Graduate Services Coordinator; Lecturer Physics
Experimental Condensed Matter Physics
Ph.D., Yale University, 2010
Novel Pulse Sequences Exploiting the Effects of Hard π-pulses
In magnetic resonance and other spectroscopies, the strong pulses used to control coherent spin evolution are often approximated as instantaneous delta function rotations. However, small corrections to the delta function model can cause surprising departures from the conventional theory in standard multipulse NMR experiments using strong π-pulses. In this dissertation, we report the exploration of the small correction terms resulting from the finite duration of realistic pulses, however strong, using average Hamiltonian theory. Investigation of role these terms could play in standard NMR experiments led to the design and demonstration of a new class of spin echoes. We present analogs of the original free induction decay (FID), Hahn echo, and CPMG echoes whose experimental design is based on terms typically ignored when strong pulses are used. Variants on the original magic echo are demonstrated as well as the quadratic echo, based on both the zeroth- and first-order average Hamiltonian expressions and which has no classic NMR spin echo analog. Finally, we present alternative approaches to overcoming the line broadening effect of dipolar interactions in solids. Using a variation on the quadratic echo pulse sequence as a building block, we develop a new approach to line-narrowing and magnetic resonance imaging of solids which allows control of both the Zeeman and dipolar phase wrapping.