Photonics Dictionary

In optical character recognition systems, the identification of a character facilitated by means of known factors governing its appearance in a particular context; e.g., the first character in the...

Continuous wave (CW) refers to a type of signal or transmission where the signal is constant and does not vary with time. In various contexts, the term is used to describe continuous, uninterrupted...

A method in optical character recognition in which a mobile light beam scans the outlines of characters for subsequent reading of these outlines.

A large-scale, precise drawing of the contours of a perfect mechanical part, often with plus and minus tolerances drawn or indicated. For quality control decisions, enlarged images of mechanically...

An inspection device in which the profile of a mechanical part is projected onto a ground-glass screen at a precisely known magnification so that the shape of the part can be compared with a scale...

Selection of specific brightness values or minimum threshold levels as contingencies for the display of digital data.

The apparent difference in brightness between light and dark areas of an image. For a light target against a dark background, contrast is computed as follows: where Lt is the luminance of the...

1. In optics, the bending of light rays toward each other, as by a convex or positive lens. 2. Turning in the eyes to view a near object. 3. In a television picture tube, the crossing of the...

Convex is an adjective used to describe a surface or shape that curves outward, bulges, or has a rounded and outwardly extending appearance. In the context of geometry or optics, a convex shape is...

An image-enhancement technique in which each pixel is subjected to a mathematical operation that groups it with its nearest neighbors and calculates its value accordingly.

A powerful and flexible machine-learning approach that can be used in machine vision to help solve difficult problems. Inspired by biological processes, multiple layers of neurons process portions of...

The simplest lens in which all primary aberrations may be corrected. It consists of two positive crown elements on either side of, and spaced away from, a negative flint element.

An infrared detector that achieves a specified sensitivity through the application of certain cryogenic temperatures.

A camera mounted on an optical bench with an easel to hold the material to be copied. Magnification can be varied over a wide range by sliding the camera and easel.

The mechanical modification of the shape of the cornea to correct a vision defect.

A corner cube, also known as a corner reflector or retroreflector prism, is a type of optical device used to reflect light or electromagnetic waves back towards their source with minimal deviation in...

A compound prism formed by cementing together two 30° prisms, one of right-handed and one of left-handed quartz. It has good ultraviolet-transmitting qualities and no double refraction.

A prism formed by dividing a Nicol prism in a plane parallel to the path of vibration of the transmitted light and taking out the wedge-shaped piece. After the pieces are rejoined, the planes of...

A technique for removing thermal noise and drift from focal plane assemblies by sampling the system output between views of scene elements and then subtracting the resulting value from the subsequent...

Law relating the illuminance (or irradiance) of a surface to the cosine of the angle, q, between the normal to the surface and the direction of the incident wave.

The ongoing expansion of the universe based on observations of the recession of distant galaxies from each other as evidenced by the redshift in their spectral lines.

A rangefinder on a camera that is integrated with the focusing mechanism so that when an object's range is determined, the camera is automatically in focus.

A technique used in integrated optics where a groove is cut on a substrate surface and covered by a thin film to facilitate the construction of filters, resonators, beamsplitters and grating couplers...

A coverslip, also known as a cover glass or cover slip, is a thin and flat piece of transparent material typically made of glass or plastic. It is used in microscopy to cover a specimen mounted on a...

A glow-discharge tube in which the discharge takes place in the conical or crater-shaped depression at one end of the tube.

Cresyl violet, also known as cresyl violet acetate or cresyl echt violet, is a synthetic organic compound belonging to the class of triarylmethane dyes. It is commonly used in histology and...

The least angle of incidence at which total internal reflection takes place. The angle of incidence in a denser medium, at an interface between the denser and less dense medium, at which the light is...

Illumination in which the light source is imaged at the object.

A positioning slide mechanism with two rows of alternately crisscrossed cylindrical rollers.

Calculation of the probability of an interaction between two types of particles, such as light absorption, excitation or energy transfers. The probability that one incident particle will interact as...

A signal-averaging technique that improves signal-to-noise ratio by comparing a sampled signal with a reference signal bearing some known relation to the received signal.

1. A defect inherent in a multiple-axis positioning system whereby an adjustment of one axis causes an undesired change in another; its severity depends upon the degree to which the positioning axes...

The positioning of two Nicol prisms so that their axes are at right angles to each other. With this arrangement, light transmitted by one prism will not be transmitted by the other.

A vacuum pump in which pressure is reduced by condensing gases on surfaces cryogenically cooled to about 20 K (liquid hydrogen) or 4 K (liquid helium).

The spectrographic analysis of matter that is in a cooled state. Generally, a mechanical refrigerator is used to lower the temperature of the sample, allowing isolation and study of the sample and...

A cryostat is a device used to maintain very low temperatures, typically below the boiling point of liquid nitrogen (77 K or -196°C) or even lower. It provides a controlled environment for...

A solid with a structure that exhibits a basically symmetrical and geometrical arrangement. A crystal may already possess this structure, or it may acquire it through mechanical means. More than 50...

The unusual and anisotropic diamagnetic quality observed in particular crystals such as those composed of bismuth.

A diode with a semiconducting material, such as germanium or silicon, for one electrode, and a fine wire "whisker'' which lies on the semiconductor, as the other electrode. The low capacitance...

The study of the transmission of radiant energy through crystals, especially anisotropic crystals, and their effects on polarization.

The axes of symmetry in a crystal structure. See also biaxial crystal; uniaxial crystal.