Showing papers on "Stark effect published in 1983"

Variational calculations on a quantum well in an electric field

Abstract: We present variational calculations of the eigenstates in an isolated-quantum-well structure subjected to an external electric field. At weak fields a quadratic Stark shift is found whose magnitude depends strongly on the finite well depth. In addition, the electric field induces a spatial shift of the particle wave function along or opposite to the field direction, depending on the sign of the particle mass. This field-induced spatial separation of conduction and valence electrons in GaAs quantum wells decreases the overlap between their associated wave functions, leading to a reduction of interband recombination.

Stark ionization in dc and ac fields: An L2 complex-coordinate approach

Abstract: A finite-dimensional-matrix technique valid for computation of complex eigenvalues and eigenfunctions useful for discussing time evolution in both dc and ac Stark fields is presented. The complex eigenvalue parameters are those of appropriately analytically continued, time-independent Stark Hamiltonians as obtained via the complex scale transformation $r\ensuremath{\rightarrow}r{e}^{i\ensuremath{\theta}}$. Such a transformation distorts the continuous spectrum away from the real axis, exposing the Stark resonances, and also allowing use of finite variational expansions employing ${L}^{2}$ basis functions chosen from a complete discrete basis. The structure of the dc and ac Stark Hamiltonians is discussed and extensive convergence studies performed in both the dc and ac cases to fully document the utility of the method. Sudden and adiabatic dc Stark time evolution is used to illustrate the power of finite-dimensional-matrix methods in describing complex, multiple-time-scale time evolution. The relationship between the ac Stark Hamiltonian used (a time-independent truncated Floquet Hamiltonian) and continued-fraction perturbation theory follows easily via use of matrix partitioning, and provides a particularly straightforward derivation of these results. Finally, some illustrative calculations of off-resonant generalized cross sections are given at low and high intensities, indicating that the method works satisfactorily at intensities the order of internal atomic field strengths. A more detailed discussion of time evolution in two-, three-, and four-photon ionization processes appears in the following paper by Holt, Raymer, and Reinhardt.

Interaction of atoms, molecules, and ions with constant electric and magnetic fields

Abstract: A thorough unified treatment is given of the quantum-mechanical operators and wave functions for a molecular system (composed of N moving charged particles) in static uniform electric and magnetic fields E and B. The treatment is rigorous within the nonrelativistic approximation. The system may either be neutral or charged. The fields may have arbitrary intensities and orientations. Close correspondence is maintained between the classical and quantum-mechanical treatments. The wave functions are expressed both in time-independent energy representation and in time-dependent wave packets. Three types of momentum play important roles. For single-particle systems they are the canonical momentum P; the mechanical momentum Pi = P(e/c) A = MR; and the pseudomomentum K = Pi-(e/c)R x B-eEt.B. For neutral molecules, the Schroedinger equation is ''pseudoseparated'' and the internal degrees of freedom are coupled to the center of mass motion by only the ''motional Stark Effect,'' which involves the constant of motion scrK. For ionic systems, only one component of the center of mass is coupled to the internal motion.

Electroabsorption by Stark effect on room‐temperature excitons in GaAs/GaAlAs multiple quantum well structures

Abstract: We report the first observation of electroabsorption in GaAs/GaAlAs multiple quantum well structures. We have been able to induce Stark shifts for room‐temperature exciton resonances of ∼10 meV for applied field ∼1.6×104 V/cm in a sample with 96‐A GaAs layers, giving large changes in optical absorption (e.g., a factor of 5 or ∼4×103 cm−1 increase). This should permit optical modulators with micron path lengths and potentially very fast operation.

Ponderomotive force and AC Stark shift in multiphoton ionisation

Abstract: A non-perturbative approach to the photoionisation of a model atom in arbitrarily strong fields is described. An explanation is given for the disappearance of the lowest energy electrons in a multiphoton ionisation experiment at very high intensities, in terms of the AC Stark shift of the ionisation potential of the atom, followed by ponderomotive acceleration of the photoelectrons.

Observation of the First-Order Stark Effect of Co on Ni(110)

Abstract: The first-order Stark effect is observed for CO adsorbed on Ni(110). The Stark tuning rate is (1.1 \ifmmode\pm\else\textpm\fi{} 0.4) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}6}$ ${\mathrm{cm}}^{\ensuremath{-}1}$/(V/cm). The present measurement agrees with a model calculation. By electric field modulation of the resonant vibrational frequency of adsorbed molecules, the derivative vibrational spectrum can be measured. The spectra of CO on Ni(110) obtained are consistent with published electron-energy-loss spectra. The new technique is zero background, surface selective, and can be used in UHV or atmospheric pressure.

Inhomogeneous light shift in alkali-metal atoms

Abstract: The dynamic Stark shift of an inhomogeneously broadened spectral transition has been studied. Our measurements show a shift in the observed $^{87}\mathrm{Rb}$ ground-state hyperfine transition which has a nonlinear dependence on light intensity when the conditions for inhomogeneous broadening are met. The nonlinearity is the result of light-intensity gradients in the signal volume, which produce an inhomogeneously broadened asymmetric microwave transition. We show that our measurements are in full agreement with the second-order perturbation-theory treatment of light-induced energy-level shifts, when the effects of inhomogeneities are properly taken into consideration. The effects of inhomogeneous broadening must be carefully considered when extracting oscillator strengths from light-shift data, or when performing high-precision laser spectroscopy.

Effects of strong electric fields on resonant structures in H - photodetachment

Abstract: Relativistic kinematics with an 800-MeV H/sup -/ beam at the Clinton P. Anderson Meson Physics Facility (LAMPF) at Los Alamos allows the observation, with very little background, of resonant structures in the photodetachment spectrum of H/sup -/ in intense electric fields. We report studies of the /sup 1/P resonances near n = 2 in H/sup -/ in electric fields as high as 1.3 MV/cm. The splitting of the /sup 1/P Feshbach resonance can be explained by Stark mixing with a nearly degenerate /sup 1/S resonance. For field values above those required to quench the Feshbach resonances a /sup 1/D state is observed, apparently induced by Stark mixing with the /sup 1/P shape resonance. The systematics of the behavior of these resonances are compared with the results of a simple perturbation model.

Precise Stark-Effect Measurements in the Σ 2 Ground State of CaCl

Abstract: By use of the molecular-beam microwave-optical double-resonance technique the first high-precision Stark-effect measurement of an alkaline-earth monohalide has been performed. Low-field Stark shifts of rotational transitions in the $v=0$, $X^{2}\ensuremath{\Sigma}$ state of CaCl exhibited an unexpectedly complicated field dependence which, however, has been shown to be in complete agreement with an exact theoretical calculation.

Optical spectra, energy levels, and crystal‐field analysis of tripositive rare‐earth ions in Y2O3. III. Intensities and g values for C2 sites

Abstract: We report measurements of the oscillator strengths between the Stark‐split ground level and numerous excited Stark levels of Nd3+, Sm3+, Er3+, and Tm3+ in the C2 sites of Y2O3. Experimental results are compared with calculations based on the Judd–Ofelt theory of induced electric‐dipole transitions, which uses the odd‐parity terms in the crystal‐field interaction (determined via an effective point‐charge model). We also compare our theoretical results with previous measurements of manifold‐to‐manifold oscillator strengths, excited‐state lifetimes, and Judd–Ofelt intensity parameters. Magnetic‐dipole contributions to the intensities are included as well. Calculated ground‐state g values for all the rare earths with an odd number of f electrons are reported. Comparison of theoretical and experimental results indicates that good agreement is obtained in most cases.

Stark broadening of isolated spectral lines of heavy elements in plasmas

Abstract: In this paper, we present results of semiclassical calculations of Stark broadening parameters for some lines of heavy neutral atoms. Comparisons with experiment show large discrepancies previously undetected for lighter elements. Critical evaluation of experimental data indicate that in most cases the experiment must be blamed for these discrepancies.

Stark effects in the rotational spectrum of the dimer H2O⋅⋅⋅HF and the variation of the electric dipole moment with excitation of the low‐frequency, hydrogen‐bond modes

Abstract: The Stark effects in the J=2←1 rotational transitions of the nearly prolate asymmetric rotor H2O⋅⋅⋅HF have been analyzed in the vibrational ground state and in each of the states (1, 0, 0), (0, 1, 0), (0, 0, 1), and (1, 1, 0). The nonmenclature (vβ(o), vβ(i), vσ) refers to the vibrational quantum numbers associated with the out‐of‐plane bending mode vβ(o), the in‐plane bending mode vβ(i) and the stretching mode vσ, respectively, which are the three lowest energy modes of the hydrogen bonded dimer. The electric dipole moment μ for each of these states determined via the Stark effect is as follows:

The AC Stark shift as an intensity probe in resonant multiphoton ionisation of xenon

Abstract: The authors report a high-resolution electron spectroscopic study of three-photon resonant, five-photon ionisation of xenon. The results are analysed in terms of a dynamic resonance of three photons with an AC Stark-shifted intermediate level (6s), followed by a saturated two-photon transition to the continuum. They demonstrate a linear relationship between detuning from the zero-field resonance position and the local momentary light intensity causing the five-photon ionisation. Thus, the AC Stark shift acts as a probe which selects a particular intensity from the wide range present in the laser focus. They determined the AC Stark shift of the 6s level the distribution function of the light intensities and the intensity dependence of the ionisation probability. High-resolution electron spectra are used in arguments to support the validity of their analysis.

Error estimates for complex eigenvalues of dilated Schrödinger operators

Abstract: Error estimates for the approximate complex eigenvalues of the dilated Schr\"odinger operators are derived. They are calculated for the resonances of the dc Stark effects in hydrogen.

Stark broadening of hydrogen lines: new results for the Balmer lines and astrophysical consequences

Abstract: On calcule les profils de Stark de la raie Hα de l'hydrogene a des densites interessantes astrophysiquement en utilisant deux methodes, que l'on compare

Observation and Quasistatic Analysis of Structure in Microwave Ionization of Highly Excited Helium Atoms

Abstract: The ionization of He(1s(napprox. =30)s) /sup 3/S/sub 1/ atoms by an oscillating electric field (9.92 GHz) is strongly dependent on the field amplitude. The ionization curves reveal structures which are absent in those for H(napprox. =30) atoms. The ionization rate does not increase monotonically near threshold and is approximately constant over one or more regions of higher field. A quasistatic model is considered which relates the structure in the ionization curves of He to the occurrence of anticrossings in He Stark states.

Molecular g values, magnetic susceptibility anisotropies, and molecular quadrupole moments in 15N2–HF, 15N2–DF, OC–HF, OC–DF, and OC–HCl van der Waals complexes

Abstract: The rotational spectrum of 15N2–DF, the rotational Stark effect in 15N2–HF, and the rotational Zeeman effect in OC–HF, OC–DF, 15N2–HF, 15N2–DF, and OC–HCl van der Waals complexes have been studied using pulsed Fourier transform microwave spectroscopy carried out in a Fabry–Perot cavity. The following spectroscopic constants have been obtained in this study: The Zeeman parameters are used to obtain the molecular quadrupole moments. The bulk magnetic susceptibility is estimated and the diamagnetic susceptibilities are calculated. The relationships between the Zeeman parameters measured for the complex and those of the free monomers are discussed. We observe that a simple zero order projection equation for g⊥ and χ∥–χ⊥ is reproducing the experimental values quite well.

Saturation of resonant third-harmonic generation due to self-defocusing and a redistribution of the population densities

Abstract: Using a high-power excimer laser, pumped dye laser third-harmonic generation in strontium was investigated around several two-photon resonances for input intensities which are well above the onset of saturation. The dominant role of self-defocusing and of the time-dependent redistribution of the population densities is demonstrated. Strong stimulated emission on several transitions branching off from the excited state of the two-photon resonance and several competing parametric processes have been observed. Good agreement is obtained with a theoretical model which accounts for the redistribution of the population densities and which shows the importance of the ac Stark effect for the central structure of the high-intensity conversion profiles.

385 µmD 2 O laser linewidth measurements to -60 dB

Abstract: First linewidth measurements over a 60 dB dynamic range of a pulsed, high-power, optically pumped far infrared laser are presented. These measurements were made possible by using a 385 μmD 2 O laser with an N 2 O absorption filter and a sensitive heterodyne receiver. Studying a 385 μmD 2 O laser oscillator we find that the low-level linewidth (<-20 dB) can be explained by the ac Stark effect due to the high-power pump field. Also, we have not observed any frequency pulling of the main Raman emission frequency due to the strong pump and FIR laser fields.

Complex scaling of ac Stark Hamiltonians

Abstract: For a two‐body atom in a temporally periodic, spatially uniform field, it is shown that in an appropriate gauge the essential spectrum of the Floquet Hamiltonian rotates about a certain set of thresholds when subjected to a complex scaling transformation.

Electric fields in coronal magnetic loops

Abstract: We analyze spectra taken with the 40 cm coronograph at Sacramento Peak Observatory, for evidence of Stark effect on Balmer lines formed in coronal magnetic structures. Several spectra taken near the apex of a bright post-flare loop prominence show significant broadening from H10 to the limit of Balmer line visibility in these spectra, at about H20 The most likely interpretation of the increasing width is Stark broadening, although unresolved blends of Balmer emissions with metallic lines could also contribute to the trend. Less significant broadening is seen in 3 other post-flare loops, and the data from 5 other active coronal condensations observed in this study show no broadening tendency at all, over this range of Balmer number. The trend clearly observed in one post-flare loop requires an ion density of n i ≃ 2 × 1012 cm−3, if it is to be explained entirely as Stark effect caused by pressure broadening. But mean electron densities measured directly from the Thomson scattering at λ3875 in the same SPO spectra, yield n e ≲ 3−7 × 1010 cm−3 for the same condensations observed within that loop. Comparison of this evidence from electron scattering, with densities derived from emission measures and line-intensity ratios, argues against a volume filling factor small enough to reconcile the values of n i and n e derived in this study. This discrepancy leads us to suggest that the Stark effect observed in these loops, and possibly also in flares, could be caused by macroscopic electric fields, rather than by pressure broadening. The electric field required to explain the Stark broadening in the brightest post-flare loop observed here is approximately 170 V cm−1. We suggest an origin for such an electric field and discuss its implications for coronal plasma dynamics.