Definitions

In a crystalline substance, the spectral range of states of energy that contains the crystal's binding valence electrons.

Van der Waals forces refer to the attractive or repulsive forces between molecules (or parts of molecules) that arise from fluctuations in electron distribution. These forces are relatively weak...

Lasers based on neodymium-doped yttrium or gadolinium vanadate crystals. These include yttrium vanadate (Nd:YVO4), gadolinium vanadate (Nd:GdVO4), and lutetium vanadate (Nd:LuVO4). Vanadate lasers...

A method of cleaning and drying coated optical components. The cooled parts are placed in a container above a boiling solvent, whose vapors condense on the parts. When the parts reach the temperature...

An Abbe condenser in which the upper lens element is fixed. The lower lens may focus the illumination between the elements so that it emerges from the fixed lens as a large-diameter parallel bundle....

The bands found by Vegard in the spectrum of the aurora borealis and by Kaplan in the nitrogen afterglow. They are formed by the effect of metastable nitrogen molecules.

A brightness, superimposed on the image of the retina, that decreases its contrast and that often results in decreased visibility.

Diffuse stray light at the image plane of an optical system that results in reduced contrast and resolution.

Short-distance scattering of light in holography caused by random index inhomogeneities and the developing index that interferes with the incident beam, thus recording a hologram of the scattered...

The degree to which a pair of fine lines can be aligned to each other. A normal observer will demonstrate an accuracy of 10 arc seconds and a repeatability of 5 arc seconds.

The reciprocal of the back focal distance of a spectacle lens.

With respect to a television system, a pulse transmitted at the end of each field to break off the cathode-ray beam as it begins the next field.

A laser that has a surface-emitting semiconductor gain element coupled to an external mirror designed to complete the laser resonator. VECSELs can be electrically or optically pumped. The extended...

In television system specifications, the number of parallel horizontal black and white lines of equal thickness, that can be resolved from top to bottom of the raster. (One line equals either a black...

With respect to microscopy, light that is directed through the specimen by a substage condenser.

A type of surface-emitting laser diode that uses dielectric mirrors to produce surface emission. The laser cavity is established in a vertical direction with respect to the plane of the active region.

Two electrodes that shift the electron beam vertically on a cathode-ray tube screen using electrostatic deflection.

Consists of a pair of radio telescopes concentrated on a single celestial object. This technique creates a single radio telescope with a diameter equal to the distance between the pair, which allows...

In integrated circuits, a pathway, hole, or other passage through the substrate.

Vibrational circular dichroism (VCD) is a spectroscopic technique used to probe the chiral properties of molecules. It measures differences in the absorption of left- and right-circularly polarized...

A vibrational transition refers to a change in the vibrational energy of a molecule. Molecules consist of atoms that are connected by chemical bonds, and these atoms are not stationary but are in...

A device, such as a thermionic or crystal diode, that is introduced into the vision channel of a television receiver to select the signal from the intermediate-frequency carrier.

A display standard no longer in use and originally defined for IBM PCs, with 640 3 480 pixels in 16 colors and a 4:3 aspect ratio. There is also a text mode with 720 3 400 pixels. The standard has...

A device that calibrates the size, position or distance of objects imaged on a video screen.

Videography refers to the process of capturing moving images and recording them in a digital format. It involves the use of video cameras, lighting equipment, and audio recording devices to create...

A small television tube originally developed for closed-circuit television. It is about 1 inch in diameter and 5 inches long. Its controls are relatively simple and can be operated by unskilled...

A camera that permits adjustments in the perspective of an image; this is accomplished by the camera design, which permits tilt, swing, rise or fall of the image transmitted. Also known as a...

In an optical system, the gradual reduction of image illuminance as the off-axis angle increases, resulting from limitations of the clear apertures of elements within the system.

The product of the actual base or baseline of a rangefinder or heightfinder, and the power or magnification of the instrument.

An image that is formed when rays emerging from an optical system are diverging from the optical axis. The virtual image is formed where the bundle of diverging rays appear to intersect each other...

Virtual reality (VR) is a computer-generated simulation of a three-dimensional environment or experience that can be interacted with and explored by an individual using electronic devices, such as a...

The use of miniature scanners to project raster-scanned video images directly onto the surface of the human retina, eliminating the need for a projection surface.

The maximum distance at which the eye can perceive and evaluate objects.

1. An instrument used to determine the visual range in an environment. 2. A type of photometer that artificially reduces an object's visibility to threshold limits and records the quantity of...

That term pertaining to the spectral region that can be perceived by the eye.

An instrument that uses an erbium:glass laser to determine cloud height from the ground.

The numerical definition of the ability of an observer to perceive fine detail. The average value may be taken as one minute, or 6.7 cycles/mm, at 250 mm (normal viewing distance).

An imaginary line between the object, through the nodal point of the eye, and the fovea, or point of finest retinal acuity.

A pair of stars (double star) that can be seen separately with a telescope, generally by setting a filar micrometer for the separation and position angle. Observation of visual binaries improves with...

Visual detection and ranging (ViDAR) is a technology that utilizes optical sensors, such as cameras or other imaging devices, to detect and track objects in the surrounding environment. Unlike...

The angular field of view that is seen by the eyes when fixed on a point straight ahead. The normal binocular visual field is approximately 130° in diameter.

Having the characteristics of glass.

The transparent fluid that fills the portion of the eye between the eye lens and the retina (the posterior chamber).

A blank area (caused by insufficient inking of the paper) that falls within the range of an intended character stroke in an optical character-recognition system.

The induced birefringence in isotropic gases that results when the gases are placed in strong fields.

Volume Bragg gratings (VBGs) are specialized optical elements that consist of periodic variations in refractive index throughout the volume of a transparent material, typically a photosensitive glass...