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Glossary and List of Formula Symbols
On this page, you first find the glossary of photonics terms, and further below a list of common formular symbols.
Glossary of Photonics Terms
This page summarizes the definitions of photonics terms, as they appear below the headings of many of the encyclopedia pages.
| A | B | C | D | E | F | G | H | I | J | K | L | M |
| N | O | P | Q | R | S | T | U | V | W | X | Y | Z |
ABCD matrix: a 2-by-2 matrix describing the effect of an optical element on a laser beam
acousto-optic modulators: optical modulators based on the acousto-optic effect
active mode locking: a technique of mode locking, based on active modulation of the intracavity losses or the round-trip phase change
additive-pulse mode locking: a technique for mode locking a laser, using a nonlinear interaction in an external resonator
adiabatic soliton compression: a pulse compression technique based on the adaptation of solitons to slowly varying propagation parameters
alignment sensitivity: the sensitivity of a laser, an optical resonator or some other device with respect to misalignment
all-solid-state lasers: laser systems containing solid-state devices only, in particular no discharge lamps or gas or dye lasers
amplification factor: the factor by which the power of a signal is amplified
amplified spontaneous emission: a process where spontaneously emitted radiation (luminescence) is amplified
amplifier chains: amplifiers consisting of several stages
amplifier noise: noise introduced to a signal in an amplifier device
amplifiers: devices for amplifying the power of light beams
amplitude-squeezed light: light with an intensity noise below the shot noise level
anti-reflection coatings: optical thin-film coatings for reducing reflections from surfaces
argon ion lasers: gas lasers based on light amplification in ionized argon in a gas discharge
arrayed waveguide gratings: optical filter or multiplexer device based on arrays of waveguides
autocorrelators: devices for measuring the intensity or field autocorrelation function of light, mostly used for determining the duration of ultrashort pulses
avalanche photodiodes: photodiodes with internal signal amplification through an avalanche process
B integral: a measure of the nonlinear phase shift of light, e.g. in an amplifier
bandwidth: the width of some frequency or wavelength range
bandwidth–distance product: product of length and maximum data rate of a fiber-optic link
bandwidth-limited pulses: pulses with a duration as short as possible with their optical spectrum
beam combining: a class of techniques for power scaling of laser sources by combining the outputs of multiple devices
beam divergence: a measure for how fast a laser beam expands far from its focus
beam parameter product: product of the beam radius in a focus and the far-field beam divergence
beam pointing fluctuations: fluctuations of the propagation direction of a laser beam
beam profilers: devices for measuring the intensity profile of a laser beam
beam quality: a measure for how well a laser beam can be focused
beam radius: a measure of the transverse extension of a light beam
beam shapers: optical devices for modifying the shapes of laser beams
beam splitters: devices for splitting a laser beam into two or more beams
beam waist: location with minimum beam radius
beat note: an oscillation of the optical intensity arising from the superposition of light with different optical frequencies
bend losses: propagation losses in an optical fiber (or other waveguide) caused by bending
birefringence: the phenomenon of double refraction, or the polarization dependence of the refractive index in a medium
birefringent phase matching: a technique of phase matching based on the birefringence of a crystal material
birefringent tuners: device for wavelength tuning of lasers, based on birefringence and polarization rotation
bit error rate: average fraction of wrongly transmitted bits in a communication link
blue lasers: lasers emitting blue light
Bragg gratings: reflecting structures with a periodic refractive index modulation
Bragg mirrors: mirror structures based on Bragg reflection at a period structure
Brewster plates: coplanar plates inserted into beams at Brewster's angle
Brewster windows: transparent plates which are oriented at Brewster's angle
brightness: a term mostly used in a qualitative way, related to the output power and beam quality of a laser; quantitatively: synonymous with luminance
brightness converters: optically pumped devices where the generated optical output has a higher brightness than the optical pump source
Brillouin scattering: a nonlinear scattering effect involving acoustic phonons
broad area laser diodes: laser diodes with a strongly asymmetric shape of the emitting region
bulk lasers: lasers based on bulk crystals as gain media
carrier–envelope offset: the offset between the optical phase and the maximum of the wave envelope of an optical pulse
causality: the concept of relating effects to causes, or the compatibility of phenomena with this concept
cavities: resonators for light (or for microwaves)
cavity dumping: a method for extracting intense short or ultrashort pulses from a laser, using an optical switch in the laser resonator
ceramic gain media: laser gain media which have a ceramic (polycrystalline) microscopic structure
chemiluminescence: luminescence arising from chemical reactions
chirp: time dependence of the instantaneous frequency of an optical pulse
chirped mirrors: Bragg-type dispersive mirrors with a spatial variation of the Bragg wavelength
chirped-pulse amplification: a technique for amplifying pulses to very high optical intensities while avoiding excessive nonlinear pulse distortions or optical damage
chromatic dispersion: the frequency dependence of the phase velocity in a transparent medium
chromium-doped gain media: laser gain media doped with chromium ions
cladding modes: modes in optical fibers (or other waveguides) which are not restricted to the region around the core
clustering: the tendency e.g. of laser-active ions in laser gain media to form clusters in their host medium
CO2 lasers: lasers based on a gas mixture in which light is amplified by carbon dioxide molecules
coherence: a fixed phase relationship between the electric field values at different locations or at different times
coherence length: a measure of temporal coherence, expressed as the propagation distance over which the coherence significantly decays
coherence time: a measure of temporal coherence, expressed as the time over which the field correlation decays
coherent beam combining: a class of methods for beam combining, requiring mutual coherence of the combined beams
coherent states: a special kind of pure quantum-mechanical states
collimated beams: laser beams with weak divergence
composite laser crystals: laser crystals consisting of several parts of different materials or with different chemical compositions (e.g. doping concentrations)
continuous-wave operation: operation mode of a laser with continuous light emission
cooperative lasing: the phenomenon that laser action at one wavelength can facilitate lasing at another wavelength
core-less end caps: end pieces attached to fibers, containing no fiber core
critical phase matching: phase matching of a nonlinear interaction by adjustment of a propagation direction
cross-phase modulation: a nonlinear effect where the optical intensity of one beam influences the phase change of another beam
cryogenic lasers: lasers where the gain medium is operated at cryogenic temperatures
decibel: a logarithmic measure for power ratios, applied e.g. to optical powers or to noise powers
depolarization loss: losses of optical power in a laser resonator, caused by depolarization e.g. in a laser crystal
diameter–divergence product: product of the diameter (at a beam waist) and the divergence angle of a laser beam
dichroic mirrors: mirrors with significantly different reflection or transmission properties at two different wavelengths
dielectric coatings: thin-film coatings made of transparent dielectric materials, e.g. for laser mirrors or anti-reflection coatings
dielectric mirrors: mirrors consisting of multiple thin layers of different transparent optical materials
diffraction-limited beams: beams with a minimum possible beam divergence for a given waist radius
diode bars: a type of semiconductor laser containing a one-dimensional array of broad-area emitters
diode-pumped lasers: solid-state lasers which are pumped with laser diodes
diode stacks: arrangements of multiple diode bars, delivering very high output power
dispersion: the dependence of the phase velocity in a medium on the optical frequency or the propagation mode
dispersion compensation: the control of the overall chromatic dispersion of a system by adding optical elements with a suitable amount of dispersion
dispersion compensation modules: modules used for dispersion compensation
dispersion-decreasing fibers: optical fibers where the chromatic dispersion changes monotonously along the propagation direction
dispersion management: the use of tailored chromatic dispersion to enhance the function of optical devices or systems
dispersion-shifted fibers: fibers with a non-standard zero dispersion wavelength
dispersive wave: a linearly propagating wave which is split off by a soliton wave under certain conditions
distributed amplifiers: fiber amplifiers in fiber-optic data links, where the amplification occurs within a large length of transmission fiber
distributed Bragg reflector lasers: lasers containing distributed Bragg reflectors as end mirrors
distributed feedback lasers: lasers where the whole laser resonator consists of a periodic structure, in which Bragg reflection occurs
divided-pulse amplification: a method of amplifying intense ultrashort pulse while avoiding excessive nonlinear effects
doped insulator lasers: lasers with a solid-state gain medium containing a laser-active dopant
doping concentration: the concentration of some dopant, e.g. of laser-active ions in a laser gain medium
Doppler broadening: broadening of the linewidth of atomic transitions, caused by random motion of the emitting atoms
Doppler cooling: a technique of laser cooling based on velocity-dependent absorption processes
Doppler limit: a limit for the temperature which is achievable with certain laser cooling techniques
double-clad fibers: optical fibers with different waveguide structures for pump and signal light
double pulses: two closely spaced optical pulses
dye lasers: lasers based on liquid or solid dyes as gain media
edge-emitting semiconductor lasers: semiconductor lasers emitting light along the plane of the wafer
effective cross sections: a modified type of transition cross sections which apply to optical transitions between Stark level manifolds
effective mode area: a quantitative measure of the area which a waveguide or fiber mode effectively covers in the transverse dimensions
effective refractive index: a number quantifying the phase delay per unit length in a waveguide, relative to the phase delay in vacuum
electro-optic effect: the phenomenon that the refractive index of a material can be modified with an electric field
electro-optic modulators: optical modulators based on the electro-optic effect
electro-optic sampling: an optical sampling technique based on the electro-optic effect
electroabsorption modulators: optical modulators based on the Franz–Keldysh effect
electroluminescence: luminescence arising from electrical influences
electronic dispersion compensation: a method for mitigating the effects of chromatic dispersion in fiber-optic communication links with electronic components in the receiver
end pumping: a technique of optically pumping a laser medium in a direction along the laser beam
energy transfer: the phenomenon that dopant ions in laser-active media can exchange excitation energy among each other
enhancement cavities: optical cavities for exploiting the resonant enhancement of the power of circulating light
erbium-doped fiber amplifiers: fiber amplifiers based on erbium-doped optical fibers
erbium-doped gain media: laser gain media doped with erbium ions
etalons: monolithic interferometric devices containing two parallel reflecting surfaces
excimer lasers: lasers where optical amplification occurs in a plasma containing excited dimers (or other molecules) with an anti-binding electronic ground state
excited-state absorption: absorption of light by ions or atoms in an excited electronic state, rather than in the electronic ground state
external-cavity diode lasers: non-monolithic diode lasers where the laser cavity (resonator) is completed with external optical elements
eye-safe lasers: lasers emitting in a wavelength region with relatively low hazards for the human eye
Fabry–Pérot interferometers: interferometers consisting of two highly reflecting mirrors, forming a standing-wave resonator
Faraday isolators: optical isolators based on the Faraday effect
Faraday rotators: devices which can rotate the polarization state of light, exploiting the Faraday effect
femtosecond lasers: lasers emitting pulses with durations between a few femtoseconds and hundreds of femtoseconds
fiber amplifiers: optical amplifiers with doped fibers as gain media
fiber Bragg gratings: reflective structures in the core of an optical fiber with a periodic or aperiodic perturbation of the effective refractive index
fiber core: the region in an optical fiber which guides light
fiber-coupled diode lasers: diode laser devices where the generated light is coupled into an optical fiber
fiber couplers: fiber devices for coupling light from one or several input fibers to one or several output fibers
fiber fuse: the effect that an optical fiber "burns" from the output end under the influence of an intense laser beam launched into the other end
fiber joints: permanent or removable connections between fiber ends
fiber lasers: lasers with a doped fiber as gain medium, or (sometimes) just lasers where most of the laser resonator is made of fibers
fiber-optic links: optical communication links where the signal light is transported in fibers
fiber-optic networks: communication systems consisting of fiber-optic links
fiber-optic sensors: optical sensors based on fiber devices
fiber polarization controllers: devices which allow one to control the state of polarization of light within fibers
fiber to the home: the technology of providing data connections to private homes via optical fibers rather than electric cables
fibers: a kind of long and thin optical waveguides which can be bent to some degree
finesse: free spectral range divided by FWHM width of resonances of an optical resonator
fluorescence: luminescence arising from irradiation with light
fluorescence microscopy: a technique for acquiring microscopic images using fluorescence which is excited in the sample
fluorescent lamps: lamps which emit fluorescent light, usually generated by irradiation of a phosphor with light from an electric gas discharge
fluoride fibers: optical fibers based on fluoride glasses
focal length: a measure of how strongly an optical system focuses or defocuses light
forbidden transitions: transitions between different energy levels of some atoms or ions for which dipole transitions are suppressed via symmetries
four-level and three-level gain media: laser gain media without/with reabsorption from the lower laser level
four-wave mixing: an interaction of light waves based on a χ(3) nonlinearity
free electron lasers: laser devices where light amplification occurs by interaction with fast electrons in an undulator
free-space optical communications: optical data transmission through free space, usually through air or vacuum
free spectral range: frequency spacing of the axial modes of an optical resonator
frequency combs: optical spectra consisting of equidistant lines
frequency doubling: the phenomenon that an input wave in a nonlinear material can generate a wave with twice the optical frequency
frequency metrology: the field of technology dealing with precise frequency measurements
frequency noise: noise of the instantaneous frequency of an oscillating signal
frequency quadrupling: the phenomenon that an input laser beam generates a beam with four times the optical frequency
frequency-resolved optical gating: a technique for the complete characterization of optical pulses
frequency tripling: the phenomenon that an input laser beam generates a beam with three times the optical frequency
Fresnel number: a parameter determining the regime of diffraction effects
Füchtbauer–Ladenburg equation: an equation used for calculating emission cross sections of laser gain media
fundamental mode locking: mode locking with a single pulse circulating in the laser resonator
fusion splicing of fibers: a technique of making low-loss fiber joints by fusing fiber ends together
gain: a measure of the strength of optical amplification
gain bandwidth: the width of the optical frequency range in which significant gain is available from an amplifier
gain clamping: a firm limitation of the gain of some amplifier or laser, usually caused by lasing action
gain efficiency: small-signal gain of an optical amplifier per unit pump power or per unit stored energy
gain equalization: a technique for making the gain spectrum of an optical amplifier device flatter over a certain optical frequency range
gain guiding: guiding of light based on spatially inhomogeneous optical gain
gain media: media for laser amplification
gain narrowing: the phenomenon that the bandwidth of light can be reduced during amplification in a medium with a limited gain bandwidth
gain saturation: the phenomenon that the gain of an amplifier is reduced for high input signal powers
gain switching: a technique for generating short optical pulses in a laser by modulating the laser gain
gas lasers: lasers with a gas (or plasma) as gain medium
Gaussian beams: light beams where the electric field profile in a plane perpendicular to the beam axis can be described with a Gaussian function, possibly with an added parabolic phase profile
Gaussian pulses: pulses with a temporal intensity profile which has a Gaussian shape
Gires–Tournois interferometers: linear optical resonators used for introducing chromatic dispersion
Gordon–Haus jitter: a timing jitter originating from fluctuations of the center frequency
Gouy phase shift: an additional phase shift occurring in the propagation of focused Gaussian beams
green lasers: lasers emitting in the green spectral region
group delay: a measure of the time delay experienced by narrow-band light pulses in an optical device
group delay dispersion: the frequency dependency of the group delay, or (quantitatively) the corresponding derivative with respect to angular frequency
group index: the ratio of the vacuum velocity of light to the group velocity in a medium
group velocity: the velocity with which the envelope of a weak narrow-band optical pulse propagates in a medium
group velocity dispersion: the frequency dependence of the group velocity in a medium, or (quantitatively) the derivative of the inverse group velocity with respect to angular frequency
group velocity mismatch: the phenomenon that pulses become separated in a medium due to different group velocities, or (quantitatively) the difference of inverse group velocities
guided waves: waves for which diffraction is suppressed by a waveguide structure
harmonic mode locking: mode locking of a laser where multiple pulses are circulating in the laser resonator with equal temporal spacing
Haus Master equation: an analytical equation describing the evolution of ultrashort pulses in a laser resonator
helium–neon lasers: gas lasers based on a helium–neon mixture
Hermite–Gaussian modes: propagation modes or resonator modes which are described with Hermite–Gaussian functions
high harmonic generation: the phenomenon that very high harmonics of an intense input laser beam are generated in a gas
high-power fiber lasers and amplifiers: fiber lasers and fiber amplifiers with high output powers of e.g. > 10 W
high-power lasers: lasers emitting very high optical powers
higher-order modes: transverse modes of a resonator or waveguide, excluding the fundamental (axial) modes
higher-order solitons: optical pulses in a nonlinear and dispersive medium which exhibit periodic oscillations of their temporal and spectral shape
homogeneous broadening: the increase in the linewidth of an atomic transition caused by effects which affect different radiating or absorbing atoms in the same way
homogeneous saturation: saturation of an absorption or gain, where the shape of the absorption or gain spectrum is not modified
hyper Raman scattering: Raman scattering processes involving two pump photons
infrared light: invisible light with wavelengths roughly between 750 nm and 1 mm
inhomogeneous broadening: the increase in the linewidth of an atomic transition caused by effects which act differently on different radiating or absorbing atoms
inhomogeneous saturation: gain saturation effects which alter the shape of the gain spectrum
injection locking: a technique for enforcing operation of a laser on a certain optical frequency by injecting light with that frequency into the laser resonator
injection seeding: a technique for enforcing narrowband operation of a laser or optical parametric oscillator by injecting light into its resonator
instantaneous frequency: temporal derivative of the oscillation phase divided by 2π
integrated optics: the technology dealing with the construction of photonic integrated circuits
integrating spheres: devices with a diffusely reflecting inner surface, used for certain optical measurements
intensity noise: noise of the optical intensity or power of a laser beam
interference: a range of phenomena associated with the superposition of waves
interferometers: optical devices utilizing the phenomenon of interference
interlocks: safety devices for automatically switching off a laser power or interrupting a laser beam
intermodal dispersion: the phenomenon that the group velocity of light propagating in a waveguide structure depends on the waveguide mode
intracavity frequency doubling: frequency doubling with a nonlinear crystal within the laser resonator
intracavity laser absorption spectroscopy: a method of laser spectroscopy, based on the evolution of the spectrum of intracavity radiation under the influence of narrowband absorption features
Kelly sidebands: sidebands in the spectrum of certain mode-locked lasers, related to a periodic disturbance of soliton pulses in the laser resonator
Kerr effect: a nonlinear interaction of light in a medium with an instantaneous response, related to the nonlinear electronic polarization
Kerr lens: a lensing effect arising from the Kerr nonlinearity
Kerr lens mode locking: a technique for mode locking a laser, exploiting nonlinear self-focusing
Kramers–Kronig relations: mathematical relations between absorption and refractive index of transparent media
Kuizenga–Siegman theory: a theory predicting the durations of pulses from actively mode-locked lasers
lamp-pumped lasers: lasers which are pumped with flash lamps or arc lamps, or in rare cases with tungsten halogen lamps
large mode area fibers: optical fibers with relatively large mode areas and a single transverse mode or only a few modes
laser applications: applications involving laser devices
laser beams: light beams propagating dominantly in one direction
laser cooling: a variety of techniques for reducing the temperature (i.e., the random motion) of small particles such as atoms or ions
laser crystals: transparent crystals with laser-active dopants, used as laser gain media
laser development: the process of developing a laser device
laser diode modules: modules containing diode lasers, and possibly also some optics, cooling devices, electrical elements, etc.
laser diodes: semiconductor lasers with a current-carrying p–n junction as the gain medium
laser dynamics: the temporal evolution of quantities such as the optical power and gain in a laser
laser guide stars: small bright spots in the sky, generated with laser beams for use in astronomy with adaptive optics imaging
laser heads: assemblies containing a mounted gain medium and means for pumping and cooling, or the complete optical parts of a laser, or assemblies for directing a laser beam to a workpiece
laser-induced breakdown: a kind of spark, initiated by intense laser light
laser light: light generated with a laser device
laser marking: a group of methods for labelling materials with lasers
laser microscopy: a technique for generating microscopic images by scanning objects with a laser
laser mirrors: high-quality mirrors used in laser resonators and other optical setups
laser modeling: the investigation of phenomena and quantitative relations in lasers, using theoretical models and computational methods
laser noise: fluctuations of various parameters of laser light, such as the optical power and phase
laser physics: the field of physics dealing with phenomena in lasers
laser pointers: devices used for pointing at items with laser beams
laser resonators: optical resonators serving as basic building blocks of lasers
laser safety: safety of the use of laser devices
laser threshold: an operation condition of a laser where laser emission just starts to occur
laser transitions: optical transitions where stimulated emission is used to obtain optical amplification
lasers: devices generating visible or invisible light, based on stimulated emission of light
lasing without inversion: the quantum-optical phenomenon of laser emission occurring without the presence of a population inversion
light-emitting diodes: semiconductor diodes that emit light via electroluminescence
light forces: forces associated with absorption, reflection or scattering of light
linewidth: width of the spectrum of a light beam or an absorption feature
linewidth enhancement factor: a parameter quantifying the amplitude–phase coupling in a laser
lower-state lifetime: the lifetime of the population of the lower laser level in the absence of radiation
luminescence: light emission which is not caused by heating
Lyot filters: optical filter devices based on birefringence, exhibiting a wavelength-dependent transmission
M2 factor: a parameter for quantifying the beam quality of laser beams
master laser: a single-frequency laser used for injection locking one or several other lasers
master oscillator fiber amplifier: a laser system containing a fiber amplifier for boosting the output power
master oscillator power amplifier: a laser system consisting of a seed laser and a laser amplifier for boosting the output power
McCumber theory: a theory applied to absorption and emission properties of laser gain media, in particular to solid-state media
metal–semiconductor–metal photodetectors: fast photodetector devices based on metal–semiconductor (Schottky) contacts
metastable states: excited states (particularly electronic states in laser gain media) which have a relatively long lifetime due to slow radiative and non-radiative decay
microbends of fibers: microscopic bends of optical fibers
microchip lasers: solid-state lasers with a quasi-monolithic setup
mid-infrared laser sources: light sources emitting mid-infrared radiation in the form of a laser-like beam
mode cleaner cavities: optical cavities used as filters for improving the beam quality of laser beams
mode cleaners: devices which can improve the beam quality of laser beams
mode competition: the phenomenon that different resonator modes experience laser amplification in the same gain medium, leading to cross-saturation effects
mode coupling: a concept for describing and calculating light propagation in certain situations, e.g. involving nonlinear interactions
mode hopping: the phenomenon that a laser exhibits sudden jumps of optical frequency, which are associated with transitions between different modes of its resonator
mode-locked diode lasers: diode lasers which are actively, passively or hybrid mode-locked for generating ultrashort pulses
mode-locked fiber lasers: ultrafast fiber lasers which are actively or passively mode-locked for generating ultrashort pulses
mode-locked lasers: lasers which emit ultrashort pulses on the basis of the technique of mode locking
mode locking: a group of techniques for generating ultrashort pulses in lasers
mode matching: the precise spatial matching of the electric field distributions of laser beams and resonator modes or waveguide modes
mode radius: a measure of the transverse extent of a laser mode or laser beam
modes: self-consistent electric field distributions in waveguides, optical resonators or in free space
modulation depth: a relative modulation amplitude, or (for a saturable absorber) the maximum change in absorption
monolithic solid-state lasers: solid-state lasers where the whole laser resonator consists only of one piece of crystal or glass
multi-phonon transitions: transitions between electronic levels of atoms or ions in solid media, involving the emission of multiple phonons
multimode fibers: fibers supporting more than one guided mode per polarization direction
nanofibers: optical fibers with transverse dimensions below one micrometer
nanosecond lasers: lasers emitting optical pulses with nanosecond durations
narrow-linewidth lasers: single-frequency lasers with a narrow optical emission spectrum
neodymium-doped gain media: laser gain media containing laser-active neodymium ions
noise eaters: devices for reducing the intensity noise of an optical beam by automatically adjusting the degree of power attenuation
noise figure: a measure of the excess noise added in an amplifier
nonclassical light: light with properties which can be explained only within quantum optics
noncritical phase matching: a technique of phase matching which does not require a critical angular adjustment
nonlinear crystal materials: crystal materials exhibiting an optical nonlinearity, usually of χ(2) type
nonlinear frequency conversion: the conversion of input light to light of other frequencies, using optical nonlinearities
nonlinear index: a parameter for quantifying the Kerr nonlinearity of a medium
nonlinear optics: the part of optics dealing with optical nonlinearities and their applications
nonlinear polarization: the part of the light-induced electric polarization which depends nonlinearly on the electric field of the light
nonlinear polarization rotation: the phenomenon that the change in the polarization direction of light in a fiber can depend on the optical intensity
nonlinear pulse distortion: distortion of the spatial, temporal or spectral characteristics of an optical pulse, resulting from optical nonlinearities
nonlinearities: optical phenomena involving a nonlinear response to a driving light field
nonplanar ring oscillators: a type of monolithic single-frequency lasers, based on a nonplanar ring resonator
numerical aperture: sine of the maximum angle of an incident beam of some optical device, or the sine of the acceptance angle of a waveguide or fiber
optical clocks: time measurement devices based on optical frequency standards
optical clockworks: devices which can phase-coherently relate optical frequencies to microwave frequencies
optical data transmission: the transmission of information using light beams, e.g. in fibers
optical fiber communications: the technology of transmitting information through optical fibers
optical filters: devices with a wavelength-dependent transmission or reflectivity
optical frequency standards: frequency standards using optical transitions in atoms, ions or molecules
optical heterodyne detection: a sensitive method of photodetection, reaching the standard quantum limit even for weak signal powers
optical intensity: optical power per unit area
optical metrology: the science and technology of performing measurements with light
optical modulators: devices allowing one to manipulate properties of light beams, such as the optical power or phase
optical molasses: an arrangement of laser beams used for cooling atoms or ions
optical parametric amplifiers: optical amplifiers based on parametric nonlinear interactions
optical parametric chirped-pulse amplification: parametric amplification of chirped ultrashort pulses
optical parametric generators: light sources based on parametric amplifiers with no signal or idler input
optical parametric oscillators: coherent light sources based on parametric amplification within an optical resonator
optical pumping: electronically exciting a medium with light, or specifically populating certain electronic levels
optical refrigeration: a technique for cooling macroscopic samples via laser-induced fluorescence
optical resonators: arrangements of optical components which allow a beam of light to circulate
optical sampling: a technique of sampling signals using laser light, often in the form of ultrashort pulses
optical thickness: the geometric thickness times the refractive index
optical tweezers: arrangements for capturing and moving particles with laser beams
optoelectronics: the technology of electronic devices that interact with light
output couplers: partially transparent laser mirrors, used for extracting output beams from laser resonators
output coupling efficiency: a factor influencing the power efficiency of a laser, taking into account intracavity losses
p–i–n photodiodes: photodiodes with a p–i–n semiconductor structure
parabolic pulses: pulses with a parabolic intensity profile
parametric amplification: a process of optical amplification based on a parametric nonlinearity
parametric fluorescence: light emitted by a parametric amplifier without signal or input inputs
parametric nonlinearities: instantaneous optical nonlinearities based on the χ(2) or χ(3) nonlinear tensor of a transparent medium
parasitic lasing: unwanted laser operation in a laser or amplifier device
paraxial approximation: a frequently used approximation, essentially assuming small angular deviations of the propagation directions from some beam axis
passive mode locking: a technique of mode locking, based on a saturable absorber inside the laser resonator
peak power: maximum optical power of a pulse
periodic poling: a technique for achieving quasi-phase matching of nonlinear interactions in a transparent crystal material
phase matching: a group of techniques for achieving efficient nonlinear interactions in a medium
phase-matching bandwidth: width of an optical frequency range in which some process (e.g. a nonlinear interaction) can be efficient due to more or less precise phase matching
phase modulators: devices for manipulating the phase of a laser beam
phase noise: noise of the optical phase of a beam or of an electric signal
phase velocity: the velocity with which phase fronts propagate in a medium
phonons: quantized microscopic vibrations in solid media
phosphorescence: a luminescence which lasts for a relatively long time after excitation of a medium
photoconductive sampling: a technique of optical sampling with photoconductive switches
photoconductive switches: electric switches controlled by light via photo-induced conductivity
photodarkening: the phenomenon that the optical power losses in a medium can grow when the medium is irradiated with light at certain wavelengths
photodetectors: devices used for the detection of light
photodiodes: semiconductor devices with a p–n or p–i–n structure for the detection of light
photoluminescence: emission of light which is caused by the irradiation of a material with other light
photomultipliers: photodetection devices based on the photoelectric effect and charge multiplication by secondary emission of electrons
photon counting: photodetection at low light levels where single photon absorption events are counted
photonic bandgap fibers: optical fibers where light is guided based on a photonic bandgap effect
photonic crystal fibers: optical fibers with a built-in microstructure, in most cases consisting of small air holes in glass
photonic integrated circuits: integrated circuits with optical functions
photonic metamaterials: nanostructured materials with special optical properties
photonics: the science and technology of light
photons: quanta of light energy
picosecond lasers: lasers emitting pulses with picosecond durations
planar waveguides: waveguide structures guiding light only in one dimension
plastic optical fibers: optical fibers made of polymer materials
Pockels cells: electro-optic devices, used for building modulators
Pockels effect: the phenomenon that the refractive index of a medium exhibits a modification which is proportional to the strength of an applied electric field (linear electro-optic effect)
polarization beam combining: a technique for combining two polarized laser beams
polarization-maintaining fibers: specialty optical fibers with strong built-in birefringence, preserving the properly oriented linear polarization of an input beam
polarization mode dispersion: the polarization dependence of the propagation characteristics of light waves in optical fibers
polarization of laser emission: direction of the electric field oscillation of a laser beam
polarization waves: patterns of electric (or magnetic) polarization of a medium which are usually caused by light waves
population inversion: a state of a medium where a higher-lying electronic level has a higher population than a lower-lying level
power over fiber: delivery of power for electronic devices via light in an optical fiber
power scaling of lasers: a procedure for substantially increasing the output power of lasers
power spectral density: optical power or noise power per unit frequency interval
powermeters: devices for optical power measurements, based on heating of an absorber structure
prism pairs: combinations of two prisms, mostly used for dispersion compensation
propagation constant: phase change per unit length for light propagating in a medium or waveguide
pulse compression: linear or nonlinear techniques for reducing the durations of optical pulses
pulse front tilt: the phenomenon that the arrival time of an ultrashort pulse varies across the beam profile
pulse pickers: electrically controlled optical switches used for extracting single pulses from a pulse train
pulse propagation modeling: working with physical models describing the propagation of ultrashort pulses e.g. in lasers or optical fibers
pulse repetition rate: the number of pulses emitted per second e.g. by a mode-locked or Q-switched laser
pulsed laser deposition: a method for fabricating thin films on substrates by evaporating materials with laser pulses
pulsed lasers: lasers emitting light in the form of pulses
pulses: flashes of light
pump absorption: the absorption of pump light, e.g. in a laser or a laser amplifier
pump depletion: reduction in the transmitted pump power in a laser or nonlinear conversion device
pump parameter: the ratio of pump power and threshold pump power of a laser
pump–probe measurements: techniques for investigating ultrafast phenomena, where a pump pulse excites a sample and a probe pulse is used for probing the sample after an adjustable delay time
Q factor: a measure of the damping of resonator modes
Q-switched lasers: lasers which emit optical pulses, relying on the method of Q switching
Q-switched mode locking: an operation regime of mode-locked lasers with strong fluctuations of the pulse energy
Q switches: optical switches which are typically used for generating nanosecond pulses in lasers
Q switching: a method for obtaining energetic pulses from lasers by modulating the intracavity losses
Q-switching instabilities: instabilities of passively mode-locked lasers where the pulse energy is unstable
quantum cascade lasers: semiconductor lasers relying on intersubband transitions, normally emitting in the mid-infrared spectral region
quantum cryptography: methods to encrypt information securely, relying on quantum-mechanical phenomena
quantum defect: energy difference between pump and laser photons
quantum dots: microscopic structures confining charge carriers in three dimensions
quantum efficiency: percentage of input photons which contribute to a desired effect
quantum key distribution: methods for the secure distribution of encryption keys
quantum noise: noise arising from quantum fluctuations
quantum optics: the part of optics which deals with quantum effects
quantum wells: thin layers confining carriers in one dimension
quarter-wave mirrors: dielectric mirrors based on a sequence of quarter-wave layers
quasi-continuous-wave operation: an operation mode of lasers (e.g. diode bars) where the pump power is switched on for short time intervals in order to limit thermal effects
quasi-phase matching: a technique of achieving a kind of phase matching, using a periodic structure
quasi-soliton pulses: soliton-like pulses in lasers or fiber-optic links
quenching: the reduction or limitation of an excited-state population, mostly by unwanted effects
Rabi oscillations: oscillations of level populations (or quantum mechanical probability amplitudes) under the influence of an incident light field
radiation-balanced lasers: lasers where the heat generation in the gain medium is compensated by optical refrigeration in the same medium
radiative lifetime: lifetime of an electronic state in the (hypothetical) situation where only radiative processes depopulate that level
Raman amplifiers: amplifiers based on Raman gain
Raman gain: optical gain arising from stimulated Raman scattering
Raman lasers: lasers based on Raman gain rather than on laser gain from stimulated emission
Raman scattering: a nonlinear scattering process involving optical phonons
rare-earth-doped fibers: optical glass fibers which are doped with rare earth ions
rare-earth-doped gain media: laser gain media which are doped with rare earth ions
rate equation modeling: a method of modeling the dynamics of laser gain media
Rayleigh length: the distance from a beam waist where the mode radius increased by a factor square root of 2
reciprocity method: a spectroscopic method which is often used for obtaining the scaling of emission spectra of laser gain media
recirculating fiber loops: fiber loops in which light can circulate many times
recoil limit: a lower limit for the temperature which can be reached with some laser cooling techniques
red lasers: lasers emitting red light
reference cavities: optical cavities serving as a kind of frequency reference
refractive index: a measure of the reduction in the velocity of light in a medium
regenerative amplifiers: optical amplifiers with a resonator in which a light pulse can do multiple round trips before being coupled out
relative intensity noise: noise of the optical intensity (or actually power), normalized to its average value
relaxation oscillations: small mutually coupled oscillations of the laser power and laser gain around their steady-state values
resonant frequency doubling: frequency doubling with a nonlinear crystal placed in a resonant enhancement cavity
resonator design: the description of the optical components from which an optical resonator is made, and their exact arrangement
resonator modes: modes of an optical or microwave resonator
responsivity: photocurrent per unit optical power incident on a photodetector
RGB sources: source of red, green and blue light, which is usually provided in the form laser beams
ring lasers: lasers with a ring resonator
rod lasers: solid-state lasers with a rod-shaped gain medium
saturable absorbers: light absorbers with a degree of absorption which is decreases at high optical intensities
saturable Bragg reflectors: a special type of saturable semiconductor absorbers
saturation energy: a measure of the incident optical pulse energy required for achieving significant saturation of an absorber or a gain medium
saturation power: a measure of the incident optical power required for achieving significant saturation of an absorber or a gain medium
Schawlow–Townes linewidth: linewidth of a single-frequency laser with quantum noise only
sech2-shaped pulses: pulses with a temporal intensity profile which has the shape of a sech2 function
seed lasers: lasers which are used for generating some seed light into an amplifier or another laser
self-focusing: focusing of a beam in a transparent medium, caused by the beam itself through a nonlinear process in the medium
self-heterodyne linewidth measurement: a technique for laser linewidth measurements, based on a beat note between the beam and a delayed version of itself
self-phase modulation: nonlinear phase modulation of a beam, caused by its own intensity via the Kerr effect
self-starting mode locking: mode locking which is quickly achieved after turning on a laser, without external intervention
self-terminating laser transitions: laser transitions which can not be continuously operated due to the accumulation of population in the lower laser level
Sellmeier formula: an equation for calculating the wavelength-dependent refractive index
semiconductor lasers: lasers based on semiconductor gain media
semiconductor optical amplifiers: optical amplifiers based on semiconductor gain media
semiconductor saturable absorber mirrors: saturable semiconductor absorber devices acting as nonlinear mirrors
shot noise: quantum-limited intensity noise
side pumping: a technique of pumping a solid-state laser in directions which are approximately transverse to its beam direction
signal-to-noise ratio: the ratio of signal power to noise power in a detector
silica fibers: optical fibers based on fused silica or related materials
silicon photonics: photonic technology based on silicon chips
single-atom lasers: lasers with only a single atom as the gain medium
single-frequency lasers: lasers emitting radiation in a single resonator mode
single-frequency operation: an operation mode of a laser where only a single resonator mode acquires a significant power
single-mode fibers: optical fibers supporting only a single guided mode per polarization direction
single-mode operation: operation of a laser on axial (longitudinal) resonator modes only, or even on a single axial mode
single-polarization fibers: optical fibers which transmit only light with a certain polarization
Sisyphus cooling: a mechanism for laser cooling of atoms or ions
slab lasers: solid-state bulk lasers where the gain medium has the form of a slab
slave laser: a laser which is injection-locked to another laser
slope efficiency: differential power efficiency of a laser
small-signal gain: optical gain for small signal intensities, where no amplifier saturation occurs
solid-state lasers: lasers based on solid-state gain media (usually ion-doped crystals or glasses)
soliton mode locking: a mechanism for laser mode locking based on soliton pulses
soliton period: the distance over which higher-order solitons reproduce their temporal and spectral shape
solitons: pulses with a certain balance of nonlinear and dispersive effects
spatial hole burning: a distortion of the gain shape in a laser medium (or the loss spectrum in a saturable absorber medium), caused by saturation effects of a standing wave
spatial walk-off: the phenomenon that the intensity distribution of a beam in an anisotropic crystal drifts away from the direction of the wave vector
speckle: light patterns resulting from the reflection of coherent light at rough surfaces
spectral beam combining: a class of methods for beam combining, based on wavelength-sensitive beam combiners
spectral brightness: brightness per unit optical bandwidth
spectral interferometry: a class of interferometric methods, where interference in the frequency domain is exploited
spectral phase: the phase of the electric field in the frequency domain
spectrograms: a type of diagrams which visualize optical or other signals
spiking: the tendency of some lasers to emit spikes of output power, particularly after being switched on
spontaneous emission: a quantum effect, causing the spontaneous decay of excited states of atoms or ions
squeezed states of light: nonclassical states of light with noise below the standard quantum limit in one quadrature component
stability zones: parameter regions of an optical resonator where the resonator is geometrically stable
stabilization of lasers: measures applied to lasers in order to improve their stability in terms of output power, optical frequency, or other quantities
standard quantum limit: a limit for noise levels set by quantum mechanics
step-index fibers: optical fibers with a step-index refractive index profile
stimulated emission: a quantum effect, where photon emission is triggered by other photons
Stokes shift: the reduction in photon energy in certain processes
sum and difference frequency generation: nonlinear processes generating beams with the sum or difference of the frequencies of the input beams
supercontinuum generation: a nonlinear process for strong spectral broadening of light
superfluorescence: collective emission of radiation by an ensemble of excited atoms or ions
superluminal transmission: transport of some quantity with a velocity exceeding that of light in vacuum
superluminescence: fluorescence which is enhanced by laser amplification
superluminescent diodes: broadband semiconductor light sources based on superluminescence
superluminescent sources: optical sources based on superluminescence
supermirrors: laser mirrors with a very high reflectivity
superradiance: collective emission of an ensemble of atoms or ions after coherent excitation
surface-emitting semiconductor lasers: semiconductor lasers where the generated light propagates in the direction perpendicular to the wafer surface
synchronous pumping: pumping of a laser or an optical parametric oscillator with short light pulses in synchronism with the emitted pulses
tapered fibers: optical fibers which are over some length stretched out to a very small diameter
telecom fibers: optical fibers for use in optical fiber communications
temporal walk-off: the loss of temporal overlap of pulses, caused by group velocity mismatch
thermal lensing: a lensing effect induced by temperature gradients
thin-disk lasers: solid-state bulk lasers having a very thin disk of laser-active material as the gain medium
third-order dispersion: chromatic dispersion related to a third-order dependence of the phase change on the frequency offset
threshold pump power: the pump power at which the laser threshold is reached
thresholdless lasers: lasers with a threshold power which is virtually zero
time–bandwidth product: product of temporal and spectral width of a pulse
time division multiplexing: a multiplexing technique operating in the time domain
time-of-flight measurements: distance measurements based on measuring the time of flight of a light pulse
timing jitter: fluctuations of the temporal positions of pulses
timing phase: a phase reflecting timing deviations by relating them to the pulse period
titanium–sapphire lasers: lasers based on a Ti:sapphire gain medium
transform limit: the minimum pulse duration possible for a given optical spectrum
transition cross sections: material parameters for quantifying the likelihood or rate of optical transition events
transition-metal-doped gain media: lasers based on gain media which are doped with transition metal ions
triangulation: a method for distance measurements
tunable lasers: lasers the output wavelengths of which can be tuned
tungstate lasers: solid-state lasers based on tungstate crystals as gain media
twisted-mode technique: a technique for achieving single-frequency operation of a laser, based on quarter-wave plates on both sides of the gain medium
two-photon absorption: a nonlinear absorption process where two photons are simultaneously absorbed
ultrafast amplifiers: amplifiers for ultrashort optical pulses
ultrafast laser physics: the area of laser physics dealing with ultrashort processes
ultrafast lasers: lasers emitting ultrashort pulses
ultrafast optics: the part of optics dealing with ultrafast phenomena
ultrashort pulses: optical pulses with durations of picoseconds or less
ultraviolet lasers: lasers (or other laser-based light sources) generating ultraviolet light
ultraviolet light: invisible light with wavelengths shorter than ∼ 400 nm
upconversion: a process where light can be emitted with photon energies higher than those of the light generating the excitation
upconversion lasers: lasers relying on upconversion processes
upper-state lifetime: the lifetime of the population of the upper laser level
V number: a normalized frequency parameter, which determines the number of modes of a step-index fiber
vacuum noise: quantum noise of the vacuum state, or quantum noise introduced into an optical system via a vacuum input
vanadate lasers: lasers based on rare-earth-doped yttrium, gadolinium or lutetium vanadate crystals, usually Nd:YVO4
velocity-matched photodetectors: a type of photodetector where propagation velocities of light and electrical signals are matched in order to achieve a very high detection bandwidth
vertical cavity surface-emitting lasers: a monolithic kind of semiconductor lasers with beam emission perpendicular to the wafer surface
vertical external-cavity surface-emitting lasers: surface-emitting semiconductor lasers with an external laser resonator
vibronic lasers: lasers based on gain media with a large gain bandwidth, caused by a strong interaction of electronic transitions with phonons
visible lasers: lasers (or other laser-based light sources) emitting visible light
wall-plug efficiency: total electrical-to-optical power efficiency of a laser system
waveguide dispersion: chromatic dispersion arising from waveguiding effects
waveguide lasers: lasers with a waveguide structure in the gain medium
waveguides: spatially inhomogeneous transparent structures for guiding light
wavelength division multiplexing: a multiplexing technique working in the wavelength domain
wavelength tuning: the manipulation of the output wavelength of an optical device such as a laser or an optical parametric oscillator
wavemeters: devices for precise measurements of laser wavelengths
wavenumber: the phase delay per unit length, or that quantity divided by 2π
waveplates: transparent plates with a defined amount of birefringence, used for modifying the polarization of light
white light interferometers: interferometers using broadband light inputs
white light sources: light sources with very broad optical bandwidth
X-ray lasers: lasers emitting in the X-ray spectral region
YAG lasers: lasers based on YAG (yttrium aluminum garnet) crystals, usually Nd:YAG
yellow and orange lasers: lasers emitting yellow or orange light
YLF lasers: lasers based on YLF (yttrium lithium fluoride) crystals, usually Nd:YLF
ytterbium-doped gain media: laser gain media containing laser-active ytterbium ions
z-scan measurements: a technique for measuring the strength of the Kerr nonlinearity of a material, relying on self-focusing
zero dispersion wavelength: a wavelength where the group delay dispersion of a fiber is zero
List of Formula Symbols
| Symbol | Explanation | SI Units |
|---|---|---|
| a | core radius of a fiber | m |
| b | confocal parameter of a laser beam (twice the Rayleigh length) | m |
| c | velocity of light | m/s |
| deff | effective nonlinear coefficient of a nonlinear crystal material | m/V |
| dij | components of the χ(2) nonlinear tensor | m/V |
| e | elementary electric charge | C |
| f | focal length (e.g., of a lens) | m |
| f | noise frequency | Hz |
| frep | pulse repetition rate | Hz |
| fro | relaxation oscillation frequency | Hz |
| g | gain coefficient | 1 or m−1 |
| g(τ) | complex degree of coherence | 1 |
| gB | nonlinear gain coefficient for Brillouin scattering | m/W |
| gR | nonlinear gain coefficient for Raman scattering | m/W |
| gss | small-signal gain coefficient | 1 or m−1 |
| h | Planck's constant | J s |
| k | wavenumber | m−1 |
| kB | Boltzmann constant | J/K |
| Δk | phase mismatch of a parametric nonlinear process | rad/m |
| lrt | round-trip losses of a resonator | 1 |
| n | refractive index | 1 |
| ne | extraordinary refractive index | 1 |
| neff | effective refractive index | 1 |
| ng | group index | 1 |
| no | ordinary refractive index | 1 |
| n2 | nonlinear index | m2/W |
| q | complex q parameter (→ Gaussian beams) | m |
| r | radius (e.g., in fiber core or distance from beam axis) | m |
| r | pump parameter of a laser | 1 |
| rij | components of the electro-optic tensor | m/V |
| vg | group velocity | m/s |
| vp | phase velocity | m/s |
| w | Gaussian beam radius | m |
| w0 | beam radius at the beam waist | 1 |
| zR | Rayleigh length | m |
| zs | soliton period | m |
| A | amplitude of pulse envelope | |
| Aeff | effective mode area | m2 |
| B | B integral | rad |
| B | noise bandwidth | Hz |
| B | brightness | W/(m2 rad2) |
| BPP | beam parameter product | mm mrad |
| D2 | group delay dispersion | s2 |
| Dλ | dispersion parameter | ps/(nm km) |
| E | electric field strength | V/m |
| Ep | pulse energy | J |
| Esat | saturation energy | J |
| F | finesse | 1 |
| F | noise figure | 1 |
| Fsat | saturation fluence | J/m2 |
| GX(τ) | autocorrelation function of some variable X | |
| I | optical intensity | W/m2 |
| Isat | saturation intensity | W/m2 |
| Lcoh | coherence length | m |
| M2 | M2 factor | 1 |
| NF | Fresnel number | 1 |
| Ndop | doping concentration | m−3 |
| NA | numerical aperture | 1 |
| P | optical power | W |
| P | electric polarization of a medium | C/m2 |
| Pout | output power | W |
| Pp | peak power of a pulse | W |
| Psat | saturation power of a gain medium or saturable absorber | W |
| Q | Q factor | 1 |
| R | power reflectivity (of a mirror) | 1 |
| R | radius of curvature (e.g., of wavefronts) | m |
| R | responsivity of a photodiode | A/W |
| ΔR | modulation depth of a saturable absorber | 1 |
| Sφ(f) | power spectral density of a phase value | rad2/Hz |
| T | temperature | K or °C |
| Tg | group delay | s |
| Toc | output coupler transmission | 1 |
| Trt | round-trip time of an optical resonator | s |
| V | V number of a step-index fiber | 1 |
| α | absorption coefficient | m−1 |
| α | linewidth enhancement factor | 1 |
| α | thermal expansion coefficient | K−1 |
| β | propagation constant | rad/m |
| β2 | group velocity dispersion | s2/m |
| γSPM | self-phase modulation coefficient | rad/(W m) |
| ε0 | electric permittivity of vacuum | C/Vm |
| ε | relative electric permittivity | 1 |
| η | efficiency | 1 |
| ηoc | output coupling efficiency | 1 |
| θ | beam divergence half-angle | rad |
| θ | polar angle | rad |
| κ | thermal conductivity | W/(m K) |
| λ | optical wavelength | m |
| λp | pump wavelength | m |
| λs | signal wavelength | m |
| μ | relative magnetic permeability | 1 |
| μ0 | magnetic permeability of vacuum | N/A2 |
| ν | optical frequency | Hz |
| νB | Brillouin frequency shift | Hz |
| νceo | carrier–envelope offset frequency | Hz |
| ν(t) | instantaneous frequency | Hz |
| Δν | optical bandwidth | Hz |
| ρ | walk-off angle | rad |
| σabs | absorption cross section | m2 |
| σem | emission cross section | m2 |
 2 |
upper-state lifetime | s |
| coh |
coherence time | s |
| p |
pulse duration | s |
| rad |
radiative lifetime | s |
| φ | azimuth angle | rad |
| φ | optical phase or phase shift | rad |
| φG | Gouy phase shift | rad |
| φnl | nonlinear phase shift from the Kerr effect | rad |
| φt | timing phase | rad |
| Δφceo | carrier–envelope offset phase | rad |
| χ(2), χ(3) | nonlinear tensor | 1 |
| ω | angular frequency | rad/s, s−1 |
| Λ | modulation period of a fiber Bragg grating | m |
