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Population Inversion (population + inversion)
Selected AbstractsEnergy Transfer and Population Inversion in Heavy Metal Oxide Glasses Doped with Tm3+ and Tb3+JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2004Jay Hyok Song Emission properties and energy transfer of PbO,Bi2O3,Ga2O3,GeO2 glasses codoped with Tm3+ and Tb3+ ions were investigated. The 1.48-,m emission due to the Tm3+:3H4,3F4 transition can be used to amplify the S-band (1460,1530-nm) signal light. With Tb3+ addition, the lifetime and emission intensity of the Tm3+:3F4 level decreased sharply via the Tm3+:3F4,Tb3+:7F0,1,2 energy transfer. Population densities of the 3F4 and 3H4 levels in Tm3+ calculated from rate equations clearly verified that population inversion in Tm3+ ions became possible with as little as 0.1 mol% of Tb3+ addition. [source] Population inversion of photoexcited electrons and holes in graphene and its negative terahertz conductivityPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2008Victor Ryzhii Abstract We demonstrate that sufficiently strong optical excitation may result in the population inversion in graphene, so that the real part of the ac conductivity can be negative in the terahertz range of frequencies. We study also how the heating of the electron-hole system influences the effect of negative ac conductivity. The effect of population inversion and negative ac conductivity might be used in graphene-based coherent sources of terahertz electromagnetic radiation. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Interaction of a two-level cyclic XY n -spin model with a two-mode cavity field in off-resonant statesINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 2 2008Horacio Grinberg Abstract The interaction of the XY n -spin cyclic model with a two-mode cavity field in the rotating-wave approximation is investigated in the framework of a generalized Jaynes,Cummings two-level system consisting of the vacuum state and a thermally averaged manifold of excited sates. Computation of the energy of this manifold allows this interaction to be examined in off-resonant states. Time evolution of the population inversion, photon distribution, and temperature distribution for an excited initial state are computed via second- and third-order perturbation expansion of the time evolution operator matrix elements for the excited and ground states, respectively and for an ideal squeezed initial coherent state of the cavity field. It was assumed that the two modes have initially the same photon distribution. The pattern of the spin population inversion appears as a manifestation of multiple and complicated inerferences, which is mathematically reflected in a double discrete summation that appears in the calculation of the dynamics. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source] Energy Transfer and Population Inversion in Heavy Metal Oxide Glasses Doped with Tm3+ and Tb3+JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2004Jay Hyok Song Emission properties and energy transfer of PbO,Bi2O3,Ga2O3,GeO2 glasses codoped with Tm3+ and Tb3+ ions were investigated. The 1.48-,m emission due to the Tm3+:3H4,3F4 transition can be used to amplify the S-band (1460,1530-nm) signal light. With Tb3+ addition, the lifetime and emission intensity of the Tm3+:3F4 level decreased sharply via the Tm3+:3F4,Tb3+:7F0,1,2 energy transfer. Population densities of the 3F4 and 3H4 levels in Tm3+ calculated from rate equations clearly verified that population inversion in Tm3+ ions became possible with as little as 0.1 mol% of Tb3+ addition. [source] Dynamic resonances in ultra-short laser pulsesLASER PHYSICS LETTERS, Issue 6 2007N.V. Bordyug Abstract Dynamic multiphoton resonances in ultra-short superintense laser pulses consisting of 50,200 field periods are considered numerically for a two-level system. The impact of nonresonant (Bloch-Siegert) and carrier-envelope effects on the dynamics of a two-level system was studied numerically, and conditions for complete population inversion were derived. The widths of multiphoton resonances increase with the increasing of the laser field. Results do not depend practically on the pulse duration. Effective resonance frequencies for multiphoton resonances increases strongly in a super-intense field. Multiphoton resonances are shifted and unified with each other in super-intense laser fields. (© 2007 by Astro Ltd., Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source] Astrophysical laser operating in the O i 8446-Å line in the Weigelt blobs of , CarinaeMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2005S. Johansson ABSTRACT Within the framework of a simple model of photophysical processes in the Weigelt blobs in the vicinity of the luminous blue variable (LBV) star , Carinae, we explain the presence of the fluorescent ,O i, 8446-Å and forbidden [O i] 6300-Å lines as well as the absence of the allowed O i 7774-Å line in spectra recorded with the Hubble Space Telescope (HST)/STIS instrument (Gull et al.). From atomic data and estimated stellar parameters we demonstrate that there is a population inversion and stimulated emission in the 3p 3P,3s 3S transition ,8446 due to photoexcitation by accidental resonance (PAR) by H Ly, radiation. [source] Electron and phonon dynamics in zincblende gallium nitridePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2009R. Brazis Abstract This report presents new Monte Carlo simulation results revealing the ballistic stage of growth of the phonon number, electron velocity and energy upon the switching-on electric field, the shape of electron and phonon stationary distributions in high electric fields, as well as electron cooling and phonon number relaxation rates after switching-off the field in zincblende gallium nitride crystals. LO phonon band population inversion is feasible here up to the room temperature relative to the TO phonons, and below T < 80 K , relative to the LA-phonon band provided that the phonon lifetimes satisfy the conditions of , 2 ps (LO) and , 2 ns (LA). Phonon decay scenarios with the stimulated emission of infrared-range photons are discussed including phonon difference transitions. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Population inversion of photoexcited electrons and holes in graphene and its negative terahertz conductivityPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2008Victor Ryzhii Abstract We demonstrate that sufficiently strong optical excitation may result in the population inversion in graphene, so that the real part of the ac conductivity can be negative in the terahertz range of frequencies. We study also how the heating of the electron-hole system influences the effect of negative ac conductivity. The effect of population inversion and negative ac conductivity might be used in graphene-based coherent sources of terahertz electromagnetic radiation. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] |