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Optical absorption via intersubband transition of electrons in GaAs/Al <sub/>x</sub> Ga <sub/>1?x</sub> As multi-quantum wells in an electric field
摘要： Based on the effective mass approximation, the Schr?dinger equation and Poisson equation in GaAs/AlxGa1?xAs multi-quantum wells (MQWs) are self-consistently solved to obtain the wave functions and energy levels of electrons in the conduction band for the ground first excited state by considering a lateral electric field (LEF). Then, the effects of size, ternary mixed crystal, doping concentration, and temperature on linear and nonlinear intersubband optical absorption coefficients (IOACs), and refractive index changes (RICs) due to the transition between ground states and the first excited states of electrons are discussed based on Fermi’s golden rule. The results show that, under a fixed LEF, with increase of Al composition and doping concentration, the IOACs produce a red shift. With increases of both widths of the wells and barriers IOACs appear as blue shifts and their amplitudes increase, but the barrier width change is much more important to affect nonlinear IOACs, whereas increasing the temperature results in a blue shift first and then a red shift of IOACs. When the other parameters are fixed but there is an increase in the LEF, IOACs occur with a blue shift, and the RICs have similar properties.
关键词： multi-quantum wells,optical absorption of electronic intersubband transition,refractive index changes,lateral electric field
更新于2025-09-23 15:22:29
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Rydberg-state ionization dynamics and tunnel ionization rates in strong electric fields
摘要： Tunnel ionization rates of triplet Rydberg states in helium with principal quantum numbers close to 37 have been measured in electric fields at the classical ionization threshold of ～197 V/cm. The measurements were performed in the time domain by combining high-resolution continuous-wave laser photoexcitation and pulsed electric field ionization. The observed tunnel ionization rates range from 105 to 107 s?1 and have, together with the measured atomic energy-level structure in the corresponding electric fields, been compared to the results of calculations of the eigenvalues of the Hamiltonian matrix describing the atoms in the presence of the fields to which complex absorbing potentials have been introduced. The comparison of the measured tunnel ionization rates with the results of these, and additional calculations for hydrogenlike Rydberg states performed using semiempirical methods, have allowed the accuracy of these methods of calculation to be tested. For the particular eigenstates studied the measured ionization rates are ～5 times larger than those obtained from semiempirical expressions.
关键词： Rydberg states,tunnel ionization,electric field ionization,complex absorbing potentials,helium
更新于2025-09-23 15:22:29
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Polarization, inner and outer field and surface charge compensation of a molecular crystal
摘要： The polarization of molecules embedded in crystals is of fundamental importance for understand and modeling of dielectric properties of these materials. Typically, the simulations concern ideal crystals, meaning infinite objects lacking of any defect and of any truncation. But in real life, crystals of finite sizes, and containing defects, are used. In this work, we focus on the calculation of the polarization of crystals of 4-iodo-4’-nitrobiphenyl (belonging to the polar class mm2), by mimicking several finite sizes and analyzing the effects of surfaces. This simulation implies calculation of the inner electric field, starting from the dipole of each molecule or, for a better accuracy, of each atom in the crystal. Using the atomic/molecular polarizabilities, calculations are repeated iteratively until a self-consistency is achieved. These simulations enable calculation of the polarization of several kinds of crystal shapes, up to ca. 80 nm scale range. Needle-like crystals slightly enhance (10%) the average dipole moment in polar direction of the constituting molecules, compared to their values in vacuo, whereas plate-like crystals severely reduce it (ca. 50%). In real systems, the effects of screening charges on the crystal surfaces cannot be neglected. A simple model enables to calculate that the dipole of needle-like crystals, under the effect of compensating charges, can be reduced close to extinction. On the other hand, the situation of plate-like crystals does not differ significantly under the influence of screening charges.
关键词： polar crystals,compensation,outer electric field,polarization,surface charge density,inner electric field
更新于2025-09-23 15:21:21
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The effect of machining on domain configuration in [001]-oriented tetragonal Pb(Mg <sub/>1/3</sub> Nb <sub/>2/3</sub> )O <sub/>3</sub> –PbTiO <sub/>3</sub> single crystals
摘要： Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN–PT) single crystals have attracted increasing attention in electro-optic and nonlinear optical applications. In this paper, it was found that the domain configuration of PMN–PT single crystals was influenced by machining and electric process, such as cutting, grinding, polishing, and electrical field poling. The ordered herringbone/stripe domain pattern can be changed into an unexpected disordered domain state in tetragonal PMN–PT crystals which was observed in some crystal samples. Those chaotic structures can decrease transmittance and increase possibility of cracking during poling. However, the disordered domain pattern can be eliminated by a temperature cycling process. Crack-free single-domain crystals were successfully obtained by electric field poling, exhibiting complete optical extinction in an orthogonal polarized light microscope. The results suggest that the domain configuration of PMN–PT single crystals is sensitive to machining process and can be controlled by proper temperature and electric field.
关键词： domain configuration,optical properties,electric field poling,PMN–PT single crystals,temperature cycling,machining
更新于2025-09-23 15:21:21
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Spatial heterodyne spectroscopy for high speed measurements of Stark split neutral beam emission in a high temperature plasma
摘要： Measurement of electrostatic potential, or local electric field, turbulence is a critical missing component in validating nonlinear turbulence and transport simulations of fusion plasmas. A novel diagnostic is being developed for measuring local electric field fluctuations, ?E(r, t), via high-speed measurements of the light emitted from a hydrogenic neutral beam. It exploits the proportionality of the spectral line splitting from the Motional Stark Effect to the total electric field experienced by the neutral atom at the excitation site. The measurement is localized by the usual cross-beam geometry of beam-spectroscopy measurements. The corner stone of the diagnostic is a high spectral resolution, high etendue spatial heterodyne spectrometer (SHS). A SHS design with high etendue (～5 mm2 sr) and resolution (～0.14 nm) meets the formidable spectrometer requirements. Field tests of the spectrometer at the DIII-D tokamak demonstrate that the beam emission spectrum produced by the SHS agrees with that of a traditional spectrometer and that the measured flux is adequate for turbulence studies.
关键词： Stark split neutral beam emission,electric field fluctuations,spatial heterodyne spectroscopy,turbulence diagnostics,high temperature plasma
更新于2025-09-23 15:21:21
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Identification of spherical and non-spherical protein by solid-state nanopore
摘要： Three-dimensional structure of a protein plays an important role in protein dynamics in biological system of human. By now, it remains challenge to characterize and quantify the shape of a protein at single-molecule level. Nanopore, as a novel single-molecule sensor, has been widely applied in many fields such as DNA sequencing and human diseases diagnosis. In this paper, we investigated the translocation of sphere-like con.A and the prolate Bovine Serum Albumin (BSA) under electric field by solid-state nanopore. By analyzing the ionic current, the con.A and the BSA could be characterized and differentiated due to their intrinsic shape difference. Because the prolate BSA will have the preferred orientations for higher electric field when it is residing inside the nanopore, thus multiple ionic current blockade levels will be observed. While for the spherical con.A, there is only one ionic current blockade level. This method presented here will be potentially applied to fingerprint a single protein as a new method having features of low-cost and high-throughput in the near future.
关键词： orientation,solid-state nanopore,shape,electric field,ionic current,protein
更新于2025-09-23 15:21:21
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[IEEE 2017 International Conference on Computer Technology, Electronics and Communication (ICCTEC) - Dalian, China (2017.12.19-2017.12.21)] 2017 International Conference on Computer Technology, Electronics and Communication (ICCTEC) - Three-Dimensional Pulse Electric Field Test System with Optical Fiber
摘要： A three-dimensional pulse electric field system with optical fiber is developed. It is made up of electric field testing probe, optical transmission system, optical receiver and display, which can realize three-dimensional pulse electric field measurement in the whole space. This paper introduced the three-Dreceiving antenna, the three-D electric field signal synthesis and photoelectric receiver and then analyzed the design of the three-D receiving antenna and the method of last, the three dimensional electric field synthesis. At performance of the testing system is measured. Results show that the system has good test performance whose bandwidth can reach 1KHz-1GHz, dynamic range can be up to 60dB.
关键词： dynamic range,bandwidth test,Pulse electric field,3-D electric field sensor
更新于2025-09-23 15:21:01
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The laser field controlling on the nonlinear optical specifications of the electric field-triggered Rosen-Morse quantum well
摘要： We consider, for the first time, optical specifications such as the nonlinear optical rectification (NOR), the second harmonic generation (SHG) and the third harmonic generation (THG) of quantum well (QW) that has the Rosen-Morse potential confinement and is generated by GaAs/GaAlAs heterostructure. To do this, QW structure is firstly asymmetrized by applying an external electric field, as 10 kV/cm. Therefore, the electric field-triggered (F = 10 kV/cm) Rosen-Morse QW (eftRMQW) is taken into consideration throughout the study. In this study, it is elucidated that how to control NOR, SHG and THG optical responses through monochromatic linearly polarized intense laser field (ILF). In order to be able to investigate the ILF effects, the time-dependent of ILF is removed to potential energy term of the wave equation by using Kramers-Henneberger (KH) and the dipole approximations, building the laser-dressed potential. Then, the bound state energies and the wave functions of eftRMQW are obtained using the diagonalization method within the effective mass approach and the parabolic approximation. The influences of the ILF and structural parameters of eftRMQW on NOR, SHG and THG coefficients are discussed in detail. The optimum of structure is ferreted out for devices design and applications that will consider eftRMQW, and for this optimum the alternative parameter analysis is carried out.
关键词： Nonlinear optical properties,Laser field,Electric field,Rosen-Morse quantum well
更新于2025-09-23 15:21:01
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Influence of DC electric and magnetic fields on silicon solar cells/modules
摘要： In this study, the impact of DC electric and magnetic fields on the output power, open-circuit voltage, and photocurrent density of a silicon photovoltaic (PV) cell/module is assessed. In this regard, the influence of DC electric and magnetic fields is first evaluated in theory by formulating and discussing related basis and concepts. Then, experimental measurements and data obtained from two different sets of experiments are given that verify theoretical results. In theory and practice, it is shown that depending on the direction of a DC electric field applied to a silicon PV cell/module, it causes an increase or reduction in the output power and open-circuit voltage of the PV cell/module. In detail, when the DC electric field points in the direction of the junction electric field of the PV cell(s), the output power and open-circuit voltage of the silicon PV cell/module increase, otherwise the output power and open-circuit voltage decrease. Regarding the magnetic field, it is proved that depending on the direction of a DC magnetic field applied to a silicon PV cell/module, different effects are observed. In detail, when the DC magnetic field points along the junction electric field of the PV cell(s), it has no effect on the output power and open-circuit voltage of the silicon PV cell/module. But, the output power and open-circuit voltage of the silicon PV cell/module decrease when the DC magnetic field points in the other directions. Moreover, the reduction in the output power and open-circuit voltage reaches its peak when the DC magnetic field is applied in the direction perpendicular to the junction electric field.
关键词： DC electric field,solar energy,silicon PV cell,silicon PV module,DC magnetic field
更新于2025-09-23 15:21:01
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Electric field strength-dependent accuracy of TiAlN thin film composition measurements by laser-assisted atom probe tomography
摘要： Accurate quantification of absolute concentrations represents a major challenge for atom probe tomography (APT) since the field evaporation process is affected significantly by the measurement parameters. In the present work we investigate systematically the effect of laser pulse parameters on the accuracy of laser-assisted APT for a TiAlN thin film previously quantified by ion beam analysis, combining Rutherford backscattering spectrometry and time-of-flight elastic recoil detection analysis. The electric field strength is estimated from the Al2+/Al+ charge state ratio for all systematically varied measurement parameters. Subsequently, the absolute concentrations from laser-assisted APT are compared to ion beam analysis data. An increase of the electric field strength from approximately 25–28 V nm?1 improves the accuracy of absolute concentrations measured by laser-assisted APT from 11.4 to 4.1 at% for N, from 8.8 to 3.0 at% for Al and from 2.8 to 0.9 at% for Ti. Our data emphasize that the measurement accuracy of laser-assisted APT for TiAlN is governed by the electric field strength. It is shown that the smallest compositional discrepancies between ion beam analysis and APT are obtained for the maximum electric field strength of approximately 28 V nm?1 at 10 pJ laser pulse energy. This can be rationalized by considering the enhanced ionization of neutral fragments caused by the increased electric field strength.
关键词： accuracy,chemical composition,atom probe tomography,TiAlN,electric field strength
更新于2025-09-23 15:21:01