EQuAL Seminar: Antonin Sojka & Brad Price

"Development of Frequency Agile ESR Powered by ITST’s Free Electron Laser"

In the last decade, electron spin resonance (ESR) has been moving to higher fields and frequencies to achieve better resolution and sensitivity, and to get access to high-spin systems with large zero field splittings (also called single ion anisotropy). Nowadays, frequencies above 100 GHz have become standard. Our work focuses on establishing a versatile broadband high field ESR spectrometer using UCSB’s free electron laser (FEL) as a microwave source. Importantly, for sources as powerful as the FEL (microsecond long, kW power pulses), eliminating standing waves and spectrometer ring-down (“dead-time”) is critical. To enable pulsed FEL-ESR measurements, we have developed and tested a new generation of modular quasi-optical pulse slicer for kW-power amplitude modulation. Given a quasi-cw input, the two outputs of a module are (1) a pulse with programmable duration and (2) its complement. The quasi-optical design incorporates a laser-driven silicon switch at Brewster’s angle to the incoming THz beam, which limits undesired reflections before the switch is activated such that THz power is only transmitted when the switch is “on.” An “off” switch ensures that no power is leaked after the pulse and that the switching profile is sharp. In the second part of the talk, we present a quasioptical sample holder (QSH) that enables significantly improved induction mode isolation and signal-to-noise of continuous wave and rapid-scan ESR and allows us to do zero-dead time measurements in pulse EPR mode.