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233 terms

Photonics Dictionary

1. With respect to radiation, a device used to attenuate particular wavelengths or frequencies while passing others with relatively no change. 2. See digital filter.

filter factor

The necessary increase of a photograph's exposure time as the result of the additional absorption of light by the filter being used.

filter grating

A grating used as a reflectance filter, particularly in the far-infrared. Small plane gratings, blazed for the wavelength of the unwanted radiation, are produced for this purpose.

filter kernal

A function used in a convolution filtering operation. The image to be filtered is convolved with the filtering kernel to obtain the enhanced image.

filter spectrophotometer

A spectrophotometer that makes use of filters to isolate narrow bands of the spectrum.

filter wheel

A device that holds a number of filters and allows the filter with the desired characteristics to be rotated into an optical aperture.

acousto-optic tunable filter

A bulk crystalline optic which permits the propagation of light through a volume of index altered material. The variation in refractive index along the material volume is due to a piezoelectric...

band-elimination filter

A filter that suppresses a given range of frequencies, transmitting only those above and below that band. Also called bandstop 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.

bandstop filter -> band-elimination filter

A filter that suppresses a given range of frequencies, transmitting only those above and below that band. Also called bandstop filter.

binary phase-only filtering -> phase-only filter

A type of matched filter that responds only to the phase of incoming light; the output has a much greater intensity than that of a classical matched filter, which responds to phase and amplitude. The...

birefringent filter

A filter that transmits light in a series of sharp, widely spaced wavelength bands by its sandwich construction of alternating layers of polarizing films and plates cut from birefringent crystal.

broadband filter

A broadband filter is an electronic or electromagnetic device designed to pass a range of frequencies or signals within a specified bandwidth while attenuating or rejecting signals outside of that...

Butterworth filter

An electric filter that is characterized by a passband of the flattest possible shape.

Christiansen-effect filter

A transparent powdered solid immersed in a liquid or plastic of similar refractive index but widely different dispersion; used to isolate narrow spectral regions.

circular variable filter

An optical interference coating, vacuum-deposited on a circular substrate, whose transmission characteristics may be varied by physical rotation.

clear filter -> compensating glass

Also known as clear glass or clear filter. The clear glass plate is used to simulate a filter, in converging or diverging light, to maintain focus.

color conversion filter

A filter that serves to alter the color temperature and the mired value of the radiation emitted by a source.

color filter -> optical filter

An optical filter is a device that selectively transmits or blocks specific wavelengths, or colors, of light. Optical filters are used to control the spectral content of light in various...

comb filter

A filter that passes a series of wavelength regions that are at equal distances from one another, such that its output resembles the teeth of a comb. In video transmission, a comb filter is used to...

compensating filter

A filter used in photography to change the spectral composition of light entering a camera, or to adjust color balance during printing.

composite wave filter

A transducer composed of more than one high-pass, bandpass, low-pass or band-elimination filter.

contrast filter

A filter designed to improve contrast in an imaging system. For visual and black and white photosystems, a yellow filter is used.

crystal filter

A bandpass filter with piezoelectric crystal components for the passage or impedance of electrical signals of various frequencies.

dielectric filter -> interference filter

A filter that controls the spectral composition of transmitted energy partially by the effects of interference. Frequently, these filters are made up of thin layers of metals and dielectrics,...

diffuse-cutting filter

A color filter that is designed to gradually increase or decrease its absorption with wavelength.

diffusing filter

A filter purposely made to be placed before a lens to render the image rather unclear.

digital filter

A linear computation or algorithm performed on a selected series in the form of an input signal that produces a new series as output. The computational device may be a specifically designed...

dispersion filter

A complex filter that uses polarization and interference to transmit light that is nearly monochromatic.

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.

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,...

electron filter lens

An electrostatic device that uses an electric potential barrier to allow the transmittance of electrons at or above a set level of energy while stopping the passage of those below it.

exciter filter

In ultraviolet and fluorescence photography, the term applied to the filter used in the photographic system and with the exciting source to screen out ambient radiations and to transmit the exciting...

flash photographic density filter

A filter, partially opaque to near-ultraviolet, visible and infrared radiation, that may be made by exposing and processing photographic film. Such materials are almost equally opaque to radiation of...

gas filter correlation

A technique for measuring the concentration of any gases. Identical infrared beams are alternately chopped, one passing through a reference cell and the other passing through a cell with the gas...

gray filter -> neutral density filter

A light filter that equally decreases the intensity of all wavelengths of light without altering the relative spectral distribution of the energy.

haze filter

A filter, used in photography, that absorbs the ultraviolet and extreme blue violet radiation scattered by atmospheric haze.

heat filter -> heat-transmitting filter

A filter that allows heat radiation from an incident beam to pass without absorption or reflection.

heat-absorbing filter

A glass filter that transmits visible light while absorbing infrared energy (heat).

heat-transmitting filter

A filter that allows heat radiation from an incident beam to pass without absorption or reflection.

high-pass filter

A filter possessing one transmission band that extends from a cutoff frequency other than zero to frequency at infinity.

holographic matched filter

A specific type of hologram that will transmit a pure plane wave when the hologram is illuminated by the type of wave it is matched to.

ideal filter

Any filter in which the range of frequencies within a chosen radius suffers no attenuation and the range of frequencies outside the radius is entirely attenuated.

infrared filter

A filter exhibiting transparency, absorption or reflectance characteristics specifically for spectral control of wavelengths longer than 700 µm.

interference filter

A filter that controls the spectral composition of transmitted energy partially by the effects of interference. Frequently, these filters are made up of thin layers of metals and dielectrics,...

invisible light filter

A filter that transmits infrared and ultraviolet but is opaque to visible radiation.

kinoform filter

A computer-generated kinoform used for data processing because of its use of incoherent light and its wide field of view, which facilitates parallel processing of two-dimensional data.

laser line filter

A narrow linewidth optically transmissive or reflective component intended for use with a highly monochromatic or single mode source.

light balancing filter -> color conversion filter

A filter that serves to alter the color temperature and the mired value of the radiation emitted by a source.

light filter

A homogeneous optical medium or coating that transmits only in particular regions of the spectrum. It is used to change or modify the total or relative energy distribution of a beam of light.

Photonics Dictionary