PhD Defense: Eric Lowe

ADVISOR: Dr. Jason Kestner

TITLE: Dispersionless Broadband Frequency-Swept Pulse Design for Electron Paramagnetic Resonance

ABSTRACT: Pulse electron paramagnetic resonance (EPR) spectroscopy is a powerful tool for structural biology, but its sensitivity is limited by the narrow bandwidth of the microwave pulses relative to the width of typical EPR spectra. Frequency-swept pulses can excite far broader bandwidths, but they leave a frequency-dependent phase dispersion that must be refocused, and their performance is limited by available microwave power, pulse length, and distortions from the amplifier and resonator. This dissertation develops broadband, dispersionless pulses that account for these constraints. First, we numerically optimize the pulse shapes of a Hahn echo sequence, parameterized as neural networks, amplitude-limited Fourier series, and discrete time series, including a model of the full transmitter chain. Second, we introduce frequency-swept observer pulses for 4-pulse DEER, using a Kunz–B¨ohlen–Bodenhausen pair followed by a 1:2:1 composite swept refocusing pulse. We estimate improvement using spin-dynamics optimizations that include the resonator transfer function and a power constraint and compare with conventional Gaussian observer pulses. Finally, we show that two frequency-swept tones broadcast simultaneously over the same bandwidth, with linear sweep rates in a 2:1 ratio, implement an offset-independent π/2 point-to-point pulse and tunable transverse pulse through a direct analogue of the Hahn echo.