Resonant laser ablation: A mechanistic study of a novel solid sampling technique with detection by microwave-induced plasma atomic emission spectrometry

Laser ablation refers to the explosive process by which a solid sample is vaporized though a violent laser-material interaction resulting in a plume of atoms, ions, and molecules. It has been demonstrated that an increase in sensitivity and selectivity of an analyte can be achieved by tuning the laser wavelength to match that of a resonant gas phase transition of the analyte. Tuning the ablation laser to such a wavelength has been termed Resonant Laser Ablation (RLA). Chapter 1 contains a review of the current theory and applications of RLA. ^ The analytical utility of RLA is hindered by the lack of understanding of the mechanism by which this enhancement occurs and an uncontrollable ablation process. Chapter 2 outlines both resonant and non-resonant interactions in both the Chemistry and Physics literature lending insight into factors that might have been overlooked in the description of the currently accepted theory of RLA. ^ The data presented in Chapter 3 demonstrates the enhancement effect of trace metals in stainless steel samples, and pure copper and aluminum samples in both ablation wavelength scans and emission scans. Optical and SEM images illustrate changes in surface morphology as the laser wavelength approaches the resonant wavelength of the target material. Based on this date, a mechanism is presented in Chapter 4 to account for the increase in atomic signal, as well as a distinct laser-material interaction. ^ Chapter 5 explores a wide range of applications of Near Infrared Spectroscopy (NIRS) in various fields of analytical chemistry, taking advantage of its inherent rapid analysis time and minimal sample preparation. A novel PbS spectrometer is also characterized using a variety of samples demonstrating its usefulness as an analytical tool and also it\u27s shortcomings and limitations. ^ Appendix A outlines detailed experiments for the coupling of RLA with an Inductively Coupled Mass Spectrometer (ICP-MS) through the use of a novel cell design. Appendix B and C outlines the RLA apparatus alignment and basic operating principles of the Optical Parametric Oscillator (OPO) laser, respectively. Appendix D describes the use of computer-interfaced stepper motor for sample and attenuator control.