Bilirubin, a yellow pigment, is formed by the breakdown of hemoglobin. Neonates are susceptible to high bilirubin levels in their blood which places them at risk of neuronal damage, and monitoring of the bilirubin levels in these neonates is clinically required. Transcutaneous optical monitoring of the bilirubin will provide a non-invasive, inexpensive measurement of bilirubin in the skin. The optical properties of skin are important for interpretation of the reflected light from the skin. In this report, the optical properties of neonatal skin were measured in the visible range on twenty in vitro skin samples. The scattering of the skin is dominated by the collagen fiber bundles in the dermis. Scattering in the dermis increases linearly with gestational maturity due to the accompanying increase in the size and number of the collagen fiber bundles. Scattering in the dermis was modelled by Mie and Rayleigh scattering. The collection efficiency of an optical patch used for reflectance measurements at the skin surface varies with the skin's optical properties. The collection efficiency of the optical patch as a function of optical properties was determined by measurements in phantoms, and by Monte Carlo computer models. Dermal absorbers and epidermal melanin affect the reflected signals differently, and have to be analyzed separately. In addition to bilirubin content of neonatal skin, other sources of variation include skin maturity, skin thickness, melanin content, blood depth, and blood content. Each of these factors affects the reflected spectrum. Each source of variation was analyzed individually and an algorithm was developed to determine the absorbances of bilirubin and blood in the dermis from optical patch reflectance measurements. The algorithm was applied to analyze reflectance measurements performed on a heterogeneous clinical population consisting of 47 neonates. The algorithm was then adjusted to minimize a score designed to ensure that the determined in vivo cutaneous bilirubin concentrations were invariable with skin melanin and blood content. Consideration of optical transport in the skin has enabled the determination of cutaneous bilirubin concentration in heterogeneous neonatal populations.

Molecular spectroscopy is used to probe a quantum degenerate gas of 7Li atoms. Several effects are investigated using both single-color and two-color (Raman) photoassociative spectroscopy. An unusual spectral shift with laser intensity is observed for single-color photoassociation and the intensity dependence agrees with theoretical predictions. Additionally, the prospects for altering the interactions between ground-state atoms is investigated for both the single-color and Raman schemes. The single-color scheme is found to be impractical experimentally (although feasible theoretically) while the Raman scheme may be experimentally feasible as well. The Raman spectra display an interesting lineshape which is found to reflect the rate for inelastic collisions involving ground-state molecules (produced via the Raman process) as well as the attractive mean-field interactions between atoms in the condensate. Under certain circumstances, a dispersive Raman lineshape is observed which may be due to coherence properties of both the condensate and the thermal gas. Additionally, the Raman lineshape appears to reflect the kinetic time scale for thermal atoms to enter the condensate via elastic collisions. The Raman technique is applied to studies of the condensate growth and collapse dynamics caused by attractive interactions between condensate atoms, and enables the first direct observations of this phenomenon.

Low-energy electron transfer in collisions between a Rydberg atom and a target molecule can result in the formation of negative ions. Depending as to the properties of the target molecule the electron may be bound in a localized molecular orbital (valence-bound) or bound by its dipole potential in a diffuse orbital located at the positive end of the dipole (dipole-bound). Here we examine the properties of valence-bound and dipole-bound negative ions created through electron transfer in collision with Rydberg atoms, in particular, their lifetimes, collisional properties and electric-field-induced detachment characteristics. Intercomparison of the various data also leads to new insights into electron attachment to molecules that can support both valence-bound and dipole-bound negative ion states.

The study of computation occurring in single neurons and small networks of interconnected neurons is often limited by (1) the number of sites that can be simultaneously probed with electrophysiology tools such as patch pipettes and (2) the recording speed of fluorescence imaging tools such as confocal or multiphoton microscopy. Even in the line scan mode of galvanometer-based scanners, where one scan dimension is sacrificed to gain overall speed, the effective frame rate is limited to less than 1 kHz with no flexibility in site selection. To overcome these limitations and allow the study of many sites throughout the dendritic arbor, we have developed an addressable confocal laser-scanning microscope that permits recording from user-selected sites-of-interest at high frame rates, in addition to conventional full frame imaging. Our system utilizes acousto-optic deflectors (AODs) in the illumination pathway to allow for rapid user-defined positioning of a focused laser spot. However, since AODs rely on diffraction to steer a laser beam, they cannot effectively descan the fluorescence emission spectrum as done in mirror-based systems which utilize reflection; this prevents the use of a stationary pinhole as a spatial filter. Instead, we implement an addressable spatial filter using a digital micromirror device (DMD) in conjunction with the AODs to achieve confocality. A registration algorithm synchronizes the AODs and DMD such that point illumination and point detection are always colocalized in conjugate image planes. The current version of the confocal system has a spatial resolution of ∼1 mum. Furthermore, by letting the user tailor which sites are visited, we have shown that recordings can be made at an aggregate frame rate of ∼40 kHz. We have successfully demonstrated that the system is capable of optical sectioning and thus exhibits the main advantage of a confocal microscope for light-scattering biological tissue. This property was used to create three-dimensional reconstructions of fluorescently labeled test specimens. Additionally, we have used the system to record intracellular calcium transients using the fluorescent calcium indicator Oregon Green BAPTA-1. The transients were a result of back-propagating action potentials elicited via 1 nA current injections in cultured hippocampal neurons from wild-type mice.

Understanding the effects of interactions on the ground-state of a paired degenerate Fermi gas throughout the BEC-BCS crossover has been a long standing physical quest for which countless papers have been written. The crossover describes the smooth transition of the physics of a BEC of tightly bound dimers to that of a paired BCS superfluid. A Feshbach resonance is used to tune the interactions necessary to study the crossover. Right around resonance the interactions are expected to be parameterized by a single universal parameter beta [1--3]. This thesis describes a measurement of the axial size of paired, 6Li clouds in the BEC-BCS crossover and provides a comparison with theory. In the BEC regime, absolute measurements of the molecular scattering length are compared with the atomic scattering length and the ratio is compared with theory. Finally, a measurement of beta is made and compared with theory.

A 461 nm laser was constructed for the purposes of studying ultracold neutral strontium. The dipole-allowed 1 S0 → 1P1 transition at 460.862 nm can be used in laser cooling and trapping; optical imaging, Zeeman slowing, and photoassociative spectroscopy. We produce light at this wavelength by converting infrared light at 922nm from various IR sources, notably a Ti:Sapphire laser, via second harmonic generation in a frequency doubling cavity using a potassium niobate crystal. This thesis will discuss the motivation, optical resonator, locking electronics, and characterization of a 461 nm laser.

The theory of continuous wave difference frequency generation (DFG) is studied for a mixing of two waves in a nonlinear medium, the absorption effect of the material is included and optimization conditions are studied. Trace concentrations of nitric oxide were observed in a mixture of ambient air using a DFG source with periodically poled lithium niobate (PPLN) as the nonlinear medium. A sensitivity of 300 ppb was achieved. The design and development of a fiber-coupled DFG sensor are reported. This sensor applied to the observation of carbon monoxide.

The theory of difference frequency generation has been further developed. Derived from basic principles, the equations developed here accurately predict the conversion of power to the idler wave. Critical phasematching can now be modeled with ellipticity in both beams and the effects of double refraction and non-normal incidence upon the crystal treated. It is no longer necessary to focus the beams into the center of the crystal nor is it necessary to have an equal confocal parameter in the two drive beams. A mid-infrared spectrometer based on titanium:sapphire pumped difference frequency generation in silver thiogallate (AgGaS$\sb2$) has been constructed in order to conduct high resolution spectroscopy on free radicals. Detector limited sensitivity has been demonstrated with an estimated source bandwidth of 0.00003 cm$\sp{-1}$. The process used to calibrate scans has been improved and calibration accuracy of 0.001 cm$\sp{-1}$ is now routine. With the silver thiogallate spectrometer, the infrared spectrum of the monodeuterated propargyl radical (CH$\sb2$CCD) has been acquired. Approximately 250 lines have been positively identified and assigned to the $\nu\sb1$ C-D stretch in the region between 2300 cm$\sp{-1}$ and 2400 cm$\sp{-1}$. The spectrum consists of a-type transitions ($\Delta$K$\sb{\rm a}$ = 0) with a fully resolved K subband structure, in contrast to the CH stretch of the normal radical. This resolved structure is due to a P$\sb{\rm a}$-type Coriolis interaction or a Fermi resonance in the molecule. These interactions may be responsible for the fact that we were unable to identify the odd K subbands, though positive identification of the K$\sb{\rm a}$ = 0, 2, 4, and 6 subbands was made and used to determine rotational constants for the radical. A spectrometer based on difference frequency generation in gallium selenide (GaSe) was constructed. Precise phasematching characteristics were determined as well as the potential power produced in the process. The instrument is continuously tunable in the 8.8-15.0 $\mu$m wavelength region.

A general technique for solving Maxwell's equations exactly, based on expansion of the solution in a complete set of vector basis functions has been developed. These vector eigenfunctions are derived from the complete set of separable solutions to the scalar Helmholtz equation in a particular coordinate system and are shown to form a complete set. The method is applicable to a variety of problems including the study of near and far field electromagnetic scattering from particles with arbitrary shapes, plasmon resonances in spherical nanoparticles with spherically concentric 'shells' and the calculation of plasmon resonances in the sphere-plane geometry. An exact method for solving the inhomogenous Maxwell's equation (i.e., in the presence of charges and currents) is also outlined.

A thorough knowledge of the excited state dynamics in conjugated polymers is necessary for efficient use of these novel materials. Triplet excitons are believed to play an important role in conjugated polymer-based device operation. Triplet excitons are also believed to play a primary role in photo-oxidative degredation of polymer devices. Two-photon photoemission is used to probe triplet exciton relaxation dynamics in pristine conjugated polymer films and triplet-triple annihilation is determined to be an important deexcitation mechanism. Controlled photo-oxidation of conjugated polymer films is studied using two-photon photoemission. The triplet exciton-derived photoemission peak is observed to shift and narrow dramatically upon photo-oxidation. The peak narrowing is attributed to narrowing of the distribution of polymer conjugation lengths in the film. The peak shift is attributed to formation of defects at the ends of the polymer chains which change the average triplet exciton energy.