In this work with atomic Strontium, the atoms are first laser cooled and subsequently trapped, in a MOT operating on the strong E1 allowed transition at 461 nm. During the operation of this blue MOT, a fraction of the atoms decay into the 3P2 and 3P1 states, but can be recovered by applying light from repumper lasers at 679 nm, and 707 nm. Atoms trapped in the blue MOT are subsequently transferred into a magneto-optical trap operating on the intercombination line at 689 nm, known as the red MOT. Photoassociation experiments are carried out on these atoms using an independent tunable source of blue light at 461 nm. These experiments map out the underlying molecular potentials, and are useful in determining the atom-atom interaction strength. Additionally, atoms trapped in the red MOT can be transferred into an optical dipole trap (ODT) operating at 1064 nm, resulting in a cold dense sample suitable for collision studies, lifetime measurements, and evaporative cooling towards Bose-Einstein condensation.

Electron transfer in collisions between atoms in high Rydberg states and polar targets can lead to the formation of dipole-bound negative ions in which the excess electron is weakly bound by the dipole potential of the neutral molecule. Their lifetimes and collisional destruction rates are studied using a Penning ion trap. Ion decay in the trap is characterized by a single exponential lifetime, ∼60 to 100 mus governed by BBR-induced photodetachment. The rate constants for destruction of these ions by rotational energy transfer in collisions with residual target gas present in the trap are large, ∼ 10-7cm3s-1. The dynamics of CH3CN- ion production through electron transfer are examined using velocity selected Rydberg atoms. The CH3CN- ion formation rate shows a strong velocity dependence and is relatively small, the associated rate constants being ∼ 0.5--1.0 x 10-8cm 3s-1. A curve-crossing model, which considers the effect of crossings between the diabatic potential curves for the covalent K(np)/CH3CN system and the ionic K+/CH 3CN- system is discussed and provides a clear explanation for the observations. Electron transfer in collisions between dipole-bound negative ions (CH 3CN- and C2H3CN-) and target gas, including attaching molecules like SF6 and polar molecules like CH3NO2, is examined using the Penning trap. A free-electron capture model is used to describe electron transfer to attaching molecules. A near-resonant charge transfer model is employed to describe collisions between dipole-bound anions and polar molecules. The rate constants predicted by these models are consistent with the experimental observations.

The remarkable level of control of atomic wavepackets that can be achieved using very-high-n Rydberg atoms (n ≥ 350) is demonstrated. This control is accomplished with carefully-tailored sequences of short unidirectional electric-field pulses, termed half-cycle pulses (HCPs), with duration Tp ≪ Tn, where Tn is the classical orbital period. In this limit, each HCP simply delivers an impulsive momentum transfer or "kick" to the Rydberg electron. We show that strongly polarized very-high-n (n ∼ 600) potassium Rydberg atoms can be produced by manipulating lower- n (n ∼ 350) polarized atoms. This enables us to study the response of such quasi-one-dimensional (quasi-1D) very-high- n Rydberg atoms to a periodic train of HCPs at high scaled frequencies, nu 0 > 15. Pronounced non-monotonic structure in the survival probability is observed as N, the number of HCPs in the train, is increased. This behavior is very sensitive to the polarization of the Rydberg states. A different protocol that enables us to localize and to steer Rydberg wavepackets in phase space is explained using classical phase-space portraits and confirmed experimentally by navigating phase-space localized wavepackets to targeted positions. Very-high-n quasi-1D Rydberg atoms also provide a valuable laboratory for studying irreversible dephasing, i.e., decoherence. This is demonstrated by observing the evolution of a Stark wavepacket containing states of different n in an external electric field. Based on a quantum beat echo technique we report the first demonstration of the reversibility of the dephasing of an ensemble of electric dipoles which is monitored by a probe HCP. This technique allows the measurement of decoherence in the presence of strong dephasing, which can be very important for quantum information processing. All experimental results are explained with the aid of classical trajectory Monte-Carlo simulations (CTMC) and good agreement is seen.

Many areas of study, from particle-surface interactions to magnetic properties of surfaces and thin films, can benefit from electron spin analysis. These experiments frequently employ Mott polarimeters. In the past, Mott polarimeters were bulky, and operated at high voltages (∼150 kV). Modern retarding-potential Mott polarimeters operate in the 20 kV range, and are small enough to be mounted inside a vacuum system. A new, ultra-compact Mott polarimeter is described here which occupies a significantly smaller volume than previous designs. This polarimeter, when equipped with a thorium target and operating with an accelerating potential of 25 kV obtained a figure of merit of ∼1.3 x 10-4, which is similar to the best values achieved by previous Mott polarimeters. Thus this design is well suited for a variety of applications involving angle- and/or energy-resolved polarization measurements.

The optimization of an optically-pumped, flowing helium afterglow for use as a high-current dc polarized electron source with high electron spin polarization is described. The atomic electron spins of He (2$\sp3\rm S\sb1$) metastable atoms created by a microwave discharge are aligned in the presence of a weak magnetic field by circularly polarized radiation from a recently developed LNA laser. The polarized outer 2s electrons are liberated in spin-conserving Penning ionization reactions with CO$\sb2$ and are extracted from the flow tube for polarization analysis. Polarizations approaching 90% were obtained at currents below.1 $\mu$A, falling gradually to 70% at 20 $\mu$A. Comparisons with other sources, chiefly photoemission from GaAs, suggest that for most applications requiring dc currents less than 50 $\mu$A, the flowing afterglow source is superior. Possible future improvements to the present source are also discussed.

For several years Metastable Atom Deexcitation Spectroscopy (MDS) has been employed as a probe of surface electronic structure offering unparalleled surface specificity. In MDS a thermal-energy beam of rare-gas metastable atoms is directed at the surface under study, and the energy distribution of electrons ejected as a result of metastable atom deexcitation is measured. However, correct interpretation of the data requires detailed knowledge of the dynamics of the deexcitation process. In the present work spin-labeling techniques, specifically the use of electron-spin-polarized metastable He(2$\sp3S$) atoms, coupled with spin analysis of the ejected electrons, are used to probe the dynamics of He(2$\sp3S$) deexcitation at a variety of surfaces. Such measurements, coupled with studies of the deexcitation of He(2$\sp1S$) and He(2$\sp3P$) atoms at Cu(100) and Au(100) show that each species deexcites exclusively through resonance ionization followed by Auger neutralization. The data also provide the first direct confirmation of spin correlation in the Auger neutralization of ions outside a paramagnetic surface. Two proposed models for spin correlation are discussed and potential experimental tests for distinguishing between them are suggested. Studies of SPMDS at surfaces comprising layers of Ar or Xe atoms frozen onto a cryogenically cooled substrate are described and exhibit behavior similar to that observed in gas phase Penning ionization studies indicating that ejection results, in part, from surface Penning ionization (SPI). For Xe, however, additional features are observed and can be attributed to resonance ionization of the incident excited atoms followed by neutralization of the resulting He$\sp+$ ions through an interaction involving neighboring Xe atoms in the film. These results provide a rare example of a surface at which the rates for resonance ionization and Auger deexcitation are comparable. Also, the data show that the electron yield from both films is substantially higher than that from atomically clean metal surfaces. Potential experimental applications of the large spin correlation in He(2$\sp3S$) deexcitation at Cu and Au, and of deexcitation at Xe(100) and Ar(100) films are discussed.

Approximately$4\times10\sp8$ ground state lithium atoms have been confined in a non-zero magnetic field minimum produced by six permanent magnets in an Ioffe configuration. These atoms have a kinetic temperature of 1.1 mK and a peak density of $8\times10\sp9$ cm$\sp{-3}$ The trapped atom lifetime is 240 seconds, limited by collisions with background gas. The tightly confining fields generated through the use of permanent magnets create a trap which is an excellent environment for the study of quantum statistical effects, atomic collisions, and other ultra-low temperature phenomena.

Development of a low energy spin polarized He$\sp+$ source for application in studies of electron spin correlations in ion neutralization at surfaces is described. The source is based on an optically pumped helium discharge. An rf discharge is used to produce metastable helium atoms in a clean pyrex glass cell. A 300 mW Ti:sapphire laser operating at 1.083 $\mu$m is used to optically pump the He(2$\sp3$S) atoms on the $\rm 2\sp3S\sb1\leftrightarrow 2\sp3P\sb1\ (D\sb1)$ transition to preferentially populate the $\rm He(2\sp3S)\ M\sb{j}(M\sb{s}) = +1\ or\ -1$ magnetic sublevels. The electron spin polarization of the resulting atoms is measured using optical absorption. He(2$\sp3$S) polarizations of $\sim$60-70% can be routinely achieved. He$\sp+$ ions, which are produced in metastable-metastable collisions and therefore are expected to be polarized, are extracted from the discharge cell and are focused using a system of ion optics. The ion energy spread is large, $\sim$30-40 eV, but can be reduced to $\sim$3-4 eV by energy filtering. The resulting ion current, $\sim$0.5 nA, is sufficient to study spin dependences in a variety of ion-surface interactions.

Oxygen atoms are the most abundant constituent in the Earth's atmosphere between 200km and 600km, and thus are the most probable targets for precipitating ions and atoms at these altitudes. Differential cross sections for collisions involving oxygen atoms supply information necessary for numerically modeling the conditions in the Earth's upper atmosphere. Absolute cross sections, differential in angle, for electron capture by 500, 1500, and 5000eV protons in collisions with oxygen atoms are presented. The target, a mixture of atomic and molecular oxygen produced in a microwave discharge, is confined to a very short ($<$1mm) teflon-coated cell. The abundance of atomic and molecular oxygen in the target is determined using an electron-impact-ionization time-of-flight-mass spectrometer. The mass spectrometer signal, yielding the atomic oxygen density in the target cell, is calibrated by comparing the direct scattering of He(500eV) + O to the direct scattering of O(2000eV) + He. The charge transfer cross sections are integrated and compared to total cross sections reported in the literature.

Negative ion formation through electron transfer in collisions between K(nd) Rydberg atoms (10 $\leq$ n $\leq$ 110) and C$\sb7$F$\sb{14}$ and 1,1,1-C$\sb2$Cl$\sb3$F$\sb3$ is studied and provides a novel means to explore electron capture by these molecules at sub-thermal energies. The data suggest electron attachment to C$\sb7$F$\sb{14}$ occurs through two channels, one leading to the formation of long-lived C$\sb7$F$\sb{14}\sp-$ ions and the other to C$\sb7$F$\sb{14}\sp-$ ions that experience rapid autodetachment. On the other hand, electron attachment to 1,1,1-C$\sb2$Cl$\sb3$F$\sb3$ results directly in dissociation and the formation of Cl$\sp-$ ions. The present data are discussed in light of earlier results obtained with swarm and threshold photoelectron spectroscopy techniques.