Developing Sample Holders for Ultrafast Electron Spin Resonance

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, ESR has revealed critical structural information of proteins that have otherwise resisted structural techniques in biology. At UCSB we have developed a 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 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 are studied. After initial analysis of different shapes and materials, a holder with a cone top and bottom, in either Teflon or Rexolite, appears to be the most promising. This set-up, as well as variations of this design, were fabricated in the machine shop, and will be tested under the FEL. Further analysis of each tested holder will determine which shape yields the most effective improvements, pointing us towards further optimization designs.