The NICE-OHVMS technique: realizing the full potential of precision molecular ion spectroscopy
Noise Immune Cavity Enhanced Optical Heterodyne Velocity Modulation Spectroscopy (NICE-OHVMS) is one of the most sensitive spectroscopic techniques specific to molecular ions. NICE-OHVMS relies on the combination of three separate techniques, each of which is a powerful tool. Cavity enhancement extends the interaction pathlength of the light through the absorber, frequency modulation (heterodyning) encodes the detected signal at radio frequencies to minimize the 1/f noise, and velocity modulation makes the technique specific to ions. The optical cavity also results in a large power enhancement through the absorber which can saturate molecular transitions. The Lamb dips in the spectra, due to saturation, can be fit with high precision, and the use of an optical frequency comb as an accurate frequency reference allows transitions to be recorded with MHz/sub-MHz uncertainty. In many cases, these represent a two order of magnitude improvement on the transition frequency measurement. This thesis is an exploration of the NICE-OHVMS technique. It begins with a description of the low uncertainty measurements that have been made, and then transitions into a discussion on the lineshapes that result from velocity modulation and NICE-OHVMS. The goal of studying these lineshapes is to develop NICE-OHVMS into a quantitative technique that can determine information about the absorber, such as ion mobility, drift velocity, translational temperature, and axial electric field. Understanding the lineshapes can give accurate transition intensities, which are useful in Boltzmann analyses and saturation spectroscopy. The thesis concludes with a proposed series of measurements that can be used to study saturation on a single transition. This information can be used to understand relaxation rates of the transition and the transition dipole moment. NICE-OHVMS is a remarkable experiment with outstanding prospects for future experiments. From frequency metrology applications to saturation studies, NICE-OHVMS is rich with opportunity.
Molecular Ion, Noise Immune Cavity Enhanced Optical Heterodyne Velocity Modulation Spectroscopy (NICE-OHVMS), NICE-OHMS, Velocity Modulation, Mid-infrared, Spectroscopy, Cavity-enhanced
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign