| Description |
This dissertation is focused on an exploration of the strong-drive regime in magnetic resonance, in which the amplitude of the linearly-oscillating driving field is on order the quantizing field. This regime is rarely accessed in traditional magnetic resonance experiments, due primarily to signal-to-noise concerns in thermally-polarized samples which require the quantizing field to take on values much larger than those practically attainable in the tuned LC circuits which typically produce the driving field. However, such limitations are circumvented in the two primary experiments discussed herein, allowing for novel and systematic exploration of this magnetic resonance regime. First, spectroscopic data was taken on 129Xe nuclear spins, hyperpolarized via spin-exchange optical pumping (SEOP). Since SEOP creates a nuclear spin polarization that is independent of the quantizing field magnitude, magnetic resonance experiments can be performed at arbitrarily low resonance frequency, where the strong drive regime can be trivially accessed. The spectroscopic data are attained by studying the amplitude and frequency of 129Xe Rabi oscillations as a function of the driving frequency, for various values of the applied field and driving field magnitudes. These Rabi oscillations can be observed in real-time via an indirect optical detection scheme, designed and built in the Saam lab. Second, we explore the spectrum of Rabi oscillations of protons in a conventional water sample, acquired under longitudinal field modulation, which reproduces the conditions of the strong drive regime in the rotating frame. The modulation regimes on which this work focuses tend to create multiple strong frequency components, as well as exhibiting a strong sensitivity to the phase of the modulation field. To account for these complications, we use a phase-averaged Fourier transform analysis, with which modulation-related effects on the Rabi dynamics can be studied systematically by tracking the position and magnitude of components in the Rabi oscillation Fourier spectrum. Additional material covers a study of longitudinal nuclear spin relaxation times in two organic semiconducting polymers, MEH-PPV and DOO-PPV, with the intention of informing the feasibility of angular momentum transfer to the nuclear spins from spin-polarized charge carriers in active spintronic devices. |
