Photonics Dictionary: D

A telescope similar to the customary Cassegrain telescope, but having a primary mirror that is ellipsoidal and a secondary that is spherical.

In a gas, an electrical discharge that has no luminance.

A disc contained within an electronic cell counter for regulating light transmission.

A technique whereby the sample is illuminated by a hollow cone of light larger than the acceptance angle of the objective, so that only scattered light is seen, revealing any irregularities of the...

Description of a material, such as a water-soluble salt, that will continue absorbing moisture from the surrounding atmosphere until it dissolves into a liquid.

The ray refracted by a sphere of transparent material that travels back as closely as possible to the original path formed by the incident ray.

A discharge lamp filled with deuterium to produce high-intensity ultraviolet radiation for use in spectroscopic analysis.

A telescope that corrects dispersion and spherical aberration through the use of one or more lenses, usually smaller than the objective lens, that are positioned at a distance from the objective lens.

1. An optical device used for projection of enlarged images of transparencies or lantern slides on a screen. 2. A device designed to hold and backlight transparencies so that their images can be...

A device used to investigate the dichroism of crystals.

An eyepiece used in a polariscope or polarizing microscope to give a comparison view of the same object under illumination by the two complementary rays of polarized light.

Differential interference contrast (DIC) microscopy, also known as Nomarski interference contrast microscopy, is an optical imaging technique used in microscopy to enhance the contrast of transparent...

Elastic scattering that occurs when inelastic processes eliminate particles from the beam.

Diffuse reflectance spectroscopy (DRS) is a nondestructive analytical technique used to investigate the optical properties of materials, particularly in the field of spectroscopy. Unlike traditional...

In printing, a translucent screen used with lenses to provide an even distribution of diffused light.

Digital holographic microscopy (DHM) is an advanced imaging technique that combines holography and digital image processing to capture and reconstruct three-dimensional images of objects. This method...

A scale located on the eyepiece focusing screw and used to measure the amount of defocusing of the eyepiece in diopters. The reciprocal of the image distance in meters is a measure of the amount of...

A scanning technique in which the object is illuminated the entire time, and in which picture elements of the object are viewed singly by the television camera.

In a camera, the focusing of an image on the screen located at the camera's film plane. Once the image is in complete focus, the recording medium is inserted in place of the screen.

With respect to atomic fluorescence spectroscopy, the fluorescence that is emitted by an atom at a spectral line of a wavelength that is longer than that of the stimulating radiation.

A small handheld instrument consisting of a slit and collimator that feeds light into a small direct-vision dispersing prism. The eye is placed behind the prism to observe the spectrum of a colored...

A piece of glass that eventually becomes the bifocal segment as it appears prior to being fused to the blank.

A device that provides simple and reliable laser power and energy measurement. Essentially a heat flux sensor producing an output proportional to the power, rather than the energy input.

A colorimeter using a spinning disc made of different colored sections for colorimetric analysis.

A laser having a rod that is a stacked array of discs immersed in a transparent flowing coolant fluid. In this way, the cooling rate is increased, the temperature gradients are basically parallel to...

A composite derived from aluminum alloy powder and silicon carbide, used as an optical substrate in air- and spacecraft applications. It is as light as aluminum but exhibits greater strength and...

An individual circuit component, complete in itself, such as a resistor, diode, capacitor or transistor. It is used as an individual and separable circuit element.

A mathematical transformation used in image and video compression that changes two-dimensional representation of data into data defined by the frequency content. Adapted in JPEG and MPEG standards.

A spectrum of component wavelengths whose values are separate from each other.

The degree to which a vision system is capable of sensing differences in light intensity between two regions.

A circuit incorporated into counter systems that records only pulses that have amplitudes between two preselected limits.

A lens with one surface convex and the other concave, the latter having the greater curvature. It also is known as a diverging meniscus lens.

A scanning technique in optical character recognition in which an array of photocells is used to scan each character to determine its horizontal and vertical characteristics.

A type of transversely excited laser with a uniform arc-free discharge of large cross-sectional area that can be scaled to very large systems.

A CRT screen on which two phosphors differing in color and persistence are deposited.

See periscopic lens; rapid rectilinear lens.

An astronomical scanning technique for capturing images of stars without moving the sensor. To perform a drift scan, a CCD sensor's readout rate must be synchronized with the motion of celestial...

An image-processing device that scans in a straight line parallel to the axis of a rotating cylinder to which the material to be recorded is affixed.

A microscope that has been modified to permit the quantitative analysis of dust samples.

A type of erasable data storage device that uses a medium deposited on the disc in two layers, each dyed to absorb a different wavelength of laser light. To record data, the lower layer is heated by...

A spectroscopic technique used to display the intensity of an optical pulse as functions of time and frequency simultaneously.

A hole filled with dirt such as a polishing abrasive and located in an optical surface. See dig; scratch.

Continuous conversion of oscillatory energy into heat, relative to time or distance.

The portion of a glow discharge tube that permits little or no light transmission.