Photonics Dictionary: F

A featherlike flaw in a body of glass.

In image processing and machine vision, the process in which an initial measurement pattern or some subsequence of measurement patterns is transformed to a new pattern feature. In image pattern...

The differential luminance threshold divided by the luminance.

To supply a signal to some point.

The transfer of a part of a device's or circuit's output back to its input.

An amplifying device that returns a portion of its output to its input as a means of modifying the device's performance.

A circuit that permits feedback in an electronic device.

The placement of a device or an additional circuit into a feedback control system to improve its response in relation to a specific characteristic of the system.

A system designed to control the output quantity of a device by returning a portion of its output signal to its input. This results in the manipulation of the input quantity so that the desired...

A waveguide or coaxial cable that transmits a signal from an antenna to a receiver or from a transmitter to an antenna.

The signal-to-noise ratio (SNR) obtained with a Fourier transform spectrometer when detector noise prevails, which exceeds the SNR of a scanning spectrometer in the same time by a factor proportional...

The prefix denoting 10-15. (f).

A femtosecond laser is a type of laser that emits ultrashort pulses of light with durations on the order of femtoseconds, where one femtosecond is equal to 10-15 seconds. These lasers are capable of...

In microscopy, the measured distance between theoretical parallel lines that are drawn tangent to the particle profile and perpendicular to the ocular scale.

The principle that a light ray extending from one point to another will, after any number of reflections and refractions, follow the path requiring the least transit time. This is also known as the...

The mathematical expression of the probability of any given state of energy being occupied when a semiconductor is in thermal equilibrium.

A crystal capable of being polarized in the reverse direction when an electric field is applied.

The region of a ferroelectric crystal where spontaneous polarization is uniformly directed.

Film in which electric polarization is reversible when influenced by an electric field.

Ferroelectric materials are a type of dielectric materials that exhibit spontaneous electric polarization, meaning they possess a permanent electric dipole moment even in the absence of an external...

The phenomenon whereby certain crystals exhibit spontaneous electric polarization. It is analogous with ferromagnetism.

The properties of certain materials that cause them to have relative permeabilities that exceed unity. This permeability permits the materials to exhibit hysteresis.

A mechanical fixture, generally a rigid tube, used to confine the stripped end of a fiber or a fiber bundle.

The law stating that the critical fusion frequency is approximately proportional to the logarithm of the luminance and the area.

A prism with curved faces that collimates, reflects and refracts incident light. Often used in the production of spectrographs.

A multiple-beam interferometer, usually consisting of two flat plates, with high reflective ability. The plates are set parallel to one another by spacers so that lightwaves may bounce back and forth...

A photodetector employing photoregeneration of carriers in the channel region of an FET structure to provide photodetection with current gain.

A type of interferometer noted for producing narrow multiple-beam interference fringes. As a result, when compared with the Twyman-Green, the Fizeau interferometer has fewer optical components, does...

Fluorescence lifetime refers to the average time it takes for a fluorophore, a molecule that absorbs light at one wavelength and emits it at another, to return to its ground state after being excited...

Fluorescence lifetime imaging (FLIM) is an advanced imaging technique that provides information about the lifetime of fluorescence emissions from fluorophores within a sample. Unlike traditional...

Förster resonance energy transfer (FRET) is a mechanism describing the transfer of energy between two closely spaced fluorescent molecules. This phenomenon is named after the German scientist...

The Foucault test is performed by moving a knife edge laterally into the image of a small point source. The eye, or a camera, is placed immediately behind the knife edge, and the exit pupil of the...

Observed lengthening in wavelengths of the optical absorption edge of a semiconductor with the application of an electric field.

A far-field pattern holographically reproduced image that is categorically considered with three-dimensional lensless photographs.

The dark absorption lines observed in the spectrum of the photosphere of the sun. There are thousands of these lines, the most prominent of which were observed and named by Fraunhofer early in the...

A crystal defect that is a combination of a vacancy and an interstitial created by the removal of an ion from a lattice and its placement in an interstitial position.

A free-electron laser (FEL) is a type of laser that generates coherent, high-intensity electromagnetic radiation by using a beam of accelerated electrons as the lasing medium. Unlike traditional...