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Pulsed electron paramagnetic resonance spectroscopy powered by a free-electron laser


Electron paramagnetic resonance (EPR) spectroscopy interrogates unpaired electron spins in solids and liquids to reveal local structure and dynamics; for example, EPR has elucidated parts of the structure of protein complexes that other techniques in structural biology have not been able to reveal1,2,3,4. EPR can also probe the interplay of light and electricity in organic solar cells5,6,7 and light-emitting diodes8, and the origin of decoherence in condensed matter, which is of fundamental importance to the development of quantum information processors9,10,11,12,13. Like nuclear magnetic resonance, EPR spectroscopy becomes more powerful at high magnetic fields and frequencies, and with excitation by coherent pulses rather than continuous waves. However, the difficulty of generating sequences of powerful pulses at frequencies above 100 gigahertz has, until now, confined high-power pulsed EPR to magnetic fields of 3.5 teslas and below. Here we demonstrate that one-kilowatt pulses from a free-electron laser can power a pulsed EPR spectrometer at 240 gigahertz (8.5 teslas), providing transformative enhancements over the alternative, a state-of-the-art 30-milliwatt solid-state source. Our spectrometer can rotate spin-1/2 electrons through π/2 in only 6 nanoseconds (compared to 300 nanoseconds with the solid-state source). Fourier-transform EPR on nitrogen impurities in diamond demonstrates excitation and detection of EPR lines separated by about 200 megahertz. We measured decoherence times as short as 63 nanoseconds, in a frozen solution of nitroxide free-radicals at temperatures as high as 190 kelvin. Both free-electron lasers and the quasi-optical technology developed for the spectrometer are scalable to frequencies well in excess of one terahertz, opening the way to high-power pulsed EPR spectroscopy up to the highest static magnetic fields currently available.

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Figure 1: Towards high-frequency, high-power pulsed EPR spectroscopy.
Figure 2: Rabi oscillation measurements with BDPA.
Figure 3: Fourier-transform EPR measurements with diamond.
Figure 4: Hahn echo measurements with TEMPO.


  1. 1

    Hubbell, W. L., Mchaourab, H. S., Altenbach, C. & Lietzow, M. A. Watching proteins move using site-directed spin labeling. Structure 4, 779–783 (1996)

    CAS  Article  Google Scholar 

  2. 2

    Pannier, M., Veit, S., Godt, A., Jeschke, G. & Spiess, H. W. Dead-time free measurement of dipole-dipole interactions between electron spins. J. Magn. Reson. 142, 331–340 (2000)

    CAS  Article  ADS  Google Scholar 

  3. 3

    Saxena, S. & Freed, J. H. Double quantum two dimensional Fourier transform electron spin resonance: distance measurements. Chem. Phys. Lett. 251, 102–110 (1996)

    CAS  Article  ADS  Google Scholar 

  4. 4

    Borbat, P. & Freed, J. H. Multiple-quantum ESR and distance measurements. Chem. Phys. Lett. 313, 145–154 (1999)

    CAS  Article  ADS  Google Scholar 

  5. 5

    Smilowitz, L. et al. Photoexcitation spectroscopy of conducting polymer-C60 composites: photoinduced electron transfer. Phys. Rev. B 47, 13835–13842 (1993)

    CAS  Article  ADS  Google Scholar 

  6. 6

    Dyakonov, V. et al. Photoinduced charge carriers in conjugated polymer-fullerene composites studied with light-induced electron-spin resonance. Phys. Rev. B 59, 8019–8025 (1999)

    CAS  Article  ADS  Google Scholar 

  7. 7

    Ogiwara, T., Ikoma, T., Akiyama, K. & Tero-Kubota, S. Spin dynamics of carrier generation in a photoconductive C60-doped poly(N-vinylcarbazole) film. Chem. Phys. Lett. 411, 378–383 (2005)

    CAS  Article  ADS  Google Scholar 

  8. 8

    McCamey, D. R. et al. Spin Rabi flopping in the photocurrent of a polymer light-emitting diode. Nature Mater. 7, 723–728 (2008)

    CAS  Article  ADS  Google Scholar 

  9. 9

    Takahashi, S., Hanson, R., van Tol, J., Sherwin, M. S. & Awschalom, D. D. Quenching spin decoherence in diamond through spin bath polarization. Phys. Rev. Lett. 101, 047601 (2008)

    Article  ADS  Google Scholar 

  10. 10

    Gruber, A. et al. Scanning confocal optical microscopy and magnetic resonance on single defect centers. Science 276, 2012–2014 (1997)

    CAS  Article  Google Scholar 

  11. 11

    Lyon, S. A. Spin-based quantum computing using electrons on liquid helium. Phys. Rev. A 74, 052338 (2006)

    Article  ADS  Google Scholar 

  12. 12

    Hanson, R., Kouwenhoven, L. P., Petta, J. R., Tarucha, S. & Vandersypen, L. M. K. Spins in few-electron quantum dots. Rev. Mod. Phys. 79, 1217–1265 (2007)

    CAS  Article  ADS  Google Scholar 

  13. 13

    Takahashi, S. et al. Decoherence in crystals of quantum molecular magnets. Nature 476, 76–79 (2011)

    CAS  Article  Google Scholar 

  14. 14

    Freed, J. H. New technologies in electron spin resonance. Annu. Rev. Phys. Chem. 51, 655–689 (2000)

    CAS  Article  ADS  Google Scholar 

  15. 15

    Earle, K. A., Dzikovski, B., Hofbauer, W., Moscicki, J. K. & Freed, J. H. High-frequency ESR at ACERT. Magn. Reson. Chem. 43, S256–S266 (2005)

    CAS  Article  Google Scholar 

  16. 16

    van Tol, J. et al. High-field phenomena of qubits. Appl. Magn. Reson. 36, 259–268 (2009)

    Article  Google Scholar 

  17. 17

    Hofbauer, W., Earle, K. A., Dunnam, C. R., Moscicki, J. K. & Freed, J. H. High-power 95 GHz pulsed electron spin resonance spectrometer. Rev. Sci. Instrum. 75, 1194–1208 (2004)

    CAS  Article  ADS  Google Scholar 

  18. 18

    Cruickshank, P. A. S. et al. A kilowatt pulsed 94 GHz electron paramagnetic resonance spectrometer. with high concentration sensitivity, high instantaneous bandwidth, and low dead time. Rev. Sci. Instrum. 80, 103102 (2009)

    Article  ADS  Google Scholar 

  19. 19

    Communications and Power Industries (CPI).

  20. 20

    Nanni, E. A., Shapiro, M. A., Sirigiri, J. R. & Temkin, R. J. Design of a 250 GHz photonic band gap gyrotron amplifier. 2010 IEEE Int. Vacuum Electron. Conf. (IEEE, 2010)

    Google Scholar 

  21. 21

    Ramian, G. the new UCSB free-electron lasers. Nucl. Instrum. Methods Phys. A 318, 225–229 (1992)

    Article  ADS  Google Scholar 

  22. 22

    Takahashi, S., Ramian, G., Sherwin, M. S., Brunel, L.-C. & van Tol, J. Submegahertz linewidth at 240 GHz from an injection-locked free-electron laser. Appl. Phys. Lett. 91, 174102 (2007)

    Article  ADS  Google Scholar 

  23. 23

    Takahashi, S., Ramian, G. & Sherwin, M. S. Cavity dumping of an injection-locked free-electron laser. Appl. Phys. Lett. 95, 234102 (2009)

    Article  ADS  Google Scholar 

  24. 24

    Hegmann, F. A. & Sherwin, M. S. Generation of picosecond far-infrared pulses using laser-activated semiconductor reflection switches. Proc. SPIE 2842, 90–105 (1996)

    CAS  Article  ADS  Google Scholar 

  25. 25

    Doty, M. F., Cole, B. E., King, B. T. & Sherwin, M. S. Wavelength-specific laser-activated switches for improved contrast ratio in generation of short THz pulses. Rev. Sci. Instrum. 75, 2921–2925 (2004)

    CAS  Article  ADS  Google Scholar 

  26. 26

    Rolland, C. & Corkum, P. B. Generation of 130-fsec midinfrared pulses. J. Opt. Soc. Am. B 3, 1625–1629 (1986)

    CAS  Article  ADS  Google Scholar 

  27. 27

    Mitsudo, S. et al. Development of a sub-THz cw gyrotron for the millimeter wave pulsed ESR spectrometer. Proc. IRMMW-THz 2010 (IEEE, 2010)

  28. 28

    Smith, G. M., Lesurf, J. C. G., Mitchell, R. H. & Riedi, P. C. Quasi-optical cw mm-wave electron spin resonance spectrometer. Rev. Sci. Instrum. 69, 3924–3937 (1998)

    CAS  Article  ADS  Google Scholar 

  29. 29

    van Tol, J., Brunel, L.-C. & Wylde, R. J. A quasioptical transient electron spin resonance spectrometer operating at 120 and 240 GHz. Rev. Sci. Instrum. 76, 074101 (2005)

    Article  ADS  Google Scholar 

  30. 30

    Rabi, I. I. Space quantization in a gyrating magnetic field. Phys. Rev. 51, 652–654 (1937)

    CAS  Article  ADS  Google Scholar 

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This work was supported by the NSF (CHE-0821589, DMR-0520481 and DMR-0703925) and the W. M. Keck Foundation. We thank D. Enyeart, S. El Abbadi, N. Krauss, K. Akabori, M. Anholm, T. Visher, J. Bricker and G. Kontsevich for support of the development and operation of the FEL.

Author information




S.T. and M.S.S. contributed to the writing of the manuscript. M.S.S., S.H., L.-C.B. and J.v.T. conceived the development of the FEL-powered EPR spectrometer. The development was carried out by S.T., D.T.E., G.R., L.-C.B., S.H. and M.S.S. S.T., D.T.E., J.v.T. and M.S.S. conceived the EPR experiments. The measurements were carried out by S.T., D.T.E. and L.-C.B.

Corresponding author

Correspondence to M. S. Sherwin.

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The authors declare no competing financial interests.

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Takahashi, S., Brunel, LC., Edwards, D. et al. Pulsed electron paramagnetic resonance spectroscopy powered by a free-electron laser. Nature 489, 409–413 (2012).

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