Showing papers on "Spontaneous emission published in 2011"
TL;DR: The analogy between the propagation of fields around black holes and surface waves on moving water and the measured amplitudes of the converted waves demonstrate the thermal nature of the conversion process for this system attest to the generality of the Hawking process.
Abstract: Hawking argued that black holes emit thermal radiation via a quantum spontaneous emission. To address this issue experimentally, we utilize the analogy between the propagation of fields around black holes and surface waves on moving water. By placing a streamlined obstacle into an open channel flow we create a region of high velocity over the obstacle that can include surface wave horizons. Long waves propagating upstream towards this region are blocked and converted into short (deep-water) waves. This is the analogue of the stimulated emission by a white hole (the time inverse of a black hole), and our measurements of the amplitudes of the converted waves demonstrate the thermal nature of the conversion process for this system. Given the close relationship between stimulated and spontaneous emission, our findings attest to the generality of the Hawking process.
490 citations
TL;DR: Noise-induced coherence enables us to break detailed balance and get more power out of a laser or photocell QHE, and this coherence can be induced by the same noisy (thermal) emission and absorption processes that drive the QHE.
Abstract: Laser and photocell quantum heat engines (QHEs) are powered by thermal light and governed by the laws of quantum thermodynamics. To appreciate the deep connection between quantum mechanics and thermodynamics we need only recall that in 1901 Planck introduced the quantum of action to calculate the entropy of thermal light, and in 1905 Einstein's studies of the entropy of thermal light led him to introduce the photon. Then in 1917, he discovered stimulated emission by using detailed balance arguments. Half a century later, Scovil and Schulz-DuBois applied detailed balance ideas to show that maser photons were produced with Carnot quantum efficiency (see Fig. 1A). Furthermore, Shockley and Quiesser invoked detailed balance to obtain the efficiency of a photocell illuminated by "hot" thermal light (see Fig. 2A). To understand this detailed balance limit, we note that in the QHE, the incident light excites electrons, which can then deliver useful work to a load. However, the efficiency is limited by radiative recombination in which the excited electrons are returned to the ground state. But it has been proven that radiatively induced quantum coherence can break detailed balance and yield lasing without inversion. Here we show that noise-induced coherence enables us to break detailed balance and get more power out of a laser or photocell QHE. Surprisingly, this coherence can be induced by the same noisy (thermal) emission and absorption processes that drive the QHE (see Fig. 3A). Furthermore, this noise-induced coherence can be robust against environmental decoherence.Fig. 1.(A) Schematic of a laser pumped by hot photons at temperature T(h) (energy source, blue) and by cold photons at temperature T(c) (entropy sink, red). The laser emits photons (green) such that at threshold the laser photon energy and pump photon energy is related by Carnot efficiency (4). (B) Schematic of atoms inside the cavity. Lower level b is coupled to the excited states a and β. The laser power is governed by the average number of hot and cold thermal photons, and . (C) Same as B but lower b level is replaced by two states b(1) and b(2), which can double the power when there is coherence between the levels.Fig. 2.(A) Schematic of a photocell consisting of quantum dots sandwiched between p and n doped semiconductors. Open circuit voltage and solar photon energy ℏν(h) are related by the Carnot efficiency factor where T(c) is the ambient and T(h) is the solar temperature. (B) Schematic of a quantum dot solar cell in which state b is coupled to a via, e.g., solar radiation and coupled to the valence band reservoir state β via optical phonons. The electrons in conduction band reservoir state α pass to state β via an external circuit, which contains the load. (C) Same as B but lower level b is replaced by two states b(1) and b(2), and when coherently prepared can double the output power.Fig. 3.(A) Photocell current j = Γρ(αα) (laser photon flux P(l)/ℏ(ν(l))) (in arbitrary units) generated by the photovoltaic cell QHE (laser QHE) of Fig. 1C (Fig. 2C) as a function of maximum work (in electron volts) done by electron (laser photon) E(α) - E(β) + kT(c) log(ρ(αα)/ρ(ββ)) with full (red line), partial (brown line), and no quantum interference (blue line). (B) Power of a photocell of Fig. 2C as a function of voltage for different decoherence rates , 100γ(1c). Upper curve indicates power acquired from the sun.
406 citations
TL;DR: In this paper, the authors reviewed approaches to enhanced light extraction grouped into two sets depending on whether their application results in the change in the spontaneous emission rate or the angular distribution, or both.
284 citations
TL;DR: The results, which are supported by fully vectorial calculations, confirm the potential of photonic nanowires for a nearly perfect, broadband SE control.
Abstract: We experimentally investigate the spontaneous emission (SE) rates of single InAs quantum dots embedded in GaAs photonic nanowires. For a diameter leading to the optimal confinement of the fundamental guided mode HE11, the coupling to HE11 dominates the SE process and an increase of the SE rate by a factor of 1.5 is achieved. When the diameter is decreased, the coupling to this mode vanishes rapidly, thus allowing the coupling to the other radiation modes to be probed. In these conditions, a SE inhibition factor of 16, equivalent to the one obtained in state-of-the-art photonic crystals, is measured. These results, which are supported by fully vectorial calculations, confirm the potential of photonic nanowires for a nearly perfect, broadband SE control.
229 citations
TL;DR: This work presents full directional control of the fluorescence emission from molecules in water solution by an optical antenna made of a nanoaperture surrounded by a periodic set of shallow grooves in a gold film and provides a new approach for high-sensitivity screening of molecular species in solution.
Abstract: Spontaneous emission of fluorescent molecules or quantum dots is radiated along all directions when emitters are diluted in a liquid solution, which severely limits the amount of collected light. Besides, the emission direction does not carry any useful information and cannot be used to sort different molecules. To go beyond these limits, optical antennas have been recently introduced as conceptual tools to control the radiation properties for nanoemitters fixed on a substrate. Despite intense recent research, controlling the luminescence directivity remains a challenge for emitters with random positions and orientations, which is a key for several biomolecular screening applications. Here, we present full directional control of the fluorescence emission from molecules in water solution by an optical antenna made of a nanoaperture surrounded by a periodic set of shallow grooves in a gold film. For each emission wavelength, the fluorescence beam can be directed along a specific direction with a given angul...
189 citations
TL;DR: In this paper, the spontaneous emission characteristics of green and red-emitting InGaN quantum wells (QWs) on ternary In-GaN substrate were analyzed, and the radiative recombination rates for the QWs were compared with those of QWs on GaN templates.
Abstract: The spontaneous emission characteristics of green- and red-emitting InGaN quantum wells (QWs) on ternary InGaN substrate are analyzed, and the radiative recombination rates for the QWs grown on ternary substrate were compared with those of InGaN QWs on GaN templates. For green- and red-emitting InGaN QWs on In0.15Ga0.85N substrate, the spontaneous emission rates were found as ∼2.5-3.2 times of the conventional approach. The enhancement in spontaneous emission rate can be achieved by employing higher In-content InGaN ternary substrate, which is also accompanied by a reduction in emission wavelength blue-shift from the carrier screening effect. The use of InGaN substrate is expected to result in the ability for growing InGaN QWs with enhanced spontaneous emission rates, as well as reduced compressive strain, applicable for green- and red-emitting light-emitting diodes.
176 citations
TL;DR: In this article, a simple method to fabricate metal-dielectric hyperbolic metamaterials on flat, flexible, and curvilinear substrates, which allows for functionalization of dielectric layers by dye molecules, was developed.
Abstract: We have developed a simple method to fabricate lamellar metal-dielectric hyperbolic metamaterials on flat, flexible, and curvilinear substrates, which allows for functionalization of dielectric layers by dye molecules. The control of spontaneous emission of dye molecules with hyperbolic metamaterials has been studied in two different sample configurations, and the effect has been found to be much stronger when emitters are placed inside the metamaterial rather than on its surface.
164 citations
TL;DR: In this article, a combined experimental and density-functional theory (DFT) study of ZnO doping by copper (Zn2+ substitution by Cu2+) is presented, where the authors demonstrate the possibility to tune the band-gap by copper doping for nano-LEDs.
Abstract: The band-gap engineering of doped ZnO nanowires is of the utmost importance for tunable light-emitting-diode (LED) applications. A combined experimental and density-functional theory (DFT) study of ZnO doping by copper (Zn2+ substitution by Cu2+) is presented. ZnO:Cu nanowires are epitaxially grown on magnesium-doped p-GaN by electrochemical deposition. The heterojunction is integrated into a LED structure. Efficient charge injection and radiative recombination in the Cu-doped ZnO nanowires are demonstrated. In the devices, the nanowires act as the light emitters. At room temperature, Cu-doped ZnO LEDs exhibit low-threshold emission voltage and electroluminescence emission shifted from the ultraviolet to violet–blue spectral region compared to pure ZnO LEDs. The emission wavelength can be tuned by changing the copper content in the ZnO nanoemitters. The shift is explained by DFT calculations with the appearance of copper d states in the ZnO band-gap and subsequent gap reduction upon doping. The presented data demonstrate the possibility to tune the band-gap of ZnO nanowire emitters by copper doping for nano-LEDs.
157 citations
TL;DR: The effects of spatial inhomogeneity, nonradiative decay, and transition dipole orientations on the observed inhibition in the band gap are discussed.
Abstract: We present time-resolved emission experiments of semiconductor quantum dots in silicon 3D inverse-woodpile photonic band gap crystals. A systematic study is made of crystals with a range of pore radii to tune the band gap relative to the emission frequency. The decay rates averaged over all dipole orientations are inhibited by a factor of 10 in the photonic band gap and enhanced up to 2× outside the gap, in agreement with theory. We discuss the effects of spatial inhomogeneity, nonradiative decay, and transition dipole orientations on the observed inhibition in the band gap.
150 citations
TL;DR: Strong confinement of the optical field is demonstrated by depositing a micron sized metallic disk on a planar distributed Bragg reflector and an inhibition of spontaneous emission by a factor 40±4 is observed, a record value in the optical domain.
Abstract: We demonstrate strong confinement of the optical field by depositing a micron sized metallic disk on a planar distributed Bragg reflector. Confined Tamm plasmon modes are evidenced both experimentally and theoretically, with a lateral confinement limited to the disk area and strong coupling to TE polarized fields. Single quantum dots controllably coupled to these modes are shown to experience acceleration of their spontaneous emission when spectrally resonant with the mode. For quantum dots spectrally detuned from the confined Tamm plasmon mode, an inhibition of spontaneous emission by a factor $40\ifmmode\pm\else\textpm\fi{}4$ is observed, a record value in the optical domain.
142 citations
TL;DR: This work investigated photoluminescence from the neutral biexciton in a single semiconductor quantum dot coupled with a high Q photonic crystal nanocavity and observed spontaneous two-photon emission from a solid-state single quantum emitter.
Abstract: Spontaneous two-photon emission from a solid-state single quantum emitter is observed. We investigated photoluminescence from the neutral biexciton in a single semiconductor quantum dot coupled with a high $Q$ photonic crystal nanocavity. When the cavity is resonant to the half energy of the biexciton, the strong vacuum field in the cavity inspires the biexciton to simultaneously emit two photons into the mode, resulting in clear emission enhancement of the mode. Meanwhile, the suppression of other single photon emission from the biexciton was observed, as the two-photon emission process becomes faster than the others at the resonance.
TL;DR: An experimental technique to map and exploit the local density of optical states of arbitrary planar nanophotonic structures by nanopositioning, which shows that the decay rate of a pointlike source of fluorescence can be reversibly and repeatedly changed by a factor of 2.
Abstract: We report an experimental technique to map and exploit the local density of optical states of arbitrary planar nanophotonic structures The method relies on positioning a spontaneous emitter attached to a scanning probe deterministically and reversibly with respect to its photonic environment while measuring its lifetime We demonstrate the method by imaging the enhancement of the local density of optical states around metal nanowires By nanopositioning, the decay rate of a pointlike source of fluorescence can be reversibly and repeatedly changed by a factor of 2 by coupling it to the guided plasmonic mode of the wire
TL;DR: In this article, a two-level atom with a quantized propagating pulse in free space was considered and the probability of finding the atom in the excited state at any time was investigated.
Abstract: State mapping between atoms and photons, and photon-photon interactions play an important role in scalable quantum information processing. We consider the interaction of a two-level atom with a quantized propagating pulse in free space and study the probability ${P}_{e}(t)$ of finding the atom in the excited state at any time $t$. This probability is expected to depend on (i) the quantum state of the pulse field and (ii) the overlap between the pulse and the dipole pattern of the atomic spontaneous emission. We show that the second effect is captured by a single parameter $\ensuremath{\Lambda}\ensuremath{\in}[0,8\ensuremath{\pi}/3]$, obtained by weighting the dipole pattern with the numerical aperture. Then, ${P}_{e}(t)$ can be obtained by solving time-dependent Heisenberg-Langevin equations. We provide detailed solutions for both single-photon Fock state and coherent states and for various temporal shapes of the pulses.
TL;DR: In this article, a scheme for two-dimensional atom localization in the subwavelength domain via controlled spontaneous emission was proposed for a five-level M-type atomic system interacting with two orthogonal standing-wave laser fields and the vacuum of the radiation field.
Abstract: A scheme is proposed for two-dimensional atom localization in the subwavelength domain via controlled spontaneous emission. We consider a five-level M-type atomic system interacting with two orthogonal standing-wave laser fields and the vacuum of the radiation field. The interaction of the atom with space-dependent standing-wave fields can provide information about the position of the atom passing through, thus leading to atom localization. It is found that the localization is significantly improved due to the interference effect between the spontaneous decay channels and the dynamically induced quantum interference generated by the two standing-wave fields. By properly varying the system parameters, we can achieve high-precision and high-resolution atom localization.
TL;DR: The efficiency droop of InGaN blue light-emitting diodes can be reduced considerably as the uniformity of current spreading is improved by increasing the resistivity of the p-type current spreading layer or decreasing the sheet resistance of the n-GaN layer.
Abstract: We investigate the effects of current spreading on the efficiency droop of InGaN blue light-emitting diodes with lateral injection geometry based on numerical simulation. Current crowding near the mesa edge and the decrease in the current spreading length with current density are shown to cause significant efficiency droop. It is found that the efficiency droop can be reduced considerably as the uniformity of current spreading is improved by increasing the resistivity of the p-type current spreading layer or decreasing the sheet resistance of the n-GaN layer. The droop reduction is well interpreted by the uniformity of carrier distribution in the plane of quantum wells.
TL;DR: A quantitative treatment shows that the frequency-noise power spectral density of a room-temperature distributed-feedback quantum cascade laser emitting at λ = 4.36 μm can be explained by a temperature-dependent mechanism governing the transport processes in resonant tunnelling devices, confirming the predominant effect of the heterostructure in determining shape and magnitude of the frequency noise spectrum in QCLs.
Abstract: The frequency-noise power spectral density of a room-temperature distributed-feedback quantum cascade laser emitting at λ = 4.36 μm has been measured. An intrinsic linewidth value of 260 Hz is retrieved, in reasonable agreement with theoretical calculations. A noise reduction of about a factor 200 in most of the frequency interval is also found, with respect to a cryogenic laser at the same wavelength. A quantitative treatment shows that it can be explained by a temperature-dependent mechanism governing the transport processes in resonant tunnelling devices. This confirms the predominant effect of the heterostructure in determining shape and magnitude of the frequency noise spectrum in QCLs.
TL;DR: In this article, the authors systematically studied quantum yields when the shell is excited as a function of both core size and shell volume, and they found that quantum yields are determined by a balance between radiative and non-radiative recombination rates, and not by single-carrier trapping.
Abstract: CdSe/CdS core/shell nanorods can exhibit high photoluminescence quantum yields, but it is not yet clear what processes determine the yields and how they can be controlled. Moreover, the effective band alignment between the core and the shell affects quantum yield, but its nature is still under debate. We systematically studied quantum yields when the shell is excited as a function of both core size and shell volume. Using time-resolved photoluminescence decay measurements and transient-absorption spectroscopy, we found that quantum yields are determined by a balance between radiative and nonradiative recombination rates, and not by single-carrier trapping. The radiative recombination rate decreases as the nanorod volume increases, independent of the core size. The results indicate that high quantum yields can be obtained only by limiting the size of the shell and point to an effective quasi-type-II band alignment for all of the nanorods in this study.
TL;DR: The metallo-dielectric cavity significantly enhances the quality factor of the wavelength and subwavelength scale lasers and the pedestal structure significantly reduces the threshold gain which can potentially enable laser operation at room temperature.
Abstract: Electrically driven subwavelength scale metallo-dielectric pedestal pillar lasers are designed and experimentally demonstrated. The metallo-dielectric cavity significantly enhances the quality factor (Q > 1500) of the wavelength and subwavelength scale lasers and the pedestal structure significantly reduces the threshold gain (< 400 cm(-1)) which can potentially enable laser operation at room temperature. We observed continuous wave lasing in 750 nm gain core radius laser at temperatures between 77 K and 140 K with a threshold current of 50 μA (at 77 K). We also observed lasing from a 355 nm gain core radius laser at temperatures between 77 K and 100 K.
Abstract: Resonantly enhanced emission from the zero-phonon line of a diamond nitrogen-vacancy (NV) center in single crystal diamond is demonstrated experimentally using a hybrid whispering gallery mode nanocavity. A 900 nm diameter ring nanocavity formed from gallium phosphide, whose sidewalls extend into a diamond substrate, is tuned onto resonance at a low temperature with the zero-phonon line of a negatively charged NV center implanted near the diamond surface. When the nanocavity is on resonance, the zero-phonon line intensity is enhanced by approximately an order of magnitude, and the spontaneous emission lifetime of the NV is reduced by as much as 18%, corresponding to a 6.3X enhancement of emission in the zero photon line.
TL;DR: It is shown that the optical pumping can be tailored so that the many-body atomic state asymptotically reaches an arbitrary stabilizer state regardless of the initial state.
Abstract: We propose a scheme of optical pumping by which a system of atoms coupled to harmonic oscillators is driven to an entangled steady state through the atomic spontaneous emission. It is shown that the optical pumping can be tailored so that the many-body atomic state asymptotically reaches an arbitrary stabilizer state regardless of the initial state. The proposed scheme can be suited to various physical systems. In particular, the ion-trap realization is well within current technology.
TL;DR: In this article, the in-plane emission of highly polarized single photons from an InAs quantum dot embedded into a photonic crystal waveguide was demonstrated, and the spontaneous emission rates were Purcellenhanced by coupling the quantum dot to a slow-light mode of the waveguide.
Abstract: We demonstrate the in-plane emission of highly polarized single photons from an InAs quantum dot embedded into a photonic crystal waveguide. The spontaneous emission rates are Purcell-enhanced by the coupling of the quantum dot to a slow-light mode of the waveguide. Photon-correlation measurements confirm the sub-Poissonian statistics of the in-plane emission. Under optical pulse excitation, single photon emission rates of up to 19 MHz into the guided mode are demonstrated, which corresponds to a device efficiency of 24%. These results herald the monolithic integration of sources in photonic quantum circuits.
TL;DR: The photoluminescence (PL) characteristics of Mn(2+)-bonded reduced graphene oxide (rGO) are studied in details and the theoretical calculation corroborates the experimental results and appears to be responsible for the enhanced long-wavelength emission.
Abstract: The photoluminescence (PL) characteristics of Mn2+-bonded reduced graphene oxide (rGO) are studied in details The Mn2+-bonded rGO is synthesized using MnO2-decorated GO as the intermediate products and ideal tunable PL is obtained by enhancing the long-wavelength (450–550 nm) emission The PL spectra excited by different wavelengths are analyzed to elucidate the mechanism, and the resonant energy transfer between Mn2+ and sp2 clusters of the rGO appears to be responsible for the enhanced long-wavelength emission To examine the effect of Mn2+ on the long-wavelength emission from the Mn2+-bonded rGO, the PL characteristics of Mn2+-bonded rGO with smaller Mn concentrations are studied and weaker emission is observed Our theoretical calculation corroborates the experimental results
TL;DR: In this paper, a time-domain travelling-wave model for the simulation of passive mode-locking in quantum dot (QD) lasers is presented, where accurate expressions for the time varying QD optical susceptibility and the QD spontaneous emission noise source are introduced in the 1-D wave equations and numerically described using a set of infinite-impulse response filters.
Abstract: We present a time-domain travelling-wave model for the simulation of passive mode-locking in quantum dot (QD) lasers; accurate expressions for the time varying QD optical susceptibility and the QD spontaneous emission noise source are introduced in the 1-D wave equations and numerically described using a set of infinite-impulse response filters. The inhomogeneous broadening of the density of states of the whole QD ensemble as well as the homogeneous linewidth of each QD interband transition are properly taken into account in the model. Population dynamics in the QD, quantum well, and barrier states under both forward and reverse bias conditions are modeled via proper sets of multi-population rate equations coupled with the field propagation equations. The model is first applied to the study of gain and absorption recovery in a QD semiconductor optical amplifier under both forward and reverse bias conditions. Simulations of passive mode-locking in a two-section QD laser are then performed as a function of the bias parameters. Gain and absorption dynamics leading to the generation of mode-locking pulses is described. The onset of a trailing-edge instability at low currents is observed and fully explained in the framework of the described model.
TL;DR: In this paper, the optical polarization ratio of spontaneous emission was investigated by electroluminescence measurements for semipolar (202¯1¯) InGaN/GaN light-emitting diodes, covering the blue to green spectral range.
Abstract: The optical polarization ratio of spontaneous emission was investigated by electroluminescence measurements for semipolar (202¯1¯) InGaN/GaN light-emitting diodes, covering the blue to green spectral range. Devices fabricated on semipolar (202¯1¯) substrates exhibit polarization ratios ranging from 0.46 at 418 nm to 0.67 at 519 nm. These polarization ratios are significantly higher than those reported on semipolar (202¯1) devices. The valence band energy separation is extracted from spectral measurements and is consistent with the increased polarization ratio and theoretical predictions. Quantum well interdiffusion induced valence band mixing is suggested as a possible explanation for the low experimental value of polarization ratio observed for the (202¯1) devices.
TL;DR: In this article, spatial phase mismatching is used to silence the standard two-pulse echo and a secondary echo is radiated from a non-inverted medium, avoiding contamination by gain and spontaneous emission noise.
Abstract: We propose an original quantum memory protocol. It belongs to the class of rephasing processes and is closely related to two-pulse photon echo. It is known that the strong population inversion produced by the rephasing pulse prevents the plain two-pulse photon echo from serving as a quantum memory scheme. Indeed gain and spontaneous emission generate prohibitive noise. A second $\pi$-pulse can be used to simultaneously reverse the atomic phase and bring the atoms back into the ground state. Then a secondary echo is radiated from a non-inverted medium, avoiding contamination by gain and spontaneous emission noise. However, one must kill the primary echo, in order to preserve all the information for the secondary signal. In the present work, spatial phase mismatching is used to silence the standard two-pulse echo. An experimental demonstration is presented.
TL;DR: In this article, a single-junction strain-balanced quantum well solar cell (SB-QWSC) has achieved an efficiency of 28.3% in the presence of radiative recombination.
Abstract: The band gap of the quantum well (QW) solar cell can be adapted to the incident spectral conditions by tailoring the QW depth. The single-junction strain-balanced quantum well solar cell (SB-QWSC) has achieved an efficiency of 28.3%. The dominant loss mechanism at the high concentrator cell operating bias is due to radiative recombination, so a major route to further efficiency improvement requires a restriction of the optical losses. It has been found that (100) biaxial compressive strain suppresses a mode of radiative recombination in the plane of the QWs. As biaxial strain can only be engineered into a solar cell on the nanoscale, SB-QWSCs are seen to have a fundamental efficiency advantage over equivalent bulk cells. Strain-balanced quantum wells in multi-junction solar cells can current match the sub-cells without the introduction of dislocations. Calculations are shown which predict efficiency limits as a function of QW absorption and band gap for such cells. A dual-junction InGaP/GaAs solar cell with QWs in the bottom sub-cell has been grown and characterized. Laboratory and calculated efficiencies relative to control cells are presented for the reported cell and a modeled device, respectively. Copyright © 2011 John Wiley & Sons, Ltd.
TL;DR: In this article, the authors study the dynamics of single-photon absorption by a single emitter coupled to a one-dimensional waveguide that simultaneously provides channels for spontaneous emission (SE) decay and a channel for the input photon.
Abstract: We study the dynamics of single-photon absorption by a single emitter coupled to a one-dimensional waveguide that simultaneously provides channels for spontaneous emission (SE) decay and a channel for the input photon. We have developed a time-dependent theory that allows us to specify any input single-photon wavepacket guided by the waveguide as the initial condition, and calculate the excitation probability of the emitter, as well as the time evolution of the transmitted and reflected fields. For single-photon wavepackets with a Gaussian spectrum and temporal shape, we obtain analytical solutions for the dynamics of absorption, with maximum atomic excitation s40%. We furthermore propose a terminated waveguide to aid the single-photon absorption. We found that for an emitter placed at an optimal distance from the termination, the maximum atomic excitation due to an incident single-photon wavepacket can exceed 70%. This high value is a direct consequence of the high SE -factor for emission into the waveguide. Finally, we have also explored whether waveguide dispersion could aid single-photon absorption by pulse shaping. For a Gaussian input wavepacket, we found that the absorption efficiency can be improved by
TL;DR: This work investigates electrically pumped, distributed feedback (DFB) lasers, based on gap-plasmon mode metallic waveguides, which have nano-scale widths below the diffraction limit and incorporate vertical groove Bragg gratings, and shows strong line narrowing and super linear light current curves for these plasmon Mode devices even at room temperature.
Abstract: We investigate electrically pumped, distributed feedback (DFB) lasers, based on gap-plasmon mode metallic waveguides. The waveguides have nano-scale widths below the diffraction limit and incorporate vertical groove Bragg gratings. These metallic Bragg gratings provide a broad bandwidth stop band (~500nm) with grating coupling coefficients of over 5000/cm. A strong suppression of spontaneous emission occurs in these Bragg grating cavities, over the stop band frequencies. This strong suppression manifests itself in our experimental results as a near absence of spontaneous emission and significantly reduced lasing thresholds when compared to similar length Fabry-Perot waveguide cavities. Furthermore, the reduced threshold pumping requirements permits us to show strong line narrowing and super linear light current curves for these plasmon mode devices even at room temperature.
TL;DR: In this paper, an individual gold nanorod as an optical antenna to modulate single-molecule fluorescence spontaneous emission behaviors is investigated theoretically, and 2D and 3D numerical finite-difference time-domain methods are implemented to investigate changes in the excitation rate, spontaneous emission rate, quantum efficiency, and emission spectral shape as functions of the separation between the emitter and nanors.
Abstract: An individual gold nanorod as an optical antenna to modulate single-molecule fluorescence spontaneous emission behaviors is investigated theoretically. 2D and 3D numerical finite-difference time-domain methods are implemented to investigate changes in the excitation rate, spontaneous emission rate, quantum efficiency, and emission spectral shape as functions of the separation between the emitter and nanorod. Our simulations reveal that the 3D relative configuration between the gold nanorod and the single dipole definitely affects the quantum efficiency and emission spectral shape. The orientation of the dipole and the polarization of the excitation light are also investigated to clarify the polarization dependence of the plasmonic-enhanced fluorescence. Furthermore, we calculate the modified quantum efficiency and emission spectral shape of a single Cy5 dye molecule in the vicinity of a single gold nanorod taking experimental requirements into account.
TL;DR: In this article, the polarization of spontaneous emission was investigated for various indium compositions and quantum wells on m-plane oriented gallium nitride (GaN) light emitting diodes (LEDs) grown on bulk-GaN substrates.
Abstract: The polarization of spontaneous emission was investigated for various indium compositions and quantum wells on m-plane oriented gallium nitride (GaN) light emitting diodes (LEDs) grown on bulk-GaN substrates. Internal light scattering and depolarization was mitigated with application of absorber materials to the LED die. The polarization ratio (ρ) was measured under electrical injection for devices with InGaN active regions emitting up to 520 nm and observed as high as 96%. Values of ρ were independent of drive current. The valence band energy separation (ΔE) was characterized using spectral measurement and temperature dependent optical analysis of valence band hole distributions.