Photonics Dictionary

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linewidth

1. The range of frequencies or wavelengths over which radiations are absorbed or emitted in a transition between a specific pair of atomic energy levels. The full width is determined between...

long-pass filter

A long-pass filter is an optical filter that allows longer wavelengths of light to pass through while blocking or attenuating shorter wavelengths. These filters are designed to transmit light with a...

long-wave infrared

Long-wave infrared (LWIR) refers to a specific range of the infrared spectrum. Infrared radiation is divided into three main categories based on wavelength: near-infrared (NIR), mid-wave infrared...

lookup table

In image processing, the memory that stores the values for the point processes. Input pixel values are those for the original image, while output values are those displayed on the monitor as altered...

lumen

A lumen is a unit of measurement used to quantify the amount of luminous flux, which is the perceived power of light. In other words, the lumen measures the total amount of visible light emitted by a...

luminous flux

Descriptive of the radiant power of visible light modified by the eye response. It is the measure of the flow of visible light energy past any given point in space in a given time period, and is...

Luneburg lens

A dielectric sphere with an index of refraction that varies with distance from the sphere center. A parallel beam of rays is focused on the lens surface at a point diametrically opposite the...

macula lutea

The small central portion of the human retina that is responsible for providing the clearest, and most distinct aspects of human vision. Light from an object directly forms an image on the macula...

magnetically focused image tube

A vacuum tube in which a magnetic field is superimposed onto the tube's electrical field. When the two fields are aligned, electrons from the photocathode are accelerated through the tube in a spiral...

magnifier

A lens or lens system that produces an enlarged virtual image of an object placed near its front focal point.

magnon

A magnon is a quasiparticle representing a quantized spin wave in a magnetic material. In other words, it is a collective excitation of the spins of electrons in a magnetic solid, analogous to the...

mapping function

In image processing, the mathematical relationships that link pixel brightnesses of input images to those of output images in point processes. Mapping functions are commonly used to apply...

marginal rays

Also referred to as the axial ray (or a-ray), a marginal ray originates from the axial point of the object and passes through the edge or margin of the entrance pupil (or aperture stop) of the lens...

MCF

mutual coherence function — The mutual coherence function is a complex quantity that is the time-averaged value of the cross correlation function of a light field at two points within an aperture with a time delay that relates the path difference to the point of observation of the interference fringes. The mutual coherence function is the key function in coherence theory and the study of partially coherent light.

mean spherical luminous intensity

The average luminous intensity of a point light source measured over all directions.

mechanical tube length

In a microscope, the physical distance between the focal points of the objective lens and the eyepiece. The standard tube length for a microscope is typically 160 mm).

micro-optics

Micro-optics refers to the design, fabrication, and application of optical components and systems at a microscale level. These components are miniaturized optical elements that manipulate light at a...

microfluidics

Microfluidics is a multidisciplinary field that involves the manipulation and control of very small fluid volumes, typically in the microliter (10-6 liters) to picoliter (10-12 liters) range, within...

microphotometry

The measurement of the intensity of spectral lines by the examination of a very small area under a microscope and the measurement of the density at any point of the image.

microstereology

Microscopic investigation of two-dimensional areas of a three-dimensional object that can be quantitatively evaluated by consideration of the line intersections or point counts obtained via...