Time-resolved Fourier spectroscopy has been applied to the observation of Rydberg O(I) and O(,2) infrared emission from a pulsed discharge at 0.1 torr. The emission of a 2.5 meter long column through the negative glow was observed with a newly designed discharge apparatus. A computer-controlled interferometer step-servo was developed to enable 100 microsecond time- and 0.12 cm('-1) spectral-resolution capabilities. The Rydberg features were enhanced with respect to those of contaminates by signal processing methods that utilized their individual temporal behavior. Line position determinations of the 7h - 5g, 7g - 5f, 5g - 4f and 6g - 4f O(I) lines have been made to an accuracy of 0.015 cm('-1). Polarization constants of the O(II) core have been deduced from this data. Nine newly observed and four previously observed line-like features have been attributed to Rydberg O(,2).

Quasi-one-dimensional Rydberg atoms exposed to alternating positive and negative electric field pulses (kicks) are an example of a chaotic atomic system. Chaotic ionization is predicted in this system via a phase space turnstile mechanism, and we have explored this experimentally. Turnstiles form a general transport mechanism for numerous chaotic systems, and this study is the first to explicitly illuminate their relevance to atomic ionization. Two experiments are presented. In the first we show that the ionization of the electron depends not only on the initial electron energy, but also on the phase space position of the electron with respect to the turnstile--that part of the electron packet inside the turnstile ionizes quickly, after one period of the applied field, while that part outside the turnstile ionizes after multiple kicking periods. In the second experiment we show the signature of the turnstile manifests itself in the step-function-like behavior of the ionization fraction as a function of the kick strength. This behavior persists for different values of kicking periods and starting electron energies.

This thesis presents calculations of the magnetic helicity injection due to rotating sunspots and a determination of the characteristics of the rotating sunspots in the active regions with simple magnetic configurations. Four active regions are investigated to study the relationship between rotating sunspots and magnetic helicity. The observations indicate that significantly more helicity is injected during the period of rotation in polarities with strong magnetic field. This may be a result of the emergence of a magnetic flux rope from below the solar surface. Moreover, our preliminary study on a large sample of 90 active regions shows that the level of flaring activity increases with the rate of helicity injection. Finally, a statistical study is carried out to determine the relation between rotating sunspots and the emergence of magnetic flux tubes. Among 82 active regions which exhibit flux emergence, 93% are associated with rotating sunspots. Among 50 active regions without well-defined flux emergence, 60% of sunspots are observed to be rotating, though relatively slowly. In addition, we find that sense of the rotation (i.e., clockwise or counter-clockwise) of the sunspots shows a weak hemispherical tendency.

We have investigated $\sp3$He spin diffusion in two dilute solutions of $\sp3$He in $\sp4$He, with atomic fraction $x\sp3=1.82\times 10\sp{-3}$ and 6.26 $\times$ 10$\sp{-4}$, spin-polarized by an 8 T field. We do not find evidence that the diffusion coefficient for spins transverse to the average magnetization ($D\sb\perp$) declines or saturates at temperatures down to 0.20$T\sb{\rm F}$, contrary to previous experiment (Gully and Mullin 1984) but in accord with current theory. We have compared our measurements with the latest theory of Jeon and Mullin (1991); our data is mostly in good agreement with their theory if a slightly modified version of a $\sp3$He-$\sp3$He interaction due to Ebner (1967) is used. The congruence between data and theory supports the conclusion that the s-wave approximation to the interaction is not useful for transport calculations even for these rather dilute solutions. There may be an one unresolved discrepancy: our diffusion constant for the lowest concentration at the lowest temperatures is 25% higher than theory predicts. This could be due to a polarization dependance for $D\sb\perp$ or to a modification of the boundary condition by a bound $\sp3$He state, or possibly due to errors in the theoretical calculation.

Collisional excitation and ionization cross sections suitable to highly excited states of the target atom at low and intermediate kinetic energy of the scattering particle have been derived following the semiclassical Impact Parameter approximation. An analytical expression for cross section involving transitions with $\Delta l > 1$ has been obtained when the semiclassical requirement and the Ehrhardt conditions are valid. The analytical cross sections are explicit functions of the initial quantum number of the target atom, the incident velocity of the colliding particle and $\Delta n$ (for bound-bound transitions), allowing a generalization to any transition needed in a spectral modeling code. The cross sections obtained with the Impact Parameter approximation present a close agreement with previous theoretical results for dipole and quadrupole ($\Delta l$ = 2) cross sections of bound-bound transitions. Results of octupolar ($\Delta l$ = 3) cross sections are also given for $\Delta n$ = 1 and $\Delta n$ = 2 and a wide range of incident energies. The results indicate that the cross sections corresponding to transitions with $\Delta l > 1$ are significant up to incident energies about 100 times the transition energy. The Impact Parameter cross sections for bound-free transitions present a very good agreement with experimental values, in particular at low incident energies.

We have used the narrow 2 S 1/2 [arrow right] 3 P 3/2 transition in the ultraviolet (UV) to laser cool and magneto-optically trap (MOT) 6 Li atoms. Laser cooling of lithium atoms is usually performed on the 2 S 1/2 [arrow right] 2 P 3/2 (D2) transition, where temperatures of twice the Doppler limit, or ∼300 μ K for lithium, are achieved. The linewidth of the UV transition is seven times narrower than the D2 line, resulting in a lower Doppler limit. We show that a MOT operating on the UV transition reaches temperatures as low as 59 μ K. We load 6 million atoms from this UV MOT into a 1070 nm optical dipole trap (ODT). We show that the light shift of the UV transition in the ODT is small and blue-shifted, facilitating efficient loading. Evaporative cooling of a two spin-state mixture of 6 Li in the ODT produces a quantum degenerate Fermi gas with 3 million atoms in only 11 seconds.

The ionization of xenon Rydberg atoms at metallic surfaces is examined. The data show that, when the effects of stray electric "patch" fields present on the surface are taken into account, ionization is well described by a simple over-the-barrier model. The patch fields are determined from direct measurements of the potential variations across the target surfaces using Kelvin probe force microscopy. Monte Carlo techniques are used to model the atom-surface interaction. The results confirm the important role that patch fields can play during Rydberg atom-surface interactions and suggest that such interactions can provide a sensitive probe of stray fields at surfaces. To demonstrate this, measurements of the threshold conditions required to observe ions resulting from surface ionization are used to estimate how large such stray fields can be. The data show that the stray fields can be sizable, as large as ∼ 10 3 V · cm -1 100 nm from the surface and ∼ 10 V · cm -1 500 nm from the surface, and illustrate the potential of Rydberg atoms for detecting and characterizing surface electric fields. Methods to enhance the surface ionization signal using electrode arrays patterned on a surface are investigated. Simulations show that bias voltages applied to a series of parallel wires comprised of two interleaved comb-shaped electrodes can have a dramatic impact on ion collection efficiency. It is suggested that such a surface can be used to efficiently collect low- n Rydberg atoms ( n [Special characters omitted.] 10). Significant progress towards fabrication of a functioning surface of 1 μm wide wires with 1 μm spacing is documented.

High angular momentum Rydberg wave packets are studied. Application of carefully tailored electric fields to low angular momentum, high- n ( n ∼ 300) Rydberg atoms creates coherent superpositions of Stark states with near extreme values of angular momentum, [cursive l]. Wave packet components orbit the parent nucleus at rates that depend on their energy, leading to periods of localization and delocalization as the components come into and go out of phase with each other. Monitoring survival probability signals in the presence of position dependent probing leads to observation of characteristic oscillations based on the composition of the wave packet. The discrete nature of electron energy levels is observed through the measurement of quantum revivals in the wave packet localization signal. Time-domain spectroscopy of these signals allows determination of both the population and phase of individual superposition components. Precise manipulation of wave packets is achieved through further application of pulsed electric fields. Decoherence effects due to background gas collisions and electrical noise are also detailed. Quantized classical trajectory Monte-Carlo simulations are introduced and agree remarkably well with experimental results.

This thesis presents the experimental study on the two-spin component, strongly interacting 6 Li Fermi gases in 3D and 1D traps. The interaction strength is tuned from the molecular BEC regime to the BCS regime using a Feshbach resonance. The trap dimension can be tuned from 3D to 1D with the implementation of optical lattice. The evaporation of imbalanced Fermi gases in 3D trap is studied. The anisotropic and fast evaporation is the cause of the deformation observed in the 2006 Rice experiment. In a balanced Fermi system, the fraction of correlated states is measured as a function of interaction and temperature. At unitarity, the fraction of correlated states is ∼85% and exists above T c . The one-body-like photoexcitation rate can be related to the contact quantity. Lastly, the spin-imbalance in a one-dimensional Fermi gas is studied. The 1D phase diagram is mapped out. The result agrees well with the 1D theory, in which the partially polarized regime is predicted to be a FFLO phase, an exotic superfluid with pairs carrying finite center-of-mass momentum proposed almost 50 years ago.

This thesis describes the measurements of collective effects in strongly coupled ultra-cold neutral plasmas (UNPs). It shows the implementation of experimental techniques that perturb either the density or velocity distribution of the plasma and it describes the subsequent excitation, observation and analysis of the aforementioned collective phenomena. UNPs are interesting in that they display physics of strongly coupled systems. For most plasma systems, collective effects are well described with classical hydrodynamic or kinetic descriptions. However, for strongly coupled systems, the Coulomb interaction energy between nearest neighbors exceeds the kinetic energy, and these descriptions must be modified as the plasma crosses over from a gas-like to liquid-like behavior. Strongly coupling can be found in exotic plasma systems found astrophysics, dusty plasmas, non-neutral trapped ion plasmas, intense-laser/matter interactions and inertial confinement fusion experiments. Compared to other strongly coupled plasmas, UNPs are ideal for studying collective effects in this regime since they have lower timescales, precisely controllable initial conditions and non-invasive diagnostics. Previous studies of UNPs concentrated on plasma expansion dynamics and some collective effects such as disorder induced heating, but little work had been done in relaxation or collision rates and collective modes in UNPs. This thesis presents a method for measuring collision rates by perturbing the velocity distribution of the plasma, observing plasma relaxation and measuring the relaxation rate. It also presents a new technique for observing collective modes in the plasma by perturbing the initial density of the plasma and how this results in the excitation of ion acoustic waves and a measurement of its dispersion relation. Finally, this thesis presents how this last technique can be used to create a gap in the center of the plasma and how this leads to hole propagation and plasma streaming and presents a characterization of both phenomena. The result of these experiments will be valuable for predicting the behavior of collective effects in other strongly coupled plasmas and for comparison with theories that describe them.