Showing papers on "Spontaneous emission published in 1999"
TL;DR: In this paper, the authors show that the magnitude of the spontaneous emission rate can be quantitatively understood by considering both the Purcell figure of merit F/sub p/ of such cavities and the spatial/spectral distribution of the inhomogeneous collection of atom-like emitters.
Abstract: A strong enhancement of the spontaneous emission rate (Purcell effect) has been observed for self-assembled InAs/GaAs quantum boxes inserted in GaAs-based pillar microcavities (/spl times/5) and microdisks (/spl times/15) using time-resolved as well as c.w. photoluminescence experiments. We show that the magnitude of the Purcell effect can be quantitatively understood by considering both the Purcell figure of merit F/sub p/ of such cavities (F/sub p//spl Gt/1) and the spatial/spectral distribution of the inhomogeneous collection of atom-like emitters. These results open the way to the development of single-photon devices such as photon-guns or photon-turnstiles, able to emit photons one-by-one in a deterministic way.
399 citations
TL;DR: In this paper, a promising thin-slab light-emitting diode (LED) design was described, which uses a highly efficient coherent external scattering of trapped light by a two-dimensional (2D) photonic crystal.
Abstract: We describe a promising thin-slab light-emitting diode (LED) design, which uses a highly efficient coherent external scattering of trapped light by a two-dimensional (2D) photonic crystal. The light generation region was an unpatterned heterostructure surrounded by the light extraction region, a thin film patterned as a 2D photonic crystal. A six-fold photoluminescence enhancement was observed compared to an unpatterned thin film LED. That corresponded to 70% external quantum efficiency.
375 citations
TL;DR: In this paper, the authors used the method of adiabatic following to prepare a single molecule in its fluorescing excited state, and showed that up to 74% of the sweeps lead to the emission of a single photon.
Abstract: We use the method of adiabatic following to prepare a single molecule in its fluorescing excited state. Spontaneous emission from this state gives rise to a single photon. With our current experimental conditions, up to 74% of the sweeps lead to the emission of a single photon. Since the adiabatic passage is done on command, the molecule performs as a high rate source of triggered photons. The experimental results are in quantitative agreement with quantum Monte Carlo simulations.
361 citations
Abstract: Electromagnetic band structure can produce either an enhancement or a suppression of spontaneous emission from two-dimensional (2-D) photonic crystal thin films. We believe that such effects might be important for light emitting diodes. Our experiments were based on thin-film InGaAs-InP 2-D photonic crystals at ambient temperature, but the concepts would apply equally to InGaN thin films, for example. We show that the magnitude of Purcell enhancement factor, F/sub p//spl sim/2, for spatially extended band modes, is similar to that for a tiny mode in a three dimensional (3-D) nanocavity. Nonetheless, light extraction enhancement that arises from Zone folding or Bragg scattering of the photonic bands is probably the more important effect, and an external quantum efficiency >50% is possible. Angle resolved photoluminescence from inside the photonic crystal gives a direct spectral readout of the internal 2-D photonic band dispersion. The tradeoffs for employing various photonic crystal structures in high efficiency light-emitting diodes are analyzed.
319 citations
TL;DR: In this article, a 3-nm InGaN/GaN quantum well (QW) is positioned 12 nm from an 8-nm silver layer, well within the surface plasmon fringing field depth.
Abstract: The coincidence in excitation energy between surface plasmons on silver and the GaN band gap is exploited to couple the semiconductor spontaneous emission into the metal surface plasmons. A 3-nm InGaN/GaN quantum well (QW) is positioned 12 nm from an 8-nm silver layer, well within the surface plasmon fringing field depth. A spectrally sharp photoluminescence dip, by a factor \ensuremath{\approx}55, indicates that electron-hole energy is being rapidly transferred to plasmon excitation, due to the spatial overlap between the semiconductor QW and the surface plasmon electric field. Thus, spontaneous emission into surface plasmons is \ensuremath{\approx}55 times faster than normal spontaneous emission from InGaN quantum wells. If efficient antenna structures can be incorporated into the metal film, there could be a corresponding increase in external light emission efficiency.
316 citations
TL;DR: In this article, the AlF6/ZnSe multilayer structure developed by means of standard optical technology was found to have a reflection coefficient of more then 99% in the range of incident angles 0°-86° at the wavelength of 632.8nm for s-polarization.
Abstract: AlF6/ZnSe multilayer structure developed by means of standard optical technology. The structure was found to have a reflection coefficient of more then 99% in the range of incident angles 0°-86°at the wavelength of 632.8 nm for s-polarization. The results are likely to stimulate new experiments on photonic crystals and controlled spontaneous emission.
300 citations
TL;DR: In this article, a quasi-two-dimensional optical system consisting of a triangular array of air cylinders etched through a laser-like Ga(Al)As waveguiding heterostructure is described.
Abstract: We describe experiments on a quasi-two dimensional (2-D) optical system consisting of a triangular array of air cylinders etched through a laser-like Ga(Al)As waveguiding heterostructure. Such a configuration is shown to yield results very well approximated by the infinite 2-D photonic crystal (PC). We first present a set of measurements of the optical properties (transmission, reflection, and diffraction) of slabs of these photonic crystals, including the case of in-plane Fabry-Perot cavities formed between two such crystals. The measurement method makes use of the guided photoluminescence of embedded quantum wells or InAs quantum dots to generate an internal probe beam. Out-of-plant, scattering losses are evaluated by various means. In a second part, in-plane micrometer-sized photonic boxes bounded by circular trenches or by two-dimensional photonic crystal are probed by exciting spontaneous emission inside them. The high quality factors observed in such photon boxes demonstrate the excellent photon confinement attainable in these systems and allow to access the detail of the modal structure. Last, some perspectives for applications are offered.
238 citations
TL;DR: In this paper, the authors demonstrated room temperature lasing from optically pumped single defects in a two-dimensional (2D) photonic bandgap (PBG) crystal is demonstrated, where high-Q optical microcavities are formed by etching a triangular array of air holes into a half-wavelength multiquantum-well waveguide.
Abstract: Room temperature lasing from optically pumped single defects in a two-dimensional (2-D) photonic bandgap (PBG) crystal is demonstrated. The high-Q optical microcavities are formed by etching a triangular array of air holes into a half-wavelength thick multiquantum-well waveguide. Defects in the 2-D photonic crystal are used to support highly localized optical modes with volumes ranging from 2 to 3 (/spl lambda//2n)/sup 3/. Lithographic tuning of the air hole radius and the lattice spacing are used to match the cavity wavelength to the quantum-well gain peak, as well as to increase the cavity Q. The defect lasers were pumped with 10-30 ns pulses of 0.4-1% duty cycle. The threshold pump power was 1.5 mW (/spl ap/500 /spl mu/W absorbed).
204 citations
TL;DR: An analytical expression was derived for light amplification by stimulated emission in arbitrary photonic crystals, which showed and enhancement due to small group velocity, which was evaluated quantitatively for a two-dimensional crystal with a finite thickness.
Abstract: An analytical expression was derived for light amplification by stimulated emission in arbitrary photonic crystals, which showed and enhancement due to small group velocity. This enhancement was evaluated quantitatively for a two-dimensional crystal with a finite thickness, and an extremely large enhancement due to group-velocity anomaly peculiar to two- and three-dimensional crystals was found even for quite a thin crystal.
178 citations
TL;DR: In this paper, the authors calculated the lasing characteristics of current injection microdisk lasers of several microns in diameter, taking account of the scattering loss at center posts and the carrier diffusion effect.
Abstract: We have calculated lasing characteristics of current injection microdisk lasers of several microns in diameter, taking account of the scattering loss at center posts and the carrier diffusion effect. We found that the optimum width of the disk wing exposed to the air is 0.6-0.7 /spl mu/m and the minimum threshold current is nearly 10 /spl mu/A for the disk diameter of 2 /spl mu/m. The internal differential quantum efficiency can be 95% if the transparent carrier density is reduced to 7.5/spl times/10/sup 17/ cm/sup -3/ and the diffusion constant is increased to 8 cm/sup 2//s. In the experiment, we have obtained the room temperature continuous-wave operation of a GaInAsP-InP device of 3 /spl mu/m in diameter, for the first time, with a record low threshold of 150 /spl mu/A. This achievement was mainly owing to the reduction of the scattering loss at the disk edge, and hence the reduction of the threshold current density. The spontaneous emission factor was estimated to be 6/spl times/10/sup -3/. This value was much reduced by the large detuning of the lasing wavelength against the spontaneous emission peak. A larger value over 0.1, which is expected for such a small device, will be obtained by the wavelength tuning and the narrowing of the spontaneous emission spectrum.
176 citations
TL;DR: In this paper, an interference effect for electron-phonon interactions in coupled semiconductor quantum dots that can dominate the nonlinear transport properties even for temperatures close to zero was found.
Abstract: We find an interference effect for electron-phonon interactions in coupled semiconductor quantum dots that can dominate the nonlinear transport properties even for temperatures close to zero. The intradot electron tunneling process leads to a ``shake up'' of the phonon system and is dominated by a double-slit-like interference effect of spontaneously emitted phonons. The effect is closely related to subradiance of photons (Dicke effect) in a laser-trapped two-ion system and explains the oscillations in the nonlinear current-voltage characteristics of coupled dots observed recently.
TL;DR: In this paper, the authors demonstrate coherent control of spontaneous emission for a three-level atom located within a photonic band-gap structure with one resonant frequency near the edge of the photonic bands gap.
Abstract: We demonstrate the coherent control of spontaneous emission for a three-level atom located within a photonic band-gap structure with one resonant frequency near the edge of the photonic band gap. Spontaneous emission from the three-level atom can be totally suppressed or strongly enhanced depending on the relative phase between the steady-state control laser coupling the two upper levels and the pump laser pulse used to create an excited state of the atom in the form of a coherent superposition of the two upper levels. Unlike the free-space case, the steady-state inversion of the atomic system is strongly dependent on the externally prescribed initial conditions. This nonzero steady-state population is achieved by virtue of the localization of light in the vicinity of the emitting atom. It is robust to decoherence effects provided that the Rabi frequency of the control laser field-atom interaction exceeds the rate of dephasing interactions. As a result, such a system may be relevant for a single-atom, phase-sensitive, optical memory device on the atomic scale. The protected electric dipole within the photonic band gap provides a basis for a qubit to encode information for quantum computations.
TL;DR: It is concluded that the spatial carrier distribution is primarily governed by the in uence of pump induced current spreading and is only secondarily inenced by further effects such as spatial hole burning, and thermal gradients in the laser.
Abstract: We present experimental studies on the transverse mode emission behaviour of oxide-confined Vertical Cavity Surface Emitting Lasers (VCSELs). VCSELs with aperture diameters of 6um and 11um exhibit a wide variety of emission patterns from low order Hermite- Gaussian modes to high order Laguerre-Gaussian modes. We obtain detailed information about the spatial gain distribution by recording spontaneous emission intensity profiles during lasing operation. We conclude from these profiles, that the spatial carrier distribution is primarily governed by the in uence of pump induced current spreading and is only secondarily in uenced by further effects such as spatial hole burning, and thermal gradients in the laser. The combination of these mechanisms causes a strong tendency towards the emission of high order transverse modes.
TL;DR: In this paper, a general numerical method to calculate the spontaneous emission lifetime in an arbitrary microcavity, using a finite-difference time-domain algorithm, was developed, which is limited only by numerical error and finite reflection at the absorbing boundaries.
Abstract: We developed a general numerical method to calculate the spontaneous emission lifetime in an arbitrary microcavity, using a finite-difference time-domain algorithm. For structures with rotational symmetry we also developed a more efficient but less general algorithm. To simulate an open radiation problem, we use absorbing boundaries to truncate the computational domain. The accuracy of this method is limited only by numerical error and finite reflection at the absorbing boundaries. We compare our result with cases that can be solved analytically and find excellent agreement. Finally, we apply the method to calculate the spontaneous emission lifetime in a slab waveguide and in a dielectric microdisk, respectively.
TL;DR: In this paper, a multimechanism model fitting measured spectra and spectra measured by other researchers is presented and justified, and the success of the model indicates that indirect recombination of electrons and holes is the dominant emission mechanism below the light intensity peak (/spl sim/1.8-2.0 eV), that indirect intraband recombination dominates at intermediate energies up to /spl sim 2.3 eV, and that direct interband recombination between high-field populations of carriers near k=0 dominates above 2.4-3.4 eV
Abstract: Light emission from three device types ((1) commercial silicon JFETs, (2) bipolar transistors, and (3) a custom diode) with p-n junctions biased in controlled avalanche breakdown, has been measured over the photon energy range 1.4-3.4 eV, Previously published models are compared with these data to elucidate the mechanisms responsible for avalanche light emission in silicon. A multimechanism model fitting measured spectra and spectra measured by other researchers is presented and justified. The success of the model indicates that indirect recombination of electrons and holes is the dominant emission mechanism below the light intensity peak (/spl sim/1.8-2.0 eV), that indirect intraband recombination dominates at intermediate energies up to /spl sim/2.3 eV, and that direct interband recombination between high-field populations of carriers near k=0 dominates above /spl sim/2.3 eV. For junctions with overlayer passivation, an interference model must be applied to model measured spectra.
TL;DR: In this paper, it was shown that it is possible to have unbounded line narrowing in the spontaneous emission spectrum simultaneously with control of the corresponding intensity, by employing a laser driven doublet of excited atomic, molecular, or semiconductor states with almost parallel dipole orientation.
Abstract: We show that it is possible at least in principle to have unbounded line narrowing in the spontaneous emission spectrum simultaneously with control of the corresponding intensity. For this purpose we employ a laser driven doublet of excited atomic, molecular, or semiconductor states with almost parallel dipole orientation, which is decaying to a ground state. Incoherent pumping is applied to control the population and thus the spontaneous emission intensity of the dressed state associated with the ultranarrow spectral line.
TL;DR: In this paper, significant differences in the temperature dependent and time-resolved photoluminescence (PL) from low and high surface density InGaAs/GaAs quantum dots (QDs) were reported.
Abstract: We report significant differences in the temperature dependent and time-resolved photoluminescence(PL) from low and high surface density InGaAs/GaAs quantum dots (QDs).
TL;DR: In this paper, the authors report stochastic polarization switching in vertical-cavity semiconductor lasers, with residence times that vary by 8 orders of magnitude for a single such laser by changing its switch current with a hot-spot technique.
Abstract: We report stochastic polarization switching in vertical-cavity semiconductor lasers, with residence times that vary by 8 orders of magnitude for a single such laser by changing its switch current with a hot-spot technique. In spite of the potentially complicated polarization dynamics of these lasers, the experimental results agree with Kramers hopping in a 1D double-well potential initiated by quantum fluctuations. We confirm the validity of this surprisingly simple theoretical model by independent measurements of the potential barrier between the wells and the spontaneous emission noise strength.
TL;DR: In this article, the authors presented a general method for the /spl beta/ factor calculation in optical microcavities based on the classical model for atomic transitions in a semiconductor active medium, which is used to evolve the electromagnetic fields of the system and calculate the total radiated energy, as well as the energy radiated into the mode of interest.
Abstract: We present a general method for the /spl beta/ factor calculation in optical microcavities. The analysis is based on the classical model for atomic transitions in a semiconductor active medium. The finite-difference time-domain method is used to evolve the electromagnetic fields of the system and calculate the total radiated energy, as well as the energy radiated into the mode of interest. We analyze the microdisk laser and compare our result with the previous theoretical and experimental analyses. We also calculate the /spl beta/ factor of the microcavity based on a two-dimensional (2-D) photonic crystal in an optically thin dielectric slab. From the /spl beta/ calculations, we are able to estimate the coupling to radiation modes in both the microdisk and the 2-D photonic crystal cavity, thereby showing the effectiveness of the photonic crystal in suppressing in-plane radiation modes.
TL;DR: In this paper, the authors examined the inhibited spontaneous emission in photonic bandgap (PBG) materials with dye molecules, semiconductor nanoparticles (quantum dots), and rare-earth ions.
Abstract: Photonic crystals based on silica colloidal crystals (artificial opals) exhibit pronounced stopbands for electromagnetic wave propagation and the corresponding modification of the photon density of states in the visible range. These spectrally selective features can be enhanced by impregnating opals with higher refractive materials like, e.g., polymers. Doping of these structures with dye molecules, semiconductor nanoparticles (quantum dots), and rare-earth ions provides a possibility to examine the challenging theoretical predictions of the inhibited spontaneous emission in photonic bandgap (PBG) materials. First experiments are discussed in which pronounced modification of spontaneous emission spectra and noticeable changes in decay kinetics were observed.
TL;DR: In this article, a layer of low refractive index, sandwiched between two multilayer stacks made from commonly used dielectric materials, was designed to be completely free of all modes within a band of frequencies, i.e., to support a species of full photonic bandgap.
TL;DR: In this paper, a simple method to obtain the spontaneous emission rate of a dipole placed in a general microcavity is proposed and demonstrated, where the equations are solved directly in real space instead of k space by the finite-difference time domain method with a free-space boundary condition.
Abstract: A simple method to obtain the spontaneous emission rate of a dipole placed in a general microcavity is proposed and demonstrated. In our approach, Maxwell's equations are solved directly in real space instead of k space by the finite-difference time-domain method with a free-space boundary condition. It is advantageous that allowed eigenmodes need not be calculated and the total radiation rates to all the allowed modes are obtained from the beginning. All the localized modes, guided modes, and extended modes are inherently included in this formulation. The validity of the method is tested for a dipole placed in an ideal planar microcavity and the calculated results agree well with the closed-form analytic solutions. The enhancement and the inhibition of the spontaneous emission rate in several photonic band-gap structures are studied. Point dipole analyses show three-dimensional effects in two-dimensional in-plane photonic band gaps and the effects of localized, guided and extended modes on radiation rates.
TL;DR: In this article, a closed-form model was developed to characterize the spectral and spatial portions of amplified spontaneous emission in a flashlamp-pumped Nd:YAG laser with a threshold of 12 J and a slope efficiency of 0009.
Abstract: Amplified spontaneous emission can seriously degrade the Q-switched performance of a strong four-level transition such as the 1064 /spl mu/m Nd:YAG transition or can even prevent oscillation on a weaker quasi-four-level transition such as the 0946-/spl mu/m Nd:YAG transition To characterize, and thus be able to mitigate, amplified spontaneous emission, a closed-form model is developed By employing a closed-form solution, the differential equations describing both the evolution and decay of the upper laser manifold population density can be solved exactly An advantage of this model is the separation of the spectral and spatial portions of amplified spontaneous emission Gain measurements, as a function of time and pump energy, are compared with the model and good agreement is found With these principles in mind, a flashlamp-pumped Nd:YAG laser was designed to operate at 0936 /spl mu/m At room temperature, a threshold of 12 J and a slope efficiency of 0009 was achieved
TL;DR: In this article, a very small apertured microcavities with quantum-dot light emitters were used to obtain electronic confinement within the aperture, and a 2.3 increase in the averaged spontaneous emission rate was achieved.
Abstract: Spontaneous lifetime control is demonstrated using very small apertured microcavities, with quantum-dot light emitters used to obtain electronic confinement within the aperture. A factor of 2.3 increase in the averaged spontaneous emission rate is achieved due to the optical confinement. The enhancement/inhibition ratio of the spontaneous emission rate tracks the optical mode size and spectral response of the apertured microcavity.
TL;DR: In this paper, the spontaneous emission spectra and lasing characteristics of long-wavelength (1.3/spl mu/m) quantum-dot lasers are studied and it is found experimentally that nonradiative recombination can dominate the room-temperature efficiency and limit threshold.
Abstract: The spontaneous emission spectra and lasing characteristics of long-wavelength (1.3-/spl mu/m) quantum-dot lasers are studied. It is found experimentally that nonradiative recombination can dominate the room-temperature efficiency and limit threshold, By describing the quantum-dot spectral emission as due to energy levels of a two-dimensional harmonic oscillator, rate equations are developed to account for the temperature-dependent spontaneous and lasing characteristics.
TL;DR: In this article, the authors demonstrate the enhancement of light extraction efficiency in two-dimensionally arranged microcolumns by using the inductively coupled plasma etching and show that the internal efficiency in the microcolumn was reduced by the surface recombination at sidewalls.
Abstract: This paper experimentally demonstrates the strong enhancement of light extraction efficiency in two-dimensionally arranged microcolumns. They were designed like a honeycomb photonic crystal and fabricated into GaInAsP-InP wafers by using the inductively coupled plasma etching. For the laterally directed light passing through the microcolumns, peculiar transmission characteristics were observed, which could be explained by the Bragg reflection theory, namely, the photonic bandgap (PBG). The measurement of spontaneous lifetime showed that the internal efficiency in the microcolumns was reduced by the surface recombination at sidewalls. In contrast, the light extraction efficiency evaluated from the measured photoluminescence intensity, and the internal efficiency was more than ten times that for a planar wafer. This was thought to be due to the expanded escape cone of internal light by the low effective refractive index, and also due to the strong diffraction and scattering of laterally directed light, which corresponds to the second-order Bragg condition. Such effects are expected not only in photonic crystals but also in some disordered structures. We expect this structure to allow a high-efficiency light-emitting diode (LED), since electronic elements needed for current injection devices can be added independently of the effects.
TL;DR: In this paper, the authors showed that spontaneous emission can create coherences in a multilevel atom having close-lying levels, subject to the condition that the atomic dipole matrix elements are nonorthogonal.
Abstract: Spontaneous emission can create coherences in a multilevel atom having close-lying levels, subject to the condition that the atomic dipole matrix elements are nonorthogonal. This condition is rarely met in atomic systems. We report the possibility of bypassing this condition and thereby creating coherences by letting the atom with orthogonal dipoles interact with the vacuum of a preselected polarized cavity mode rather than the free-space vacuum. We derive a master equation for the reduced density operator of a model four-level atomic system, and obtain its analytical solution to describe the interference effects. We report the quantum beat structure in the populations.
TL;DR: In this paper, the results of time integrated and time resolved photoluminescence spectroscopy were reported as a function of excitation density at 6 K on high quality self-organized InAs/GaAs quantum dots.
Abstract: In this article we report the results of time integrated and time resolved photoluminescence spectroscopy and photoluminescence time decay measurements as a function of excitation density at 6 K on high quality self-organized InAs/GaAs quantum dots. To understand the form of the experimentally observed photoluminescence transients a Monte Carlo model has been developed that allows for the effects of random capture of photo-excited carriers. By comparison with the results of our model we are able to ascribe the excitation density dependence of the overall form of the decay of the emission from the quantum dot ground states and the biexponential nature of the decay of the first excited state emission as being due to the combined effects of radiative recombination, density dependent carrier scattering, and the restriction of carrier scattering due to state blocking caused by the effects of Pauli exclusion. To successfully model the form of the biexponential decay of the highest energy excited states we have ...
TL;DR: In this paper, the Judd-Ofelt theory has been applied to the measured values of absorption line strengths to evaluate the spontaneous emission probabilities from the 4F3/2 level, quantum efficiencies and stimulated emission cross sections of the 4I11/2 transition for Nd3+.
TL;DR: In this article, the photoluminescence (PL) characteristics of pure nanoscale silicon quantum wires (SiQW's) were evaluated under ultraviolet photoexcitation.
Abstract: The recent success of bulk synthesis of pure nanoscale silicon quantum wires (SiQW's) enables us to evaluate their photoluminescence (PL) characteristics under ultraviolet photoexcitation. Intensive multiple light emissions ranging from dark red to blue regions were revealed for as-grown and partially oxidized SiQW samples. The red light emission was ascribed to a quantum confinement effect originating from the crystalline core of the SiQW's that is closely mediated by the interface. However, the PL emission from green to blue is found to be definitely unrelated to quantum confinement; instead they are attributed to the radiative recombination from defect centers in the overcoating layer of the amorphous silicon oxide outside the SiQW's.