Laser

Red (660 & 635 nm), green (532 & 520 nm) and blue-violet (445 & 405 nm) lasers
A laser beam used for welding
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A helium–neon laser demonstration. The glow running through the center of the tube is an electric discharge. This glowing plasma is the gain medium for the laser. The laser produces a tiny, intense spot on the screen to the right. The center of the spot appears white because the image is overexposed there.
Spectrum of a helium–neon laser. The actual bandwidth is much narrower than shown; the spectrum is limited by the measuring apparatus.
Lidar measurements of lunar topography made by Clementine mission.
Laserlink point to point optical wireless network
Mercury Laser Altimeter (MLA) of the MESSENGER spacecraft
Aleksandr Prokhorov
Charles H. Townes
LASER notebook: First page of the notebook wherein Gordon Gould coined the acronym LASER, and described the elements required to construct one. Manuscript text: "Some rough calculations on the feasibility / of a LASER: Light Amplification by Stimulated / Emission of Radiation. /
Conceive a tube terminated by optically flat / [Sketch of a tube] / partially reflecting parallel mirrors..."
Graph showing the history of maximum laser pulse intensity throughout the past 40 years.
Wavelengths of commercially available lasers. Laser types with distinct laser lines are shown above the wavelength bar, while below are shown lasers that can emit in a wavelength range. The color codifies the type of laser material (see the figure description for more details).
A 50 W FASOR, based on a Nd:YAG laser, used at the Starfire Optical Range
A 5.6 mm 'closed can' commercial laser diode, such as those used in a CD or DVD player
Close-up of a table-top dye laser based on Rhodamine 6G
The free-electron laser FELIX at the FOM Institute for Plasma Physics Rijnhuizen, Nieuwegein
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.
The US–Israeli Tactical High Energy weapon has been used to shoot down rockets and artillery shells.
Laser application in astronomical adaptive optics imaging

Device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation.

- Laser
Red (660 & 635 nm), green (532 & 520 nm) and blue-violet (445 & 405 nm) lasers

153 related topics

Alpha

Blue, green, and red LEDs in 5 mm diffused cases

Light-emitting diode

Semiconductor light source that emits light when current flows through it.

Semiconductor light source that emits light when current flows through it.

Blue, green, and red LEDs in 5 mm diffused cases
Parts of a conventional LED. The flat bottom surfaces of the anvil and post embedded inside the epoxy act as anchors, to prevent the conductors from being forcefully pulled out via mechanical strain or vibration.
Close-up image of a surface mount LED
A bulb-shaped modern retrofit LED lamp with aluminum heat sink, a light diffusing dome and E27 screw base, using a built-in power supply working on mains voltage
Green electroluminescence from a point contact on a crystal of SiC recreates Round's original experiment from 1907.
A 1962 Texas Instruments SNX-100 GaAs LED contained in a TO-18 transistor metal case
LED display of a TI-30 scientific calculator (ca. 1978), which uses plastic lenses to increase the visible digit size
X-Ray of a 1970s 8-digit LED calculator display
Illustration of Haitz's law, showing improvement in light output per LED over time, with a logarithmic scale on the vertical axis
Blue LEDs
Combined spectral curves for blue, yellow-green, and high-brightness red solid-state semiconductor LEDs. FWHM spectral bandwidth is approximately 24–27 nm for all three colors.
RGB LED
Spectrum of a white LED showing blue light directly emitted by the GaN-based LED (peak at about 465 nm) and the more broadband Stokes-shifted light emitted by the Ce3+:YAG phosphor, which emits at roughly 500–700 nm
LEDs are produced in a variety of shapes and sizes. The color of the plastic lens is often the same as the actual color of light emitted, but not always. For instance, purple plastic is often used for infrared LEDs, and most blue devices have colorless housings. Modern high-power LEDs such as those used for lighting and backlighting are generally found in surface-mount technology (SMT) packages (not shown).
Image of miniature surface mount LEDs in most common sizes. They can be much smaller than a traditional 5mm lamp type LED, shown on the upper left corner.
Very small (1.6×1.6×0.35mm) red, green, and blue surface mount miniature LED package with gold wire bonding details.
High-power light-emitting diodes attached to an LED star base (Luxeon, Lumileds)
RGB-SMD-LED
Composite image of an 11 × 44 LED matrix lapel name tag display using 1608/0603-type SMD LEDs. Top: A little over half of the 21 × 86 mm display. Center: Close-up of LEDs in ambient light. Bottom: LEDs in their own red light.
Simple LED circuit with resistor for current limiting
Daytime running light LEDs of an automobile
Red and green LED traffic signals
LED for miners, to increase visibility inside mines
Los Angeles Vincent Thomas Bridge illuminated with blue LEDs
LED costume for stage performers
LED wallpaper by Meystyle
A large LED display behind a disc jockey
Seven-segment display that can display four digits and points
LED panel light source used in an experiment on plant growth. The findings of such experiments may be used to grow food in space on long duration missions.

Unlike a laser, the light emitted from an LED is neither spectrally coherent nor even highly monochromatic.

A telecommunications tower with a variety of dish antennas for microwave relay links on Frazier Peak, Ventura County, California. The apertures of the dishes are covered by plastic sheets (radomes) to keep out moisture.

Microwave

Form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter corresponding to frequencies between 300 MHz and 300 GHz respectively.

Form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter corresponding to frequencies between 300 MHz and 300 GHz respectively.

A telecommunications tower with a variety of dish antennas for microwave relay links on Frazier Peak, Ventura County, California. The apertures of the dishes are covered by plastic sheets (radomes) to keep out moisture.
The atmospheric attenuation of microwaves and far infrared radiation in dry air with a precipitable water vapor level of 0.001 mm. The downward spikes in the graph correspond to frequencies at which microwaves are absorbed more strongly. This graph includes a range of frequencies from 0 to 1 THz; the microwaves are the subset in the range between 0.3 and 300 gigahertz.
Waveguide is used to carry microwaves. Example of waveguides and a diplexer in an air traffic control radar
Disassembled radar speed gun. The grey assembly attached to the end of the copper-colored horn antenna is the Gunn diode which generates the microwaves.
A satellite dish on a residence, which receives satellite television over a Ku band 12–14 GHz microwave beam from a direct broadcast communications satellite in a geostationary orbit 35,700 kilometres (22,000 miles) above the Earth
The parabolic antenna (lower curved surface) of an ASR-9 airport surveillance radar which radiates a narrow vertical fan-shaped beam of 2.7–2.9 GHz (S band) microwaves to locate aircraft in the airspace surrounding an airport.
Small microwave oven on a kitchen counter
Microwaves are widely used for heating in industrial processes. A microwave tunnel oven for softening plastic rods prior to extrusion.
Absorption wavemeter for measuring in the Ku band.
1.2 GHz microwave spark transmitter (left) and coherer receiver (right) used by Guglielmo Marconi during his 1895 experiments had a range of 6.5 km
ku band microstrip circuit used in satellite television dish.
Heinrich Hertz's 450 MHz spark transmitter, 1888, consisting of 23 cm dipole and spark gap at focus of parabolic reflector
Jagadish Chandra Bose in 1894 was the first person to produce millimeter waves; his spark oscillator (in box, right) generated 60 GHz (5 mm) waves using 3 mm metal ball resonators.
Microwave spectroscopy experiment by John Ambrose Fleming in 1897 showing refraction of 1.4 GHz microwaves by paraffin prism, duplicating earlier experiments by Bose and Righi.
Augusto Righi's 12 GHz spark oscillator and receiver, 1895
Antennas of 1931 experimental 1.7 GHz microwave relay link across the English Channel.
Experimental 700 MHz transmitter 1932 at Westinghouse labs transmits voice over a mile.
Southworth (at left) demonstrating waveguide at IRE meeting in 1938, showing 1.5 GHz microwaves passing through the 7.5 m flexible metal hose registering on a diode detector.
The first modern horn antenna in 1938 with inventor Wilmer L. Barrow
thumb|Randall and Boot's prototype cavity magnetron tube at the University of Birmingham, 1940. In use the tube was installed between the poles of an electromagnet
First commercial klystron tube, by General Electric, 1940, sectioned to show internal construction
British Mk. VIII, the first microwave air intercept radar, in nose of British fighter. Microwave radar, powered by the new magnetron tube, significantly shortened World War II.
Mobile US Army microwave relay station 1945 demonstrating relay systems using frequencies from 100 MHz to 4.9 GHz which could transmit up to 8 phone calls on a beam.

A maser is a solid state device which amplifies microwaves using similar principles to the laser, which amplifies higher frequency light waves.

A ruby laser head. The photo on the left shows the head unassembled, revealing the pumping cavity, the rod and the flashlamps. The photo on the right shows the head assembled.

Laser pumping

A ruby laser head. The photo on the left shows the head unassembled, revealing the pumping cavity, the rod and the flashlamps. The photo on the right shows the head assembled.
Various laser pumping cavity configurations.
Laser pumping lamps. The top three are xenon flashlamps while the bottom one is a krypton arc lamp
External triggering was used in this extremely fast discharge. Due to the very high speed, (3.5 microseconds), the current is not only unable to fully heat the xenon and fill the tube, but is still in direct contact with the glass.
The spectral outputs for flashlamps using various gases, at a current density approaching that of greybody radiation.
Optical pumping of a laser rod (bottom) with an arc lamp (top). Red: hot. Blue: cold. Green: light. Non-green arrows: water flow. Solid colors: metal. Light colors: fused quartz.
These gas-discharge lamps show the spectral line outputs of the various noble gases.
A dye laser tuned to 589nm (amber yellow), pumped with an external, frequency-doubled Nd:YAG laser @ 532nm (yellowish-green). The closeness between wavelengths results in a very small Stokes shift, reducing energy losses.

Laser pumping is the act of energy transfer from an external source into the gain medium of a laser.

An early Raman spectrum of benzene published by Raman and Krishnan.

Raman scattering

Inelastic scattering of photons by matter, meaning that there is both an exchange of energy and a change in the light's direction.

Inelastic scattering of photons by matter, meaning that there is both an exchange of energy and a change in the light's direction.

An early Raman spectrum of benzene published by Raman and Krishnan.
Schematic of a dispersive Raman spectroscopy setup in a 180° backscattering arrangement.

Modern Raman spectroscopy nearly always involves the use of lasers as an exciting light source.

A test target bursts into flame upon irradiation by a continuous-wave kilowatt-level carbon-dioxide laser.

Carbon-dioxide laser

One of the earliest gas lasers to be developed.

One of the earliest gas lasers to be developed.

A test target bursts into flame upon irradiation by a continuous-wave kilowatt-level carbon-dioxide laser.
A medical CO2 laser

Carbon-dioxide lasers are the highest-power continuous-wave lasers that are currently available.

Atoms and molecules as depicted in John Dalton's A New System of Chemical Philosophy vol. 1 (1808)

Atom

Smallest unit of ordinary matter that forms a chemical element.

Smallest unit of ordinary matter that forms a chemical element.

Atoms and molecules as depicted in John Dalton's A New System of Chemical Philosophy vol. 1 (1808)
The Geiger–Marsden experiment:
Left: Expected results: alpha particles passing through the plum pudding model of the atom with negligible deflection.
Right: Observed results: a small portion of the particles were deflected by the concentrated positive charge of the nucleus.
The Bohr model of the atom, with an electron making instantaneous "quantum leaps" from one orbit to another with gain or loss of energy. This model of electrons in orbits is obsolete.
The binding energy needed for a nucleon to escape the nucleus, for various isotopes
A potential well, showing, according to classical mechanics, the minimum energy V(x) needed to reach each position x. Classically, a particle with energy E is constrained to a range of positions between x1 and x2.
3D views of some hydrogen-like atomic orbitals showing probability density and phase (g orbitals and higher are not shown)
This diagram shows the half-life (T½) of various isotopes with Z protons and N neutrons.
These electron's energy levels (not to scale) are sufficient for ground states of atoms up to cadmium (5s2 4d10) inclusively. Do not forget that even the top of the diagram is lower than an unbound electron state.
An example of absorption lines in a spectrum
Graphic illustrating the formation of a Bose–Einstein condensate
Scanning tunneling microscope image showing the individual atoms making up this gold (100) surface. The surface atoms deviate from the bulk crystal structure and arrange in columns several atoms wide with pits between them (See surface reconstruction).
Periodic table showing the origin of each element. Elements from carbon up to sulfur may be made in small stars by the alpha process. Elements beyond iron are made in large stars with slow neutron capture (s-process). Elements heavier than iron may be made in neutron star mergers or supernovae after the r-process.

This physical property is used to make lasers, which can emit a coherent beam of light energy in a narrow frequency band.

A pseudocolor image of two people taken in long-wavelength infrared (body-temperature thermal) radiation.

Infrared

Electromagnetic radiation (EMR) with wavelengths longer than those of visible light.

Electromagnetic radiation (EMR) with wavelengths longer than those of visible light.

A pseudocolor image of two people taken in long-wavelength infrared (body-temperature thermal) radiation.
This false-color infrared space telescope image has blue, green and red corresponding to 3.4, 4.6, and 12 μm wavelengths, respectively.
Plot of atmospheric transmittance in part of the infrared region
Materials with higher emissivity appear closer to their true temperature than materials that reflect more of their different-temperature surroundings. In this thermal image, the more reflective ceramic cylinder, reflecting the cooler surroundings, appears to be colder than its cubic container (made of more emissive silicon carbide), while in fact, they have the same temperature.
Active-infrared night vision: the camera illuminates the scene at infrared wavelengths invisible to the human eye. Despite a dark back-lit scene, active-infrared night vision delivers identifying details, as seen on the display monitor.
Thermography helped to determine the temperature profile of the Space Shuttle thermal protection system during re-entry.
Hyperspectral thermal infrared emission measurement, an outdoor scan in winter conditions, ambient temperature −15 °C, image produced with a Specim LWIR hyperspectral imager. Relative radiance spectra from various targets in the image are shown with arrows. The infrared spectra of the different objects such as the watch clasp have clearly distinctive characteristics. The contrast level indicates the temperature of the object.
Infrared light from the LED of a remote control as recorded by a digital camera
Reflected light photograph in various infrared spectra to illustrate the appearance as the wavelength of light changes.
Infrared hair dryer for hair salons, c. 2010s
IR satellite picture of cumulonimbus clouds over the Great Plains of the United States.
The greenhouse effect with molecules of methane, water, and carbon dioxide re-radiating solar heat
Beta Pictoris with its planet Beta Pictoris b, the light-blue dot off-center, as seen in infrared. It combines two images, the inner disc is at 3.6 μm.
An infrared reflectogram of Mona Lisa by Leonardo da Vinci
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Thermographic image of a snake eating a mouse
Infrared radiation was discovered in 1800 by William Herschel.

However, particularly intense near-IR light (e.g., from IR lasers, IR LED sources, or from bright daylight with the visible light removed by colored gels) can be detected up to approximately 780 nm, and will be perceived as red light.

Structure of KTP crystal, viewed down b axis, used in second harmonic generation.

Nonlinear optics

Branch of optics that describes the behaviour of light in nonlinear media, that is, media in which the polarization density P responds non-linearly to the electric field E of the light.

Branch of optics that describes the behaviour of light in nonlinear media, that is, media in which the polarization density P responds non-linearly to the electric field E of the light.

Structure of KTP crystal, viewed down b axis, used in second harmonic generation.
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Vortex photon (blue) with linear momentum is excited within mirror.
Comparison of a phase-conjugate mirror with a conventional mirror. With the phase-conjugate mirror the image is not deformed when passing through an aberrating element twice.
Dark-red gallium selenide in its bulk form

The non-linearity is typically observed only at very high light intensities (when the electric field of the light is >108 V/m and thus comparable to the atomic electric field of ~1011 V/m) such as those provided by lasers.

Fig.1. Simplified scheme of levels a gain medium

Active laser medium

Fig.1. Simplified scheme of levels a gain medium
Laser rods (from left to right): Ruby, Alexandrite, Er:YAG, Nd:YAP

The active laser medium (also called gain medium or lasing medium) is the source of optical gain within a laser.

Circular polarization on rubber thread, converted to linear polarization

Polarization (waves)

Property applying to transverse waves that specifies the geometrical orientation of the oscillations.

Property applying to transverse waves that specifies the geometrical orientation of the oscillations.

Circular polarization on rubber thread, converted to linear polarization
cross linear polarized
A "vertically polarized" electromagnetic wave of wavelength λ has its electric field vector E (red) oscillating in the vertical direction. The magnetic field B (or H) is always at right angles to it (blue), and both are perpendicular to the direction of propagation (z).
Electric field oscillation
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Animation showing four different polarization states and three orthogonal projections.
A circularly polarized wave as a sum of two linearly polarized components 90° out of phase
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Color pattern of a plastic box showing stress-induced birefringence when placed in between two crossed polarizers.
Paths taken by vectors in the Poincaré sphere under birefringence. The propagation modes (rotation axes) are shown with red, blue, and yellow lines, the initial vectors by thick black lines, and the paths they take by colored ellipses (which represent circles in three dimensions).
A stack of plates at Brewster's angle to a beam reflects off a fraction of the s-polarized light at each surface, leaving (after many such plates) a mainly p-polarized beam.
Stress in plastic glasses
Photomicrograph of a volcanic sand grain; upper picture is plane-polarized light, bottom picture is cross-polarized light, scale box at left-center is 0.25 millimeter.
Effect of a polarizer on reflection from mud flats. In the picture on the left, the horizontally oriented polarizer preferentially transmits those reflections; rotating the polarizer by 90° (right) as one would view using polarized sunglasses blocks almost all specularly reflected sunlight.
One can test whether sunglasses are polarized by looking through two pairs, with one perpendicular to the other. If both are polarized, all light will be blocked.
The effects of a polarizing filter (right image) on the sky in a photograph
Colored fringes in the Embassy Gardens Sky Pool when viewed through a polarizer, due to stress-induced birefringence in the skylight
Circular polarization through an airplane plastic window, 1989

Especially impacted are technologies such as lasers, wireless and optical fiber telecommunications, and radar.