Relativistic R-matrix close-coupling calculations for photoionization of Ne-like Al IV

We present relativistic close-coupling photoionization calculations of Al IV using the Breit-Pauli R-matrix method to obtain photoionization cross-section of Al IV from the ground state and the lowest two J=0 (even) excited states. A multi-configuration eigenfunctions expansion of the core Al V is employed with spectroscopic configurations 2s²2p⁵, 2s2p⁶, 2s²2p⁴3s, 2s²2p⁴3p, 2s²2p⁴3d and 2s²2p⁴4s. We have included, for the first time, the lowest 68 level target states of Al V in the photoionization calculations of Al IV. Extensive configuration interaction wavefunctions are used to describe both the initial Al IV states and the final Al V states. Cross-sections are compared from three level calculations including only 2s² 2p^{5 2}P^o _3/2, _1/2 and 2s 2p^{6 2}S_1/2 levels of Al V. The present calculation using the lowest 68 target levels of Al V are presented for the first time and should provide reasonably complete database for practical application for photoionization cross-section for Al IV, where high-energy cross-sections along with near-threshold photoionization cross-section is required.     

Rb atomic absorption line reference for single Sr+ laser cooling systems

85 Rb, 5s²S_1/2(F”=2)→6p²P_1/2(F’=2,3) absorption resonance with the ⁸⁸Sr⁺, 5s²S_1/2→5p²P_1/2 transition is exploited to provide a simple, effective frequency reference for a laser cooling/fluorescence excitation source applied to single Sr⁺ ions. A modulation-free frequency stabilization system has been designed which uses the differential signal from two frequency-displaced beams traversing a Rb cell and which probe the Doppler-broadened Rb S–P lineshape at microwatt power levels. The method is applied to frequency lock a 422-nm frequency-doubled diode laser system that is used for excitation of a single ⁸⁸Sr⁺ ion. Stable, long-term laser cooling and fluorescence are achieved using the frequency-stabilized 422-nm source resulting in observed ion confinement times without adjustment of over 8 h, together with an improvement in single-ion loading efficiency. Received: 12 February 1998     

Dynamic stark effect of an optical line observed by cross-saturated absorption

Cross-saturated absorption at the neon line 2s ₂–2p ₄ caused by the saturating line 3s ₂–2p ₄ has been applied to the observation of the dynamic Stark effect by 1) power broadening, due to triple-quantum and higher multiple-quantum transitions, of the light shift contribution to the susceptibility, and 2) a direct splitting in the electronic Raman-Stokes contribution which occurs because of the partial compensation of the Doppler broadening. Work supported by the “Deutsche Forschungsgemeinschaft”.     

Experimental Stark broadening studies of the CI transition 3s1P1o ? 3p1S0 at 833.5 nm

Experimental Stark broadening studies of the infrared CI transition 3s ¹ P ₁ ^o − 3p ¹ S ₀ at 833.5 nm are reported for the first time. A high-current wall-stabilized arc, operated in a mixture of helium, argon, carbon dioxide and hydrogen, was applied as the plasma source. Radiation emitted from homogeneous and optically thin plasma layers was analyzed. Stark broadening studies of the selected CI transition and the hydrogen Balmer β line were performed. As expected from theoretical considerations, the CI line width depends linearly on the electron density of the plasma. Applying theoretical Stark broadening data for the H _gb line, the measured Stark widths of the CI line were calibrated for the purpose of electron density determination in low temperature plasmas.     

Low contact resistance of n+-Si/Ti/WNx/Al submicron contact structures

+ -Si/Ti/WN_x/Al multi-layer metallization scheme. The contact resistance has been strongly related to the plasma nitridation of the Ti surface because the contact resistance of n⁺-Si/Ti/WN_x/Al with contact size of 0.49 μm² about 100–130 Ω, whereas without the nitridation of the Ti surface the contact resistance rises up to 200–390 Ω. ¹⁹F (p,αγ) nuclear resonance analysis and Auger electron spectroscopy reveal that F adatoms on the Ti surface are successfully removed by the 30 s nitridation and as a result, the low contact resistance can be achieved. Received: 16 July 1996/Accepted: 5 November 1996     

Excitation of doublet <Emphasis Type="Italic">D</Emphasis>-levels of a lutetium atom by electron impact

The electron-impact excitation of doublet D-levels of the lutetium atom is studied by the method of extended crossing beams. At the exciting electron energy of 50 eV, 64 excitation cross sections are measured. In the electron energy range of 0–250 eV, nine excitation optical functions are recorded. The occurrence of perturbations in the spectral series 6s ²(¹ S)6p ² P ₁^2/○ − 6s ²(¹ S)nd ² D _3/2 is discussed.     

Laser-induced fluorescence measurements of velocity within a Hall discharge

The results of a study of laser-induced fluorescence velocimetry of neutral and singly ionized xenon in the plume and interior portions of the acceleration channel of a Hall thruster plasma discharge operating at powers ranging from 250 to 725 W are described. Axial ion and neutral velocity profiles for four discharge voltage conditions (100 V, 160 V, 200 V, 250 V) are measured as are radial ion velocity profiles in the near-field plume. Ion velocity measurements of axial velocity both inside and outside the thruster as well as radial velocity measurements outside the thruster are performed using laser-induced fluorescence with nonresonant signal detection on the xenon ion 5d[4]_7/2–6p[3]_5/2 excitation transition while monitoring the signal from the 6s[2]_3/2–6p[3]_5/2transition. Neutral axial velocity measurements are similarly performed in the interior of the Hall thruster using the 6s[3/2]⁰ ₂–6p[3/2]₂transition with resonance fluorescence collection. Optical access to the interior of the Hall thruster is provided by a 1-mm-wide axial slot in the insulator outer wall. While the majority of the ion velocity measurements used partially saturated fluorescence to improve the signal-to-noise ratio, one radial trace of the ion transition was taken in the linear fluorescence region and yields a xenon ion translational temperature between 400 and 800 K at a location 13 mm into the plume. Received: 27 September 2000 / Revised version: 2 March 2001 / Published online: 9 May 2001     

Hyperfine interactions in the alkaline-earth Sr ions by collinear fast beam laser spectroscopy

The magnetic dipole hyperfine structure constants of the⁸⁷SrII 5s²S_1/2 ground state and the 5p²P_1/2 excited state, and the isotope shifts of the ionic 5s²S_1/2 → 5p²P_1/2 resonance transition for all stable Sr isotopes, measured by collinear fast beam laser spectroscopy, are reported.     

Spin correlations of \varLambda[`\varLambda]\varLambda{\bar{\varLambda}} pairs as a probe of quark–antiquark pair production

The polarizations of Λ and [`\varLambda]{\bar{\varLambda}} are thought to retain memories of the spins of their parent s quarks and [`(s)]{\bar{s}} antiquarks, and are readily measurable via the angular distributions of their daughter protons and antiprotons. Correlations between the spins of Λ and [`\varLambda]{\bar{\varLambda}} produced at low relative momenta may therefore be used to probe the spin states of s [`(s)]s {\bar{s}} pairs produced during hadronization. We consider the possibilities that they are produced in a ³P₀ state, as might result from fluctuations in the magnitude of á[`(s)] s ?\langle {\bar{s}} s \rangle, a <sup>1</sup>S<sub>0</sub> state, as might result from chiral fluctuations, or a <sup>3</sup>S<sub>1</sub> or other spin state, as might result from production by a quark–antiquark or gluon pair. We provide templates for the p [`(p)]p {\bar{p}} angular correlations that would be expected in each of these cases, and discuss how they might be used to distinguish s [`(s)]s {\bar{s}} production mechanisms in pp and heavy-ion collisions.     

Absolute frequency and isotope shift measurements of the cooling transition in singly ionized indium

We report greater than two orders of magnitude improvements in the absolute frequency and isotope shift measurements of the In⁺ 5s^{2 1}S₀ (F = 9/2)–5s5p ³P₁ (F = 11/2) transition near 230.6 nm. The laser-induced fluorescence from a single In⁺ in a radio-frequency trap is detected. The fourth-harmonic of a semiconductor laser is used as the light source. The absolute frequency is measured with the help of a frequency comb referenced to a Cs atomic clock. The resulting transition frequencies for isotopes ¹¹⁵In⁺ and ¹¹³In⁺ are measured to be 1 299 648 954.54(10) MHz and 1 299 649 585.36(16) MHz, respectively. The deduced cooling transition frequency difference is 630.82(19) MHz. By taking into account of the hyperfine interaction, the isotope shift is calculated to be 695.76(1.68) MHz.     

Theoretical studies on dielectronic recombination of neonlike gold and its effects on plasma ionization balance and radiation energy

The dielectronic recombination (DR) of neonlike gold ions is investigated employing the flexible atomic code based on the relativistic configuration interaction method, and its influence on the ionization balance and radiation energy in high-temperature plasma is also studied. The total resonance strength for LMM configuration complex is in a good agreement with the experimental measurement and other theoretical works. The DR rate coefficients are calculated and compared with the three-body recombination and radiative recombination rate coefficients. The DR process is the dominant recombination mechanism of Ne-like gold ions for plasma with temperature T_e≥6.5 keV and density n_e≤2×10²² cm^-3, which is close to the condition of X-ray conversion region in the inertial confinement fusion. Moreover, the DR satellite spectra of LMM, LMN and LMO resonances are simulated, and compared with the intensities of the corresponding resonance lines induced by the electron impact excitation. The intensity ratio of the satellite line 3D’ [(2p⁵_3/23d_3/23d_5/2)_J=5/2[(2p^{5}_{3/2}3d_{3/2}3d_{5/2})_{J=5/2}–(2p⁶3d_3/2) _J=3/2](2p^{6}3d_{3/2})_{ J=3/2}] and the resonance line 3D [(2p⁵_3/23d_5/2)_J=1[(2p^{5}_{3/2}3d_{5/2})_{J=1}–(2p⁶)_J=0](2p^{6})_{J=0}] is given, which can be applied for diagnostics of plasma temperature.     

Two-photon resonant four-wave mixing processes in atomic barium

By means of a N₂-laser pumped dye-laser (P _L ≈20kW, Δv _L < 10 GHZ) different two-photon resonant four-wave coupling processes in Ba vapour (n _Ba≈10¹⁶ cm⁻³) using the Ba states 6s8s ¹ S _o and 7s5d ¹ D ₂ were investigated. Coherent line radiation with conversion rates up to 10⁻³ was generated within the range of λ=190–200 nm by sumfrequency mixingv _UV=2v ₁+v ₂ of 3 laser photons and within the range of λ=250–380 nm by couplingv _UV=2v ₁±v _IR of 2 laser photons with one photonv _IR stimulated emitted in laser-induced Ba transitions. For the second coupling type the various nonlinear processes contributing to the formation of the coupling components are discussed. The power of the UV-component as function of inensity and resonance detuning of the laser as well as on the phase-mismatch was calculated on the basis of the small signal theory and compared to the experimental data.     

Isotope shift in the resonance lines of131cesium

Reactor produced¹³¹Cs (T _1/2=9.7 d) was used to investigate the isotope shift against the stable nuclide¹³³Cs in the resonance lines of the Cs I spectrum. Special techniques to prepare the hollow cathode and a completely digitalized method of measuring and evaluation of the hyperfine structure made it possible to investigate short-lived isotopes with high accuracy. The following results were obtained:Δv _IS(133?131; 6p ² P _1/2?6s ² S _1/2)=?0,39 (9) mKΔv _IS(133?131; 6p ² P _3/2?6s ² S _1/2)=?0,28 (20) mK.     

Postcollision interaction upon electron excitation of 4sns1S0, 3S1 and 4snd1D2, 3DJ levels of zinc atom

The optical excitation functions (OEFs) for four series of spectral lines of the Zn atom at the transitions 4sn ₁ s ¹ S ₀ → 4s4p ¹ P ₁^∘ (n ₁ = 6–10), 4sn ₂ s ³ S ₁ → 4s4p ³ P ₂^∘ (n ₂ = 6−8), 4sn ₃ d ¹ D ₂ → 4s4p ¹ P ₁^∘ (n ₃ = 4−6), 4sn ₄ d ³ D _{1, 2, 3} → 4s4p ³ P ₂^∘ (n ₄ = 4−7) excited by a monoenergetic (0.04–0.08 eV) electron beam with energies from the excitation threshold to 18–19 eV are measured. In the energy dependences of the excitation cross sections, the effect of post-collision interaction of slow (scattered) and fast (emitted after the autoionization state decay) electrons is observed and described. This interaction leads to the capture of a slow electron into the listed discrete levels and the appearance of maxima in the excitation functions. The energies of the maxima are used to determine the energies and widths of single autoionization states or their groups by approximate formulas of the classical approach. The autoionization levels of the zinc atom responsible for the maxima observed are determined. Possible transfer of the orbital angular momentum between electrons is analyzed.     

Relativistic calculations of 3s2 1S0-3s3p 1P1 and 3s2 1S0-3s3p 3P1,2 transition probabilities in the Mg isoelectronic sequence

Using the multi-configuration Dirac-Fock self-consistent field method and the relativistic configuration-interaction method,calculations of transition energies,oscillator strengths and rates are performed for the 3s 2 1 S 0-3s3p 1 P 1 spinallowed transition,3s 2 1 S 0-3s3p 3 P 1,2 intercombination and magnetic quadrupole transition in the Mg isoelectronic sequence(Mg I,Al II,Si III,P IV and S V).Electron correlations are treated adequately,including intravalence electron correlations.The influence of the Breit interaction on oscillator strengths and transition energies are investigated.Quantum electrodynamics corrections are added as corrections.The calculation results are found to be in good agreement with the experimental data and other theoretical calculations.     

Isotope-selective trapping of rare calcium ions using high-power incoherent light sources for the second step of photo-ionization

Rare calcium isotope ⁴⁸Ca⁺ (0.187%) has been selectively loaded in a linear Paul trap using two ultraviolet light emitting diodes with the output power of 85 mW for the second excitation in a two-step photo-ionization process. Isotope selectivity has been achieved by utilizing the isotope shifts for the 4s^{2 1} S ₀–4s4p¹ P ₁ transition of neutral calcium atom. Sympathetic cooling of ⁴⁸Ca⁺ ions has been demonstrated using ⁴⁰Ca⁺ ions as refrigerant ions. Purification of rare isotope ⁴²Ca⁺ ions (0.647%) from a mixture of ⁴⁰Ca⁺ (96.9%) and ⁴²Ca⁺ ions has been performed by adjusting the detuning of the cooling laser frequency, which overcomes the imperfect selectivity for some rare isotopes having close resonance frequencies to that of ⁴⁰Ca in the 4s^{2 1} S ₀–4s4p¹ P ₁ transition. The methods can be applied to ⁴³Ca⁺ ion (0.135%) that has been considered as one of the attractive candidates for quantum information processing as well as for an optical frequency standard. PACS 32.80.Fb; 32.80.Pj; 32.80.Rm     

Large-scale collisional energy transfer in laser-pumped metastable Ca atoms: Excitation of resonance states of Ca II

We report the first experimental observation of the excitation of the 4p ² P _{3/2, 1/2} resonance states of Ca II (located at 74 720.4 and 74 497.5 cm^–1 above the ground state of Ca I) following pulsed-laser pumping of the 4s ^{2 1} S _O–4s4p ³P₁ intercombination transition of Ca I (E _ex = 15 210 cm^–1). Large scale collisional transfer of energy between the laser-excited atoms is believed to be responsible for this. This is possibly because sufficient time is available (_rad of the 4s4p ³ P ₁ state is approximately 350 µs) for collisions to build such a high level of excitation. Some interesting additional features of the fluorescence spectra of the laser-pumped Ca vapor, such as temperature dependence of the fluorescence intensities and evolution in time of some selected states, are also presented.     

A new bound-exciton emission band in ZnSe crystals and multiplasmon optical transitions

We have investigated cathodoluminescence both in unannealed ZnSe crystals and in crystals annealed in a Bi melt at a temperature of 1200K for 120 h with subsequent quenching. In the wavelength range 450–480 nm we have detected a new line series I _i ^s -nLO-mPl consisting of the bound-exciton emission line I _i ^s with wavelength λ=455.9 nm and its plasmon and LO-phonon echoes I _i ^s -LO (λ ₁=461.3 nm), I _i ^s -2LO (λ ₂=466.8 nm), I _i ^s -3LO (λ ₃=472.4 nm), and I _i ^s -4LO (λ ₄=478.3 nm). We have determined the mean number of emitted LO phonons N _LO=2.2±0.1 per photon. It is shown that the observed finer structure of the band may be due to multiphonon optical transitions. At low plasma densities (ω _p ≪ω _LO ) the Coulomb interaction causes broadening of the I _i ^s -nLO series. In samples with denser plasma, in which the condition ω _p ⩽ω _LO is met, multiplasmon satellites of the series I _i ^s -nLO-mPl are observed. Theoretical calculations of the shape of the emission band agree with experiment. Fiz. Tverd. Tela (St. Petersburg) 41, 1176–1180 (July 1999)     

Photoionization of Al IV (neon-type) from its ground 2s 22p 6 1 S e and excited 2s 22p 53p 3,1 P 0 3 S e states using the R-matrix method

The R-matrix method is used to calculate the total photoionization cross-sections from the ground 2s ²2p ^{6 1} S ^e and the first three excited 2s ²2p ⁵3p ^3,1 S ^e states of Al IV, for photon energies ranging from the first ionization threshold to just above the second threshold of the residual ion Al V. The two lowest LS terms of Al V − 2s ²2p ^{5 2} P ⁰, 2s2p ^{6 2} S ^e, 2s2p ^{6 2} S ^e, represented by sophisticated configuration interaction wavefunctions, are included in the R-matrix calculation. The resulting cross-sections are affected by Rydberg series of resonances converging to the 2s2p ^{6 2} S ^e excited threshold.