Photonics Dictionary: E

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.

A device consisting of an airtight quartz tube that holds the material to be analyzed. When a high-frequency electrostatic field, generated by microwaves, is applied to the tube, it emits energy of a...

An electrochemical process of metal fabrication using an electrolyte, an anode to supply the metal, and a control of the electrical current and of the deposit of metal on the matrix of a reflector.

The deposition of a metallic coating, usually nickel, on a component by chemical means rather than by electroplating; the component is immersed in a solution containing a reducing agent.

The freeing of electrons from an electrode into the surrounding space.

A nonmagnetic instrument utilizing an electrofocus and deflection tube with a photocathode for imaging purposes. The optical image is converted into a photoelectric output at the photocathode and is...

A process used in document copying and printing that involves the visible rendering of an invisible electrostatic image on a photoconductive material by its treatment with oppositely charged pigment...

A hologram imprinted on plastic or another medium; e.g., those commonly found on credit cards.

The line or lines emitted by an element when its radiation particles travel from one energy level to another.

A type of electron microscope in which the specimen also serves as the cathode source.

Thermal emission caused by the unity in absorption bands that must be discriminated when calculating radiation intensity of any celestial object.

A study of the energies and wavelengths of radiation emitted by atoms and molecules when particular physical conditions are applied to them.

An emission spectrum is a graphical representation or a characteristic pattern of the wavelengths or frequencies of light emitted by a source, such as an atom, molecule, or celestial object. It shows...

The emissivity of a body times the emissive power of a blackbody at the same temperature. For a blackbody, it is the total radiation per unit area of radiating surface.

The ratio of an object's radiance to that emitted by a blackbody radiator at the same temperature and at the same wavelength.

A computer-generated routine for achieving true-temperature readings in thermal infrared imaging systems.

The use of a material's emissivity to measure absorption. It is useful as an absorption loss measurement technique, since at thermal equilibrium, emittance is equal to absorptance.

An enzyme-linked immunosorbent assay (ELISA) is a laboratory technique used to detect and measure the presence of specific substances, such as antibodies, antigens, proteins, hormones, or other...

A factor, F, indicating the increase in shot noise in an avalanche photodiode as compared with the ideal multiplier, which is noiseless. The noise, which results from variations in avalanche gains,...

A type of optical fiber loss resulting from the misalignment of fibers in a splice or connector.

Synonym of extrinsic fiber loss.

In a waveguide, a change in direction of the axis without deviating from the plane of polarization.

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.

A lens mounting with eccentric rings that may be rotated to shift the axis of the lens to a prescribed position.

In the tolerancing of optical elements, the displacement of the optical axis from the mechanical axis.

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...

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.

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...

The flat or angled surface, usually fine-ground, that limits the aperture of a lens or prism surface.

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.

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.

In image processing, a segmentation algorithm for isolating a region in an image by following its edge.