Lifetimes of some highly excited levels in the Pb-I spectrum measured by the hanle method

Natural lifetimes of some highly excited levels in the Pb-I spectrum have been measured by the zero field level crossing (Hanle) method. The levels were reached by optical excitation from the metastable 6p ^{2 3} P ₂ and 6p ^{2 3} P ₁ states, were a considerable population had been created by means of adc discharge in a Pb atomic beam. An atomic beam source producing atoms in metastable states is described. For the lifetimes τ of the investigated levels we find:τ(6p(1/2)6d ³ D ₁)=3.74(28) ns,τ(6p(1/2)6d ³ F ₂)=25.8(1.3) ns,τ(6p(1/2)6d ³ D ₂)=4.17_(?31) ^(?49) ns,τ(6p(1/2)6d ³ F ₃)=6.08(26) ns,τ(6p(3/2)7s)³ P ₂=5.85(27) ns. These results are compared with lifetimes derived from oscillator strengths given in the literature.     

Atomic fluorescence under monochromatic excitation: A level crossing experiment on the 6s6p 1P1 level of Ba I

A level crossing experiment on the 6s 6p ¹P₁ level of Ba I was performed using a narrow-band tunable dye laser and a strongly collimated atomic beam. The observed linewidth of the Hanle signal was minimally 45% of the width obtained with broad-band excitation.     

Laser spectroscopy of the 1s22s2p 3P2-3P1 transition in beryllium-like argon using the Oxford EBIT

A study of the 1s²2s2p ³P₂-³P₁ fine-structure transition in beryllium-like argon is planned on the Oxford electron beam ion trap (EBIT), using laser-induced resonance. This transition wavelength was measured previously as 594.373(4) nm, which is accessible using a dye laser. The ions are produced and excited in the EBIT and are confined during laser irradiation using the magnetic trapping mode. The ³P₂ level population is depleted by the laser and by subsequently monitoring the emitted fluorescence a laser resonance signal can be obtained. This revised version was published online in July 2006 with corrections to the Cover Date.     

Self-Alignment of 1P1-Levels of Alkaline-Earth Elements in a Hollow Cathode Discharge

The self-alignment of some ¹P¹- level of alkaline-earth elements in a hollow cathode discharge is investigated. The radiative lifetimes and the signal broadening constants are determined from the Hanle signals.     

Lifetime measurement of the (5d6p)3D3 state of barium by dye-laser spectroscopy

We have measured the radiative lifetime of the (5d6p)³D₃ state of barium by Hanle effect. This state was populated by cw dye laser excitation of an atomic beam of Ba in the metastable (5d6s)³D₃ state. The metastable state was populated by a dc discharge. With dye laser excitation, the shape of the Hanle effect curve is strongly modified due to optical pumping of the metastable state. A brief discussion of the expected and observed signal shapes is given. The radiative lifetime of the (5d6p)³D₃ state is measured to be τ = 10.2 ± 1.5 ns.     

Kr2F1 and Kr12 radiative lifetime measurements

Atomic krypton was excited in presence of SF₆ by an intense electron beam. The radiation emitted by the Kr₂F¹(²B₂→ A₁) transition was studied at 430 nm using time resolved spectroscopic techniques. The radiative lifetimes of Kr₂F¹ and of Kr¹₂ were found to be 200 ns and 270 ns respectively.     

Polarization effects in theP 3/2→P 1/2 fine structure transition cross section forK(4P)-He collisions

Taking the energy dependence of theP _3/2→P _1/2 fine structure transition cross section ofK(4P) colliding with He as an example, theoretical and experimental studies have been made to illustrate the large possibilities opened by the combination of beam experiments with laser excitation in the investigation of the atomic collisional processes. Explicit calculations, experimentally confirmed, show a strong dependence of the above process on the laser excitation schema for producing the excited stateK(4² P _3/2).     

Radiative lifetime measurements of odd-parity high-excited levels of Sn I by time-resolved laser spectroscopy

Natural radiative lifetimes of five higher-lying odd-parity levels 5p7s ³P₁^o, 5p5d ¹P₁^o, 5p6d ³F₂^o, ³D₁^o and ³F₃^o in neutral tin are measured by the time-resolved laser-induced fluorescence (TR-LIF) technique and the atomic beam method. All these lifetimes are not longer than 100 ns and they are found to be shorter than the lifetimes of even-parity levels in the same energy region. The results reported in this paper provide important transition parameters for highly-excited atomic Sn, which may be useful for theoretically calculating excited heavy atoms.     

A redetermination of the lifetime of the 4s 5s (3S1) level in Ca by high-rate electron—photon stepwise pulse excitation

The radiative lifetime of the 4s 5s (³S₁) level in Ca was measured using two-step excitation of atoms in a beam which traverses a cold-cathode Penning discharge, where, by electron impact the atoms are excited to the metastable 4s 5p (³P_{2, 1, 0}) states. Immediately thereafter, the beam is crossed with a pulse-modulated cw dye laser beam to populate the final state selectively. Using a pulse-modulation frequency of 0.5 MHz, a preliminary value of 12.4 ± 0.5 ns was obtained with a statistical error of 0.4%. The wide limits of systematic error reflect an assumed uncertainty in the excitation function and possible distortion in the fluorescence decay requiring further study.     

Measurement of the photoionization cross-section of the 3p 2P1/2, 3/2 excited levels of sodium

The photoionization cross-section and number density of the 3p ²P_1/2,3/2 excited levels of sodium have been measured as a function of the laser energy using two-step laser excitation in conjunction with a thermionic diode working in the space charge limited mode. Employing the saturation technique, the cross-sections for the 3p ²P_1/2 and 3p ²P_3/2 levels are determined as 2.16 (43) Mb and 3.74 (74) Mb respectively.     

Lifetime Measurements of the DΠ State of HfS and the bΠ1 State of HfO

Lifetime measurements of individual rotational levels in excited states of hafnium oxide and hafnium sulfide have been performed using population probing by resonant two-photon ionization in a molecular beam. For the b³Π₁ state of HfO rotational levels in the vibrational level v=0 were found to have lifetimes in the region 650-700 ns. For the D¹Π state of HfS rotational level lifetimes in the vibrational levels v=0 and v=1 were determined to be around 240 ns. The technique used here provides very accurate results and the uncertainty in the reported values is only about 2%. Possible sources of errors are examined. The absorption oscillator strengths from the ground state are calculated.     

Lifetimes and oscillator strengths in the triplet system of ZnI

Selective laser excitation was used to measure the radiative lifetimes of the ZnI triplet states 4sns ³ S ₁(n=5–7) and 4snd ³ D ₃,³ D ₂ and³ D ₁(n=4–6). These states were excited from the metastable 4s4p ³ P states, which were collisionally populated in an atomic beam. The values are compared with the results of other experimental methods (beam-foil, pulsed electron excitation, Hanle effect) and with theoretical calculations. The corresponding oscillator strengths are discussed with respect to the astrophysical determination of the Zn photospheric abundance.     

Measurement of the population of the4 P 5/2-state in Ar15+ by cascading processes

The population of the⁴ P _5/2-state in Ar¹⁵⁺-ions by cascading processes was measured. The corrected lifetime is (0.55±0.04) ns and is in very good agreement with the theoretical value of 0.56 ns. At a specific beam energy of 1.4 MeV/u the lifetime of the³ P ₂-state of Ar¹⁶⁺ is not influenced by cascading processes and is (1.44±0.08) ns. The energies of the³ P ₂ →¹ S ₀- and⁴ P _5/2 →² S _1/2-transitions are (3127.2±0.5) and (3090.0±0.7) eV, respectively.     

Excitation transfer and quenching induced in inelastic collisions of Zn 41P1 and 43P1 atoms

Quenching of excited Zn(4¹P₁) and Zn(4³P₁) atoms by collisions with Ar, N₂, H₂, CO and CO₂ has been investigated using methods of fluorescence spectroscopy. Mixtures of Zn vapor and quenching gases topped-up with Ar to maintain constant pressure were irradiated in a quartz cell with 2139 or 3076 Å resonance radiation which excited the 4¹P₁ or the 4³P₁ state, respectively. The resulting resonance fluorescence and sensitized fluorescence were monitored in relation to the gas density. Intensity measurements yielded the following cross sections Q_tot for the overall collisional deexcitation of the ¹P₁ state, Q₃ for quenching of the ³P₁ state, and Q₁₃ for ¹P₁→³P_J excitation transfer.For N₂: Q_tot = 26, Q₃ = 4.4, Q₁₃ = 5.8; for H₂: Q_tot = 12, Q₃ = 21, Q₁₃ < 5 × 10^-3; for CO: Q_tot = 28, Q₃ = 14, Q₁₃ = 17; for CO₂: Q_tot = 76, Q₃ = 23. All values are in Ų.     

Coherent spectroscopy of the 87RbFg=1→ Fe=0 closed transition

This paper has observed linewidth narrowing of dark states in rubidium cell by using the Hanle configuration. The reduction of the coherent resonance width under the transition of ^87Rb Fg = 1 → Fe = 0 is observed and the qualitative explanation about its mechanism is presented. Multiple subnatural width dips are obtained with a linearly polarized laser beam for the transitions of ^87Rb Fg = 1→Fe = 0, 1, 2. The feature of negative and positive slope, namely dispersionlike feature, is observed in the transmitted light.     

Isotopic shift in the3P1-3P0 Mg transition

High precision frequency measurements of the³ P ₁-³ P ₀ transitions have been performed for the three natural abundant Mg-isotopes in a metastable atomic beam. A second order hyperfine theory for two-electron atoms allows the determination of the centre-of-gravity for²⁵Mg and then the evaluation of the isotopic shift displacements. The high resolution frequency measurements (10^?8) show a noticeable departure of the total shift from a linear dependence with respect to the atomic mass.     

单口径相干合成系统激光光束的M2因子研究

单口径相干合成系统激光光束的光束质量是一个亟待解决的重要问题.基于二阶矩定义, 文中给出了单口径TEM₀₀, TEM₀₁及TEM₁₀两两相干光束M²因子的解析表达式, 并比较分析了束腰宽度、传输距离、振幅之比,以及源场位置矢量对相干光束M²因子的影响, 得到了诸如源场位置参量d₁<100λ时,各相干光束M²因子恒定,反之, 其随位置参量d₁的增大而增大等一些结论.最后,文章对两TEM₀₀模相干光束M²因子的 部分理论进行了实验验证.     

Measurement of the lifetime of the3 P 2 and4 P 5/2 states in Ar16+ and Ar15+

Promptly decaying levels in Li- and Be-like Ar could be identified in the delayed x-ray and electron spectrum in addition to the four known metastable (1s2s)¹ S ₀, (1s2s)³ S ₁, (1s2p)³ P ₂, and (1s2s2p)⁴ P _5/2 states in He- and Li-like systems. The states having lifetimes of about 10^?14s still contribute to the spectrum observed 10^?9s after the ions have passed a foil. This observation is explained by cascading processes from states of high principal quantum numbern≧14. The measured lifetime of the⁴ P _5/2 state subtracting the contribution of cascades is (0.594±0.016) ns and slightly larger than the theoretically predicted value of 0.563 ns. The³ P ₂ state is depopulated at short distances behind the foil by cascading processes. Its measured lifetime of (1.44±0.08) ns compares to a theoretical value of 1.48 ns.     

Isotopic shift measurement of the 3P1-3P0 fine structure transition of 24Mg and 26Mg

The isotopic frequency shift for the ³P₁-³P₀Δm_j=0 fine structure transition in the first metastable triplet of ²⁴Mg and ²⁶Mg is reported. The transitions corresponding to the two even isotopes of Mg have been observed via the fluorescence emission at 4571 Å of the intercombination line ³P₁-¹P₀ in a metastable atomic beam. The center frequencies have been measured with an uncertainty of 7×10^-9; the isotopic shift turned out to be 1706 ± 2 kHz.     

Properties of excited levels in102Rh by the102Ru(p,nγ) reaction

The level scheme of¹⁰²Rh has been investigated by the¹⁰²Ru(p, nγ) reaction in the proton energy range 3.1 MeV≦E _p≦6 MeV. Excitation functions,γ-γ coincidences and pulsed beam measurements have been performed and a level scheme including 33 excited states up toE _x≈650 keV has been constructed. Theγ-branchings of several levels have also been measured. The lifetimes of 5 excited states have been determined with the centroid-shift method:τ _m(105.2 keV)=(1.3±0.3) ns,τ _m(123.7 keV)=(0.6±0.3) ns,τ _m(178.6 keV)=(1.5±0.3) ns,τ _m(208.7 keV)=(0.5±0.3) ns,τ _m(359.6 keV)=(0.8±0.4) ns. Upper limits have been placed for the lifetimes of 20 other levels.