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transverse mode

In the context of optics and lasers, a transverse mode refers to a specific spatial pattern of the electric field within the cross-section of a laser beam. These modes represent the different...

trapezium distortion

The distortion of an image formed by a cathode-ray tube, caused by unbalanced deflection voltages or deflection voltages that are not symmetrically aligned with the resultant anode potential.

triad

In a color cathode-ray tube, a grouping of three color dots (red, blue and green) that represent one pixel in the final image.

trichromacy

The basis of color vision in the human eye. Three types of cones have been identified, each having a unique spectral response (red, green and blue).

triclinic

With respect to a crystal, having three unequal axes intersecting at angles, only two of which can be equal and only one of which can measure 90°.

trinoscope

A color-television viewing system with three kinescopes, three lenses and three deflection yokes used to form the red, green and blue images required for a tricolor television projection.

triplet

A lens assembly made up of three lens elements that may or may not be cemented.

tristimulus colorimeter -> colorimeter

A colorimeter is a device used to measure and quantify the color characteristics of an object or a light source. It provides objective and standardized color information, typically expressed in terms...

true field

The size of the field of view in the object space of an optical system as differentiated from that in the image space (apparent field).

two-dimensional Fourier transform

The Fourier series representation of a two-dimensional periodic field, assuming that the original image is periodic both horizontally and vertically.

Twyman-Green interferometer

A testing device that provides a contour map of the emergent wavefront for the observer in terms of the given wavelength of the light.

uhlbricht sphere -> integrating sphere

A hollow sphere coated internally with a white diffusing material and provided with openings for incident beam, specimen and detector used for measuring the diffuse reflectance or transmittance of...

ultrasonic holography -> acoustical holography

The optical reconstruction of image information contained in a sound field. First the diffraction pattern, formed by an object irradiated by ultrasonic rays, interferes with a mutually coherent...

ultrasonic imaging

The formation and display of three-dimensional images by ultrasonic energy. In one technique, the energy pulses from an ultrasonic transducer scan the object through a liquid medium and, receiving...

ultraviolet microscopy

The study and photographing of microscope specimens in ultraviolet light; using an optical microscope containing fluorite and quartz components to efficiently image wavelengths much shorter than the...

ultraviolet photomicrography

The photographic recording that uses ultraviolet radiation to irradiate the microscope sample being examined and to form an image of the object on a photographic medium. The components of the...

umbra -> penumbra

A source of light will not cast a distinct shadow of an interfering, opaque object, but will cast a shadow having two parts: 1. the umbra, or the central, totally dark part of the shadow; and 2. the...

uniformly redundant array

Array used in coded-aperture imaging experiments with two-beam CO2 lasers that provide an artifact-free process, faithful reproduction of the true image, and more photon collection than the pinhole...

unit plane -> principal plane

In a lens or lens system, that surface at which the projections of an entering and exiting ray intersect. Also known as the equivalent refracting surface, the principal plane is most often not...

upper rim ray -> rim ray

A ray of an image-forming bundle that passes through the edge of the entrance pupil or aperture stop. Usually used in connection with meridian rays, an upper rim ray is one that passes through the...

V-number -> normalized frequency

Also referred to as the V number in fiber optics; the normalized frequency is a dimensionless quantity, denoted by the symbol V, given by: where a is waveguide core radius, l is wavelength in vacuum,...

vacuum

In optics, the term vacuum typically refers to a space devoid of matter, including air and other gases. However, in practical terms, achieving a perfect vacuum, where there is absolutely no matter...

variable-focus condenser

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....

vector correlation

A machine vision technique of image correlation whereby the correlation kernel (template of the desired image) is transformed into a group of vectors, each representing a specific feature of the...

veiling brightness

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

veiling glare

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

Verdet constant

A factor of an equation of the Faraday effect, which is the rotation of the plane of light polarization by transparent materials in a magnetic field. Therefore, in the equation: where a...

vertical external cavity surface-emitting laser

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...

vertical-cavity laser diode

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.

vertical-cavity surface-emitting laser -> vertical-cavity laser diode

video measuring gauge

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

video scan converter

A device that changes the number of lines per frame of a video image to adapt to a lower resolution format, either by deleting lines, compressing lines or by imaging only a part of the original...

video-intensified microscopy

The observation of specimens by a microscope linked to a television camera and an image processor.

videography

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...

vidicon

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...

view camera

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...

vignetting

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.

virtual histology

Virtual histology refers to the use of digital technology and computational methods to simulate or recreate histological images and structures without the need for traditional physical slides and...

virtual reality

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...

virtual retinal display

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.

voltage contrast analysis

A nondestructive testing method for very large scale integration circuits, using a scanning electron microscope to monitor changes in the electronic state of the chip as it is fed test voltages while...

volume Bragg gratings

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...

volumetric imaging

Volumetric imaging refers to the capture, visualization, and analysis of three-dimensional (3D) information from a volume of space. Unlike traditional two-dimensional (2D) imaging, which provides...

voxel

An element within a three-dimensional data set image.

Wadsworth mounting

A system used for gratings that consists of a concave mirror, a grating and a plate holder mounted normal to the grating to reduce astigmatism and spherical aberration. The mounting yields a...

wafer tube

An image intensifier tube in which the photocathode and the output of the microchannel plate are proximity-focused on the microchannel plate input and output phosphor screen, respectively.

wavefront reconstruction -> holography

Holography is a technique used to capture and reconstruct three-dimensional images using the principles of interference and diffraction of light. Unlike conventional photography, which records only...

wedge ring detector

A diffraction pattern sampling unit composed of a 32-element monolithic silicon photodiode array and a readout unit. The intensity on each detector element can be separately read out by means of a...

wedge

An optical element having plane-inclined surfaces. Usually the faces are inclined toward one another at very small angles. Wedges divert light toward their thicker portions, and may be circular,...

Weissenberg method

The Weissenberg method, named after the German physicist Karl Weissenberg, is a technique used in x-ray crystallography for obtaining high-quality diffraction patterns from single crystals. This...

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