Photonics Dictionary

Enhanced picture archiving and communication system (PACS) display (ePAD) is a software tool used in medical imaging to view, manipulate, and analyze radiological images, such as x-rays, CT scans,...

The amount of x-rays used to penetrate and diffuse a target sample undergoing electron-probe microanalysis.

The angle between a light ray emerging from an optical system and the optical axis of that system.

A ray that has a nonisotropic speed in a doubly refracting crystal. It does not necessarily obey Snell's law upon refraction at the crystal surface.

A set of rays through a lens originating at a common point and contained in one plane.

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 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...

A fiber optic spectrometer is a device used for measuring the spectral content of light. It utilizes optical fibers to transmit light from a source to a spectrometer unit, where the light is...

An X-Y electrically addressable series of arrays with individual electron emitters bombarding a phosphor-coated transparent plate. The phosphor is induced into luminescence, similar to traditional...

The field of view (FOV) refers to the extent of the observable world or the visible area that can be seen at any given moment through a device, such as an optical instrument, camera, or sensor. It is...

A technique used in radiography to obtain an unblurred image of a moving object by the use of very short x-ray exposures, such as one microsecond, to record the image.

Fluence is a term used in various scientific and technical disciplines to describe the amount of something per unit area. The specific meaning of fluence can vary depending on the context in which it...

The photographic recording of a subject that exhibits luminescence only for an extremely short time (10-8 s) after the exciting source is removed. In the process, the subject may be illuminated by...

A fluorescent screen refers to a phosphorescent or fluorescent-coated surface that emits visible light when exposed to other forms of electromagnetic radiation, such as x-rays or ultraviolet light....

A camera with a very high aperture lens or mirror system for photographing x-ray fluorescent screen images, mainly to save the cost of large pieces of 11 x 14-in. film. The film may be 4 x 5-in. cut...

A lens having an extremely high aperture and used in the recording of x-ray fluorescent screen images. It often is specially designed for the camera, the color of the light and the image...

A microscope that uses a flying spot scanner, directed through the eyepiece, as a light source to determine the features of a transparent specimen. The flying spot is modulated by the varying density...

The focal length of a lens is the distance between the lens's optical center (or principal point) and the image sensor or film when the lens is focused at infinity. In simple terms, it is the...

A linear or two-dimensional matrix of individual detector elements, typically used at the focus of an imaging system.

That point on the optical axis of a lens, to which an incident bundle of parallel light rays will converge.

Decrease in cosmic ray activity that is observed approximately 24 hours after a solar flare, attributed to a shielding effect produced by magnetic fields contained in the plasma of the cloud emitted...

The application of ultraviolet, x-ray, infrared and conventional photography to law enforcement.

Frame rate refers to the frequency at which consecutive images, or frames, are displayed in a video sequence. It is typically measured in frames per second (fps) and determines the smoothness and...

A Fresnel lens is a type of optical lens that consists of a series of concentric grooves or steps carved into a flat, thin piece of transparent material, typically plastic or glass. This design...

A GaAlAs laser is a type of semiconductor laser diode that emits light in the near-infrared region of the electromagnetic spectrum. It is composed of layers of gallium, aluminum, and arsenic, hence...

GaN (gallium nitride) distributed feedback (DFB) lasers refer to a specific type of semiconductor laser based on Gallium Nitride materials and designed with a distributed feedback structure. These...

A field of physics that deals with light as if it truly were composed of rays diverging in various directions from the source and abruptly bent by refraction or turned by reflection into paths...

A type of birefringent polarizing prism that transmits the extraordinary ray and removes the ordinary ray through total internal reflection. It consists of two calcite prisms with an air gap...

In image processing, machine vision and television, discrete brightness values quantized for a group of pixels. They can range from white, through various shades of gray, to black.

An image consisting of an array of pixels that can have more than two values (black and white). Typically, up to 16 levels are possible per pixel.

Image enhancement operations that involve altering gray-scale values. For instance, brightness sliding involves adding or subtracting an identical brightness value to or from each pixel in an image;...

A telescope with an ellipsoidal secondary concave mirror that reflects rays from a parabolic primary mirror through an opening in the center of the primary, where the image is viewed with an eyepiece.

The soft x-rays used in the industrial radiography of materials having too small a range of densities to produce an image with normal x-rays.

A GRIN (gradient index) lens is a type of optical lens that utilizes a gradient in refractive index across its volume rather than having a uniform refractive index like conventional lenses. This...

1. In a cathode-ray tube, the glow surrounding a bright spot that appears on the fluorescent screen as the result of the screen's light being reflected by the front and rear surfaces of the tube's...

Text or images printed on paper or another tangible medium, as opposed to those viewed electronically on a cathode-ray-tube screen.

A type of x-ray that is capable of deep penetration; its wavelength is about 10-8 cm.

A test for spherical aberration, coma or astigmatism in which incident rays from a point source are isolated by small holes in a metal disc located close to the lens or mirror under test....

An optical system that superimposes a synthetic display providing navigational or weapon-aiming information on a pilot's or driver's field of view. The system includes a cathode-ray tube, collimating...

High harmonic generation (HHG) refers to a nonlinear optical process in which intense laser light interacts with a gaseous medium, typically an atom or a molecule, to produce harmonics of the...

A method of producing x-ray exposures as short as 0.03 µs; the primary application is in ballistic radiography.

The perceptual term for that aspect of color described by words such as red, yellow or blue. Achromatic colors, such as white, gray and black, do not exhibit hue.

A device where each pixel in the detector array is mated with a preamplifier on a single silicon chip, providing sensing and signal processing capabilities.

A hyperspectral imaging camera is a sophisticated imaging device capable of capturing and processing data across a wide range of wavelengths within the electromagnetic spectrum, typically from...

A crystal that is devoid of any mosaic structure and that can reflect x-rays, relative to the Darwin-Ewald-Prins law.

Also referred to as image visibility, the contrast of an image is the variation in the intensity of an image formed by an optical system, where the image pixels are defined on a gray scale scheme of...