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Home > Optics Terms/Definitions

General Terms

AAberration Deviation from what is normal, right, or natural. In optics, defects of a lenssystem that cause its image to deviate from the rules of paraxial imagery.

Absorption The loss of light as it passe s through a material, gene rally due to itsconversion to other energy forms (usually heat).

Achromatic Free o f color; a color perceived to have no hue, such as neutral grays.

Acousto-optics The study of the interactions between sound waves and light in a solidmedium.

Afocal An optical system with object and image points at infinity. Literally a systemwithout focal length.

Amorphous The disordered, glassy so lid state of a subs tance, as distinguished from thehighly ordered crystalline solid state.

Amplification See Gain.

Angle of incidence The angle formed between a ray of light striking a surface and thenormal to that surface a t the point of incidence.

Angle ofincidence

Angle of reflection The angle formed be tween the normal to a surface and the reflectedray. This angle lies in a common plane with the angle of incidence, and is equal to it.

Angle of refraction The angle formed be tween the reflected ray and the normal to thesurface. This angle lies in a common plane with the angle of incidence.

Angstrom - A unit of distance corresponding to 10-10 m. One angstrom () is 0.1 nm sothat 200 nm corresponds to 2000 .

Antisolar point - The point where an imaginary ray connecting the sun and yourself meetsthe sky. If the sun is above the horizon, the antisolar point is below the horizon. If thesun is setting in the west, the antisolar point is on the eastern horizon. If the sun is

below the horizon, the antisolar point is above the horizon on the other side of the sky.

Aperture An opening or hole through w hich radiation or mater may pass.

Aperture stop A physical restraint that limits the diameter of the bundle of light allowedto pass through a lens, shown be low by "a."

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Aperture stop

Aplanatic A lens corrected for spherical abe rration and coma.

Apodization The use of a variable transmission filter at the aperture stop of a lens tomodify its diffraction patte rn. Reduced transmission favors pe rformance at highfrequencies while reduced transmission favors low frequency performance.

Aspheric Not spherical; an element having one or more surfaces that are not spherical.

Astigmatism A lens aberration that results in the vertical and horizontal image planesbeing spread to form lines instead of points.

Atomic number - The number of protons in an atomic nucleus. For a neutral atom, thisalso corresponds to the number of e lectrons orbiting the nucleus. This number alsodenotes an atom's place on the Periodic Table of the Elements and the Chart of Nuclides.Carbon has an atomic number of 6: 6 protons and 6 e lectrons.

Attenuation The loss of optical power.

Axis A straight line passing through a body and indicating its center.

BBack focal length The distance from the last surface of a lens to its image plane.

Back focal length

Baffle An opaque shielding device des igned to reduce the e ffects of stray light on anoptical system.

Beam 1) A bundle of light rays. 2) A concentrated unidirectional stream of particles. 3) Aconcentrated unidirectional flow of electromagnetic waves.

Beamsplitter An optical device for dividing a beam into two or more separate beams.

Beamsplitter

Bifocal A two-part lens that has a different focal length for each part. Used ineyeglasse s to correct for near and far vision.
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Binocular An instrument having a pa ir of decentered lenses , one for each eye thatfocuses on a single object as a magnifier.

Biocular A term pertaining to devices de signed for use w ith both eyes viewing througha single element.

Biocular

Birefringence The separation of a light beam as it penetrates a doubly refracting objectinto the ordinary and extraordinary beams.

Birefringence

Bore a central hole running the length of a waveguide or laser tube.

CCamera A light-tight box that receives light from an object or scene and focuses it toform an image on a light-sensitive material or a detector.

Catoptric system An optical system in which the only image-forming elements arecurved-surface mirrors.

Cavity The optical resonator in a laser formed by two coaxial mirrors, one totallyreflective and the other partially reflective, positioned such that oscillations occur.

Center of curvature The center of the sphere of which the surface of a lens or mirror

forms a portion.

Chief ray The ray that passes through the center of an aperture stop in an opticalsystem.

Chief ray

Chromatic Having color.

Chromatic aberration The lens aberration resulting from the normal increase inrefractive index of all common materials toward the blue end of the spectrum.


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Cladding The low-refractive-index material that surrounds the core of an optical fiber tocontain core light while protecting against surface contaminant scattering.

Clear aperture The opening of an optical system, or its components, which limits theextent of the bundle of rays on the given surface. Is usually circular and specified by itsdiameter.

Coherence length The length over which energy in two separate waves remainsconstant.

Cold mirror A mirror whose coating reflects only visible radiation while transmitting theinfrared.

Collimation The process by which a divergent beam of radiation or particles isconverted into a parallel beam.

Color The hue, saturation and brightness that is visibly detectable.

Coma A lens aberration resulting form different magnifications in the various lens zones.

Concave A hollow curved surface; curved inward.

Concentric Characterized by having the same center.

Condenser A single pos itive lens or group of lenses in a projection system that collectlight and cause it to be evenly distributed.

Confocal Elements whose focal points coincide.

Conjugates Light emitted from one element is focused on the other and vice versa.

Contrast The apparent difference in brightness between light and dark areas o f animage.

Convergence The bending of light rays toward each other.

Convex Spherically shaped; curves outward.

Core The light-conduction portion of an optical fiber, defined by the region of highrefractive index.

Critical angle The smallest angle of incidence at which total internal reflection occurs.When the critical angle is exceeded, the light is totally reflected back into the dense rmedium. The critical angle will vary with the indices of refraction of the two media:sin(Icrit)=n/n and is shown below by c.

Critical angle

Curvature The measure of departure from a flat surface, as applied to lenses; thereciprocal of radius.

DDecibel (dB) The standard unit used to express ga in or loss and relative pow er levels.DB = 10 log (P2/P1).

Deflection Any bending of a wave of radiation away from its expected path.


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Diffraction - As a wavefront passes by an opaque edge or through an opening, weakersecondary wavefronts are generated that appear to originate at the edge . Thesewavefronts interfere w ith the original wavefront as w ell as each other to form diffractionpatterns.

Diffraction

Diffraction grating A device used to break light into its component wave lengths. Itusually composed of a material with tiny grooves cut into it which disperses the light as itpasses through or bounces o ff the grating (depending on the type o f grating). Physicists

and astronomers often use diffraction gratings to study the nature of light.

Diffusion The scatte ring of light by reflection or transmission. Diffuse reflection resultswhen light strikes an irregular surface such as a frosted window or the surface of afrosted or coated light bulb.

Diffusion

Diopter (D) A unit of optical powe r that expresses the refractive power of a lens orprism.

Direct ray A ray that travels w ithout being reflected or refracted.

Dispersion The separation of a beam into its various wavelength components .

Distortion The situation where an image is not a true-to-scale reproduction of anobject.

Divergence The bending of rays away from each other.

Diverging lens A lens that causes parallel rays of light to spread out. Examples include:negative lens, divergent lens, concave lens, or dispersive lens.

Diverging lens


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Doppler effect Radiation emitted from a source that moves away from an observerappears to be of lower frequency than the radiation emitted from a stationary source.

Doublet A compound lens consisting of two elements.

EEdge The surface that limits the aperture of a lens or prism.

Electro-optic effect The change in the refractive index of a material under the influence

of an electric field.

Electromagnetic force - One of the four fundamental forces in nature. Refers to thecombination of two separate forces -- the electric force and the magnetic force. EM forcesact on objects w ith electric charges and/or magnetic fields. See also e lectron.

Electromagnetic spectrum The total range of wavelengths that can be generatedphysically. The range extends from practically zero to infinity and includes the visibleportion of the spectrum known as light.

Electromagnetic spectrum

Electron One of the e lementary particles of nature. The e lectron has a charge of -1.6 x10-19 Coulombs and a mass of 9.1 x 10-31 kg. Electrons orbit the nuclei of atoms and arethe principle tool of molecular bonding.

Electroscope - A device that enables you to determine if two objects have opposite o r likecharges.

Emission spectrum The spectrum formed by radiation from an emitting source.

Emitter A source of radiation.

Etalon Two flat glass surfaces separated by a spacer, with the inner surfaces of theplates coated with a partially reflecting layer.

Exit pupil The image of the aperture stop as seen from image space in an opticalsystem.

Eye The organ of vision or light sensitivity.

Eyepiece The lens system between the final real image on a visual optical system andthe eye. Often seen in microscopes.

FFabry-Perot interferometer A multiple beam interferometer, usually cons isting of twoflat plates with high reflective ability. The plates are parallel to each other so light canbounce back and forth several times.

Fabry-Perot interferometer
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Fermats principle Light will take the path that requires the least transit time.

Fiber see Optical fiber.

Field of View The maximum area that can be seen through a lens or an opticalinstrument.

Field stop An aperture located at an image plane of an optical system that determinesthe size and shape of the image.

Filter A device that attenuates particular wavelengths or frequencies while transmittingothers w ith little change.

Fizeau interferometer A type of interferometer noted for producing narrow multiple-beam interference fringes. As a result, when compared with the Twyman-Green, theFizeau interferometer has fewer optical components, does not have the largebeamsplitter and can be adjusted to a greater accuracy.

Fizeau interferometer

Fluorescence The emission of light or other electromagnetic radiation of longerwavelengths by a substance as a result of the absorption of some other radiation.

F number (f/#) The express ion denoting the ratio of the equivalent focal length of alens to the diameter of the entrance pupil.

Focal Length - The d istance from a lens or mirror to its focal point.

Focal length (f) The effective focal length (EFL) is the distance from the principal pointof focal point. The back focal length (BFL) is the distance from the vertex of the last lens tothe second focal point. The front focal length (FFL) is the distance from the first lenssurface to the first focal point.

Focal length (f)

Focal plane The plane on which the bes t focus is formed.
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Focal point The point on the optical axis of a lens, to which an incident bundle ofparallel rays will converge.

Focus 1) The focal point. 2) To adjust the eyepiece or objective so that the image isclearly seen.

Fraunhoffer diffraction The diffraction pa ttern of a source observed at an infinitedistance from the source. Far field diffraction.

Fresnel diffraction - Near field diffraction. The diffraction obtained when the source orthe observing screen are a finite distance from the diffraction aperture or obstacle.

Fringe An interference band.

Fundamental mode The lowest order mode (lowest energy) of a waveguide.

Fused silica Glass made of pure silicon dioxide (Si02).

GGain The increase in a signal that is transmitted from one point to another.

Gaussian beam A beam of light whose electrical field amplitude distribution is Gaussian.A circular cross section amplitude may be expressed as : E(r) = E(0)exp[-(r/w)^2] where ris the distance from the beam center and w is the radius at w hich the amplitude is 1/e ofits value on the axis; w is called the beam width.

Geometric optics A filed of physics that deals w ith light as if it truly were composed ofrays diverging in various directions from the source and a re abruptly bent or turned byrefraction or reflection.

Glass A noncrystalline, inorganic mixture of various metallic oxides fused by hea ting withglassifiers such as silica.

Grating A framework or latticework having an even a rrangement of rods or long narrowobjects used to d isperse light by interference.

Grinding The process in optical system manufacturing that gives an element its requiredshape.

HHologram An interference pattern that is recorded on a high-reso lution plate, the twointerfering beams formed by a coherent beam from a laser and light scattered by anobject. After formation, if lit and viewed correctly, a 3-D image of the object is seen.

Hologram

Homogeneous A property of subs tance that is the same in all directions.

IIllumination The application of light to something.

Image The reproduction of an object produced by light rays. If the beam converges to apoint, a rea l image is formed. If the beam diverges, a virtual image is formed.
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Incident - Falling or shining upon. When light is incident on something, the light may bereflected, refracted, absorbed, o r any combination of these.

Incoherent The lack of a fixed phase relationship between two waves.

Index of refraction A ratio of the velocity of light in a vacuum to the velocity of light in arefractive material for a given wavelength.

Infrared - The invisible portion of the electromagnetic spectrum that lies between about0.75 and 1000 m. Radiation in the near-infrared produces a sensation of heat.

Interaction - Any action and reaction that takes place be tween two objects. In physics,interactions (or forces) fall into four main categories. These categories are gravitationalinteractions, electromagnetic interactions (electric and magnetic forces), and the strongand weak interactions (which affect atomic nuclei and fundamental particles).

Interface - The boundary between two different materials or media.

Interference The additive process whereby the amplitude of two or more overlappingwaves are systematically attenuated and reinforced.

Interferometer An instrument that employs the interference o f lightwaves to measurethe accuracy of optical surfaces. It can measure a length in terms of the length o f a waveof light.

Interferometry The study and utilization of interference phenomena.

Ionization - The gaining or losing of electrons by an atom. If an atom loses an electron(s),it becomes a positive ion. If an atom gains an electron(s), it becomes a negative ion.

Iris A mechanical device designated to smoothly vary the e ffective diameter of a lens bycontrolling the amount of light allowed through.

LLaser Light Amplification by Stimulated Emission of Radiation. A laser is a cavity, withplane or spherical mirrors at the ends, that is filled with a lasable material (one in whichthe atoms are capable of being excited by light or an electric discharge). Light is emitted

as the atoms drop back down to their ground states.

Lateral color A lens aberration resulting in image size variation as a function ofwavelength.

Law of reflection States that the angle of reflection is equal to the angle of incidence.

Law of refraction States that the ratio of the sine of the angle be tween the normal andrefracted ray is a constant.

Law of refraction

Lens A transparent optical component consisting of one or more pieces of optical glasswith surfaces so curved that they serve to converge or diverge the transmitted rays froman object, thus forming a real or virtual image of that object.

Light Electromagnetic radiation detectable by the eye, ranging from 400 to 750nm inwavelength.

Lightning - Most simply defined as the discharge of electricity from one cloud to another,


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or from a cloud to the ground.

Light dispersion The process by which white light is separated into its componentwavelengths. Prisms and gratings are dispersion devices.

Light dispersion

Lightning - Most simply defined as the discharge of electricity from one cloud to another,or from a cloud to the ground.

Liquid crystal A material that possesses less geometrical regularity or order thannormal solid crystals, and whose order varies in response to alterations in temperatureand other quantities.

Liquid crystal displays A display formed by sandwiching a layer of liquid crystal materialbetween two sheets of glass; a transparent conductive coating on the glass is etched toform character segments. An applied voltage causes the appropriate segments to darkenas the liquid crystal changes arrangement.

Lossy A medium that scatters or absorbs radiation that passes through it.

MMach-Zender interferometer An interferometer de rived from the Twyman-Greeninterferometer. Light passing through a sample region in one direction recombines w ith asecond leg without traversing the sample twice. The instrument is used to s tudytransparent objects and is particularly useful in studying wind tunne l gas dynamics.

Mach-Zender interferometer

Magnify - To cause an image to appear larger or smaller than the corresponding object.When we look through a lens, we often see things magnified: convex lenses oftenmagnify objects larger, while concave lenses always magnify objects smaller. Mirrors canalso magnify objects.

Magnifying power The ability of an optical system to make an object appear larger.

Marginal rays Rays that pass through an optical system near the edge of the aperture.

Maser Microwave Amplification by Stimulated Emission of Radiation. The predecessorof the laser.

Meniscus a lens that has one convex surface and the other is concave.

Meridional ray A ray that lies in the plane that contains the optical axis.

Meter 1) The basic unit of length in the SI system. 2) Any device used for measuring.


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Metrology The science o f measurement, particularly of angles and lengths.

Microscope An instrument consisting of essentially a tube 160mm long, with anobjective lens at the distant end and an eyepiece at the near end. The objective forms areal image of the object in focal plane of the eyepiece where it is observed by the eye.The tota l magnification is equa l to the linear magnification of the objective multiplied bythe magnifying pow er of the eyepiece.

Microscopy - Investigation by means of a microscope.

Mirage The distortion of an objects true image as the result of abnormal atmosphericdisturbances along the path traveled by the light.

Mirror A smooth, highly polished surface, for reflecting light that may be plane orcurved. The actual reflecting surface is usua lly a thin coating of silver or aluminum onglass.

Mode 1) The characteristic of the propagation of the light through a waveguide that canbe designated by a radiation pattern in a plane transverse to the direction of travel. 2)The state of an oscillating system such as a laser that corresponds to a pa rticular fieldpattern and one of the possible resonant frequencies of the system.

Modulation Changes in a wave train caused by another wave, such as amplitude orfrequency modulation in radio. Is also used to mean contrast w hen applied to a se riesof parallel lines ad spaces as imaged by a lens.

Moir pattern A pattern developed from interference or light blocking when gratings,screens, or regularly spaced patterns are supe rimposed on one another. Whenconverging lines in the picture are practically parallel to the scanning lines, a moirpatte rn will naturally form.

Monochromatic light Light consisting of only one w avelength or a very narrow band o fwavelengths.

Monochrometer An instrument for isolating narrow portions of the spectrum by using aprism or grating.

NNeutral density filter A light filter that decreases the intensity of the light withoutaltering the relative spectral distribution o f the energy.

Night-vision device A device that uses low-level visible radiation or IR radiation toproduce a visual image of a night scene.

Nodal points The two po ints at which rays from off-axis object points appear tointersect the axis.

Nodal points

Normal - Perpendicular. If one line is normal to another, then they are at right angles.

OObject The figure seen through or imaged by an optical system.

Objective The optical element that receives light from the object ad forms the first orprimary image in telescopes and microscopes.

Object space The space between the object being viewed and the system entrancepupil.
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Optical activity The capacity of a substance to rotate the plane of polarized light that istransmitted through it.

Optical axis The line passing through both the centers of curvature of the opticalsurfaces o f a lens.

Optical fiber - A thin filament of drawn or extruded glass or plastic having a central coreand a cladding of lower index of refraction to promote internal reflection.

Optical fiber

Optical path length The product of the geometrical distance and the refractive index, ina medium of constant index of refraction.

Orthoscopic Corrected for distortion.

Oscilloscope A system in which a supplied signal causes the deflection of the e lectronbeam in a cathode-ray tube, forming a visible trace on the phosphor of the screen of thetube.

PParabolic An optic whose surface is in the shape of a pa rabola.

Parallax The optical phenomenon that causes relative motion between two objectpoints when the eyepoint is moved laterally.

Periodic wave A wave of energy in which each point of the wave is repeatedlydisplaced at equal time intervals.

Periscope An optical instrument designed to displace the line of sight in a verticaldirection. Used often in submarines.

Periscope

Phase In a pe riodic function, the segment of the period that has e lapsed, measuredfrom some fixed origin.

Photoelectric effect - A phenomenon discovered by Einstein in the early 20th century inwhich electrons are e jected from a solid when impinged upon by e lectromagneticradiation. This led to the understanding of light as particles, or photons. The energyrequired to s trip an electron from an atom is called the ionization energy.

Photography The process of recording of an image on a light sensitive medium.

Photon A quantum of electromagnetic energy of a single mode; a single wavelength,polarization, and direction.

Photonics The technology of generating and harnessing light and other forms of radiant


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energy whose quantum unit is the photon.

Physical optics The branch of optics which studies interference, diffraction, polarizationand other phenomena for which the ray approximation of geometric optics is not valid.

Pinhole camera A lensless camera that use s a small sharp-edged hole as its aperture.The light passed by this aperture onto the cameras film plane produces a soft-edgedimage that has a w ide filed of view, is free form distortion, and e xhibits a large depth offield.

Plane A surface that has no curvature.

Planoconcave lens A lens w ith one plane surface and one concave surface.

Planoconvex lens A lens w ith one plane surface and one convex surface.

Polarization With respect to light radiation, the restriction o f the vibrations of themagnetic or electric field to a single plane. For electromagnetic radiation, the polarizationdirection is always the direction of the electric field vector. The polarization vector isalways perpendicular to the beam direction.

Polarize - To align something in one direction or another. Natural light is a combination oftwo polarization states. A polarizer can be used to block out one of the po larizationstates and a llowing the other to pass.

Polishing The optical process, following grinding, that puts a highly finished, smoothsurface on a lens or mirror.

Power With respect to a lens, it is the reciprocal of the focal length.

Principal plane The surface in a lens or lens system at which the projections o f enteringand exiting rays intersect.

Principal ray The ray that passes through the center of the pupils of an optical system.

Prism A transparent optical element having at least two po lished plane faces inclinedrelative to each other, from which light is reflected or through which light is refracted.

Proton - One of the e lementary particles of nature. The proton has a charge of 1.6 x 10-19 Coulombs and a mass of 1.67 x 10-27 kg, much higher than an electron. The protonresides in the nucleus of an atom, sharing the space w ith neutrons, neutrally chargedparticles.

Pupil 1) In the eye, the opening in the iris that permits light to pass and be focusedonto the re tina. 2) In a lens, the image o f the aperture stop as seen from object andimage space.

RRadiation The emission and/or propaga tion of energy through space or through amedium in the form of either waves o f corpuscular emission.

Ray A geometric representation of a light path through an optical device; a line normalto the wavefront indicating the d irection of radiant energy flow.

Ray tracing - A process used in optics by w hich the position and orientation of an imagecan be es tablished if one knows the focal length of the lens and the position of theobject. This process use s strateg ic rays from the object passing through the lens to locatethe image.

Real image - A type of image created by converging light rays. This type o f image wouldform on the image side of a lens, where it could be projected. The opposite of a rea limage is a virtual image .

Reflect - When light bounces off an object. Usually we associate reflection with a smooth,polished surface; however the surface doesn't have to be smooth. Light reflects off yourshirt, therefore others can see that you're wearing one.

Reflectance The ratio of reflected light to incident light.

Reflection The return of radiation by a surface, without change in wavelength. It maybe specular from a smooth surface or diffuse from a rough surface, or a combination of thetwo. The angle o f the incident ray is equal to the angle of the reflected ray.


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Reflection

Refraction The bending of oblique incident rays as they pass from a medium of onerefractive index into a medium of a different re fractive index.

Resolution The ability of a lens system to reproduce the po ints, lines and surfaces in anobject as separate entities in the image.

Resonance A large amount of vibration in s system as a result of a small stimulus thathas about the same period as the na tural vibration period of the system.

Reticle An optical element located at an image plane that contains a pattern thatassists in pointing an instrument or measuring target characteristics.

Reticle

Retina The photosensitive membrane on the inside o f the human eye OR a scanningmechanism in optical character generation.

Retroreflection Reflection in which the radiation is re turned in directions close to thosefrom which it came.

SSaturation The decrease o f the absorption coefficient of a medium near some transitionfrequency when the pow er of the incident radiation near that frequency exceeds a certainvalue.

Scattering A change o f the spatial distribution of a beam of radiation when it interactswith a surface or a heterogeneous medium in which there is no change o f the wave lengthof the radiation.

Sensitivity The ratio of the output to the input in a radiation detector.

Silicon dioxide Or s ilica A common optical material from which lenses are made.

Source A physical source of radiation.

Speckle pattern A power intensity pattern produced by the mutual interference ofpartially coherent beams that are subject to minute spatial and temporal fluctuations.

Spectral Pertaining to or as a function of wavelength.

Spectrum - The result of breaking up light into its various wavelengths.

TTelecentric lens A lens in which the aperture s top is located at the front focus, resultingin the chief ray be ing parallel to the optical axis in image space (exit pupil is at infinity).


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Telephoto lens A compound lens constructed so that its overall length is equal to orless than its effective focal length.

Telephoto lens

Telescope An afocal optical device that made of lenses and/or mirrors, usua lly with amagnification greater than unity, that renders distant objects more distinct by enlargingtheir image on the retina.

Thick lens a lens with an axial thickness adequate to make it producible.

Thin film A thin layer of a substance deposited on an element, often for antireflection,filtering, or polarization effects (among others).

Toric surface A surface that is sw ept out by revolving a circle about an axis that lies inthe plane of the circle but that does not intersect its center.

Transmission The conduction of radiant energy through a medium.

Transparent Capable of transmitting light w ith little absorption and no appreciablescattering or diffusion.

Transverse Orthogonal to the incoming field.

Twyman-Green interferometer - A testing device that provides a contour map o f theemergent wavefront for the observer in terms of the given wavelength of the light.

Twyman-Green Interferometer

Total internal reflection - A phenomenon occurring when light is incident on an interface

between two transparent materials at a very shallow angle. The light must be travelingthrough a medium with a higher index of refraction than the ne ighboring medium. At theinterface, all of the light is reflected back into the surrounding material and none of thelight is refracted out into the neighboring material.

UUltraviolet (UV) Wavelengths from 1 - 400nm.

VVertex The highest point of a figure or shape .

Visible That pertaining to the spectral region that can be seen by the eye.

Visible spectrum Wavelengths from 400 700nm.

Vitreous That having the characteristics of glass.


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WWatt (W) The power that gives rise to the production of energy at the rate o f 1 jouleper second.

Wave An undulation or vibration; a form of movement by which all radiant ene rgy of theelectromagnetic spectrum is estimated to travel.

Waveguide A system or material designed to confine and direct electromagnetic wavesin a direction determined by its physical boundaries.

Wavelength The physical distance covered by one cycle of a wave of electromagneticenergy. Inversely proportional to frequency.

Wave number The frequency of a wave d ivided by its velocity of propagation; thereciprocal of wavelength.

XXerography A printing process of electrostatic electrophotography that uses aphotoconductive insulating medium, in conjunction with infrared, visible, or ultravioletradiation to produce latent electrostatic charge pa tterns for an observable record.

ZZoom To control, by magnifying or reducing, the size of a televised image, eitherelectronically or optically.

Zoom lens An optical system of variable focal length w ith the focal plane remaining in afixed position. Some components are moved w hile others remain stationary.

Zoom lens

Compiled with help from: Photonics Dictionary,MicroWorlds and OSA Student Chapte rMembers.

Optical Society of America
http://www.osa.org/http://www.osa.org/membership/studentservices/chapters/default.aspxhttp://www.lbl.gov/MicroWorlds/ALSTool/EMSpec/EMSpec2.htmlhttp://www.photonics.com/dictHome.aspxhttp://osa.magnet.fsu.edu/terms/general.html#alphahttp://osa.magnet.fsu.edu/terms/general.html#alphahttp://osa.magnet.fsu.edu/terms/general.html#alpha

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