The fine structure of high-angular-momentum
n=9 and 10 Rydberg states of barium has been measured precisely, using the resonant excitation Stark ionization spectroscopy method. Optical transitions corresponding to $(n,{n}^{\ensuremath{'}})=(10,30)$, (9,17), and (9,20) were induced with a Doppler-tuned
CO2 laser, determining the fine-structure energies corresponding to all
n=9 and 10 levels with $L\ensuremath{\geqslant}6$. The pattern of these fine-structure energies conforms closely with an effective potential model, by comparison with which the dipole and quadrupole polarizabilities of
Ba+ can be determined. Combining our data with earlier measurements made it possible to deduce, in addition, the portion of ${\ensuremath{\alpha}}_{2}$ due to the lowest excited
D state of
Ba+. Our best estimates of these three properties are ${\ensuremath{\alpha}}_{1}=124.30(16){a}_{0}^{3}$, ${\ensuremath{\alpha}}_{2}=2462(361){a}_{0}^{5}$, and ${\ensuremath{\alpha}}_{2}^{0}=1828(88){a}_{0}^{5}$.
We present experimental energy-level positions for Ba high-l Nsnl double Rydberg states with N=8 (n=13--15, l\ensuremath{\geqslant}7) and N=9 (n=13--15, l\ensuremath{\geqslant}7). These data as well as previously reported measurements for N=7 (n=12--15, l\ensuremath{\geqslant}5) and N=10 (n=13--15, l\ensuremath{\geqslant}10) are parametrized in order to yield values for the
Ba+ Ns effective dipole ${\mathrm{\ensuremath{\alpha}}}_{\mathrm{d}}^{\ensuremath{'}}$ and quadrupole ${\mathrm{\ensuremath{\alpha}}}_{\mathrm{q}}^{\ensuremath{'}}$ polarizabilities. The obtained ${\mathrm{\ensuremath{\alpha}}}_{\mathrm{d}}^{\ensuremath{'}}$ values are 1.25(5)\ifmmode\times\else\texttimes\fi{}
103, 7.05(4)\ifmmode\times\else\texttimes\fi{}
103, 2.95(4)\ifmmode\times\else\texttimes\fi{}
104, 9.39(15)\ifmmode\times\else\texttimes\fi{}
104 in
a03 units and the ${\mathrm{\ensuremath{\alpha}}}_{\mathrm{q}}^{\ensuremath{'}}$ values are 1.7(8)\ifmmode\times\else\texttimes\fi{}
104, 1.8(2)\ifmmode\times\else\texttimes\fi{}
105, -1.0(2)\ifmmode\times\else\texttimes\fi{}
106, -1.0(2)\ifmmode\times\else\texttimes\fi{}
107 in
a05 units for N=7, 8, 9, and 10, respectively. The ${\mathrm{\ensuremath{\alpha}}}_{\mathrm{d}}^{\ensuremath{'}}$ evolution with N is found to follow a
N∗6.9(1) power law, while calculated static polarizabilities present somewhat lower power dependence. From this small difference it is not possible to appreciate the importance of nonadiabatic effects between the two asymmetrically excited electrons. On the other hand, the larger discrepancies appearing between the calculated static and fitted quadrupole polarizabilities show clear evidence of nonadiabatic effects. Particularly the negative ${\mathrm{\ensuremath{\alpha}}}_{\mathrm{q}}^{\ensuremath{'}}$ sign for N\ensuremath{\geqslant}9 is attributed to the increasing strength of dynamical effects on the Ns core electron caused by the motion of the outer high-l electron. It gives evidence of the increasing importance of nonadiabatic radial correlation between two planetary electrons when the Ns inner electron is sufficiently radially extended to be characterized as an inner Rydberg electron without, nevertheless, any appreciable overlapping with the outer electron.
We present observations of Stark spectra of barium in highly excited Rydberg states in the energy region around n = 35. The one-photon excitation concerns the π transition. The observed Stark spectra at electric fields ranging from 0 to 60 V·cm −1 are well explained by the diagonalization of the Hamiltonian incorporating the core effects. From the Stark maps, the anti-crossings between energy levels are identified experimentally and theoretically. The time of flight spectra at the specified Stark states are recorded, where the deceleration and acceleration of barium atoms are observed. This is very consistent with the prediction derived from the Stark maps from the point of view of energy conservation.
Quantum interference between an electric-quadrupole transition and a Stark--induced-dipole-transition amplitude leads to a net orientation of an atomic excited state. When the barium 6
s2 1S-6s5d
1D transition is excited in the presence of an electric field, we find the induced orientation of the 6s5d
1D state to be (2.86\ifmmode\pm\else\textpm\fi{}0.59)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}6}$(V/cm${)}^{\mathrm{\ensuremath{-}}1}$.
A study of the detailed structure of the bound odd-parity Rydberg states of barium has been undertaken using a cw dye laser in combination with an atomic beam. Special attention has been paid to the
6snf configurations, of which the hyperfine structure has been analyzed in terms of a small set of parameters. In addition to an effective Slater-exchange integral, an effective spin-orbit interaction, and a contact hyperfine parameter, a new parameter representing two-body magnetic effects, has been introduced. The introduction of this new parameter is discussed in some detail. Good agreement between the calculated and experimental hyperfine energies is achieved in this way.
The even-parity spectra of strontium and barium are very complex due to strong perturbation by several doubly excited configurations and this also increases discrepancies between theory and experiment in accurate level assignment and energy level and atomic structure data, particularly for the spectra of highly excited atoms and their behaviour in external fields and collisional processes which are of fundamental importance in the emerging applications in physics of cold atoms, quantum computing, precision atomic clocks and in the crossed-field problem. This thesis presents results from an experimental study to improve and extend the previously published observations in the two-photon spectra of the high-lying Rydberg states of SrI and Bal placed under a variety of test conditions such as external fields, collisions etc. Orthogonal excitation of a novel atomic jet in a purpose-built heat-pipe setup using a Xenon Chloride excimer laser pumped tunable narrow bandwidth dye laser and high sensitivity space-charge ionization in thermionic diode with complimentary optical detection was used for measurements. Presented are the two-photon spectra covering the dye laser wavelength (air) range of 460 - 425 nm for strontium and 495 - 467 nm for barium by which the J = 0,2 even-parity Rydberg series and autoionizing resonances just above the ionization limits labeled as; (4d2+5p2) 1D2 in strontium and 5d5f2p1 in barium were observed. Original new energy level values are presented with substantial extension to the data in the literature for even-parity Rydberg series: Sr I: 5sns 1S0 (12 < n < 46), 5snd 3D2 (9 < n < 47) and 5snd 1D2 (9 < n < 82) Ba I: 6sns 1S0 (13 < n < 68), 6snd 3D2 (11 < n < 46) and 6snd 1D2 (11 < n < 88) New observation of certain anomalies including a Stark shift reversal effect and zero-field thermionic diode detection with remarkable sensitivity preserving all spectral features of Rydberg states is also presented. Controlled configuration mixing by exploiting electric field and collisions has allowed new observations for the two-photon forbidden odd-parity Rydberg series of SrI: 5s2 1S0 -> 5snp 1P1o (32 < n < 46) and 5s2 1S0 -> 5snf 1F30 (29 < n < 44) Extensive study of collision involving Rydberg atoms with neutral rare gas atoms has allowed to obtain new data for shift and broadening rates for Sr I series: 5sns 1S0 and 5snd 1,3D2 in the perturbed region which clearly exhibit Ramsauer effect. Collisional evolution of a remarkably broad resonance, labeled as 4d2 1G4, also exhibiting Ramsauer effect, is presented besides new level data for strontium 4d2 3PJ states accessed by two distinct processes- direct two-photon excitation and single-photon sequential excitation. Furthermore, the thesis presents the results of a novel experimental technique involving time-resolved gated pulsed field detection technique (GPT) employed for the first time to examine the time decay of Rydberg atoms yielding their effective lifetimes.