Photonics Dictionary

Ratio of the radiant flux at a particular wavelength lm to that at any other wavelength l, such that both radiations produce equally intense luminous sensations. The wavelength lm is chosen so that...

Radiance per unit wavelength interval at a given wavelength, expressed in watts per steradian per unit area per wavelength interval.

Spectral repeatability refers to the consistency and reproducibility of spectral measurements across multiple trials or instances. It is a measure of how well a measurement instrument or system can...

A spectral signature, in the context of remote sensing and spectroscopy, refers to the unique pattern or characteristic spectral response of a material or object across different wavelengths of the...

An automatic scanning instrument that is used to study a substance's fluorescence over a wide range of wavelengths. It consists of a radiation source, a grating that functions as the monochromator in...

Spectra can be conveniently recorded on photographic film or plates. The portions that are occupied by regions of the recorded developed images on the film or plate can be determined with some...

An optical instrument for forming the spectrum of a light source and recording it on a film. The dispersing medium may be a prism or a diffraction grating. A concave grating requires no other means...

The slits in a spectrograph that form images of spectral lines. Slits may be bilateral or unilateral, and generally close down to 0.01 mm and open up to almost a whole millimeter. The edges of the...

An instrument in which an image of the sun is scanned by the entrance slit of a monochromator, the exit slit simultaneously scanning a photographic plate for analysis of the solar spectral lines. If...

An instrument similar to the spectroheliograph, but having a scanning method that is performed by a pair of rapidly oscillating slits or a rotating glass block located before a pair of fixed slits at...

A high-contrast transparency of the gas sought, or an array of exit slits that correlates with some features of the spectrum. No standardized formula for positioning, number or thickness has been...

A kind of spectrograph in which some form of detector, other than a photographic film, is used to measure the distribution of radiation in a particular wavelength region.

An analytical technique used to determine, identify and localize impending malfunctions. It is based upon quantitative and qualitative measurement of submicroscopic particles suspended in lubricating...

A spectroradiometer is a device used to measure the intensity of light at different wavelengths across the electromagnetic spectrum. It provides a detailed spectral distribution of light, breaking...

In a general sense, any one of a class of instruments used to disperse radiation, visible or invisible, into its component wavelengths and for determining or measuring the resultant spectrum. In a...

Spectroscopy is a technique used in the study of interactions between matter and electromagnetic radiation. It involves measuring and analyzing how different materials absorb, emit, or scatter light,...

A scanning device used to cyclically tune through a given frequency range to determine the amplitude-frequency distribution of the signals present, usually by displaying output on a chart or...

Pertaining to the manner in which light is reflected, as by a mirror or speculum.

A spheric lens, also known as a spherical lens, is a type of optical lens with at least one surface that is part of a sphere. This means that the lens surface is curved in a symmetrical manner,...

Spherical aberration is an optical aberration that occurs when light rays passing through a lens or curved optical surface do not converge or diverge to a single focal point. Instead of focusing to a...

A semiconductor laser that operates in the infrared and that is pumped with strong pulses of radiation from a second laser. Dependent on quantum-mechanical principles, it can be tuned over a large...

A loose term for a single polishing machine. In a lens factory it is the minimum unit of production.

A device through which scintillations are observed or counted through a magnifying lens system.

A close-up lens, semicircular in shape, that is mounted in front of a conventional lens focused at infinity. The result is an image made up of two sections; one focused through the split lens on near...

A cooling system used to attain and maintain desired low temperatures in infrared systems. The Stirling type is a mechanical refrigeration system capable of temperatures from 10 to 77 K.

A mask-alignment microscope used to produce and inspect microcircuits in the electronics industry. It provides flat-field, distortion-free images at all magnifications with a high-intensity vertical...

Radiation emitted when a quantum mechanical system drops spontaneously from an excited level to a lower level. This radiation is emitted according to the laws of probability without regard to the...

The probability that an atom in one state will move spontaneously to a lower state within a given unit of time.

Sputtering equipment is machinery used in the process of physical vapor deposition (PVD), specifically sputtering. Sputtering is a method of depositing thin films of material onto a substrate surface...

A sputtering target is a solid material used in the process of physical vapor deposition (PVD), specifically sputtering. Sputtering targets are typically made of metals, metal alloys, or compounds...

A plane-parallel interferometer that yields extremely high contrast over a wide range of finesse values without significantly reducing transmission.

In microscopy, a calibrated scale on a slide that may be viewed to determine the exact magnification factor of the microscope.

The refraction that would take place in an idealized atmosphere where the refractive index is reduced uniformly with height at the rate of 39 x 10-6 per kilometer.

In infrared imaging systems used for mass screening of printed circuit boards or other quality control applications, an image of an ideal component that is stored in the system's memory and then...

The combination of two waves having the same frequency and amplitude and traveling in opposite directions. Standing waves are indicated by a stationary set of nodes spaced one-half wavelength apart...

In a laser, the voltage necessary to initiate electrical discharge, somewhat higher than that needed to sustain it.

A technique for creating optimal performance in a system by producing a specific beam irradiance distribution, usually through the use of geometric optics. A common design involves the use of ray...

STED microscopy, or stimulated emission depletion microscopy, is a superresolution imaging technique in fluorescence microscopy that surpasses the diffraction limit, enabling the visualization of...

The utilization of photometric measurement to determine the relative magnitudes of the heavenly bodies.

An optical fiber in which the core is of uniform refractive index.

A profile of an optical component, usually a fiber, in which the core is of uniform refractive index and the cladding or surrounding optical surface of a different, usually lower, index.

A positioning drive that rotates a fraction of a 360° turn when the motor coils are activated, resulting in linear or rotary motion. They are generally one of two types, either variable...