Continued improvement of a single-mode frequency-stabilized 1.083 $\mu$m LNA laser developed at this laboratory has resulted in greater frequency stability and higher output power. Use of this laser with the Rice Flowing Helium Afterglow apparatus has resulted in considerable insight into Penning ionization reaction processes. Also, in the present work, a modified Coherent Inc. CR899-21 Ti:Sapphire laser is being used as a source of 1.083 $\mu$m radiation. A simple technique using a confocal Fabry-Perot etalon and stabilized helium-neon laser is used to limit long-term drift in the laser output frequency to $\leq$1 MHz per day. Measurements using a beam of He(2$\sp3$S) atoms show that the laser can provide stable He(2$\sp3$S) optical pumping resulting in polarizations approaching 100%. The laser is also being employed in studies of He(2$\sp3$P) collisions at low temperatures using laser-induced fluorescence and line-shape analysis. (Abstract shortened with permission of author.)

The first experimental realization of a measurement of the weak value of a variable, a concept recently introduced by Aharonov, Albert and Vaidman, is presented. Weak measurements (measurements of a weak value) address the situation in which the separation of the eigenvalues caused by a weakly interacting measurement device is small compared to the width of the distribution of the individual eigenvalues. By appropriate choice of the pre- and post-selected state it is possible that the overlapping eigenvalues will interfere producing a value outside the range of eigenvalues. We demonstrate that the weak value is a practical method of amplifying and resolving the separation between overlapping eigenvalues in an optical experiment proposed by Duck, Stevenson and Sudarshan. In this experiment a birefringent crystal spatially separates two linear polarization components of a Gaussian laser beam by a distance much smaller than the beam waist.

A theoretical discussion of laser cooling of multilevel atomic systems using intense, blue detuned laser beams is given. A method based on matrix continued fractions is presented, which enables the efficient calculation of the semi-classical force on a multilevel system. The method is applied to a three-level system driven by one standing wave and one travelling wave. The force curves obtained exhibit strong cooling features. Cooling of the three-level system is simulated using the fully quantum mechanical Monte Carlo wave function technique. The simulation predicts efficient cooling to sub-Doppler temperatures. The three-level model is related to a multilevel cooling experiment performed on $\sp7$Li. The experimental results are found to be in reasonable agreement with the three-level model. However, a comparison of the simulation and experiment for a two-level atomic system reveals significant discrepancies, which raises questions about the model and experiment.

Multiphoton excitation of molecular probes has become an important tool in experimental neurobiology owing to the intrinsic optical sectioning and low light scattering it affords. Using molecular functional indicators, multiphoton excitation allows physiological signals within single neurons to be observed from within living brain tissue. Ideally, it would be possible to record from multiple sites located throughout the elaborately branching dendritic arbors, in order to study the correlations of structure and function both within and across experiments. However, existing multiphoton microscope systems based on scanning mirrors do not allow optical recordings to be obtained from more than a handful of sites simultaneously at the high rates required to capture the fast physiological signals of interest (>100Hz for Ca2+ signals, >1kHz for membrane potential transients). In order to overcome this limitation, two-dimensional acousto-optic deflection was employed, to allow an ultrafast laser beam suited for multiphoton excitation to be rapidly repositioned with low latency (∼15mus). This supports a random-access scanning mode in which the beam can repeatedly visit a succession of user-selected sites of interest within the microscope's field-of-view at high rates, with minimal sacrifice of pixel dwell time. This technique of acousto-optic multiphoton laser scanning microscope (AO-MPLSM) was demonstrated to allow the spatial profile of signals arising in response to physiological stimulation to be rapidly mapped. Means to compensate or avoid problems of dispersion which have hampered AO-MPLSM in the past are presented, with the latter being implemented. Separately, the combination of photon counting detection with multiphoton excitation, termed generally multiphoton photon counting spectroscopy (MP-PCS), was also considered, with particular emphasis on the technique of fluorescence correlation spectroscopy (FCS). MP-PCS was shown to allow information about molecular numbers and mobility, as well as the focal volume itself, to be obtained. This capability may in the future be employed to study the number and transport of native neuronal signaling molecules. MP-PCS was also found to be a promising off-line tool which can allow the performance of AO-MPLSM to be optimized, with respect to both the instrument and the indicators employed.

Plasmon resonances in metal nanoparticles control the far field and near field optical properties of these metallic structures. The enhanced electromagnetic near field is strongest at the surface of the nanoparticles and rapidly decays away from the surface. This enhanced near field is exploited in surface enhanced spectroscopies including Surface Enhanced Raman Spectroscopy (SERS) and Metal Enhanced Fluorescence Spectroscopy (MEFS). A measurement of the decay profile of the fringing field is important both for further development of surface enhanced spectroscopy for sensor device application, and for understanding from a fundamental physics point of view. Gold nanoshells are spherical colloidal nanoparticles with a silica core covered by a thin gold shell. The plasmon resonance of nanoshells can be controllably tuned in the visible and infrared parts of the spectrum. The near field profile of nanoshells can be theoretically calculated on the basis of Mie scattering theory. The thesis describes a series of experiments designed to experimentally verify the near field profile of nanoshells. A scaffold of ss-DNA is used to place a fluorescein dye molecule at varying distances from the nanoshell surface. The SERS intensity from both the scaffold molecules and the fluorescein placed at the end of the tether is measured simultaneously and self consistently. The fluorescein-ss-DNA nanoshell conjugate structures are also used to study the distance dependence of the fluorescence emission from fluorescein. The thesis discusses the results of the SERS intensity profile agreement with the intensity profile calculated using Mie scattering theory. The quenching and enhancement of the fluorescence emission at varying distances from the nanoshell surface are also discussed.

Gold nanoshells consist of a dielectric core surrounded by an ultra thin shell of gold. By adjusting the ratio between the radius of the core and the thickness of the shell the plasmon resonance of the nanoshell can be placed at any wavelength from 500 nm--2500 nm. As the dimensions of the nanoshell approaches the wavelength of incident light, the extinction spectrum becomes a superposition of the multipole plasmon resonances. Adjustments to the core:shell ratio centered either the dipole or quadrupole mode at 830 mn. The distinct far field scattering distribution from each multipolar mode agreed well with calculations. The plasmon resonance condition and the local surface roughness give rise to intense local fields at the surface of the particle. When mercaptoaniline was absorbed onto nanoshells that had a plasmon resonance in the near IR, enhancements of the Raman signal by more than five orders of magnitude were recorded.

A systematic investigation of surface enhanced Raman scattering (SERS) was performed using metal nanoshells as the substrate. Nanoshells are a dielectric sphere coated with a thin metal shell, which have a well understood, geometrically tunable plasmon resonance. This tunability allows for the engineering of the optical near field for SERS. A simple model connecting the nanoshell electromagnetic near field at the incident frequency to that at the Raman shifted frequency is discussed. This theory is compared to the measured SERS response of the nonresonant molecule para-mercaptoaniline (pMA) adsorbed on silver and gold nanoshells. Using a solution of silver nanoshells, at an excitation wavelength of 1064 nm enhancements on the order of 106 to 108 were observed. Accounting for reabsorption of the Raman scattered light as it traverses the solution suggests enhancements of 1012. To mitigate the reabsorption, film geometries were investigated. For film measurements a 782 nm excitation laser was used. The SERS response of a dense film of silver nanoshells followed the calculated single nanoshell response of the nanoshells whose plasmon resonance was tuned near the excitation wavelength. In contrast, for nanoshells blue shifted from the excitation laser, the film Raman response followed an estimated dimer response. The Raman response as a function of nanoshell density was studied using films of gold nanoshells dispersed on the surface of polyvinylpyridine (PVP) coated glass slides. A linear dependence of the Raman modes on the nanoshell density was observed confirming that the single nanoshell plasmon dominates the SERS response. The SERS enhancements for nanoshell films calculated by direct comparison to an unenhanced measurement were on the order of 10 10 to 1012. The Raman response as a function of incident intensity was measured for dense silver nanoshell films. An optical pumping model allowing for stimulation of the Raman emission is proposed. Using this model, an effective unenhanced Raman cross section of the order of 10-27 cm2 is found. This is comparable to cross sections obtained in unenhanced Raman measurements. Evidence for two photon photoluminescence by nanoshells is presented. It is proposed the Raman emission is stimulated by the two photon photoluminescence.

An in depth study of both the predicted and actual imaging characteristics of an existing design for a multi-component relay lens was conducted. A numerical tolerancing analysis located a flaw in the current assembly procedure for the lens system. This procedure was then modified and an interferometric lens alignment station was designed and built to allow for highly accurate assembly of the multi-component lens. The system was then retested and a significant improvement in image quality was observed.

This thesis presents an experimental and theoretical study of the optical properties for two distinct planer metallic structures: metallodielectric gratings with subwavelength slots and metal nanoshells above a conducting plane. For metallodielectric gratings, two types of anomalies are present in the spectra: an edge anomaly associated with the Rayleigh wavelength, and a resonant anomaly associated with the excitations of surface plasmons. The zeroth-order transmission and reflection were measured to determine the spectral location of these anomalies and their dispersion relationships. The experimental data is compared to theoretical curves calculated using a surface impedance boundary condition approximation. The surface plasmons exhibit an energy gap in their dispersion, which is sensitive to the dielectric properties of the surrounding media. The surrounding media is changed by attaching a second grating to form a crossed grating structure, submerging the gratings in a variety of solvents, or chemically functionalizing the grating. In the first two cases, the plasmon dispersion is shifted to lower energies, the plasmon travel at a slower group velocity, and smaller energy gap is measured. The response of the plasmon dispersion to chemical functionalization is identical, except that the energy gap is increased. The difference in this trend is explained by comparing plasmons traveling on periodic structures to electrons traveling in a periodic potential. The optical properties of metal nanoshells above a conducting plane are also investigated. When a nanoshell is positioned close to a conducting plane, the surface electrons of the plane will arrange themselves to mimic the electromagnetic field of the nanoshell and its mirror image. This interaction between a nanoshell and its image plasmon approximates a nanoshell dimmer. Transmission spectra are measured as a function of the angle of polarization and compared to the expected spectra of a nanoshell dimer. The thickness of the conducting plane is also varied, which leads to a blue shift in the plasmon resonances. This shift in energy is qualitatively explained by explained using a plasmon hybridization model.

A 422 nm laser was constructed for the purpose of studying a strontium ultra-cold neutral plasma. Since strontium ions have atomic lines in the visible, we can optically image the plasma via the 88 Sr+ 2S1/2 → 2 P1/2 transition using 422 nm light. We produce light at this wavelength by converting infrared light at 844 nm from a commercial semiconductor infrared diode laser via second-harmonic generation in an semi-monolithic linear enhancement cavity. This thesis will cover the experimental details pertaining to nonlinear optics, optical resonator design, and locking electronics used to create a 422 nm laser.