Study of Laser Melted Liquids and of Interfacial Ions by Nonlinear Spectroscopy
The content of this thesis can be broken into two distinct parts. The first summarizes experimental efforts to develop a better understanding of the structure and properties of liquid carbon and silicon after melting appropriate targets with an intense femtosecond laser pulse. Further research into the properties and structure of liquid carbon, particularly that focused on understanding the relationship between the thermodynamic state of the liquid and the material properties, is critical for resolving the many current controversies. Moreover, as laser synthesis grows in popularity as a tool for the production of nanomaterials, it has become increasingly critical to characterize the liquid melt which serves as an intermediate in the synthesis process, as well as the ensuing nucleation of nanostructures in the melt. To address these issues, we have carried out experiments on laser melted graphite and silicon substrates using a wide array of techniques including linear and non-linear laser spectroscopy as well as x-ray scattering to study the properties of the liquids on ultrafast timescales. The results of these studies provided new insights both into the structure and properties of the non-thermally melted liquid as well as the subsequent dynamics of the ablation plume that forms after laser melting.
The second half of the text discusses nonlinear spectroscopy experiments studying the thermodynamics of ion solvation at the water surface in solutions containing surfactants or mixed salts. Only recently has it been recognized that certain specific anions exhibit enhanced interfacial populations relative to the solution bulk. The interfacial affinity for these ions that accumulate at the interface follows the inverse of the well-known Hoffmeister series. The physics that drive these ions to accumulate at the water surface, contradicting predictions from older theories of ion solvation, remain incompletely understood. The presence of these ions, however, has profound implications for biology and atmospheric chemistry. As such, it is critical to further advance our understanding of the mechanisms that result in selected ions localizing to the interface. The nonlinear optics experiments detailed in the second half of this thesis expand the understanding of the interfacial solvation physics of ions by extending beyond the simple single salt systems studied in previous work. Measurement of the thermodynamics of ion adsorption in these more complex solutions permits the validity of different thermodynamics models of ion adsorption to be assessed and so facilitates the development of a universal model for ion solvation physics at the interface between media. Additionally, the systems studied in the experiments detailed in this thesis are relevant to real-world atmospheric and biological systems and may lead advances in these areas.