Sonnenschein, Volker Laser developments and high resolution resonance ionization spectroscopy of actinide elements Jyväskylä: University of Jyväskylä, 2014, 176 p. Department of Physics Research Report ISSN 0075-465X; 1/2015) ISBN 978-951-39-6049-0 (paper version) ISBN 978-951-39-6050-6 (electronic version) Diss. Laser development of pulsed Ti:sapphire laser systems has been carried out at the IGISOL facility in the University of Jyväskylä, Finland. To further the applications of Ti:sapphire technology in the domain of resonance laser ionization, several new laser resonator designs have been implemented. Studies for the development of ionization schemes have been simplified by use of a grating-based cavity. For increased spectroscopic resolution a dual-etalon as well as an injection-locked Ti:sapphire laser have been built and characterized. Increased output power of higher harmonics has been achieved with the technique of intra-cavity frequency doubling. Extension to a new frequency domain has been realized using difference frequency mixing. These new developments have been successfully applied in experimental studies at the University of Mainz (Germany), the LISOL facility (Belgium) as well as at IGISOL (Finland). High resolution resonance ionization spectroscopy has been used to study the ground state hyperfine structure of 229Th in an ongoing effort to identify a highly sought after nuclear isomer. Further high resolution work has been carried out on 227Ac as well as several isotopes of plutonium. Systematic studies of the hyperfine structure of natural copper have been employed to determine the accuracy of future in-source laser spectroscopy applications at IGISOL.

Laser developments and high resolution resonance ionization spectroscopy of actinide elements

The theory is developed for one- and two-atom interactions when the atom has a Rydberg electron attached to a hyperfine-split core state. This situation is relevant for some of the rare-earth and alkaline-earth atoms that have been proposed for experiments on Rydberg-Rydberg interactions. For the rare-earth atoms, the core electrons can have a very substantial total angular momentum $J$ and a nonzero nuclear spin $I$. In the alkaline-earth atoms there is a single ($s$) core electron whose spin can couple to a nonzero nuclear spin for odd isotopes. The resulting hyperfine splitting of the core state can lead to substantial mixing between the Rydberg series attached to different thresholds. Compared to the unperturbed Rydberg series of the alkali-metal atoms, the series perturbations and near degeneracies from the different parity states could lead to qualitatively different behavior for single-atom Rydberg properties (polarizability, Zeeman mixing and splitting, etc.) as well as Rydberg-Rydberg interactions (${C}_{5}$ and ${C}_{6}$ matrices).

Theory of long-range interactions for Rydberg states attached to hyperfine-split cores

Theory of long range interactions for Rydberg states attached to hyperfine split cores

Three-color three-step laser resonance ionization spectroscopy has been employed to investigate the autoionization spectra of atomic samarium in the energy region 50,330 - 51,160 cm−1. The measurements were carried out in an atomic beam coupled to a linear time of flight mass spectrometer. Fifty-five odd-parity autoionization levels of atomic samarium in the above-mentioned energy region have been observed using three excitation schemes. Among these, fifty autoionization levels are new. The total angular momenta of eighteen odd-parity autoionization levels have been assigned uniquely.

Investigations of odd-parity autoionization levels of atomic samarium using three-color resonance ionization spectroscopy

Laser-induced photoionization and fluorescence signals were simultaneously observed in atomic samarium using two Nd:YAG-pumped dye lasers. Two-color, three-photon photoionization and two-color fluorescence signals were recorded simultaneously under similar experimental conditions and their dependence as a function of the second-step laser power was studied to understand the behavior of these signals. The laser-induced fluorescence and photoionization techniques have been used simultaneously for the first time to understand the behavior of these signals so that these techniques can be used efficiently in complementary manner to investigate the high-lying energy levels. The even-parity energy levels of atomic samarium in the energy region 36 510–36 875 cm-1 have been investigated based on these experiments. Total 21 high-lying even-parity energy levels have been identified and the two energy levels amongst them are reported as new energy levels after comparing our results with those reported in the literature.

Investigations of high-lying even-parity energy levels of atomic samarium using simultaneous observation of two-color laser-induced fluorescence and photoionization signals

Spectra of even-parity highly excited states of the Sm atom have been systematically studied using the two-color three-step excitation and photoionization detection method. With three different excitation paths distinguished by three different intermediate states with the 4f66s6p configuration, the atom is resonantly excited to given highly excited states in the energy region between 30 040 and 38 065 cm−1, where it is detected by photoionization. The wavelength of the second laser is scanned from 440 to 700 nm, while that of the first laser is fixed at 638.96, 636.92 or 627.50 nm. Based on precise calibration of the wavelength, the energy levels of 198 even-parity states are determined with the relative line intensities of the related transitions. A unique value of J, the total angular momentum, is assigned to all detected states by comparing the three spectra obtained with the different excitation paths. Except that the energy levels of 113 states are confirmed in this work, the rest of the information mentioned above has not been previously reported.

http://iopscience.iop.org/article/10.1088/0953-4075/44/19/195001/pdf

Study on even-parity highly excited states of the Sm atom

Spectra of autoionizing states of the Sm atom in an energy region between 45948.9 cm−1 and 46943.6 cm−1 are systematically investigated by a three-color multi-step resonant excitation scheme with three different excitation paths. The three intermediate states, 4f 66s7s 7F3, 4f 66s7s 7F4, and 4f 66s7s 9F5 are employed for the three paths, respectively. Based on precise calibration of wavelength, the level energies of 112 autoionizing states are determined with the line widths and the relative line intensities of the related transitions. The possible influence of configuration interaction on the line shape of autoionizing state is also discussed. In addition, a unique value of J, the total angular momentum, is assigned to all detected states by comparing the three spectra obtained with the different excitation paths.

Autoionization spectra of Sm atom

Progress of Luminescent Behaviors of Mn2+-Mn2+ Pair with Magnetic Coupling Interaction

The effect of co-doping and line-doping of N/P/S and heavy metals (TMs, Ti, V, Fe, Ni) in stanene on the geometric structure, electronic behaviors, and quantum capacitance was systematically studied using density functional theory (DFT). The calculated results suggested that the line-doping enlarged the quantum capacitance (CQ) of stanene more effectively than that of co-doping. The electron density of states indicated the increase of CQ was attributed to the hybridization of TM-dopant and sn-atoms around the Fermi level. However, the performance of quantum capacitance of doped-stanene was at a disadvantage to that of doped-graphene. We hope our results give further insights into the improvement of CQ of stanene-based supercapacitors. 

Shi-Wei Ye

Papers

Study on even-parity highly excited states of the Sm atom

Autoionization spectra of Sm atom

Progress of Luminescent Behaviors of Mn2+-Mn2+ Pair with Magnetic Coupling Interaction

Influence of the co-doping and line-doping on the quantum capacitance of stanene for supercapacitor electrodes