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Spontaneous Emission (spontaneous + emission)
Kinds of Spontaneous Emission Selected AbstractsAmplified Spontaneous Emission of Poly(ladder-type phenylene)s , The Influence of Photophysical Properties on ASE Thresholds,ADVANCED FUNCTIONAL MATERIALS, Issue 20 2008Frédéric Laquai Abstract Amplified spontaneous emission (ASE) of a series of blue-emitting poly(ladder-type phenylene)s (LPPP)s has been studied in thin film polymer waveguide structures. The chemically well-defined step-ladder polymers consist of an increasing number of bridged phenylene rings per monomer unit starting from fully arylated poly(ladder-type indenofluorene) up to poly(ladder-type pentaphenylene). The ASE characteristics of the polymers including the onset threshold values for ASE, the gain and loss coefficients as well as the photoluminescence (PL) properties, i.e., the solid state fluorescence lifetimes, decay kinetics and solid state quantum efficiencies have been studied by time-resolved PL spectroscopy. A fully arylated polyfluorene has been synthesized and its photophysical properties were compared to the step-ladder polymers. Steady-state photoinduced absorption and ultrafast transient absorption spectroscopy have been used to study excited state absorption of singlet and triplet states and polarons present in the solid state. The results demonstrate a minimum regarding the onset threshold value of ASE for a fully arylated poly(ladder-type indenofluorene) and a successive increase of the ASE threshold for the step-ladder polymers with more bridged phenylene rings. In particular, carbazole-containing step-ladder LPPPs exhibit significantly increased ASE threshold values as compared to their carbazole-free analogues due to a pronounced overlap of stimulated emission (SE) and photoinduced absorption (PA). [source] Effect of Molecular Morphology on Amplified Spontaneous Emission of Bis-Styrylbenzene DerivativesADVANCED MATERIALS, Issue 40 2009Ryota Kabe Molecular aggregation greatly affects the fluorescence quantum efficiency, transient lifetime, and amplified spontaneous emission (ASE) of bis-styrylbenzene derivatives. We compare the optical properties for various morphologies (solution, film, doped film, and single crystalline state) (see figure) and demonstrate that ambipolar operation of a 1,4-bis(4-methylstyryl) benzene layer in field-effect transistors leads to intense blue electroluminescence with a rather sharp emission width. [source] Theoretical investigations on anisotropic optical properties in semipolar and nonpolar InGaN quantum wellsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 9 2008Kazunobu Kojima Abstract The anisotropic band structures and spontaneous emission of the non c plane InGaN/GaN quantum wells (QWs) were computed based on the k·p perturbation theory. Spontaneous emission due to the A valence band is strongly polarized perpendicular to the c axis, while that from the B band has 90º-rotated polarization, for the crystal angle , larger than 50°. However, it was found that excited carriers can distribute into both the A and B bands, so that the effective polarization Peff defined by the integrated luminescence intensity is much reduced even for nonpolar InGaN/GaN QWs. Thus, Peff was systematically studied for arbitrary planes. We found that the energy separation between the A and B bands becomes significant and carrier population of the B valence band is suppressed as the In content increases, when Peff approaches unity. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Spontaneous emission from semiconductor nanocrystals in coupled spherical microcavitiesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2005Yu. P. Rakovich Abstract We report on the coherent coupling of whispering gallery modes (WGM) in a photonic molecule formed from two melamine-formaldehyde spherical microcavities coated with a thin shell of light-emitting CdTe nanocrystals (NCs). Utilizing different excitation conditions the splitting of the WGM resonances originating from bonding and anti-bonding branches of the photonic states is observed and fine structure consisting of very sharp peaks resulting from lifting of the WGM degeneracy has been detected. Time-resolved measurements showed a slight increase in the spontaneous emission rate of NCs in a photonic molecule when compared to the spontaneous emission rate for NCs coating a single microsphere. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The origins and present status of the radio wave controversy in NMRCONCEPTS IN MAGNETIC RESONANCE, Issue 4 2009D.I. Hoult Abstract The origins, history, and present status of the controversy surrounding a quantum description of the NMR signal as being due to radio waves are traced. With the Principle of Relativity and Coulomb's Law as formal starting points and the minimum of mathematics needed for understanding, the derivation of a classical electromagnetic theory of signal reception is first given. The agreement between that classical theory and a recent NMR experiment is then presented, leading to proof that, except for the highest field imaging experiments, there is no significant contribution of radio waves to the signal. Attention is drawn to the very different properties of the near and far energy, momenta, and fields inherent in the derivation. The role of the Correspondence Principle in formulating a quantum description is then emphasized and it is shown that the standard NMR interpretation of Dicke's theory of coherent spontaneous emission,that the latter is responsible for the NMR signal,cannot be correct. Finally, the author speculates on some of the intriguing relationships found in the classical electrodynamics of NMR signal reception and attempts to relate them to a common quantum electrodynamic precept of near field interaction: that the free induction decay voltage present at the terminals of an open-circuit receiving coil is based on an exchange of virtual photons between the nuclei in a sample and the free electrons in a receiving coil. © 2009 Crown in the right of Canada. Concepts Magn Reson Part A 34A: 193,216, 2009. [source] Cavity QED with a trapped ionFORTSCHRITTE DER PHYSIK/PROGRESS OF PHYSICS, Issue 2-3 2003W. Vogel A trapped ion in a leaky cavity is studied in the regime of strong atom-field coupling. Particular emphasis is paid on nonlinearities due to smooth localization of the ion's wavefunction and on decoherence effects caused by spontaneous emission and cavity losses. Possibilities of quantum-state preparation are analyzed and single-ion lasing is considered. [source] Low-Threshold Distributed-Feedback Lasers Based on Pyrene-Cored Starburst Molecules with 1,3,6,8-Attached Oligo(9,9-Dialkylfluorene) ArmsADVANCED FUNCTIONAL MATERIALS, Issue 17 2009Ruidong Xia Abstract Here, a detailed characterization of the optical gain properties of sky-blue-light-emitting pyrene-cored 9,9-dialkylfluorene starbursts is reported; it is shown that these materials possess encouragingly low laser thresholds and relatively high thermal and environmental stability. The materials exhibit high solid-state photoluminescence (PL) quantum efficiencies (>90%) and near-single-exponential PL decay transients with excited state lifetimes of ,1.4,ns. The thin-film slab waveguide amplified spontaneous emission (ASE)-measured net gain reaches 75,78,cm,1. The ASE threshold energy is found to remain unaffected by heating at temperatures up to 130,°C, 40 to 50,°C above Tg. The ASE remained observable for annealing temperatures up to 170 or 200,°C. 1D distributed feedback lasers with 75% fill factor and 320,nm period show optical pumping thresholds down to 38,65,Wcm,2, laser slope efficiencies up to 3.9%, and wavelength tuning ranges of ,40,nm around 471,512,nm. In addition, these lasers have relatively long operational lifetimes, with N1/2,,,1.1,×,105,pulses for unencapsulated devices operated at ten times threshold in air. [source] Amplified Spontaneous Emission of Poly(ladder-type phenylene)s , The Influence of Photophysical Properties on ASE Thresholds,ADVANCED FUNCTIONAL MATERIALS, Issue 20 2008Frédéric Laquai Abstract Amplified spontaneous emission (ASE) of a series of blue-emitting poly(ladder-type phenylene)s (LPPP)s has been studied in thin film polymer waveguide structures. The chemically well-defined step-ladder polymers consist of an increasing number of bridged phenylene rings per monomer unit starting from fully arylated poly(ladder-type indenofluorene) up to poly(ladder-type pentaphenylene). The ASE characteristics of the polymers including the onset threshold values for ASE, the gain and loss coefficients as well as the photoluminescence (PL) properties, i.e., the solid state fluorescence lifetimes, decay kinetics and solid state quantum efficiencies have been studied by time-resolved PL spectroscopy. A fully arylated polyfluorene has been synthesized and its photophysical properties were compared to the step-ladder polymers. Steady-state photoinduced absorption and ultrafast transient absorption spectroscopy have been used to study excited state absorption of singlet and triplet states and polarons present in the solid state. The results demonstrate a minimum regarding the onset threshold value of ASE for a fully arylated poly(ladder-type indenofluorene) and a successive increase of the ASE threshold for the step-ladder polymers with more bridged phenylene rings. In particular, carbazole-containing step-ladder LPPPs exhibit significantly increased ASE threshold values as compared to their carbazole-free analogues due to a pronounced overlap of stimulated emission (SE) and photoinduced absorption (PA). [source] Effect of Molecular Morphology on Amplified Spontaneous Emission of Bis-Styrylbenzene DerivativesADVANCED MATERIALS, Issue 40 2009Ryota Kabe Molecular aggregation greatly affects the fluorescence quantum efficiency, transient lifetime, and amplified spontaneous emission (ASE) of bis-styrylbenzene derivatives. We compare the optical properties for various morphologies (solution, film, doped film, and single crystalline state) (see figure) and demonstrate that ambipolar operation of a 1,4-bis(4-methylstyryl) benzene layer in field-effect transistors leads to intense blue electroluminescence with a rather sharp emission width. [source] Organic,Inorganic Sol,Gel Composites Incorporating Semiconductor Nanocrystals for Optical Gain ApplicationsADVANCED MATERIALS, Issue 17 2009Miri Kazes Organic-inorganic sol-gel composite incorporating highly emitting CdSe/ZnS quantum dots and CdSe/CdS/ZnS quantum rods is reported. Optical gain measurements conducted on a quantum rod/sol-gel composite film show stable room temperature amplified spontaneous emission under ambient conditions. [source] Photonic Crystals from Monodisperse Lanthanide-Hydroxide-at-Silica Core/Shell Colloidal Spheres,ADVANCED MATERIALS, Issue 4 2007Y.-S. Lin A facile one-pot synthesis of size- controlled monodisperse lanthanide- hydroxide-at-SiO2 core/shell colloids is reported. The base-synthesized lanthanide-hydroxide-at-SiO2 particles are nonsticky enough to be well-suspended in solution, and they self-organize into 3D photonic crystals (see figure) that show a strong suppression of spontaneous emission in the photonic stop band. [source] A method for controlling the spins of atoms using optical near-fieldsJOURNAL OF MICROSCOPY, Issue 3 2003A. Shojiguchi Summary On the basis of the procedure for controlling the spins of atoms using circularly polarized evanescent light proposed by Hori et al.[(1996) Abstracts of the 1st Asia-Pacific Workshop on Near-field Optics] we discuss the influence of boundary conditions on the probability of spontaneous emission and thus on the spin polarization efficiency, which was not considered in the Hori et al. study. Using the Carniglia,Mandel mode expansion of electromagnetic fields, we derive the spontaneous emission and spin polarization probabilities of atoms near a dielectric surface, and show the atom,surface distance dependence and refractive index dependence. Numerical evaluation for the 6P1/2,6S1/2 transition of a Cs atom indicates an increase in the efficiency of spin polarization by 30%. [source] Future possibilities of the Linac Coherent Light SourceJOURNAL OF SYNCHROTRON RADIATION, Issue 3 2004M. Cornacchia A study of the potential for the development of the Linac Coherent Light Source (LCLS) beyond the specifications of the baseline design is presented. These future developments include delivery of X-ray pulses in the 1,fs regime, extension of the spectral range, increase of the FEL power, exploitation of the spontaneous emission, and a more flexible time structure. As this potential is exploited, the LCLS can maintain its role as a world-leading instrument for many years beyond its commissioning in 2008 and initial operation as the world's first X-ray free-electron laser. [source] Dynamical diffraction of ultrashort X-ray free-electron laser pulsesJOURNAL OF SYNCHROTRON RADIATION, Issue 5 2001S. D. Shastri Calculations are presented for the femtosecond time-evolution of intensities of beams diffracted by perfect Bragg crystals illuminated with radiation expected from X-ray free-electron lasers (XFELs) operating through the self-amplified spontaneous emission (SASE) process. After examining the case of transient diffraction of an electromagnetic delta-function impulse through flat, single- and double-crystal monochromators, the propagation of a 280,fs-duration SASE XFEL pulse of 8,keV photons through the same optics is discussed. The alteration of the sub-femtosecond spiky microbunched temporal structure of the XFEL pulse after it passes through the system is shown for both low-order (broad bandwidth) and high-order (narrow bandwidth) crystal reflections. Finally, the shot-to-shot statistical fluctuations of the integrated diffracted intensity is simulated. Implications of these results for XFEL applications are addressed. [source] Single-stage gain-clamped L-band EDFA with C-band ASE self-oscillation in ring cavityLASER PHYSICS LETTERS, Issue 2 2008M.A. Mahdi Abstract We demonstrate single-stage gain-clamped L-band Er3+ -doped fiber amplifier (EDFA) utilizing self-oscillation modes as the control light. The amplifier structure exploits the characteristics of C/L-band coupler to isolate between lasing modes and L-band signal. The self-lasing cavity modes are obtained without any tunable bandpass filter in the loop and generated from the amplified spontaneous emission in the C-band region. The amplifier configuration has lower noise figures as opposed to a dual-stage partially gain-clamped amplifier. The gain and noise figure fluctuations are less than ±0.4 dB in the gainclamping region. The transient analysis confirms that the maximum power excursion is less than 0.3 dB for 10-dB add/drop. (© 2007 by Astro Ltd., Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source] All optical multi-tap microwave filter with high sidelobe suppression using peak profile of ASE and one multiwavelength FBGMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 10 2009Li Xia Abstract A new all optical 10-tap microwave filter is proposed using a broadband amplified spontaneous emission (ASE) light source and a single specially designed multiwavelength FBG. Measured results show that the sidelobe suppression is larger than 20 dB. The filter response is insensitive to the polarization state of light. This technique enables one to obtain a simple and low cost photonic microwave filter with a stable response. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2522,2524, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24666 [source] Enhancement of Brillouin stokes powers in multiwavelength fiber laser utilizing band-pass filterMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 5 2004S. Saharudin Abstract We report an increased number of stokes when used with a band-pass filter in multiwavelength Brillouin erbium-doped fiber laser (BEFL). A total of 15 Stokes were achieved as compared with seven in a system without the band-pass filter. The efficiency of generating Brillouin Stokes improved due to the suppression of out-of-band amplified spontaneous emission in the BEFL. The band-pass filter provides a specific range of lasing window that coincide with the Brillouin pump signal. The flatness of the Brillouin stokes is also improved in the proposed design. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 40: 408,410, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11395 [source] Efficient multiwavelength linear cavity erbium-doped fiber laser over 1570,1600 nmMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 4 2002Chun-Liu Zhao Abstract A simple and efficient L-band multiwavelength linear cavity fiber laser was obtained at room temperature by recycling detrimental 1550-nm band amplified spontaneous emission as a secondary pump source for the unpumped EDF section of fiber laser. The cavity was formed by two linear fiber loops. By changing the states of PCs inserted to fiber loops, stable dual- and tri-wavelength lasers with about 1-mW/channel were generated at room temperature. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 34: 296,299, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10441 [source] Polarization of eigenmodes in laser diode waveguides on semipolar and nonpolar GaNPHYSICA STATUS SOLIDI - RAPID RESEARCH LETTERS, Issue 1-2 2010Jens Rass Abstract Recent calculations of the eigenmodes in waveguides grown on semipolar GaN suggest that the optical polarization of the emitted light as well as the optical gain depends on the orientation of the resonator. Our measurements on separate confinement heterostructures on semipolar (112) and (102) GaN show that for laser resonators along the semipolar [11] and [011] directions (i.e. the projection of the c -axis onto the plane of growth) the threshold for amplified spontaneous emission is lower than for the nonpolar direction and that the stimulated emission is linearly polarized as TE mode. For the waveguide structures along the nonpolar [100] or [110] direction on the other hand, birefringence and anisotropy of the optical gain in the plane of growth leads not only to a higher threshold but alsoto a rotation of the optical polarization which is not any more TE- or TM-polarized but influenced by the ordinary and extraordinary refractive index of the material. We observe stimulated emission into a mode which is linearly polarized in extraordinarydirection nearly parallel to the c -axis. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Optical gain and gain saturation of blue-green InGaN quantum wellsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2010Dmitry Sizov Abstract Using varied stripe length method we systematically studied optical gain properties of blue-green 3,nm InGaN QWs grown on c -plane and (11,22) semipolar substrates. We determined that for such structures when the product of modal net gain at peak and stripe length exceeds factor 5 the gain saturation occurs due to depletion of pumped carriers. We then focused our attention on the gain in unsaturated conditions. We observed strong gain peak position blue shift with increase of pumping power for both substrate orientations due to quantum well state filling and for c -plane due to piezoelectric field screening. Thus in order to increase lasing wavelength, minimizing optical losses, and maximizing modal gain are essential. We then found that for the semipolar QWs the gain at ,500,nm was 2× higher with the stripe along [,1,123] direction despite the fact that at low pumping level the polarization switching of spontaneous emission resulted predominant E||[,1,123]. Finally we compared the semipolar and c -plane QWs and found that the gain increase with pumping power of c -plane QW is slower than that for semipolar QW in high gain direction while the transparency pumping power is lower for c -plane. [source] Microcavity modified spontaneous emission of single quantum dotsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 8 2007G. S. Solomon Abstract We summarize our earlier research showing how the radiative properties of an individual InAs quantum dot exciton state can be altered by their spatial and spectral position with respect to a discrete semiconductor microcavity mode. The InAs quantum dot is formed epitaxially in GaAs, and the microcavity is processed from a one-wavelength distributed Bragg reflector planar microcavity of GaAs and AlAs to form a sub-micrometer diameter pillar. Two states are tuned through a discrete cavity mode through sample temperature changes and show a spontaneous emission enhancement of 4. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Optically pumped lasing and gain formation properties in blue Inx Ga1,x N MQWsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 12 2004K. Kojima Abstract Lasing and gain formation properties have been studied in an InxGaN1,x multiple quantum wells lasing at around 460 nm by employing the modified variable stripe length method (VSLM) and pump and probe spectroscopy (P&P). It was found that the spontaneous emission (Esp) appeared far below absorption edge (Ea) that is observed as a photo-bleaching negative-peak in P&P, indicating the formation of localized tail states. Lasing peaks appeared in between Esp and Ea with wide spectral distribution. This is consistent with the results where VSLM revealed the broad feature of optical gain spectra associated with rapid peak saturation of lasing even just above the threshold photo-pumping power density. Such mechanism observed in In-rich InxGa1,xN MQWs is contributed not only from the broad distribution of localized density-of-states but also from hot carrier distribution (determined by Maxwell,Boltzmann statistics), temperature of which is raised up due to long energy relaxation time to localized tail states. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Ultrafast intensity correlation measurements of quantum dot microcavity lasersPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2009M. Aßmann Abstract We present an experimental technique, which allows us to determine the second order correlation function g(2) (t, t + ,) with picosecond time resolution. The method involves a streak camera which is modified such that a signal at fixed wavelength can be monitored after each pulsed laser excitation. From these measurements insight into the quantum optical properties of light emission from semiconductor nanostructures with dynamics on the sub-ns time scale can be taken. To demonstrate the possibilities of our setup, we present time resolved g(2) -measurements of quantum dot VCSEL micropillar emission. We show, that our measurement scheme enables us to determine the transition from predominantly spontaneous emission towards stimulated emission and the temporal evolution of the intensity correlation function. Additionally, we are also able to identify unexpected features like dynamical antibunching. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Theoretical investigations on anisotropic optical properties in semipolar and nonpolar InGaN quantum wellsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 9 2008Kazunobu Kojima Abstract The anisotropic band structures and spontaneous emission of the non c plane InGaN/GaN quantum wells (QWs) were computed based on the k·p perturbation theory. Spontaneous emission due to the A valence band is strongly polarized perpendicular to the c axis, while that from the B band has 90º-rotated polarization, for the crystal angle , larger than 50°. However, it was found that excited carriers can distribute into both the A and B bands, so that the effective polarization Peff defined by the integrated luminescence intensity is much reduced even for nonpolar InGaN/GaN QWs. Thus, Peff was systematically studied for arbitrary planes. We found that the energy separation between the A and B bands becomes significant and carrier population of the B valence band is suppressed as the In content increases, when Peff approaches unity. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Comprehensive modelling of resonant-cavity light-emitting diodePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 5 2007Z. Q. Li Abstract We extended the theory by Henry (J. Lightwave Technol. LT-4, 288 (1986) [1]) to accurately treat the coupling of spontaneous emission noise with microcavity modes. The Green's function method is employed to solve the inhomogeneous wave equation including a Langevin force F, which accounts for spontaneous emission by carriers at angular frequency ,. The optical wave equation is coupled with the self-consistent calculations of the material spontaneous emission rate of quantum well/dot using envelope wavefunction method. Finally the carrier transport equations are solved within the framework of 2D/3D drift-diffusion model implemented in the Crosslight Software package APSYS (Crosslight APSYS User's Manuals, Copyright © Crosslight Software Inc. (version 2005. 11) [2]). (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Microscopic theory for intersubband spontaneous emissionPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2007M. F. Pereira Jr. Abstract The amplified spontaneous emission spectra of quantum-cascade laser structures is computed with a Keldysh Green's functions theory. We show that the emission spectra are sharpened in comparison to gain spectra due to wave guide propagation. In addition the different dependence on level occupation causes moderate differences between gain and emission peak positions. Our fit-parameter-free theory is valid in ranges of strong nonequilibrium, where fit-parameters do not even exist. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Coherent effects in coupled resonator optical waveguidesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2007Vassilios Yannopapas Abstract We analyze the spontaneous emission and the probe absorption-dispersion spectra of ,-type atomic systems embedded in a coupled resonator optical waveguide (CROW), where one of the atomic transitions decays spontaneously in a CROW and the other decays spontaneously in free space vacuum. We first show that double dark lines can appear in this system. We also show that the atoms become transparent at two different frequencies of a probe laser field coupled to the free space transition. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Characteristics of amplified spontaneous emission of high indium content InGaN/GaN quantum wells with various silicon doping conditionsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2003Yung-Chen Cheng Abstract We compared the temperature dependent spectral variations of the amplified spontaneous emission (ASE) between InGaN/GaN quantum well samples of no doping, well doping, and barrier doping of silicon. The comparisons were particularly made between two series of samples with a low and a high indium content. The results show that a multi-peak ASE spectral feature and a low energy stimulated emission peak, existing at the photoluminescence shoulder, could be observed only in the high-indium-content, barrier-doped sample. Such results are supposed to originate from the formation of quantum dots of various sizes, concentrations, and shapes under the condition of barrier doping in the sample. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Light transport and correlation length in a random laserANNALEN DER PHYSIK, Issue 12 2009R. Frank Abstract A random laser is a strongly disordered, laser-active optical medium. The coherent laser feedback, which has been demonstrated experimentally to be present in these systems beyond doubt, requires the existence of spatially localized photonic quasimodes. However, the origin of these quasimodes has remained controversial. We develop an analytical theory for diffusive random lasers by coupling the transport theory of the disordered medium to the semiclassical laser rate equations, accounting for (coherent) stimulated and (incoherent) spontaneous emission. From the causality of wave propagation in an amplifying, diffusive medium we derive a novel length scale which we identify with the average mode radius of the lasing quasi-modes. We show that truly localized modes do not exist in the system without photon number conservation. However, we find that causality in the amplifying medium implies the existence of a novel, finite intensity correlation length which we identify with the average mode volume of the lasing quasimodes. We show further that the surface of the laser-active medium is crucial in order to stabilize a stationary lasing state. We solve the laser transport theory with appropriate surface boundary conditions to obtain the spatial distributions of the light intensity and of the occupation inversion. The dependence of the intensity correlation length on the pump rate agrees with experimental findings. [source] Spontaneous emission of light from atoms: the modelANNALEN DER PHYSIK, Issue 7 2005P. Marecki Abstract We investigate (non-relativistic) atomic systems interacting with quantum electromagnetic field (QEF). The resulting model describes spontaneous emission of light from a two-level atom surrounded by various initial states of the QEF. We assume that the quantum field interacts with the atom via the standard, minimal-coupling Hamiltonian, with the A2 term neglected. We also assume that there will appear at most single excitations (photons). By conducting the analysis on a general level we allow for an arbitrary initial state of the QEF (which can be for instance: the vacuum, the ground state in a cavity, or the squeezed state). We derive a Volterra-type equation which governs the time evolution of the amplitude of the excited state. The two-point function of the initial state of the QEF, integrated with a combination of atomic wavefunctions, forms the kernel of this equation. [source] | ||||||||||||||||||||||||||||