Photonics Dictionary: I

In a heterodyne optical receiver, the frequency that is the difference between that of an incoming laser signal and that of the local oscillator laser. Also called beat frequency.

In an optical system with a series of lenses, images formed prior to the final focal plane.

With reference to absorbance, absorptance, transmittance and the like, the processes occurring within a specimen between the entry and exit surfaces.

The effect in which photons are absorbed and excite the electrons; the electrons move from the valence band to the conduction band (intrinsic photoeffect), from the valence band to impurity levels or...

The creation of free electrons within a solid by the absorption of a sufficient amount of photons. The effect produces an increase in the conductivity of the solid.

A material that is present or added to a sample undergoing spectroscopic analysis, to serve as an intensity reference for spectral measurements.

A spectral line of an internal standard; used to compare radiant energy of the line being analyzed.

A nonoptical surface, within lenses and lens mounts, that contributes largely to flare by reflecting light into the image space. As a result, such surfaces, so located, are finished with a dull...

The ratio of the radiant power transmitted to the second surface of a medium to the corresponding radiant power that has just passed through the first surface. Internal transmittance does not denote...

A unit of measurement of luminous intensity based on a physical standard, a set of calibrated carbon filament lamps. The old candle unit was superseded by the new candle or candela.

The internet of things (IoT) refers to a network of interconnected physical devices, vehicles, appliances, and other objects embedded with sensors, actuators, software, and network connectivity....

The distance between the two eye pupils when the observer is viewing distant objects (normal = 62 mm).

Measures the refractive indices axially from the fiber profile. Microscopy technique provides an interferogram with high contrast with demonstrated improvements in relation to the Pluta two-beam...

The separation between the exit pupils of a binocular instrument. This usually is adjustable so that it can be set equal to the observer's interocular distance, a normal range being from 55 to 75 mm.

Sharp and narrow absorption lines found in the spectra of stars. They result from the absorption of a part of a star's emittance by interstellar gases.

An absorbing coating medium between fibers, used in some fused fiber optic plates to absorb unwanted light. Such coatings are sometimes called EMA (extramural absorption).

A position inside a crystal lattice that is not one of the proper lattice sites in the crystal. Impurity ions of the proper size can occupy such positions in an otherwise regular lattice.

With respect to laser radiation, the subjection of the human eye to all or a portion of the laser beam.

That distortion resulting from dispersion of the group velocity of a propagating mode. It is the only distortion occurring in single-mode waveguides.

A lens that is implanted within the eye to replace the eye lens, which has been removed because of cataract or other defect.

Intravital microscopy is an imaging technique used to visualize biological processes within living organisms, typically in real-time. Unlike traditional microscopy, which involves the examination of...

A photodetector composed of a photoconductive material that, when exposed to radiation, conducts without the aid of added impurities and does not have to be cooled to the level of extrinsic material....

Loss intrinsic to the fiber caused by parameter (core dimension, profile parameter) mismatches when two nonidentical fibers are joined.

The absorption of a photon raising an electron across the forbidden gap from valence to conduction band of the semiconductor where conductivity is increased and incident radiation may be measured.

The photoemission that would occur if a crystal were pure and its structure perfect.

A material often used in the construction of optical instruments because of its low coefficient of thermal expansion (0.9 x 10-6/ °C).

Collisional absorption of energy that occurs in inertial confinement fusion systems when hydrodynamic expansion of the plasma causes an electron passing through the field of an ion to absorb...

The interaction between a photon and an energetic electron, caused by collision, that transfers energy from the electron to the photon, thus raising the energy of the photon.

The changing of the kinetic energy of a mobile electron into radiant energy, as in formation of x-rays.

The resulting contraction or expansion of a piezoelectric crystal along an electric axis when the crystal is under the influence of an electric field in the same direction.

Any problem that requires retrieval of the distribution of some internal properties, such as temperature concentration, etc., from remotely sensed data.

The law stating that the illuminance (or irradiance) from a point source varies as the inverse square of the distance between the source and the receiver.

See inverted image; population inversion.

An image that is similar to the object but rotated 180° about the axis of the system.

A microscope designed so that the specimen is located face down above the objective.

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

A development aimed at extending the life of a tungsten filament. The iodine vapor in the lamp envelope combines with the tungsten vapor emitted by the hot filament, but the compound is decomposed by...

A fusion system conductor capable of carrying current in opposite directions in alternating time phases.

An atom that has gained or lost one or more electrons and, as a result, carries a negative or positive charge.

The ejecting of ions from the surface of a material.

A method of fabricating a graded-index optical waveguide by means of an ion exchange process.