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Showing papers on "Spontaneous emission published in 2007"


Journal ArticleDOI
15 Nov 2007-Nature
TL;DR: This work demonstrates a cavity-free, broadband approach for engineering photon–emitter interactions via subwavelength confinement of optical fields near metallic nanostructures and shows that efficient coupling is accompanied by more than 2.5-fold enhancement of the quantum dot spontaneous emission, in good agreement with theoretical predictions.
Abstract: Control over the interaction between single photons and individual optical emitters is an outstanding problem in quantum science and engineering. It is of interest for ultimate control over light quanta, as well as for potential applications such as efficient photon collection, single-photon switching and transistors, and long-range optical coupling of quantum bits. Recently, substantial advances have been made towards these goals, based on modifying photon fields around an emitter using high-finesse optical cavities. Here we demonstrate a cavity-free, broadband approach for engineering photon-emitter interactions via subwavelength confinement of optical fields near metallic nanostructures. When a single CdSe quantum dot is optically excited in close proximity to a silver nanowire, emission from the quantum dot couples directly to guided surface plasmons in the nanowire, causing the wire's ends to light up. Non-classical photon correlations between the emission from the quantum dot and the ends of the nanowire demonstrate that the latter stems from the generation of single, quantized plasmons. Results from a large number of devices show that efficient coupling is accompanied by more than 2.5-fold enhancement of the quantum dot spontaneous emission, in good agreement with theoretical predictions.

1,412 citations


Journal ArticleDOI
TL;DR: In this paper, the authors describe the recent experimental progress in the control of spontaneous emission by manipulating optical modes with photonic crystals, which can contribute to the evolution of a variety of applications, including illumination, display, optical communication, solar energy and even quantum information systems.
Abstract: We describe the recent experimental progress in the control of spontaneous emission by manipulating optical modes with photonic crystals. It has been clearly demonstrated that the spontaneous emission from light emitters embedded in photonic crystals can be suppressed by the so-called photonic bandgap, whereas the emission efficiency in the direction where optical modes exist can be enhanced. Also, when an artificial defect is introduced into the photonic crystal, a photonic nanocavity is produced that can interact with light emitters. Cavity quality factors, or Q factors, of up to 2 million have been realized while maintaining very small mode volumes, and both spontaneous-emission modification (the Purcell effect) and strong-coupling phenomena have been demonstrated. The use of photonic crystals and nanocavities to manipulate spontaneous emission will contribute to the evolution of a variety of applications, including illumination, display, optical communication, solar energy and even quantum-information systems.

936 citations


Journal ArticleDOI
TL;DR: In this paper, the first laser operation in an electrically pumped metallic-coated nanocavity formed by a semiconductor heterostructure encapsulated in a thin gold film was reported.
Abstract: Metallic cavities can confine light to volumes with dimensions considerably smaller than the wavelength of light. It is commonly believed, however, that the high losses in metals are prohibitive for laser operation in small metallic cavities. Here we report for the first time laser operation in an electrically pumped metallic-coated nanocavity formed by a semiconductor heterostructure encapsulated in a thin gold film. The demonstrated lasers show a low threshold current and their dimensions are smaller than the smallest electrically pumped lasers reported so far. With dimensions comparable to state-of-the-art electronic transistors and operating at low power and high speed, they are a strong contender as basic elements in digital photonic very large-scale integration. Furthermore we demonstrate that metallic-coated nanocavities with modal volumes smaller than dielectric cavities can have moderate quality factors.

824 citations


Journal ArticleDOI
TL;DR: Angular and spectrally resolved luminescence show that the polariton emission is beamed in the normal direction with an angular width of +/-5 degrees and spatial size around 5 microm.
Abstract: We observe a room-temperature low-threshold transition to a coherent polariton state in bulk GaN microcavities in the strong-coupling regime. Nonresonant pulsed optical pumping produces rapid thermalization and yields a clear emission threshold of 1 mW, corresponding to an absorbed energy density of 29 mu J cm(-2), 1 order of magnitude smaller than the best optically pumped (In,Ga)N quantum-well surface-emitting lasers (VCSELs). Angular and spectrally resolved luminescence show that the polariton emission is beamed in the normal direction with an angular width of +/- 5 degrees and spatial size around 5 mu m.

820 citations


Journal ArticleDOI
TL;DR: In this article, the basic theory of the start-up, the exponential growth, and the saturation of the high-gain process is reviewed, emphasizing the self-amplified spontaneous emission.
Abstract: High-gain free-electron lasers (FELs) are being developed as extremely bright sources for a next-generation x-ray facility. In this paper, we review the basic theory of the start-up, the exponential growth, and the saturation of the high-gain process, emphasizing the self-amplified spontaneous emission. The radiation characteristics of an x-ray FEL, including its transverse coherence, temporal characteristics, and harmonic content, are discussed. FEL performance in the presence of machine errors and undulator wakefields is examined. Various enhancement schemes through seeding and beam manipulations are summarized.

509 citations


Journal ArticleDOI
TL;DR: In this article, a staggered InGaN quantum well with step-function-like In content in the quantum well offers significantly improved radiative recombination rate and optical gain in comparison to the conventional type-I In-GaN QW.
Abstract: Staggered InGaN quantum wells (QWs) grown by metal-organic chemical vapor deposition are demonstrated as improved active region for visible light emitters. Theoretical studies indicate that InGaN QW with step-function-like In content in the quantum well offers significantly improved radiative recombination rate and optical gain in comparison to the conventional type-I InGaN QW. Experimental results of light emitting diode (LED) structure utilizing staggered InGaN QW show good agreement with theory. Polarization band engineering via staggered InGaN quantum well allows enhancement of radiative recombination rate, leading to the improvement of photoluminescence intensity and LED output power.

305 citations


Journal ArticleDOI
TL;DR: It is concluded that materials with a significant difference between electron and hole effective masses such as III-V semiconductors should exhibit a CM threshold near the apparent 2Eg limit and the possibility of achieving sub-2Eg CM thresholds through strong exciton-exciton attraction, which is feasible in NQDs.
Abstract: Carrier multiplication (CM) is a process in which absorption of a single photon produces not just one but multiple electron-hole pairs (excitons). This effect is a potential enabler of next-generation, high-efficiency photovoltaic and photocatalytic systems. On the basis of energy conservation, the minimal photon energy required to activate CM is two energy gaps (2Eg). Here, we analyze CM onsets for nanocrystal quantum dots (NQDs) based upon combined requirements imposed by optical selection rules and energy conservation and conclude that materials with a significant difference between electron and hole effective masses such as III-V semiconductors should exhibit a CM threshold near the apparent 2Eg limit. Further, we discuss the possibility of achieving sub-2Eg CM thresholds through strong exciton-exciton attraction, which is feasible in NQDs. We report experimental studies of exciton dynamics (Auger recombination, intraband relaxation, radiative recombination, multiexciton generation, and biexciton shift) in InAs NQDs and show that they exhibit a CM threshold near 2Eg.

291 citations


Journal ArticleDOI
TL;DR: Efficient exciton-plasmon-photon conversion and guiding is demonstrated along with a modification in the spontaneous emission rate of the coupled exciton and plasmon system.
Abstract: A silver-nanowire cavity is functionalized with CdSe nanocrystals and optimized towards cavity quantum electrodynamics by varying the nanocrystal-nanowire distance d and cavity length L. From the modulation of the nanocrystal emission by the cavity modes a plasmon group velocity of v (gr) approximately 0.5c is derived. Efficient exciton-plasmon-photon conversion and guiding is demonstrated along with a modification in the spontaneous emission rate of the coupled exciton-plasmon system.

280 citations


Journal ArticleDOI
TL;DR: It is shown that, using structures manufacturable with today's nanotechnology, it is possible to increase the radiative decay rate by three orders of magnitude while keeping a quantum efficiency larger than 80% in the near-infrared regime.
Abstract: We apply two- and three-dimensional numerical calculations to study optical nanoantennae made of two coupled gold nanostructures, enclosing a single emitter in their gap. We show that, using structures manufacturable with today's nanotechnology, it is possible to increase the radiative decay rate by three orders of magnitude while keeping a quantum efficiency larger than 80% in the near-infrared regime. We examine the competition between the radiative and nonradiative processes in the presence of the antennae as a function of wavelength and antenna geometry. Our results hold great promise for improving the quantum efficiency of poor emitters such as silicon nanocrystals or carbon nanotubes.

273 citations


Journal ArticleDOI
TL;DR: The present paper reports on the first successful continuous-wave operation at room temperature for the smallest nanolaser reported to date, achieved through fabrication of a laser with a low threshold of 1.2 muW.
Abstract: Photonic crystal slab enables us to form an ultrasmall laser cavity with a modal volume close to the diffraction limit of light. However, the thermal resistance of such nanolasers, as high as 10(6) K/W, has prevented continuous-wave operation at room temperature. The present paper reports on the first successful continuous-wave operation at room temperature for the smallest nanolaser reported to date, achieved through fabrication of a laser with a low threshold of 1.2 muW. Near-thresholdless lasing and spontaneous emission enhancement due to the Purcell effect are also demonstrated in a moderately low Q nanolaser, both of which are well explained by a detailed rate equation analysis.

250 citations


Journal ArticleDOI
TL;DR: In this paper, the spontaneous emission rate enhancement (Purcell factor) and propagation mode of a planar-photonic-crystal waveguide with single quantum dots was derived.
Abstract: A theoretical formalism to calculate the spontaneous emission rate enhancement (Purcell factor) and propagation mode $\ensuremath{\beta}$ factor from single quantum dots in a planar-photonic-crystal waveguide is presented. Large Purcell factors for slow light modes, and enormous $\ensuremath{\beta}$ factors ($g0.85$) over a broadband (10 THz) spectral range are subsequently predicted. The local density of photon states is found to diverge at the photonic band edge, but we discuss why this divergence will always be broadened in real samples, most notably due to structural disorder. Applications towards ``on-chip'' single photon sources are highlighted.

Journal ArticleDOI
TL;DR: In this paper, a system consisting of two singlemode cavities spatially separated and connected by an optical fiber and multiple two-level atoms trapped in the cavities is considered, and an ideal quantum state transfer and highly reliable quantum swap, entangling and controlled-Z gates can be deterministically realized between the distant cavities.
Abstract: A system consisting of two single-mode cavities spatially separated and connected by an optical fiber and multiple two-level atoms trapped in the cavities is considered. If the atoms resonantly and collectively interact with the local cavity fields but there is no direct interaction between the atoms, we show that an ideal quantum state transfer and highly reliable quantum swap, entangling, and controlled-Z gates can be deterministically realized between the distant cavities. We find that the operation of state transfer and swap, entangling, and controlled-Z gates can be greatly speeded up as number of the atoms in the cavities increases. We also notice that the effects of spontaneous emission of atoms and photon leakage out of cavity on the quantum processes can also be greatly diminished in the multiatom case.

Journal ArticleDOI
TL;DR: A comprehensive review of spin-polarized light-emitting diodes and surface emitting lasers is provided in this paper, concluding with a discussion of future prospects and operation principles and design of spinpolarised light sources.
Abstract: Spin-polarized light sources are a new class of devices in which the radiative recombination of spin-polarized carriers results in luminescence exhibiting a net circular polarization. The operation principles and design of spin-polarized light sources are discussed. A comprehensive review of experimental work on spin-polarized light-emitting diodes and surface-emitting lasers is provided, concluding with a discussion of future prospects.

Journal ArticleDOI
TL;DR: In this article, the authors present a statistical analysis of time-resolved spontaneous emission decay curves from ensembles of emitters, such as semiconductor quantum dots, with the aim of interpreting ubiquitous non-single-exponential decay.
Abstract: We present a statistical analysis of time-resolved spontaneous emission decay curves from ensembles of emitters, such as semiconductor quantum dots, with the aim of interpreting ubiquitous non-single-exponential decay. Contrary to what is widely assumed, the density of excited emitters and the intensity in an emission decay curve are not proportional, but the density is a time integral of the intensity. The integral relation is crucial to correctly interpret non-single-exponential decay. We derive the proper normalization for both a discrete and a continuous distribution of rates, where every decay component is multiplied by its radiative decay rate. A central result of our paper is the derivation of the emission decay curve when both radiative and nonradiative decays are independently distributed. In this case, the well-known emission quantum efficiency can no longer be expressed by a single number, but is also distributed. We derive a practical description of non-single-exponential emission decay curves in terms of a single distribution of decay rates; the resulting distribution is identified as the distribution of total decay rates weighted with the radiative rates. We apply our analysis to recent examples of colloidal quantum dot emission in suspensions and in photonic crystals, and we find that this important class of emitters is well described by a log-normal distribution of decay rates with a narrow and a broad distribution, respectively. Finally, we briefly discuss the Kohlrausch stretched-exponential model, and find that its normalization is ill defined for emitters with a realistic quantum efficiency of less than 100%.

Journal ArticleDOI
G. Sagué1, E. Vetsch1, Wolfgang Alt1, Dieter Meschede1, Arno Rauschenbeutel1 
TL;DR: This work introduces an ultrathin unclad optical fiber into a cold-atom cloud and investigates the interaction of a small number of cold cesium atoms with the guided fiber mode and with the fiber surface.
Abstract: The strong evanescent field around ultrathin unclad optical fibers bears a high potential for detecting, trapping, and manipulating cold atoms. Introducing such a fiber into a cold-atom cloud, we investigate the interaction of a small number of cold cesium atoms with the guided fiber mode and with the fiber surface. Using high resolution spectroscopy, we observe and analyze light-induced dipole forces, van der Waals interaction, and a significant enhancement of the spontaneous emission rate of the atoms. The latter can be assigned to the modification of the vacuum modes by the fiber.

Journal ArticleDOI
TL;DR: In this article, the authors introduce a semiconductor theory, originating from a microscopic Hamiltonian, to describe lasing from quantum dots embedded in microcavities, which includes modified contributions of spontaneous and stimulated emission as well as many-body effects.
Abstract: When it comes to laser phenomena in quantum-dot-based systems, usually atomic models are employed to analyze the characteristic behavior. We introduce a semiconductor theory, originating from a microscopic Hamiltonian, to describe lasing from quantum dots embedded in microcavities. The theory goes beyond two-level atomic models and includes modified contributions of spontaneous and stimulated emission as well as many-body effects. An extended version, which incorporates carrier-photon correlations, provides direct access to the photon autocorrelation function and thereby on the statistical properties of the laser emission. In comparison to atomic models, we find deviations in the dependence of the input/output curve on the spontaneous emission coupling $\ensuremath{\beta}$. Modifications of the photon statistics are discussed for high-quality microcavities with a small number of emitters.

Journal ArticleDOI
TL;DR: The physics behind spontaneous emission rate enhancements from a single quantum dot embedded in a finite-size, planar photonic-crystal waveguide are explained and a "single-photon gun" with on-chip unidirectional collection efficiencies greater than 60% into an output wire waveguide is proposed.
Abstract: Spontaneous emission rate enhancements from a single quantum dot embedded in a finite-size, planar photonic-crystal waveguide are investigated. Short waveguide lengths of only 10 to 20 unit cells are found to produce very large Purcell factors associated with a waveguidelike sharp resonance feature in the local density of photon states. Aided by theoretical insight and rigorous computational calculations, we explain the physics behind these remarkable emission enhancements and subsequently propose a "single-photon gun" with on-chip unidirectional collection efficiencies greater than 60% into an output wire waveguide. The advantages over recent proposals for infinitely long photonic-crystal waveguides are highlighted.

Journal ArticleDOI
TL;DR: In this article, a quantum network consisting of a quantum dot coupled to a source cavity, which in turn is coupled to the target cavity via a waveguide is presented, and single photon emission from the high-Q/V source cavity is characterized by twelvefold spontaneous emission (SE) rate enhancement, SE coupling efficiency β ∼ 0.98 into the source cavity mode, and mean wavepacket indistinguishability of ∼67%.
Abstract: We present a basic building block of a quantum network consisting of a quantum dot coupled to a source cavity, which in turn is coupled to a target cavity via a waveguide. The single photon emission from the high-Q/V source cavity is characterized by twelve-fold spontaneous emission (SE) rate enhancement, SE coupling efficiency β ∼ 0.98 into the source cavity mode, and mean wavepacket indistinguishability of ∼67%. Single photons are efficiently transferred into the target cavity via the waveguide, with a target/source field intensity ratio of 0.12 ± 0.01. This system shows great promise as a building block of future on-chip quantum information processing systems.

Journal ArticleDOI
TL;DR: In this article, a field emission tip electron source that is triggered with a femtosecond laser pulse can generate electron pulses shorter than the laser pulse duration (100 fs), and the emission process is sensitive to a power law of the laser intensity, which supports an emission mechanism based on multiphoton absorption followed by over the barrier emission.
Abstract: We show that a field emission tip electron source that is triggered with a femtosecond laser pulse can generate electron pulses shorter than the laser pulse duration (100 fs). The emission process is sensitive to a power law of the laser intensity, which supports an emission mechanism based on multiphoton absorption followed by over-the-barrier emission. Observed continuous transitions between power laws of different orders are indicative of field emission processes. We show that the source can also be operated so that thermionic emission processes become significant. Understanding these different emission processes is relevant for the production of sub-cycle electron pulses.

Journal ArticleDOI
TL;DR: In this paper, the photoluminescence (PL) spectra were measured at room temperature and some interesting features were found on the PL spectra, including surface-state trapped exciton emission, including single phonon-one photon coupling course with the Eg(ν1) phonon attendance.

Journal ArticleDOI
TL;DR: In this article, an electrically pumped ultraviolet (UV) random lasing in c-axis oriented ZnO polycrystalline films has been demonstrated, where a metal-oxide-semiconductor structure of Au∕SiOx(x < 2)∕ZnO film was fabricated on a silicon substrate.
Abstract: The electrically pumped ultraviolet (UV) random lasing in c-axis oriented ZnO polycrystalline films has been demonstrated. For this demonstration, a metal-oxide-semiconductor structure of Au∕SiOx(x<2)∕ZnO film was fabricated on a silicon substrate. With ever-higher forward bias where the negative voltage was connected to the silicon substrate, the UV electroluminescence from such a ZnO-based device transformed from the spontaneous emission to the random lasing in the ZnO film. It is believed that the recurrent scattering and interference of the enough strong electroluminescent UV light in the in-plane random cavities formed in the ZnO film leads to electrically pumped UV random lasing.

Journal ArticleDOI
TL;DR: In this article, a mode converter that transforms a plane electromagnetic wave into an inward-moving dipole wave is described, which is intended to bring a single atom or ion from its ground state to an excited state by absorption of a single photon wave packet with near-100% efficiency.
Abstract: In this article, we describe how to develop a mode converter that transforms a plane electromagnetic wave into an inward-moving dipole wave. The latter one is intended to bring a single atom or ion from its ground state to an excited state by absorption of a single photon wave packet with near-100% efficiency.

Journal ArticleDOI
TL;DR: In this paper, the authors developed a rigorous theory of the enhancement of spontaneous emission from a light emitting device via coupling the radiant energy in and out of surface plasmon polaritons (SPPs) on the metal-dielectric interface.
Abstract: The authors develop a rigorous theory of the enhancement of spontaneous emission from a light emitting device via coupling the radiant energy in and out of surface plasmon polaritons (SPPs) on the metal-dielectric interface. Using the GaN∕Ag system as an example, the authors show that using SPP pays off only for emitters that have a low luminescence efficiency.

Journal ArticleDOI
TL;DR: In this article, the complex emission spectra from a disordered amplifying material with static disorder are investigated in a configuration with controlled, stable experimental conditions, and it is found that, upon repeated identical excitation, the emission spectrum are distinct and uncorrelated.
Abstract: We report on an experimental and numerical study of chaotic behavior in random lasers. The complex emission spectra from a disordered amplifying material with static disorder are investigated in a configuration with controlled, stable experimental conditions. It is found that, upon repeated identical excitation, the emission spectra are distinct and uncorrelated. This behavior can be understood in terms of strongly coupled modes that are triggered by spontaneous emission, and is expected to play an important role in most pulsed random lasers.

Journal ArticleDOI
TL;DR: In this paper, the external quantum efficiency of polycrystalline ZnO/CdS/Cu(In,Ga)Se 2 heterojunction solar cells is compared to that of poly-crystallin silicon cells, and the reciprocity between the external (photovoltaic) quantum efficiency and the electroluminescent emission of both devices is fulfilled.

Journal ArticleDOI
TL;DR: In this paper, a 1.55μm Si-based photonic crystal microcavity light emitters utilizing PbSe quantum dots were designed and characterized. And the authors reported on the design, fabrication, and characterization of 1.
Abstract: The authors report on the design, fabrication, and characterization of 1.55μm Si-based photonic crystal microcavity light emitters utilizing PbSe quantum dots. Efficient coupling of emission from PbSe quantum dots to Si photonic crystal membrane microcavity is achieved by inserting the quantum dots in a central air hole in the microcavity. Enhancement of spontaneous emission with linewidth of ∼2.0nm is observed at 1550nm at room temperature. The Purcell factor and the spontaneous emission coupling factor are estimated to be 35 and 0.04, respectively.

Journal ArticleDOI
TL;DR: It is shown that quasi-metallic carbon nanotubes in the ballistic transport regime their spontaneous emission spectra have a universal frequency and bias voltage dependence, which raises the possibility of utilizing this effect for high-frequency nanoelectronic devices.
Abstract: We demonstrate theoretically that quasi-metallic carbon nanotubes emit terahertz radiation induced by an applied voltage. It is shown that in the ballistic transport regime their spontaneous emission spectra have a universal frequency and bias voltage dependence, which raises the possibility of utilizing this effect for high-frequency nanoelectronic devices.

Journal ArticleDOI
TL;DR: In this article, the authors investigated the modification of fluorescence when an emitter is placed close to a nanostructure, in order to control the wealth of parameters that contribute to this process.
Abstract: The coupling of nanostructures with emitters opens ways for the realization of man-made subwavelength light emitting elements. In this article, we investigate the modification of fluorescence when an emitter is placed close to a nanostructure. In order to control the wealth of parameters that contribute to this process, we have combined scanning probe technology with single molecule microscopy and spectroscopy. We discuss the enhancement and reduction of molecular excitation and emission rates in the presence of a dielectric or metallic nanoparticle and emphasize the role of plasmon resonances in the latter. Furthermore, we examine the spectral and angular emission characteristics of the molecule-particle system. Our experimental findings are in excellent semi-quantitative agreement with the outcome of theoretical calculations. We express our results in the framework of optical nanoantennae and propose arrangements that could lead to the modification of spontaneous emission by more than 1000 times.

Journal ArticleDOI
TL;DR: In this paper, evanescent tunneling transmission of effective surface plasmon polaritons between two counterstreaming electron beams noticeably increases Smith-Purcell radiation (SPR) intensity by about two orders of magnitude as well as lower its transition threshold from a spontaneous emission to a stimulated one.
Abstract: The authors show that evanescent tunneling transmission of effective surface plasmon polaritons between two counterstreaming electron beams noticeably increases Smith-Purcell radiation (SPR) intensity by about two orders of magnitude as well as lower its transition threshold from a spontaneous emission to a stimulated one. An emission mechanism of the superradiant SPR is theoretically analyzed by the dielectric conversion of the structured metal surface and the boundary matching condition of Maxwell’s equations in comparison with numerical simulations.

Journal ArticleDOI
TL;DR: It is demonstrated that such photonic crystal lasers strongly improve the performances of terahertz quantum cascade material in terms of threshold current, waveguide losses, emission mode selection, tunability and maximum operation temperature.
Abstract: We combine photonic crystal and quantum cascade band engineering to create an in-plane laser at terahertz frequency. We demonstrate that such photonic crystal lasers strongly improve the performances of terahertz quantum cascade material in terms of threshold current, waveguide losses, emission mode selection, tunability and maximum operation temperature. The laser operates in a slow-light regime between the M saddle point and K band-edge in reciprocal lattice. Coarse frequency control of half of a terahertz is achieved by lithographically tuning the photonic crystal period. Thanks to field assisted gain shift and cavity pulling, the single mode emission is continuously tuned over 30 GHz.