Weak Intercombination Line Research Articles

Nonlinear spectroscopy of Sr atoms in an optical cavity for laser stabilization

We study the non-linear interaction of a cold sample of strontium-88 atoms coupled to a single mode of a low finesse optical cavity in the so-called bad cavity limit and investigate the implications for applications to laser stabilization. The atoms are probed on the weak inter-combination line $\lvert 5s^{2} \, ^1 \textrm{S}_0 \rangle \,-\, \lvert 5s5p \, ^3 \textrm{P}_1 \rangle$ at 689 nm in a strongly saturated regime. Our measured observables include the atomic induced phase shift and absorption of the light field transmitted through the cavity represented by the complex cavity transmission coefficient. We demonstrate high signal-to-noise-ratio measurements of both quadratures - the cavity transmitted phase and absorption - by employing FM spectroscopy (NICE-OHMS). We also show that when FM spectroscopy is employed in connection with a cavity locked to the probe light, observables are substantially modified compared to the free space situation where no cavity is present. Furthermore, the non-linear dynamics of the phase dispersion slope is experimentally investigated and the optimal conditions for laser stabilization are established. Our experimental results are compared to state-of-the-art cavity QED theoretical calculations.

Log gfvalues for astrophysically important transitions Fe II

Aims. In a recent measurement, Melendez & Barbuy (2009, A&A, 497, 611) report accurate log gf values for 142 important astrophysical lines with wavelengths in the range 4000 A to 8000 A. Their results include both solar and laboratory measurements. In this paper, we describe a theoretical study of these lines.Methods. The CIV3 structure codes, combined with our “fine-tuning” extrapolation process, are used to undertake a large-scale CI calculation involving the lowest 262 fine-structure levels belonging to the 3d6 4s, 3d7 , 3d5 4s2 , 3d6 4p, and 3d5 4s4p configurations. Results. We find that many of the 142 transitions are very weak intercombination lines. Other transitions are weak because the dominant configurations in the two levels differ by two orbitals.Conclusions. The comparison between our log gf values and the experimental values generally shows good agreement for most of these transitions, with our theoretical values agreeing slightly more closely with the solar than with the laboratory measurements. A detailed analysis of the small number of transitions for which the agreement between theory and experiment is not as good shows that such disagreements largely arise from severe cancellation due to CI mixing.

Efficient photo-ionization for barium ion trapping using a dipole-allowed resonant two-photon transition

Two efficient and isotope-selective resonant two-photon ionization techniques for loading barium ions into radio-frequency (RF)-traps are demonstrated. The scheme of using a strong dipole-allowed transition at \lambda=553 nm as a first step towards ionization is compared to the established technique of using a weak intercombination line (\lambda=413 nm). An increase of two orders of magnitude in the ionization efficiency is found favoring the transition at 553 nm. This technique can be implemented using commercial all-solid-state laser systems and is expected to be advantageous compared to other narrowband photoionization schemes of barium in cases where highest efficiency and isotope-selectivity are required.

A robust method for frequency stabilization of 556-nm laser operating at the intercombination transition of ytterbium

A frequency-stabilized 556-nm laser is an essential tool for experimental studies associated with 1S0-3P1 intercombination transition of ytterbium (Yb) atoms. A 556-nm laser light using a single-pass second harmonic generation (SHG) is obtained in a periodically poled MgO:LiNbO3 (PPLN) crystal pumped by a fiber laser at 1111.6 nm. A robust frequency stabilization method which facilitates the control of laser frequency with an accuracy better than the natural linewidth (187 kHz) of the intercombination line is developed. The short-term frequency jitter is reduced to less than 100 kHz by locking the laser to a home-made reference cavity. A slow frequency drift is sensed by the 556-nm fluorescence signal of an Yb atomic beam excited by one probe beam and is reduced to less than 50-kHz by a computer-controlled servo system. The laser can be stably locked for more than 5 h. This frequency stabilization method can be extended to other alkaline-earth-like atoms with similar weak intercombination lines.

Photoionization and photoelectric loading of barium ion traps

Simple and effective techniques for loading barium ions into linear Paul traps are demonstrated. Two-step photoionization of neutral barium is achieved using a weak intercombination line (6s2 1S0 <-> 6s6p 3P1, 791 nm) followed by excitation above the ionization threshold using a nitrogen gas laser (337 nm). Isotopic selectivity is achieved by using a near Doppler-free geometry for excitation of the triplet 6s6p 3P1 state. Additionally, we report a particularly simple and efficient trap loading technique that employs an in-expensive UV epoxy curing lamp to generate photoelectrons.

Modeling the NeixTriplet Spectral Region of Capella with theChandraandXMM‐NewtonGratings

High-resolution X-ray spectroscopy with the diffraction gratings of Chandra and XMM-Newton offers new chances to study a large variety of stellar coronal phenomena. A popular X-ray calibration target is Capella, which has been observed with all gratings with significant exposure times. We gathered together all available data of the High Energy Transmission Grating Spectrometer (HETGS; 155 ks), Low Energy Transmission Grating Spectrometer (LETGS; 219 ks), and Reflection Grating Spectrometer (RGS; 53 ks) for comparative analysis, focusing on the Ne IX triplet at around 13.5 A, a region that is severely blended by strong iron lines. We identify 18 emission lines in this region of the High-Energy Grating (HEG) spectrum, including many from Fe XIX, and find good agreement with predictions from a theoretical model constructed using the Astrophysical Plasma Emission Code. The model uses an emission measure distribution derived from Fe XV to Fe XXIV lines. The success of the model is due in part to the inclusion of accurate wavelengths from laboratory measurements. While these 18 emission lines cannot be isolated in the LETGS or RGS spectra, their wavelengths and fluxes as measured with HEG are consistent with the lower resolution spectra. In the Capella model for HEG, the weak intercombination line of Ne IX is significantly blended by iron lines, which contribute about half the flux. After accounting for blending in the He-like diagnostic lines, we find the density to be consistent with the low-density limit (ne < 2 × 1010 cm-3); however, the electron temperature indicated by the Ne IX G-ratio is surprisingly low (~2 MK) compared to the peak of the emission measure distribution (~6 MK). Models show that the Ne IX triplet is less blended in cooler plasmas and in plasmas with an enhanced neon-to-iron abundance ratio.

EPR and Optical Spectra of Cobalt in SrLaAlO4

The paramagnetic resonance and optical spectra of Co 2+ ions in SrLaAlO 4 single crystals are reported. The EPR spectrum shows one electronic transition consisting of eight hyperfine lines with anisotropic g-factor and nearly isotropic hyperfine interaction constant. A tetragonal distortion of the octahedral crystal field acting on Co 2+ ions has been found. The optical spectrum consists of intensive lines corresponding to transition ΔS = 0 and weak intercombination lines. In the weak-field coupling scheme satisfactory agreement is obtained between the observed and calculated spectrum with Dq = 1030 cm -1 and Racah parameter B = 810 cm -1 . Both the optical and EPR data indicate a covalent bonding of Co 2+ to the nearest oxygen atoms.

EPR and Optical Spectra of Cobalt in SrLaAlO4

The paramagnetic resonance and optical spectra of Co2+ ions in SrLaAlO4 single crystals are reported. The EPR spectrum shows one electronic transition consisting of eight hyperfine lines with anisotropic g-factor and nearly isotropic hyperfine interaction constant. A tetragonal distortion of the octahedral crystal field acting on Co2+ ions has been found. The optical spectrum consists of intensive lines corresponding to transition ΔS = 0 and weak intercombination lines. In the weak-field coupling scheme satisfactory agreement is obtained between the observed and calculated spectrum with Dq = 1030 cm—1 and Racah parameter B= 810 cm—1. Both the optical and EPR data indicate a covalent bonding of Co2+ to the nearest oxygen atoms.

Accuratef‐Values for Ultraviolet Transitions from the 3d\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $^{5}$ \end{document} ( \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $^{6}$ \end{document}S)4pLevels in Mnii

We have measured branching fractions for ultraviolet electric dipole transitions from upper levels belonging to the 3d5(6S)4p7P and 3d5(6S)4p5P terms of Mn II. The levels were excited in a hollow cathode lamp and the spectra were observed with a Fourier transform spectrometer. The high signal-to-noise ratio of the Mn II lines in our spectra permitted the measurement of branching fractions even for the weakest transitions in the ultraviolet, which are of particular astrophysical interest. A comparison with previous measurements revealed that many of these measurements, including the most recent, show systematic distortions that may indicate that they are affected by self-absorption. Absolute oscillator strengths, based on the new branching fraction measurements, were determined using existing experimental lifetime data. The uncertainty of the f-values is less than 5% for strong transitions. Oscillator strengths for several very weak intercombination lines with log gf < -2 are reported for the first time.

Branching fractions and transition probabilities for transitions from 2p^4 3p, 2p^4 3d, and 2p^4 4s levels of Ne II

Branching fractions for electric dipole transitions from 2p4 3p,2p4 3d, and 2p4 4s upper levels in singly ionized neon atoms excited in a high-current hollow-cathode lamp were measured. Transition probabilities for many weak intercombination lines were determined for the first time to the authors’ knowledge. The measurements were carried out with two different techniques to minimize the effect of systematic errors, first in an experiment with a 2-m grating monochromator and then with a Fourier transform spectrometer. The uncertainty of the branching fraction data is 4%(1σ) for lines corresponding to LS-allowed transitions and 30%(1σ) for weak intercombination lines. For 14 upper levels complete sets of transitions could be measured that enabled us to determine absolute transition probabilities when lifetime data for the upper levels were available.

Problems in the calculation of intercombination line strengths

The calculation of weak intercombination line strengths sometimes requires an especially careful treatment of a combination of factors, including configuration mixing, spin-orbit interactions and relativistic effects. Fully relativistic ab initio MCDF calculations, when available, can provide an excellent guide to the Z-dependence of these transition probabilities for the upper portion of an isoelectronic sequence. For low to moderate ionization stages, good results may sometimes be obtained using an LS-coupled basis, MCHF or CI wavefunctions, and a treatment of the spin-mixing interactions which is guided by empirical data. These ideas are illustrated by examples from the configurations 2s3p in the Be isoelectronic sequence, 3s4p in the Mg sequence, and 3s3p3 in the Si sequence. Revised wavelength predictions for the 3s23p2 3P1,2-3s3p3 5S2 lines in the Si sequence are also presented.

Paramagnetic and Optical Spectra of Divalent Cobalt in Cubic Crystalline Fields

The optical and paramagnetic resonance spectra of divalent cobalt in MgO single crystals are reported. The optical spectrum consists of stronger lines which correspond to transitions between Stark levels of the same multiplicities and weak intercombination lines. If the Slater integrals are taken as free parameters then in the intermediate coupling scheme good agreement is obtained between the observed and calculated spectrum with $Dq=960$ ${\mathrm{cm}}^{\ensuremath{-}1}$. The Slater integrals are reduced by about 8-10% from those of the free ion. The paramagnetic resonance spectrum shows one electronic isotropic transition consisting of eight hyperfine lines at $g={4.278}_{5}\ifmmode\pm\else\textpm\fi{}0.001$ and $A=({97.7}_{9}\ifmmode\pm\else\textpm\fi{}0.2)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ ${\mathrm{cm}}^{\ensuremath{-}1}$. The interpretation of these results shows that the orbital reduction factor $k=0.89\ensuremath{-}0.85$. Both the optical and paramagnetic results indicate covalent bonding. The effect of charge transfer is (1) to shield the nuclear charge and (2) to normalize the wave functions. Both these effects results in smaller Coulomb energy, hyperfine structure, and spin-orbit coupling constant.No distortions of octahedral symmetry have been found to within ${10}^{\ensuremath{-}3}$ ${\mathrm{cm}}^{\ensuremath{-}1}$. The static Jahn-Teller effect which predicts such a distortion is, therefore, very small.