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The hot electron generation in plasmonic nanoparticles is the key to efficient plasmonic photocatalysis. In the paper, we study theoretically for the first time the effect of Tamm states (TSs) at the interface metal-semiconductor on hot electron generation and Landau damping (LD) in metal nanoparticles. TSs can lead to resonant hot electron generation and to the LD rate enhanced by several times. The resonant hot electron generation is reinforced by the transition absorption due to the jump of the permittivity at the metal-semiconductor interface., Comment: 8 pages, 5 figures

Nonlinear Heisenberg-Langevin equations are solved analytically by operator Fourier-expansion for the laser in the LED regime. Fluctuations of populations of lasing levels are taken into account as perturbations. Spectra of operator products are calculated as convolutions, preserving Bose commutations for the lasing field operators. It is found that fluctuations of population significantly affect spontaneous and stimulated emissions into the lasing mode, increase the radiation rate, the number of lasing photons and broad the spectrum of a bad cavity thresholdless and the superradiant lasers. The method can be applied to various resonant systems in quantum optics., 13 pages and 5 figures

We consider the small, of the size of the order of the wavelength, interferometer with the main mode excited by a quantum field from a nano-LED or a laser. The input field is detuned from the interferometer mode with, on average, a few photons. We find the field and the photon number fluctuation spectra inside and outside the interferometer and identify the contributions of quantum and classical noise in the spectra. Structures of spectra are different for the field, the photon number fluctuations inside the interferometer; for the transmitted, and the reflected fields. We note asymmetries in spectra. Differences in the spectra are related to the colored (white) quantum noise inside (outside) the interferometer. We calculate the second-order time correlation functions; they oscillate and be negative under certain conditions. Results help the study, design, manufacture, and use small elements of quantum optical integrated circuits, such as delay lines and optical transistors., Comment: 16 pages, 9 figures

Landau Damping (LD) mechanism of the Localized Surface Plasmon (LSP) decay is studied for the hybrid nanoplasmonic (metal core/dielectric shell) structures. It is shown that LD in hybrid structures is strongly affected by permittivity and electron effective mass in the dielectric shell in accordance with previous observations by Kreibig, and the strength of LD can be enhanced by an order of magnitude for some combinations of permittivity and effective mass. The physical reason for this effect is identified as electron spillover into the dielectric where electric field is higher than in the metal and the presence of quasi-discrete energy levels in the dielectric. The theory indicates that the transition absorption at the interface metal-dielectric is a dominant contribution to LD in such hybrid structures. Thus, by judicious selection of dielectric material and its thickness one can engineer decay rates and hot carrier production for important applications, such as photodetection and photochemistry.

A laser model is formulated in terms of quantum harmonic oscillators. Emitters in the low lasing states are usual harmonic oscillators, and emitters in the upper states are inverted harmonic oscillators. Diffusion coefficients, consistent with the model and necessary for solving quantum nonlinear laser equations analytically, are found. Photon number fluctuations of the lasing mode and fluctuations of the population of the lasing states are calculated. Collective Rabi splitting peaks are predicted in the intensity fluctuation spectra of the superradiant lasers. Population fluctuation mechanisms in superradiant lasers and lasers without superradiance are discussed and compared with each other., Comment: Preprint: 18 pages, 6 figures, 1 table

In this paper, we study light emission from a tunnel contact between the Au film on a glass substrate and the Au-coated tungsten probe of the scanning tunneling microscope at ambient conditions. We...

Internal surface photoemission of electrons from 1D crystal into a barrier with participation of Tamm state (TS) at the interface crystal barrier is considered theoretically for the first time, to the best of our knowledge. It is shown that resonant tunneling of electrons through a TS could lead to substantial enhancement of the quantum efficiency and lowering the red border to a value defined by the TS. In contrast to the Fowler quadratic law, the photocurrent scales linearly with photon energy near the red border. The results suggest that the efficiency of hot electron generation with plasmonic metal nanoparticles could reach several tens of percent, which is very attractive for application in energy conversion technologies such as water splitting.

International audience; A generic model of two dissimilar antenna-type resonators coupled both via near-field and farfield and embedded in active gain and/or loss medium is considered. Conditions required for hitting the superscattering regime corresponding to the threshold of lasing emission operation are established. It is shown that modulation of the medium gain and losses level within realistic parameters is an efficient approach for implementation of tunability. This two-antenna setup can serve as an inspiration for the implementation of high-contrast tunable metasurfaces.

Quantum efficiencies of surface (SPE) and volume (VPE) photo-emissions from metal nanoparticles are calculated by quantum mechanical perturbation theory and compared with each other. Along with discontinuities in the potential barrier and dielectric function, the discontinuity in electron effective mass on the metal-environment interface is taken into account. General formulas for quantum efficiencies of SPE and VPE are derived. An example of spherical gold particles with rectangular potential barrier on the interface is considered, analytical formulas for quantum efficiencies of SPE and VPE on the red border of photoemission are derived. It is found that the efficiency of SPE is less decreased with the reduction of the electron effective mass than the efficiency of VPE, so SPE is more efficient that VPE for small particles and large discontinuity in effective mass. Nanoparticle size, when SPE is more efficient than VPE, is found to be tens of nm or less., preprint

International audience; We investigate the influence of a static electric field on the incoherent nonlinear response of an unloaded electrically contacted nanoscale optical gap antenna. Upon excitation by a tightly focused near-infrared femtosecond laser beam, a transient elevated temperature of the electronic distribution results in a broadband emission of nonlinear photoluminescence (N-PL). We demonstrate a modulation of the yield at which driving photons are frequency up-converted by means of an external control of the electronic surface charge density. We show that the electron temperature and consequently the N-PL intensity can be enhanced or reduced depending on the command polarity and the strength of the control static field. A modulation depth larger than 100% is observed for activation voltages of a few volts.

Landau damping in the metal nanosphere is considered beyond the quasistatic approximation with the use of the exact Mie theory when an incident plane wave can excite not only the dipole mode but also higher-order modes. In resonance approximation, when one considers excitation of a single mode, the analytical formula for the Landau damping coefficient for various modes has been derived. It was demonstrated that the simultaneous excitation of several eigenmodes, which are overlapped in the frequency domain, can lead to substantial correction of the Landau damping coefficients for the modes.

It was recently demonstrated in the experiments [1,2] that the internal photoemission efficiency can reach several tens of percents because of "coherent" or, "surface" photoemission. In present work we provide theoretical description of this effect assuming the surface photoemissionin the structureconsisting ofthe Schottky-barrier metal-semiconductor interface with the Quantum Well (QW) inside. We take into account the difference of dielectric permittivities for the metal and the semiconductor which strongly affects the photoemission efficiency. We show that QW inside the Schottky-barrier can lead to (a) lowering the threshold energy of the photoemission due to resonance tunneling of electrons through the intermediate quasi-level of energy in QW; (b) the photoemission efficiency can be increased by several orders of magnitude.

We propose a new concept of localized surface plasmon polariton (SPP) mode excitation in a spherical nanoparticle, which utilizes a collective mechanism of dissipative instability in an adjacent 2D plasma carrying a DC electric current. We show that 2D DC current becomes unstable at optical frequencies when the drift velocity exceeds the speed of sound in the 2D plasma. Dissipative instability emerges as a result of self-consistent 2D plasma oscillations coupled to the electromagnetic modes of the nanosphere, the material of which is absorbing at given frequency (i.e., the dielectric permittivity Ime > 0), and instability is absent in the case of transparent material. We derive the dispersion equation for this dissipative instability by a self-consistent solution of the Maxwell equations for the electromagnetic modes and the hydrodynamic equations for the 2D plasma current. Our estimates demonstrate attainment of very high instability increments Imω ~ 1015 s−1, which makes the proposed concept very promising for excitation of plasmonic nanoantennas.

A compact acousto-optically Q-switched Yb : Er laser emitting 20-ns pulses at λ = 1.5 μm with an energy of 8 mJ and a repetition rate of 10 Hz is developed. The laser radiation divergence at the exit of an optical forming system is 1 mrad. The experimental sample can stably operate in a wide temperature range with unchanged output parameters. The developed laser is 110 × 30 × 30 mm in size taking into account the dimensions of the optical forming system. Life tests demonstrated stable continuous operation of the sample for 50000 pulses.

We describe superradiance of a few emitters in a dissipative environment with nonradiative decay in the Schrodinger approach, which is simpler than the density matrix formalism. We find that superradiance increases the quantum efficiency of the radiation if the baths, responsible for dissipation, do not come to equilibrium. The reason is that decoherence destroys Dicke “dark” states, lets emitters radiate, and does not affect the fast radiation from “bright” Dicke states.

The emission spectrum of a superradiant laser is calculated analytically using quantum Langevin equations. New sideband peaks and fine structure in the spectrum are predicted for lasers with strong relaxation oscillations.

A new approach for analytically solving quantum nonlinear Langevin equations is proposed and applied to calculations of spectra of superradiant lasers where collective effects play an important role. We calculate lasing spectra for arbitrary pump rates and recover well-known results such as the pump dependence of the laser linewidth across the threshold region. We predict new sideband peaks in the spectrum of superradiant lasers with large relaxation oscillations as well as new nonlinear structures in the lasing spectra for weak pump rates. Our approach sheds new light on the importance of population fluctuations in the narrowing of the laser linewidth, in the structure of the lasing spectrum, and in the transition to coherent operation., Comment: 19 pages, 10 figures

The interaction strength of light and matter can be greatly influenced by altering the environment of the emitters and the electric field. In a photonic cavity the emitter-field coupling strength may become sufficiently large that the emitters and the field can exchange an excitation multiple times before it decays, giving rise to Rabi oscillations. In a passive cavity with one (several) two-level emitter(s), this manifests itself as a (collective) Rabi splitting of the transmissions spectrum [1–3], and it has recently been shown that incoherently pumped single emitters in cavities may exhibit Rabi splitting of the emission spectrum at large coupling strengths [4,5]. We present a fully analytical model describing a large collection of incoherently pumped two-level emitters in a single-mode cavity (e.g. quantum dots in a nano-cavity) and show that collective Rabi splitting of the emission spectrum can occur in these systems as well [6]. We derive a condition in terms of system parameters for the splitting to occur, and show that this is different from the condition typically associated with strong emitter-field coupling. Moreover, we show that the collective Rabi splitting decreases with increasing pump rate P, giving a transition from the strong-coupling regime to the weak-coupling regime, and possibly lasing at large P (Fig. 1(a)).

We observe anomalous visible to near-infrared electromagnetic radiation emitted from electrically driven atomic-size point contacts. We show that the number of photons released strongly depends on the quantized conductance steps of the contact. Counter-intuitively, the light intensity features an exponential decay dependence with the injected electrical power. We propose an analytical model for the light emission considering an out-of-equilibrium electron distribution. We treat photon emission as bremsstrahlung process resulting from hot electrons colliding with the metal boundary and a find qualitative accord with the experimental data., Main manuscript plus supplementary information

We analytically calculate the optical emission spectrum of nanolasers and nano-LEDs based on a model of many incoherently pumped two-level emitters in a cavity. At low pump rates, we find two peaks in the spectrum for large coupling strengths and numbers of emitters. We interpret the double-peaked spectrum as a signature of collective Rabi splitting, and discuss the difference between the splitting of the spectrum and the existence of two eigenmodes. We show that an LED will never exhibit a split spectrum, even though it can have distinct eigenmodes. For systems where the splitting is possible, we show that the two peaks merge into a single one when the pump rate is increased. Finally, we compute the linewidth of the systems, and discuss the influence of inter-emitter correlations on the lineshape.

Enhancement of the surface photoemission from metal into semiconductor by resonance tunneling of photoexcited electrons through (quasi-) discrete level in quantum well, located within Schottky barrier of the metal-semiconductor interface, is studied theoretically taking into account the difference between the electron masses in metal and semiconductor. It is shown, in particular, that resonance tunneling through the discrete level can lead to the redshift of the threshold wavelength of surface photoeffect, higher slope linear growth in photocurrent near the threshold (in contrast to quadratic growth, i.e., Fowler's law), and the possibility to increase substantially the photoemission efficiency similarly to recent experimental results on hot carrier generation in plasmonic structures with a discrete energy level at metal interface. The difference in the effective masses is shown to significantly affect the results. Double-barrier tunneling structures with resonant tunneling may become attractive for applications in photochemistry and in plasmonic photodetectors in near IR and middle IR regions of the spectrum.

We show that the rate of stimulated emission by electron, passing through nanoscale constriction, can beenhanced substantially (by several orders) with proper tailoring of the constriction shape.

Traditionally, the active material in a laser is modelled as independent emitters, but in recent years it has become increasingly clear that radiative coupling between emitters can significantly change the characteristics of small lasers. Collective effects in free space such as superradiance have been studied extensively [1,2], but the effects of inter-emitter correlation in micro- and nano-cavities need further examination to be put on firm theoretical ground. Several studies of collective effects in nano-cavities have been made [3-6], but the theoretical models employed are intricate, and numerical methods are needed both to generate the dynamic equations and to solve them. We propose a model where the complexity is strongly reduced, allowing analytical solutions [7]. We consider a collection of identical two-level emitters interacting with a single cavity mode. We start from Maxwell-Bloch equations, but instead of making the typical adiabatic elimination of the polarization, we allow the polarization decay rate to be of the same magnitude or smaller than other decay rates. Hence, the traditional laser rate equations for the photon number and the population inversion must be supplemented by equations for the emitter-field correlation and the emitter-emitter correlation. This gives us four generalized laser rate equations, which we solve analytically in steady state. Comparing with the steady state results obtained from the traditional laser rate equations we see that inclusion of collective effects leads to a reduction of the photon number for small pump rates, similarly to what is found in [4]. From the generalized laser rate equations, we derive a measure of the strength of collective effects in terms of laser parameters: This describes the difference between results with and without inter-emitter correlations, and it goes smoothly to zero as we approach parameter values where the traditional laser rate equations become valid. To gain insight into the photon statistics of the laser, we construct dynamic equations for higher order correlations of operators. We derive an analytical expression for the zero-delay photon auto-correlation function, and for low pump rates we find that the interaction of emitters results in super-thermal values of the auto-correlation. This feature is observed in experiments and numerical models [4-5], and with our analytical expressions, we are able to pinpoint the parameter combinations for which the collective effects have the largest impact. Considering the same model in terms of the Fourier components of the operators, we find results for the photon number that agree well with the previous approach, while allowing computation of the linewidth. Thus, we can examine how emitter-emitter correlation affects the line broadening of the laser.

Electrically driven optical antennas can serve as compact sources of electromagnetic radiation operating at optical frequencies. In the most widely explored configurations, the radiation is generated by electrons tunneling between metallic parts of the structure when a bias voltage is applied across the tunneling gap. Rather than relying on an inherently inefficient inelastic light emission in the gap, we suggest to use a ballistic nanoconstriction as the feed element of an optical antenna supporting plasmonic modes. We discuss the underlying mechanisms responsible for the optical emission and show that, with such a nanoscale contact, one can reach quantum efficiency orders of magnitude larger than with standard light-emitting tunneling structures.

Background: Electrically controlled optical metal antennas are an emerging class of nanodevices enabling a bilateral transduction between electrons and photons. At the heart of the device is a tunnel junction that may either emit light upon injection of electrons or generate an electrical current when excited by a light wave. The current study explores a technological route for producing these functional units based upon the electromigration of metal constrictions.Results: We combine multiple nanofabrication steps to realize in-plane tunneling junctions made of two gold electrodes, separated by a sub-nanometer gap acting as the feedgap of an optical antenna. We electrically characterize the transport properties of the junctions in the light of the Fowler–Nordheim representation and the Simmons model for electron tunneling. We demonstrate light emission from the feedgap upon electron injection and show examples of how this nanoscale light source can be coupled to waveguiding structures.Conclusion: Electromigrated in-plane tunneling optical antennas feature interesting properties with their unique functionality enabling interfacing electrons and photons at the atomic scale and with the same device. This technology may open new routes for device-to-device communication and for interconnecting an electronic control layer to a photonic architecture.

We present an approximate analytical method of analysis of stationary states of nonlinear quantum systems with noise. As an example, we consider a quantum nonlinear oscillator excited by a fluctuating force and obtain a range of parameters with more than one stationary solution. The existence of such a range is a necessary condition for bistability. We neglect fluctuations in the amplitude of oscillations but do not neglect fluctuations in its phase. Then, the oscillator noise power spectrum depends on the oscillator mean energy n, which leads to a nonlinear integral equation for n. We can find an analytical solution of this equation. We derive the oscillator stationary states for various spectra of fluctuations of the exciting force. Linear stability analysis of stationary states was carried out. This approach is a generalization of our previous analysis of thresholdless lasers.

We study mechanisms of photoemission of hot electrons from plasmonic nanoparticles. We analyze the contribution of “transition absorption”, i.e., loss of energy of electrons passing through the boundary between different materials, to the surface mechanism of photoemission. We calculate photoemission rate and transition absorption for nanoparticles surrounded by various media with a broad range of permittivities and show that photoemission rate and transition absorption follow the same dependence on the permittivity. Thus, we conclude that transition absorption is responsible for the enhancement of photoemission in the surface scenario. We calculate the ratio of photoemission cross-section for a gold nanosphere embedded in different materials such as silicon, zinc oxide, and titanium dioxide. For the calculations, we include both surface and bulk mechanisms of photoemission, using quantum calculations for the former one and a three-step phenomenological approach for the latter one. By comparison of both m...

Assuming that the number of emitters (atoms) near a spherical metal nanoparticle is large (more than a few hundred), so that their interaction with each other is strong and sufficient for the emergence of their collective states (Dicke states), it is shown that the nanoparticle accelerates the superradiance of the emitters in a similar way as it accelerates the spontaneous emission of a single emitter. In this case, part of the energy stored by the emitters is absorbed by a nanoparticle, and the rest of the energy is radiated as a superradiance pulse. For the parameters selected in this paper, the energy absorbed by the nanoparticle is approximately equal to the emitted energy. We have found the collective states of the emitters and nanoparticle and have derived expressions for the time dependence of the superradiance pulse power, pulse duration and time delay with respect to the moment of excitation of the emitters.

We elaborate a semi-analytical model for calculation of the bulk internal emission of photoelectrons from metal nanoparticles into a semiconductor matrix. We introduce important effects in the model as the jump of the effective electron mass at the metal–semiconductor interface and cooling of the hot electrons because of electron–electron and electron–nanoparticle surface collisions in the metal. We study the interplay between the plasmonic electric dipole and quadrupole resonances and reveal the optimum parameters for different geometrical shapes of nanoparticles with respect to the photoemission cross section. We find that the absorption cross section well-predicts the optimum size of the dipolar nanoparticle. This opens the possibility for the fast optimization and design of the photoelectric devices.

Internal emission of photoelectrons from metal films and nanoparticles (nanowires and nanospheres) into a semiconductor matrix is studied theoretically by taking into account the jump of the effective electron mass at the metal – semiconductor interface and the cooling effect of hot electrons due to electron – electron collisions in the metal. The internal quantum efficiency of photoemission for the film and nanoparticles of two types (nanospheres and nanowires) is calculated. It is shown that the reduction of the effective mass of the electron during its transition from metal to semiconductor may lead to a significant (orders of magnitude and higher) decrease in the internal quantum efficiency of bulk photoemission. (nanostructures)

The paper presents our analytical and numerical results of calculations of bulk photoemission from metal nanoparticles of various shapes and sizes, embedded into semiconductor matrix. Software tools for calculation of characteristics of the effect are also developed.

Electrically Driven Optical Antennas represent promising issues for integrated plasmonic nanosources. However, their low quantum efficiency (QE) remains a major hurdle. To address this issue, we analyze the different light emission mechanisms in planar nanoscale devices. We found that the electrical properties of the device are dictating the processes at play. For low device conductance, photons are essentially emitted by inelastic tunneling events and the applied voltage sets the highest photon energy. For high conductance gap antennas, we show that the spectrum released by the device originates from the spontaneous emission of out-of-equilibrium electronic distribution. We then propose a novel route for increasing the QE. Estimation shows that if the nanoantennas are excited by electrons passing ballistically through mesoscopic contacts constituting the antenna, the excitation QE may reach ∼ 0.01–0.1. Finally, we explore an alternative approach based on charge injection in semiconductor Mie resonators.

We propose a single cavity dual comb source based on a diode pumped Yb:YAG laser modelocked by quantum dot semiconductor absorber mirror. Its output consists of two orthogonally polarized pulse trains with different repetition rate. We use two phase locked loops to simultaneously stabilize both dual comb repetition rates to an external microwave reference using an electrooptical KTP crystal and a piezoelectric transducer.

Description of superradiance (SR) of few quantum emitters with non-radiative decay is carried out in the frame of Schrodinger picture taking into account non-equilibrium bath states. Quantum efficiencies (QE) of SR of two and three emitters are calculated and compared with QE of spontaneous emission of two and three independent emitters. Maximum increase of QE is 9% for two emitters and 16% for three emitters, it is reached at certain relationships between non-radiative and radiative decay rates and at non-equilibrium in baths of non-radiative decay.

We model output characteristics of the 1645 nm 8 mJ 10 ns 100 Hz Q-switched Er:YAG DPSSL. The laser is end pumped at a wavelength of 1532 nm. Fiber-coupled diode laser module was 10 nm FWHM, 12 W CW, 200 μm, NA 0.22. Various tapering of the active rod has been considered for 1 mm diameter, 20 mm long and 0.5% Er doping. We discuss the heat deposition process, the energy storage efficiency and the average power limitations for Q-switched regime of generation and amplification, and find the system scalable for the high power operation.

Electrically driven optical antennas are attracting much attention, in particular, due to necessity to develop integrated electrical source of surface plasmons for future plasmonic nanocircuitries. By default, this term denotes a metal nanostructure, in which electromagnetic oscillations at optical frequencies are excited by electrons, tunneling between metallic parts of the structure when a bias voltage is applied between them. Instead of relying on an inefficient inelastic light emission in a tunnel gap, we are suggesting to use ballistic nanoconstrictions as the feed element of an optical antennas in order to excite electromagnetic plasmonic modes. Similarly to tunneling structures, the voltage applied at the constriction falls over the contact of nanoscale length. Electron passing through the contact ballistically can gain the energy provided by the bias ~1eV and exchange it into an mode of the optical antenna. We discussed the underlying mechanisms responsible for the optical emission, and show that with nanoscale contact, one can reach quantum efficiency orders of magnitude larger than with standard tunneling structures.

Quantum emitters, such as q-dots and dye molecules, in the immediate vicinity of plasmonic nanostructures, resonantly excite surface plasmon-polaritons (SPPs) under incoherent pump. The efficiency in the excitation of SPPs per emitter increases with the number of the emitters, because the SPP field synchronizes emission of the coupled emitters, in analogy with the superadiance (SR) in free space. Using fully quantum mechanical model for two emitters coupled with a metal nanorod, we predict up to 15% increase in the emission yield of single emitter compared to only one emitter near the nanorod. Such emission enhancement is stationary and should be observable even with strong dissipation and dephasing under incoherent pump of emitters. Solid-state quantum emitters with blinking behaviors may be utilized to demonstrate such plasmonic SR emission enhancement. Plasmonic SR may find implications in the excitation of nonradiative modes in plasmonic waveguides, in lowing threshold of plasmonic nanolasers.