Radiative lifetimes in Ce I and Ce II

New radiative lifetime measurements based on time-resolved laser-induced fluorescence techniques are reported for 18 even-parity levels belonging to the 4f5d^26p and 4f ²5d ² configurations of Ce I and 6 even-parity levels belonging to the 5d^26s, 4f5d6p, and 4f6s6p configurations of Ce II. Free neutral and singly ionized cerium atoms were produced by laser ablation. The Ce I and Ce II levels range in energy from 26 545 to 29 102 cm^-1, and 42 573 to 48 152 cm^-1, respectively. Received 25 September 2002 Published online 4 March 2003     

High resolution measurements of the hyperfine structure in 10 levels of Tm I

High resolution laser spectroscopy has been performed on an atomic beam of thulium. Accurate values for the magnetic dipole coupling constants of 9 excited levels belonging to the 4f¹³ 6s6p and 4f¹²5d6s² configurations and of the metastable level at 8771 cm^?1 belonging to the 4f¹³6s² ground state configuration have been obtained.     

Hyperfine structure investigations in the configuration 4f 125d6s 2 of Tm I by laser-atomic-beam spectroscopy

High resolution laser-atomic-beam spectroscopy has been applied to study the hyperfine structure of transitions starting from metastable states of the configuration 4f¹²5d6s² of Tm I. Precise values for the hyperfine constants of 8 levels belonging to the configuration 4f¹²5d6s² and 9 levels belonging to excited odd levels have been determined.     

Isotope shift studies in UV lines of Sm I on FTS: level isotope shifts and configuration assignments of the energy levels of neutral samarium atom

Isotope shifts in 200 spectral lines of neutral samarium atom (Sm I) in the region of 355-455 nm (28160-21970 cm^-1) have been measured using a Fourier Transform Spectrometer. Isotope shift data in 187 spectral lines of Sm I are being reported for the first time. Level isotope shifts, of 119 high odd- and 7 low even-parity energy levels have been evaluated using present isotope shift data combined with the earlier available data. These values have enabled us to check the assignments to 4f ⁶6s6p and 4f ⁵5d6s ² configurations of the odd-parity levels made earlier on the basis of parametric calculations. For several levels, the reported compositions of the mixed configuration of type [4f ⁵(⁶H⁰, ⁶F⁰) 5d6s ² + 4f ⁶(⁷F) 6s6p(³P⁰)] have been interpreted with the help of our values. 20 unassigned energy levels have been uniquely assigned to 4f ⁵5d6s ² configuration. The present study provides values of the levels, which were tentatively assigned to 4f ⁵5d ²6s and 4f ⁶5d6p configurations. We could also identify 4f ⁶5d6p configuration for 12 unassigned levels.Received: 16 December 2004, Published online: 7 September 2004PACS: 31.30.Gs Hyperfine interactions and isotope effects, Jahn-Teller effect     

Blue laser cooling transitions in Tm I

We have studied possible candidates for laser cooling transitions in ¹⁶⁹Tm in the spectral region of 410–420 nm. By means of saturation absorption spectroscopy, we have measured the hyperfine structure and rates of two nearly closed cycling transitions from the ground state 4f¹³6s²(²F₀)(J_g=7/2) to upper states 4f¹²(³H₅)5d_3/26s²(J_e=9/2) at 410.6 nm and 4f¹²(³F₄)5d_5/26s²(J_e=9/2) at 420.4 nm and evaluated the life times of the excited levels as 15.9(8) ns and 48(6) ns, respectively. Decay rates from these levels to neighboring opposite-parity levels are evaluated by means of Hartree–Fock calculations. We conclude that the strong transition at 410.6 nm has an optical leak rate of less then 2×10^-5 and can be used for efficient laser cooling of ¹⁶⁹Tm from a thermal atomic beam. The hyperfine structure of two other even-parity levels, which can be excited from the ground state at 409.5 nm and 418.9 nm, is also measured by the same technique. In addition, we give a calculated value of 7(2) s^-1 for the rate of magnetic-dipole transition at 1.14 μm between the fine structure levels (J_g=7/2)↔(J’_g=5/2) of the ground state which can be considered as a candidate for applications in atomic clocks. PACS 32.70.Cs; 32.10.Fn; 32.80.Pj     

Tensor polarizabilities of levels of the configurations 4f 13 6s6p and 4f 12 5d6s 2 in thulium I

The level-crossing technique with parallel electric and magnetic fields was used to measure the tensor polarizabilities of six levels of the configuration 4f ¹³ 6s6p + 4f ¹² 5d6s ² in the Tm I-spectrum. Using intermediate coupling wave functions given by Camus and the experimental values of the tensor polarizabilities, the radial integrals for electric dipole transitions from levels of the configuration 4f ¹³6s6p + 4f ¹²5d6s ² to levels of the configuration 4f ¹³ 5d6s + 4f ¹² 6s ²6p have been determined. The results areI(4f ¹³6s6p,4f ¹³5d6s)=1.98(45)ea ₀ andI(4f ¹²5d6s ²,4f ¹²6s ²6p) = 0.88(25)ea ₀. A comparison between the experimental and the calculated values of the tensor polarizabilities shows an excellent agreement, provided that these radial integrals and the radial integrals for the electric dipole transitions to the ground state configuration 4f ¹³6s ² as determined by Wallenstein from lifetime measurements are used in the calculation, instead of radial integrals computed by Camus with Hartree-Fock wave functions.     

Observation and interpretation of the Tm<Superscript> 3+</Superscript> free ion spectrum

The emission spectrum of thulium produced by a vacuum spark source was observed in the wavelength range from 700 to 2320 ? on the 10.7 m normal-incidence vacuum ultraviolet spectrograph at the Paris-Meudon observatory. In the unknown spectrum of Tm IV, more than 760 lines have been identified for the first time as transitions between 157 levels of 4f¹¹5d, 33 levels of 4f¹¹6p, 9 levels of 4f¹¹6s and 10 levels of the 4f¹² ground configuration. A parametric interpretation of the levels has been carried out using the Cowan codes. Configuration interaction effects are discussed, in particular with the core-excited configurations 5p⁵4f¹³ and 5p⁵4f¹²5d. Radial Slater parameters derived from 4f¹² levels are larger than those pertaining to trivalent Tm ions in compounds. A selection of 105 prominent lines is given.     

Excitation of even levels of erbium atoms without a change in the number of 4<Emphasis Type="Italic">f</Emphasis> electrons

The excitation of even levels of erbium atoms by slow electrons that occurs without a change in the number of electrons in the 4f shell is experimentally studied. The levels investigated belong to the 4f ¹²6s7s, 4f ¹²5d6s, 4f ¹²6s6d configurations. The cross sections measured at an electron energy of 30 eV lie within the range (0.2–18) × 10^?18 cm².     

Sub-doppler laser cooling of thulium atoms in a magneto-optical trap

Sub-Doppler laser cooling in a magneto-optical trap for thulium atoms at a wavelength of 410.6 nm has been experimentally studied. Without any dedicated molasses period of sub-Doppler cooling, the cloud of 3 × 10⁶ atoms at a temperature of 25(5) μK was observed. The measured temperature is significantly lower than the Doppler limit of 240 μK for the cooling transition at 410.6 nm. The high efficiency of the sub-Doppler cooling process is due to a near-degeneracy of the Landé g-factors of the lower 4f ¹³6s ² (J = 7/2) and the upper 4f ¹²5d _3/26s ² (J = 9/2) cooling levels.     

Recent hyperfine structure investigations in the configurations 4f 136s 2, 4f 136s6p,and 4f 125d6s 2 of Tm I

By use of optical hyperfine structure investigations in the Tm I spectrum theA- values of 20 levels of the configurations 4f ¹³ 6s 6p and 4f ¹² 5d 6s ² and theA-value of 4f ¹³ 6s ^{2 2} F _5/2 were determined very accurately. These data and tenA-factors from former experiments are used for theoretical calculations. 30A-factors have been interpolated from intermediate coupling wave functions using 9 effective mono-electronic parameters. The r.m.s. deviation between experimental and theoreticalA- values amounts to 0.5 10^?3 cm^?1 and represents 3/100 of the average value of the measuredA-factors.     

Lifetime measurements and calculations in La I

Radiative lifetime measurements have been performed, with a time-resolved laser-induced fluorescence technique, for 20 odd-parity levels of La I belonging to the configurations 5d ²6p, 5d6s6p and 4f5d6s. The new results are compared with the few experimental data available in the literature and with theoretical calculations including configuration interaction effects. The agreement theory-experiment is generally satisfying but discrepancies are observed for some levels emphasizing the difficulty to get a reliable theoretical model in such a heavy and complex neutral element.Received: 26 January 2004, Published online: 22 June 2004PACS: 32.70.Cs Oscillator strengths, lifetimes, transition moments - 42.62.Fi Laser spectroscopy     

Doppler limited laser spectroscopy on hafnium lines. Part II: Hyperfine structure of odd-parity levels

The hyperfine structure of selected odd-parity levels of the configurations 5d6s ^26p and 5d ^26s6p of I was studied in 10 lines lying in the red spectral region. Hyperfine spectra were obtained by the method of laser induced fluorescence in the plasma of a liquid nitrogen cooled hollow cathode discharge. The observed hyperfine structure constants A and B, together with results from earlier studies were analyzed by means of a parametric method. The interpretation has been carried out based on a refined multiconfigurational fine structure calculation including the main Rydberg series configurations mutually interacting. The set of fine structure parameters as well as the leading eigenvector percentages of levels relevant for this paper are given. The following single electron hfs parameters were deduced for : , ,, for the lowest configuration. Received: 16 November 1998 / Received in final form: 5 February 1999     

Relaxation dynamics of excited states of Tm3+ in SrGdGa3O7 crystals activated with Tm3+ and Tb3+

3 H₄ and ³F₄ states of Tm in SrGdGa₃O₇ single crystal was evaluated. Tm-Tb energy transfer reduces effectively the lifetime of terminal level in a potential ³H₄-³F₄ laser transition but gives rise to parasitic nonradiative relaxation of the initial ³H₄ level. SrGdGa₃O₇ crystal single doped with thulium possesses combination of properties advantageous for laser oscillations near 1.9 μm, namely high rate of cross relaxation process leading to population buildup on the initial ³F₄ level and relatively high crystal field splitting of the ground ³H₆ level. Received: 25 April 1996/Revised version: 10 October 1996     

Space- and time-resolved investigation of gain lines in Na-like copper

We report space- and time-resolved measurements of the gain coefficient for four gain lines in sodium-like copper. The lines investigated include the twon = 1 transitions 5g–4f and 5f–4d at 11.1 nm and 10.3nm and the twon = 2 transitions 6g–4f and 6f–4d at 7.2 nm, and 6.9 nm. The investigations were carried out for four irradiation intensities from 4 × 10¹² W/cm² to 3 × 10¹³ W/cm² using the Asterix IV high-power iodine laser at Garching (wavelength 1.315 µm, pulse duration 450 ps).The main results may be summarized as follows: On varying the laser intensity it was found that the highest values of the gain could be seen at an irradiation of 8 × 10¹² W/cm². For then = 1 lines the spatial maximum of the gain occurred at a distance of 300 µm from the target, and for then = 2 lines at 200 µm. The temporal gain maximum occurred at a time of 1.8 ns after the pulse maximum. The gain values range up to 2.6 cm^–1.Dedicated to the memory of the late Prof. Shi-shen Chen, who contributed to the early phase of this work     

Spontaneous Raman scattering upon resonant three-photon ionization of a samarium atom

The manifestation of spontaneous Raman scattering upon the three-photon ionization of a samarium atom has been investigated. The dependence of the Sm⁺ yield on the laser frequency, along with the peaks due to the two-photon excitation of bound states from different levels of the 4f ⁶6s ^{2 7} F ground term, exhibits a strong peak due to single-photon excitation of the 4f ⁵5d6s ^{2 7} D°₃ state from the 4f ⁶5d6s ⁹ H ₂ excited state. The 4f ⁶5d6s ⁹ H ₂ state was populated as a result of spontaneous Raman scattering. The large amplitude of the observed peak indicates a high efficiency of this process. The estimations performed indicate that the probability of resonant ionization through an excited state populated due to spontaneous Raman scattering can be comparable with the probability of three-photon ionization through the two-photon intermediate resonance. The necessary conditions for implementing this channel of resonant three-photon ionization are formulated.     

Excitation of transitions terminating at the 4f 12(3 H)5d6s 2(6,3/2) levels of the thulium atom

The excitation of transitions terminating at the 4f ¹²(³ H)5d6s ²(6,3/2) levels of the thulium atom are studied experimentally. Seventy-five cross sections of the TmI spectral lines are measured at an excitation electron energy of 50 eV. Five optical excitation functions are recorded in the electron energy range of 0–200 eV.     

Effects of magnetic anisotropy and exchange in Tm2Fe17

Neutron diffraction experiments have been carried out to study the magnetocrystalline anisotropy of two (2b and 2d) Tm sublattices and four (4f, 6g, 12j, and 12k) Fe sublattices in ferrimagnetic compound Tm₂Fe₁₇ (space group P6₃/mmc). We have determined the temperature dependence of the magnitude and orientation of magnetization for each of the thulium and iron sublattices in the range (10?C300) K. A spontaneous rotation (at about 90 K) of the Tm and Fe sublattice magnetizations from the c-axis to the basal plane is accompanied by a drastic change in the magnetization magnitude, signifying a large magnetization anisotropy. Both Tm sublattices exhibit an easy-axis type of the magnetocrystalline anisotropy. The Fe sublattices manifest both the uniaxial and planar anisotropy types. The sublattice formed by Fe atoms at the 4f position reveals the largest planar anisotropy constant. The Fe atoms at the 12j position show a uniaxial anisotropy. We find that the inelastic neutron scattering spectra measured below and above the spin-reorientation transition are remarkably different.     

Experimental and theoretical lifetimes in Yb III

Lifetimes of three levels belonging to the configuration 4f ¹³5d with J = 1 in Yb III have been measured for the first time using the time-resolved laser-induced fluorescence method. Experimental transition probabilities have been deduced for the transitions between the levels studied and the ground state. The comparison of the experimental lifetimes with theoretical data, deduced within the relativistic Hartree-Fock (HFR) approach, underlines the dramatic importance of an adequate consideration of core-polarization effects in the theoretical model and the sensitivity of one of the lifetime values to small correlation effects. Received 2 April 2001     

Electronic structure of the surface of rare Earth metals

A qualitative model describing the surface of rare earth metals with an uncompleted 4f electron shell (Ce-Yb) and the process of thermal evaporation from this surface is proposed. The model is based on a correlation established between the energies of the lowest-lying levels of the 4f^N?15d6s² configuration and the temperatures of equal saturated-vapor pressures of these metals.     

Spectroscopic characteristics of YSGG:Cr,Ho, YSGG:Cr, Tm and YSGG:Cr,Tm,Ho

In this paper some spectroscopic properties of Y₃Sc₂Ga₃O₁₂ (YSGG):Cr,Ho, YSGG:Cr,Tm and YSGG:Cr,Tm,Ho are presented. The three lowest energetic manifolds of Ho³⁺ and Tm³⁺ in YSGG have been determined at 10 K. Time-resolved fluorescence build-up and decay of the laser active ions was measured in three crystals with different dopant concentrations. The transitions investigated were⁵I₇ ⁵I₈ for Ho³⁺ near 2000 nm and³H₄ ³H₆ for Tm³⁺ near 1800 nm. The data found on time-resolved fluorescence and energy level positions are useful for the discussion of the energy transfer characteristics of the system.