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Journal of Physics B Atomic and Molecular Physics

Photoionisation of Ne(2p53p3D3) atoms and the production of state-selected, polarised Ne+(2p5 2P3/2) ions

J. Ganz, B Lewandowski, Augustin Siegel, Wolfgang Bussert, H. Waibel, M -W Ruf, Hartmut Hotop

Published Jul 28, 1982• 24 citations
Publisher

Abstract

State- and isotope-selective perpendicular excitation of a thermal energy, mixed metastable Ne(2p53s 3P2, 3P0) atom beam with a polarised 640.2 nm laser beam yields a well defined sample of 20Ne(2p53p 3D3) atoms, which are ionised by UV photons (wavelength range 331-412 nm). Core-switching processes are found to be negligible: autoionisation features in the region between the two Ne+(2P3/2,1/2) fine-structure thresholds and photoelectrons corresponding to Ne+(2P1/2) ions could not be detected. The application of these results for the production of state-selected, polarised Ne+(2p5 2P3/2) ions is briefly discussed.

DOI
10.1088/0022-3700/15/14/001

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Journal of Physics B Atomic and Molecular Physics•Jul 14, 1979•9 citations
State- and isotope-selective perpendicular excitation of a thermal energy, mixed metastable Ne(2p53s 3P2, 3P0) atom beam with a polarised 640.2 nm laser beam yields a well defined sample of 20Ne(2p53p 3D3) atoms, which are ionised by UV photons (wavelength range 331-412 nm). Core-switching processes are found to be negligible: autoionisation features in the region between the two Ne+(2P3/2,1/2) fine-structure thresholds and photoelectrons corresponding to Ne+(2P1/2) ions could not be detected. The application of these results for the production of state-selected, polarised Ne+(2p5 2P3/2) ions is briefly discussed.
Trapped single ions provide an ideal platform for studying quantum optics, light-matter interactions, and quantum information processing. Many of these applications rely on the availability of well-defined and reproducible quantum emitters as well as precise control over the internal states of ions. To study both of these concepts, this thesis focuses on the isotope selectivity of neutral Barium (Ba) transitions as well as the state preparation of single trapped 138Ba+ ions. The first part of this thesis introduces the theoretical framework for experiments, focusing on single Ba+ ions and light-matter interactions. Therefore, the working principle of Paul traps is presented, the Ba ion is introduced and fundamental light-matter interaction tightly related to the experiments and simulations presented in this work are established. In the second part, the isotope selectivity of the neutral Ba 6s2 1S0 to 6s6p 1P1 transition at 553 nm is investigated and compared with the isotope selectivity of the 6s2 1S0 to 5d6p 3D1 transition at 413 nm. A secondary photon can be used in both cases to achieve isotope selective ionization of Ba+ ions. The isotope selectivity of the 553 nm transition was tested by carrying out spectroscopy and comparing the results with existing data. The isotope selectivity for other naturally available Ba isotopes is simulated for both transitions (553 nm and 413 nm) and for different angles between atomic beam and laser beam (90°, 85° and 80°). The simulations show, that under ideal conditions (when the atomic beam and ionization laser beam are orthogonal) both transitions perform similarly. However, the 553 nm transition exhibits greater robustness against Doppler shifts as the angle deviates from 90°. At an angle of 80° between the atomic beam and the laser beam, the maximum probability of generating 138Ba+ is 99 % using 553 nm, while the maximum probability of generating the isotope using 413 nm does not exceed 94 %. In the third part of this thesis, we focus on state preparation of Ba+ ions in the 6P1/2 state. A heralding state preparation scheme that exploits the spontaneous emission of a 389 nm photon during the decay of the excited state 6D3/2 is introduced. The detection of a photon at this wavelength projects the ion into the desired state 6P1/2 in a deterministic fashion. A simulation of this scheme shows that the preparation probability may exceed 78 %, and the heralding process ensures state preparation with 100 % fidelity, if a photon at a wavelength of 389 nm is detected. The state preparation method will be adopted in near-future experiments that are provided as an outlook at the end of this thesis.
The authors describe the details of an experiment using a sodium atomic beam and two dye lasers. By stepwise excitation they have selectively populated highly excited ns, nd and, using Stark mixing, np states fron n=20-50. The excited atoms were detected by field ionisation. The results obtained for the ionisation threshold fields for these states are presented and compared with the theoretical classical law F c =(2n*) -4 . A suitable field shape and detection technique allows the observation of multiple thresholds with high sensitivity. Multiple thresholds for nd states have been observed, as expected. Some ns singlet states also show multiple thresholds. Using suitably polarised laser beams the mod m L mod dependence of the ionisation threshold fields for the 20d state has been observed. The approach proposed recently by Gallagher for predicting the threshold fields is generally confirmed.
Non-perturbative completely analytic calculations of the spin polarisation of photoelectrons produced in resonant two-photon ionisation of alkali atoms with exciting and ionising light beams are presented. A well justified alkali atom model composed of four discrete states and the continuum is applied. Contrary to simpler models it enabled one to obtain results valid when the effective resonance Rabi frequency exceeds the frequency separation between the two components forming a given fine-structure energy doublet at resonance. It is shown that in this limit the photoelectron polarisation depends critically on whether a light or heavy alkali atom is ionised. In the former case the photoelectron polarisation is proved to be a copy of the electronic polarisation of the atom, whereas in the case of heavier alkalis it departs appreciably from that of the ionised atom due entirely to spin-orbit perturbation of radial wavefunctions of P discrete states. It is also shown how the author's present results go over into those previously obtained for weaker exciting fields.
In the two-photon ionisation of Cs atoms resonances may be expected which correspond to a quadrupole 6s-nd transition associated with the first photon. At the 6D 5/2 and 6D 3/2 resonances the ratio of photoionisation cross sections for circularly polarised and for linearly polarised light (ion asymmetry) and the spin polarisation of the photoelectrons ejected by circularly polarised light have been measured. The ratios of the radial transition matrix elements from the 6D to the epsilon P and epsilon F continuum states were derived from the experimental results.