Developing Sample Holders for Ultrafast Electron Spin Resonance
Authors:Mary Lou Bailey, Devin Edwards
Mentor:Mark Sherwin, Physics Professor, University of California Santa Barbara
Electron Spin Resonance (ESR) spectroscopy investigates unpaired electron spins in solids and liquids to reveal their local environment. ESR has many applications in various fields, including physics, chemistry, materials science, and biology. For instance in biology, ESR has revealed critical structural information of proteins that have otherwise resisted structural techniques. At UCSB we have developed a high-field ESR spectrometer capable of exciting and detecting spins 100x faster than is other possible by using a Free Electron Laser (FEL) source, which provides the highest power at the frequencies necessary for high-field ESR. The pulse emitted from the FEL is directed at a sample in a sample holder “bucket,” where rapidly decaying signals emitted by the electron spins are measured by a detector. The current sample holder reflects some of the FEL pulse back to the detector, obscuring the signal and requiring the detector be turned on 80 ns after the initial pulse. In order to realize the full potential of the spectrometer, it is crucial to shorten this time. To create a holder that minimizes interference, size, geometry, and material were studied. After initial analysis of different shapes and materials, a holder with a cone top and bottom, in either Teflon or Rexolite, appeared to be the most promising. This set-up, as well as variations of this design, were fabricated in the machine shop, and tested under the FEL. Our initial results suggest that Rexolite is a better material, showing considerably less reflections than any holder made of Teflon. However, the magnitude of reflections with the cone-shaped holders showed substantial variations in many tests, making it unclear whether these new shapes offer reliably improved performance. Further analysis of each holder with a sample loaded in it will determine which shape yields the most effective improvements.