title: Two-photon spectra of Rydberg states of alkaline-earth atoms (strontium and barium)
Creators: name: Philip, George
Publisher: name: The Open University
Year: 2008

description: 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. <br><br>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. <br><br>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 <i>J</i> = 0,2 even-parity Rydberg series and autoionizing resonances just above the ionization limits labeled as; (4d<sup>2</sup>+5p<sup>2</sup>) <sup>1</sup>D<sub>2</sub> in strontium and 5d5f<sup>2</sup>p<sub>1</sub> in barium were observed. <br><br>Original new energy level values are presented with substantial extension to the data in the literature for even-parity Rydberg series: <br>Sr I: 5s<i>n</i>s <sup>1</sup>S<sub>0</sub> (12 &lt; <i>n</i> &lt; 46), 5s<i>n</i>d <sup>3</sup>D<sub>2</sub> (9 &lt; <i>n</i> &lt; 47) and 5s<i>n</i>d <sup>1</sup>D<sub>2</sub> (9 &lt; <i>n</i> &lt; 82) <br>Ba I: 6s<i>n</i>s <sup>1</sup>S<sub>0</sub> (13 &lt; <i>n</i> &lt; 68), 6s<i>n</i>d <sup>3</sup>D<sub>2</sub> (11 &lt; <i>n</i> &lt; 46) and 6s<i>n</i>d <sup>1</sup>D<sub>2</sub> (11 &lt; <i>n</i> &lt; 88) <br><br>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: <br>5s<sup>2 1</sup>S<sub>0</sub> -&gt; 5s<i>n</i>p <sup>1</sup>P<sub>1</sub><sup>o</sup> (32 &lt; <i>n</i> &lt; 46) and 5s<sup>2 1</sup>S<sub>0</sub> -&gt; 5s<i>n</i>f <sup>1</sup>F<sub>3</sub><sup>0</sup> (29 &lt; <i>n</i> &lt; 44) <br><br>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: 5s<i>n</i>s <sup>1</sup>S<sub>0</sub> and 5s<i>n</i>d <sup>1,3</sup>D<sub>2</sub> in the perturbed region which clearly exhibit Ramsauer effect. Collisional evolution of a remarkably broad resonance, labeled as 4d<sup>2</sup> <sup>1</sup>G<sub>4</sub>, also exhibiting Ramsauer effect, is presented besides new level data for strontium 4d<sup>2</sup> <sup>3</sup>P<sub>J</sub> states accessed by two distinct processes- direct two-photon excitation and single-photon sequential excitation. <br><br>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.