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Topic: Lasing threshold

	Theory of quantum dot lasers
		Concurrent with the increase of threshold current, an increase of the multimode generation threshold is shown to occur with a rise in temperature.
		The minimum threshold current density and optimum parameters of the structure (surface density of QDs and thickness of the waveguide region) are calculated as universal func tions of the main dimensionless parameter of the theory developed.
		This parameter is the ratio of the stimulated transition rate in QDs at the lasing threshold to the spontaneous transition rate in the waveguide region at the transparency threshold.
	www.ece.sunysb.edu /~asryan/qdl.html (3031 words)

	Lasing threshold - Wikipedia, the free encyclopedia
		In a laser, the lasing threshold is the lowest excitation level at which the laser's output is dominated by stimulated emission rather than by spontaneous emission.
		Above threshold, the slope of power vs. excitation is orders of magnitude greater.
		The lasing threshold is reached when the optical gain of the laser medium is exactly balanced by the sum of all the losses experienced by light in one round trip of the laser's optical cavity.
	en.wikipedia.org /wiki/Lasing_threshold (128 words)

	Journal of Electronic Materials: RT lasing via nanoscale CdSe islands in a (Zn, Mg)(S,Se) matrix (Site not responding. Last check: 2007-10-09)
		As it follows from this figure, lasing spectrum recorded in the waveguide geometry is still 16 meV Stokes shifted toward lower energies with respect to the PL peak recorded from the structure surface and the exciton resonance energy in the OR spectrum.
		Lasing threshold is clearly demonstrated by the characteristic increase in the differential efficiency with increase in the excitation density and by the respective narrowing of the emission spectrum.
		One should underline that the lasing wavelength is as low as 460 nm (2.69 eV) in the structure with the matrix bandgap energy E^sub g^ = 2.86 eV at 300K indicating the possibility of the ultimate shift of the lasing energy to the matrix bandgap.
	newssearch.looksmart.com /p/articles/mi_qa3776/is_199802/ai_n8802283 (1358 words)

	Organic Vertical-Cavity Surface-Emitting Laser
		Higher lasing thresholds typically observed for OSLs grown on flexible plastic sheets were due to increased waveguide losses induced by substrate roughness.
		The lasing threshold and emission wavelength are found to be strongly dependent on the concentration of DCM in Alq
		However, the demonstration of lasing in organic semiconductor DH devices over a range of wavelengths spanning the visible spectrum, is a crucial precursor to an electrically pumped OSL, providing strong motivation for further research.
	www.ieee.org /organizations/pubs/newsletters/leos/oct97/html/organic.htm (2070 words)

	Integrated optics - US Patent 5351261 (Site not responding. Last check: 2007-10-09)
		Lasing threshold for a whispering mode laser is reduced by appropriate placement of a reflector.
		This is of consequence for the microdisk laser in which retention of the lasing mode is by internal reflection within the periphery of the disk.
		The lasing threshold is linearly proportional to the reciprocal of the enhancement factor.
	www.patentstorm.us /patents/5351261.html (4848 words)

	Organic Vertical-Cavity Surface-Emitting Laser
		A clear lasing threshold is observed for both the slab and DH devices (Fig.
		The lasing threshold and emission wavelength are found to be strongly dependent on the concentration of DCM in Alq
		However, the demonstration of lasing in organic semiconductor DH devices over a range of wavelengths spanning the visible spectrum, is a crucial precursor to an electrically pumped OSL, providing strong motivation for further research.
	ieee.org /organizations/pubs/newsletters/leos/oct97/html/organic.htm (2070 words)

	Laser system providing power ramp-up and method of operating same - US Patent 6115397 (Site not responding. Last check: 2007-10-09)
		In a laser system which produces radiation which is highly absorbed by water, the pump voltage supplied to the laser rod is slowly increased between the lasing threshold voltage and the full operational voltage of the pump.
		According to an alternate embodiment, the pump voltage is increased from a lasing threshold voltage, which is the pump voltage at which the laser begins to lase.
		This is because the pump energy is related to the square of the pump voltage and the output energy is somewhat proportional to the pump energy after the voltage threshold is reached.
	www.patentstorm.us /patents/6115397.html (3240 words)

	Theory for the photon statistics of random lasers
		It was demonstrated that the lasing action was indeed due to the randomness of the medium by measuring the emitted radiation at different points on the surface of the sample, and showing that the peaks in the radiation spectrum were completely different at different points.
		Cao [9] speculates that the overlap of different modes prevents the formation of a fixed photon number in one particular mode as photons are exchanged between modes with similar frequencies all the time.
		Furthermore, the Petermann factor of the lasing mode becomes significantly large [22] which might or might not increase the amount of fluctuations.
	www.lorentz.leidenuniv.nl /~patra/quantumoptics/qo10 (4688 words)

	Lee, Reginald K. (2000-05-22) Lasing and modified spontaneous emission in photonic crystal structures and ...
		Pulsed lasing is also demonstrated with the lasing threshold at 66 mW peak incident optical pump power at a duty cycle of less than 1% in order to minimize membrane heating.
		This behaviour is explained in terms of mode Q, lasing threshold and enhanced spontaneous emission into the mode.
		Pulsed lasing at 143 K under optical pumping is demonstrated.
	etd.caltech.edu /etd/available/etd-06102005-082207 (415 words)

	Lasers
		To understand this and to see how the threshold current can be reduced we need to discuss what the threshold current is. It is the current required to give a sufficient population inversion for the round trip gain in the cavity to be greater than the round trip loss.
		This is particularly important at threshold as it is the spontaneous photons travelling along the cavity axis and being reflected back into the gain region which initiate the laser action.
		Fig 3 shows how this may be used in single and double heterostructures to confine the carriers to a small region which is defined, not by the nature of the materials, but by the thickness the layers are grown to.
	frequency-1.net (1262 words)

	Decay Rate Distributions of Disordered Slabs and Application to Random Lasers (Site not responding. Last check: 2007-10-09)
		The lasing threshold is the amplification rate at which the intensity of the emitted radiation diverges in a linear model.
		The lasing threshold is given by the value of the smallest decay rate of all eigenmodes in the amplification window [32].
		The difference to the diffusive regime is that the lasing threshold can be lowered efficiently not only by increasing the length but also decreasing the width N and hence driving the system farther into localisation.
	www.lorentz.leidenuniv.nl /~patra/quantumoptics/qo11 (6529 words)

	SPIE Proceedings Vol. 3283 (Site not responding. Last check: 2007-10-09)
		Extremely small lasing threshold is observed when the cavity resonance is tuned to the low energy tail of the inhomogeneous exciton distribution.
		A preliminary analysis indicates that the small lasing threshold observed is due to the enhanced dipole coupling rate in the microcavity as well as the very small number of localization sites resonant with the cavity when the cavity is tuned to the low energy tail of the inhomogeneous exciton distribution.
		Abstract: The lasing mode characteristics of planar and dielectrically-apertured one-wave and two-wave Fabry-Perot microcavities are analyzed theoretically using a semiclassical model, in the limit that the dielectric apertures are optically thin.
	www.spie.org /web/abstracts/3200/3283.html (11900 words)

	Er-Doped Sol-Gel Toroids
		In the low concentration limit, the threshold power increases sharply because Er3+ ions are not able to give sufficient gain required for loss compensation; while in high concentration limit, the threshold again increases due to increases of concentrationdependent loss mechanism, such as upconversion and ionpair induced quenching.
		This ultralow threshold originates from the small mode volume, high quality factor of the microcavity, and homogeneous distribution of the Er3+ inside the cavity, which enable the optimized overlap between the active region and the pump modes.
		The lasing threshold is 660 nW with pump wavelength at 1442 nm and lasing wavelength at 1553 nm.
	www.its.caltech.edu /~vahalagr/html/er-doped_sol-gel_toroids.html (562 words)

	==> All about Optics threshold (Site not responding. Last check: 2007-10-09)
		We demonstrate optical binary threshold logic by using an optoelectronic circuit.
		14, the optical threshold voltage is expressed as optics threshold.
		perceptron with a soft optical threshold is implemented as a precursor to an optics threshold.
	cri.ch /about/optics_threshold.html (212 words)

	MIJ-NSR Volume 3, Article 35
		In case of MQW active layers, homogeneous injection of carriers in all quantum wells is assumed [35] and the cumulative thickness of the active region is just the sum of the thicknesses of all the individual active regions.
		The infuence of changes in the radius of active region, in the dislocation density and in the reflectivity of resonator mirrors on the threshold currents of VCSELs with bulk, SQW and MQW active regions is shown in Table 3.
		The dependence of the threshold current density on the reflectivity of resonator mirrors for the both GG and IG VCSEL designs are plotted in Figure 4.
	nsr.mij.mrs.org /3/35/complete.html (4166 words)

	e-Prints Soton - Coexistence of low threshold lasing and strong coupling in microcavities
		We report the coexistence of low threshold lasing and strong coupling in a high-quality semiconductor microcavity under near-resonant optical pumping.
		The lasing is produced by low density localized exciton states, which are weakly coupled to the cavity mode.
		The appearance of this lasing mode distinguishes quantum-well excitons into those which are strongly or weakly coupled with the cavity mode.
	eprints.soton.ac.uk /11159 (296 words)

	Photonics aids explosives detection (Site not responding. Last check: 2007-10-09)
		The polymer can undergo lasing action at lower operating powers than previously observed, and the researchers demonstrate that the stimulated light emission from the lasing modes of the polymer displays inherently greater sensitivity to explosives vapors.
		Because the new polymer undergoes stimulated emission at lower thresholds than earlier SOP materials, the intensity of the ultraviolet light needed to start the lasing action (pump power) is reduced by more than tenfold.
		By adjusting the pump power to just over the threshold needed for lasing, it is possible to dramatically attenuate the lasing emission with parts-per-billion doses of TNT vapor.
	oemagazine.com /newscast/2005/042205_newscast01.html (454 words)

	Raman source cuts lasing threshold - optics.org
		The researchers report an ultralow lasing threshold of only 86 µW at a red-shifted wavelength of 1670 nm.
		Vahala says efficiently coupling light to and from the microspheres contributes to the low lasing threshold, but adds that the whispering gallery mode is also crucial to the lasing action.
		Vahala believes he can reduce the lasing threshold even further by decreasing the microsphere diameter to between 10 and 20 µm.
	optics.org /articles/news/8/2/9/1 (505 words)

	Photonics.com Printer Friendly View
		Above a threshold of about 0.3 nJ of pump power, the wideband output spectrum narrowed to one with a 0.22-nm-wide peak at 382 nm.
		Cao would like to lower the lasing threshold for the disordered-media laser, but the options may be limited.
		For the present, she is intrigued by the paradoxical lasing from a random medium.
	www.photonics.com /printerFriendly.aspx?contentID=79241 (441 words)

	Ultra-Low Threshold Index-Confined Microcavity Lasers - Storming Media
		The threshold was reduced to ^40 micro A for 3 micrometers laterally sized devices.
		Studies have also shown that diffraction loss due to the optical penetration depth of the lasing mode into the lower AlAs/GaAs DBR is a real problem when the device size is made smaller than -3 micrometers diameter.
		The thickness of the oxide aperture layer is an important parameter in the mode confinement, and if the aperture is too thin higher efficiency is achieved at the expense of a large mode area (loss of optical confinement).
	www.stormingmedia.us /89/8901/A890123.html (163 words)

	Infrared room temperature lasing of nanoparticles coated on a dielectric microsphere (Site not responding. Last check: 2007-10-09)
		The cw Ti:sapphire pump input and laser output are efficiently coupled to and from whispering-gallery modes of the microresonator by tapered fibers.
		Near-thresholdless behavior (threshold less than the uncertainty of the linear fit to the data, 2 um) was observed.
		Taking into account losses due to scattering and to outcoupling via the second fiber, the 2-um upper limit on the threshold is an overestimate by an order of magnitude.
	ses.confex.com /ses/2004tm/techprogram/P1613.HTM (276 words)

	[No title] (Site not responding. Last check: 2007-10-09)
		In (3) and (5), the first and second terms are the current densities associated with the spontaneous radiative recombination in QDs and in the OCL, respectively.
		Threshold current density versus (a) the normalized surface density of QDs, (b) RMS of relative QD size fluctuations and (c) cavity length.
		The electron and hole level occupancies at the lasing threshold may be expressed as a function of the root mean square (RMS) of relative QD size fluctuations
	www.edu.ioffe.ru /register/?doc=nano2000/asryan (1346 words)

	oe magazine - eye on technology (Site not responding. Last check: 2007-10-09)
		Misawa says one of the technical challenges the team faced in fabrication was that a considerable increment of emission could be expected with high Q and a small cavity.
		Lasing was observed at the rim of the microparticles at point L or S, whichever was illuminated by the excitation light.
		"The lasing threshold we observed during the experiments proved lasing emission and we detected tenfold lasing threshold discrimination for the two perpendicular polarizations of excitation," Misawa says.
	oemagazine.com /FromtheMagazine/oct03/eyeontech.html (1540 words)

	SurfWax: News, Reviews and Articles On Lasing
		In a good lasing material, electrons that are pumped up with energy release that energy in the form of coherent photons of light.
		In the April 14 issue of Nature, scientists describe a polymer that undergoes lasing action at lower operating powers than previously observed, and they demonstrate that the stimulated light emission from the lasing modes of the polymer displays inherently greater sensitivity to explosives vapors...
		By measuring the change in lasing, the scientists were able to detect TNT at concentrations as low as five parts per billion.
	telecom.surfwax.com /files/Lasing.html (899 words)

	L Squared UK - Laser Engraving, Marking and Etching Services UK : How a laser works (Site not responding. Last check: 2007-10-09)
		The population inversion is the number of atoms in the excited state versus the number in ground state.
		The ruby rod is the lasing medium and the flash tube pumps it.
		Solid-state lasers have lasing material distributed in a solid matrix (such as the ruby or neodymium:yttrium-aluminum garnet "Yag" lasers).
	www.lasermarked.com /howlasersworks.html (2174 words)

	Laser diodes
		For lasing to occur, the optical gain of the selected modes must exceed the optical loss during one round-trip through the cavity.
		The lasing threshold is the lowest drive current level at which the output of the laser results primarily from stimulated emission rather than spontaneous emission.
		However, after the threshold current is reached, the optical output power increases significantly with small changes in drive currents.
	www.tpub.com /neets/tm/110-5.htm (650 words)

	Global rate equation description of a laser (Site not responding. Last check: 2007-10-09)
		For a single mode Fabry-Perot laser, we prove that the contribution to the steady state intensity from the lasing mode varies from 75% close to the lasing threshold to zero at high intensity.
		The remainder is the contribution from the harmonics of the lasing mode.
		Analyzing the steady state single mode intensity equation in terms of the pump gratings, we prove that close to the lasing threshold only the space average of the pump and its grating oscillating at twice the lasing wave number do not vanish.
	www.ulb.ac.be /sciences/ont/abstract/abs-mandel-28.html (294 words)

	Plasma Laser Stars
		If the lasing medium is contained within a Fabry-Perot type of resonant cavity, and if the radiation intensity is larger that a well defined threshold where gain exceeds loss, then almost all of the excited ions decay prematurely by stimulated emission.
		In a lasing medium with a population inversion (to any degree), since the lasing medium acts like an amplifier it will amplify any radiation at the precise wavelength of the laser transition.
		Photons that produce the quantum transition by spontaneous emission have a much better chance of being amplified because they are more numerous than stellar photons at that particular wavelength that those from the nearby flbody, and so the emission line laser radiation from quasars is mostly from amplified spontaneous emission rather than amplified photospheric emission.
	laserstars.org /glossary/laser.html (1039 words)

	IngentaConnect Low-threshold lasing and broad-band multiphoton-excited light emi... (Site not responding. Last check: 2007-10-09)
		Low-threshold lasing and broad-band multiphoton-excited light emission from Ag aggregate-adsorbate complexes in microcavity
		A novel class of composites for optics, microcavities doped with metal fractal aggregates, is studied.
		Lasing and broad-band Stokes and anti-Stokes emission from (Ag colloidal aggregates)/(adsorbed molecules)/(microcavity) composite at low-intensity cw and pulse laser excitation has been found.
	www.ingentaconnect.com /content/tandf/tmop/2002/00000049/F0020003/art00028 (267 words)

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