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86-641: An atlas or atlantid or telamon is a male version of a caryatid, i.e. , a sculpted male statue serving as an architectural support. The term is first recorded in the Latin form caryatides by the Roman architect Vitruvius . He stated in his 1st century BC work De architectura (I.1.5) that certain female figures represented the punishment of the women of Caryae , a town near Sparta in Laconia , who were condemned to slavery after betraying Athens by siding with Persia in

172-519: A gain medium , a mechanism to energize it, and something to provide optical feedback . The gain medium is a material with properties that allow it to amplify light by way of stimulated emission. Light of a specific wavelength that passes through the gain medium is amplified (power increases). Feedback enables stimulated emission to amplify predominantly the optical frequency at the peak of the gain-frequency curve. As stimulated emission grows, eventually one frequency dominates over all others, meaning that

258-471: A lens system, as is always included, for instance, in a laser pointer whose light originates from a laser diode . That is possible due to the light being of a single spatial mode. This unique property of laser light, spatial coherence , cannot be replicated using standard light sources (except by discarding most of the light) as can be appreciated by comparing the beam from a flashlight (torch) or spotlight to that of almost any laser. A laser beam profiler

344-464: A broad spectrum of light or emit different wavelengths of light simultaneously. Certain lasers are not single spatial mode and have light beams that diverge more than is required by the diffraction limit . All such devices are classified as "lasers" based on the method of producing light by stimulated emission. Lasers are employed where light of the required spatial or temporal coherence can not be produced using simpler technologies. A laser consists of

430-549: A chapter devoted to chimneypieces in his Idea della archittura universale . Those in the apartments of princes and important personages, he considered, might be grand enough for chimneypieces with caryatid supporters, such as one he illustrated and a similar one he installed in the Sala dell'Anticollegio , also in the Doge's Palace. In the 16th century, from the examples engraved for Sebastiano Serlio 's treatise on architecture, caryatids became

516-436: A coherent beam has been formed. The process of stimulated emission is analogous to that of an audio oscillator with positive feedback which can occur, for example, when the speaker in a public-address system is placed in proximity to the microphone. The screech one hears is audio oscillation at the peak of the gain-frequency curve for the amplifier. For the gain medium to amplify light, it needs to be supplied with energy in

602-419: A device lacks the spatial and temporal coherence achievable with lasers. Such a device cannot be described as an oscillator but rather as a high-gain optical amplifier that amplifies its spontaneous emission. The same mechanism describes so-called astrophysical masers /lasers. The optical resonator is sometimes referred to as an "optical cavity", but this is a misnomer: lasers use open resonators as opposed to

688-469: A fallen caryatid. Robert Heinlein described this piece in Stranger in a Strange Land : "Now here we have another emotional symbol... for almost three thousand years or longer, architects have designed buildings with columns shaped as female figures... After all those centuries it took Rodin to see that this was work too heavy for a girl... Here is this poor little caryatid who has tried—and failed, fallen under

774-819: A fixture in the decorative vocabulary of Northern Mannerism expressed by the Fontainebleau School and the engravers of designs in Antwerp . In the early 17th century, interior examples appear in Jacobean interiors in England; in Scotland the overmantel in the great hall of Muchalls Castle remains an early example. Caryatids remained part of the German Baroque vocabulary and were refashioned in more restrained and "Grecian" forms by neoclassical architects and designers, such as

860-508: A gain medium must have a gain bandwidth sufficiently broad to amplify those frequencies. An example of a suitable material is titanium -doped, artificially grown sapphire ( Ti:sapphire ), which has a very wide gain bandwidth and can thus produce pulses of only a few femtoseconds duration. Such mode-locked lasers are a most versatile tool for researching processes occurring on extremely short time scales (known as femtosecond physics, femtosecond chemistry and ultrafast science ), for maximizing

946-480: A given pulse energy, this requires creating pulses of the shortest possible duration utilizing techniques such as Q-switching . The optical bandwidth of a pulse cannot be narrower than the reciprocal of the pulse width. In the case of extremely short pulses, that implies lasing over a considerable bandwidth, quite contrary to the very narrow bandwidths typical of CW lasers. The lasing medium in some dye lasers and vibronic solid-state lasers produces optical gain over

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1032-399: A higher energy level with energy difference ΔE, it will not stay that way forever. Eventually, a photon will be spontaneously created from the vacuum having energy ΔE. Conserving energy, the electron transitions to a lower energy level that is not occupied, with transitions to different levels having different time constants. This process is called spontaneous emission . Spontaneous emission is

1118-471: A laser beam, it is highly collimated : the wavefronts are planar, normal to the direction of propagation, with no beam divergence at that point. However, due to diffraction , that can only remain true well within the Rayleigh range . The beam of a single transverse mode (gaussian beam) laser eventually diverges at an angle that varies inversely with the beam diameter, as required by diffraction theory. Thus,

1204-471: A laser is normally a material of controlled purity, size, concentration, and shape, which amplifies the beam by the process of stimulated emission described above. This material can be of any state : gas, liquid, solid, or plasma . The gain medium absorbs pump energy, which raises some electrons into higher energy (" excited ") quantum states . Particles can interact with light by either absorbing or emitting photons. Emission can be spontaneous or stimulated. In

1290-427: A lightbulb or a star, the energy is emitted from many different levels giving photons with a broad range of energies. This process is called thermal radiation . The underlying physical process creating photons in a laser is the same as in thermal radiation, but the actual emission is not the result of random thermal processes. Instead, the release of a photon is triggered by the nearby passage of another photon. This

1376-578: A motif on its eastern facade. In 1905 American sculptor Augustus Saint Gaudens created a caryatid porch for the Albright–Knox Art Gallery in Buffalo, New York in which four of the eight figures (the other four figures holding only wreaths) represented a different art form, Architecture, Painting, Sculpture , and Music . Auguste Rodin 's 1881 sculpture Fallen Caryatid Carrying her Stone (part of his monumental The Gates of Hell work) shows

1462-418: A multi-level system as a method for obtaining the population inversion, later a main method of laser pumping. Townes reports that several eminent physicists—among them Niels Bohr , John von Neumann , and Llewellyn Thomas —argued the maser violated Heisenberg's uncertainty principle and hence could not work. Others such as Isidor Rabi and Polykarp Kusch expected that it would be impractical and not worth

1548-441: A process called pumping . The energy is typically supplied as an electric current or as light at a different wavelength. Pump light may be provided by a flash lamp or by another laser. The most common type of laser uses feedback from an optical cavity —a pair of mirrors on either end of the gain medium. Light bounces back and forth between the mirrors, passing through the gain medium and being amplified each time. Typically one of

1634-462: A quantum-mechanical effect and a direct physical manifestation of the Heisenberg uncertainty principle . The emitted photon has a random direction, but its wavelength matches the absorption wavelength of the transition. This is the mechanism of fluorescence and thermal emission . A photon with the correct wavelength to be absorbed by a transition can also cause an electron to drop from the higher to

1720-418: A relatively long time. In laser physics , such a material is called an active laser medium . Combined with an energy source that continues to "pump" energy into the material, it is possible to have enough atoms or molecules in an excited state for a chain reaction to develop. Lasers are distinguished from other light sources by their coherence . Spatial (or transverse) coherence is typically expressed through

1806-432: A seminar on this idea, and Charles H. Townes asked him for a copy of the paper. In 1953, Charles H. Townes and graduate students James P. Gordon and Herbert J. Zeiger produced the first microwave amplifier, a device operating on similar principles to the laser, but amplifying microwave radiation rather than infrared or visible radiation. Townes's maser was incapable of continuous output. Meanwhile, in

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1892-431: A small volume of material at the surface of a workpiece can be evaporated if it is heated in a very short time, while supplying the energy gradually would allow for the heat to be absorbed into the bulk of the piece, never attaining a sufficiently high temperature at a particular point. Other applications rely on the peak pulse power (rather than the energy in the pulse), especially to obtain nonlinear optical effects. For

1978-646: A very narrow frequency spectrum . Temporal coherence can also be used to produce ultrashort pulses of light with a broad spectrum but durations as short as an attosecond . Lasers are used in optical disc drives , laser printers , barcode scanners , DNA sequencing instruments , fiber-optic and free-space optical communications, semiconductor chip manufacturing ( photolithography , etching ), laser surgery and skin treatments, cutting and welding materials, military and law enforcement devices for marking targets and measuring range and speed, and in laser lighting displays for entertainment. Semiconductor lasers in

2064-430: A wide bandwidth, making a laser possible that can thus generate pulses of light as short as a few femtoseconds (10 s). In a Q-switched laser, the population inversion is allowed to build up by introducing loss inside the resonator which exceeds the gain of the medium; this can also be described as a reduction of the quality factor or 'Q' of the cavity. Then, after the pump energy stored in the laser medium has approached

2150-492: A wide range of technologies addressing many different motivations. Some lasers are pulsed simply because they cannot be run in continuous mode. In other cases, the application requires the production of pulses having as large an energy as possible. Since the pulse energy is equal to the average power divided by the repetition rate, this goal can sometimes be satisfied by lowering the rate of pulses so that more energy can be built up between pulses. In laser ablation , for example,

2236-445: Is coherent . Spatial coherence allows a laser to be focused to a tight spot, enabling applications such as optical communication, laser cutting , and lithography . It also allows a laser beam to stay narrow over great distances ( collimation ), a feature used in applications such as laser pointers , lidar , and free-space optical communication . Lasers can also have high temporal coherence , which permits them to emit light with

2322-538: Is a classical boundary marker or wayside monument to a god which is usually a square pillar with only a carved head on top, about life-size, and male genitals at the appropriate mid-point. Figures that are rightly called Atlantes may sometimes be described as herms. Atlantes express extreme effort in their function, heads bent forward to support the weight of the structure above them across their shoulders, forearms often lifted to provide additional support, providing an architectural motif. Atlantes and caryatids were noted by

2408-522: Is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation . The word laser is an anacronym that originated as an acronym for light amplification by stimulated emission of radiation . The first laser was built in 1960 by Theodore Maiman at Hughes Research Laboratories , based on theoretical work by Charles H. Townes and Arthur Leonard Schawlow . A laser differs from other sources of light in that it emits light that

2494-404: Is a transition between energy levels that match the energy carried by the photon or phonon. For light, this means that any given transition will only absorb one particular wavelength of light. Photons with the correct wavelength can cause an electron to jump from the lower to the higher energy level. The photon is consumed in this process. When an electron is excited from one state to that at

2580-477: Is also required for three-level lasers in which the lower energy level rapidly becomes highly populated, preventing further lasing until those atoms relax to the ground state. These lasers, such as the excimer laser and the copper vapor laser, can never be operated in CW mode. In 1917, Albert Einstein established the theoretical foundations for the laser and the maser in the paper " Zur Quantentheorie der Strahlung " ("On

2666-441: Is called stimulated emission . For this process to work, the passing photon must be similar in energy, and thus wavelength, to the one that could be released by the atom or molecule, and the atom or molecule must be in the suitable excited state. The photon that is emitted by stimulated emission is identical to the photon that triggered its emission, and both photons can go on to trigger stimulated emission in other atoms, creating

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2752-413: Is called an optical amplifier . When an optical amplifier is placed inside a resonant optical cavity, one obtains a laser. For lasing media with extremely high gain, so-called superluminescence , light can be sufficiently amplified in a single pass through the gain medium without requiring a resonator. Although often referred to as a laser (see, for example, nitrogen laser ), the light output from such

2838-421: Is formed by single-frequency quantum photon states distributed according to a Poisson distribution . As a result, the arrival rate of photons in a laser beam is described by Poisson statistics. Many lasers produce a beam that can be approximated as a Gaussian beam ; such beams have the minimum divergence possible for a given beam diameter. Some lasers, particularly high-power ones, produce multimode beams, with

2924-443: Is frequently used in the field, meaning "to give off coherent light," especially about the gain medium of a laser; when a laser is operating, it is said to be " lasing ". The terms laser and maser are also used for naturally occurring coherent emissions, as in astrophysical maser and atom laser . A laser that produces light by itself is technically an optical oscillator rather than an optical amplifier as suggested by

3010-421: Is impossible. In some other lasers, it would require pumping the laser at a very high continuous power level, which would be impractical, or destroying the laser by producing excessive heat. Such lasers cannot be run in CW mode. The pulsed operation of lasers refers to any laser not classified as a continuous wave so that the optical power appears in pulses of some duration at some repetition rate. This encompasses

3096-504: Is to pump the laser material with a source that is itself pulsed, either through electronic charging in the case of flash lamps, or another laser that is already pulsed. Pulsed pumping was historically used with dye lasers where the inverted population lifetime of a dye molecule was so short that a high-energy, fast pump was needed. The way to overcome this problem was to charge up large capacitors which are then switched to discharge through flashlamps, producing an intense flash. Pulsed pumping

3182-426: Is typically life-size or larger; smaller similar figures in the decorative arts are called terms . The body of many Atlantes turns into a rectangular pillar or other architectural feature around the waist level, a feature borrowed from the term. The pose and expression of Atlantes very often show their effort to bear the heavy load of the building, which is rarely the case with terms and caryatids. The herma or herm

3268-430: Is used to measure the intensity profile, width, and divergence of laser beams. Diffuse reflection of a laser beam from a matte surface produces a speckle pattern with interesting properties. The mechanism of producing radiation in a laser relies on stimulated emission , where energy is extracted from a transition in an atom or molecule. This is a quantum phenomenon that was predicted by Albert Einstein , who derived

3354-625: The Argonauts , who was the father of Ajax . The caryatid is the female precursor of this architectural form in Greece, a woman standing in the place of each column or pillar. Caryatids are found at the treasuries at Delphi and the Erechtheion on the Acropolis at Athens for Athene. They usually are in an Ionic context and represented a ritual association with the goddesses worshiped within. The Atlante

3440-747: The Greco-Persian Wars . However, Vitruvius's explanation is doubtful; well before the Persian Wars, female figures were used as decorative supports in Greece and the ancient Near East. Vitruvius's explanation is dismissed as an error by Camille Paglia in Glittering Images and not even mentioned by Mary Lefkowitz in Black Athena Revisited . They both say the term refers to young women worshipping Artemis in Caryae through dance. Lefkowitz says that

3526-410: The phase of the emitted light is 90 degrees in lead of the stimulating light. This, combined with the filtering effect of the optical resonator gives laser light its characteristic coherence, and may give it uniform polarization and monochromaticity, depending on the resonator's design. The fundamental laser linewidth of light emitted from the lasing resonator can be orders of magnitude narrower than

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3612-421: The transverse modes often approximated using Hermite – Gaussian or Laguerre -Gaussian functions. Some high-power lasers use a flat-topped profile known as a " tophat beam ". Unstable laser resonators (not used in most lasers) produce fractal-shaped beams. Specialized optical systems can produce more complex beam geometries, such as Bessel beams and optical vortexes . Near the "waist" (or focal region ) of

3698-497: The "pencil beam" directly generated by a common helium–neon laser would spread out to a size of perhaps 500 kilometers when shone on the Moon (from the distance of the Earth). On the other hand, the light from a semiconductor laser typically exits the tiny crystal with a large divergence: up to 50°. However even such a divergent beam can be transformed into a similarly collimated beam employing

3784-542: The Acropolis temples and the return of the stolen Caryatid to Athens along with the rest of the so-called Elgin Marbles is the subject of a major international campaign. The Acropolis Museum holds the other five figures, which are replaced onsite by replicas. The five originals that are in Athens are now being exhibited in the new Acropolis Museum, on a special balcony that allows visitors to view them from all sides. The pedestal for

3870-738: The Early Classical Greek temple of Zeus, the Olympeion , in Agrigento , Sicily. Atlantes also played a significant role in Mannerist and Baroque architecture . During the eighteenth and nineteenth centuries, the designs of many buildings featured glorious atlantes that looked much like Greek originals. Their inclusion in the final design for the portico of the Hermitage Museum in St. Petersburg that

3956-843: The Erechtheion caryatids, installing copies in the Forum of Augustus and the Pantheon in Rome , and at Hadrian's Villa at Tivoli . Another Roman example, found on the Via Appia , is the Townley Caryatid . In Early Modern times, the practice of integrating caryatids into building facades was revived, and in interiors they began to be employed in fireplaces , which had not been a feature of buildings in Antiquity and offered no precedents. Early interior examples are

4042-670: The Quantum Theory of Radiation") via a re-derivation of Max Planck 's law of radiation, conceptually based upon probability coefficients ( Einstein coefficients ) for the absorption, spontaneous emission, and stimulated emission of electromagnetic radiation. In 1928, Rudolf W. Ladenburg confirmed the existence of the phenomena of stimulated emission and negative absorption. In 1939, Valentin A. Fabrikant predicted using stimulated emission to amplify "short" waves. In 1947, Willis E. Lamb and R.   C.   Retherford found apparent stimulated emission in hydrogen spectra and effected

4128-683: The Roman late Republican architect Vitruvius , whose description of the structures, rather than surviving examples, transmitted the idea of atlantes to the Renaissance architectural vocabulary. Not only did the Caryatids precede them, but similar architectural figures already had been made in ancient Egypt out of monoliths . Atlantes originated in Greek Sicily and in Magna Graecia , Southern Italy . The earliest surviving atlantes are fallen ones from

4214-503: The Soviet Union, Nikolay Basov and Aleksandr Prokhorov were independently working on the quantum oscillator and solved the problem of continuous-output systems by using more than two energy levels. These gain media could release stimulated emissions between an excited state and a lower excited state, not the ground state, facilitating the maintenance of a population inversion . In 1955, Prokhorov and Basov suggested optical pumping of

4300-423: The acronym. It has been humorously noted that the acronym LOSER, for "light oscillation by stimulated emission of radiation", would have been more correct. With the widespread use of the original acronym as a common noun, optical amplifiers have come to be referred to as laser amplifiers . Photons , the quanta of electromagnetic radiation are released and absorbed from energy levels in atoms and molecules. In

4386-476: The beam. A beam produced by a thermal or other incoherent light source has an instantaneous amplitude and phase that vary randomly with respect to time and position, thus having a short coherence length. Lasers are characterized according to their wavelength in a vacuum . Most "single wavelength" lasers produce radiation in several modes with slightly different wavelengths. Although temporal coherence implies some degree of monochromaticity , some lasers emit

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4472-425: The blue to near-UV have also been used in place of light-emitting diodes (LEDs) to excite fluorescence as a white light source; this permits a much smaller emitting area due to the much greater radiance of a laser and avoids the droop suffered by LEDs; such devices are already used in some car headlamps . The first device using amplification by stimulated emission operated at microwave frequencies, and

4558-410: The caryatid removed to London remains empty, awaiting its return. From 2011 to 2015, they were cleaned by a specially constructed laser beam , which removed accumulated soot and grime without harming the marble's patina . Each caryatid was cleaned in place, with a television circuit relaying the spectacle live to museum visitors. Although of the same height and build, and similarly attired and coiffed,

4644-410: The caryatides and their burden borne in poetic metaphor on the song "Caryatid Easy" from their 1997 album Straightaways , with singer Jay Farrar reproving an unidentified lover with the line "you play the caryatid easy." Atlas (architecture) In European architectural sculpture , an atlas (also known as an atlant , or atlante or atlantid ; plural atlantes ) is a support sculpted in

4730-561: The effect of nonlinearity in optical materials (e.g. in second-harmonic generation , parametric down-conversion , optical parametric oscillators and the like). Unlike the giant pulse of a Q-switched laser, consecutive pulses from a mode-locked laser are phase-coherent; that is, the pulses (and not just their envelopes ) are identical and perfectly periodic. For this reason, and the extremely large peak powers attained by such short pulses, such lasers are invaluable in certain areas of research. Another method of achieving pulsed laser operation

4816-478: The figures of Heracles and Iole carved on the jambs of a monumental fireplace in the Sala della Jole of the Doge's Palace, Venice , about 1450. In the following century Jacopo Sansovino , both sculptor and architect, carved a pair of female figures supporting the shelf of a marble chimneypiece at Villa Garzoni, near Padua. No architect mentioned the device until 1615, when Palladio 's pupil Vincenzo Scamozzi included

4902-595: The first demonstration of stimulated emission. In 1950, Alfred Kastler (Nobel Prize for Physics 1966) proposed the method of optical pumping , which was experimentally demonstrated two years later by Brossel, Kastler, and Winter. In 1951, Joseph Weber submitted a paper on using stimulated emissions to make a microwave amplifier to the June 1952 Institute of Radio Engineers Vacuum Tube Research Conference in Ottawa , Ontario, Canada. After this presentation, RCA asked Weber to give

4988-509: The form of a man, which may take the place of a column , a pier or a pilaster . The Roman term for such a sculptural support is telamon (plural telamones or telamons). The term atlantes is the Greek plural of the name Atlas —the Titan who was forced to hold the sky on his shoulders for eternity. The alternative term, telamones , also is derived from a later mythological hero, Telamon , one of

5074-676: The four terracotta caryatids on the porch of St Pancras New Church , London (1822). Many caryatids lined up on the facade of the 1893 Palace of the Arts housing the Museum of Science and Industry in Chicago . In the arts of design, the draped figure supporting an acanthus -grown basket capital taking the form of a candlestick or a table-support is a familiar cliché of neoclassical decorative arts. The John and Mable Ringling Museum of Art in Sarasota has caryatids as

5160-515: The goddesses Athena and Artemis . The Erectheion caryatids, in a shrine dedicated to an archaic king of Athens, may therefore represent priestesses of Artemis in Caryae, a place named for the "nut-tree sisterhood" – apparently in Mycenaean times, like other plural feminine toponyms , such as Hyrai or Athens itself. The later male counterpart of the caryatid is referred to as a telamon (plural telamones ) or atlas (plural atlantes ) –

5246-422: The laser power inside the cavity; this equilibrium determines the operating point of the laser. If the applied pump power is too small, the gain will never be sufficient to overcome the cavity losses, and laser light will not be produced. The minimum pump power needed to begin laser action is called the lasing threshold . The gain medium will amplify any photons passing through it, regardless of direction; but only

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5332-501: The lasing medium or pumping mechanism, then it is still classified as a "modulated" or "pulsed" continuous wave laser. Most laser diodes used in communication systems fall into that category. Some applications of lasers depend on a beam whose output power is constant over time. Such a laser is known as a continuous-wave ( CW ) laser. Many types of lasers can be made to operate in continuous-wave mode to satisfy such an application. Many of these lasers lase in several longitudinal modes at

5418-414: The latter case, the photon is emitted in the same direction as the light that is passing by. When the number of particles in one excited state exceeds the number of particles in some lower-energy state, population inversion is achieved. In this state, the rate of stimulated emission is larger than the rate of absorption of light in the medium, and therefore the light is amplified. A system with this property

5504-503: The linewidth of light emitted from the passive resonator. Some lasers use a separate injection seeder to start the process off with a beam that is already highly coherent. This can produce beams with a narrower spectrum than would otherwise be possible. In 1963, Roy J. Glauber showed that coherent states are formed from combinations of photon number states, for which he was awarded the Nobel Prize in physics . A coherent beam of light

5590-402: The literal cavity that would be employed at microwave frequencies in a maser . The resonator typically consists of two mirrors between which a coherent beam of light travels in both directions, reflecting on itself so that an average photon will pass through the gain medium repeatedly before it is emitted from the output aperture or lost to diffraction or absorption. If the gain (amplification) in

5676-464: The load.... She didn't give up, Ben; she's still trying to lift that stone after it has crushed her..." In Act 2 of his 1953 play 'Waiting for Godot', author Samuel Beckett has Estragon say "We are not caryatids!" when he and Vladimir tire of "cart(ing) around" the recently blinded Pozzo. Agnes Varda made two short films documenting Caryatid columns around Paris. 1984 Les Dites Cariatides 2005 Les Dites Cariatides Bis. The musical group Son Volt evoke

5762-522: The lower level, emitting a new photon. The emitted photon exactly matches the original photon in wavelength, phase, and direction. This process is called stimulated emission. The gain medium is put into an excited state by an external source of energy. In most lasers, this medium consists of a population of atoms that have been excited into such a state using an outside light source, or an electrical field that supplies energy for atoms to absorb and be transformed into their excited states. The gain medium of

5848-412: The maximum possible level, the introduced loss mechanism (often an electro- or acousto-optical element) is rapidly removed (or that occurs by itself in a passive device), allowing lasing to begin which rapidly obtains the stored energy in the gain medium. This results in a short pulse incorporating that energy, and thus a high peak power. A mode-locked laser is capable of emitting extremely short pulses on

5934-498: The medium is larger than the resonator losses, then the power of the recirculating light can rise exponentially . But each stimulated emission event returns an atom from its excited state to the ground state, reducing the gain of the medium. With increasing beam power, the net gain (gain minus loss) reduces to unity and the gain medium is said to be saturated. In a continuous wave (CW) laser, the balance of pump power against gain saturation and cavity losses produces an equilibrium value of

6020-631: The name refers to the legend of Atlas , who bore the sphere of the heavens on his shoulders. Such figures were used on a monumental scale, notably in the Temple of Olympian Zeus in Agrigento , Sicily . Some of the earliest known examples were found in the treasuries of Delphi , including that of Siphnos , dating to the 6th century BC. However, their use as supports in the form of women can be traced back even earlier, to ritual basins, ivory mirror handles from Phoenicia , and draped figures from archaic Greece. The best-known and most-copied examples are those of

6106-451: The order of tens of picoseconds down to less than 10  femtoseconds . These pulses repeat at the round-trip time, that is, the time that it takes light to complete one round trip between the mirrors comprising the resonator. Due to the Fourier limit (also known as energy–time uncertainty ), a pulse of such short temporal length has a spectrum spread over a considerable bandwidth. Thus such

6192-410: The output being a narrow beam, which is diffraction-limited . Laser beams can be focused to very tiny spots, achieving a very high irradiance , or they can have a very low divergence to concentrate their power at a great distance. Temporal (or longitudinal) coherence implies a polarized wave at a single frequency, whose phase is correlated over a relatively great distance (the coherence length ) along

6278-418: The photons in a spatial mode supported by the resonator will pass more than once through the medium and receive substantial amplification. In most lasers, lasing begins with spontaneous emission into the lasing mode. This initial light is then amplified by stimulated emission in the gain medium. Stimulated emission produces light that matches the input signal in direction, wavelength, and polarization, whereas

6364-406: The possibility of a chain reaction . For this to happen, many of the atoms or molecules must be in the proper excited state so that the photons can trigger them. In most materials, atoms or molecules drop out of excited states fairly rapidly, making it difficult or impossible to produce a chain reaction. The materials chosen for lasers are the ones that have metastable states , which stay excited for

6450-409: The power output is essentially continuous over time or whether its output takes the form of pulses of light on one or another time scale. Of course, even a laser whose output is normally continuous can be intentionally turned on and off at some rate to create pulses of light. When the modulation rate is on time scales much slower than the cavity lifetime and the period over which energy can be stored in

6536-662: The properties of the emitted light, such as the polarization, wavelength, and shape of the beam. Electrons and how they interact with electromagnetic fields are important in our understanding of chemistry and physics . In the classical view , the energy of an electron orbiting an atomic nucleus is larger for orbits further from the nucleus of an atom . However, quantum mechanical effects force electrons to take on discrete positions in orbitals . Thus, electrons are found in specific energy levels of an atom, two of which are shown below: An electron in an atom can absorb energy from light ( photons ) or heat ( phonons ) only if there

6622-457: The relationship between the A coefficient , describing spontaneous emission, and the B coefficient which applies to absorption and stimulated emission. In the case of the free electron laser , atomic energy levels are not involved; it appears that the operation of this rather exotic device can be explained without reference to quantum mechanics . A laser can be classified as operating in either continuous or pulsed mode, depending on whether

6708-410: The same time, and beats between the slightly different optical frequencies of those oscillations will produce amplitude variations on time scales shorter than the round-trip time (the reciprocal of the frequency spacing between modes), typically a few nanoseconds or less. In most cases, these lasers are still termed "continuous-wave" as their output power is steady when averaged over longer periods, with

6794-414: The six Caryatids are not the same: their faces, stance, draping, and hair are carved separately; the three on the left stand on their right foot, while the three on the right stand on their left foot. Their bulky, intricately arranged hairstyles serve the crucial purpose of providing static support to their necks, which would otherwise be the thinnest and structurally weakest part. The Romans also copied

6880-671: The six figures of the Caryatid porch of the Erechtheion on the Acropolis at Athens. One of those original six figures, removed by Lord Elgin in the early 19th century in an act which severely damaged the temple and is widely considered to be vandalism and looting, is currently in the British Museum in London. The Greek government does not recognise the British Museum's claims to own any part of

6966-508: The term comes from the Spartan city of Caryae, where young women did a ring dance around an open-air statue of the goddess Artemis, locally identified with a walnut tree. Bernard Sergent specifies that the dancers came to the small town of Caryae from nearby Sparta. Nevertheless, the association of caryatids with slavery persists and is prevalent in Renaissance art . The ancient Caryae supposedly

7052-425: The two mirrors, the output coupler , is partially transparent. Some of the light escapes through this mirror. Depending on the design of the cavity (whether the mirrors are flat or curved ), the light coming out of the laser may spread out or form a narrow beam . In analogy to electronic oscillators , this device is sometimes called a laser oscillator . Most practical lasers contain additional elements that affect

7138-410: The very high-frequency power variations having little or no impact on the intended application. (However, the term is not applied to mode-locked lasers, where the intention is to create very short pulses at the rate of the round-trip time.) For continuous-wave operation, the population inversion of the gain medium needs to be continually replenished by a steady pump source. In some lasing media, this

7224-589: Was built for Tsar Nicholas I of Russia in the 1840’s made the use of atlantes especially fashionable. The Hermitage portico incorporates ten enormous atlantes, approximately three times life-size, carved from Serdobol granite , which were designed by Johann Halbig and executed by the sculptor Alexander Terebenev . Similar carved stone columns or pillars in the shape of fierce men at some sites of Pre-Columbian Mesoamerica are typically called Atlantean figures . These figures are considered to be "massive statues of Toltec warriors". Laser beam A laser

7310-598: Was called a maser , for "microwave amplification by stimulated emission of radiation". When similar optical devices were developed they were first called optical masers , until "microwave" was replaced by "light" in the acronym, to become laser . Today, all such devices operating at frequencies higher than microwaves (approximately above 300 GHz ) are called lasers (e.g. infrared lasers , ultraviolet lasers , X-ray lasers , gamma-ray lasers ), whereas devices operating at microwave or lower radio frequencies are called masers. The back-formed verb " to lase "

7396-424: Was one of the six adjacent villages that united to form the original township of Sparta, and the hometown of Menelaos ' queen, Helen of Troy . Girls from Caryae were considered especially beautiful, strong, and capable of giving birth to strong children. A caryatid supporting a basket on her head is called a canephora ("basket-bearer"), representing one of the maidens who carried sacred objects used at feasts of

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