Precision frequency measurement of visible intercombination lines of strontium

We report the direct frequency measurement of the visible 5s(2) 1S0-5s5p 3P1 intercombination line of strontium that is considered a possible candidate for a future optical-frequency standard. The frequency of a cavity-stabilized laser is locked to the saturated fluorescence in a thermal Sr atomic beam and is measured with an optical-frequency comb generator referenced to the SI second through a global positioning system signal. The 88Sr transition is measured to be at 434 829 121 311 (10) kHz. We measure also the 88Sr-86Sr isotope shift to be 163 817.4 (0.2) kHz.     

Ratio of intercombination to resonance line intensities for He-like oxygen ions in TFR tokamak plasmas

The ratio of intercombination to resonance line intensities has been measured in TFR tokamak plasmas, using space-and time-resolved soft X-ray spectroscopy. The experimental ratio values are compared to those obtained with available theoretical atomic models.     

The absorption spectrum of B II,C III,N IV and O V beryllium-like ions

Energy terms, dipole oscillator strenghts and photoionization cross sections from the ground state are calculated for beryllium-like ions. Autoionizing state transition energies and line widths for the ¹P⁰ resonances in the continuum are also obtained. The configuration interaction method for initial and final states is used, and the atomic orbitals are generated through angular- momentum-dependent, scaled Thomas-Fermi-Dirac potentials.     

4s-4p transitions including intercombination lines in Zn-like Zr XI,Nb XII and Mo XIII

Energy levels of the configurations 4s4p and 4p² in zink-like Zr, Nb and Mo have been derived through the identification of spectral lines emitted from laser-produced plasmas. Intercombination lines in the 4s4p-4p² transition connect the singlet and triplet systems. Wavelengths for spinforbidden and magnetic quadrupole ground term combinations have been derived from the energy levels.     

Atomic lifetimes and transition probabilities in boron-like (Na VII) and beryllium-like (Na VIII) sodium ions

Spectra and decay curves of boron-like (Na VII) and beryllium-like (Na VIII) sodium ions produced by beam-foil excitation have been recorded in the 30-60 nm spectral range and the radiative lifetimes of seven n=2 levels have been measured. The experimental results are compared with the available theoretical values and with new results obtained in the framework of two theoretical approaches: the Relativistic Hartree-Fock approximation and the Multiconfiguration Dirac-Fock method. Corroborated by the fair agreement of the new theory data with experiment, a new set of accurate transition probabilities for the 2s^22p-2s2p² and 2s2p²-2p³ transitions of Na VII is presented.     

Saturation-dips in the weak calcium intercombination line

Lamb-dips have been observed in the weak calcium intercombination line by monitoring resonance fluorescence in an atomic beam excited by light of a stabilized cw dye laser inside or outside the laser cavity. A highly sensitive detection scheme is described.     

Radiative decay of the 2 3Po0 level of beryllium-like ions

A Z-expansion technique is used to estimate the radiative rate for the $\text{2}{}^3\text{P}{}^{\mathrm{<mtext>o</mtext>}}{}_0\text{?2}{}^1\text{S}{}_0$ transition in berryllium-like ions. It is concluded that the transition rate is so slow as to be unobservable.     

A nonlinear electrodynamical shift of spectral lines in the hydrogen atom and hydrogen-like ions

The shift of spectral lines in the hydrogen atom and hydrogen-like ions is calculated using Born-Infeld nonlinear electrodynamics. The formulas obtained show that the position of the s levels in hydrogen-like ions and muonic atoms should be most strongly affected by the nonlinearity of electrodynamics of vacuum.     

锶原子互组跃迁谱的实验研究

观测了热原子束中锶原子(5s²)¹S₀—(5s5p)³P₁ 互组跃迁的荧光谱和饱和荧光谱, 实验测定了不同的参量下 ⁸⁸Sr(5s²)¹S₀—(5s5p)³P₁ 互组跃迁荧光谱. 研究结果表明: 不同的实验参数(温度、激光光强、激光扫描频率)对谱线有较大的影响, (5s5p)³P₁态的长寿命特点导致谱线强度随激光扫描频率呈倒数关系变化; 由于Doppler增宽, 渡越增宽等因素的影响, 谱线线宽远大于其自然线宽且随激光扫描频率呈正比关系变化.     

Relativistic correlation correction to the binding energies of the ground configuration of beryllium-like, neon-like, magnesium-like and argon-like ions

Total electronic correlation corrections to the binding energies of the isoelectronic series of beryllium, neon, magnesium and argon, are calculated in the framework of relativistic multiconfiguration Dirac-Fock method. Convergence of the correlation energies is studied as the active set of orbitals is increased. The Breit interaction is treated fully self-consistently. The final results can be used in the accurately determination of atomic masses from highly charged ions data obtained in Penning-trap experiments.     

The spectral lines of highly charged gold ions

Extreme ultraviolet spectra of highly charged gold were produced with an electron beam ion trap at the University of Electro-Communications, Tokyo. The X-ray spectra (3240–3360?eV) of Au with well-defined maximum charge states ranging from Cu- to Se-like ions were recorded. Guided by configuration interaction calculations, the strongest 3d–5f transitions have been well defined.     

Density dependence of solar emission lines of carbon-like ions

Steady state level population of 15 levels of carbon-like ions: NeV, MgVII, SiIX, and SXI have been computed as a function of electron density and temperature taking into account collisional processes and spontaneous radiative ones. Photo-excitation among the ground term levels has also been considered. Knowing the level density, line intensities have been computed as a function of electron density and temperature. This study indicates that line intensity ratios for carbon-like ions can be used as a diagnostic in the determination of these two parameters of the solar plasma. The resulting line fluxes from these ions at earth distance are compared with observation. Presented at the 5th Annual Radio and Space Sciences Symposium, National Physical Laboratory New Delhi, January 1979.     

A review of optically pumped far-infrared laser lines from methanol isotopes

The technique of optical pumping in polar molecules is the most efficient for Far-Infrared (FIR) laser generation, providing also a versatile and powerful tool for molecular spectroscopy in this spectral region. Methanol (CH₃OH) and its isotopic varieties are the best media for optically pumped FIR laser, with over thousand lines observed, and the most widely used for investigations and applications. In this sense, it is important organize and make available catalogues of FIR laser lines as complete as possible. Since the last critical reviews of 1984 [1] on methanol and its isotopic varieties [2,3,4], over hundred papers have been published dealing with hundreds of new FIR laser lines. In 1992 a review of FIR laser lines from CH₃OH was presented [5]. In this communication we extend this work to the other methanol isotopes, namely CH₃OD, CD₃OH, CD₃OD,¹³CH₃OH,¹³CD₃OH,¹³CD₃OD, CH₃ ¹⁸OH, CH₂DOH, CHD₂OH and CH₂DOD.Work supported by FAPESP, CNPq, FAEP-Brasil, and CNR-Italia     

Plasma satellites of X-ray lines of ions in a picosecond laser plasma

We present the results of our measurements of the spectra for multicharged ions in a plasma produced by moderately intense (about 10¹⁷Wcm^?2) picosecond laser pulses. They suggest the existence of intense plasma oscillations with a frequency appreciably lower than the frequency of the laser radiation. The observed spectrum for the plasma satellites of the Lyman Ly_α doublet of the hydrogenic F IX ion in a dense plasma was modeled theoretically. The resulting doublet profile was shown to have a complex structure that depends non-trivially both on the plasma density and on the frequency and amplitude of the plasma oscillations. The positions of the satellites and their separations allowed them to be associated with intense electrostatic oscillations with an amplitude of (4–6)×10⁸Vcm^?1 and a frequency near (0.7–1)×10¹⁵s^?1. Assuming the oscillation frequency to be determined by the strength of the magnetic field B generated in the plasma, we obtained an estimate of B that is in reasonable agreement with other measurements and estimates of this quantity. Our theoretical analysis allowed explanation of the emission spectra observed when flat fluoroplastic targets were heated by intense picosecond laser pulses.     

Radiative de-excitation of the 1s22s3 p 3P0 level in beryllium-like ions: A competition between an E2 and a two-electron one-photon E1 transition

I have performed a complete Multi-Configuration Dirac-Fock calculation of the radiative de-excitation of the 1s²2s3p³P₀ level in beryllium-like ions. Initial and final wave functions are fully optimized, and include valence and core polarization correlation (Coulomb and Magnetic). Non-orthogonality between initial and final state spin-orbitals is exactly accounted for. I show that the main mode of de-excitation of the 1s²2s3p³P₀ level at high Z is an E2 transition to the 1s²2s2p³P₂ and that a two-electron one-photon E1 transition to the 1s²2p^{2 3}P₁ plays an important role at low Z. The latter transition appears to be the difference of two large matrix elements which cancel almost exactly and thus has a very complicated Z dependence, which is studied in the present paper. This revised version was published online in August 2006 with corrections to the Cover Date.     

The escape of positive ions from quantized vortex lines in superfluid helium

We have observed trapping of positive ions by quantized vortex lines in superfluid helium. The thermally activated escape rate has been measured as a function of temperature and electric field and is compared with existing theories and a model calculation.     

Astrocyte and ions metabolism during epileptogenesis:A review for modeling studies

As a large group of cells in a central nervous system, astrocytes have a great influence on ion and energy metabolism in a nervous system. Disorders of neuronal ion and energy metabolism caused by impaired astrocytes play a key role in the pathogenesis of epilepsy. This paper reviews the existing computational models of epileptogenesis resulting from impaired astrocytes and presents several open perspectives with regard to ion and energy metabolism-induced epileptogenesis in a neuron-astrocyte-capillary coupled model.     

Stark broadening of lines from multiply-charged carbon ions in a high-density arc plasma

Profiles of C(III) and C(IV) lines emitted in the VUV and visible regions from a pulsed arc (N_e=1.5×10¹⁸ cm^-3, T_e=5.3×10⁴K) have been measured with time resolution. The experimental results are in satisfactory agreement with the predictions of electron impact theory for (3-3) and (3-4) transitions for which the energy separation between the upper level and the nearest perturbing level is smaller than the electron thermal energy. For lines from (2-2) transitions for which the plasma is optically thick, damping constants determined experimentally agree with theoretical values within a factor of two.     

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 1 S 0-3 P 1 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:LiNbO 3 (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.