Chloe Wheeler

Major: Physics
Mentors: Antonin Sojka, Professor Mark Sherwin

Development of Tunable Phase Shifter for Electron Paramagnetic Resonance Spectroscopy

Electron Paramagnetic Resonance (EPR) is a powerful technique to study spin magnetization relaxation times. Typically, these relaxation times are studied by pulsed EPR, where a series of high-power mi- crowave pulses are applied to change the sample magnetization. At fre- quencies above 100 GHz, most spectrometers cannot operate at broad frequency ranges with sufficient power. The alternative is Free Electron Laser (FEL), which can provide kW power at a wide frequency range of 140-500 GHz. However, the high power of FEL often buries the signal in the background. Therefore, we employ a phase cycling technique that shifts the phase between two applied EPR pulses, which allows us to minimize background in post processing. Currently, this shift is realized by inserting an HDPE plate, optimized for one particular frequency, into the optical path of one FEL pulse. In our project were developing a novel solution which employs a single phase shifter with a plastic-oil interface and tunable components that allow us to vary the phase shift at any frequency within the FEL-EPR spectrometer range. To accomplish this project we designed a testing apparatus to evalu- ate the refractive index and absorption coefficient of different oil and plastic interfaces. From the investigation we chose the combination of high impact polystyrene (HIPS) and SAE 20W-50 (engine oil) which will be integrated into our tunable phase shifter design. Successfully accomplishing this project will expand phase cycling treatment to the whole FEL-EPR spectrometer range and thus expand its use to new systems and scientific problems.