level. Quantum theory generalizes all classical theories, including mechanics ...quantum-mechanical and thermodynamicalThe starting point for most thermodynamic considerations are the laws of thermodynamics, which postulate that energy can be exchanged between physical systems as heat or work. They also postulate the existence of a quantity named entropy, which can be defined for any system. In thermodynamics, interactions between large ensembles of objects are studied ...thermodynamical process discussed in more detail below. As a light source, a laser can have various properties, depending on the purpose for which it is designed and calibrated. A typical laser emits light in a narrow, low-divergenceThe beam divergence of an electromagnetic beam is the increase in beam diameter with distance from the aperture from which the beam emerges in any plane that intersects the beam axis. Beam divergence is usually used to characterize electromagnetic beams in the optical regime, in other words cases in which the aperture from which the beam emerges is very large with respect to the wavelength. Beam divergence usually ...divergence beam and with a well-defined wavelengthIn physics, wavelength is the distance between repeating units of a propagating wave of a given frequency. It is commonly designated by the Greek letter lambda (λ). Examples of wave-like phenonomena are light, water waves, and sound waves. In a wave, a property varies with the position. For example, this property can be the air pressure for a sound wave, or the magnitude of the electric or the magnetic field for light. The ...wavelength (corresponding to a particular colorColor (or colour, see spelling differences) is the visual perceptual property corresponding in humans to the categories called red, yellow, white, etc. Color derives from the spectrum of light (distribution of light energy versus wavelength) interacting in the eye with the spectral sensitivities of the light receptors. Color categories and physical specifications of color are also associated with objects, materials, light sources, etc., based on their physical properties ...color if the laser is operating in the visible spectrumThe visible spectrum (or sometimes optical spectrum) is the portion of the electromagnetic spectrum that is visible to (can be detected by) the human eye. Electromagnetic radiation in this range of wavelengths is called visible light or simply light. There are no exact bounds to the visible spectrum; a typical human eye will respond to wavelengths in air from 400 to 700 nm, although some people may be able to perceive wavelengths from 380 to 780 nm. The corresponding wavelengths in water and ...visible spectrum). This is in contrast to a light source such as the incandescent light bulbThe incandescent light bulb or incandescent lamp is a source of artificial light that works by incandescence. An electrical current passes through a thin filament, heating it and causing it to become excited, releasing thermally equilibrated photons in the process. The enclosing glass bulb prevents the oxygen in air from reaching the hot filament, which otherwise would be destroyed rapidly by oxidation. Incandescent bulbs are also called electric lamps, extending the use of a term applied to the original arc lamps, ...incandescent light bulb, which emits into a large solid angle and over a wide spectrumThe electromagnetic (EM) spectrum is the range of all possible electromagnetic radiation. The "electromagnetic spectrum" (usually just spectrum) of an object is the frequency range of electromagnetic radiation with wavelengths from thousands of kilometres down to fractions of the size of an atom. It is commonly said that EM waves beyond these limits are uncommon, although this is ...spectrum of wavelength. These properties can be summarized in the term coherenceCoherence is the property of wave-like states that enables them to exhibit interference. It is also the parameter that quantifies the quality of the interference (also known as the degree of coherence). It was originally introduced in connection with Young’s double-slit experiment in optics but is now used in any field that involves waves, such as acoustics, electrical engineering, neuroscience, and quantum physics. In interference, at least two wave-like entities ...coherence.

A laser consists of a gain medium inside an optical cavity, with a means to supply energy to the gain medium. The gain mediumWithin a laser, the active laser medium or gain medium is the material that exhibits optical gain. This gain is generally generated by stimulated emission on electronic or molecular transitions to a lower energy state, starting from a higher energy state to which it had been previously stimulated by means of a pump source. Examples of active laser media include *certain crystals, typically doped with some rare-earth ions (e.g. of neodymium, ytterbium, or erbium) or transition metal ions (e.g. of titanium or chromium), most often yttrium aluminium ...gain medium is a material (gas, liquid, solid or free electrons) with appropriate optical properties. In its simplest form, a cavityAn optical cavity or optical resonator is an arrangement of mirrors that forms a standing wave cavity resonator for light waves. Optical cavities are a major component of lasers, surrounding the gain medium and providing feedback of the laser light. They are also used in optical parametric oscillators and some interferometers.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 couplerAn output coupler (OC) is a partially reflective mirror used in lasers to extract a portion of the laser beam from the optical resonator. Lasers operate by reflecting light between two or more mirrors which have an active laser medium between them. The medium amplifies the light by stimulated emission. For lasing to occur, the gain of the active medium must be larger than the total loss, which includes both unwanted effects such as absorption, ...output coupler, is partially transparent. The output laser beam is emitted through this mirror.

Light of a specific wavelength that passes through the gain medium is amplifiedAn optical amplifier is a device that amplifies an optical signal directly, without the need to first convert it to an electrical signal. An optical amplifier may be thought of as a laser without an optical cavity, or one in which feedback from the cavity is suppressed. Stimulated emission in the amplifier's gain medium causes amplification of incoming light. Optical amplifiers are important in optical communication and laser physics.amplified (increases in power); the surrounding mirrors ensure that most of the light makes many passes through the gain medium. Part of the light that is between the mirrors (i.e., is in the cavity) passes through the partially transparent mirror and appears as a beam of light. The process of supplying the energy required for the amplification is called pumpingLaser pumping is the act of energy transfer from an external source into the laser gain medium. The energy is absorbed in the medium, producing excited states in its atoms. When the number of particles in one excited state exceeds the number of particles in the ground state or a less-excited state, population inversion is achieved. In this condition, the mechanism of stimulated emission can take place and the medium can act as a laser or an optical amplifier. The pump power must be higher than the lasing ...pumping and the energy is typically supplied as an electrical current or as light at a different wavelength. In the latter case, the light source can be a flash lampA xenon flash lamp is an electric glow discharge lamp designed to produce extremely intense, incoherent, full-spectrum white light for very short durations.flash lamp or another laser. Most practical lasers contain additional elements that affect properties such as the wavelength of the emitted light and the shape of the beam.

The first working laser was demonstrated in May 1960Year 1960 (MCMLX) was a leap year starting on Friday (link will display full calendar) of the Gregorian calendar. The year 1960 is known as the "Year of Africa."1960 by Theodore MaimanTheodore Harold "Ted" Maiman (July 11, 1927 - May 5, 2007) was an American physicist who made the first working laser. Maiman received the Japan Prize in 1987. He was the author of a book titled The Laser Odyssey.Theodore Maiman at Hughes Research LaboratoriesIn the 1940's, Howard Hughes created a R&D facility in Culver City, California; by the early 1960's, it had been moved to Malibu, California. Through a series of business transactions, it was brought under the ownership of Boeing and General Motors, its LLC partners. For more detail, please see Hughes Aircraft. It receives funding from its LLC partners, US defense contracts, and other commercial ...Hughes Research Laboratories. Recently, lasers have become a multi-billion dollar industry. The most widespread use of lasers is in optical storageOptical storage is a term from engineering referring to the storage of data on an optically readable medium. Data is recorded by making marks in a pattern that can be read back with the aid of light. An ancient example of optical storage is using a stick to draw in a patch of sand or dirt. A common modern technique ...optical storage devices such as compact discA Compact Disc or CD is an optical disc used to store digital data, originally developed for storing digital audio. The CD, available on the market since late 1982, remains the standard playback carrier medium for commercial audio recordings as of 2007. An audio CD consists of one or more ...compact disc and DVDDVD (also known as "Digital Versatile Disc" or "Digital Video Disc") is a popular optical disc storage media format that can be used for data storage, including movies with high video and audio quality. DVDs are modeled in size after the compact disc (i.e. diameter: 120 mm or 4.72 in, occasionally 80 mm or 3.15 in.); ...DVD players, in which the laser (a few millimeters in size) scans the surface of the disc. Other common applications of lasers are bar codeA barcode (also bar code) is a machine-readable (using dark ink on white substrate to create high and low reflectance which is converted to 1s and 0s) representation of information in a visual format on a surface. Originally barcodes stored data in the widths and spacings of printed parallel lines, but today they ...bar code readers and laser pointersA 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 presentation. Most laser pointers have low enough power that the projected beam is ...laser pointers. In industry, lasers are used for cuttingLaser cutting is a technology that uses a laser to cut materials, and is usually used in industrial manufacturing. Laser cutting works by directing the output high power laser, by computer, at the material to be cut. The material then either melts, burns or vaporizes away leaving an edge with a high quality surface finish. Industrial laser cutters are used to cut flat-sheet material as well as structural and piping materials. Some 6-axis lasers can perform cutting operations on parts that have been pre-formed ...lasers are used for cutting steel and other metals and for inscribing patterns (such as the letters on computer keyboards). Lasers are also commonly used in various fields in scienceScience (from the Latin, 'knowledge') is a system of acquiring knowledge based on the scientific method, as well as the organized body of knowledge gained through such research."science" defined by various dictionaries at "reference.com" Science as defined here is sometimes termed pure science to differentiate it from applied science, which is the application of scientific research to specific human needs. Fields of science are commonly classified along ...science, especially spectroscopySpectroscopy is the study of the interaction between radiation (electromagnetic radiation, or light, as well as particle radiation) and matter. Spectrometry is the measurement of these interactions and an instrument which performs such measurements is a spectrometer or spectrograph. A plot of the interaction is referred to as a spectrogram, or, informally, a spectrum. Historically, spectroscopy referred to a branch of science in which visible light was used for the theoretical study ...spectroscopy, typically because of their well-defined wavelength or short pulse duration in the case of pulsed lasers. Lasers are also used for military and medical applications.