Edward F. Thenell
Friday, December 9, 2016 3:00PM (B-1 JFB)
Title: Rabi Oscillations in Strongly-Driven Magnetic Resonance Systems
The strong-drive regime, in which the amplitude of an oscillating driving field is on order the energy separation between states in a two-level system, is frequently realized in atomic and optical systems. However, it is rarely accessed in traditional magnetic resonance experiments, due primarily to signal-to-noise concerns in thermally-polarized samples. However, such limitations are circumvented in the two 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 frequency, where the strong drive regime can be easily 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 quantizing field and driving field magnitudes. 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.