Photonics Dictionary

A term used to describe a nondirectionally diffusing surface that, when illuminated, appears equally bright from all angles. An example of this kind of surface is the screen used for the forward...

One of two types of solar time - the other being apparent solar time - the mean solar time is the time measured by the average hour angle position of the sun in the sky compiled over a period of one...

A wedge in a rangefinder or heightfinder used to displace the image produced by one telescope so that it coincides with that produced by the other telescope, thus affording a measurement of the...

An optical experiment carried out conclusively in 1887 that demonstrated that the ether, a hypothetical medium postulated by physicists to explain how light could travel in a wave motion through...

Equivalent to 10-6 radian, where 1 radian equals 180/pi degrees. A rod 1 km in length will be moved by an angle of 1 µrad if the end of the rod is raised 1 mm.

Mie scattering, named after the German physicist Gustav Mie, refers to the scattering of electromagnetic radiation (such as light) by spherical particles. Unlike Rayleigh scattering, which is...

Minimum object distance, often abbreviated as MOD, refers to the closest distance at which a camera lens or optical system is capable of producing a sharp and focused image. In photography, this term...

The smallest object that may be seen, measured in terms of the angle subtended by the object measured at the eye. Also referred to as minimum perceptible color difference (MPCD) which is a unit of...

The least space between two parallel lines that can be discriminated as a gap to the human eye. It is measured in terms of the angle subtended by the gap measured at the eye.

The smallest area of uniform brightness that can be seen by the eye. It is measured in terms of the solid angle subtended by that area from the eye.

With respect to a crystal, a monoclinic crystal consists of three unequal axes, two of which intersect each other obliquely and yet still form right angles to the third.

1. Viewed with one eye. 2. Describing an image as viewed from a single angle.

In an optical waveguide,- typically a multimode fiber - the distortion resulting from differential mode delay, i.e. axial rays (modes), with the shortest path length, will have the shortest...

A lithography method that allows the transfer of fine-pitch gratings from a phase mask into photoresist. The exposure takes place with the light coming under an oblique angle to the mask. The...

A prism invented by William Nicol in 1828 that is made of calcite, the end faces of which are ground to an angle of 68° between one vertical side and the end surface. The prism is cut diagonally...

Sometimes referred to as the surface normal or 'surface norm'; the normal is an axis that forms right angles with a surface that light is incident upon or with other lines. The normal is used to...

Light striking a surface at an angle perpendicular to the surface.

The sine of the vertex angle of the largest cone of meridional rays that can enter or leave an optical system or element, multiplied by the refractive index of the medium in which the vertex of the...

A common technique in microscopy, oblique illumination is one in which the object is illuminated by a light source that is at an oblique angle (on the side) to the optical axis. This technique is...

A hemispherical covering that is rotatable about a central axis. There is a slit opening along one side wide enough to allow a telescope to be directed at any vertical angle up to 90°.

A family of specialized instruments used by ophthalmologists and optometrists to study a patient's eyes and prescribe spectacles. It includes the ophthalmoscope to observe and photograph the retina;...

Also referred to as the opposition surge, the opposition effect is a photometric phenomenon in which a rough retroreflective surface appears brighter when illuminated from directly behind the...

An optical combiner, in the context of optics and display technologies, refers to a device or component that combines multiple optical signals or images into a single output. The purpose of an...

A device for measuring diffraction grating efficiency at any angle of incidence, consisting of a reflectometer wherein the detector rotates around the grating at a specific distance and is attached...

A measure of image quality produced by an optical system. May be specified in terms of cycles per millimeter, referencing a repeating bar pattern; or angular resolution, referencing the angle...

An optical testing instrument is a device or system used to evaluate and measure the performance, quality, and characteristics of optical components, systems, and devices. These instruments play a...

Optics is the branch of physics that studies the behavior and properties of light, including its interactions with matter and its manifestation as both particle and wave phenomena. It encompasses the...

An organic light-emitting diode (OLED) is a type of light-emitting diode (LED) technology that utilizes organic compounds to produce light. OLEDs are commonly used in display technologies, such as...

Having three unequal angles perpendicular to each other.

In a cathode-ray tube, the deflection of the beam of the tube over an angle that surpasses the angle that subtends the suitable area of the screen.

Totally coherent radiation is produced by a purely monochromatic point source. In the real world the energy will have a limited bandwidth and the point source will subtend some angle resulting in...

A form of dispersing prism, often used in monochromators, that consists of a common right-angle prism with a 30° dispersing prism attached to each of its square faces. The spectrum formed by the...

A five-sided prism containing two reflecting surfaces at 45° to each other, and two refracting faces perpendicular to the entering and emerging beams. The deviation angle of 90° is...

The ability to see over large angles of view.

Photogrammetry is a technique used to obtain accurate three-dimensional measurements of objects and environments through the analysis of photographs or imagery. It involves extracting information...

The maximum angle of view that can be recorded by a camera. Field is a function of lens focal length and film format.

A still or motion-picture camera designed to photograph through a microscope. Photomicrographic equipment usually contains a beamsplitter or other means for simultaneously viewing, orienting and...

An instrument in which visible light beyond the critical angle from a metallurgical microscope is focused on a reference surface. A certain fraction of the incident light tunnels through air to the...

Photonic crystals are artificial structures or materials designed to manipulate and control the flow of light in a manner analogous to how semiconductors control the flow of electrons. Photonic...

A camera equipped with angular scales in altitude and azimuth. The scale readings are imprinted on the film when an exposure is made. The exact point indicated by the scale readings is shown by...

An aberration of a lens system caused by an increase in lens focal length as the field angle increases. The amount of distortion normally increases as the cube of the image height.

Geometrical partition possible with a sphere that can be four, six, eight, 12 or 20 solid-angle wedges. Each platonic mass is made up of a given number of regular polygonal faces and is classified...

Polarization refers to the orientation of oscillations in a transverse wave, such as light waves, radio waves, or other electromagnetic waves. In simpler terms, it describes the direction in which...