O. Poulsen

Radiative lifetimes in Zn(II), Cd(II) and Hg(II) measured by fast-beam zero-field level-crossing technique

Abstract The zero-field level-crossing technique has been used to determine radiative lifetimes of excited states in singly ionized zinc, cadmium, and mercury. The excited levels in Zn(II), Cd(II) and Hg(II) were populated by collisions between fast ions and helium gas. Particular attention has been paid to the systematic errors occurring in radiative lifetimes by this technique. The results are compared with the lifetimes obtained by beam-foil, phase-shift, delayed-coincidence techniques and theoretical calculations.

Laser cooling of a fast ion beam

A theoretical analysis of light-pressure cooling of a fast ion beam is given. The light-induced velocity changes are compensated by accelerating the ions by an external electric field. By analyzing the Fokker–Planck equation, cooling times and the ultimate temperature of the ions are given. It is argued that the transverse heating and the diffusion to velocities that are not cooled should pose no serious problems in realistic experimental cases. The particular physical conditions in a heavy-ion storage ring are finally discussed.

Doubly Excited States in Be III

The triplet spectrum of doubly excited Be III has been studied in the wavelength region of 75-5000 A in order to test the validity of the theoretical term values reported by Lipsky et al. The beam-foil excitation technique was applied to effectively populate the doubly excited states. The identified lower-lying, doubly excited states 2p2 3P, 2pnp 3P, or 3D, and 2pnd 3P, or 3D (n = 3, 4) show that the theoretical term values should be slightly modified.

Velocity and high-voltage measurements using resonant collinear, fast-beam/laser interactions

Abstract The velocity of fast-moving absorbers can be precisely determined using resonant collinear fast-beam/laser interactions. We discuss three methods of obtaining high-velocity resolution, i.e., (1) parallel/antiparallel linear interactions, (2) resonant two-photon interactions, and, finally, (3) simultaneous resonant absorption of counter-propagating laser fields in an [inverted] V configuration, making possible an ‘autocalibration’ of particle velocities without any knowledge of the laser frequency. Problems in relating velocities to high voltage are discussed.

Problems related to lifetime measurements in complex atoms using beam-foil and fast-beam/laser spectroscopy

Abstract Problems associated with the measurements of lifetimes in heavy or complex atoms and ions are discussed. Besides the now classical beam-foil method, two new techniques are introduced, which both utilize fast-beam/CW dye-laser modulation spectroscopy. Lifetimes are reported for excited states in Ne I, Zr I, Au I, Tl III, U I, and U II. The advantages of the selective laser-based techniques as compared to the beam-foil method are discussed.

Observation of population trapping in a two-photon resonant three-level atom

Abstract We report narrow structures observed in the population of the intermediate level of a two-photon transition in a fast beam of metastable 20 Ne ∗ atoms. Steady-state theory provides a description of two coherent processes leading to population trapping. Both processes proceed via the ordinary two-photon coherence. One is then completed with a reversed-time ordering of the last two interactions, leading to a dispersive variation of the population of the real intermediate level, the other creates a hole in this population. A narrow Doppler profile enhances the visibility of these processes.

235 U II hyperfine structures measured by collinear fast-beam-laser and radio-frequency-laser double-resonance spectroscopy

Collinear fast-beam-laser and rf-laser double-resonance spectroscopy have been carried out in 235U ii, allowing a detailed study of the hyperfine structure (hfs) of the three low odd configurations 5f3(7S2 + 6d7s + 6d2). Intermediate coupling wave functions, using parametric fitting, have been determined, allowing a parameterization of the hyperfine interaction. Ab initio Dirac–Fock calculations combined with this parameterization of our experimental data have allowed an analysis of the hfs of 235U ii, resulting in a new value for the magnetic-dipole moment μI = −0.38(3) nm and a spin density a7s10 = −2880(75) MHz of the 7s electron.

Lifetimes and hyperfine structures in Ho II

In this work we have measured lifetimes, oscillator strengths and hyperfine structures in Ho II. Accurate atomic structure data are of importance for element identification in steller atmospheres as well as in atomic structure studies. Lifetimes of 3 excited levels, all observed in stellar spectra, have been measured using electro-optic modulation spectroscopy in the ultraviolet. Oscillator strengths have furthermore been extracted by analyzing the time evolution of the laser excitation in the Rabi-regime. Previous to this study no lifetime and oscillator strength data were known in Ho II. In addition, the hyperfine structures of 3 low odd levels and 2 excited levels, has been accurately measured using fast beam laser spectroscopy. These data are analyzed using Multi-Configuration Dirac-Fock (MCDF) wavefunctions.

Lifetime measurements of the 6p2P and 6d2D levels in Hg(II)

Abstract The radiative lifetimes of the 6p2P levels in Hg(II) have been measured to be τ(6p 2 P 3 2 )= 3.92±0.12) ns and τ(6p 2 P 1 2 )=(2.3±0.3) ns by the beam-gas-Hanle and the beam-foil techniques, respectively. The result for the 6p 2 P 1 2 level differs from recent theoretical calculations, whereas there is good agreement for the 6p 2 P 3 2 level.

Lifetime measurements in singly ionized erbium using fast-beam laser-modulation spectroscopy

Precise transition energies for several transitions in singly ionized erbium are presented, together with lifetimes for a number of excited levels. The lifetime results obtained make possible a general correction to the oscillator strength previously reported by Corliss and Bozman [ Nat. Bur. Stand. (U.S.) Monogr.53 ( 1962)].