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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.

Photoelectric properties of noncentrosymmetric, similarly oriented metallic nanoparticles embedded in a homogeneous semiconductor matrix are theoretically studied. Because of the asymmetric shape of the nanoparticle boundary, photoelectron emission acquires a preferred direction, resulting in a photocurrent flow in that direction when nanoparticles are uniformly illuminated by a homogeneous plane wave. This effect is a direct analogy of the photogalvanic (or bulk photovoltaic) effect known to exist in media with noncentrosymmetric crystal structure, such as doped lithium niobate or bismuth ferrite, but is several orders of magnitude stronger. Termed the giant plasmonic photogalvanic effect, the reported phenomenon is valuable for characterizing photoemission and photoconductive properties of plasmonic nanostructures and can find many uses for photodetection and photovoltaic applications.

The use of Virtual Private Networks (VPNs) has witnessed an outstanding rise as they aim to provide confidentiality and anonymity to communication. Despite this enormous and ubiquitous usage, VPNs come with various security, misconfiguration, and performance related issues thereby hindering the users to take maximum advantage of this revolutionary technology. To address this concern, VPN users must choose the most secure and perfect VPN solution for the smooth functioning of daily life activities. Generally, no clear set of directions is available for assisting a common VPN user thereby accentuating the need to develop an elucidated and coherent checklist that thoroughly helps in evaluating any VPN based on its security, performance, auditing, and management function. This research comprehensively surveys VPN technologies, its features, working principles, and compliance principles that evolved over the last two decades. Based on it, this research presents a new methodology in the form of a feature-enriched template to comprehensively analyze a VPN solution. Each VPN feature is given its score against the potential damage it may cause in case of failure and the probability of occurrence of that failure. In this way, the corporate sector and individual users can quantitatively and qualitatively grade available options while choosing a VPN and use it effectively. [ABSTRACT FROM AUTHOR]

Spectra of the small Fabry–Perot interferometer (FPI) of the size of the order of the wavelength, with the main mode excited by a quantum field from a nano–LED or a laser, are investigated. The input field is detuned from the FPI mode with only a few photons. We formulate the convenient model for the FPI interacting with a quantum field, and provide novel explicit expressions for the field and the photon number fluctuation spectra inside and outside the FPI, with clearly identified contributions of the quantum and the classical noise. As a result, we found the spectra structures are quite different for the field, the photon number fluctuations inside the FPI, for the transmitted and the reflected fields and note asymmetries in spectra. The quantum noise is colored (or white) inside (or outside) the FPI, which explains differences in spectra. As another novel result, we calculate the second-order time auto–correlation functions for the FPI field; they oscillate and are negative under certain conditions. Results will help the study, design, manufacture, and use of the small elements of quantum optical integrated circuits, such as delay lines or optical transistors. [ABSTRACT FROM AUTHOR]

The hot electron generation in plasmonic nanoparticles is the key to efficient plasmonic photocatalysis. Here, the effect of Tamm states (TSs) at the metal–semiconductor interface on hot electron generation and Landau damping (LD) in metal nanoparticles is studied theoretically for the first time. 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. Since electron states in the metal and the quasi‐discrete TS are coupled coherently ("bound state in continuum"), the absorption spectrum of light by electrons has a Fano‐type shape. The results demonstrate clearly the importance of taking into account details of the semiconductor band structure and surface states at the metal–semiconductor interface, including Tamm surface states, for a proper description of the hot carrier generation and LD. The results are in correspondence with earlier experimental works on coherent electron transport and chemical‐induced damping in plasmonic nanostructures. Thus, by judicious selection of semiconductor materials with Tamm surface states one can engineer decay rates and hot carrier production for important applications, such as photodetection and photochemistry. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We investigate the surface photoemission (SPE) and the volume (VPE) photoemission from metal nanoparticles into semiconductor environments with a varied height of the potential barrier at the metal–semiconductor interface. We show that the internal quantum efficiency of the SPE becomes several times larger than the one of the VPE, when the barrier height decreases and the contact on the interface approaches to the ohmic one. Discontinuities in the electron effective mass and in dielectric functions at the interface are taken into account in the calculations. Results are important for efficient generation of hot electrons from metal nanostructures for such applications as photocatalysis and water splitting. [ABSTRACT FROM AUTHOR]

We observe anomalous visible to near-infrared electromagnetic emission 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. Counterintuitively, 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 a Bremsstrahlung process resulting from hot electrons colliding with the metal boundary, and find qualitative accord with the experimental data. [ABSTRACT FROM AUTHOR]

We propose an original concept for on-chip excitation and amplification of surface plasmon polaritons. Our approach, named nanoresotron, utilizes the collective effect of dissipative instability of a 2D direct current flowing in vicinity of a metal surface. The instability arises through the excitation of self-consistent plasma oscillations and results in the creation of a pair of collective surface electromagnetic modes in addition to conventional plasmon resonances. We derive the dispersion equations for these modes using self-consistent solutions of Maxwell's and 2D hydrodynamics equations. We find that the phase velocities of these new collective modes are close to the drift velocity of 2D electrons. We demonstrate that the slow mode is amplified while the fast mode exhibits absorption. Estimates indicate that very high gain are attainable, which makes the nanoresotron a promising scheme to electrically excite and regenerate surface plasmon polaritons. [ABSTRACT FROM AUTHOR]

We describe superradiance of a few emitters in a dissipative environment with nonradiative decay in the Schrödinger 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. [ABSTRACT FROM AUTHOR]

Transition absorption of a photon by an electron passing through a boundary between two media with different permittivities is described both classically and quantum mechanically. Transition absorption is shown to make a substantial contribution to photoelectron emission at a metal/semicon-ductor interface in nanoplasmonic systems, and is put forth as a possible microscopic mechanism of the surface photoelectric effect in photodetectors and solar cells containing plasmonic nanoparticles. [ABSTRACT FROM AUTHOR]

We theoretically study the characteristics of photoelectron emission in plasmonic nanoparticle arrays. Nanoparticles are partially embedded in a semiconductor, forming Schottky barriers at metal/semiconductor interfaces through which photoelectrons can tunnel from the nanoparticle into the semiconductor; photodetection in the infrared range, where photon energies are below the semiconductor band gap (insufficient for band-to-band absorption in semiconductor), is therefore possible. The nanoparticles are arranged in a sparse rectangular lattice so that the wavelength of the lattice-induced Rayleigh anomalies can overlap the wavelength of the localized surface plasmon resonance of the individual particles, bringing about collective effects from the nanoparticle array. Using full-wave numerical simulations, we analyze the effects of lattice constant, embedding depth, and refractive index step between the semiconductor layer and an adjacent transparent conductive oxide layer. We show that the presence of refractive index mismatch between media surrounding the nanoparticles disrupts the formation of a narrow absorption peak associated with the Rayleigh anomaly, so the role of collective lattice effects in the formation of plasmonic resonance is diminished. We also show that 5-20 times increase of photoemission can be achieved on embedding of nanoparticles without taking into account dynamics of ballistic electrons. The results obtained can be used to increase efficiency of plasmon-based photodetectors and photovoltaic devices. The results may provide clues to designing an experiment where the contributions of surface and volume photoelectric effects to the overall photocurrent would be defined. [ABSTRACT FROM AUTHOR]

We study the spectral dependence of the internal quantum efficiency of electron photoemission on the size of spherical metallic nanoparticles embedded in a semiconductor matrix and discuss theoretically the volume mechanism of the photoeffect. We take into account the change in the Schottky-barrier shape with the nanoparticle radii and the doping concentration in the surrounding matrix in calculations of the potential barrier at the boundary between the nanoparticle and the matrix. [ABSTRACT FROM AUTHOR]

We propose to use collective lattice resonances in plasmonic nanoparticle arrays to enhance and tailor photoelectron emission in Schottky barrier photodetectors and solar cells. We show that the interaction between narrow-band lattice resonances (the Rayleigh anomaly) and broader-band individual-particle excitations (localized surface plasmon resonances) leads to stronger local field enhancement. In turn, this causes a significant increase of the photocurrent compared to the case when only individual-particle excitations are present. The results can be used to design new photodetectors with highly selective, tunable spectral response, which are able to detect photons with the energy below the semiconductor bandgap. The findings can also be used to develop solar cells with increased efficiency. [ABSTRACT FROM AUTHOR]

We present a quantum mechanical approach to calculate broadening of plasmonic resonances in metallic nanostructures due to collisions of electrons with the surface of the structure. The approach is applicable if the characteristic size of the structure is much larger than the de Broglie electron wavelength in the metal. The approach can be used in studies of plasmonic properties of both single nanoparticles and arrays of nanoparticles. Energy conservation is insured by a self-consistent solution of Maxwell's equations and our model for the photon absorption at the metal boundaries. Consequences of the model are illustrated for the case of spheroid nanoparticles, and results are in good agreement with earlier theories. In particular, we show that the boundary-collision broadening of the plasmonic resonance in spheroid nanoparticles can depend strongly on the polarization of the impinging light. [ABSTRACT FROM AUTHOR]

A theory for pulse amplification and saturation in quantum dot (QD) semiconductor optical amplifiers (SOAs) is developed. In particular, the maximum bit rate at which a data stream of pulses can be amplified without significant patterning effects is investigated. Simple expressions are derived that clearly show the dependence of the maximum bit rate on material and device parameters. A comparative analysis of QD, quantum well (QW), and bulk SOAs shows that QD SOAs may have superior properties; calculations predict patterning-free amplification up to bit rates of ∼150-200 Gb/s with pulse output energies of ∼0.2-0.4 pJ. The superiority of QD SOAs is based on: 1) the faster achievement of the regime of maximum gain in QD SOAs compared to QW and bulk SOAs and 2) the lower effective cross section of photon-carrier interaction in QDs. [ABSTRACT FROM AUTHOR]

Presents information on quantum electronics, demonstrating how carrier cooling and carrier heating influence saturation in semiconductor absorbers. Information on the neglecting field effects of carrier cooling; Details on the corresponding dynamics of the absorption coefficient; Conclusion reached on the demonstration.

In contrast to absorbers, where the delay time via wave mixing saturates to its maximum with increasing device length due to decay of pump power along the device, in semiconductor optical amplifiers (SOAs) the delay time increases with the device length and is limited by the corresponding growth of the SOA gain, which can lead to unacceptable amplified stimulated emission in the SOA. The number of pulses which can be stored in an SOA, defined by the gain and group velocity dispersion, also is given ultimately by this SOA gain limitation, and is estimated between one and two. [ABSTRACT FROM PUBLISHER]

Nano‐mechanical oscillator (NMO) based on amorphous carbon nanowhisker (CNW) with nanotraps for resonant weighting of nanoparticles in range of mass (10−14–10−15) g is presented. NMO with nanotraps is fabricated on the top of tungsten tip using focused electron beam technique. For resonant weighting the gold nanospheres are captured under the exposure of an electron beam by nanotraps locate on the top of CNW. Jump of gold nanoparticle to the nanotrap and oscillations of CNW are visualized using scanning electron microscope (SEM). The NMO amplitude‐frequency characteristics are calculated via automated numerical analysis of the sequence of SEM images obtained during the oscillations frequency sweeping. In order to calibrate the resonance mass detector based on CNW with nanotrap the gold nanosphere with diameter of (170 ± 5) nm and mass of (49.6 ± 9.2) × 10−15 g is weighed in vacuum. The resonant mass detector (RMD) based on carbon nanowhiskers with traps for weighing nanoobjects is presented. The carbon nanostructures are created using additive technique in a scanning electron microscope. Mechanical traps can reliably fix nanoparticles. It is shown that one can determine the mass of the nanoparticles with a sufficiently high accuracy in the range of (10−14–10−15) g using RMD. [ABSTRACT FROM AUTHOR]