Showing papers on "Spontaneous emission published in 1983"
TL;DR: It has been observed that the spontaneous-emission lifetime of Rydberg atoms is shortened by a large ratio when these atoms are crossing a high-Q$ superconducting cavity tuned to resonance with a millimeter-wave transition between adjacent Ryd Berg states as mentioned in this paper.
Abstract: It has been observed that the spontaneous-emission lifetime of Rydberg atoms is shortened by a large ratio when these atoms are crossing a high-$Q$ superconducting cavity tuned to resonance with a millimeter-wave transition between adjacent Rydberg states.
689 citations
337 citations
TL;DR: In this paper, it was shown that the additional phase changes also give rise to line shape structure in the form of additional peaks separated from the main peak by multiples of the relaxation oscillation frequency.
Abstract: Spontaneous emission alters the phase and amplitude of the laser field. The amplitude changes induce relaxation oscillations, which cause additional phase changes while restoring the field amplitude to the steady state value. It was previously shown that the additional phase changes greatly enhance the linewidth. We show here that the additional phase changes also give rise to line shape structure in the form of additional peaks separated from the main peak by multiples of the relaxation oscillation frequency. The calculated mean square phase change and power spectrum are in good agreement with published observations.
302 citations
TL;DR: In this paper, four different theoretical formulations for AM and FM quantum noise properties in semiconductor lasers are compared with each other for AlGaAs lasers, based on van der Pol, Fokker-Planck, rate, and photon density matrix equations.
Abstract: Four different theoretical formulations for AM and FM quantum noise properties in semiconductor lasers are compared with each other for AlGaAs lasers. These formulations are based on van der Pol, Fokker-Planck, rate, and photon density matrix equations. Experimental results with AM noise spectra, FM noise spectra, and spectral linewidths for four different types of AlGaAs lasers are also delineated and compared with the theoretical predictions. The spontaneous emission coefficient β and population inversion parameter n sp , which are basic parameters for determining the quantum noise properties of semiconductor lasers, were calculated by the density of states with Kane function interpolated to Halperin-Lax bandtail and the Stern's improved matrix element. Experimental AM and FM quantum noise properties show good agreement with the theoretical predictions derived through use of estimated β and n sp values.
144 citations
TL;DR: In this article, the authors analyzed the oscillating transverse and longitudinal modes in semiconductor injection lasers using the density matrix formalism and derived the optimal range to obtain stable fundamental transverse mode operation with respect to several guiding factors.
Abstract: Mechanisms which determine the oscillating transverse and longitudinal modes in semiconductor injection lasers are discussed in this paper. The analysis is based on the semiclassical method in which the optical field is represented by Maxwell equations and the lasing phenomenon is analyzed quantum mechanically using the density matrix formalism. Guided modes are classified by the relation between refractive index and gain-loss differences at the boundaries of the active region as normal guided mode (index guiding), active-guided mode (gain guiding), and leaky mode (anti-index guiding). The guiding loss and cutoff conditions are given for these modes. The optimum range to obtain stable fundamental transverse mode operation is discussed with respect to several guiding factors, such as width of active region, the refractive index difference, and gain-loss differences at the boundaries of the active region. Longitudinal mode behavior is discussed in terms of electron transition mechanism in semiconductor crystals. The relaxation effect of the electron wave is introduced in this model. Profiles of the saturated gain and the spatial diffusion of the electron are related to this relaxation effect. Mode competition phenomena are analyzed, and a strong gain suppression among the longitudinal modes is shown to be as an intrinsic property of semiconductor lasers. The possibility of obtaining single longitudinal mode operation is postulated. Physical influences for stable single longitudinal mode operation are discussed in terms of transverse mode control (or stripe structure), spontaneous emission, threshold current level, impurity concentration in the active region, and direct modulation. Some experimental results are also given to support these analyses.
114 citations
TL;DR: In this article, the authors measured the temperature dependence of GaInAsP/InP lasers in terms of the gain, the loss, the spontaneous emission, and the carrier lifetime, and showed that both the absorption and the nonradiative components significantly influence the temperature characteristics of threshold current.
Abstract: Various factors influencing the temperature dependence of the threshold current of GaInAsP/InP lasers in the wavelength region of 1.5-1.6\mu m were measured in terms of the gain, the loss, the spontaneous emission, and the carrier lifetime. The effects of the intervalence band absorption influence the differential quantum efficiency or the loss, while the nonradiative recombination and the carrier leakage over the heterobarrier influence the carrier lifetime. It is shown from the measured results that both the absorption and the nonradiative components significantly influence the temperature characteristics of threshold current. The rapid increase in the threshold current near room temperature is a reflection of the increase in the intervalence band absorption. The heating effect due to the injection current is also significant. The possible maximum temperature of CW operation is expected to be as high as 150°C with optimized structural parameters.
85 citations
TL;DR: In this paper, the problem of the lamb shift and the spontaneous emission of light in a framework of nonrelativistic quantum electrodynamics by using an exactly soluble model of a harmonic oscillator atom interacting with a quantized electromagnetic field was studied.
Abstract: We study rigorously the problem of the lamb shift and the spontaneous emission of light in a framework of nonrelativistic quantum electrodynamics by using an exactly soluble model of a harmonic oscillator atom interacting with a quantized electromagnetic field. We show that, under the perturbation of the electromagnetic field, all the point spectra corresponding to the excited states of the unperturbed atom disappear. This means that the ‘‘energy level shifts’’ (Lamb shifts) of the excited states of the atom cannot be described simply in terms of shifts of point spectra. Then, we give a rigorous mathematical meaning to both formal perturbation theories for the ‘‘energy level shifts’’ and for the transitions of the excited states due to the spontaneous emission of light, showing that the ‘‘energy level shifts’’ and the ‘‘decay probabilities’’ of the excited states of the atom are characterized in terms of the resonance pole of the S‐matrix for the photon scattering by the atom. We also discuss broken symmetry aspects and infinite mass‐renormalization of the model.
67 citations
TL;DR: In this paper, the authors considered two-level "atoms" in interaction with a single-mode resonant electromagnetic field and gave a nonrelativistic solution for all times for the case of spontaneous emission, when only one atom is initially excited.
Abstract: $N$ two-level "atoms" are considered in interaction with a single-mode resonant electromagnetic field. The exact solution is given nonrelativistically for all times for the case of spontaneous emission, when only one atom is initially excited. The solution is given for the general case of the $N$ atoms in inequivalent mode positions.
65 citations
TL;DR: In this paper, the nonlinear integro-differential equation, obtained from the coupled Maxwell-Dirac equations by eliminating the potential Aμ, is solved by iteration rather than perturbation.
Abstract: The nonlinear integro-differential equation, obtained from the coupled Maxwell-Dirac equations by eliminating the potential Aμ, is solved by iteration rather than perturbation. The energy shift is complex, the imaginary part giving the spontaneous emission. Both self-energy and vacuum polarization terms are obtained. All results, including renormalization terms, are finite.
51 citations
TL;DR: In this paper, a fully quantized many-particle theory of the standard free-electron laser in the small-signal, cold-beam regime is presented, based on an evaluation of the time-evolution operator in the interaction picture to first order in the quantum-mechanical recoil.
Abstract: A fully quantized many-particle theory of the standard free-electron laser in the small-signal, cold-beam regime is presented. The approach is based on an evaluation of the time-evolution operator in the interaction picture to first order in the quantum-mechanical recoil. For algebraic convenience we use the moving (Bambini-Renieri) frame, in which resonance occurs for zero electron momentum. Though we neglect space-charge effects, genuine many-particle contributions still show up, because the radiation emitted by one electron can be amplified by another electron. Our main results are gross features of the amplification, such as gain and spread, are virtually without many-particle effects. These effects are mainly important in the case of spontaneous emission. For a sufficiently high current, the buildup of the laser field from vacuum is enhanced by amplified spontaneous emission. Incoherence of the spontaneous radiation from several electrons induces deviations from Poisson statistics even if gain is neglected. For a dilute electron beam, spontaneous radiation is slightly antibunched for negative gain. Squeezing is obtained for positive gain independent of the number of electrons. However, owing to some idealizations used in the model, it is uncertain whether this applies to a physically realizable situation.
51 citations
TL;DR: In this article, the lifetime of the metastable 3s3p(3)P(0)1 level of Si(2+) (Si III), which decays by photon emission at 189.2 nm to the 3s2(1)S0 state, is reported.
Abstract: Measurement of the lifetime of the metastable 3s3p(3)P(0)1 level of Si(2+) (Si III), which decays by photon emission at 189.2 nm to the 3s2(1)S0 state, is reported. The data were taken from spontaneous emission from metastable Si III stored in an RF ion trap. The Si III ions were produced through electron bombardment of SiH4 and SiF4 at pressures of 1/100,000,000-1/10,000,000 Torr. A photomultiplier was employed to count the photon emissions from the transitions. A total of 11 decay curves were generated for analysis, with Poisson statistics used to set the uncertainties at within 8 pct. Significant systematic effects were controlled, and the lifetime was found to be within 3.6 microsec of 59.9 microsec. The method used is concluded valid for determining the lifetimes of metastable levels of low-Z ions with low charge, and thereby the transition probabilities.
TL;DR: In this paper, the properties of a GaAs/AlGaAs quantum well (QW) laser diode were studied under strong magnetic fields up to 30 Tesla and the spontaneous emission spectrum was found to shift toward the higher photon energy, following the shift \hbarωc/2 of the lowest Landau level.
Abstract: Characteristics of a GaAs/AlGaAs quantum well (QW) laser diode are studied for the first time under strong magnetic fields up to 30 Tesla. When field normal to QW plane is increased, the spontaneous emission spectrum is found to shift toward the higher photon energy, following the shift \hbarωc/2 of the lowest Landau level in the region of strong magnetic fields. Moreover, the emission spectrum is shown to be very little affected when magnetic fields are applied parallel to the QW plane. These results give evidence of light emission from a fully-quantized zero-dimensional carrier system in GaAs QW structures with strong magnetic fields normal to the QW plane.
TL;DR: In this paper, the spontaneous emission spectrum of mesa lasers was analyzed to determine the absorption and gain spectra at threshold, and the radiative current density at threshold was found to be 4.4 kA cm-2μm-1, which is 60 percent of the total current density for the lowest threshold mesa laser.
Abstract: The spontaneous emission spectrum of mesa lasers was analyzed to determine the absorption and gain spectra at threshold. The radiative current density at threshold was found to be 4.4 kA cm-2μm-1, which is 60 percent of the total current density for the lowest threshold mesa laser. The increase in radiative lifetime due to reabsorption of emitted radiation was calculated to be 1.5, using file measured absorption and emission spectra. Contrary to other studies, our investigation of an LED and 3 lasers of different types yielded no evidence of carrier heating.
TL;DR: In this paper, a quasi-static gain approximation is introduced and the dynamics of the electron and photon population are modeled by three coupled nonlinear difference equations which can be numerically solved with very little computation time.
Abstract: Diode lasers with an intracavity electroabsorption modulator have been operated with full on/off modulation at rates of 3 GHz. In addition, modulation of the lasers has been shown up to a detector-limited frequency of 6 GHz. A new model of these devices, which includes amplified spontaneous emission and high gain is developed in this paper. A quasi-static gain approximation is introduced and the dynamics of the electron and photon population are modeled by three coupled nonlinear difference equations which can be numerically solved with very little computation time. The model predicts the possibility of a new mode of Q -switched operation with the capacity for repetition rates of tens of gigahertz and binary pulse position modulation at rates of the order of 10 Gbits/s.
TL;DR: In this article, the rate equation for the energy (photon) density inside the resonant cavity of a laser oscillator is derived from Maxwell's equations, which can be used to obtain the well-known expression for the ratio of the power that is spontaneously emitted into a single laser mode relative to the total amount of spontaneous emission.
Abstract: In this paper, the rate equation for the energy (photon) density inside the resonant cavity of a laser oscillator is derived from Maxwell's equations. By comparison to the familiar photon rate equation, this classical derivation can be used to obtain the well-known expression for the ratio of the power that is spontaneously emitted into a single laser mode relative to the total amount of spontaneous emission. This independent derivation does not require mode counting procedures and settles the following question: what fraction of the total power that is spontaneously emitted into the wavelength range of the fluorescent linewidth is utilized for increasing the energy in a given laser mode?
TL;DR: In this article, an analysis of the free-electron-laser (FEL) oscillator startup problem in the linear regime is presented, where the wiggler field is assumed to occupy a portion of the finite $Q$ resonator.
Abstract: An analysis of the free-electron-laser (FEL) oscillator startup problem in the linear regime is presented. The model is spatially one dimensional, though many important three-dimensional effects are included heuristically. The electron beam consists of pulses of arbitrary shape separated by approximately twice the radiation transit time. The small gain per pass approximation is employed in deriving an energy rate equation, which describes the evolution of the radiation pulses within the resonator. The wiggler field is assumed to occupy a portion of the finite $Q$ resonator. In the energy rate equation, the spontaneous (incoherent) radiation term is represented by a source matrix, while the stimulated (coherent) radiation term is represented by a gain matrix. The effect of small variations in the mirror separation are investigated in the context of laser lethargy. Our analysis suggests possible methods which could substantially shorten the startup times in FEL oscillators. Finally, our results are compared with the FEL oscillator experiments performed at Stanford University.
TL;DR: In this paper, the n=1, 2, and 3 subbands of the conduction and valence bands of a multiple quantum well heterostructure of GaAs•Al0.6Ga0.4As are seen in spontaneous emission under high excitations.
Abstract: Allowed transitions between the n=1, 2, and 3 subbands of the conduction and valence bands of a multiple quantum well heterostructure of GaAs‐Al0.6Ga0.4As are seen in spontaneous emission under high excitations. The observed peaks agree very well with the calculated locations of the peaks when the finite depth of the potential well and the nonparabolicity of the conduction band are taken into account. The same basic features are seen under cw or picosecond pulse excitation and at room temperature, 77 K, or 4.2 K.
TL;DR: The spectral linewidth of the longitudinal laser modes has been measured as a function of mode power for different types of gain-guided as well as index-guided (GaAl) as double heterostructure laser diodes.
Abstract: The spectral linewidth of the longitudinal laser modes has been measured as a function of mode power for different types of gain-guided as well as index-guided (GaAl)As double heterostructure laser diodes. Various effects contributing to line broadening, such as spontaneous emission, carrier density fluctuations, changes of the resonator parameters, and mode competition are discussed.
TL;DR: The results of this investigation indicate that, for diode lasers, the Fabry-Perot approach to modeling the steady-state behavior should be preferred.
Abstract: The steady-state light-vs-pumping characteristic for lasers is modeled by a rate-equation and Fabry-Perot approach. It is found that the two models predict a similar dependence of the output power on pumping rate in the limit of vanishingly small gain and loss. It is also discovered that the Fabry-Perot result contains multiplicative factors which arise from an explicit consideration of the resonator. These factors are missing in the rate-equation analysis but can be included by redefining the equivalent cavity loss and scaling the spontaneous emission factor and gain in an appropriate fashion. The results of this investigation indicate that, for diode lasers, the Fabry-Perot approach to modeling the steady-state behavior should be preferred.
TL;DR: A re-analysis of the recombination data of Su et al. on lightly doped InGaAsP lasers indicates that their figure for the Auger coefficient is uncertain and up to three times too low, does not support their claim of saturation in the radiative recombination, but confirms the presence of a second nonradiative mechanism more sensitively dependent on carrier concentration than the cube as discussed by the authors.
Abstract: A re-analysis of the recombination data of Su et al. on lightly doped InGaAsP lasers indicates that their figure for the Auger coefficient is uncertain and up to three times too low, does not support their claim of saturation in the radiative recombination, but confirms the presence of a second nonradiative mechanism more sensitively dependent on carrier concentration than the cube.
Patent•
19 Aug 1983TL;DR: In this article, an injection laser is provided with quantum size effect transparent waveguiding, where the active layer has passive waveguide end regions between the active region and the laser end facets that are sufficiently thin in layer thickness to form a transparent waveguide having a quantum well effect so that radiative recombination will not occur in these regions.
Abstract: An injection laser is provided with quantum size effect transparent waveguiding. The laser includes an active layer having an active region wherein carrier recombination occurs under lasing conditions. The active layer has passive waveguide end regions between the active region and the laser end facets that are sufficiently thin in layer thickness to form a transparent waveguide having a quantum well effect so that radiative recombination will not occur in these regions.
TL;DR: In this paper, spontaneous and stimulated emission spectrum and the different characteristics between TE and TM polarizations were investigated on a GaAs-AlGaAs multi-quantum-well (MQW) laser diode grown by molecular beam epitaxy.
Abstract: Spontaneous and stimulated emission spectrum and the different characteristics between TE and TM polarizations were investigated on a GaAs–AlGaAs multi‐quantum‐well (MQW) laser diode grown by molecular beam epitaxy. The MQW laser lases at 38 meV below the photoluminescence peak energy corresponding to the lowest confined electron to heavy hole recombination energy E1h, calculated using the Kronig–Penney model. However, this energy separation cannot be interpreted in terms of the LO‐phonon assisted recombination which is usually accepted. The LO‐phonon assisted recombination model can be ruled out by comparing the spontaneous emission and the stimulated emission for various injection current levels. The emission energy of the TE polarization was lower than that of the TM polarization. The intensity of the TE is much larger than the TM polarization. These differences can be interpreted in terms of the selection rule for the dipole recombination between confined electron to heavy hole and electron to light h...
TL;DR: In this article, it was shown that spontaneous radiation is distributed according to thermal statistics for the high electron currents used in present-day free-electron lasers, and that this is the case for all freeelectron laser systems.
Abstract: We show that, for the high electron currents used in present-day free-electron lasers, spontaneous radiation is distributed according to thermal statistics.
TL;DR: In this paper, the problem of oscillator evolution and mode competition in free electron lasers is studied, where Relativistic quantum field theory is used to calculate electron wave functions, the angular distribution of spontaneous emission and the transition rates for stimulated emission and absorption in each mode.
Abstract: The problem of oscillator evolution and mode competition in free electron lasers is studied. Relativistic quantum field theory is used to calculate electron wave functions, the angular distribution of spontaneous emission, and the transition rates for stimulated emission and absorption in each mode. The photon rate equation for the weak-field regime is presented. This rate equation is applied to oscillator evolution with a conventional undulator, a two-stage optical klystron, and a tapered undulator. The effects of noise are briefly discussed.
TL;DR: In this article, the intensity fluctuations expected in the output of cw semiconductor lasers are studied analytically using linearized multimode rate equations, and the correlation of the low-frequency noise of different laser modes is investigated.
Abstract: The intensity fluctuations expected in the output of cw semiconductor lasers are studied analytically using linearized multimode rate equations. Spontaneous emission causes intrinsic fluctuations of the laser wave. A power-independent contribution to the intensity fluctuations may occur due to inversion-induced modulation noise. The correlation of the low-frequency noise of different laser modes is investigated. The results are in agreement with experimental data reported in the literature.
TL;DR: The problem of very-low-threshold, daylight-pumped lasers in a general thermodynamic framework is cast and some luminescent material systems that might be able to satisfy these rigid requirements are described.
Abstract: We cast the problem of very-low-threshold, daylight-pumped lasers in a general thermodynamic framework. We calculate that the requirements to reach threshold are that the Stokes shift of such a laser be greater than 13.3kT calculate the absorption ratio of the pump/emission band and the geometrical aspect ratio both be greater than and that exp(13.3). We describe some luminescent material systems that might be able to satisfy these rigid requirements.
TL;DR: In this paper, the direct dependence of the longitudinal mode spectrum on active and passive waveguiding and stripewidth of metal-cladded ridge-waveguide-stripe lasers is presented.
Abstract: The direct dependence of the longitudinal mode spectrum on active and passive waveguiding and stripewidth of metal‐cladded ridge‐waveguide‐stripe lasers is presented. Since the investigated lasers originate from the same epitaxial wafer, the influence of other laser parameters, such as layer characteristics and material quality, can be neglected. Experimental results agree well with a theory, based on the spontaneous emission coefficient as the dominant parameter, which is affected by the curvature of wave fronts.
TL;DR: In this paper, the thermal properties of broad-contact double-heterostructure GaAs-(AlGa)As laser diodes under steady-state conditions are presented, where the nonhomogeneous, layered structure of the laser diode has been reduced to the thermally equivalent, homogeneous GaAs structure.
Abstract: The thermal properties of broad-contact double-heterostructure GaAs-(AlGa)As laser diodes under steady-state conditions are presented in this paper. The nonhomogeneous, layered structure of the laser diode has been reduced to the thermally equivalent, homogeneous GaAs structure. The active layer heating due to nonradiative recombination and reabsorption of radiation, the radiative transfer of spontaneous radiation through the wide-gap passive layers, and Joule heating have been taken into consideration. The temperature dependence of the GaAs thermal conductivityλ(T) has been also taken into account. The relative influence on the temperature distributions of the individual heat sources, the internal quantum efficiency of the spontaneous emission, and the thickness and the resistivities of the individual layers have been discussed. The model may be used for all broad-contact laser diodes including the high-power large-optical-cavity laser diodes.
TL;DR: In this article, the shape of the deflection profile of a monoenergetic atomic beam crossing a laser standing wave is calculated in a situation where many spontaneous emission processes occur during the interaction time.