EQuAL Student Seminar: Alex Giovannone

Measuring Nanosecond Lifetimes with High-Field, High-Power, Pulsed Electron Spin Resonance

A central challenge in realizing pulsed Electron Spin Resonance (ESR) above 100 GHz is generating pulses with sufficient power. At UCSB, we are nearing completion on a unique pulsed ESR spectrometer designed to slice the output of a free-electron laser (FEL) into high-power microwave pulses with independently controllable duration, phase, and amplitude. The FEL can generate kW power for a few microseconds, or 10s of kW in 40 ns pulses when cavity-dumped. We aim to use this source to measure nanosecond lifetimes in the high field regime. In this talk, I will report on progress in the pulse slicing subsystem of the FEL powered agile electron spin resonance spectrometer. Pulse slicing is achieved using laser-driven silicon semiconductor switches, in which ultrapure silicon wafers with passivated surfaces are driven from a transmissive to a highly reflective state by 532 nm laser pulses. Three broadband stacked complementary-channel pulse slicers, separated by two frequency-agile phase shifters, enable slicing the FEL output into up to three kilowatt-level microwave pulses. I will describe measurements of the insertion loss, leakage between channels, and pulse slicing demonstrations. We measured the pulse slicing system with silicon wafers whose thickness is designed for optimal performance at 205 GHz and 410 GHz. The frequency-agile phase shifters, which control the relative phase of sub-THz pulses by mechanically varying the path length of one channel, will also be characterized. Together, these subsystems bring our new spectrometer close to its first pulsed ESR measurements on systems with nanosecond relaxation times. This work is supported by NSF DMR 2117994.