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8,289 terms

Photonics Dictionary

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positive dielectric anisotropy

The dielectric coefficient parallel to the director in a liquid crystal display (LCD), rather than perpendicular to the director.

positive spherical aberration -> spherical aberration

Spherical aberration is an optical aberration that occurs when light rays passing through a lens or curved optical surface do not converge or diverge to a single focal point. Instead of focusing to a...

positron -> electron

A charged elementary particle of an atom; the term is most commonly used in reference to the negatively charged particle called a negatron. Its mass at rest is me = 9.109558 x 10-31 kg, its charge is...

positron emission tomography

A medical imaging device that uses a ring of crystal/photomultiplier tube assemblies encircling the patient to detect gamma rays emitted by positrons colliding with electrons.

positronium

Basically, a hydrogen atom with two alterations, positronium is the lightest atom in the universe and has an extremely light positron in its nucleus that replaces hydrogen's proton so that its atomic...

posterization

In image processing, the effect caused by large jumps between gray levels, rather than a gradual change.

pot

potentiometer

potassium titanyl phosphate

A crystalline material with a high electro-optic coefficient, capable of operating at short wavelengths, with applications in laser, optical disc, printing and microwave systems.

potentiometer

A device designed to measure electromotive force or electrical difference potential.

potting -> imbedding material

A thermoplastic or thermosetting material used to hold an object fixed and keep it from deterioration. In microcircuitry, the process of imbedding is known as potting.

powder camera

A camera system that uses a fine powder to diffract x-rays from the specimen. A beam of monochromatic x-rays passes through a collimator onto the specimen. Diffracted x-rays are recorded on the film...

powder radiography

A technique used in radiography to determine a crystal's structure by obtaining radiographs of it in powder form, normally by the use of a powder camera that forms an image of the crystal's x-ray...

power

With respect to a lens, the reciprocal of its focal length. The term power, as applied to a telescope or microscope, often is used as an abbreviation for magnifying power.

power average

For a pulsed laser, the product of the energy per pulse (joule) and the pulse frequency (hertz); expressed in watts.

power efficiency

The ratio of emitted power to input power.

power flow equation

Optical fiber channel characterization scheme based on three assumptions; the discrete mode spectrum can be replaced by a continuum; the loss due to coupling between guided and radiation modes...

power modulation

Power modulation refers to the intentional variation of power levels in a signal, often in the context of electronic communication systems. This modulation technique is used to encode information...

power ratio -> radiant power

The time rate of flow of radiant energy, expressed in watts (W), and carries the units of Joule per second (J/s). The prefix often is dropped and the term "power" used.

power scanning laws

Laws that predict the maximum power output as a function of tube diameter for a hydrogen cyanide laser of a given discharge length and cavity losses, all other parameters being optimized.

power spectrum equalization

A filtering method that restores a blurred image by setting its power spectrum equal to that of the original image.

power supply

Refers to the voltage and current necessary for the operation of circuit devices.

Poynting vector

In remote sensing technology, this represents the intensity of energy flow in the direction of wave propagation.

PP junction

A transition boundary between two regions having different properties in a P-type semiconducting material.

ppb

parts per billion

PPF

polarization-preserving fiber

PPFD

photosynthetic photon flux density

PPKTP

periodically poled potassium titanyl phosphate

PPLN

periodically poled lithium niobate

ppm

pulses per minute; parts per million

PPM

pulse position modulation

pps

pulses per second

PPSLT

periodically poled stoichiometric lithium tantalate

power ratio; photoreflectance

Prandtl number

Ratio of the molecular diffusion coefficients of momentum in terms of heat; used in convection studies.

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...

preform

A glass structure from which an optical fiber waveguide may be drawn.

prefusing

A step before fusion splicing that involves cleaning the fiber end with low-current electricity.

prelasing

When uncontrolled laser energy leaks from a laser cavity prematurely, it causes serious damage to optical components and significant downtime for repair.

Prentice's rule

A method of determining prism power at any point on a lens. Prism power equals the product of the dioptric power and the distance, in centimeters, from the optical center.

presbyopia

A state in which the human eye has very little or no power of accommodation. A common and normal condition in the eyes of those age 50 and older.

pressing

A blank having basic surface curves attained by forming heat-softened glass that is pressed in a mold.

pressure broadening -> collision broadening

The broadening of spectral lines due to the collision of radiating particles with one another and the resulting interruption of the radiative process.

pressurization

Injecting a gas (usually nitrogen) with a very low moisture content into the body of an optical instrument to create a positive internal pressure. This prevents the entrance of moisture, which could...

PRF

pulse repetition frequency

PRI

pulse repetition interval

primary chromatic aberration

Also referred to as primary color, this is the classic chromatic aberration of a single element caused by the variation of index of refraction as a function of wavelength.

primary coating

In a waveguide, the material in intimate contact with the cladding surface, applied to preserve the integrity of that surface.

primary colors

A set of three colored lights which, when mixed, give the sensation of white light. The set used in color television, for example, is red, green, blue (RGB).

primary fluorescence

Fluorescence produced as a result of the intrinsic property of the material itself or the doping of the material with trace elements.

primary spectrum

The first-order spectrum formed by a diffraction grating.

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Photonics Dictionary

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