Showing papers on "Spontaneous emission published in 1984"
TL;DR: In this article, the luminescence properties of the bismuth compounds Bi2Ge3O9, Bi12MO20, Bi2Al4O9 and PbM2O4 (M = Al, Ga) are reported and discussed.
147 citations
TL;DR: In this article, the authors derived analytical expressions for the power spectral densities of intensity and frequency noise of single mode semiconductor lasers in the presence of an optical feedback and obtained a behavior which, at high frequencies significantly differs from the usual one, and is in good agreement with recent experimental results.
Abstract: We derive analytical expressions for the power spectral densities of intensity and frequency noise of single mode semiconductor lasers in the presence of an optical feedback. By explicitly taking into account the spontaneous emission processes into the laser mode, we obtain a behavior which, at high frequencies significantly differs from the usual one, and is in good agreement with recent experimental results. In particular, we are able to show in which way the intensity and frequency noise, besides being influenced by the external cavity length, are affected by the presence of the well known resonant peaks in the noise spectra of the solitary laser and how a substantial lowering and flattening in the noise spectra can be obtained with external cavity round trip times shorter than the inverse of the peak resonant frequency. We also present experimental results in good agreement with the theoretical ones.
122 citations
TL;DR: In this article, the first observation of coherent light by an electron beam bunched at 1.06 µm by a Nd-doped yttrium aluminum garnet laser focused into an optical klystron was reported.
Abstract: We report the first observation of the emission of coherent light by an electron beam bunched at 1.06 \ensuremath{\mu}m by a Nd-doped yttrium aluminum garnet laser focused into an optical klystron. An enhancement of ${10}^{2}$ to ${10}^{3}$ over its spontaneous emission level at 355 nm has been observed in these experiments performed at the ACO storage ring at Orsay.
93 citations
TL;DR: In this paper, the interaction of a damped cavity with a two-level atom was examined and the effect of damping and fluctuations in the walls of the cavity on the atom-cavity interaction, at zero temperature and in the limit of small damping.
Abstract: The interaction of a damped cavity with a two-level atom is examined. The treatment is fully quantum mechanical. Expressions are obtained for the effect of damping and fluctuations in the walls of the cavity on the atom-cavity interaction, at zero temperature and in the limit of small damping. The physical situation can be realized with Rydberg atoms and a cavity.
80 citations
TL;DR: In this article, the energy gap shrinkage in the MQW structures is considered theoretically by modifying the well-known bulk theory for gap shrinkages and taking the effective mass anisotropy into account.
Abstract: Recombination radiation below the lowest confined particle transition energy observed in GaAs/AlGaAs multi-quantum-well heterostructure lasers was studied in comparison with that in conventional GaAs double-heterostructure lasers. The spontaneous emission shows lower-energy-side broadening in proportion to the 1/2.6 power of the injected carrier density for both the MQW structures and the conventional DHs. This carrier density dependence suggests that the observed low-energy-side broadening of the spontaneous emission is due to carrier-induced energy-gap shrinkage. The energy gap shrinkage in the MQW structures is considered theoretically by modifying the well-known bulk theory for gap shrinkage and taking the effective mass anisotropy into account. This theory is found to account satisfactorily for the observed lower-energy-side broadening. The results suggests that lasing below the lowest confined particle transition energy in MQW laser diodes is due to gap shrinkage rather than to LO-phonon participation as reported by other workers.
74 citations
TL;DR: In this paper, the quantum mechanical description of a spontaneous emission of phonons is presented to derive a critical current, which destroys the non-dissipative current in the regime of the quantum Hall effect.
Abstract: The quantum mechanical description of a spontaneous emission of phonons is presented to derive a critical current, which destroys the non-dissipative current in the regime of the quantum Hall effect.
62 citations
TL;DR: In this article, the Glauber distribution P(α) for the free-electron laser is derived, obtaining the displaced gaussian which represents the superposition of a coherent field (stimulated emission) and an incoherent one (spontaneous emission).
45 citations
TL;DR: In this article, the spontaneous emission of systems with intersecting potential energy curves and strong nonadiabatic effects was studied from first principles, and the authors derived expressions for the transition operator and the intensity of fluorescence which are virtually exact in the small molecule limit.
Abstract: In this paper we study the spontaneous emission of systems with intersecting potential energy curves and strong nonadiabatic effects from first principles. Within the dipole approximation for the spontaneous emission process and a two‐state description of the vibronic coupling system we derive expressions for the transition operator and the intensity of fluorescence which are virtually exact in the small molecule limit. The concept of a radiative damping matrix is introduced and formulated as an operator in vibrational space. Apart from energy prefactors, the probability of photon emission is found to be governed by the probability of occupying the upper of the vibronically interacting electronic states. It follows that the usual autocorrelation function is no longer an appropriate measure of the fluorescence in systems with strong nonadiabatic effects. As an application we study the A→X internal conversion in C2H+4 for broadband excitation and find an ultrafast nonradiative decay (decay time ≊3 fs).
43 citations
TL;DR: In this paper, a GaAlAs laser was injected into a non-lasing Fabry-Perot mode separated by up to 22 mode spacings from the free-running lasing mode.
Abstract: Injection locking of a GaAlAs laser by coupling light into a nonlasing Fabry-Perot mode separated by up to 22 mode spacings (60 A) from the free-running lasing mode is demonstrated. The gain spectra for operation above threshold are determined from measurements of the wavelength dependence of the injected power required for locking. These results are compared to gain curves deduced from spontaneous emission spectra measured slightly below threshold. For the greatest wavelength separation, the gain difference was found to be about 4 cm-1, with injected power levels of 1 percent of the total slave laser power required to obtain 75 percent of the total energy at the master laser frequency.
32 citations
TL;DR: In this paper, the linear stage of the coherent emission of a modulated beam injected in a cold plasma is investigated, and the feature of the radiation produced is governed by the ratio ω2p/ω2c of the background plasma.
Abstract: The linear stage of the coherent emission of a modulated beam injected in a cold plasma is investigated. The feature of the radiation produced is shown to be governed by the ratio ω2p/ω2c of the background plasma. This kind of emission provides an efficient way to convert the kinetic energy of the beam particles into electromagnetic wave energy: The power given to waves averaged over periods of the beam modulation is found to be an appreciable part of the initial beam power. The transfer can be maximized in the electron whistler range (Cerenkov emission) for electron beams whose characteristics are designed to met the ‘‘focalization condition’’ (double pole in the dispersion relation). The most suitable mode is the normal Doppler shift ion cyclotron mode for ion beams. Application to relevant ionospheric plasmas is considered.
29 citations
TL;DR: In this article, the feasibility of exploiting solid-state superlattices with short spatial periods to obtain both spontaneous and stimulated emission in the extreme ultraviolet and soft x-ray range using nonrelativistic beams was demonstrated.
Abstract: High‐energy electrons emit resonant electromagnetic radiation when passing through a spatially periodic medium. It is conventionally assumed that ultrarelativistic electron beams are required to obtain significant emission. We demonstrate theoretically the feasibility of exploiting solid‐state superlattices with short spatial periods to obtain both spontaneous and stimulated emission in the extreme‐ultraviolet and soft x‐ray range using nonrelativistic beams.
TL;DR: In this paper, the basic aspects of power calculations for high gain semiconductor lasers are briefly reviewed, and a straightforward one-dimensional model is described, and the relative importance of spontaneous emission, distributed losses, band-to-band absorption, and high single-pass gain are investigated in detail.
Abstract: The basic aspects of power calculations for high‐gain semiconductor lasers are briefly reviewed, and a straightforward one‐dimensional model is described. The relative importance of spontaneous emission, distributed losses, band‐to‐band absorption, and high single‐pass gain are investigated in detail.
TL;DR: In this article, the dispersion of the linewidth enhancement factor α in an AlGaAs injection laser has been determined from the changes in spontaneous emission spectra as bias current is varied below threshold.
Abstract: The dispersion of the linewidth enhancement factor α in an AlGaAs injection laser has been determined from the changes in spontaneous emission spectra as bias current is varied below threshold. It is demonstrated that the results are in good agreement with a simple model which takes account of the gain spectra and the associated anomalous dispersion of the refractive index in parabolic bands.
TL;DR: In this paper, a 5-wavelength integrated GaInAsP/InP DFB laser array has been realized, and the average lasing wavelength separation was 49 A, which was in very good agreement with the designed value.
Abstract: The simultaneous CW operation of a 5-wavelength integrated GaInAsP/InP DFB laser array has been realized. The average lasing wavelength separation was 49 A, which was in very good agreement with the designed value. Threshold currents were 57 to 75 mA and differential quantum efficiencies were 11 to 21%. A simultaneous CW operation was obtained at up to 40°C with each stable single longitudinal mode. It was found that the threshold current was almost independent of wavelength within a range of 500 A on the long wavelength side of the spontaneous emission peak and could be reduced to as little as 20 mA by fabricating deep, uniform gratings and by increasing the crystal homogeneity of the wafer.
TL;DR: In this paper, the authors observed well correlated stimulated and spontaneous emission peaks corresponding to electronic transitions from the n=1 and 2 subbands of the conduction band to the corresponding states in the valence band of GaAs•Al0.6Ga0.4As multiple quantum well structure grown by metalorganic chemical vapor deposition were observed.
Abstract: Well correlated stimulated and spontaneous emission peaks corresponding to electronic transitions from the n=1 and 2 subbands of the conduction band to the corresponding states in the valence band of GaAs‐Al0.6Ga0.4As multiple quantum well structure grown by metalorganic chemical vapor deposition were observed. No evidence of phonon‐assisted transitions was seen in any of our samples.
TL;DR: In this article, it was shown that the widely accepted form of the K factor is based on a derivation which is not appropriate for the typical laser situation where the spontaneous emission factor is much smaller than unity.
Abstract: The expression for the spontaneous emission factor for lasers with gain induced waveguiding has a factor K , called by Petermann "the astigmatism parameter." This factor has been invoked to explain spectral and dynamic characteristics of this class of lasers. We contend that the widely accepted form of the K factor is based on a derivation which is not appropriate for the typical laser situation where the spontaneous emission factor is much smaller than unity. An alternative derivation is presented which leads to a different form for the K factor, The new expression predicts much smaller values under conditions where the previous theory gave values large compared to unity. Petermann's form for the K factor is shown to be relevant to large gain linear amplifiers where the power output is amplified spontaneous emission noise. The expression for the power output has Petermann's value of K as a factor. The difference in the two situations is that in the laser oscillator the typical atom of interest couples a small portion of its incoherent spontaneous emission into the dominant mode, whereas in the amplifier only the atoms at the input end are important as sources and their output is converted to a greater degree into the dominant mode through the propagation process. In our analysis we use a classical model of radiating point dipoles in a continuous medium characterized by a complex permittivity. Since uncritical use of this model will lead to infinite radiation resistance we address the problem of its self-consistency.
TL;DR: In this paper, the authors measured the FM-noise spectrum of index-guided GaAlAs-diode lasers for different lengths of the laser cavity and determined the linewidth enhancement factor.
Abstract: The FM-noise spectrum of index-guided GaAlAs-diode lasers is measured for different lengths of the laser cavity. The observed FM-noise peak near the internal laser resonance and the decrease of the FM noise with increasing cavity length is in agreement with a model which is considering the spontaneous emission noise source. From the measured noise data, the linewidth enhancement factor is determined.
TL;DR: In this article, multiquantum well structures of GaSb/Al06Ga04Sb were grown by molecular beam epitaxy and their spontaneous and stimulated emission properties were studied.
Abstract: Multiquantum well structures of GaSb/Al06Ga04Sb were grown by molecular beam epitaxy and their spontaneous and stimulated emission properties were studied The luminescence spectra exhibited high efficiency with the upward energy shift from λ=172 μm of GaSb up to λ=131 μm for the well width of ∼40 A Optically induced lasing has been obtained at the wavelength as short as λ=1207 μm at 80 K and in the spectral region of λ=15–16 μm at temperatures as high as 80 °C The optical thresholds of the quantum well lasers are similar to that of the more conventional GaSb/AlGaSb heterostructures
TL;DR: In this article, the electron density determination from continuum emission was compared experimentally with the method of Stark broadening measurement of spectral lines, using a stationary argon cesium discharge.
Abstract: The method of electron density determination from continuum emission is often used in the nonstationary plasma of an MHD-generator because of its simplicity. An assumption in the analysis is that recombinative radiation forms the main contribution to the continuum. Next to this the method carries with it some other uncertainties. In this work the method is compared experimentally with the method of Stark broadening measurement of spectral lines, using a stationary argon cesium discharge. Both techniques involve corrections for plasma inhomogeneities. Agreement within 20% is found. The contribution of Cs 2 molecules to the continuum emission, which is significant in saturated vapor at moderate temperatures (500–1000 K), is estimated to be of minor importance in the generator plasma.
TL;DR: In this article, the spontaneous-emission coupling into the lasing mode of a gain-guided semiconductor laser is addressed using a heuristic approach based on the notion of the angular-spectrum width.
Abstract: The problem of the spontaneous-emission coupling into the lasing mode of a gain-guided semiconductor laser is addressed using a heuristic approach based on the notion of the angular-spectrum width. By using physical arguments, it is shown that a gain-guided laser has enhanced contribution from spontaneous emission simply because it has wider lateral angular spectra and far fields compared with those obtained for an index-guided laser. In contrast to previous work, here much lower values of the enhancement factor are predicted.
TL;DR: In this paper, a practical scheme for computing time-dependent properties, such as excitation probabilities and dipole correlation functions of a multilevel atom strongly excited by a laser in the presence of noise, is described in detail.
Abstract: In this paper, a practical scheme for computing time-dependent properties, such as excitation probabilities and dipole correlation functions of a multilevel atom strongly excited by a laser in the presence of noise, is described in detail. The method, which is based on the notion of randomly interrupted, multivalued jump processes, can be used to treat laser phase, amplitude, and/or frequency noise, and fluctuating microfields. The method provides analytic expressions, which are based on eigenvalues and eigenvectors of a finite-dimensional matrix, for time dependence and spectral dependence, and it permits computation of time-dependent fluorescence emitted from atoms excited by a noisy laser. The method is illustrated by application to time-dependent spectra.
TL;DR: In this article, an analytic model for the modulation response of buried heterostructure (BH) semiconductor lasers is presented, which takes into account the combined effects of carrier diffusion and spontaneous emission for the transient decay time of the relaxation oscillations and the small-signal modulation response for the carriers and photons.
Abstract: This paper describes an analytic model for the modulation response of buried heterostructure (BH) semiconductor lasers. Using a space-averaged carrier density approach, explicit expressions that take into account the combined effects of carrier diffusion and spontaneous emission are derived for the transient decay time of the relaxation oscillations, and the small-signal modulation response for the carriers and photons. The dynamic shift of the lasing wavelength is estimated by calculating the fluctuations of the carrier density during small-signal modulation. Using the analytic solutions obtained, a network synthesis approach is used to derive two-port circuit models for the device. The validity of the theoretical model is verified by comparing the modulation characteristics of a BH laser measured experimentally to that simulated by circuit analysis.
TL;DR: In this paper, the authors describe time-resolved absorption and emission studies of an XeCl* laser discharge, in order to gain a better understanding of the causes leading to the premature termination of both spontaneous emission and laser pulses in the device.
Abstract: In this paper we describe time-resolved absorption and emission studies of an XeCl* laser discharge. The studies we carried out in order to gain a better understanding of the causes leading to the premature termination of both spontaneous emission and laser pulses in our device. This is a feature showed by all discharge pumped rare gas halide lasers.
Metz1
TL;DR: The strong emission line at 24346 cm -1 (4.2 K) is attributed to the radiative recombination of excitons bound to neutral acceptors (A 0, X) as mentioned in this paper.
TL;DR: In this article, the problem of stimulated recombination at a resonance was investigated by a time-dependent, non-perturbative approach, and the number of pairs recombined by a laser pulse was computed as a function of the intensity, of the pulse duration, and of the initial electron-energy distribution.
Abstract: The problem of stimulated recombination at a resonance is investigated by a time-dependent, non-perturbative approach. The number of pairs recombined by a laser pulse is computed as a function of the intensity, of the pulse duration, and of the initial electron-energy distribution (as well as of the parameters which characterize the atomic resonance and its field-induced coupling to the final bound state). The role of spontaneous emission (or other paths) from the recombined state (if it is excited) is also discussed. Numerical results are given including an example of recombination to the ground state in the Sr atom.
TL;DR: In this paper, a mathematical model is developed to relate wavelength tuning with surface potential and forward voltage shift, which suggests the possibility of wavelength tuning via surface band-bending changes deriving from surface electric field changes, as is done with MIS devices.
Abstract: Wavelength tuning via shallow junction GaAs LED's as a result of gamma irradiation is increased significantly when the irradiated LED's are operated in vacuum. Vacuum operation is seen to be essentially equivalent to increased gamma ray dosage for low irradiation levels as a result of desorptive processes common to both phenomena. They give rise to decreased nonradiative and increased radiative components of surface recombination photon emission. It is this spectrum which is shifted according to changes in surface potential and forward voltage deriving from alterations in surface state populations. A mathematical model is developed to relate wavelength tuning with surface potential and forward voltage shift. This technique is, in principle, a general technique independent of semiconductor material. It suggests the possibility of wavelength tuning via surface band-bending changes deriving from surface electric field changes, as is done with MIS devices. Examination of irradiated diode properties in vacuum and under pressure permits greater insight into the basic nature of surface phenomena long suspected to play a significant role in the diode electronic property changes brought about by nuclear irradiation.
TL;DR: In this article, the free electron transitions to acceptor-type (VGaTeAs) VAScomplexes are responsible for the non-copper induced emission observed in n-type GaAs.
Abstract: A new (non-copper induced) emission band peaked at hνm(77 K) = 135 eV is observed in n-type GaAs Pronounced features of this emission are: it disappears as copper atoms are introduced into GaAs and appears again as the copper atoms are afterwards removed from the GaAs interior Evidence is presented that the free electron transitions to acceptor-type (VGaTeAs) VAScomplexes are responsible for the non-trivial emission observed Temperature and doping variations of the peak positions, intensities, and half-widths of the new 135 eV emission band are presented An analysis of these results shows that the energy levels of the (VGaTeAs) VAS complexes are localized not far (e = 01 eV) from the top of the valence band; these complexes readily capture both, free electrons (capture coefficient cn = 10−11cm3/s) and holes (capture coefficient cn= 10−8cm3/s); rather strong electron-phonon coupling exists in (VGaTeAs) VAScomplexes – phonons are effectively emitted during the free electron radiative recombination
[Russian Text Ignored]
TL;DR: O2- centers in KCl which are excited at low temperatures with single pulses of a mode-locked Neodymium-YAG laser exhibit spontaneous emission of coherent light at two different wavelengths.
TL;DR: In this paper, the spectral linewidth of a single longitudinal laser mode is re-examined on the basis of a phase diffusion model, and the contribution to the linwidth resulting from the coupling of phase and amplitude (self-coupling term described by the enhancement factor α) is investigated exactly.
Abstract: The theory of the spectral linewidth of a single longitudinal laser mode is re‐examined on the basis of a phase diffusion model. The contribution to the linewidth resulting from the coupling of phase and amplitude (self‐coupling term described by the enhancement factor α) is investigated exactly. In particular, the commonly used approximation of a small spontaneous emission rate and/or strongly damped relaxation resonance is not applied. The self‐coupling then results no longer in a constant enhanced slope in the Schawlow‐Townes formula. The enhancement linewidth itself is now no linear function of the inverse optical power and decreases to zero in the limit of high spontaneous emission rates and small optical power. Therefore, deviations from the linear dependence of the mode linewidth on mode power are predicted.