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Topic: Spontaneous emission

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	Spontaneous fission - Wikipedia, the free encyclopedia
		Spontaneous fission (SF) is a form of radioactive decay characteristic of very heavy isotopes, and is theoretically possible for any atomic nucleus whose mass is greater than or equal to 100 amu (elements near ruthenium).
		For uranium and thorium, the spontaneous fission mode of decay does occur but is not seen for the majority of radioactive breakdowns and is usually neglected except for the exact considerations of branching ratios when determining the activity of a sample containing these elements.
		However, spontaneous fissions release neutrons as all fissions do, so radioisotopes for which spontaneous fission is a nonnegligible decay mode may be used as neutron sources; californium-252 (half-life 2.645 years, SF branch ratio 3.09%) is often used for this purpose.
	en.wikipedia.org /wiki/Spontaneous_fission (261 words)

	Spontaneous emission - Wikipedia, the free encyclopedia
		Spontaneous emission is the process by which an atom or molecule in an excited state drops to the ground state, resulting in the creation of a photon.
		The phase of the photon in spontaneous emission is random as is the direction the photon propagates in.
		It can be seen that spontaneous emission occurs in a way rather similar to the decay of radioactive particles, in particular that the lifetime is analogous to a half-life.
	en.wikipedia.org /wiki/Spontaneous_emission (482 words)

	Spontaneous emission -- Facts, Info, and Encyclopedia article (Site not responding. Last check: 2007-11-05)
		If the atom is in the excited state with energy, it may spontaneously decay into the ground state, with energy, releasing the difference in energies between the two states as a photon.
		The (Any distinct time period in a sequence of events) phase of the photon in spontaneous emission is random as is the direction the photon propagates in.
		Meta-stable states form a very important feature that is exploited in the construction of (An acronym for light amplification by stimulated emission of radiation; an optical device that produces an intense monochromatic beam of coherent light) lasers.
	www.absoluteastronomy.com /encyclopedia/s/sp/spontaneous_emission.htm (490 words)

	OLYMPUS MIC-D: Interactive Java Tutorial - Spontaneous and Stimulated Processes (Site not responding. Last check: 2007-11-05)
		Excited atoms or molecules have a characteristic spontaneous emission time, which is the average time that they remain in the excited higher energy state before they drop to the lower energy level and emit a photon.
		The primary problem in achieving stimulated laser emission is that under normal conditions of thermodynamic equilibrium, the population, or number of atoms or molecules at each energy level, is not favorable to stimulated emission.
		The reason that stimulated emission is difficult to achieve becomes apparent when considering the likely events surrounding the drop of an electron from an exited state with the subsequent and spontaneous emission of light.
	www.mic-d.com /java/electroncycle (875 words)

	Rates of Light Absorption (Site not responding. Last check: 2007-11-05)
		The process of returning from the excited state to the ground state with the emission of a photon in phase with the exciting electromagnetic field is referred to as stimulated emission.
		In contrast to stimulated absorption and emission, spontaneous emission does not require the existence of an electromagnetic field at the resonance frequency.
		Spontaneous emission from the excited state is one mechanism which limits the lifetime of the excited state.
	stingray.bio.cmu.edu /~web/sbio00/abs_1/node8.html (435 words)

	Spontaneous Emission and Laser Oscillation in Microcavities
		Spontaneous Emission and Laser Oscillation in Microcavities presents the basics of optical microcavities.
		The effect of dephasing of vacuum fields on spontaneous emission in a microcavity and the effects of atomic broadening on spontaneous emission in an optical microcavity are examined.
		Spontaneous emission in microcavity surface emitting lasers is covered, as are the effects of electron confinement in semiconductor quantum wells, wires, and boxes also given.
	www.ramex.com /title.asp?id=4804 (685 words)

	Definition of Stimulated emission
		When an electron decays due to "timeout" it is said to be due to "spontaneous emission." The phase associated with the photon that is emitted is random and has to do with some quantum mechanical ideas concerning the atom's internal state.
		If the atom is in the excited state, it may decay into the ground state by the process of spontaneous emission, releasing the difference in energies between the two states as a photon.
		The critical detail of stimulated emission is that the emitted photon is identical to the stimulating photon in that it has the same frequency, phase and polarisation (thus the two photons are totally coherent).
	www.wordiq.com /definition/Stimulated_emission (773 words)

	Luminescence (Site not responding. Last check: 2007-11-05)
		The underlying physical mechanism that are responsible for the generation of light affect the interplay between spontaneous and induced radiation and consequently the spatial and spectral emission properties.
		The spatial coherence of spontaneous emission and amplified spontaneous emission is even more important in devices close to threshold or devices with a light field output dominated by spontaneous emission such as superluminescent diodes and ultra low threshold semiconductor lasers.
		In order to understand the physical origin for the specific emission characteristics of a semiconductor laser it is necessary to investigate the microscopic processe that 'create' and consequently determine the physical properties of light such as e.g.
	www.ee.surrey.ac.uk /Research/CQE/research/semilaser/lum.html (481 words)

	The Manila Times Internet Edition \| ENTERTAINMENT > Improving spontaneous light emission (Site not responding. Last check: 2007-11-05)
		Whereas the stimulated emission of light is the basis of laser operation, spontaneous emission tends to waste energy in optoelectronic devices.
		They observed that when the emission spectrum of a sample lay inside the photonic band gap, the overall spontaneous emission rate was reduced by a factor of five.
		“Spontaneous emission is a fundamental bottleneck that limits the performance of devices in various fields including photonics, illumination, displays, solar cells and even quantum-information systems,” Noda told PhysicsWeb.
	www.manilatimes.net /national/2005/jun/07/yehey/enter/20050607ent4.html (312 words)

	Modification of Spontaneous Emission and Applications to Semiconductor Lasers - Storming Media
		However, the residual spontaneous emission must be taken into account when considering laser characteristics other than the threshold pumping rate, for example, laser linewidth.
		For almost fully inhibited spontaneous emission, the accepted laser models are not applicable, since they are based on a statistical approach valid when a large number of modes participate in the spontaneous emission loss.
		For a partial suppression of spontaneous emission, the model is applicable, mainly with modification of the atomic decay rate.
	www.stormingmedia.us /24/2444/A244423.html (200 words)

	Optical systems and devices employing spectrally flattened amplified spontaneous emission - Patent 5668821
		When the rare earth doped fiber is pumped to operate as an amplified spontaneous emission source, the grating flattens and broadens the output spectrum.
		The extinction ratio of the grating is determined by the height of the peak at.lambda.p relative to the rest of the amplified spontaneous emission spectrum.
		The device, without a long period grating, was excited to spontaneous emission by the pump, leading to an output power of 34 mw, spectral width of 7 nm and maximum slope of 2.2 dB/nm between 1060 nm and 1100 nm.
	www.freepatentsonline.com /5668821.html (2730 words)

	Measurement Offers Insight into Diodes - April, 2002 (Site not responding. Last check: 2007-11-05)
		In a new method for measuring the true spontaneous emission spectrum of a laser diode, researchers analyze the radiation from the end of the device, which is divided into segments (1-5) that can be driven independently, correcting for amplification or absorption in the structure.
		The method interrogates the spontaneous emission spectrum in both the transverse electric (TE) and transverse magnetic (TM) polarizations.
		Previous investigators employed a geometry that avoided amplification or absorption by observing the emission via a top-contact window in the substrate or through the side of a narrow, buried heterostructure or mesa device.
	www.photonics.com /spectra/tech/XQ/ASP/techid.1346/QX/read.htm (555 words)

	Spontaneous Emission (Site not responding. Last check: 2007-11-05)
		Spontaneous emission is an inherently quantum mechanical and random effect.
		Spontaneous emission links the upper level to the lower level, which in turn increases the population in the lower level and decreases the population in the upper level.
		The normalization of the system is preserved in this case because the population of the upper state is being drained into the lower state and not into some level outside the two--state system.
	webphysics.davidson.edu /Projects/AnAntonelli/node27.html (207 words)

	Untitled Document (Site not responding. Last check: 2007-11-05)
		A fun and timely problem in cavity quantum electrodynamics is the question of whether atoms are actually radiating anything when their spontaneous emission is inhibited by a cavity.
		We have planned a demonstration of this that will use the process of spontaneous parametric downconversion, in which a "pump" photon may be split into two lower energy "signal" and "idler" photons within a nonlinear crystal.
		It has already been shown that this process may be frustrated by forming a cavity around the signal and idler modes, in precise analogy to the inhibited spontaneous emission of atoms, but with the advantage that much larger cavities may be used.
	www.nist.gov /sigmaxi/Posters00/Abst/Branning-abs.html (204 words)

	Amazon.com: Books: Spontaneous Emission and Laser Oscillation in Microcavities (Site not responding. Last check: 2007-11-05)
		In spite of the increasing importance of microcavities, device physics or the observable phenomena in optical microcavities such as enhanced or inhibited spontaneous emission and its relation with the laser oscillation has not been systematically well-described-until now.Spontaneous Emission and Laser Oscillation in Microcavities presents the basics of optical microcavities.
		Spontaneous emission in microcavity surface emitting lasers is covered, as are the effects of electron confinement in semiconductor quantum wells, wires, and boxes also given.The volume extends the controlling spontaneous emission phenomenon to laser oscillation.
		In its standard textbook description, spontaneous emission is the irreversible emission of a photon by an atom into the free space modes of the electromagnetic field, accompanied by a transition of the atom from an electronic state of energy E2 to one of lower energy E1.
	www.amazon.com /exec/obidos/tg/detail/-/0849337860?v=glance (798 words)

	ABSTRACT (Site not responding. Last check: 2007-11-05)
		The spontaneous emission from luminescent Si photonic layer-by-layer crystals is studied.
		The spontaneous emission is strongly suppressed for wavelengths between 1.4 and 1.7 µm.
		A spectral attenuation of ~5 dB per unit cell is derived from the spontaneous emission data, consistent with theory and transmission data.
	www.dedood.demon.nl /abstracts/abstract13.html (127 words)

	First Observation of Self-Amplified Spontaneous Emission in the Near-Infrared and Visible
		Enhancement of the emissions from 2 to 6 times the spontaneous emission level is observed at the highest charges.
		The straight line represents the expected spontaneous emission dependence, as extrapolated from the low charge points, if variation of the beam distribution, such as energy spread and emittance, are not included.
		This emission displays enhancement similar to that observed at 1064 nm, therefore any coherent enhancement at both wavelengths would require even smaller structure to be present in the electron beam distribution.
	www.bnl.gov /ATF/publications/SASE.htm (4920 words)

	Section 2.3: Principles of Lasers—
		Atoms at higher energy levels tend to, or spontaneously jump to lower energy levels, in the same time they give out the electromagnetic radiation having the energy equal to the difference between the two energy levels.
		Spontaneous radiation is only one of the two forms of atomic relaxation or decay, the other is non-radiation relaxation processes like collision, thermal dissipation, etc. So the total decay time of E2 to E1 is composed of both radiative and non-radiative parts, T
		In the same time, under the action of the incident electromagnetic field with the corresponding frequency, the atoms at upper level have the same possibility to jump to the corresponding lower levels, emitting electromagnetic waves or photons with the same frequency, direction and phase with the incident waves.
	www.columbia.edu /cu/mechanical/mrl/ntm/level2/ch02/html/l2c02s03.html (520 words)

	Dipole Emission in Finite Photonic Bandgap Structures: An Exactly Solvable One-Dimensional Model (ResearchIndex) (Site not responding. Last check: 2007-11-05)
		3 Inhibited spontaneous emission by a Rydberg atom (context) - Hulet, Hilfer et al.
		2 Resonant scattering and spontaneous emission in dielectrics:..
		1 Coherence in spontaneous emission in the presence of a diele..
	citeseer.ist.psu.edu /dowling99dipole.html (601 words)

	Spontaneous Emission in Microcavity Lasers (Site not responding. Last check: 2007-11-05)
		The abstract provided by the Pentagon follows: An understanding of spontaneous emission processes within microcavities is crucial in addressing the need to make tomorrow's microlasers more efficient.
		One approach to improving the device efficiency is to reduce the threshold input energy at which lasing begins to occur.
		It has been suggested that the threshold in a microcavity laser can be decreased by increasing the fraction of spontaneous emission into the lasing mode, this can be accomplished by preferentially coupling the gain medium of the laser to the electromagnetic cavity mode of interest.
	www.mini-bikes-online.com /prod/1423566645/Spontaneous_Emission_in_Microcavity_Lasers.html (279 words)

	Green's Functions for Maxwell's Equations: Application to Spontaneous Emission (Site not responding. Last check: 2007-11-05)
		Using the close relationship between the Green's function and the density of states (DOS), we apply our method to calculate the spontaneous emission rate as a function of the distance to a material surface.
		The spontaneous emission rate can be calculated using Fermi's Golden Rule, which can be expressed in terms of the DOS of the optical modes available to the emitted photon.
		It is shown that the enhancement or suppression of spontaneous emission strongly depends on the frequency of the light.
	www.sst.ph.ic.ac.uk /photonics/abstracts/wijnands97a.html (224 words)

	Stimulated Emission (Site not responding. Last check: 2007-11-05)
		The incoming photon is a boson, and for this reason it stimulates the emission of a second photon in the same state, inducing an atomic transition.
		From the point of view of quantum field theory, even random quantum quantum events such as so called 'spontaneous emission' are really 'stimulated' by the vacuum's zero point energy.
		"From the perspective of quantum electrodynamics, spontaneous emission is a type of stimulated emission induced by fluctuations in the electromagnetic field of the vacuum.
	www.nonlocal.com /hbar/stimulated.html (269 words)

	Collisions and Spontaneous Emission
		Spontaneous emission makes it harder to find the atom in the upper state; so, the constant of proportionality is positive in the lower state and negative in the upper state.
		Spontaneous emission has an effect on the off--diagonal elements as well via the coupling of the differential equations.
		Collisions and spontaneous emission alter the system homogeneously, i.e., they alter the entire system in the same way.
	webphysics.davidson.edu /Projects/AnAntonelli/node14.html (482 words)

	Definition: spontaneous emission (Site not responding. Last check: 2007-11-05)
		spontaneous emission: Radiation emitted when the internal energy of a quantum mechanical system drops from an excited level to a lower level without regard to the simultaneous presence of similar radiation.
		Note: Examples of spontaneous emission include radiation from an LED, and radiation from an injection laser below the lasing threshold.
		This HTML version of Telecom Glossary 2K was last generated on Wed May 8 15:36:48 MDT 2002.
	www.its.bldrdoc.gov /projects/devglossary/_spontaneous_emission.html (68 words)

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