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At least 1,531 records · Page 85
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DOE OSTI2019

Optimization of the frequency response of a novel GaAs plasmonic terahertz detector

Previously there was reported a new type of high-speed plasmonic THz detector that can operate at room temperature. As an extension of that work, the sensitivity of the detector was investigated over a wide range of sub-THz frequencies. The measured frequency response is not purely monotonic but exhibits oscillatory behaviour with a number of maxima and minima. Our study reveals that such frequency dependence is caused by the interference of electromagnetic waves inside the detector substrate, as the frequencies of these extrema are found to be governed by the substrate thickness. We demonstrate that sensitivity of this type of detector can be optimized for the desired operating frequency within 0.06–0.7 THz spectrum by adjusting the substrate thickness. We also show that a monotonic frequency response with eliminated minima can be achieved by mounting the detector on a specially designed silicon lens.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Structural and optical properties of Sm{sup 3+}-doped borate glasses for luminescent applications

In this work, most interesting optical investigations are carried out with the glass composition (20 − x) CdCO{sub 3} + 15 Li{sub 2}CO{sub 3} + 15 Na{sub 2}CO{sub 3} + 50 H{sub 3}BO{sub 3} + xSm{sub 2}O{sub 3} (where x = 0.1, 0.5, 1.0, 3.0, 4.0 and 5.0 mol%) prepared with conservative melt-quenching technique. DSC verifies the annealing temperature and thermal stability of the prepared glass. X-ray diffraction technique is employed to inspect the amorphous structure of the glasses. FTIR technique helps to view the vibrational band positions of the host material. For optical studies, optical absorption and emission measurements are used. From the absorption spectra, Judd–Ofelt (JO) parameters (Ω{sub 2}, Ω{sub 4}, Ω{sub 6}), rms value of oscillator strength (δ{sub rms}), nephelauxetic parameter ( β-bar ), bonding parameter (δ) and optical band gaps are evaluated. Radiative properties such as radiative transition probabilities (A{sub T}), branching ratios (β{sub cal}, β{sub exp}) and stimulated emission cross section (σ{sub emi}) are calculated using JO theory. The higher stimulated emission cross section (14.39 × 10{sup −22} cm{sup 2}), optical gain (36.69 × 10{sup −25} cm{sup 2} s) indicate that 1.0 mol% of Sm{sup 3+}-doped borate glass would be a potential gain medium for solid state laser application at 603 nm. Color coordinates of the glasses located in the reddish-orange region could be useful for white light-emitting application.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Classical and quantum description of a periodically driven multi-photon anharmonic oscillator

The Hamiltonian and hence the relevant equations of motion involving the dynamics of a driven classical anharmonic oscillator of 2m-th anaharmonicity are constructed. In order to derive the model of a driven multi-photon quantum anharmonic oscillator, we neglect the non-conserving energy terms. Assuming the periodical nature of the driven/forcing term, the dynamical nature of the field operators are expressed in terms of the coupling constant, excitation/photon number and the driven parameters. The solutions are found useful for investigating the squeezing effects and the antibunching of photons of the radiation field prepared in the initial thermal/Fock states. The squeezing effects of the radiation field is found impossible. However, a clear signature of the antibunching of photons is exhibited. It corroborates the fact that the presence of one nonclassical phenomenon does not warrant the presence of the second one. The solutions presented here are exact analytical in nature. Nevertheless, a detailed investigation on the driven quantum anharmonic oscillator is not done before. The present investigation will be of fundamental importance.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

A feasible order-arbitrarily-tunable optical differentiator

We propose a feasible temporal filtering (or spectrum weighting) system to implement optical differentiation with arbitrarily-tunable order. Differentiation order is tuned by programming the temporal weighting mask (TWM) as power function of different exponents, not limited by the structure of the system. Assembly of the system is feasible, since the active parts are implemented by electro-optic elements and some key elements are reused between sub-systems involved in the scheme. Tuning of the system is simple, since electronically pre-stored TWMs are easy to switch among each other. The order-tunable functionality is verified by numerically testing the differentiation cases of normalized input pulse duration ranging from 0.1 to 0.4, and of differentiation order tuned from 1 to 10. Good accuracy is achieved, and measured by root mean square error lower than 0.1. Feasibilities of the system are also verified in terms of accuracy maintaining and distortion avoiding. Compared with existing methods, apart from the arbitrary order-tunable capacity and good accuracy, our proposed optical differentiator also possesses properties of good compactness and constant complexity. The proposed differentiator has unique applications on multi-peak waveform generation for optical communications and photonics-aided Radars with enhanced agility and feasibility.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Complex envelope Faber polynomial method for the solution of Maxwell’s equations

A complex envelope approach for the numerical solution of Maxwell’s equations based on Faber polynomial expansions is investigated. The Faber polynomial expansion used for the approximation of the exponential time propagator offers a highly accurate and efficient calculation while allowing the application of large time steps. The complex envelope approach incorporates only the envelope around a carrier frequency. This is especially beneficial when bandlimited source field distributions are investigated as it is the case for many applications from terahertz technology or photonics.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Simulation of double buffer layer on CIGS solar cell with SCAPS software

In a CIGS thin film solar cell, the buffer layer is interposed between the absorber layer and the window layer, which plays an important role in interface electricity. CdS is often used as a buffer layer in CIGS cells. Beside the toxicity of Cd, the main drawback of CdS is its relatively narrow band gap (2.4 eV), which can lead to the current loss due to parasitic absorption. In order to reduce the use of CdS, we try other buffer layers instead of CdS and optimize buffer layer structure. Numerical simulation has been used to explore the effect of different buffer layer materials (CdS and ZnSe) on the performance of CuInGaSe{sub 2} solar cells with SCAPS-1D software. The main photovoltaic parameters of the analog device: open circuit voltage, short circuit current density, fill factor and conversion efficiency (η) were compared and analyzed. The results show that different buffer materials and thickness have great influence on the performance of the cell. In this simulation, CdS buffer layer was replaced by ZnSe material, which has a wider band gap. However, the efficiency of this kind of cell is lower than that of CIGS device with CdS buffer layer because of the bad energy band alignment. In order to improve the short-wave absorption and the efficiency of CIGS cell, we simulated a novel CdS/ZnSe double buffer layer structure. The efficiency of the optimized cell with double buffer layer increases from 18.47% (conventional cell with the same CdS buffer layer thickness) to 19.01%.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Investigation of a passively Q-switched Raman laser at 1176 nm with Nd{sup 3+}:YAG/Cr{sup 4+}:YAG/YAG composite crystal and a coupled cavity

To reduce the thermal lens effect and increase the efficiency, a composite crystal of Nd{sup 3+}:YAG/Cr{sup 4+}:YAG/YAG and a coupled cavity structure were employed in our passively Q-switched YVO{sub 4}-based Raman laser system. Both the simulation and the experiment results showed that the undoped YAG crystal bonded in the end-face of Cr{sup 4+}:YAG crystal can speed up the heat transfer of Cr{sup 4+}:YAG crystal and reduce the temperature difference between its side surfaces and the center significantly, and the coupled cavity structure can improve the laser performance, especially at high pump power. The maximum output power of Raman laser of 0.92 W at 1176 nm was obtained with an optical-to-optical efficiency of 11.51%. The corresponding repetition rate and the pulse width is 53.5 kHz and 3.22 ns, respectively.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Boundary diffraction wave theory approach to corner diffraction

The scattering process of plane waves by a discontinuous edge contour is studied with the three dimensional boundary diffraction wave theory. The edge and corner diffracted fields are obtained from the stationary phase and edge point evaluations of the line integral. A new corner diffraction coefficient is derived. The behaviors of the uniform edge and corner diffracted waves are investigated numerically.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Network coding for improving throughput in WDM optical networks with dedicated protection

Network coding (NC) has been recently emerging as an excellent technique for leveraging network efficiency. In optical networks, NC and protection appear to be a good match and indeed, NC could be effectively exploited for greater protection efficiency thanks to the opportunity of combining signals rather than duplication in the traditional approach. Motivated by this observation, we investigate the application of a simple and practical NC technique based on XOR operation to improve the network throughput in survivable optical networks. To this end, we propose the NC-based protection whose speed recovery is on a par with the conventional 1+1 dedicated protection while the capacity usage could be more efficient, paving the way for improving throughput in constrained capacity conditions. A novel mixed integer linear programming model is developed for survivable optical networks design employing the proposed NC-based protection. The model attempts to optimally determine the demands to serve, the routing for served demands and NC assignment among demands aiming at maximizing the network throughput in the constraint of bandwidth limitation. Extensive numerical evaluations on realistic topologies are provided to highlight the advantages of our NC-based protection proposal compared with the conventional dedicated protection in improving the network throughput. Encouraging results are observed when the new protection proposal based on NC could accommodate up to 30% more traffic than the conventional case.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Influences of the impurity and magnetic field on the probability density and the period of the asymmetric Gaussian potential qubit

The eigenenergies and eigenfunctions of the ground and first-excited states of an electron, which is coupled to an LO-phonon in a quantum dot with an asymmetric Gaussian (AG) potential, Coulomb bound potential and the magnetic field was studied by using Lee-Low-Pines transformation and Pekar variation method. A single qubit can be realized in this two-level quantum system. Numerical results show that the probability density of electrons in the qubit oscillates with changing the time, the well width and the well depth the AG potential. The probability density obviously fluctuates with changes in the magnetic-field cyclotron (MFC) frequency, the dielectric constant (DC) ratio and the electron–phonon coupling (EPC) strength, respectively, which is not conducive to constructing a suitable qubit. The oscillation period of the qubit decreases with increasing the DC ratio, EPC strength and the MFC frequency, respectively, which has an adverse effect on the survival time of qubit.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

What limits the efficiency of GaN-based superluminescent light-emitting diodes (SLEDs)?

Gallium-nitride-based SLEDs are attractive light sources for augmented reality displays and other applications. However, the electrical-to-optical power conversion efficiency (PCE) of SLEDs is still far below the record-high values reported for LEDs. Utilizing advanced numerical device simulation, this paper investigates the internal physical processes that cause the low PCE of SLEDs. The poor hole conductivity strongly reduces the electrical efficiency, similar to laser diodes. However, in contrast to laser diodes, the rising carrier density in the active layers is identified as main reason for enhanced Auger recombination that severely limits the internal quantum efficiency. Design improvement options are demonstrated.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Modeling of dielectric function in plasmonic quantum dot nanolaser

In this work we present a model of the dielectric function in plasmonic quantum dot (QD) nanolaser. A metal/semiconductor/metal structure was considered to attain plasmonic nanocavity with active region containing: QD, wetting layer and barrier. The dielectric function was calculated for both metal (Ag) and QD structure. The propagation constant of surface plasmon polariton (SPP) at the interface of Ag/InAs-QD structure was calculated and the dispersion relation of the plasmonic QD structure was evaluated. For frequencies far from plasma one, the gap between real and imaginary parts was large and a deviation from linear relation was obvious. The SPP field was strongly localized at the interface due to the effect of zero-dimensional QD structure which has application in the super-resolution and best sensitivity in optical imaging. Results of propagation length of SPP (L{sub spp}) also support this. According to the L{sub spp} results, the damping in the SPP energy was low in the Ag/InAs-QD compared to that in the Ag/air interface. The obtained results are in the range of experimental ones.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Self-focusing of cosh-Gaussian laser beam and its effect on the excitation of ion-acoustic wave and stimulated Brillouin backscattering in collisionless plasma

An analytical and numerical study has been carried out for self-focusing of an intense cosh-Gaussian laser beam in collisionless plasma and its impact on the excitation of ion-acoustic wave and stimulated Brillouin backscattering process. The analytical model has been developed under Wentzel–Kramers–Brillouin and paraxial ray approximations. The nonlinearities of ponderomotive force on electron and the relativistic oscillation of the electron mass have been used in this study. The nonlinear differential equations have been set up for the beam width parameters of the main beam, ion-acoustic wave, backscattered wave and back reflectivity of stimulated Brillouin scattering (SBS). These equations have been solved numerically for different values of decentred parameter (b), relative plasma density (ω{sub p0}/ω{sub 0}) and incident laser intensity (a). The results have been compared with only relativistic nonlinearity and Gaussian profile of laser beam. The focusing of laser beam, ion-acoustic wave and scattered wave are found to be strong under relativistic-ponderomotive regime compared to only relativistic regime. Further, it is observed that focusing/intensity of main laser beam, ion acoustic wave and SBS back reflectivity increases with increasing the values of b and ω{sub p0}/ω{sub 0}. Itis also found that back reflectivity of SBS process gets suppressed with the increase in the value of a. This study may be useful in laser induced fusion scheme where back scattering of SBS plays very important role.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Digital quantum simulation of non-equilibrium quantum many-body systems

Digital quantum simulation uses the capabilities of quantum computers to determine the dynamics of quantum systems, which are beyond the computability of modern classical computers. A notoriously challenging task in this field is the description of non-equilibrium dynamics in quantum many-body systems. In this study, we used the IBM quantum computers to simulate the non-equilibrium dynamics of few spin and fermionic systems. Our results reveal that with a combination of error mitigation, noise extrapolation and optimized initial state preparation, one can tackle the most important drawbacks of modern quantum devices. The systems we simulate demonstrate the potential for large-scale quantum simulations of light–matter interactions in the near future.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Solving larger maximum clique problems using parallel quantum annealing

Quantum annealing has the potential to find low energy solutions of NP-hard problems that can be expressed as quadratic unconstrained binary optimization problems. However, the hardware of the quantum annealer manufactured by D-Wave Systems, which we consider in this work, is sparsely connected and moderately sized (on the order of thousands of qubits), thus necessitating a minor-embedding of a logical problem onto the physical qubit hardware. The combination of relatively small hardware sizes and the necessity of a minor-embedding can mean that solving large optimization problems is not possible on current quantum annealers. In this research, we show that a hybrid approach combining parallel quantum annealing with graph decomposition allows one to solve larger optimization problem accurately. We apply the approach to the Maximum Clique problem on graphs with up to 120 nodes and 6395 edges.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Non-Boolean quantum amplitude amplification and quantum mean estimation

This paper generalizes the quantum amplitude amplification and amplitude estimation algorithms to work with non-Boolean oracles. The action of a non-Boolean oracle $U_\varphi $ on an eigenstate $\mathinner {|{x}\rangle }$ is to apply a state-dependent phase-shift $\varphi (x)$. Unlike Boolean oracles, the eigenvalues $\exp (i\varphi (x))$ of a non-Boolean oracle are not restricted to be $\pm 1$. Two new oracular algorithms based on such non-Boolean oracles are introduced. The first is the non-Boolean amplitude amplification algorithm, which preferentially amplifies the amplitudes of the eigenstates based on the value of $\varphi (x)$. Starting from a given initial superposition state $\mathinner {|{\psi _0}\rangle }$, the basis states with lower values of $\cos (\varphi )$ are amplified at the expense of the basis states with higher values of $\cos (\varphi )$. The second algorithm is the quantum mean estimation algorithm, which uses quantum phase estimation to estimate the expectation $\mathinner {\langle {\psi _0|U_\varphi |\psi _0}\rangle }$, i.e., the expected value of $\exp (i\varphi (x))$ for a random x sampled by making a measurement on $\mathinner {|{\psi _0}\rangle }$. It is shown that the quantum mean estimation algorithm offers a quadratic speedup over the corresponding classical algorithm. Both algorithms are demonstrated using simulations for a toy example. Potential applications of the algorithms are briefly discussed.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Simulations of Tidal Disruption Events

Numerical simulations have historically played a major role in understanding the hydrodynamics of the tidal disruption process. Given the complexity of the geometry of the system, the challenges posed by the problem have indeed stimulated much work on the numerical side. Smoothed Particles Hydrodynamics methods, for example, have seen their very first applications in the context of tidal disruption and still play a major role to this day. Likewise, initial attempts at simulating the evolution of the disrupted star with the so-called affine method have been historically very useful. Here, we provide an overview of the numerical techniques used in the field and of their limitations, and summarize the work that has been done to simulate numerically the tidal disruption process.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Amplitude-mode spectroscopy of chemically injected and photogenerated charge carriers in semiconducting single-walled carbon nanotubes

In one-dimensional semiconductors such as conjugated polymers and semiconducting single-walled carbon nanotubes (s-SWCNTs), injected charge carriers (electrons or holes) can have profound impacts on both electronic conductivity and optical spectra, even at low carrier densities. Understanding charge-related spectral features is a key fundamental challenge with important technological implications. Here, we employ a systematic suite of experimental and theoretical tools to understand the mid-infrared charge signatures of heavily p-type doped polymer-wrapped s-SWCNTs. Across a broad range of nanotube diameters, we find that hole charge carriers induce strong Fano anti-resonances in mid-infrared transmission spectra that correspond to defect-related (D-band) and in-plane tangential (G-band) Raman-active vibrational modes, along with anti-resonances arising from infrared (IR)-active polymer and SWCNT modes. We employ 13C isotope-labeled s-SWCNTs and a removable wrapping polymer to clarify the relative intensities, energies, and sources of all observed anti-resonances. Simulations performed with the "amplitude mode model" are used to quantitatively reproduce Raman spectra and also help to explain the outsized intensity of the D-band anti-resonance, relative to the G-band, observed for both moderately and degenerately doped s-SWCNTs. Here, the results provide a framework for future studies of ground- and excited-state charge carriers in s-SWCNTs and a variety of low-dimensional materials.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗