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Photonics Dictionary: P

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PDP
parallel detection polychromator
PDS
photodischarge spectroscopy
PDT
photodynamic therapy
PE
processing element
peak spectral emission
The wavelength at which a lamp radiates its highest intensity.
peak wavelength
The wavelength at which the radiant intensity of a source is maximum.
PEC
photoelectric cell
Pechan prism
A prism made up of two air-spaced components. It has the ability to revert, and not invert, an image, and can be used in convergent, divergent and parallel light. May be rotated to compensate for...
pedestal component
Present in photocurrent burst, it is the low frequency pulse that corresponds to the light scattered from the beams in the absence of heterodyne mixing.
peel point
In a fiber optic guided missile, the point at which the optical fiber pays out from the bobbin on which it is wound.
pel
Contraction of "picture element." See pixel.
pellicle mirror
A thin, stretched plastic membrane cemented to a rigid supporting ring. It may be coated to act as a beamsplitter, for example, in a color camera; it is so thin that no perceptible image doubling...
Pellin-Broca prism
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...
Peltier cooler
A Peltier cooler, also known as a thermoelectric cooler (TEC) or thermoelectric module, is a solid-state device that uses the Peltier effect to transfer heat between two electrical junctions. It can...
Peltier effect
See thermoelectric cooling.
PEM
photoelectromagnetic
pencil beam
In astronomy, the main lobe of an antenna pattern that has a small angular extent in two mutually perpendicular directions. Invisible in space, it would resemble a searchlight beam.
Penning discharge
A standard source of high-charge-state ions for accelerators that has an external magnetic field oriented perpendicularly to the two cathode faces. Also called Philips ionization gauge.
penta prism
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...
penumbra
A source of light will not cast a distinct shadow of an interfering, opaque object, but will cast a shadow having two parts: 1. the umbra, or the central, totally dark part of the shadow; and 2. the...
perceived color
The apparent color, as seen by the human eye, as distinguished from color as a measurable property of light.
perfect crystal
A crystalline substance in which all planes are parallel, or approximately parallel.
perfect diffuser
A surface that obeys Lambert's cosine law and has a reflectance of unity.
perfect lens
A theoretical, ideal lens capable of producing perfect images. Used as a lens design and analysis tool to image collimated output from an afocal system.
perimeter -> eye test apparatus
Instruments used by ophthalmologists and optometrists to study the eye. There are, for instance, the ophthalmoscope to observe and photograph the retina; the retinoscope and optometer to determine...
perimetry
The analysis of retinal zones in which different hues can be detected. Also called campimetry.
periodic wave
A wave of radiant energy in which each point of the wave is repeatedly displaced at equal time intervals.
peripheral
Near the boundary or edge of the field of an optical system; the outer fringe.
peripheral response
In a charge-coupled device, the detection of charge collected by the transport register rather than by the image-sensing elements.
peripheral vision
The ability to see over large angles of view.
periplan eyepiece
A well-corrected flat-field eyepiece with good eye relief. Similar to a Huygenian.
periscope
An optical instrument designed to displace the line of sight in a vertical direction. For submarines and other military uses the periscope is a long tube containing prisms at both ends and...
periscopic lens
Two simple meniscus lenses arranged symmetrically on either side of the aperture stop, providing reduced coma, lateral color and distortion.
permanent magnetic focusing
The focusing of an electron beam by a magnetic field that permanently retains the majority of its magnetic properties.
permeability
Typically represented by the Greek letter μ, magnetic permeability is the measure of a material's ability to generate and sustain a magnetic field within itself when an external magnetic field is...
permittivity -> dielectric constant
A number that indicates the magnitude of the shift in a solid of positive and negative charges in opposite directions when a voltage is applied across the solid.
perovskite
The term perovskite refers to a specific crystal structure commonly found in various materials. Perovskite structures have a cubic arrangement of oxygen ions, forming a framework within which other...
perpendicular -> normal
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...
perspective distortion
The distortion that is the result of viewing a print from a point other than the center of perspective. The center of perspective is that viewpoint at which the angular subtenses of points in the...
PES
photoelectric scanner
PET
pulse energy thermography; positron emission tomography
peta
In the SI system, prefix meaning 1015.
petrographic microscope
A microscope equipped with a polarizer, an analyzer and a Bertrand lens to focus on the upper focal plane of the objective. It is used chiefly by mineralogists and crystallographers for...
petrographic specimen preparation
The grinding and polishing of rock samples, to a thickness of less than 0.05 mm, for study with petrographic microscopes. When mounted on a slide and protected with a cover, these samples, examined...
petrography
The study of and classification of rocks.
Petzval lens
A high-speed, narrow-field lens consisting of two achromats spaced about the aperture stop. Its uses include portrait photography and motion picture projection.
Petzval surface
A paraboloidal surface on which the image is located when there is no astigmatism.
pF
picofarad
PFC
point focusing and centering
PFE
photoferroelectric

Photonics DictionaryP

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