Showing papers on "Spontaneous emission published in 1979"
TL;DR: In this paper, the spontaneous emission factor of planar stripe laser with narrow stripe is calculated and it is shown that spontaneous emission is approximately proportional to the solid angle of laser radiation and nearly independent of transverse active layer dimensions.
Abstract: The fraction of spontaneous emission going into an oscillating laser mode has been calculated. It is shown that this fraction strongly depends on the strength of astigmatism in the laser output beam. Therefore the spontaneous emission factor in planar stripe lasers with narrow stripe is in the order of 10-4and by one order of magnitude larger than in injection lasers with a comparable active layer volume and with a built-in index waveguide. It is shown that the spontaneous emission factor is approximately proportional to the solid angle of laser radiation and nearly independent of the transverse active layer dimensions. Owing to the large spontaneous emission factor, the spectral width of narrow planar stripe lasers is significantly broader compared to narrow stripe lasers with a built-in index waveguide. In addition the large spontaneous emission coefficient also yields a much stronger damping of relaxation oscillations.
474 citations
TL;DR: In this article, the effect of bandwidth and coherence properties of the excitation source on the decay and dephasing of isolated large molecules was studied using three different excitation sources, a single mode dye laser, a multimode dye laser and an incoherent N2 flash lamp.
Abstract: One purpose of this paper is to present new studies on the effect of bandwidth and the coherence properties of the excitation source on the decay and the dephasing of isolated large molecules. A detailed study of the system pentacene in a p-terphenyl matrix is presented utilizing three different excitation sources, a single mode dye laser (60 KHz–6 MHz bandwidth depending on the time scale of the experiment) a multimode dye laser (240 GHz bandwidth), and an incoherent N2 flash lamp. Optical T1 (the longitudinal relaxation time) and T2 (the transverse relaxation time) are measured from the coherent and incoherent transients observed either in the forward direction of the laser or at right angles to the exciting beam. At 1.8 °K, the optical transition (1A1g-->1B2u) of pentacene in p-terphenyl exhibits four sites, the lowest of which at 16 887 cm−1 has the following parameters: T2=44±2 nsec; T1=24.9±2 nsec, and µ=0.7±0.1 D. The transition moment µ, is obtained directly from the optical nutation, which exhibits a Rabi nutation time (h-slash/µ·epsilon) of 27.3 nsec, and is corrected for the effect of the Lorentz local field inside the terphenyl crystal. The experiments presented here are categorized into two time regimes for theoretical analysis; a transient coherence regime where the observed decay is comparable with (h-slash/µ·epsilon) and T2, and a steady-state coherence regime where transient dephasing is complete and the off-diagonal elements of the density matrix have decayed to their steady-state values in the presence of the field of amplitude epsilon. Using the Wilcox–Lamb method, rate equations (with T2 expressions) describing the population flow in the ''complete'' level structure of pentacene (ground||0>, singlet ||p>, and triplet {||l}) are derived from the density matrix equations of motion. When these equations are averaged over the inhomogeneous width of the optical transition and the measured Gaussian transverse profile of our laser we obtain T1p0=24.9±2 nsec and T1pl=15.7 µsec, the time constants by which pentacene spontaneously decays to ||0> or crosses over into l, as well as the averaged population at time t. In an effort to be complete, attention is placed upon the relationship between theory and the experimental findings. First, expressions for the OFID and nutation in the solid are presented for the pentacene case in order to relate T1, T2, and µ to the level structure. Second, at low temperatures (1.8 °K), the origin of dephasing is identified as spontaneous emission from p-->0 since experimentally T2?2T1, in agreement with other work. At higher temperature, however, a strongly temperature dependent dephasing process with an onset at 3.7 °K takes place. Armed with these observations we present a theoretical treatment of these distinct dephasing channels and their temperature dependences. A discussion regarding the influence of ''accepting'' phonon modes (either optical or acoustic) on optical dephasing is also given. The results indicate that the treatment of Jones et al. can (1) explain the observed temperature dependence of T2 in pentacene; (2) distinguish dephasing as a result of scattering by acoustic phonons from that due to resonance or quasilocalized phonons with clear connections to gas and liquid state theories, but without invoking more than two approximation levels. (3) explain both the level shift and line width changes as a result of ''conventional'' dephasing or dephasing by exchange mechanisms; and (4) relate the pure dephasing term to an anisotropy in the scattering amplitudes (between the ground and excited states in the system) which contribute largely to the homogeneous width of the transition. Optical site selection of these transitions is also reported and discussed in relation to vibrational relaxation and to both homogeneous and inhomogeneous broadenings. The studies of the homogeneous broadening of the vibronic origin (267 cm−1) indicate that vibrational relaxation is fast (psec) in the excited singlet manifold of pentacene. Finally from more than ten independent experiments including single and multimode excitation, on- and off-resonance scattering, Zeeman effect and the transient decay as a function of excess energy in the molecule, a more complete picture of the pentacene level structure {||l>} is given. With this in mind, the influence of the laser bandwidth and coherence properties on state preparation and subsequent dephasing and decay is concluded. It is proposed that the slow decay, (~15 µsec) observed during narrow-band excitation represents intersystem crossing to nearby triple manifolds after the transient coherence of the 0 p subsystem is decayed. In addition, the decay of the primary state prepared in these experiments is not sensitive to the bandwidth or the correlation time of our excitation sources.
111 citations
TL;DR: A condition for single longitudinal mode operation (SMO) of index-guided injection lasers is given theoretically and supported by experiment in this article, where the transverse higher modes must be cut off by using a narrow-width index-guiding waveguide.
Abstract: A condition for single longitudinal mode operation (SMO, for short) of index-guided injection lasers is given theoretically and supported by experiment. For SMO, the transverse higher modes must be cut off by using a narrow-width index-guiding waveguide. Inclusion of the spontaneous emission into the lasing field must be reduced by using a thinner active region. In terms of the impurity concentration of the active region, the undoped case is the most stable for temperature variation. A heavily doped active region may also produce SMO. The thermal resistance must be reduced to increase temperature stability. MO with a fixed lasing wavelength is experimentally obtained by temperature control up to an injection current of twice threshold.
102 citations
TL;DR: The effect of Ga on the emission spectrum is to greatly increase the intensity of the blue part of the spectrum in epitaxial ZnSe layers grown from a pure Zn or a Zn•Ga alloy solution on ZnSxSe1−x (0⩽x1) single-crystalline substrates.
Abstract: Photoluminescence has been studied of epitaxial ZnSe layers grown from a pure Zn or a Zn‐Ga alloy solution on ZnSxSe1−x (0⩽x⩽1) single‐crystalline substrates. Intense blue emission bands at room temperature have been observed in the layers grown from a Zn‐Ga alloy solution. The spectrum of the layer at 4.2 K generally consists of a strong emission line due to radiative recombination of excitons bound to the neutral donor, I2, an associated donor‐acceptor pair emission band with LO‐phonon replicas, and a deep‐level emission, i.e., the so‐called SA emission band. The effect of Ga on the emission spectrum is to greatly increase the intensity of the blue part of the spectrum. On the basis of the comparison between the experimental results and theoretical calculations, it is tentatively proposed that the blue emisison bands at room temperature originate from the radiative recombination due to band‐to‐band transition.
91 citations
TL;DR: In this paper, the authors investigated donor-acceptor recombination in ZnS by optically detected magnetic resonance (ODMR) and confirmed that the self-activated emission is due to radiative recombination of an electron from a shallow donor with a hole on an A-centre.
Abstract: Donor-acceptor recombination has been investigated in ZnS by optically detected magnetic resonance (ODMR). Resonances due to both donors and A-centre acceptors have been observed in hexagonal and cubic ZnS containing group IIIB and group VIIB dopants. Spectral dependence measurements show that both resonances are associated with the blue self-activated emission, which lies at 2.70 eV in ZnS:Cl and 2.60 eV in ZnS:Al,I. The resonances are observed as increases of order 0.4% in the total emission intensity and are accounted for in terms of a donor-acceptor recombination process. It is found that the signals are predominantly from donor-acceptor pairs that are sufficiently close for recombination to occur before thermalisation is achieved but which are sufficiently well separated for the exchange interactions and associated line broadening to be small. The investigation confirms that the self-activated emission is due to radiative recombination of an electron from a shallow donor with a hole on an A-centre.
73 citations
TL;DR: In this article, the dependence of degradation on stress temperature, stress current, and measurement current has been empirically determined from experiments on several lots of devices and it is shown that degradation is dominated by a decrease in bulk p−side radiative recombination efficiency.
Abstract: Experimental studies have been performed on several aspects of the degradation of electroluminescent quantum efficiency in ZnO‐doped GaP light‐emitting diodes. The dependence of degradation on stress temperature, stress current (experienced during accelerated aging), and measurement current (at which quantum efficiency is evaluated) has been empirically determined from experiments on several lots of devices. It is shown that degradation is dominated by a decrease in bulk p‐side radiative recombination efficiency. The degradation of other factors (such as injection efficiency and injection ratio) contributing to the overall electroluminescent efficiency has only a secondary effect. Moreover, it is shown empirically that the dependences of degradation on temperature and stress current are separable.
45 citations
TL;DR: In this paper, the conditions for obtaining such changes are examined and particular attention is paid to the transient response of the system to sudden changes in microwave power, and a simplified rate equation approach is found to account for the essential features of the behaviour.
Abstract: Donor-acceptor radiative recombination in II-VI and other materials is subject to spin selection rules, so that the emission intensity is altered when magnetic resonance transitions are stimulated. The conditions for obtaining such changes are examined and particular attention is paid to the transient response of the system to sudden changes in microwave power. A simplified rate equation approach is found to account for the essential features of the behaviour and shows the concept of donor-acceptor pairs to be of central importance.
44 citations
TL;DR: In this paper, a detailed quantitative analysis of high-frequency spontaneous wave emissions produced by an electron beam injected into the ionospheric plasma is given, and a general discussion about individual-collective and incoherent-coherent characteristics of the emissions is given.
Abstract: This paper gives a detailed quantitative analysis of the high-frequency spontaneous wave emissions produced by an electron beam injected into the ionospheric plasma. A general discussion about individual-collective and incoherent-coherent characteristics of the emissions is given. Then attention is focused on the spontaneous coherent emission in three different modes: plasma waves, Bernstein modes, and electromagnetic whistler mode. Comparisons with experimental results obtained by several experiments (electron echo experiment, Araks) are made throughout the paper and suggest that many experimental features are well interpreted in terms of coherent emission.
36 citations
TL;DR: In this paper, multiple quantum-well AlxGa1−xAs-GaAs heterostructure laser diodes are described that exhibit tunnel injection with LO phonon participation in the injection and the recombination process.
Abstract: Stripe‐geometry multiple quantum‐well AlxGa1−xAs‐GaAs heterostructure laser diodes are described that exhibit tunnel injection with LO phonon participation in the injection and the recombination process. The diodes are constructed by Zn diffusion into n‐type AlxGa1−xAs‐GaAs heterostructures grown by metalorganic chemical vapor deposition (MO‐CVD). At bias voltages V< (1/q) Eg(AlGaAs) in which tunneling is important, laser operation (4.2–77 °K) of these quantum‐well diodes is obtained an LO phonon energy (∼36 meV) below the first electron–to–heavy‐hole (No. 1 e→hh) confined‐particle transitions of the coupled GaAs quantum wells (six wells, Lz∼120 A). In the normal injection bias range V∼ (1/q) Eg(AlGaAs), recombination radiation is identified on the No. 2 e→hh transitions and an LO phonon energy below the second electron‐to‐light‐hole (No. 2′ e→lh) confined‐particle transitions. Phonon involvement in the recombination process is identified also in the range between confined‐particle transition 1‐1′ and 2.
29 citations
TL;DR: In this paper, the dependence of relaxation oscillation on carrier diffusion length in AlGaAs lasers is analyzed using multimode rate equations containing carrier diffusion and spontaneous emission terms, and a parameter representing coupling between carrier and light field distribution is introduced.
Abstract: The dependence of relaxation oscillation on carrier diffusion length in AlGaAs lasers is analyzed using multimode rate equations containing carrier diffusion and spontaneous emission terms. A parameter representing coupling between carrier and light field distribution is introduced. The carrier diffusion shortens the delay time, the relaxation oscillation period, and the decay time constant and also makes spectral narrowing faster. The damping factor is enlarged and relaxation oscillation is suppressed as the carrier diffusion length becomes large. The diffusion length, normalized by stripe width L D /W, is estimated to be about 0.6 by comparing the numerical results with the experimental tendency of transient response. Furthermore, relaxation oscillation is suppressed as the oscillation beam spot size becomes smaller.
26 citations
TL;DR: In this article, the authors calculate the (vibrational quantum number, J prime = 0) state lifetimes under spontaneous emission for all 22 excited vibrations of HD(+) and all 19 excited vibrational vibrations of H2(+) in their ground electron states.
Abstract: Because of their simplicity, H2(+) and its isotopic species are of particular interest to molecular theorists and experimentalists. If these ions are formed in excited vibrational states under conditions of highly improbable electron-ion recombination or other reactions, spontaneous emission will occur. The present note calculates the (vibrational quantum number, J prime = 0) state lifetimes under spontaneous emission for all 22 excited vibrations of HD(+) and all 19 excited vibrations of H2(+) in their ground electron states. The lifetimes presented in Tables I and III justify the assumption that spontaneous radiative processes are unimportant under certain realizable conditions. When spontaneous radiation plays a role, however, minimum lifetime at intermediate vibrational quantum number could lead to unusual vibrational distribution functions.
TL;DR: In this paper, the authors derived analytic expressions for the spontaneous emission rates of electric and magnetic dipole transitions taking place in an atomic system embedded in a very thin layer of refractive index n 0 and optical thickness n 0 d 0 « λ/8, which is sandwiched between two dielectric loss-free media.
TL;DR: In this paper, the authors present results of intensity and line broadening investigations of spontaneous emission from atoms excited in a copper hollow-cathode discharge, which indicate a group of electrons exists in the discharge with a density of ≲1014 e−/cm3 and an effective electron temperature of 0.1 to 0.2 eV.
Abstract: We present results of intensity and line broadening investigations of spontaneous emission from atoms excited in a copper hollow‐cathode discharge. These measurements indicate a group of electrons exists in the discharge with a density of ≲1014 e−/cm3 and an effective electron temperature of 0.1 to 0.2 eV. The temperatures of atomic species present in the He‐Cu discharge have been measured. Finally, the Lorentz width of spontaneous emission from Cu II laser transitions is observed to be a large fraction of the Doppler width and is consistent with the observed homogeneouslike operation of the copper ion laser.
TL;DR: In this article, double heterostructure laser junctions have been prepared by the metalorganic vapour deposition process and evaluated for threshold current and for non-radiative recombination characteristics.
Abstract: Double heterostructure laser junctions have been prepared by the metalorganic vapour deposition process and evaluated for threshold current and for nonradiative recombination characteristics. Threshold currents around 850 A cm−2 were obtained, and measurements of carrier lifetime and spontaneous emission efficiency correlate well with a nonradiative lifetime of 20 ns. This value is similar to those obtained in junctions grown by liquid-phase epitaxy and puts an upper limit on interface recombination velocity of 500 cm s−1.
TL;DR: In this paper, the phonon assisted laser operation of multiple quantum-well AlxGa1−xAs•GaAs heterostructure diodes is described on phonon sidebands ∼36 meV below the lowest confined-particle transitions.
Abstract: The phonon‐assisted laser operation (4.2–77 °K) of multiple quantum‐well AlxGa1−xAs‐GaAs heterostructure diodes is described. Laser operation is observed on phonon sidebands ∼36 meV below the lowest confined‐particle transitions. Tunnel injection into the confined‐particle states, with light emission and negative‐resistance regions, is also observed in these multiple quantum‐well heterostructures. Two different multiple quantum‐well heterostructures grown by metalorganic chemical vapor deposition are described. The first consists of six GaAs quantum wells (Lz∼120 A) coupled by five AlxGa1−xAs (x∼0.3) layers (∼120 A), and the second is similar except for a reduction in layer size to ∼50 A.
TL;DR: In this paper, the effects of inhomogeneous broadening on the performance of cw chemical laser with a simple two-level vibrational model and a Fabry-Perot resonator are investigated.
Abstract: : The effects of inhomogeneous broadening on the performance of cw chemical lasers are investigated. A simple two-level vibrational model and a Fabry-Perot resonator are assumed. Laser performance is found to depend on certain parameters. Numerical results are presented for a cw chemical laser with laminar diffusion and with a single longitudinal optical mode. The variation of differential number density and local lasing intensity with streamwise distance and the variation of net laser output power with tuning frequency are presented. The latter exhibits a Lamb dip near linee center, which is in agreement with experimental observations. Thus, in typical devices, inhomogeneous broadening effects become negligible for p or = O(10) Torr. These effects become important in single longitudinal model lasers operating in the regime p (Torr) or = O(1) and in lasers wherein the streamwise length of the resonator is short compared with the streamwise length of the positive gain region.
TL;DR: In this paper, the superradiant amplification of the spontaneous emission along the junction was used to achieve a gain reduction of the order of 1% in GaAs junction lasers, which was made possible by the use of the strong super-radiant amplimator.
Abstract: Spectral hole burning corresponding to a gain reduction of the order of 1% has been observed in GaAs junction lasers. This observation is made possible by the use of the strong superradiant amplification of the spontaneous emission along the junction.
TL;DR: In this paper, the spontaneous emission by electrons moving in a magnetic field constant in time and periodic in space (with circular polarization) is calculated using exact solutions of the corresponding Dirac equation.
Abstract: Spontaneous emission by electrons moving in a magnetic field constant in time and periodic in space (with circular polarization) is calculated using exact solutions of the corresponding Dirac equation. In addition to the known transitions we find two harmonics connected with spin flip processes, which are, however, strongly suppressed. The gain of the free electron laser is recalculated from the rate for spontaneous emission. The results obtained by classical methods are corroborated.
TL;DR: In this article, two derivations of the fundamental laser linewidth are presented that have been used successfully in introductory courses, and the cause of the finite linearity is identified with phase fluctuations in the electric field due to spontaneous emission.
Abstract: Two derivations of the fundamental laser linewidth are presented that have been used successfully in introductory courses. The cause of the finite linewidth is identified with phase fluctuations in the electric field due to spontaneous emission. A factor of 2 discrepancy between the energy and field analyses is explained. A number of ’’back‐of‐the‐envelope’’ relationships are derived that have proven useful in teaching this subject.
TL;DR: In this paper, the influence of double-and single-grating external cavities on the spontaneous and stimulated emission of an injection laser has been investigated, and the experiments show that homogeneous broadening is evident in semiconductor lasers.
Abstract: The influence of double-grating and single-grating external cavities on the spontaneous and stimulated emission of an injection laser has been investigated. The experiments show that homogeneous broadening is evident in semiconductor lasers. High resolution spectroscopic measurements indicate that single frequency emission is possible.
TL;DR: In this paper, the luminance of high density electron-hole plasma in CdSe was observed in the 77-300 K temperature range by picosecond pulse excitation.
TL;DR: The theoretical pumping dependence of the self-pulsation frequency is consistent with the experimental data as mentioned in this paper, assuming saturable absorbing characteristics in the loss term of the rate equation, and a loss decrease of about 1% due to the saturable absorber is capable of generating self-Pulsation.
Abstract: Intensity self-pulsation in cw semiconductor lasers has been analyzed by computer simulation assuming saturable absorbing characteristics in the loss term of the rate equation. A loss decrease of about 1% due to the saturable absorber is capable of generating self-pulsation. The theoretical pumping dependence of the self-pulsation frequency is consistent with the experimental data. Reflected light in the range of 10−5∼10−3 reduces the self-pulsation. Reflected light of larger than 10−2, however, induces self pulsation whose frequency is locked with the round trip time. The contribution of spontaneous emission in the range of 10−4∼10−3 also reduces the self-pulsation, while 10−6∼10−5 is ineffective.
TL;DR: In this article, the authors measured the lasing induced change in the differential resistance for various types of stripe geometry laser, and a model was given that explains the LAS induced change quantitatively to some extent.
Abstract: The lasing-induced change in the differential resistance is measured for various types of stripe geometry laser, and a model is given that explains the lasing induced change quantitatively to some extent. The amount of the lasing-induced reduction in the differential resistance is mainly determined by a parameter that limits the carrier supply into the active layer. The exsistence of a non-lasing region at the edge of the stripe and lateral carrier diffusion also decrease the amount of the reduction. In narrow-stripe lasers the amount of the reduction is small due to lateral carrier diffusion. From the moderate change in the differential resistance near the threshold, the spontaneous emission factor representing the contribution of the spontaneous emission to the lasing mode is estimated for various types of stripe laser.
TL;DR: In this paper, a quantum model of N two-level atoms coupled by a single-mode radiation field under a restricted rotating-wave approximation is studied, assuming a dipole-interaction approximation and that the total number of excitations of the system is conserved.
Abstract: A quantum model of N two-level atoms coupled by a single-mode radiation field under a restricted rotating-wave approximation is studied, assuming a dipole-interaction approximation and that the total number of excitations of the system is conserved. A solution is found for the case of spontaneous emission when the atoms are initially prepared in the state of complete inversion. This solution is valid for all times. A general solution of the model is also found for any initial configuration of the system, in the cases of both spontaneous and stimulated emission. This solution is in a closed form and valid for times tau < tau max.
TL;DR: In this article, self-locking of axial modes was observed experimentally in a compressed-hydrogen Raman laser, where stimulated radiation was excited in a long high-Q resonator.
Abstract: Self-locking of axial modes was observed experimentally in a compressed-hydrogen Raman laser. This self-locking occurred when stimulated radiation was excited in a long high-Q resonator.
TL;DR: In this article, a theoretical model of self-sustained oscillations in D.H. injection lasers is presented, where a single or two filaments feed on two distinct carrier reservoirs, and the simultaneous effect of optical coupling by saturable absorption, carrier diffusion, and spontaneous emission.
Abstract: We analyse a theoretical model of self-sustained oscillations in D.H. injection lasers, where a single or two filaments feed on two distinct carrier reservoirs, and consider the simultaneous effect of optical coupling by saturable absorption, carrier diffusion, and by spontaneous emission. We derive conditions for instability valid for any form of the gain function and specialise the results to the case of logarithmic and linear gain. Numerical results are presented showing trajectories in the phase plane of the carrier densities as well as the time evolution of carrier and photon densities.
TL;DR: In this article, a single pulse of amplified spontaneous emission (ASE) from a neon source at 540 nm is studied and an explanation presented of the granular structure of its output intensity.
Abstract: A single pulse of amplified spontaneous emission (ASE) from a neon source at 540 nm is studied and an explanation presented of the granular structure of its output intensity. The explanation accounts quantitatively for the size and shape of the granules and for the degree of coherence observed in sources of pulsed ASE. The same approach is extended to account for the spectral structure observed in certain ASE sources. A preliminary attempt has been made of study the effect of nonuniform amplification and wall reflections in the ASE source.
TL;DR: In this article, the effect of each parameter on the initial production rate and the radiative equilibrium populations for each vibrational state are discussed, and the results indicate a rather surprising degree of vibrational selectivity.
Abstract: Calculations are performed to determine the degree of formation of vibrationally excited H+2 by stimulated radiative association. Low energy thermal collisions between the H and H+ are assumed to take place in the presence of an intense radiation field. The parameters in the system include the temperature characterizing the thermal collisions, the width, intensity, and frequency of the stimulating radiation, and the time of flight of the colliding partners in the radiation field. The effect of each parameter on the initial production rate and the radiative equilibrium populations for each vibrational state are discussed. Possible experimental procedures are also considered. The results indicate a rather surprising degree of vibrational selectivity, particularly for the early time populations of the higher states. Relative ’’initial’’ and radiative equilibrium populations and the rate coefficients for stimulated and spontaneous emission and absorption are tabulated for individual vibrational states for a s...