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Definitions: E

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E-bend
In a waveguide, a change in direction of the axis without deviating from the plane of polarization.
Eberhard effect
Observed phenomenon of a small developed image with higher density than a larger image because of variation in photographic plate densities with variations in size of opening.
eccentric mounting
A lens mounting with eccentric rings that may be rotated to shift the axis of the lens to a prescribed position.
eccentricity
In the tolerancing of optical elements, the displacement of the optical axis from the mechanical axis.
echelette grating
A diffraction grating with lines and grooves formed so as to concentrate the radiation of a particular wavelength into one specified order. This device is efficient when used in the infrared region...
echelle
A grating that serves to provide higher resolution and dispersion than the average grating, and still has a greater free spectral range than either the Fabry-Perot etalon or the reflection echelon.
echelle grating
A specialized form of diffraction grating consisting of assembled glass plates of equal thickness that resemble a flight of stairs. The light enters through the largest plate at the end and emerges...
edge
The flat or angled surface, usually fine-ground, that limits the aperture of a lens or prism surface.
edge contrast -> acutance
In photography, the density gradient across an edge separating light from darkness, a physically measurable quantity that correlates well with subjectively observed sharpness of definition. By...
edge detection
In image processing, the location of edges by employing templates that respond to the first or second derivative of gray-scale intensity in the neighborhood of each pixel.
edge enhancement
In image processing, any operation that strengthens information about the edges of objects displayed. Three types of spatial filtering are used: shift and difference, gradient and Laplacian.
edge filter -> bandpass filter
A filter with a transmission that is high for a particular band of frequencies, but that falls to low values above and below this band.
edge following
In image processing, a segmentation algorithm for isolating a region in an image by following its edge.
edge response
Intensity distribution in the image of an edge. The gradient of the edge-response curve is a measure of the image quality of the optical system under test.
edge sensing, second derivative
Technique for the precision evaluation of coincidence of a laser beam's center with the edge of the object under study and exact location of that edge by means of a double electronic differentiation...
edge thickness difference
The maximum variation in thickness of a lens as measured around a diameter centered on the optical axis. The ETD divided by that diameter yields the wedge of the lens.
edge-defined film-fed growth
Process for growth of solar cells that results in rectangular shapes consisting of many interconnected cells in a series or series-parallel arrangement. EFG cells show increased efficiency with...
edge-emitting LED
An edge-emitting light-emitting diode is a type of LED structure where light emission occurs primarily along the edge of the semiconductor chip rather than from the surface. Edge-emitting LEDs are...
edging
The finishing of the edge of an optical element by grinding.
effect filter
A color filter, generally used in photography, to emphasize certain color tones and to modify others in a picture for a more dramatic image. A blue effect filter, for example, darkens red and yellow,...
effective f number
For a lens with an obscured or noncircular aperture, the focal length divided by the effective aperture.
effective aperture
1. That portion of the aperture that functions to collect energy and deliver it to the final system detector. 2. For an obscured or noncircular aperture, the equivalent nonobscured, circular aperture.
effective beam
In photoelectric sensing, the portion of the transmitted beam that actually functions in the system; the diameter of the beam that determines the presence or absence of an object by being blocked or...
effective color
The color of an object when it is illuminated by a nonisophotic source.
effective data rate
A characterization of the throughput performance of data storage systems; the EDR is the total of data retrieved divided by the total time it takes to retrieve it, expressed as megabytes per second.
effective focal length -> focal length
The focal length of a lens is the distance between the lens's optical center (or principal point) and the image sensor or film when the lens is focused at infinity. In simple terms, it is the...
effective numerical aperture
The real numerical aperture (NA) of a fiber when the computed NA is not valid because of change in the glass indices during drawing and fusion.
efficiency
As applied to a device or machine, the ratio of total power input to the usable power output of the device.
egg-crating
A weight reducing method whereby material from the rear of a reflector is removed leaving a pattern of ribs normal to the surface in an egg-crate pattern.
eikonometer
A scale attached to a microscope eyepiece that is seen superimposed on the image and that is used to measure the dimensions of the viewed object.
einstein
A unit of energy equal to the amount of energy absorbed by one molecule of material undergoing a photochemical reaction, as determined by the Stark-Einstein law.
Einstein coefficients
Three proportional coefficients labeled Am, Bmn, and Bnm, that respectively characterize the rate of spontaneous emission, induced emission, and absorption of radiation by an atom, ion or molecule.
Einstein shift
A shift in the direction of the red in the spectral lines of light which, defined by the relativity theory, will have decreased frequencies upon emerging from a highly gravitational field.
elastic scattering
Scattering caused by the interaction between ingoing and outgoing particles of the same type, with no loss of kinetic energy.
elasto-optic effect
A change in the refractive index of an optical fiber caused by variation in the length of the fiber core in response to mechanical stress.
elastomer
Any material of a macromolecular nature that can stretch at room temperature to more than twice its length and return to approximately its original shape when stress is released.
elaterite
The organic inclusion in quartz crystal that forms delicate films and microspheres and that shows a maximum absorption at 450 nm.
elbow telescope
A refracting telescope that uses a prism to bend the line of sight 90°.
electric arc -> arc discharge
The electric arc that is a particular discharge between two electrodes in a gas or vapor which is characterized by high cathode densities and a low voltage drop.
electric CO laser
An electrically excited laser having carbon monoxide as the lasing material and in which lasing occurs in a partial inversion between adjacent, vibrational fields. Vibrational energy is cycled...
electric dichroism spectroscopy
The use of a krypton laser system for the measurement of small molecules aligned by an electric field, by analyzing the absorption of linearly polarized light.
electric lamp
Any lamp whose emission of radiant energy is dependent upon the passage of an electrical current through the emissive medium.
electric quadrupole lens
A device that uses four electrodes set in an alternating positive-negative polarity series to focus the beams of charged particles employed in electron microscopes and particle accelerators.
electric stroboscope -> stroboscope
A device that produces brief flashes of light for observing the behavior of an object during a short interval. One of the most effective means for accomplishing this is a gaseous tube energized by...
electric vector
The electric field associated with an electromagnetic wave and thus with a lightwave. The electric vector specifies the direction and amplitude of this electric field.
electric-discharge lamp
A lamp that uses the transmission of an electric current through a gas or vapor to produce illumination. Neon, mercury and argon lamps are examples of electric-discharge lamps.
electrical length
Expression of the length of a transmission medium in terms of wavelengths of the propagating wavelength. In general, electrical length is an expression of physical length in wavelengths, radians or...
electro-optic deflection
The effect whereby a light beam is deflected by a birefringent prism when its polarization is changed by voltage applied to an electro-optical crystal through which the beam passes. The deflection of...
electro-optic deflector
An electro-optic deflector is a device that can change the direction of light beams using an electric field. It operates based on the electro-optic effect, which involves the modulation of the...
electro-optic detector
A device that detects radiation by utilizing the influence of light in forming an electrical signal. It may be a phototube; a photoconductive, photovoltaic or photojunction cell; a phototransistor;...

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