Magnetic coherence transfer induced by discharge radiation and the effect of radiation trapping on the lifetime of the hidden alignment of Ne terms

The dichroism of a neon gas discharge plasma in a weak magnetic field is investigated by scanning the 3s ₂-2p ₄ transition by monochromatic laser radiation. Magneto-optical resonances of the intrinsic macroscopic alignment and hidden alignment of the 2p ₄ level are separated. Against the background of these resonances, resonances attributed to coherence transfer from the 1s _{2, 4, 5} levels and the birefringence of the wings of the nearest absorption lines from the 1s _{4, 5} levels are observed. A new type of alignment is revealed—integral hidden alignment, whose lifetime, in contrast to the case with macroscopic alignment, increases without bound with increasing radiation trapping.     

Ionization of barium through a coherent excitation of two bound intermediate states

We have investigated theoretically the asymmetrical photoionization yields into the 6s _1/2, 5d _3/2 and 5d _5/2 continuum channels of atomic barium observed by Wang, Chen and Elliott [Phys. Rev. Lett. 77, 2416 (1996)] in the study of coherent control through two-color resonant interfering paths. The atomic parameters obtained from a theoretical approach based on a combination of jj-coupled eigenchannel R-matrix and Multichannel Quantum Defect Theory are used to analyze the photoionization spectra from the and 6s7p states with polarized light beams. The studied energy range includes the 6p7p autoionizing resonances. The dynamics of the two-color photoionization is governed by the coherent excitation of the 6s6p and intermediate states. This excitation is described as an adiabatic process in the rotating wave approximation. The influence of the radiative decay, spatial distribution of the intensities of the laser beams and hyperfine interaction is discussed. Received 28 September 1999     

Observation of occupied 5d states in f.c.c. Yb metal

We propose experimental evidences for the sd character of the occupied band states of f.c.c. Yb metal. Photoionization cross-section σ¹ in the range 24–65 eV, covering the 5p core electron energies have been measured for both Yb (4ƒ¹⁴6s²5d⁰) and Lu (4ƒ¹⁴6s²5d¹). Both the hv dependence of σ¹ for the Yb valence band and the presence of photoemission resonances above the 5p edges of Lu and Yb indicate the presence of occupied 5d states at the top of the valence band of solid Yb. The Yb 4ƒ σ¹ is presented in order to distinguish the 5d band resonances from the 5p-5d giant dipole autoionization decays. L_{2, 3} X-ray absorption white lines for Yb provide a measure of the 5d bandwidth.     

Tentatively identified and predicted H- Fano resonances

Positions are calculated for the Fano resonances that are due to interactions of the discrete autoionized 1s3s, 1s3p, and 1s4p states of H^- with overlapping split-configuration continua. The two first-mentioned resonances are tentatively identified with the diffuse interstellar doublets at λλ6376,6379 and λλ5780, 5797 on the basis of the relative positions of the autoionized states and the relative intensities of the doublet components.The observed wave-numbers of the 1s2s, 1s3s, 1s2p, and 1s3p resonances seem to belong to two series that converge towards a common limit in a kind of reverse Rydberg-series fashion. The position of the limit is close to 9000 Å, in accordance with theory. An extrapolation leads to the identification of the 1s4p resonance with the diffuse λ 6614 line. A further extrapolation leads to the prediction of positions at about 7183 and 7583 Å for the 1s5p and 1s6p resonances.The half-widths calculated for the singlet components of the 1s3p and 1s4p resonances are of the order of magnetude of those observed for the diffuse lines, and of the observed distance between the probably partly mixed singlet and triplet 1s3p components. The profile of the λ 5780 resonance is calculated on the basis of an assumed helium-line value for the oscillator strength. Its shape indicates that the “λ 5778 band” may be just a misinterpretation of the asymmetric wings.Tables of Hartree functions for the 3s², 3p² and 4p² configurations of H^- are given in an appendix.     

Stark-Effekt-Untersuchungen an Strontium durch Nachweis von Δμ=1-level-crossing-Signalen mit linearpolarisiertem Licht

Zero field-level crossing signals of the 5s 5p ¹ P ₁-level of the Sr I-spectrum were investigated in superimposed homogeneous magnetic and electric fields. The electric field-dependent Δμ=1-crossings were detected by resonance scattering of linearly polarized light of the 4607 Å-line, the directions of polarization forming an oblique angle with the field axisz. The experiments yielded the tensor polarizability of the 5s 5p ¹ P ₁-level ¦α_ten¦=15.7 kHz/(kV/cm)². This value is related to oscillator strengths of electric dipole transitions from the 5s 5p ¹ P ₁-level to¹ S ₀- and¹ D ₂-levels. The level crossing signals, obtained by resonance scattering oflinearly polarized light, are discussed using a formula, originally derived by Rose and Carovillano for level crossing experiments withunpolarized light beams. The applicability of the formula to our experiments results from an equivalence of level crossing measurements with unpolarized and those with linearly polarized light beams.     

Direct observation of resonant four-photon parametric mixing conditioned by the difference of atomic multipole relaxation rates

Experimental evidence of previously predicted relaxation induced parametric processes is presented. Parametric interaction of orthogonal linearly polarized waves has been observed in the 2s₂-2p₁ (j = 1 → j = 0) Ne transition under λ = 1.52 μm He-Ne laser pumping. Coherence transfer between Zeeman sublevels eliminates the ban of the parametric interaction of orthogonal linearly polarized waves. This transfer is connected with collisions and photon-trapping processes resulting in the difference between relaxation rates of the electric quadrupole and magnetic dipole moments of the Ne atoms in the 2s₂ level.     

Interference effects in alignment and orientation processes of atoms excited by polarized radiation

The dynamics of the processes of alignment and orientation of atoms subjected to the action of polarized radiation has been studied theoretically in the energy range of excitation of autoionization resonances. The alignment parameters A ₂₀ for the 4p ⁴5p states of Kr II populated through the excitation and autoionization decay of Kr I 3d ⁹ np resonances depend on energy due to the interference between different resonance channels and the channel of direct photoionization. It is predicted that the orientation parameter O ₁₀ of some Kr II 4p ⁴5p states and the parameter of the angular distribution of photoelectrons β_e1 strongly depend on energy. The absolute photoionization cross sections are calculated for the population of the Kr II 4p ⁴5p states in the case where the energy of excitation photons corresponds to the first four 3d ⁹ np resonances. A good agreement between the calculated and measured photoionization cross sections proves that it is important to take into account the interference between different resonance channels in order to appreciate the dynamics of the Auger decay of Kr I 3d ⁹ np resonances.     

Origin of threshold electrons produced in decay of the Xe 4d−1 np resonance

Coincidence spectra of energetic electrons with threshold electrons were measured following photo-excitation of the Xe 4d_3/2, 5/2 → np resonances, in order to investigate the origin of threshold electrons, and the mechanism leading to formation of the Xe²⁺ 5p⁻² and 5s⁻¹5p⁻¹ final states. A two-step decay process was observed in the production of Xe²⁺ 5p⁻²(¹D) following decay of the 7p resonance, where the intermediate state is Xe^+* 5p⁻²(¹S)8p that autoionizes emitting a pseudo-threshold electron. This process was confirmed in a time-of-flight analysis of the coincidence spectra of the energetic electrons with the threshold photoelectrons. It is suggested that a similar two-step process also contributes to the population of excited Xe²⁺ states and is the main origin for the production of threshold electrons in decay of the 4d⁻¹ np resonances.     

Disalignment collision cross sections of the neon levels 2p 4 and 2s 2 obtained by mode crossing

Alignment destroying collision cross sections of the Ne levels 2p ₄ and 2s ₂ were measured by investigation of the zero-field mode crossing resonances of a multimode He/Ne-laser operating on the 3s ₂→2p ₄ (λ=633nm) and 2s ₂→2p ₁ (λ=1.52μm) Ne transitions respectively. The measurements were carried out with the aid of a small sample cell which was placed inside the laser cavity and filled with pure Neon or a mixture of the He and Ne. Comparison of the measured cross sections concerning the 2p ₄ level with corresponding Hanle effect measurements shows that in multimode operation velocity changing collisions do not produce an additional broadening of the mode crossing resonances. The alignment destroying cross section is almost temperature independent in the case of He collisions; it decreases, however, with increasing temperature in the case of Ne. Due to the allowed dipol transition between the 2s ₂ and the ground state of Ne, radiation trapping and resonance interaction takes place if the gas filling contains Ne. The effect on the mode crossing resonance width is investigated.     

Effects of spatial dispersion at intraband transitions in multiple quantum well structures

Effects of spatial dispersion in reflection of light from multiple quantum well structures of different symmetry have been investigated. It has been shown that with inclined incidence of linearly polarized light on the system of symmetry C _∞v , the reflected wave starts to manifest the circular polarization. Upon the incidence of s(p)-polarized light on the structure of the D _2d symmetry, the reflected wave starts to manifest p(s) component, while in the case of the point symmetry C _2v , this phenomenon also occurs for the normal incidence. The magneto-spatial dispersion in the magnetic field lying in the structure plane leads to the same conversion of polarization. Dependences of the polarization-sensitive reflection coefficients on the incidence angle are calculated. The microscopically gyrotropic contributions to the dielectric permittivity of the multiple quantum well structures are calculated for the intraband frequency range. Evaluations show that the effects of spatial dispersion in such systems can be observed experimentally.     

Isotope shifts in transitions between low-lying levels of Sr I by laser-atomic-beam spectroscopy

High-resolution laser-atomic-beam spectroscopy has been used to determine isotope shifts in five transitions between low-lying states of Sr I. With these results and existing data a parametric analysis of level isotope shifts has been performed. The transition isotope shifts have been separated into field shift and mass shift contributions with a King-plot procedure using model-independent nuclear charge equivalent radiiR _k from muonic x-ray measurements. Values for the mean-square nuclear charge radiiδ〈r ₂ 〉 have been calculated from the field shifts in the optical transitions 5s ^{2 1} S ₀-5s5p ³ P ₁ and 5s5p ³ P ₀-5s6s ³ S ₁ and compared with correspondingδ〈r ² 〉 values evaluated from muonic x-ray data.     

Isotope shift and hyperfine structure of43Ca by laser spectroscopy

The isotope shift⁴⁰Ca-⁴³Ca in the 4s ^{2 1} S ₀-4s4p ³ P ₁ intercombination line as well as the hyperfine structure splitting of the 4s4p ³ P ₁ state of⁴³Ca have been remeasured by saturation spectroscopy with a tunable stabilizedcw dye laser and an atomic beam of natural Ca as absorber. The nuclear charge radius of⁴³Ca obtained here reconciles our result with the radius obtained from measurements in muonic Ca-atoms and in the Ca resonance line. It reconfirms the fact that the charge radius of⁴³Ca is considerably smaller than the ones of both neighbouring even isotopes. The discrepancy of our previous measurement for this charge radius was due to a wrong assignment of so far unobserved absorption lines of probably molecular origin occuring in the neighbourhood of the atomic resonances under study.     

Measurement of partial radiation widths of high energy transitions from keV capture resonances in56Fe and58,60Ni

High energyγ-ray transitions to low-lying states following neutron capture in⁵⁶Fe and^58,60Ni have been investigated for individual resonances in the neutron energy range 7–70keV using a 50cc Ge(Li)-detector. Partial radiation widths fors- and 1>0 wave resonances were determined. For the 1>0 wave resonance in⁵⁸Ni at 47.8 keV a spin of 3/2 was derived. Theγ-ray strength forM1 transitions was found to be (21±17)×10^?9 and (16±7)×10^?9MeV^?3 for⁵⁶Fe and⁵⁸Ni, respectively. The partial radiation widths of the studieds-wave resonances were compared with valence model calculations.     

Polarized leptoproduction and dynamically generated spin-dependent parton distributions

The first moment of the polarized parton distributions of the proton is evaluated dynamically using the assumption that at some low resolution scale the proton consists of valence quarks only. The spin carried by gluons, ΔG, at the EMC resolution scaleQ ₀ ² =10 GeV² ispredicted to be ΔG/s _p ?5 withs _p=1/2 denoting the spin of the proton. This result furthermoreexplains the dynamical origin of the recent EMC measurement of the first moment of the polarized structure functiong ₁ ^P (x, Q ²).     

Stark-Effekt-Untersuchungen der Hyperfeinstruktur der 5s25d2D3/2- und 5s25d2D3/2-Terme im In I-Spektrum

The level-crossing technique with combined electric and magnetic fields was used to investigate the hyperfine structure of the 5s ²5d ² D _3/2- and 5s ²6d ² D _3/2-stedes of the In I-spectrum. From the shifts of the level-crossing signals due to the Stark effect of the electric field the Stark constantsβ of both states were deduced: 5s ²5d ² D _3/2: ¦β¦=0.33(3) Mc/(kV/cm)² 5s ²6d ² D _3/2: ¦β¦=6(1) Mc/(kV/cm)². By theoretical calculations with wave functions of the Coulomb approximation one can show, that the Stark effect in both states is mainly due to admixtures of the 5s ²6p- resp.5s ²7p-configuration.     

内壳层电子激发(电离)诱发的电子波函数的弛豫及其对辐射跃迁概率的影响

利用多组态Dirac_Fock(MCDF)理论方法，通过对Ar原子在基组态3p⁶和激发组态1s^-14s，2s^-14s，2p^-14s，3s^-14s，3p^-14s情况下电子波函数的计算，系统地研究了不同内壳层电子激发(或电离)引起的电子波函数的弛豫现象以及由此导致的k_α和k_β线的跃迁波长和概率的变化情况，并与以往的理论结果进行了比较. 关键词： MCDF方法 弛豫效应 电子波函数 跃迁概率     

Laser-induced effects for overlapping autoinoizing rydberg states of xenon

The effect of a laser field on the cross section of photoionization of an atom by probe radiation in the region of closely lying autoionizing resonances is studied theoretically. The cross sections in the region of the overlapping autoionizing Rydberg states 5p ⁵(² P _1/2)6d′ J = 1 and 5p ⁵(² P _1/2)8s′ J = 1 resonantly coupled with the discrete state 5p ⁵(² P _3/2)7p[1/2]₁ in the xenon atom are calculated. The behavior of the shape and position of resonances in relation to the frequency and intensity of laser radiation is studied.     

On the strong influence of inner shell resonances upon the outer shell photoionization of endohedral atoms

It is demonstrated by the example of the Xe atom stuffed inside the C₆₀ fullerene, i.e., the endohedral Xe@C₆₀, that the so-called confinement resonances in 4d subshell strongly affect the photoionization cross section of outer 5p and subvalent 5s electrons near the 4d ionization threshold. It is a surprise that these narrow inner 4d shell resonances are not smeared out in the outer shell photoionization cross section. On the contrary; the inner shell resonances affect the outer cross section by enhancing them enormously. Close to its own photoionization thresholds, 5p and 5s photoionization cross sections of Xe@C₆₀ are dominated by their own confinement resonances greatly affected by the amplification of the incoming radiation intensity due to polarization by it of the C₆₀ electron shell. Between 4d and 5p thresholds, the effect of 4d is becoming stronger while own resonances of 5p and 5s are becoming much less important.     

Fredholm approximants for potential scattering

An approximate method based on Fredholm approximants is used to solve Lippmann-Schwinger equation fors-andp-wave Yukawa ands-wave exponential potential scattering problems. The method is then applied to a problem ofπ-π scattering i nvolving the use of a well known equivalent potential. The equation for partial wave amplitudes is solved to generate the first threeπ-π resonances,ρ, f ₀, andg, in a self-consistent manner.