Showing papers on "Spontaneous emission published in 1971"
76 citations
TL;DR: In this article, the terms corresponding to the frequency shifts were properly treated and the appropriate master equation was given, and the explicit form of the frequency-shift terms was also given.
Abstract: This is an addendum to the author's previous paper [Phys. Rev. A 4, 1778 (1971)], where master equations describing the spontaneous emission from a collection of identical two-level atoms and oscillators were derived without the use of rotating-wave approximation. However, the terms corresponding to the frequency shifts were not adequately included. Here such terms are properly treated and the appropriate master equation is given. Explicit form of the frequency-shift terms is also given.
58 citations
TL;DR: In this article, free-free spontaneous radiative emission by a pair of atoms is discussed, and explicit formulae are derived for the spontaneous emission rate, which include contributions from quasi-bound resonating states.
Abstract: Free-free radiative emission by a pair of atoms is discussed, and explicit formulae are derived for the free-free spontaneous emission rate, which include contributions from quasi-bound resonating states. The theory is applied to the interpretation of helium emission near 600 A, and it is suggested that the 600 A emission bands arise primarily from transitions from quasibound resonating vibrational levels of the A 1Σu + state of He2. Analysis of the emission data leads to a dissociation energy of 2·50 eV for the A 1Σu + state.
35 citations
TL;DR: In this article, the spontaneous emission spectrum and threshold for stimulated transitions were used to show that previous reports that this material has an indirect gap are incorrect, and that at 2°K the stimulated emission peaks at 6010 A, which is ≈ 45 meV below the direct exciton absorption peak at 5800 A.
33 citations
TL;DR: In this article, an additional peak in CdS was observed on the longwavelength side of the Ex-LO band in the spontaneous emission spectra under high excitation by an electron beam from 82 to 300 °K.
Abstract: An additional peak in CdS was observed on the long‐wavelength side of the Ex‐LO band in the spontaneous emission spectra under high excitation by an electron beam from 82 to 300 °K. The shift of the additional peak from the free‐exciton line increased linearly with temperature. The laser emission occurred near the additional peak. The laser‐transition mechanism associated with the additional luminescence is discussed.
32 citations
TL;DR: In this article, the long-term spontaneous emission of a two-level atom, strongly interacting with a resonant mode, was studied. Butt et al. made an all-quantum treatment of the long term spontaneous emission and calculated the energy levels of the two-layer atom for various times of interaction and interaction strengths, and the energy level of the atom was clustered into n-blocks of two levels l+>n and [-->,~ with energies h(no)o~r where to o is the circular frequency of the field mode, a the coupling
Abstract: In this note we made an all quantum treatment of the long-term spontaneous emission of a two-level atom, strongly interacting with a resonant mode. The spectra of the spontaneous emission, as they arc registered either by a large-band detector or by a monochromatic one, are calculated for various times of interaction and interaction strengths. The energy levels of a two-level atom in interaction with a resonant field mode (atom plus field mode system or AFM system) are clustered into n-blocks of two levels l+>n and [-->,~ with energies h(no)o~ ~r where to o is the circular frequency of the field mode, a the coupling constant of the interaction between the atom and the mode and n the occupation number of the mode. If we call II> and ]2>, respectively, the atom ground-state and excited-state wave functions, the stationary states ]+>, and ]-->~ of the AFM system can be written (1)
28 citations
IBM1
TL;DR: In this paper, a gauge-invariant derivation of the radiant energy production rate, using only Maxwell's equations and the usual definitions of electric current and charge density for a many-particle material system described by Schr\"odinger's equation, is given.
Abstract: It has recently been shown by Jaynes and collaborators that semiclassical radiation theory contains a description of spontaneous emission of radiation and of radiative level shifts. The present paper gives a gauge-invariant derivation of the radiant energy production rate, using only Maxwell's equations and the usual definitions of electric current and charge density for a many-particle material system described by Schr\"odinger's equation. A complementary derivation, using the time-dependent Schr\"odinger equation, verifies the instantaneous conservation of energy and probability during the radiation process. The semiclassical rate of spontaneous emission differs from the usual formula (Einstein's $A$ coefficient) because it depends on the occupancy of both initial and final states of the material system. The implications of this with regard to thermal equilibrium and Planck's law are examined. If a new hypothesis is introduced, postulating the decomposition of the equilibrium radiation into incoherent components, each interacting with a specific pair of energy levels of the material system, then Planck's law is shown to hold for the total intensity of radiation. If this hypothesis is not introduced, the equilibrium conditions for different transitions are incompatible, and the semiclassical radiation theory is incapable of describing thermal equilibrium.
26 citations
TL;DR: In this paper, a general theory for spontaneous emission from a system of N identical atoms or molecules was developed and the normally ordered correlation functions for the oscillator system were calculated and these were then used to calculate the radiation-field correlation functions in the far zone.
Abstract: In a previous investigation, a general theory for spontaneous emission from a system of N identical atoms or molecules was developed. This theory was based on the master equation recently derived in another paper. In that paper, the master equation relating to spontaneous emission from a system of harmonic oscillators was also derived. In the present investigation, the normally ordered correlation functions for the oscillator system are calculated and these are then used to calculate the radiation-field correlation functions in the far zone. These correlation functions are compared for two different modes of excitation, viz., (i) when each of the oscillators is excited initially to a Fock state, and (ii) when each of the oscillators is excited to some coherent state. It is found that the even-order (2n) correlation functions for the second mode of excitation (superradiant excitation) are of order N 2n higher than those for the first mode of excitation. It is also shown that the photoelectron counting distribution for the superradiant excitation is Poissonian. Finally, the non-Markoffian effects in the spontaneous emission are studied in detail and their connection with exact results is described.
25 citations
TL;DR: In this article, the effect of the surface field generated near the Au-CdS interface of an Au-Schottky-barrier diode has been studied under a variety of CdS single crystals.
Abstract: Photoluminescence (edge emission) in a variety of CdS single crystals has been studied under the influence of the surface field generated near the Au–CdS interface of an Au–CdS Schottky‐barrier diode. Experimentally, above bandgap radiation is incident upon a semitransparent Au film evaporated on an air‐cleaved CdS surface. Free electrons and holes are generated within the region of the high barrier field which extends on the order of 0.5 μ into the crystal bulk. Variations of diode bias as small as 2.5 V were found to be sufficient to alter the luminescence efficiency by nearly two orders of magnitude. A model is presented (emphasizing the rapid removal of photoinjected free carriers from the barrier) which qualitatively accounts for the major features of the observed effects.
24 citations
TL;DR: The current dependence of the intensity of the spontaneous emission from GaAs injection lasers operated at 300 °K to five times threshold is reported in this article, where the long wavelength emission saturates before threshold, while the spontaneous intensity for wavelengths shorter than the lasing emission grows smoothly with no indication of the transit of threshold.
Abstract: The current dependence of the intensity of the spontaneous emission from GaAs injection lasers operated at 300 °K to five times threshold is reported. The long‐wavelength emission saturates before threshold, while the spontaneous intensity for wavelengths shorter than the lasing emission grows smoothly with no indication of the transit of threshold. At five times threshold the intensity is 2.4 times the threshold value and still growing. Similar behavior was observed with double‐heterojunction lasers exhibiting five stripes parallel to the junction in the near field, and with single‐heterojunction lasers with a single stripe. It is argued that the behavior of the spontaneous emission is in fundamental disagreement with the linear theory of lasing and that its explanation will require introduction into the rate equations of a strong nonlinearity which controls the lasing region.
24 citations
TL;DR: In this paper, the binding energy and effective mass of the donor electron were estimated to be 40 meV and 0.22m, respectively, from the hydrogen-like series of these emission lines.
Abstract: Laser‐excited luminescence has been measured in ZnO at 1.2°K. Emission due to the annihilation of the I6 bound excition with simultaneous excitation or ionization of the donor electron has been observed in stimulated emission, which was excited by intense N2 laser light. From the hydrogenlike series of these emission lines, the binding energy and the effective mass of the donor electron are estimated to be 40 meV and 0.22m, respectively.
TL;DR: In this article, a general theory for the treatment of spontaneous emission from a system of N identical two-level atoms or molecules is developed and the master equation for the reduced density operator of the atomic system alone is obtained and is used to derive an expression for the radiation rate.
TL;DR: The operating characteristics of the CO laser excited by an electrical discharge in flowing mixtures of CO and He are described in this article, and the fundamental energy transfer processes leading to population inversion in this laser are discussed, and a qualitative discussion of the steady state vibrational populations is given.
Abstract: The operating characteristics of the CO laser excited by an electrical discharge in flowing mixtures of CO and He are described. The fundamental energy transfer processes leading to population inversion in this laser are discussed, and a qualitative discussion of the steady-state vibrational populations is given.
TL;DR: An intense vacuum uv atomic line source excited in a 2450-MHz microwave discharge cavity is described and analyzed and is suitable for the detection of various species by absorption measurement in fast occurring events such as those in ballistic ranges and shock tubes.
Abstract: An intense vacuum uv atomic line source excited in a 2450-MHz microwave discharge cavity is described and analyzed. Additional features are a clean spectrum, very little window deterioration, little or no self-absorption, and easily interchangeable parts. (For the O-atom source only the 1300-A triplet shows up over the 1200-A to 1650-A region.) This source is suitable for the detection of various species by absorption measurement in fast occurring events such as those in ballistic ranges and shock tubes. Atomic line shape theory is used to analyze an O-atom line source with intensity ratios I1306A:I1305A:I1302A:1:2.9:4.5. This source is described by a 2700 ± 200 K temperature and certain self-absorption parameters as deduced from the measurement of their intensity ratios and their transmission characteristics through known concentrations of O-atoms. A good theoretical fit to the measured transmission validates the assumed uniform source temperature and excitation for the analysis. An f value (f = 0.052 ± 0.005) for the O-atom 1300-A triplet absorption and a collision diameter of 5.5 ± 1.0 A between the O-atom and the nitrogen molecule were determined in the course of this study.
TL;DR: In this paper, it has been shown experimentally that spontaneous emission in semiconductors decreases at the onset of lasing in Fabry-Perot cavities, which is consistent with earlier published theory suggesting that the spontaneous emission should saturate after lasing sets in.
Abstract: It has been shown experimentally that spontaneous emission in semiconductors decreases at the onset of lasing. This has been observed qualitatively by a visual method in CdS and GaAs lasing in a total internal‐reflection cavity under electron‐beam pumping. More quantitative observations have been made on CdSe and CdS optically pumped by a HeNe laser and Argon laser, respectively. The decrease in spontaneous emission occurs across the entire spectrum. It seems reasonable to believe that this decrease also occurs in Fabry‐Perot cavities. No explanation for the new phenomenon has been found and it seems to be inconsistent with earlier published theory suggesting that the spontaneous emission should saturate after lasing sets in.
01 Jul 1971
TL;DR: In this article, the electron beam was injected through the flow, and the resulting spontaneous emission of light was spectroscopically analyzed, and light intensity measurements were made photoelectrically, and signal amplification and averaging were accomplished with a lock-in amplifier.
Abstract: : The purpose of the experiments and calculations reported was to use the electron beam technique for rotational and vibrational temperature and density measurements in the free stream of low density, hypersonic flows of nitrogen. The variation in the flow parameters was obtained through the use of four different nozzles; each was operated at two different conditions. The electron beam was injected through the flow, and the resulting spontaneous emission of light was spectroscopically analyzed. Light intensity measurements were made photoelectrically, and signal amplification and averaging were accomplished with a lock-in amplifier.
TL;DR: In this article, the luminescence spectrum and its temperature dependence for calcium-fluoride crystals excited by low-energy electrons are found to be those obtained by X-ray irradiation except for a difference in the relative intensities of some regions of emission.
TL;DR: In this paper, a decorrelation procedure for the interaction of a single two-level atom with all modes of the radiation field which replaces the semiclassical boson approximation for the atom by an exact fermion treatment is reported.
Abstract: Reports a natural all-order decorrelation procedure for the interaction of a single two-level atom with all modes of the radiation field which replaces the semiclassical boson approximation for the atom by an exact fermion treatment. In consequence, the spontaneous emission of the semiclassical theory is extended to include stimulated emission, a semiclassical Lamb-type shift is explicitly replaced by a shift satisfying the Bethe formula manifestly due to vacuum fluctuations, and there can be two intensity-dependent terms, one of which generalizes the Bethe formula.
TL;DR: In this paper, a method for determining the band-tailing parameters in GaAs junction lasers from measurements of the wavelength shift with cavity Q and the linewidth of spontaneous emission preceding laser action is proposed.
Abstract: Ths wavelength shift with cavity Q in GaAs junction lasers with exponential band tails as experimentally observed eleswhere is related to the characteristic energies of the distribution of the tail states in both the conduction and valence bandfl. A method is then proposed for determining the band-tailing parameters in GaAs junction lasers from measurements of the wavelength shift with cavity Q and the linewidth of spontaneous emission preceding laser action. The accuracy of the method will be fairly high since the measurements on which the method is based could be done precisely and also since the assumptions involved in the method are quite valid under most of the practical situations.
TL;DR: In this paper, the line shape of spontaneous emission of an atom with closely spaced energy levels was determined using transition operator techniques, and the transition operator was used to determine the spontaneous emission line shape.
TL;DR: In this paper, the probability of de-excitation by electronic collision of the upper 3s2 and lower 2p4 levels, P52e and P21e, respectively, were obtained.
Abstract: The laser action produces changes of population in the upper and lower levels involved These population changes lead to the light intensity changes of spontaneous emission originating from the upper and lower levels, ΔI52 and ΔI21, respectively The ratio of these intensity changes, ΔI21/ΔI52, is theoretically calculated By analysing the experimental data of this ratio observed on 6328A emission in a He-Ne laser, the probabilities of de-excitation by electronic collision of the upper 3s2 and lower 2p4 levels, P52e and P21e, respectively, are obtained The value of probability P52e at a discharge current of 30 mA for a laser tube of 35 mm diameter is (34±06)×107 sec-1 and is of the same order as the total probability of radiative transition of 3s2 level, A52 The total cross section of this electronic collision process σ52e is estimated to be (68±12)×10-13 cm2 The value of P21e at 30 mA is much smaller than the value of the probability of 2p4 level, A21 This technique also yeilds the ratio of A52/A521 to be 21±08, where A521 is the probability of radiative transition from 3s2 level to 2p4 level
TL;DR: In this article, the theory of Weisskopf and Wigner is extended to describe the modifications of spontaneous emission which occur when atoms or molecules emit radiation spontaneously, while simultaneously undergoing stimulated emissions or absorptions.
Abstract: The theory of Weisskopf and Wigner is estended to describe the modifications of spontaneous emission which occur when atoms or molecules emit radiation spontaneously, while simultaneously undergoing stimulated emissions or absorptions. The theory is developed generally for radiation present initially at or off resonance. It is illustrated for the simple case that decay quanta are emitted spontaneously parallel or antiparallel to the direction of propagation of radiation causing stimulated transitions. Spectral-line profiles calculated for this case are shown in appropriate limits to agree with the results of previous theories and experiment. General theoretical procedures and explicit expressions are developed for a variety of more complex situations which might reasonably be encountered in future experiments.
TL;DR: In this article, the spectral intensity distribution of the spontaneous omission from semiconductor lasers of n-type GaAs pumped by a 40 kv electron beam is calculated using the theory of recombination statistics.
Abstract: The spectral intensity distribution of the spontaneous omission from semiconductor lasers of n-type GaAs pumped by a 40 kv electron beam is calculated using the theory of recombination statistics. The results obtained are in good agreement with the published data on experiments carried out both at 77°k and 300°K. In particular a hump is obtained in the spectral distribution on the high energy side of the spectrum of the light emitted from n-type GaAs at 77°K when the level of doping is very high. This also is in agreement with the experimental observation reported elsewhere.
TL;DR: In this article, the photon energy and the conversion efficiency for radiative recombination in Sn−doped Ge were reported for temperatures ranging from 22 to 180 K. The spectrum of the emission from Pb−Doped Ge at 77 K was shown.
Abstract: The photon energy and the conversion efficiency for radiative recombination in Sn‐doped Ge are reported for temperatures ranging from 22 to 180 K. The spectrum of the emission from Pb‐doped Ge at 77 K is shown. A model of the emission process based on the trapping of excitons at the Sn centers is proposed.
TL;DR: In this paper, the effect of the electric field on small-signal microwave conductivity has been theoretically studied and some calculations are presented in the microwave frequency region at low temperatures (77°K) in an n −InSb sample.
Abstract: dc field‐induced anisotropy of small‐signal microwave conductivity has been theoretically studied and some calculations are presented in the microwave frequency region at low temperatures (77°K) in an n‐InSb sample. Above a certain minimum value of the electric field, the spontaneous emission of optical phonons in the active region (e>ℏωl), and elastic scattering by ionized impurities and by acoustic phonons in the passive region (e>ℏωl) have been assumed to be the dominant scattering mechanisms. Comparison is made with the theoretical results at high temperatures (300°K) and, qualitatively, with the experimental results of Bonek and Richter. It is seen that the effect of electric field is much more appreciable at low temperatures than at high; many of the qualitative features of the experimental results are explained by the theory. An interesting reduction is made to the case of a parabolic semiconductor, which reveals that the anisotropy effects are greater for a nonparabolic semiconductor than the para...
TL;DR: In this paper, the laser emission of CdSe excited by Ga(AsP) laser diode has been studied near liquid helium temperature both before and after irradiation with fast neutrons.
Abstract: Laser emission of CdSe excited by Ga(AsP) laser diode has been studied near liquid helium temperature both before and after irradiation with fast neutrons. Irradiation introduces new laser peaks at ~6895A, ~690A, and ~6924A, which are situated at longer wavelengths as compared to the peaks observed before irradiation. The laser peak at ~6905A can be associated with the strong spontaneous emission that is observed at the same wavelength after irradiation. These results are interpreted in terms of the recombination of excitons bound to the defects introduced by irradiation.
TL;DR: The dependence of spontaneous emission from electron-beam-excited specimens of impure GaAs on the level of excitation is theoretically studied and is found to be in qualitative agreement with the experimental observation as discussed by the authors.
Abstract: The dependence of the intensity of spontaneous emission from electron-beam-excited specimens of impure GaAs on the level of excitation is theoretically studied and is found to be in qualitative agreement with the experimental observation.
Die Intensitatsabhangigkeit der spontanen Emission von Elektronenstrahl-angeregten dotierten GaAs-Proben vom Anregungsniveau wird theoretisch untersucht, und es wird gefunden, das sie in qualitativer Ubereinstimmung mit den experimentellen Beobachtungen ist.
01 Jan 1971
TL;DR: In this article, the spectral and current dependences of the luminescence of Ge-doped GaAs diodes were studied and a relation between the luminecence intensity J and the current I was found: I ∞ J 1/n, where n = 5−7 for small forward currents and n = 1 for large forward currents.
Abstract: The spectral and current dependences of the luminescence of Ge-doped GaAs diodes were studied. A relation between the luminescence intensity J and the current I was found: I ∞ J1/n , where n = 5–7 for small forward currents and n = 1 for large forward currents. The exact relationship between the luminescence and the current is discussed bearing in mind the competition between possible recombination processes.