Accurate time-resolved laser spectroscopy on lithium atoms

The lifetime of the lithium 2p ² P states has been measured with high accuracy using the delayed coincidence technique with a continuous mode-locked dye laser as the source of the excitation light. The value 27.22 (0.20) ns was obtained. In addition, the hyperfine structure of the⁷Li 2p ² P _3/2 state, which can normally scarcely be resolved, has been studied by recording the slow quantum beats at zero field and the very fast beats in the Paschen-Back regime. New accurate values for the²³Na 3p ² P _3/2 state hyperfine structure constants are also presented.     

Determination of radiative lifetimes in neutral nitrogen using short laser pulses from a distributed feedback dye laser

Radiative lifetimes were determined for two short-lived states in neutral nitrogen. Following photo-dissociation and two-photon excitation employing the same UV source, excitation to higher states was performed with a distributed feedback dye laser (DFDL). The lifetimes were found to be τ(2p ²4d ⁴ D _7/2)=17(3) ns and τ(2p ²5s ⁴ P _5/2)=22(3) ns.     

Accurate time-resolved laser spectroscopy on sputtered metal atoms

The delayed coincidence photon counting technique, employing a picosecond tunable dye laser as an excitation source, has been used for accurate determinations of radiative lifetimes of excited states. Excitation from meta-stable states of sputtered atoms was employed. We obtained for Cu: τ(3d ¹⁰ 4p ² P _1/2 = 7.27(0.06) ns, τ(3d ¹⁰ 4p ² P _3/2) = 7.17(0.06) ns and for Fe: τ(3d ⁷ 4p y ³ F ₂)= 9.06(0.16) ns, τ(3d ⁷ 4p y ³ F ₃) = 9.06(0.13) ns and τ(3d ⁷ 4p y ³ F ₄) = 9.11 (0.16) ns. Also, the ability of this technique to record quantum beats at frequencies up to 1 GHz is demonstrated.     

Lifetime measurements of the 2p 3d 3 D 1, 2, 3 0 and 2p 3d 1 P 1 0 levels in NII by beam-foil-laser spectroscopy

Accurate lifetimes measured by means of the cascade-free method based on laser excitation of a fast ion beam preexcited in a carbon foil are reported for four 2p 3d levels in NII. The lifetime results are: τ(2p 3d ³ D ₁ ⁰ )=0.209±0.007 ns, τ(2p 3d ³ D ₂ ⁰ )=0.219±0.007 ns, τ(2p 3d ³ D ₃ ⁰ )=0.217±0.005 ns, and τ(2p 3d ¹ P ₁ ⁰ )=0.410±0.017 ns. These results are compared to theoretical and experimental lifetimes reported previously.     

Determination of radiative lifetimes in the 3snp 1 P 1 sequence of Mg I using time-resolved VUV laser spectroscopy

The radiative lifetimes of the states in the (n=5–8) 3snp ¹ P ₁ sequence of neutral magnesium were investigated using time-resolved laser-induced fluorescence. Excitation from the 3s ^{2 1} S ₀ ground state was performed using VUV radiation, which was produced by resonant sum-difference frequency mixing in a krypton gas cell. We find τ(n=5): 54(3) ns, τ(n=6): 140(10) ns, τ(n=7): 290(20) ns. τ(n=8): 475(40) ns. These results were found to be in fair agreement with a Multi Configuration Hartree-Fock (MCHF) calculation.     

Natural radiative lifetimes in the2 S 1/2 and2 D 3/2, 5/2 sequences of neutral copper

Natural radiative lifetimes have been measured of the 3d ¹⁰ ns ² S _1/2 (n=6?10) and of the 3d ¹⁰ nd ² D _{3/2, 5/2} (n=5?9) sequences by using two step excitation of copper atoms in an atomic beam. The states investigated were populated by the light from two pulsed dye lasers pumped by the same Nd:YAG laser. The lifetimes of the² D sequence increase regularly with increasing principal quantum number. This is not the case for the² S series, because of configuration interaction in the² P series. In addition the lifetime of the 3d ¹⁰5p ² P _3/2 state has been measured together with its branching ratio.     

Fluorescence lifetimes and predissociation of the A3Π state of SH+

The high frequency deflection (HFD) technique has been used to obtain fluorescence lifetimes of the SH⁺ A³Π state. The A³Π?X³∑^? electronic transition moment function has been calculated with the complete active space SCF(CASSCF) method. Radiative lifetimes calculated with this transition moment function are compared with measured lifetimes and found to be in good agreement (τ_exp(v′=0)=1.4±0.3 µs; τ_calc=1.6 µs). Deviations between measured and calculated lifetimes forv′=0,J′ ≥ 15 andv′=1,J′=1?7 are interpretated as due to a predissociation caused by a repulsive⁵∑^? state. A simple model, based on a perturbation approach to the predissociation, is used to obtain quantitative estimates of predissociation rates. These calculated rates are in reasonable agreement with the predissociation rates that are inferred from the measured and calculated lifetimes.     

Quadrupole moments of radium isotopes from the 7p 2 P 3/2 hyperfine structure in Ra II

The hyperfine structure and isotope shift of^221–226Ra and^212,214Ra have been measured in the ionic (Ra II) transition 7s ² S _1/2–7p ² P _3/2 (λ=381.4 nm). The method of on-line collinear fast-beam laser spectroscopy has been applied using frequency-doubling of cw dye laser radiation in an external ring cavity. The magnetic hyperfine fields are compared with semi-empirical and ab initio calculations. The analysis of the quadrupole splitting by the same method yields the following, improved values of spectroscopic quadrupole moments:Q _s (²²¹Ra)=1.978(7)b,Q _s (²²³Ra)=1.254(3)b and the reanalyzed valuesQ _s (²⁰⁹Ra)=0.40(2)b,Q _s (²¹¹Ra)=0.48(2)b,Q _s (²²⁷Ra)=1.58(3)b,Q _s (²²⁹Ra)=3.09(4)b with an additional scaling uncertainty of ±5%. Furthermore, theJ-dependence of the isotope shift is analyzed in both Ra II transitions connecting the 7s ² S _1/2 ground state with the first excited doublet 7p ² P _1/2 and 7p ² P _3/2.     

Direct measurement of the radiative lifetime of the A2Σ+(υ′ = 0, K′ = 1, J′ = 32) state of OH and OD

The radiative lifetime of the A²Σ⁺(υ′ = 0, K′ = 1, J′ = 3/2) state of OH and OD has been directly measured by following the decay of fluorescence excited by light from a frequency doubled dye laser. Stern-Volmer extrapolation of the results to zero pressure gave τ(OH) = 788 ± 13 ns and τ(OD) = 754 ± 12 ns.     

The 3d states of23Na and7Li: determination of unresolved hyperfine splittings and radiative lifetimes

The electronic transitions from the ground state to the 3d states have been studied for²³Na and⁷Li atoms by two-photon Doppler-free laser spectroscopy. The positions of the resonances are used to determine the unresolved hyperfine structure of the 3d states from which the magnetic-dipole hyperfine interaction constantsA are derived. The results for theA factors are:A(3d ² D _3/2;²³Na)=+527(25) kHz;A(3d ² D _5/2;²³Na)=+108.5(2.4) kHz;A(3d ² D _3/2;⁷Li)=+843(41) kHz;A(3d ² D _5/2;⁷Li)=+343.6(1.0) kHz. For the fine structure intervals fs of the 3d doublets we obtain: fs(3d Na)=-1 494 444(44) kHz and fs(3d Li)=+1 083 936(60) kHz. The linewidths of the resonances are evaluated with respect to the natural lifetimes of the 3d states. For Na the result is τ(3d Na)=19.27(23) ns.     

Generation of harmonic radiation by helium atoms in intense laser pulses

Measurements of natural radiative lifetimes in atomic tellurium in the 5p ³7p configuration are reported. Two-step laser excitation was applied on tellurium vapour in a cell that was differentially heated and pumped through a capillary. The decay of the fluorescence signal was recorded at different vapour pressures. The following four radiative lifetime values were obtained: 7p ⁵ P ₁: 128(11) ns, 7p ⁵ P ₂: 99(8) ns, 7p ³ P ₁: 82(10) ns and 7p ³ P ₂: 124(8) ns.     

Hyperfine structure of N2 (B 3Π g andA 3Σ u + ) from LIF measurements on a beam of metastable N2 molecules

Crossing an intense beam of nitrogen molecules in the metastable N₂(A) state with the beam from a CW dye laser, laser-induced fluorescence was observed in the first positive system of N₂,B ³Π _g ?A ³Σ _u ⁺ . About 300 lines of the (10, 6) band were studied at sub-Doppler resolution (15 MHz FWHM). From the well-resolved hyperfine structure of the lines, the hyperfine splittings of both the upper and the lower state were derived for a range of rotational quantum numbers up toJ=12. Using multiple independent determinations of each splitting via lines belonging to different branches, the hfs could be measured with an accuracy of about 2 MHz. Fitting known theoretical expressions for the hyperfine energies to the data, the following nuclear coupling constants were obtained (in MHz): For theA state,v=6: α=12.86, β=?11.40,e ² q ₀ Q=?2.5. For theB state,v=10:K ₁₁=86.46,D ₁₁=12.67,D _1?1=?44.64,G ₁₁=69.18,Q ₁₁=0.64,Q _1?1=1.38. The hfs is mostly due to nuclear magnetic dipole interactions. For theA state the results are essentially in agreement with hfs constants derived from RF resonance experiments, but are superior as regards the data fit over the entireJ range covered. For theB state, the results are new and are interpreted in terms of a simple LCAO model. The Fermi contact coupling constant is in good agreement with unpublished SCF results by V. Staemmler. The striking dependences of the hfs splitting on the fine structure levels, Λ sublevels and onJ are explained both quantitatively and in terms of vector models.     

Hyperfine structure of the resonance lines of53Cr and lifetimes of some excited states of the Cr I spectrum

The hyperfine structure of the⁵³Cr resonance linesa ⁷ S ₃ ?z ⁷ P _2,3,4 has been investigated by means of laser saturation spectroscopy. By comparison of the experimental signal curves with theoretically computed spectra the hitherto unknown sign of the magnetic hyperfine coupling constant in thea ⁷ S ₃ ground state of⁵³Cr could be determined unambigiously to be negative. Further the signs of the hfs coupling constants in thez ⁷ P states — so far only evaluated by theoretical reasoning — could be confirmed. Additionally the lifetimes of the statesz ⁷ P,z ⁵ P,f ⁷ D,z ⁵ F,e ⁷ D ₅ andy ⁵ P ₃ in the Cr I spectrum have been determined from the fluorescence decay after pulsed laser excitation.     

Hyperfine structure of the 33 P state of3He and isotope shift for the 23 S-33 P 0 transition

The hyperfine structure of the³He 1s 3p ³ P state and the³He-⁴He isotope shift is determined by high precision measurements of the 1s2s ³ S ₁-1s 3p ³ p ³ P _J transition frequencies near 389 nm. A direct frequency measurement is made without the need for wavelength calibration by tuning a single laser to the atomic frequency, and using a novel heterodyne method to observe beat frequencies with a stable reference laser. A fit to a theoretical model of hyperfine structure is used to determine the hyperfine shifts. Additional off-diagonal mixing effects are investigated to resolve a possible systematic discrepancy in the hyperfine intervals. The final isotope shift without hyperfine structure of 42184308±165 kHz is used to deduce an rms nuclear charge radius for³He of 1.956±0.042 fm. This is in good agreement with other values obtained from atomic isotope shift measurements, and a recent theoretical value of 1.958±0.006 fm. The present result helps to resolve substantial differences in the³He nuclear radius derived from electron-nuclear scattering measurements, and it provides a significant test of the nuclear three-body problem.     

A test of the accuracy of atomic-beam laser spectroscopy

To determine the accuracy to which hyperfine splittings can be measured using a cw dye laser with rf sideband tuning, a series of atomic beam experiments with⁵⁹Co was performed. One hyperfine splitting of the first excited metastable atomic state was measured and compared with the results for the same splitting from magnetic rf resonance experiments. The uncertainty with the methods applied was found to be about 0.05 to 1% of the experimental linewidth in general; it is ±20 kHz or ±0.05% of the linewidth in the present Co experiment. The hyperfine splitting constants of the 3d ⁸ 4p ² F _7/2 state were found to beA=419.3(9) MHz,B=?77(17) MHz.     

Oscillator strengths for resonance transitions in neutral selenium and tellurium derived from time-resolved laser spectroscopy

We have measured radiative lifetimes for selenium and tellurium resonance levels by using short pulse laser excitation in differentially heated resonance cells. We obtained τ(³ S ₁ Se I)=2.9(5) ns and τ(³ S ₁ Te I)=3.1(5) ns, which together with branching ratio values given by Ubelis and Berzinsh yield the absorption oscillator strengthf _abs(Se I, 196.0 nm)=0.074(16) andf _abs(Te I, 214.3 nm)=0.098(17).     

Hyperfine structure and isotope shift of some even parity levels in the YbI spectrum

Using laser induced fluorescence spectroscopy the hyperfine structure of the even parity levels 4f ¹⁴6s6d ³ D ₁, 4f ¹⁴ 6s8s ³ S ₁ and 4f ¹³ 5d6s6p (7/2, 5/2)J=1,2,3 as well as of the odd parity level 4f ¹⁴ 6s6p ³ P ₂ in neutral ytterbium has been investigated. The isotope shift of the transitions 4f ¹⁴6s6p ³ P ₀ → 4f ¹⁴ 6s6p ³ D ₁ and 4f ¹⁴ 6s6p ³ P ₂ → 4f ¹⁴ 6s8s ³ S ₁, 4f ¹³ 5d6s6p (7/2, 5/2)J=1,2,3 could be measured with high accuracy. The results for the 4f ¹⁴ 6s6p ³ D ₁ level show a considerable influence of second order effects of the hyperfine interaction. The isotope shifts of the 4f ¹⁴ 6s8s ³ S ₁ and 4f ¹³ 5d6s6p (7/2, 5/2)J=1 levels indicate a possible configuration mixing for these levels.     

Heterodyne laser spectroscopy of lithium ions: 23 P fine and hyperfine structure of7Li+

The fine structure (fs) splittings in the 1s2p ³ P _J=1,2,0 multiplet of the helium-like⁷Li⁺ ion were measured with a laser spectrometer. The results with 3σ errors are: Δv ₀₁ (³ P ₀,F=3/2?³ P ₁,F=5/2)=152081.6(2.0) MHz and Δv ₀₂ (³ P ₀,F=3/2?³ P ₂,F=7/2)=82704.3(1.9) MHz. Combining the new precise fs measurements with earlier hyperfine structure (hfs) results from laser-microwave spectroscopy provided improved fs constants:D ₁=?155709.0(2.1) MHz,D ₂=?93049.2(2.0) MHz, and hfs constants:A _c =3679.0(6) MHz,A ₀=51.0(4) MHz, andA _d =?11.3(1) MHz, thus allowing for a stringent test of available theoretical data. The spectroscopic method used in this work opens up the possibility of determining Li⁺, 2³ S?2³ P absolute transition frequencies with a precision of ～2·10^?9.     

Lifetime measurements and stark mixing of autoionizing Cu I-states

Using a combination of collisional and laser excitation the lifetimes of 17 autoionizing Cu I states in the configurations 3d ⁹ 4s 6s and 3d ⁹ 4s4d were measured. The lifetimes are in the range of 1–50 ps and depend strongly on the coupling properties, the mixing with different configurations, and the radial integrals of the discrete with the continuum states. For the level 3d ⁹ 4s 4d ⁴ S _3/2 the influence of an electric field via Stark mixing of 3d ⁹ 4s 5p ⁴ P _1/2 on the autoionizing rate was investigated. The experimental values are compared with theoretical results which follow from ab initio calculations for the transition probabilities and least square fit values deduced from the experimental positions. Good agreement is found only for theJ=3/2 levels of both configurations 3d ⁹ 4s 4d and 3d ⁹ 4s 6s.     

Hyperfine structure constants of the CaII states 4s 2 S 1/2 and 4p 2 P 1/2, 3/2 and the nuclear quadrupole moment of43Ca

The hyperfine structure splittings of the 4s ² S _1/2 → 4p ² P _{1/2, 3/2} transitions in⁴³CaII have been measured by fast ion beam collinear laser spectroscopy. The resonant laser interaction was observed using non-optical detection based on optical ground state depopulation pumping, state selective neutralization and charge state separated particle counting. The extracted magnetic dipole hyperfine structure constants for⁴³CaA(² S _1/2)=?805(2) MHz,A(² P _1/2)=?145.5(1.0) MHz andA(² P _3/2)=?31.9(0.2) MHz are in excellent agreement with relativistic many body perturbation theory predictions available for this alkali-like ion. The combined results are used to evaluate the semi-empirical analysis method. From the electrical quadrupole hyperfine structure constantB(² P _3/2)=?6.7(1.4) MHz and the calculatedB/Q value for this one valence electron configuration, the nuclear quadrupole momentQ(⁴³Ca)=?0.043(9)b is derived. This result supports a previous evaluation based on the hyperfine structure of the two valence electron³ P configurations of CaI.