NEW TECHNIQUES FOR SUB-DOPPLER SPECTROSCOPY OF MOLECULAR IONS BY

This thesis details research in developing new methods for performing high-resolution sub-Doppler spec-troscopy of molecular ions in the laboratory. Molecular ions are of interest to a variety of elds, from astrochemistry to fundamental physics to the study of chemical reactive intermediates. The limiting factor in developing a deeper understanding of many ion systems is the quality of the available laboratory spectra. Traditional techniques for high-resolution spectroscopy of ions are limited by two factors: the precision is often limited by the Doppler-broadened linewidths of the observed spectra, and the accuracy is typically limited by the laser frequency calibration. Two new techniques are described in this thesis: cavity enhanced velocity modulation spectroscopy (CEVMS) and ion beam spectroscopy. Each of these techniques was rst implemented in the near-infrared spectral region using a titanium sapphire laser, and was then extended into the mid-infrared, using an optical parametric oscillator (OPO) for CEVMS and difference frequency generation (DFG) for the ion beam. Both of these techniques allow for sub-Doppler resolution to signi-cantly improve the precision beyond what was possible with traditional ion spectroscopy, and because both techniques are based on direct absorption spectroscopy, they require nothing of the ion of interest other than an allowed transition within the tuning range of the laser used, making them applicable to a wide variety of ions. The lasers used with both of these techniques have been referenced with an optical frequency comb for sub-megahertz absolute calibration accuracy of linecenters, which is a signicant improvement beyond the 20-200 MHz accuracy that was typical of ion spectroscopy before the work presented in this thesis. ii To my wonderful and loving wife, Shannon. ii