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GLOSSARY

LASER
Derived from the Acronym L.A.S.E.R. : Light Amplification by Stimulated Emission of Radiation. Name of a device or process that amplifies radiation Cooperative emission of photons from an inverted population, usually defined as a device in which more stimulated emission is occurring than spontaneous emission. (some authors have a stricter definition of LASER). Einstein can be considered as the father of the laser.
MASER
A maser is a laser operating in the microwave. Stimulated emission from an inverted population was first demonstrated by Townes. A few years later naturally occurring masers were discovered by radioastronomers.
PHASER
A laser based on a coherently prepared quantum system in which Electromagnetically Induced Transparency (EIT) is established thus leading to Lasing Without Inversion (LWI). Scully (1992) referred this type of medium as phaseonium; and he called a laser based on phaseonium a Phaseonium Laser, or phaser for short.
LIGHT AMPLIFICATION
Medium which acts like an amplifier of optical radiation. Most optical amplifiers are limited to one or a few restricted frequency bands.
RADIATIVE TRANSFER
The physics of radiation transport through a particular medium with properties which vary as a function of position, time and wavelength.
STIMULATED EMISSION
Early emission of a photon by a quantum transition which has been 'stimulated' by another photon. The result is two photons with exactly the same properties travelling in the same direction.
SPONTANEOUS EMISSION
Random emission of a photon during the decay of an excited quantum state over a period of time which is characteristic of the transitions itself. In forbidden transitions, the upper state is metastable and can remain excited much longer than other typical plasma processes such as stimulated emission. In laser rate equations spontaneous emission from metastable states can usually be neglected when compared to electron collisions or stimulated emission processes.
AMPLIFIED SPONTANEOUS EMISSION
Spontaneous emission followed by excessive stimulated emission resulting in strong laser amplification over the typicaly large scale of the stellar plasma.
PLASMA
Although a plasma can exist under many conditions we shall mainly be concerned here with the regime of a very hot gas composed mainly of ionized atoms and electrons.
QUASAR
From QUAsi-StellAr-Radio-object; from the original method by which quasars where originally discovered. Quasars must have strong or unusual emission lines not corresponding to thermodynamic equilibrium.
SELECTION EFFECT
Process by which an interpretation in rendered invalid as a result of a conscious effort made by the observer in order to collect favorable evidence while disregarding contradicatory data.
DISTANCE OVERESTIMATION
Spurious properties deduced from the erroneous overestimation of distance to various astronomical objects such as quasars. From QUAsi-StellAr-Radio-object; from the original method by which quasars where originally discovered. Quasars must have strong or unusual emission lines not corresponding to thermodynamic equilibrium.
POPULATION INVERSION
The overpopulation of the upper state relative to the lower lasing transition. Leads to excessive stimulated emission relative to spontaneous emission.
GAS CONTACT COOLING
Commonly occurs in atrophysical plasmas that are rapidely expanding into cooler circumstellar plasmas,
ADIABATIC EXPANSION
Expansion without loss or gain of heat. Associated with expansion that is so rapid that heat does not have a chance to enter the plasma from the outside. Rapid cooling is the result.
PUMPING
Effective amount of power creating a population inversion.
RECOMBINATION PUMPING
Sudden plasma cooling can lead to an overpopulation of the upper levels as the electrons rapidly recombine with the ions by three body recombination, which which dominates radiative recombination at higher electrons densities.
PHOTO-PUMPING 
Population inversion created by irradiation with strong emission line produced in another ion species. This pumping mechanism isn't likely to occur in astrophysical plasmas because the emission energy much exactly match the absorption energy. Only in extremely rare circumstances does this occur.
BOLTZMANN DISTRIBUTION 
Thermodynamic equilibrium of non-degenerate electron distribution proportional to exp(-E/kT). Higher energy quantum levels have a lower probability of being occupied.
PHOTON STATISTICS 
The photon is a massless particle, it is a quantum of electromagnetic radiation which obeys Bose-Einstein statistics.
BOSE-EINSTEIN CONDENSATION 
Under suitable conditions, bosons, which are integral spin quantum particles, have a tendency to condense into the same macroscopic quantum state.
ISOTHERMAL EXPANSION 
The same temperature (isos=equal, therme=temperature). Usually associated with an expansion that is slow enough to absorb energy from an outside system, the resulting temperature as a function of density is much higher relative to the adiabatic case.
LASING THRESHOLD 
Pumping rate required for population inversion.
LASER RESONATOR 
The gain of a lasing medium can be enhanced by placing it between a pair mirrors to increase the effective length and restrict the allowed spatial and spectral modes of operation, greatly improving coherence and reducing pumping power requirements.
INTERNAL ELECTRON DISTRIBUTION 
Probability that a discrete bound state in an ion, atom or molecule is occupied by an electron.
THREE BODY RECOMBINATION 
Recombination of an electron and ion in which a second free electron absorbs the heat; recombination occurs preferentially into the upper quantum levels. It is the main pumping mechanism in astrophysical lasers, especially at the high electron densities encountered in expanding stellar atmospheres.
RADIATIVE RECOMBINATION 
Fundamental plasma process of recombination of an electron and ion with the release of energy in the form of a photon.
LASER GAIN
Amplification factor by which the radiation intensity is multiplied after traversing a certain distance of the active laser medium. If the gain is positive, the intensity increases exponentially as a function of distance. Gain is often quoted as the factor in the exponent or e(gainXdistance) in units of inverse distance. The increase of intensity in a laser is much greater than can be obtained by spontaneous emission mechanisms.


TECHNO-BABBLE EXAMPLE :

The following paragraph makes heavy use of the technical terms in this glossary:

Laser gain is proportional to the degree of pumping therefore rapid adiabatic expansion is crucial to put the system as far away from equilibrium as possible, greatly increasing three three-body recombination and leading to a population inversion. In an isothermal expansion the electron distribution will have time to reach internal equilibrium, also the expanding plasma is not found in isolation, it is surrounded by hot plasma; the system temperature will not drop as low or as rapidly as adiabatic expansions. 

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KEYWORDS (ALPHABETICAL)

ATOMIC PROCESSES, ADIABATIC EXPANSION, AMPLIFIED SPONTANEOUS EMISSION, CENTRAL STARS OF PLANETARY NEBULA, CIRCUMSTELLAR PLASMA, EMISSION LINES, LASER, GAS CONTACT COOLING, NON-LOCAL-THERMODYNAMIC EQUILIBRIUM, OVERPOPULATION, POPULATION INVERSION, PROPER-MOTION, QUASAR, REDSHIFT, STIMULATED EMISSION, SUPER-LUMINAL, THREE BODY RECOMBINATION.

KEYWORDS (HIERARCHICAL)

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