Issues in Laser Induced Breakdown Spectroscopy for Measurements in the Deep Ocean and Other High-Pressure Environments

This dissertation describes fundamental and applied studies that have advanced the understanding and application laser induced breakdown spectroscopy (LIBS) to the deep-ocean environment and to operation on a deep-ocean submersible. Chapter one is an overview of LIBS including a brief history, LIBS theory, the instrumentation typically used, and a specific application. Chapter two analyzes the effect that monodisperse suspended particles have on LIBS emission intensity and on the formation of a LIBS plasma. This chapter demonstrates that for particle concentrations similar to those found in the neutrally buoyant regions around hydrothermal vents there is little effect on the LIBS emission intensity. Also, this chapter shows that by using 532 nm excitation and a 180° collection geometry, strong stimulated Raman of water appears at 649 nm in the spectrum. Chapter three describes an investigation into the use of hydrogen and oxygen as an internal standard for lithium and potassium in bulk aqueous solution. These investigations reveal that the precision in the measured LIBS signal for Li and K is improved by using H or O as an internal standard, with oxygen providing up to a 9-fold improvement in the relative standard deviation (RSD). Finally, chapter four describes the construction and tests of a super critical CO2 LIBS cell for LIBS measurements of samples in a Venus-type atmosphere