Many phenomena of interest to science and engineering occur at interfaces; however, access to, or discrimination of, interfacial interactions has been challenging, especially at buried interfaces. Vibrationally resonant sum-frequency generation (VR-SFG) spectroscopy is a powerful tool for investigating the molecular structure of free or buried interfaces, but spectral analysis has relied on many assumptions. To claim accurate new insights, practitioners must be able to make unique determinations from the data without experimental artifacts affecting the final results. For example, two independent and overlapping studies for the polystyrene/air interface were carried out, but reported different surface structures. Initially, this difference was attributed to the use of different substrates, but we have shown that the surface structure is independent of substrate by experimental suppression of the interfering nonresonant signal. These results show difficulties in SFG analysis that have led to faulty determinations of structural changes. Similar problems have been observed in systems assumed to have negligible nonresonant interference, demonstrating the need for proper experimental design instead of relying solely on post-experimental analysis of the data. We have investigated the inherent limitations imposed on the technique from the nature of the signal generation and nonresonant interference, and have developed methods to overcome such difficulties, depending on what is desired from the data. By nature of nonlinear spectroscopy, the desired frequency response is affected by overlapping interactions in the time domain, and these time domain interactions can be exploited to overcome challenges in analysis. By delaying the upconverting pulse, the nonresonant signal can be removed to enable accurate qualitative comparison or even quantify change; however this removal results in incomplete upconversion, or apodization, of the resonant signal, causing distortion in the observed resonant response. If absolute parameters are desired, additional work is necessary to correct the distortion of the resonant response. Correction can be accomplished by further exploiting time domain effects by collecting spectra at various delay times of the upconverting pulse, and this additional data also aids in interpretation of congested spectra. Many practical applications, however, only require a means to quantify change, and measurements of change are unaffected by the effects of apodization. These techniques have been used to more accurately analyze polystyrene and octadecylsilane surfaces.

This dissertation details the design and implementation of a state-of-the-art ambient trace analysis technique known as laser electrospray mass spectrometry. This novel technique utilizes an intense, nonresonant femtosecond laser pulse to transfer nonvolatile, fragile molecules into the gas phase from various substrates. The vaporized analyte is subsequently captured, solvated and ionized in an electrospray plume enabling mass analysis. Laser electrospray mass spectrometry is capable of analyzing samples in the liquid or solid states, mass spectral imaging of adsorbed molecules and detecting low vapor pressure analytes remotely. Experiments with biomolecules and pharmaceuticals, such as vitamin B12 and oxycodone, have demonstrated that the nonresonant femtosecond laser pulse allows for coupling into and vaporization of all molecules. This implies that sample preparation (elution, mixing with matrix and choosing samples with a particular electronic or vibrational transition) is not necessary, thus creating a universal mass analysis technique. Investigations using low vapor pressure molecules, such as lipids and proteins, led to the discovery that unfragmented molecules are transferred into the gas phase via a nonthermal mechanism. The laser electrospray mass spectrometry technique has allowed for the nonresonant femtosecond laser vaporization and mass analysis of trace amounts of a nitro-based explosive from a metal surface. The vaporization of unfragmented explosive molecules from a surface facilitates the identification of the explosive, reducing the probability of false positives and false negatives. In addition, this "soft" vaporization of molecules using nonresonant femtosecond laser pulses allows for protein to be transferred from the condensed phase into the gas phase without altering the molecule's structure, enabling ex vivo conformational analysis and possible disease typing. / Chemistry

Adhesion, heterogeneous catalysis, electrochemistry, and many other important processes and properties are driven by interactions at surfaces and interfaces. Vibrational sum frequency generation spectroscopy (VSFG) is an increasingly popular analytical technique because it can provide information about the nature and physical orientation of functional groups at these surfaces and interfaces. Analysis of VSFG data can be complicated by the presence of SFG signal that is not associated with a resonant vibration. This nonresonant sum frequency generation (NR-SFG) signal can interfere with the resonant signal and influence the detected spectrum. Methods have been developed to remove NR-SFG signal; however, these methods tend to be complicated and expensive. In fact many SFG practitioners do not have the ability to remove NR-SFG signal components, and systems designed to remove NR-SFG signal contributions may not be able to do so for some materials. We have worked to help develop a better understanding of NR-SFG. As part of this work, a better understanding of the temporal and phase behavior of NR-SFG signal has been developed, based on the behavior of NR-SFG signal from Si(111) wafers. This work calls into question some assumptions underlying nonresonant suppression methods based on time-domain detection. A new method for nondestructively testing (NDT) materials has been developed that uses nonresonant second harmonic generation, the degenerate form of SFG. This new NDT technology has the potential to detect several forms of material damage, such as aluminum sensitization, and plastic deformation of materials, which are largely invisible to current NDT technologies. Methods for extracting functional group orientation from VSFG data that contains NR-SFG contributions are also demonstrated and used to investigate how the surface of high density polyethylene changes in response to mechanical deformation. This work shows that the inability to remove NR-SFG contributions from VSFG spectra does not mean that these instruments cannot be used to make important discoveries. It simply means that NR-SFG contributions must be properly understood and accounted for during experimental design, and kept in mind during the analysis of VSFG spectra.

The exact mechanisms responsible for heating the solar atmosphere in regions such as the chromosphere (partially ionized) and the corona (fully ionized) remain quantitatively unknown. This thesis demonstrates that the ions can be heated by Alfven waves with low frequencies in fully and partially ionized low beta plasmas, which is contrary to the customary expectation. For the partially ionized case, we find the heating process to be less efficient than the scenario with no ion-neutral collisions, and that the heating efficiency depends on the ratio of ion-neutral collision frequency to the ion gyrofrequency. For Alfven waves propagating obliquely to the background magnetic field in fully ionized plasmas, we find the heating process to be more efficient than the situation with Alfven waves propagating along the background magnetic field. Furthermore, the simulation results show the parallel kinetic temperature can become even larger than the perpendicular component for the case of obliquely propagating Alfven waves.