25-30 August 2019
Henry Ford Building
Europe/Berlin timezone

Pulsed magnetic resonance with a free-electron laser

29 Aug 2019, 17:15
Max Kade Auditorium (Henry Ford Building)

Max Kade Auditorium

Henry Ford Building

Plenary talk Instrumentation Plenary Lectures


Prof. Mark Sherwin (University of California at Santa Barbara)


In the highest-field NMR magnets (currently 23.5 T, 1 GHz proton NMR frequency), the Larmor precession frequency for spin-1/2 electrons is 660 GHz. The recently-demonstrated 32 T superconducting magnet at MagLab in Tallahassee pushes the Larmor frequency to nearly 900 GHz. However, at the present time, it is difficult to generate a programmable sequence of phase-coherent narrow-band pulses with kW peak powers above 100 GHz (3.5 T), precluding the rapid coherent manipulation of electron spins that is required for high-power pulsed EPR, pulsed electron-nuclear double resonance (ENDOR), and pulsed dynamic nuclear polarization (DNP)-enhanced NMR in modern NMR spectrometers. The UC Santa Barbara Free-Electron Lasers (FELs), which generate high-power quasi-continuous-wave (cw) pulses between 0.24 and 4.5 THz, are now being used to drive a pulsed EPR spectrometer at 8.6 T (240 GHz). This talk will include a discussion of methods we have developed for converting the FEL output into a sequence of one or two pulses with durations as short as a few ns, resonator-free π/2 times below 10 ns, and, recently, multi-step phase-cycling. These pulse sequences, together with a home-built EPR spectrometer, have enabled measurements including Rabi oscillations, longitudinal and transverse relaxation times, and “instantaneous spectral diffusion” in systems including Nitrogen impurities (P1 centers) in diamond, and stable free radicals in both solid and solution phases. Current efforts to implement FEL-powered pulsed DNP and to generate more complex pulse sequences at 240 GHz will be described. Finally, I will discuss the outlook and scientific opportunities for FEL-powered EPR, DNP, and ENDOR at fields up to 30.5 T (1.3 GHz proton-NMR frequency, 854 GHz electron Larmor frequency). This work is supported by the NSF under grants DMR-1626681 and MCB-1617025.

Primary authors

Prof. Mark Sherwin (University of California at Santa Barbara) Mr C. Blake Wilson (University of California at Santa Barbara) Dr Marzieh Kavand (University of California at Santa Barbara) Dr Xiaoling Wang (University of California at Santa Barbara) Dr Jessica Clayton (University of California at Santa Barbara) Dr Nikolay Agladze (University of California at Santa Barbara) Prof. Steffen Glaser (Department of Chemistry, Technical University of Munich) Prof. Song-I Han (Department of Chemistry, University of California at Santa Barbara)

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