Hyperfine structure splitting of the positron-helium ions e +[3He(23 S)] and e +[4He(23 S)]

The hyperfine structure splittings are determined for the lowest bound state in the positron-helium ion e ⁺[³He(2³ S)] and e ⁺[⁴He(2³ S)]. In particular, it has been found that the three hyperfine structure splittings—5824.3986, 76 466.5308, and 5824.4019 MHz—can be observed for the e ⁺[³He(2³ S)] ion. In the e ⁺[⁴He(2³ S)] ion, only one hyperfine structure splitting 82963.0427 MHz can be observed. All these values can be measured in modern experiments.     

Isotope effects in the EPR spectrum of a tin-vacancy pair in silicon

The S = 1 EPR spectrum for a tin-vacancy pair in silicon reveals easily detected isotope shifts in the fine structure splitting D for the various nuclear isotopes of tin (σD/D = + 1.0 × 10^?4 per unit mass) as well as well as those for the six near neighbor silicon atoms (σD/D = ?0.67 × 10^?4 per unit mass). These are attributed to the different vibrational amplitudes vs isotopic mass.     

Experimental and theoretical investigation of the isotope shift of the 4D level in atomic potassium

Doppler-free two-photon laser spectroscopic measurements in the deep red spectral region have been performed on the transition 4² S _1/2→4² D _J in the naturally abundant isotopes 39 and 41 of atomic potassium. The 4D level isotope shift, ?81±12 MHz was obtained by combining the current results with data from Rydberg-state spectroscopy. Many-body perturbation theoretical calculations of the specific mass shift in the measured state are also presented. With the use of Brueckner orbitals the value ?70 MHz was obtained in substantial agreement with the experimental result.     

Dye laser saturation spectroscopy of the 23 S 1-23 P transition in6, 7Li+ ions

The metastable 2³ S ₁ state and the short lived 2³ P states of the helium-like^{6, 7}Li⁺ ion spectra have been investigated by dye laser saturation spectroscopy in a low-energy Li⁺ ion-beam and fluorescence light detection. The hyperfine structure splittings of all the levels, the 2³ P fine structure intervals and the isotope shift of the 2³ S ₁-2³ P transitions have been measured. These measurements were made by application of a specially constructed tunable dye laser system capable of single-mode laser scans over more than 60 GHz.     

Spin-spin and spin-other-orbit effects of optical spectra and the spin-Hamiltonian parameters for Cr ions in MgO crystals

An extended complete diagonalization method/microscopic spin-Hamiltonian (CDM/MSH) program has been developed, which is applicable for d³ ions at sites of tetragonal symmetry type I (C_4v, D_2d, D₄, D_4h) and trigonal symmetry type I (C_3v, D₃, D_3d). The Hamiltonian includes the spin-spin (SS) and spin-other-orbit (SOO) magnetic interactions besides the spin-orbit (SO) magnetic interaction usually taken into account. Utilizing the extended CDM/MSH program, the optical spectra, the spin-Hamiltonian (SH) parameters of the ground state ⁴B₁, and the splitting δ(²E) of the first excited ²E state for Cr³⁺ (3d³) ions at C_4v symmetry sites in MgO crystals have been successfully investigated. It is found that although the SO magnetic interaction is the most important one, the contributions to the SH parameters and the optical spectra from the SS and SOO magnetic interactions for Cr³⁺:MgO crystals are appreciable and should not be omitted, especially reaching 27.8% for the zero field splitting parameter D.     

Two-color three-photon excitation studies of thallium Rydberg states

We present new data on the even-parity Rydberg states of atomic thallium using two-step three-photon laser excitation technique in conjunction with a thermionic diode ion detector. Atoms are excited from the 6p ²P_1/2 ground state to the 7p ²P_1/2 intermediate state via two-photon excitation and subsequently promoted to the high lying ns ² S_1/2 and nd ²D_3/2 Rydberg states. The first ionization potential of thallium is determined as 49,266.66(1) cm^-1 using data for the ns ² S_1/2 (25 ≤ n ≤ 54) and nd ²D_3/2 (24 ≤ n ≤ 65) Rydberg series. This value is believed to be more accurate because the contribution due to the hyperfine structure splitting of the 7p ²P_1/2 state (0.07185 cm^-1) is much smaller as compared to that of the 6p ²P_1/2 ground state (0.711 cm^-1).     

Measurement of the fine-structure splitting of the 42 D state of lithium using level-crossing spectroscopy

The fine-structure splitting of the 4² D state in lithium was measured using stepwise laser excitation combined with level-crossing spectroscopy. The splitting was determined to be 456.2(0.8) MHz, a considerably higher value than the one obtained in a recent level-anticrossing measurement. The new value is in good agreement with the result of a Hartree-Fock calculation, 460.2 MHz.     

Optical delay with spectral hole burning in Doppler-broadened cesium vapor

The full frequency dependence of the optical delay in the Cs D₁ (6 ²S_1/2 ? 6 ²P_1/2) line has been observed, including all four hyperfine split components. Pulse delays of 1.6 ns to 24.1 ns are obtained by scanning across the hyperfine splitting associated with the lower ²S_1/2 state. Optical control of pulse delays in cesium vapor was demonstrated by pumping the D₂ (6 ²S_1/2 ? 6 ²P_3/2) transition and observing resulting holes in the D₁ delay spectrum. For a pump at four times the saturation intensity, the pulse delays are reduced by a maximum of 78% in a narrow region of 110 MHz. The frequency dependence of the delays of the probe laser in the vicinity of the spectral holes agrees with a Kramers–Kronig model prediction.     

Theory of the lamb shift in muonic deuterium

We present new calculation of the Lamb shift (2P _1/2 ? 2S _1/2), fine splitting of the 2P state and hyperfine splitting of the 2S state in muonic deuterium (µd) using the quasipotential method in quantum electrodynamics. The vacuum polarization, nuclear structure, and recoil effects are calculated with the account of contributions of orders α ³, α ⁴, α ⁵, and α ⁶. The obtained numerical value of the Lamb shift 202.4139 meV can be considered as a reliable estimate for the comparison with forthcoming experimental data.     

S-wave state and D-wave state of the vector meson

The S-wave state ³ S ₁ and D-wave state ³ D ₁ are investigated by applying the Salpeter equation. The coupled equations of the S-wave component and the D-wave component are obtained. In nonrelativistic limit, the coupled equations are decoupled and reduced to two Schrödinger equations describing the S-wave state and the D-wave state, respectively. It is shown that the S-D coupling will be of order v ⁴ or of higher order. For vector mesons 1^??, the contribution to the decay constant comes only from the S-wave state in the nonrelativistic limit. Even when only the simple potential, the scalar and the zero component of the vector potential are considered and the orbit-spin term and tensor term are neglected, the D-wave contribution to the decay constant should also be considered in higher order.     

Isotope shift and hyperfine structure of43Ca by laser spectroscopy

The isotope shift⁴⁰Ca-⁴³Ca in the 4s ^{2 1} S ₀-4s4p ³ P ₁ intercombination line as well as the hyperfine structure splitting of the 4s4p ³ P ₁ state of⁴³Ca have been remeasured by saturation spectroscopy with a tunable stabilizedcw dye laser and an atomic beam of natural Ca as absorber. The nuclear charge radius of⁴³Ca obtained here reconciles our result with the radius obtained from measurements in muonic Ca-atoms and in the Ca resonance line. It reconfirms the fact that the charge radius of⁴³Ca is considerably smaller than the ones of both neighbouring even isotopes. The discrepancy of our previous measurement for this charge radius was due to a wrong assignment of so far unobserved absorption lines of probably molecular origin occuring in the neighbourhood of the atomic resonances under study.     

Relative photodissociation cross-section of NaCs molecule,using argon ion laser lines

Laser-induced photodissociation of NaCs molecule has been observed when a mixture of Na and Cs metal vapour in a glass cell was irradiated by most of the lines of an argon ion laser. The photodissociation results in the 3P state of Na atoms which is correlated with theF ¹Σ⁺ and G¹π molecular states of NaCs. Distribution of photofragments over fine structure components 3² P _3/2 and 3² P _1/2 of Na has been studied. The ratio of intensity ofD ₂ line (5890 Å) toD ₁ line (5896 Å) of Na varies from around 2 at 5145 Å to about 3.5 at 4579 Å. The relative photodissociation cross-section increases monotonically as the wave-length of laser light decreases from 5145 Å to 4579 Å. It is seen that the 4579 Å photon is about 200 times more effective than the 5145 Å photon in causing the photoreaction NaCs + (Ar⁺ photon) → Na*(3P) + Cs(6S).     

Lasing conditions in recombining helium plasmas

Lasing conditions for He have been evaluated numerically. We have used a collisional radiative model to calculate overpopulation densities Δn_ij, which are defined as differences between population densities per unit statistical weight of the upper and lower excited levels i and j, respectively. Laser oscillations for the level pairs 2¹P-3¹S, 2¹P-4¹S, 2¹P-3¹D, 2¹P-4¹D, 3¹D-4¹F, 3¹P-4¹S, 3¹P-4¹D, and 3³P-4³S are possible when the electron densities are within well defined limits at low electron temperature (T_e = 0.1 eV). For level pairs of the singlet state, the inversion mechanism for He is the same as for H. Only collisional processes produce population inversion in the triplet level pair 3³P-4³S.     

Optical probing of Eu ions confined in an RF trap

The Eu ions confined in an RF quadrupole trap, has been optically detected. Using a tunable dye laser which is pumped by a Nd-YAG pulsed laser system, the resonance ⁹S₄^9S_4–6p _3/2, J = 5 transition of the Eu ions have been excited and the resulting fluorescence to the metastable ⁹D_4-6^9D_{4-6} state has been detected. In preparation to determine the ground-state hyperfine splitting of the odd isotopes we found the optimum trapping operating point. We have also observed a number of instabilities inside the region of the stability for an ideal trap. These non-linear resonances arise from higher-order contributions to the ideal quadrupole potential.     

Quenching of 6s6d and 6s7d Hg atoms by Hg*-Hg,Hg*-Ar and Hg*-N2 collisions

The radiative decays and collisional quenching of Hg 6¹D₂, 6³D₂, 7¹D₂ and 7³D₂ atoms were investigated by time-resolved methods. Hg vapour, pure or mixed with a buffer gas in a fluorescence cell, was irradiated with u.v. light pulses from a frequency-doubled N₂ laser-pumped dye laser, populating selectively each state in turn by 2-photon absorption from the 6¹S₀ ground state. Fluorescent components arising from the decays to the 6¹P₁ or 6³S₀ state were resolved with a spectrometer and their time evolutions recorded with a transient digitizer or time-to-amplitude converter and pulse-height analyzer, yielding the respective decay rates. The quenching cross sections were obtained from variations of measured decay rates with Hg or buffer-gas density.     

Level crossing measurement of the 32 D fine structure of lithium

The fine structure splitting of the 3² D-state of lithium was measured using the level crossing technique with delayed observation. Two nitrogen laser pumped dye lasers were used for a stepwise excitation. The linewidth observed was 40% smaller than the natural width. The result derived for the splitting is (1080.1±1.0)MHz.     

Two-photon spectroscopy of ytterbium

Two-photon laser spectra of the Yb vapor have been obtained. Transitions to highly excited 4f¹⁴ 6sns¹S₀ and 4f¹⁴ 6snd ¹D₂ states are seen in direct two-photon excitation. Hybrid resonances involving 4f¹⁴ 6s6p ¹P⁰₁ and 4f¹⁴ 5d6s ³D₂ intermediate states lead to transitions to 4f¹⁴ 6sns¹S₀, 4f¹⁴ 6snp ³P⁰_2,1 and 4f¹⁴ 6snd ¹D₂ levels.     

Quantum interference effects in field ionization: Application to the measurement of the fine structure splitting of highly excited Na2 D states

Quantum beats between the fine structure levels of highly excitedn ² D levels of sodium atoms have been measured by investigating the field electrons. The states were populated by stepwise excitation with two dye lasers and an electric field pulse was applied a certain time after the laser excitation. The quantum beat signal is observed when the time delay between excitation and ionization is varied. The fine structure splitting forn=21 to 31 has been measured.     

Electric field induced hyperfine level-crossings in (nD)Cs at two-step laser excitation: Experiment and theory

The pure electric field level-crossing of m_F Zeeman sublevels of hyperfine F levels at two-step laser excitation is described theoretically and studied experimentally for the nD_3/2 states in Cs with n = 7, 9 and 10, by applying a diode laser in the first 6S_1/2 → 6P_3/2 step and a diode or dye laser for the second 6P_3/2 → nD_3/2 step. Level-crossing resonance signals are observed in the nD_3/2 → 6P_1/2 fluorescence. A theoretical model is presented to describe quantitatively the resonance signals by correlation analysis of the optical Bloch equations in the case when an atom simultaneously interacts with two laser fields in the presence of an external dc electric field. The simulations describe well the experimental signals. The tensor polarizabilities α₂ (in ) are determined to be 7.45(20) × 10⁴ for the 7D_3/2 state and 1.183(35) × 10⁶ for the 9D_3/2 state; the electric field calibration is based on measurements of the 10D_3/2 state, for which α₂ is well established. The α₂ value for the 7D_3/2 state differs by ca. 15% from the existing experimentally measured value.     

Hyperfine structure of 5d 2 D 3/2 135,137Ba ions by collinear fast beam laser-rf double resonance spectroscopy

The hyperfine structure of the metastable 5d ² D _3/2 state has been measured with high precision by collinear laser-rf double resonance spectroscopy on fast^135,137Ba ion beams. The present data are about 100 times more accurate than those obtained by classical fast beam laser spectroscopy.