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Photonics Dictionary

Clear All Filters xaperture x
aperture
An opening or hole through which radiation or matter may pass.
aperture card
A combination 80-column computer card containing a 35-mm microfilm frame. Reference data can be punched onto the card to facilitate retrieval of it on film.
aperture diaphragm
The second adjustable iris diaphragm in an optical system. In the common microscope condenser system, it usually is located beneath the substage condenser on a transmitted light microscope. When the...
aperture distortion
A loss of resolution or detail in a television signal caused by the size of the electron scanning beam.
aperture illumination
The amplitude, polarization and phase contained in the field distribution over the aperture.
aperture imaging
The formation of an image by a pinhole aperture that transmits radiation, such as gamma radiation.
aperture mask
Also known as a shadow mask, a perforated plate placed between the focusing and accelerating electrodes, and the tricolor phosphor screen in a color-television tube.
aperture ratio
The ratio of the lens aperture to its focal length (1/f/#).
aperture stop
A physical constraint, often a lens retainer, that limits the diameter of the axial light bundle allowed to pass through a lens.
shadow mask -> aperture mask
Also known as a shadow mask, a perforated plate placed between the focusing and accelerating electrodes, and the tricolor phosphor screen in a color-television tube.
angular aperture
The angle between the most divergent rays that can pass through the lens to form an image. In a birefringent crystal light modulator or Pockels cell, the maximum angle in the incident light rays that...
clear aperture
The limited light-gathering area of an optical system. The area is normally restricted to an edge or outer surface of an individual component. Also known as free aperture or objective aperture. The...
coded aperture imaging
An imaging process in which the single opening of a simple pinhole camera is replaced with many openings called, collectively, the aperture. The recorded picture, which consists of many overlapping...
critical aperture
In an optical system, the aperture size at which the lens gives its best overall performance.
effective aperture
1. That portion of the aperture that functions to collect energy and deliver it to the final system detector. 2. For an obscured or noncircular aperture, the equivalent nonobscured, circular aperture.
effective numerical aperture
The real numerical aperture (NA) of a fiber when the computed NA is not valid because of change in the glass indices during drawing and fusion.
free aperture -> clear aperture
The limited light-gathering area of an optical system. The area is normally restricted to an edge or outer surface of an individual component. Also known as free aperture or objective aperture. The...
front operating aperture
The restricting aperture located at the front of the lens. It is usually defined as the maximum diameter of the entrance cone at the front vertex, for the specified field of view at infinity focus.
launch numerical aperture
The numerical aperture of an optical system used to couple (launch) power into an optical waveguide.
limiting aperture
The maximum circular area over which radiance and radiant exposure can be averaged.
microaperture
A small opening or slit in a mask.
moving aperture technique
Method for reducing laser speckle in which the object field comes from a real diffuse object or the reconstructed object field from a hologram. During recording of the image, an aperture is moved in...
numerical aperture
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...
objective aperture -> clear aperture
The limited light-gathering area of an optical system. The area is normally restricted to an edge or outer surface of an individual component. Also known as free aperture or objective aperture. The...
precision aperture
An accurately produced hole of any size and shape that is used as a masking device in an optical system. Pinhole apertures of accurate diameters often are produced by laser beam penetration or by...
rear operating aperture
The restricting opening at the rear of a lens or prism that is commonly defined as the maximum diameter of the emergent cone for the specified field of view, at infinity focus.
relative aperture
The ratio of the diameter of the entrance pupil in an optical system to the equivalent focal length of that system. The relative aperture is denoted as a fraction in which f, the equivalent focal...
semitransparent and p-phase annular aperture
An aperture consisting of a semitransparent central region whose amplitude transmittance only is varied, and the relative phase difference between the central and annular region is fixed as p -...
synthetic aperture radar
Imaging radar that increases the sweep of its along-track (or azimuth) capacity by measuring not only the time delay of the echoes returning from the microwave pulse transmitted by its antenna (or...
television aperture
The term that represents the size of one of the many small elements into which a television image is necessarily broken down for transmission.
working aperture
The maximum aperture of a lens at which it will still give a sharp image, even though its physical aperture may be larger.
accessible radiation
Electromagnetic radiation present upon the open aperture of the source within an operating environment.
angular spectrum approach
The angular spectrum approach is a mathematical and computational technique used in the field of optics to analyze and simulate the propagation of optical waves, particularly in the context of wave...
apertometer
An instrument designed to measure the numerical aperture of an objective.
apodization
The use of a variable transmission filter at the aperture stop of a lens to modify its diffraction pattern. Reduced transmission at the center of the aperture will favor performance at high...
AR
Abbe refractometer; acoustic radiometer; acoustic resonance; active region; alpha ray; amplitude ratio; antireflective; aperture ratio; applied research; argon; aspect ratio; atomic reactor; augmented reality
area concentration
The ratio of aperture area over receiving area for a specific lens. Also called geometric concentration.
astronomical mirror
An astronomical mirror, also known as a telescope mirror or primary mirror, is a key component of a reflecting telescope. It serves as the primary optical element responsible for gathering and...
astronomical telescope
An astronomical telescope is a type of optical instrument designed to gather and magnify light from distant celestial objects for observation and analysis. It typically consists of two main optical...
auto-iris lens
A device for automatic exposure control in which a motor-driven diaphragm adjusts the aperture in response to a signal from a photocell detecting ambient light.
beam diameter
1. Calculated distance between two exactly opposed points on a beam at a chosen fraction of peak power (typically 1/e2). 2. The diameter of a circular aperture that will pass a specified percentage...
beam profiler
A device that measures the spatial distribution of energy perpendicular to the propagation path of a radiant beam. An energy or power meter is typically used to monitor the amount of light passing...
beam spread -> divergence
1. In optics, the bending of rays away from each other. 2. In lasers, the spreading of a laser beam with increased distance from the exit aperture. Also called beam spread. 3. In a binocular...
beamwidth
The angular width of a radiation beam. With respect to a conical beam of light, it is the vertex angle of the cone. The beamwidth is a measure of the rate of divergence or convergence of a light...
Becke apertometer
Device used to measure the numerical aperture of a microscope, composed of a 14-mm-thick glass block with numerical aperture gradations carved onto its lower surface.
bench -> optical bench
A support for optical parts comprising a solid bed that permits precise longitudinal movement of one component relative to the others, and a number of sliders equipped with holders for lenses, lamps,...
Bertrand lens
A small convergent lens, located between the objective and eyepiece of a microscope, that focuses an image of the upper focal plane of the objective in the focal plane of the eyepiece. It is commonly...
Bessel functions
Two formulas used in diffractometer analysis, the first giving the individual diffraction patterns of each aperture, the second representing the constant of the degree of an incoherent circular...
bevel face width
The actual width of a bevel rather than its width projected along the lens aperture.
bispheric condenser -> dark-field condenser
A condenser that forms a hollow cone-shaped beam of light with its focal point in the plane of the specimen. If it is used with an objective having a numerical aperture lower than the minimum...

Photonics Dictionary


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