A frequency stabilized ring dye laser, with a linewidth of (TURN)250 kHz, has been utilized to selectively excite Rb(N('2)S, N('2)D) states in the range N = 20 - 100 by a two photon process. The highly excited atoms were detected by the technique of electric field ionization. Excited states with (VBAR)M(,L)(VBAR) < 3 have been observed to ionize along predominantly adiabatic paths and states with (VBAR)M(,L)(VBAR) (GREATERTHEQ) 3 have been observed to ionize along predominantly diabatic paths for the range of N investigated. The electric field dependence of the ionization threshold has been determined to be in good agreement with that calculated from a simple model based on the energies and ionization rates of hydrogen. Collisions between highly excited rubidium atoms and neutral xenon atoms, which result in a change in the N and L of the excited state of the rubidium atom, have been investigated. The N of the final state has been shown to be limited to those states which lie closest in energy to the initial state, in good agreement with theory. The distribution of L of the final states has been shown to be completely statistical or biased towards production of high L. The distribution of final L is definitely not biased toward production of states with low values of L.

State-changing in collisions of Rb(nS) - HF are studied using a crossed atomic beam/modulated CW laser technique and selective field ionization for values of principal quantum number n where 40 (LESSTHEQ) n (LESSTHEQ) 49. Collisions between a rotating polar molecule and a Rydberg atom often result in a near-resonant interchange of the rotational energy of the molecule, and a corresponding change in the electronic energy of the atom. A critical parameter is the energy imbalance of the reaction, defined as the difference between the atom's initial and final electronic energy and the molecule's initial and final rotational energy. The molecule used in this experiment, hydrogen fluoride, has a large rotational constant which permits study of n-changing rate constants for transitions from an initially populated s-state to a single n-manifold of high-L states. Because only one final manifold is populated, the reaction involves a single energy imbalance, and thus proves a useful test of theoretical models. n-Changing rate constants for collisions with energy imbalances ranging from 0.057 cm('-1) to 3.447 cm('-1), and ionization and L-mixing rate constants are compared to those predicted by an impulse approximation model and a semiclassical approach.

Absolute differential cross sections for charge-transfer collisions of H$\sp{+}$ and He$\sp{+}$ with a variety of rare-gas- and molecular-gas-targets are presented. The cross sections are measured within the energy range 0.25-5.0 keV, and between angles of 0.01$\sp\circ$ and 1.0$\sp\circ$ (for He$\sp{+}$ - He scattering at 0.25 and 0.5 keV, the angular range is extended to 7.8$\sp\circ$). A position-sensitive detector is used to detect both the primary and scattered particles. The data typically exhibit striking oscillations. Theoretical calculations for some of the reactions yield good agreement with the measured cross sections. The integrated cross sections match the total cross sections in the literature very well.

This thesis reports measurements of absolute cross sections, differential in angle, for elastic scattering of keV-energy atomic H and He projectiles from He, Ne, Ar, Kr, Xe, H$\sb 2$, and N$\sb 2$ at laboratory scattering angles between 0.02$\sp\circ$ and 0.5$\sp\circ$. It also reports measurements of absolute cross sections, differential in angle, for elastic scattering of keV-energy H$\sp +$ and He$\sp {+}$ projectiles from He, Ne, Ar, Kr, and Xe and H$\sb 2$ at laboratory scattering angles between 0.04$\sp\circ$ and 1.0$\sp\circ$. Comparisons are made between measured differential cross sections and those calculated from various model potentials, revealing the range of validity of potentials appearing in the literature. Experimental cross sections are also integrated over the angular range to obtain partial total cross sections, which are compared with those appearing in the literature.

A single-mode, frequency-stabilized LNA ring laser has been developed which routinely provides output powers $\sbsp{\sim}{>}$300 mW at 1.083 $\mu$m when pumped with 5 W of the 514 nm output from an Argon ion laser. A modified CR899-21 Ti:Sapphire ring laser from Coherent Laser Group of Palo Alto produces 300 mW at 1.083 $\mu$m when pumped with 21 W of all-lines Argon ion laser light. The importance of intense, stable 1.083 $\mu$m laser sources is demonstrated through several experiments. Optical pumping with either laser produces He(2$\sp3$S) atom beams of high polarization which can be maintained for periods of many hours. This allows investigation of Penning Ionization using spin labeling techniques, spin-polarized metastable atom deexcitation spectroscopy, and a novel method for absolute calibration of Mott polarimeters. Saturation of the He(2$\sp3$S) $\rightarrow$ He(2$\sp3$P) transition allows study of the interaction of mixed He(2$\sp3$S)/He(2$\sp3$P) atoms beams with surfaces. Construction of a magneto-optical trap for He(2$\sp3$S) atoms is possible utilizing the high power provided by the laser systems. Both lasers provide ample power for all applications currently envisioned involving optical pumping and optical manipulation of He(2$\sp3$S) metastable atoms.

A commercial Spectra Diode Laboratories, 1.083 $\mu$m diode laser has been used to efficiently spin polarize an atomic beam of He(2$\sp3$S) metastable atoms by optical pumping on the $\rm 2\sp3S\sb1\rightarrow2\sp3P\sb1$ (D1) transition. The diode laser is an InGaAs/GaAs strained multiquantum well with a distributed Bragg reflector to insure single longitudinal mode operation. The laser has been frequency stabilized to less than 1 MHz/hr drift. The helium metastable atom beam is produced by electron impact and the polarization is measured using a Stern-Gerlach analyzer. Atomic polarizations exceeding 97% have been obtained with $\sim$25 mW of power from the diode laser. A number of experiments currently under construction may also make use of the diode laser. These include the production of a spin polarized helium ion beam by optically pumping the metastable atoms in an rf discharge, and the trapping of helium metastable atoms in a magneto-optical trap (MOT).

The use of ordinary perturbation theory is ubiquitous in modern physics. However, it violates probability conservation, one of the fundamental laws of physics. In this thesis a unitarized perturbation theory is briefly described and its predictions for the behaviour of a number of simple systems are compared with those of ordinary perturbation theory. It is found that the new technique performs just as well as the usual perturbative approach in the regime where the latter is valid and provides improved results where perturbation theory fails. In particular, in the cases studied, the new method is found to reproduce the exact result at resonance.

We use Nonrelativistic Quantum Electrodynamics (NRQED) as an effective field theory to calculate the single photon annihilation contribution to the positronium hyperfine splitting (HFS) in its ground state at order Oa6 . Our analytical result completes the hyperfine splitting calculation to order mea6 . Using NRQED, we derive the Lamb shift of a scalar-scalar bound state and Oa5 hyperfine splitting of positronium for a general excited state. Using the same technique, we also rederive the Lamb shift of Hydrogen atom and Oa5 HFS of positronium in its ground state.

<p> The quality of beam optics is of great importance for the performance of a high energy accelerator like the Relativistic Heavy Ion Collider (RHIC). The turn-by-turn (TBT) beam position monitor (BPM) data can be used to derive beam optics. However, the accuracy of the derived beam optics is often limited by the performance and imperfections of instruments as well as measurement methods and conditions. Therefore, a robust and model-independent data analysis method is highly desired to extract noise-free information from TBT BPM data. As a robust signal-processing technique, an independent component analysis (ICA) algorithm called second order blind identification (SOBI) has been proven to be particularly efficient in extracting physical beam signals from TBT BPM data even in the presence of instrument's noise and error. We applied the SOBI ICA algorithm to RHIC during the 2013 polarized proton operation to extract accurate linear optics from TBT BPM data of AC dipole driven coherent beam oscillation. From the same data, a first systematic estimation of RHIC BPM noise performance was also obtained by the SOBI ICA algorithm, and showed a good agreement with the RHIC BPM configurations. Based on the accurate linear optics measurement, a beta-beat response matrix correction method and a scheme of using horizontal closed orbit bumps at sextupoles for arc beta-beat correction were successfully applied to reach a record-low beam optics error at RHIC. This thesis presents principles of the SOBI ICA algorithm and theory as well as experimental results of optics measurement and correction at RHIC.</p>

<p> The charge distribution associated with an electron has surprising implications for a number of outstanding mysteries in physics. Why is the universe made out of matter versus anti-matter, instead of both equally? What new particles and interactions lie beyond the current reach of accelerators like the LHC? Models which propose answers to these questions, such as Supersymmetry, tend to predict a small, yet potentially measurable, asymmetric interaction between an electron and an electric field, characterized by an electric dipole moment (EDM). Despite over six decades of experimental searching, no EDM of any fundamental particle has ever been measured; however, these experiments continue to provide some of the most stringent limits on new physics. Here, we present the results of a new search for the electron EDM, <i>d</i>_e = (-2.1 &plusmn; 3.7_stat &plusmn; 2.5syst) &times; 10^-29 e cm, which represents an order of magnitude improvement in sensitivity from the previous best limit. Since our measurement is consistent with zero, we present the upper limit of |<i>d</i>_e| &lt; 8.7 &times; 10^-29 e cm with 90 percent confidence.</p>