Showing papers on "Stark effect published in 1993"
TL;DR: In this article, it was shown that under the usual conditions of zero-electron-kinetic energy, pulsed field ionization (ZEKE-PFI) spectroscopy, the lifetimes of very high-lying Rydberg states are increased by at least approximately the factor n (in addition to the expected factor of n3), the principal quantum number, due to strong l mixing by the Stark effect.
Abstract: It is shown that under the usual conditions of zero‐electron‐kinetic‐energy, pulsed field ionization (ZEKE–PFI) spectroscopy the lifetimes of very high‐lying Rydberg states are increased by at least approximately the factor n (in addition to the expected factor of n3), the principal quantum number, due to strong l mixing by the Stark effect. Additional factors may increase lifetimes by still another factor of approximately n. Pulsed field ionization under typical conditions is shown as likely to be predominantly diabatic and the effect on resolution is assessed. Factors affecting rotational line intensities are also discussed.
429 citations
TL;DR: In this paper, the Stark broadening parameters of Al(II) have been measured in a plasma produced by ablation with a Nd:YAG laser of an aluminum target.
Abstract: The Stark broadening parameters of the 1990.53, 2631.55, 2669.17, 2816.18, 3900.68, and 5593.23 A lines of Al(II) have been measured in a plasma produced by ablation with a Nd:YAG laser of an aluminum target. In order to obtain suitable experimental conditions for the homogeneity and stability of the plasma a study of the spatial and temporal plasma evolution in helium, argon, and nitrogen at different pressures was made. The broadening parameters were obtained with the aluminum target placed in molecular nitrogen at 1000 mbar, which provides appropriate measurements conditions. The Al(II) 4663.05 A line was used to determine the electron density in all cases. For this line the Stark shift parameter has been measured. Contributions to broadening arising from mechanism different than Stark broadening were estimated for every studied line.
132 citations
TL;DR: It is shown that the high-energy oscillatory feature in the electroabsorption spectrum originates from the conduction-band threshold, which is separated from the exciton in polydiacetylenes and also plays an important role in other nonlinear optical processes such as third-harmonic generation and two-photon absorption.
Abstract: We report experimental and theoretical investigations of electroabsorption in a polydiacetylene, and determine the complete mechanism of third-harmonic generation (THG) and two-photon absorption (TPA) in linear-chain \ensuremath{\pi}-conjugated polymers. The experimental electroabsorption is studied by transmission, rather than reflectance techniques. In addition to the Stark shift of the exciton, a significant feature is observed in the difference spectrum at a higher energy, where the linear absorption is negligible. The origin of this high-energy feature has been controversial. We report several extensive theoretical calculations within the extended Hubbard model, and are able to establish a universality that exists within one-dimensional Coulomb correlated models. We show that the high-energy oscillatory feature in the electroabsorption spectrum originates from the conduction-band threshold, which is separated from the exciton in polydiacetylenes. We also demonstrate that even-parity two-photon states that occur below the one-photon exciton are not observed in electroabsorption due to a cancellation effect. However, a dominant two-photon state that is predicted to occur in between the lowest optical exciton and the conduction-band threshold should be observable. The cancellation, which is only partial for the dominant two-photon state, can, however, reduce the intensity of the resonance due to the state. We show that the conduction-band threshold state, which is an odd-parity one-photon state, also plays an important role in other nonlinear optical processes such as third-harmonic generation and two-photon absorption.Third-order optical nonlinearity in linear-correlated chains is dominated by four essential states: the ground state, the lowest optical exciton and the conduction-band threshold states, and the two-photon state that lies in between the two excited odd-parity states. The two most important predictions of our theoretical work are (a) third-harmonic-generation experiments on ideal isolated strands should find two, not merely one, three-photon resonances, originating from the exciton and the conduction-band threshold states, and (b) only one dominant two-photon resonance in the infinite-chain limit should be observable in THG and TPA. Extensive comparisons between theoretical predictions and experiments are made to prove the validity of the theory. Conjugated polymers other than the polydiacetylenes are discussed briefly.
123 citations
TL;DR: In this paper, the frequency and intensity of the fundamental vibrational transitions of a polyatomic molecule in the presence of a uniform or non-uniform electric field are reported, based on perturbation theory and taking into account, individually, first order electrical and mechanical anharmonicity.
Abstract: Expressions for the frequency and intensity of the fundamental‐vibrational transitions of a polyatomic molecule in the presence of a uniform or nonuniform electric field are reported. They have been developed on the basis of perturbation theory and take into account, individually, first‐order electrical and mechanical anharmonicity. They are more general than previously‐used expressions, since terms which are quadratic in the field strength are included. As an example of their use and of their interpretative capability, they are applied to CO.
100 citations
TL;DR: A two-electron ``atom'' in one space dimension is described, found to have only one bound state, and is similar in other ways to a negative ion.
Abstract: We describe a two-electron ``atom'' in one space dimension. This one-dimensional system is treated fully quantum mechanically and with full electron correlation. Its bare eigenstates and eigenenergies are determined numerically by solving Schr\"odinger's equation on a spatial grid. When the electron-electron interaction (of soft-core long-range Coulombic form) is taken equal in strength and opposite in sign to the electron-proton interactions, this atom is found to have only one bound state, and is similar in other ways to a negative ion. We give a Z-correlation diagram, showing the relation of the system's energy spectrum to those of its isoelectronic partners, which are one-dimensional analogs of He, ${\mathrm{Li}}^{+}$, etc. We also calculate a large number of fully correlated two-electron time-dependent wave functions for the system under excitation by a laser field, and exhibit a number of results, including one-photon and multiphoton photodetachment rates, ac Stark shifted threshold closings, photoelectron spectra, and above-threshold detachment spectra, single-electron and double-electron ionization probabilities, and light-scattering spectra.
89 citations
TL;DR: The ArF-laser-produced microplasmas environment is found to be similar in all the gases studied, in terms of both temperature and electron density, despite the considerable differences observed in the breakdown thresholds and relative energies deposited in the various gases.
Abstract: ArF-laser-produced microplasmas in CO, CO2, methanol, and chloroform are studied by time-resolved emission measurements of the plasma decay Electron densities are deduced from Stark broadening of the line profiles of atomic H, C, O, and Cl Plasma ionization and excitation temperatures are determined from measurements of relative populations of ionic and neutral species produced in the plasmas A discussion of the thermodynamic equilibrium status of ArF-laser microplasmas is presented In general, the ArF-laser-produced microplasma environment is found to be similar in all the gases studied, in terms of both temperature (15,000–20,000 K) and electron density (1017 cm−3–1018 cm−3), despite the considerable differences observed in the breakdown thresholds and relative energies deposited in the various gases
88 citations
TL;DR: In this paper, the effect of electric fields of electrochemical strength on the vibrational relaxation of CO on Cu(100) was studied by first principles molecular orbital calculations on cluster models.
86 citations
TL;DR: In this paper, two common methods of accounting for electric field-induced perturbations to molecular vibration are analyzed and compared, and the relationship between the two methods is made by developing an algebraic formalism for the latter.
Abstract: Two common methods of accounting for electric‐field‐induced perturbations to molecular vibration are analyzed and compared. The first method is based on a perturbation‐theoretic treatment and the second on a finite‐field treatment. The relationship between the two, which is not immediately apparent, is made by developing an algebraic formalism for the latter. Some of the higher‐order terms in this development are documented here for the first time. As well as considering vibrational dipole polarizabilities and hyperpolarizabilities, we also make mention of the vibrational Stark effect.
85 citations
TL;DR: In this paper, the energies and the widths of the Stark resonances for the hydrogen atom are calculated using a new approach based on the operator form of the perturbation theory of the Schrodinger equation.
Abstract: The energies and the widths of the Stark resonances for the hydrogen atom are calculated using a new approach. It is based on the operator form of the perturbation theory of the Schrodinger equation. The method includes the physically reasonable distorted-waves approximation in the frame of the formally exact quantum-mechanical procedure. The zero-order Hamiltonian possessing only stationary states is determined only by its spectrum without specifying its explicit form. The method of calculation of the perturbation theory matrix elements is described.
83 citations
TL;DR: The properties of the WKB method in the discrete representation of the tridiagonal band matrices are reviewed in this paper, where the effect of the core on the pattern of the Rydberg atom level splitting is studied.
Abstract: The properties of the WKB method in the discrete representation are reviewed. The method provides the eigenvalues and the eigenvectors of the three-term recursion relations or, which is the same thing, the tridiagonal band matrices. Applications of the method to the splitting of the Rydberg atom levels in the external electric and magnetic fields are considered. Analytical treatment is given to the problem of the oscillator strength distribution in the quadratic Zeeman and the Stark-Zeeman spectra. In the case of the nonhydrogenic Rydberg atoms, the effect of the core on the pattern of the splitting is studied. Certain alternative applications of the discrete WKB method are considered in brief (the quasienergy spectra of nonlinear oscillators in resonant fields, rotational molecular spectra, calculation of infinite continued fractions).
75 citations
TL;DR: A tunable asymmetric coupled quantum well far-infrared photodetector is proposed in this article, which is composed of two quantum wells separated by a thin barrier, and the electron in each well interacts strongly with other electrons to achieve a large Stark tuning effect.
Abstract: A tunable asymmetric coupled quantum well far‐infrared photodetector is proposed in this paper. The basic asymmetric coupled quantum wells are composed of two quantum wells separated by a thin barrier. In this way, the electron in each well interacts strongly with other electrons to achieve a large Stark tuning effect. The eigenenergies and the wave functions of the quantum‐well structures are solved by the self‐consistent method, and the effect of the exchange interaction on the ground‐state subband has also been taken into account. The absorption coefficient is evaluated by the density‐of‐states formalism. Based on theoretical calculations, tuning ranges from 8.2 to 11.3 μm and 7.8 to 10.5 μm are predicted for the proposed asymmetric coupled‐quantum‐well structure and high‐low coupled‐quantum‐well structure, respectively. This tuning capability is achieved by varying the applied electric field in the 20–90‐kV/cm range.
TL;DR: In this paper, it was shown that the dipolar character of the special pair of Rb. sphaeroides is related to the carotenoid excited states in ordered protein matrices, and the observed polarizability of ∗P can be used to estimate a likely lower limit for the matrix electrostatic field in the reaction center.
TL;DR: In this paper, the effects of X-CO 2 type complexes (X:Ne, Kr, and Xe) were studied by pulsed-nozzle Fourier transform microwave spectroscopy.
Abstract: Pure rotational spectra and their Stark effects of X-CO 2 type complexes (X:Ne, Kr, and Xe) have been studied by pulsed-nozzle Fourier-transform microwave spectroscopy. Structures, intermolecular force fields, and electric dipole moments in the ground state have been determined, which have been discussed in connection with the previously reported results of Ar-CO 2 and Hg-CO 2
TL;DR: In this article, a spectral postprocessing code has been developed to simulate experimental spectra by taking into account spatial gradients and line transfer effects, and shows good agreement with experimental data.
Abstract: Analysis is presented of K‐ and L‐shell spectra obtained from Ar and Xe dopants seeded into the fuel region of plastic capsules indirectly imploded using the Nova laser Stark broadening measurements of the n=3‐1 lines in H‐ and He‐like Ar (Ar Ly‐β and He‐β, respectively) are used to infer fuel electron density, while spatially averaged fuel electron temperature is deduced from the ratio of the intensities of these lines Systematic variations in Ar spectral features are observed as a function of drive conditions A spectral postprocessing code has been developed to simulate experimental spectra by taking into account spatial gradients and line transfer effects, and shows good agreement with experimental data It is shown that correct modeling of the x‐ray emission requires a proper treatment of the coupled radiative transfer and kinetics problem Continuum lowering effects are shown not to affect diagnostic line ratios, within the confines of a simple model A recently developed diagnostic based on fitting measured line profiles of Ar He‐β and its associated dielectronic satellites to theory is shown to provide a simultaneous measure of electron temperature and electron density L‐shell Xe spectroscopy is under development as an electron temperature and electron‐density diagnostic Density and temperature sensitive ratios of spectral features each consisting of many lines have been identified Observed Xe spectra from imploded cores show the same qualitative behavior with temperature, as predicted by model calculations of Xe emission spectra Stark broadening of Ne‐like Xe 4‐2 lines appears viable as an electron density diagnostic for Ne∼1025 cm−3 and is under continuing investigation (Based on the invited paper 8I3 at the 1992 APS/DPP annual meeting [Bull Am Phys Soc 37, 1553 (1992)])
TL;DR: In this article, the Stark broadening tables for hydrogen Lyman, Balmer and Paschen lines were used to obtain accurate results for the widths of the β lines down to relatively low electron densities, and for the far line wings in general.
Abstract: The Stark broadening tables for hydrogen Lyman, Balmer and Paschen lines published in the early seventies give accurate results for the widths of the β lines down to relatively low electron densities, and for the far line wings in general. However, the half-widths of the α lines can be in error by as much as a factor of 30, particularly at intermediate densities. Modern theoretical methods are capable of producing accurate values over the entire density range. Recent developments in the Stark broadening of non-hydrogenic species are also considered.
TL;DR: In this paper, free-electron lasers utilizing FETQS emission driven by transverse motion are proposed and the spontaneous emission power and the laser gain in these lasers are calculated with quantum mechanics under the non-correspondence principle.
Abstract: From the fact that the Smith-Purcell radiation, which was observed as being extraordinarily (i.e., 10 18 times) stronger than any classical emission in any equivalent field, is free-electron two-quantum Stark (FETQS) emission driven by axial uniform motion, free-electron lasers utilizing FETQS emission driven by transverse motion are proposed. The spontaneous emission power and the laser gain in these lasers are calculated with quantum mechanics under the “non-correspondence” principle.
TL;DR: In this paper, the authors report room temperature operation of a II-VI p-i-n quantum confined Stark effect modulator using a ZnSe•Zn0.8Cd0.2Se multiple quantum well structure within a ZdSe p-n junction.
Abstract: We report room temperature operation of a II‐VI p‐i‐n quantum confined Stark effect modulator using a ZnSe‐Zn0.8Cd0.2Se multiple quantum well structure within a ZdSe p‐n junction. A n‐type ZnSe layer was used as a novel contact to the p‐type ZnSe. Results are given for photovoltage spectroscopy, absorption, and differential absorption as a function of the applied electric field.
TL;DR: The solution of the stability problems shows that near the instability threshold only long-wavelength fluctuations are unstable, and at the initial stage of the development of the instability nonlinear effects accelerate the fluctuation growth.
Abstract: The theory of the uniform electric-field distribution instability in superlattices is developed. The instability with respect to high-field domain formation was discovered some time ago by Esaki and Chang but no microscopic theory has been proposed so far. To determine the instability condition we consider first the conductivity of a superlattice with a uniform electric-field distribution for arbitrary relations between the width of the miniband, the electric potential drop per period, and the energy uncertainty due to scattering. Such a general case can be described quantitatively with the help of the density matrix if an effective electron temperature is larger than those three characteristic energies. The instability threshold corresponds to an electric field for which the separation between Stark levels in the superlattice becomes larger than the energy uncertainty due to scattering. The physical reason for the instability is that any local increase of the field leads to a larger separation between the Stark levels and to the local decrease of the current. The solution of the instability problems shows that near the instability threshold only long-wavelength fluctuations are unstable. At the initial stage of the development of the instability nonlinear effects accelerate the fluctuation growth.
TL;DR: The calculated spectra of magnetoabsorption and of magnetoluminescence for a modulation-doped quantum wire both agree qualitatively with corresponding recent measurements.
Abstract: The quantum-confined Stark effect and the influence of magnetic confinement on the optical absorption spectra for a highly excited quantum-well wire are analyzed. The shifts of the exciton resonance and the changes of its oscillator strength are evaluated. The calculated spectra of magnetoabsorption and of magnetoluminescence for a modulation-doped quantum wire both agree qualitatively with corresponding recent measurements.
TL;DR: In this article, the authors studied the two-photon Jaynes-Cummings model with the input field assumed to be in a number state, thermal state, a squeezed vacuum state, and a coherent state.
Abstract: The emission spectrum of the atom and the cavity field spectrum of the two-photon Jaynes–Cummings model are studied, with the input field assumed to be in a number state, a thermal state, a squeezed vacuum state, and a coherent state. The effects of the Stark shift are highlighted. Both the emission and the cavity field spectra show central two-peak structures and no sidebands. A comparison with the one-photon Jaynes–Cummings model is carried out.
TL;DR: Good agreement between theory and experiment is found, but only by using a value for the PZ constant \ensuremath{\sim}30% smaller than the commonly accepted value.
Abstract: We report a spectroscopic study of high-quality piezoelectric (PZ) (111)B GaAs/(In,Ga)As strained multiple quantum wells Normally forbidden \ensuremath{\Delta}n\ensuremath{
e}0 transitions (E1HH2, E1HH3, E2HH1) are observed strongly due to the asymmetric well profile induced by the PZ field Applying a bias to oppose the PZ field reduces the quantum-confined Stark shifts and weakens the \ensuremath{\Delta}n\ensuremath{
e}0 transitions At high bias, corresponding to flat band in the well, strong lifetime broadening is observed Good agreement between theory and experiment is found, but only by using a value for the PZ constant \ensuremath{\sim}30% smaller than the commonly accepted value
TL;DR: In this article, the electric field in a growth-axis strained-layer quantum well embedded in a p i n diode is determined by measuring the polarization vector in the quantum well.
Abstract: The electric field in a [111] growth‐axis strained‐layer quantum well embedded in a p‐i‐n diode is determined by measuring the polarization vector in the quantum well The polarization is determined from the critical reverse bias necessary to produce zero electric field in the quantum well The critical reverse bias is obtained from electroreflectance spectra, which have quantum well optical features that exhibit a 180° phase change at flat band A depletion model of the p‐i‐n diode with an embedded quantum well is used to relate the electric field in the quantum well to the applied bias and the polarization vector in the well
TL;DR: In this paper, a technique based on the Stark effect is described that allows the residual electric field in a small experimental volume to be systematically reduced to ≲50 μV cm−1.
Abstract: A technique based on the Stark effect is described that allows the residual electric field in a small experimental volume to be systematically reduced to ≲50 μV cm−1. Although developed initially to allow production of Rydberg atoms in states with very large values of principal quantum number n, it will also permit high resolution studies involving near threshold photoionization or very low‐energy free electrons.
TL;DR: In this article, a pulse-amplified cw dye laser was used to excite the A-X (0,0) Q1(1) transition of 14N16O in electric fields up to 22.5 kV/cm.
Abstract: We report measurements and analysis of Stark quantum beats observed in the fluorescence of nitric oxide (NO) from which we determine the electric dipole moment of the A 2Σ+ v’=0 state. A pulse‐amplified cw dye laser was used to excite the A–X (0,0) Q1(1) transition of 14N16O in electric fields up to 22.5 kV/cm. Fourier analysis of the time‐resolved laser‐induced fluorescence signals yielded Stark tunings for each of the six ‖MF‖ hyperfine sublevels in the N=1, J=3/2 spin‐rotational level. The measurements were fit to a model Hamiltonian including fine, hyperfine, and Stark matrix elements. The resulting dipole moment was then corrected for polarizability effects to yield a value for the A 2Σ+ v’=0 state of μA=1.08±0.04 D. This result compares favorably to a previous measurement of μA in v’=3 and to our quantum theoretical calculations of the A 2Σ+ v’=0 state reported here.
TL;DR: In this article, the Stark broadening of the Rydberg states in the presence of an electric field was observed in 13.56 MHz parallel plate discharges with a high degree of spatial and temporal resolution.
Abstract: Laser excitation of helium singlet Rydberg states results in fluorescence emanating from many other states including those in the triplet system. By monitoring this fluorescence, it is possible to observe the Stark broadening of the Rydberg states in the presence of an electric field. This technique can be used to measure electric fields in 13.56 MHz parallel‐plate discharges with a high degree of spatial and temporal resolution.
TL;DR: An Al 0.36 Ga 0.64 As/Al x Ga 1-x As inverse parabolic quantum-well structure was grown by molecular-beam epitaxy using both digital and analog compositional grading techniques, in agreement with the calculations.
Abstract: An Al 0.36 Ga 0.64 As/Al x Ga 1-x As inverse parabolic quantum-well structure was grown by molecular-beam epitaxy using both digital and analog compositional grading techniques. Photoluminescence and photocurrent measurements showed distinct exciton peaks for both types of wells. A large Stark shift was found for the digital well, in agreement with the calculations. An observed deviation for the analog well was ascribed to fluctuation in quantum-well parameters. Finally, advantages and disadvantages of the two growth techniques are discussed
TL;DR: In this article, the motional Stark effect has been used to measure the toroidal magnetic field inside the JET tokamak plasma by means of the motial Stark effect, and the results of the local β increase due to ICRH and the slowing-down time of fast particles are presented.
Abstract: Measurements of the toroidal magnetic field inside the JET tokamak plasma by means of the motional Stark effect are reported. In the vicinity of the resonance layer ion cyclotron resonance heating (ICRH) generates a population of energetic ions. For the first time, the diamagnetic change in the toroidal magnetic field due to these ICRH fast ions in combination with a pressure increase of the thermal population has been measured. A magnetic field decrease of up to 4% has been observed. Oscillations of the toroidal magnetic field caused by sawtooth oscillations of the thermal plasma pressure have been resolved. First results of the local β increase due to ICRH and the slowing-down time of the fast particles are presented.
TL;DR: In this paper, it was shown that for the G: K = 1-1 states, the cyclic structure is more likely than the hydrogen-bonded one for the NH3-2 van der Waals complex.
Abstract: From the results of Stark measurements on the (NH3)2 van der Waals complex formed in a molecular jet expansion, it was possible to determine the electric dipole moment for the G: ‖K‖=1 state. The partially quenched inversion in the complex gives rise to quadratic Stark effect. We find an electric dipole moment of ‖μ‖=(0.10±0.01) D in the ground state and an upper limit of 0.09 D for the dipole moment in the excited state. These small values give evidence that for the G: ‖K‖=1–1 states, the ‘‘antiparallel’’ (cyclic) structure is more likely than the hydrogen bonded one.
TL;DR: In this paper, a Fourier transform microwave spectrometer was used to measure the rotational spectra of the trimethylamine-water complex and the dipole moment was determined to be 2.37 (1) D with use of Stark effect measurements.
Abstract: Rotational spectra were observed for 10 isotopomers of the trimethylamine-water complex with use of a Fourier-transform microwave spectrometer. The observed spectra of all 10 isotopomers were characteristic of a symmetric top and are indicative of a free internal rotation of the water about the symmetry axis of trimethylamine. Analysis of the rotational constants reveals a structure with an essentially linear single hydrogen bond (1.82 A). The dipole moment of the complex was determined to be 2.37 (1) D with use of Stark effect measurements. Ab initio calculations were used to model the structure and intermolecular potential energy surface of the complex
TL;DR: In this article, a three-step asymmetric coupled quantum well (QW) was numerically analyzed as a function of the electric field and it was shown that the change in the absorption coefficient for an n=1 heavy-hole exciton can be made larger and on-state transmission loss can be lowered by reducing oscillator strength at zero bias and increasing it at operating voltages.
Abstract: Exciton binding energies, radiuses, emission energies, and oscillator strengths in a three‐step asymmetric coupled quantum well (QW) are numerically analyzed as a function of electric field. This analysis predicts that the change in the absorption coefficient for an n=1 heavy‐hole exciton can be made larger and on‐state transmission loss can be lowered by reducing oscillator strength at zero bias and increasing it at operating voltages. The Stark shifts also can be increased, thus allowing lower operating voltages. Estimation of influences of alloy composition and thickness variations on electroabsorption reveals that the thickness of epitaxial layers must be controlled to within one monoatomic layer and that variations in alloy composition must be controlled to within ±4%. An analysis of exciton peak shifts caused by one‐monolayer change in the QW layer thicknesses predicts that interface roughness broadening may be small when the electric field is increased, in contrast to the case of conventional squar...