Emilio received his B.S. in Electrical Engineering and Physics from Missouri University of Science and Technology in 2007. After graduating he worked for the NASA Marshall Space Flight Center developing non-destructive evaluation techniques for applications related to the US space program. He completed his PhD in Electrical Engineering from the Massachusetts Institute of Technology in 2013 where he worked on high-frequency high-power THz sources and the development of Nuclear Magnetic Resonance spectrometers using Dynamic Nuclear Polarization. His thesis was on the first photonic-band-gap gyrotron travelling wave amplifier which demonstrated record power and gain levels in the THz frequency band.

He completed his postdoc at MIT with a joint appointment in the Nuclear Reactor Lab and the Research Laboratory for Electronics at MIT where he demonstrated the first acceleration of electrons with optically generated THz pulses. He joined the Technology Innovation Directorate at SLAC in August of 2015 where he continues his work on high power, high-frequency vacuum electron devices; optical THz amplifiers; electron-beam dynamics; and advanced accelerator concepts.

Academic Appointments

  • Assistant Professor, Photon Science Directorate
  • Assistant Professor, Particle Physics and Astrophysics

2023-24 Courses

Stanford Advisees

All Publications

  • Multi-objective Bayesian active learning for MeV-ultrafast electron diffraction. Nature communications Ji, F., Edelen, A., Roussel, R., Shen, X., Miskovich, S., Weathersby, S., Luo, D., Mo, M., Kramer, P., Mayes, C., Othman, M. A., Nanni, E., Wang, X., Reid, A., Minitti, M., England, R. J. 2024; 15 (1): 4726


    Ultrafast electron diffraction using MeV energy beams(MeV-UED) has enabled unprecedented scientific opportunities in the study of ultrafast structural dynamics in a variety of gas, liquid and solid state systems. Broad scientific applications usually pose different requirements for electron probe properties. Due to the complex, nonlinear and correlated nature of accelerator systems, electron beam property optimization is a time-taking process and often relies on extensive hand-tuning by experienced human operators. Algorithm based efficient online tuning strategies are highly desired. Here, we demonstrate multi-objective Bayesian active learning for speeding up online beam tuning at the SLAC MeV-UED facility. The multi-objective Bayesian optimization algorithm was used for efficiently searching the parameter space and mapping out the Pareto Fronts which give the trade-offs between key beam properties. Such scheme enables an unprecedented overview of the global behavior of the experimental system and takes a significantly smaller number of measurements compared with traditional methods such as a grid scan. This methodology can be applied in other experimental scenarios that require simultaneously optimizing multiple objectives by explorations in high dimensional, nonlinear and correlated systems.

    View details for DOI 10.1038/s41467-024-48923-9

    View details for PubMedID 38830874

    View details for PubMedCentralID PMC11148007

  • Giant Terahertz Birefringence in an Ultrathin Anisotropic Semimetal. Nano letters Sie, E. J., Othman, M. A., Nyby, C. M., Pemmaraju, D., Garcia, C. A., Wang, Y., Guzelturk, B., Xia, C., Xiao, J., Poletayev, A., Ofori-Okai, B. K., Hoffmann, M. C., Park, S., Shen, X., Yang, J., Li, R., Reid, A. H., Weathersby, S., Muscher, P., Finney, N., Rhodes, D., Balicas, L., Nanni, E., Hone, J., Chueh, W., Devereaux, T. P., Narang, P., Heinz, T. F., Wang, X., Lindenberg, A. M. 2024


    Manipulating the polarization of light at the nanoscale is key to the development of next-generation optoelectronic devices. This is typically done via waveplates using optically anisotropic crystals, with thicknesses on the order of the wavelength. Here, using a novel ultrafast electron-beam-based technique sensitive to transient near fields at THz frequencies, we observe a giant anisotropy in the linear optical response in the semimetal WTe2 and demonstrate that one can tune the THz polarization using a 50 nm thick film, acting as a broadband wave plate with thickness 3 orders of magnitude smaller than the wavelength. The observed circular deflections of the electron beam are consistent with simulations tracking the trajectory of the electron beam in the near field of the THz pulse. This finding offers a promising approach to enable atomically thin THz polarization control using anisotropic semimetals and defines new approaches for characterizing THz near-field optical response at far-subwavelength length scales.

    View details for DOI 10.1021/acs.nanolett.4c00758

    View details for PubMedID 38717626

  • Improved temporal resolution in ultrafast electron diffraction measurements through THz compression and time-stamping. Structural dynamics (Melville, N.Y.) Othman, M. A., Gabriel, A. E., Snively, E. C., Kozina, M. E., Shen, X., Ji, F., Lewis, S., Weathersby, S., Vasireddy, P., Luo, D., Wang, X., Hoffmann, M. C., Nanni, E. A. 2024; 11 (2): 024311


    We present an experimental demonstration of ultrafast electron diffraction (UED) with THz-driven electron bunch compression and time-stamping that enables UED probes with improved temporal resolution. Through THz-driven longitudinal bunch compression, a compression factor of approximately four is achieved. Moreover, the time-of-arrival jitter between the compressed electron bunch and a pump laser pulse is suppressed by a factor of three. Simultaneously, the THz interaction imparts a transverse spatiotemporal correlation on the electron distribution, which we utilize to further enhance the precision of time-resolved UED measurements. We use this technique to probe single-crystal gold nanofilms and reveal transient oscillations in the THz near fields with a temporal resolution down to 50 fs. These oscillations were previously beyond reach in the absence of THz compression and time-stamping.

    View details for DOI 10.1063/4.0000230

    View details for PubMedID 38655563

    View details for PubMedCentralID PMC11037933

  • Status and future plans for C<SUP>3</SUP> R&D JOURNAL OF INSTRUMENTATION Nanni, E. A., Breidenbach, M., Li, Z., Vernieri, C., Wang, F., White, G., Bai, M., Belomestnykh, S., Bhat, P., Barklow, T., Berg, W. J., Borzenets, V., Byrd, J., Dhar, A., Dhuley, R. C., Doss, C., Duris, J., Edelen, A., Emma, C., Frisch, J., Gabriel, A., Gessner, S., Hast, C., Jing, C., Klebaner, A., Kim, D., Krasnykh, A. K., Lewellen, J., Liepe, M., Litos, M., Lu, X., Maxson, J., Montanari, D., Musumeci, P., Nagaitsev, S., Nassiri, A., Ng, C., Othman, M. K., Oriunno, M., Palmer, D., Patterson, J., Peskin, M. E., Peterson, T. J., Power, J., Qiang, J., Rosenzweig, J., Shiltsev, V., Shumail, M., Simakov, E., Snively, E., Spataro, B., Tantawi, S., Graaf, H., Weatherford, B., Wu, J., Wootton, K. P. 2023; 18 (9)
  • Measurement of femtosecond dynamics of ultrafast electron beams through terahertz compression and time-stamping APPLIED PHYSICS LETTERS Othman, M. K., Gabriel, A. E., Snively, E. C., Kozina, M. E., Shen, X., Ji, F., Lewis, S., Weathersby, S., Vasireddy, P., Luo, D., Wang, X., Hoffmann, M. C., Nanni, E. A. 2023; 122 (14)

    View details for DOI 10.1063/5.0134733

    View details for Web of Science ID 000964331000010

  • Transformative Technology for FLASH Radiation Therapy. Applied sciences (Basel, Switzerland) Schulte, R., Johnstone, C., Boucher, S., Esarey, E., Geddes, C. G., Kravchenko, M., Kutsaev, S., Loo, B. W., Méot, F., Mustapha, B., Nakamura, K., Nanni, E. A., Obst-Huebl, L., Sampayan, S. E., Schroeder, C. B., Sheng, K., Snijders, A. M., Snively, E., Tantawi, S. G., Van Tilborg, J. 2023; 13 (8)


    The general concept of radiation therapy used in conventional cancer treatment is to increase the therapeutic index by creating a physical dose differential between tumors and normal tissues through precision dose targeting, image guidance, and radiation beams that deliver a radiation dose with high conformality, e.g., protons and ions. However, the treatment and cure are still limited by normal tissue radiation toxicity, with the corresponding side effects. A fundamentally different paradigm for increasing the therapeutic index of radiation therapy has emerged recently, supported by preclinical research, and based on the FLASH radiation effect. FLASH radiation therapy (FLASH-RT) is an ultra-high-dose-rate delivery of a therapeutic radiation dose within a fraction of a second. Experimental studies have shown that normal tissues seem to be universally spared at these high dose rates, whereas tumors are not. While dose delivery conditions to achieve a FLASH effect are not yet fully characterized, it is currently estimated that doses delivered in less than 200 ms produce normal-tissue-sparing effects, yet effectively kill tumor cells. Despite a great opportunity, there are many technical challenges for the accelerator community to create the required dose rates with novel compact accelerators to ensure the safe delivery of FLASH radiation beams.

    View details for DOI 10.3390/app13085021

    View details for PubMedID 38240007

    View details for PubMedCentralID PMC10795821

  • Transformative Technology for FLASH Radiation Therapy APPLIED SCIENCES-BASEL Schulte, R., Johnstone, C., Boucher, S., Esarey, E., Geddes, C. R., Kravchenko, M., Kutsaev, S., Loo, B. W., Meot, F., Mustapha, B., Nakamura, K., Nanni, E. A., Obst-Huebl, L., Sampayan, S. E., Schroeder, C. B., Sheng, K., Snijders, A. M., Snively, E., Tantawi, S. G., Van Tilborg, J. 2023; 13 (8)
  • A “Cool” route to the Higgs boson and beyond. The Cool Copper Collider JINST - Journal of Instrumentation Vernieri, C., Nanni, E., Dasu, S., Peskin, M., Ntounis, D., et al 2023; 18 (07)
  • High gradient off-axis coupled C-band Cu and CuAg accelerating structures APPLIED PHYSICS LETTERS Schneider, M., Dolgashev, V., Lewellen, J. W., Tantawi, S. G., Nanni, E. A., Zuboraj, M., Fleming, R., Gorelov, D., Middendorf, M., Simakov, E. I. 2022; 121 (25)

    View details for DOI 10.1063/5.0132706

    View details for Web of Science ID 000901638300005

  • Superconducting on-chip tunable mm-wave resonator Das, D., Naji, A., Multani, K. S., Safavi-Naeini, A. H., Nanni, E. A., IEEE IEEE. 2022
  • Cascaded particle accelerators reach new energy NATURE PHOTONICS Nanni, E. A. 2021
  • Spectrally reconfigurable quantum emitters enabled by optimized fast modulation NPJ QUANTUM INFORMATION Lukin, D. M., White, A. D., Trivedi, R., Guidry, M. A., Morioka, N., Babin, C., Soykal, O. O., Ul-Hassan, J., Son, N., Ohshima, T., Vasireddy, P. K., Nasr, M. H., Sun, S., MacLean, J. W., Dory, C., Nanni, E. A., Wrachtrup, J., Kaiser, F., Vuckovic, J. 2020; 6 (1)
  • Experimental demonstration of externally driven millimeter-wave particle accelerator structure APPLIED PHYSICS LETTERS Othman, M. K., Picard, J., Schaub, S., Dolgashev, V. A., Lewis, S. M., Neilson, J., Haase, A., Jawla, S., Spataro, B., Temkin, R. J., Tantawi, S., Nanni, E. A. 2020; 117 (7)

    View details for DOI 10.1063/5.0011397

    View details for Web of Science ID 000563578800002

  • Static and Dynamic Stark Tuning of the Silicon Vacancy in Silicon Carbide White, A. D., Lukin, D. M., Guidry, M. A., Trivedi, R., Morioka, N., Babin, C., Kaiser, F., Ul-Hassan, J., Son, N., Ohshima, T., Vasireddy, P., Nasr, M., Nanni, E., Wrachtrup, J., Vuckovic, J., IEEE IEEE. 2020
  • Terahertz Dual-Fed Relativistic Electron Bunch Compression Othman, M. K., Gabriel, A. E., Snively, E. C., Kozina, M. E., Shen, X., Ji, F., Lewis, S., Vasireddv, P., Weathersby, S., Wang, X. J., Matthias, C., Hoffmann, Nanni, E. A., IEEE IEEE. 2020
  • Development of a Millimeter-Wave Transducer for Quantum Networks Multani, K. S., Stokowski, H., Snively, E., Patel, R., Jiang, W., Lee, N., Welander, P. B., Nanni, E. A., Safavi-Naeini, A. H., IEEE IEEE. 2020
  • High Gradient and of Breakdown Measurements in a Millimeter-Wave Accelerating Cavity Othman, M. K., Picard, J., Schaub, S., Dolgashev, V. A., Lewis, S., Spataro, B., Temkin, R. J., Tantawi, S., Nanni, E. A., IEEE IEEE. 2020
  • Ultrafast Dynamics of a Terahertz Dual-Fed Relativistic Electron Bunch Compressor Othman, M. K., Snively, E. C., Kozina, M. E., Kramer, P. L., Shen, X., Ji, F., Weathersby, S., Wang, X. J., Hoffmann, M. C., Nanni, E. A., IEEE IEEE. 2020
  • Parallel-plate waveguides for terahertz-driven MeV electron bunch compression OPTICS EXPRESS Othman, M. K., Hoffmann, M. C., Kozina, M. E., Wang, X. J., Li, R. K., Nanni, E. A. 2019; 27 (17): 23791–800
  • Terahertz-based subfemtosecond metrology of relativistic electron beams PHYSICAL REVIEW ACCELERATORS AND BEAMS Li, R. K., Hoffmann, M. C., Nanni, E. A., Glenzer, S. H., Kozina, M. E., Lindenberg, A. M., Ofori-Okai, B. K., Reid, A. H., Shen, X., Weathersby, S. P., Yang, J., Zajac, M., Wang, X. J. 2019; 22 (1)
  • Parallel-Plate THz Waveguides for Relativistic Electron Bunch Compression Othman, M. K., Hoffmann, M. C., Li, R., Nanni, E. A., Wang, X. J., IEEE IEEE. 2019
  • Nanomodulated electron beams via electron diffraction and emittance exchange for coherent x-ray generation PHYSICAL REVIEW ACCELERATORS AND BEAMS Nanni, E. A., Graves, W. S., Moncton, D. E. 2018; 21 (1)
  • Modeling of THz Pump Induced Plasmonic Oscillations in Silicon Membranes Wang, N., Nanni, E. A., Shen, X., Li, R. K., Hoffmann, M., Ofori-Okai, B. K., Zheng, Q., Yang, J., Wang, X. J., IEEE IEEE. 2018
  • Results from mm-Wave Accelerating Structure High-Gradient Tests Nanni, E. A., Dolgashev, V., Jawla, S., Neilson, J., Othman, M., Picard, J., Schaub, S., Spataro, B., Tantawi, S., Temkin, R. J., IEEE IEEE. 2018
  • Photonic-band-gap gyrotron amplifier with picosecond pulses APPLIED PHYSICS LETTERS Nanni, E. A., Jawla, S., Lewis, S. M., Shapiro, M. A., Temkin, R. J. 2017; 111 (23): 233504


    We report the amplification of 250 GHz pulses as short as 260 ps without observation of pulse broadening using a photonic-band-gap circuit gyrotron traveling-wave-amplifier. The gyrotron amplifier operates with a device gain of 38 dB and an instantaneous bandwidth of 8 GHz. The operational bandwidth of the amplifier can be tuned over 16 GHz by adjusting the operating voltage of the electron beam and the magnetic field. The amplifier uses a 30 cm long photonic-band-gap interaction circuit to confine the desired TE03-like operating mode while suppressing lower order modes which can result in undesired oscillations. The circuit gain is >55 dB for a beam voltage of 23 kV and a current of 700 mA. These results demonstrate the wide bandwidths and a high gain achievable with gyrotron amplifiers. The amplification of picosecond pulses of variable lengths, 260-800 ps, shows good agreement with the theory using the coupled dispersion relation and the gain-spectrum of the amplifier as measured with quasi-CW input pulses.

    View details for DOI 10.1063/1.5006348

    View details for Web of Science ID 000418349100047

    View details for PubMedID 29249833

    View details for PubMedCentralID PMC5718917

  • Prototyping high-gradient mm-wave accelerating structures Nanni, E. A., Dolgashev, V. A., Haase, A., Neilson, J., Tantawi, S., Schaub, S. C., Temkin, R. J., Spataro, B., IOP IOP PUBLISHING LTD. 2017
  • Terahertz-driven, all-optical electron gun OPTICA Huang, W., Fallahi, A., Wu, X., Cankaya, H., Calendron, A., Ravi, K., Zhang, D., Nanni, E. A., Hong, K., Kaertner, F. X. 2016; 3 (11): 1209–12
  • Direct longitudinal laser acceleration of electrons in free space PHYSICAL REVIEW ACCELERATORS AND BEAMS Carbajo, S., Nanni, E. A., Wong, L., Moriena, G., Keathley, P. D., Laurent, G., Miller, R., Kaertner, F. X. 2016; 19 (2)
  • Terahertz-driven, sub-keV electron gun Huang, W., Fallahi, A., Wu, X., Nanni, E. A., Cankaya, H., Calendron, A., Zhang, D., Ravi, K., Hong, K., Kaertner, F. X., IEEE IEEE. 2016
  • Demonstration of an Ultracompact THz-driven Electron Gun Huang, W., Fallahi, A., Wu, X., Cankaya, H., Calendron, A., Ravi, K., Zhang, D., Nanni, E. A., Hong, K., Kaertner, F. X., IEEE IEEE. 2016
  • Amplification of Picosecond Pulses with a Photonic-Band-Gap Gyro-TWT Nanni, E. A., Jawla, S., Lewis, S. M., Shapiro, M., Temkin, R. J., IEEE IEEE. 2016
  • Toward a terahertz-driven electron gun SCIENTIFIC REPORTS Huang, W., Nanni, E. A., Ravi, K., Hong, K., Fallahi, A., Wong, L., Keathley, P. D., Zapata, L. E., Kaertner, F. X. 2015; 5: 14899


    Femtosecond electron bunches with keV energies and eV energy spread are needed by condensed matter physicists to resolve state transitions in carbon nanotubes, molecular structures, organic salts, and charge density wave materials. These semirelativistic electron sources are not only of interest for ultrafast electron diffraction, but also for electron energy-loss spectroscopy and as a seed for x-ray FELs. Thus far, the output energy spread (hence pulse duration) of ultrafast electron guns has been limited by the achievable electric field at the surface of the emitter, which is 10 MV/m for DC guns and 200 MV/m for RF guns. A single-cycle THz electron gun provides a unique opportunity to not only achieve GV/m surface electric fields but also with relatively low THz pulse energies, since a single-cycle transform-limited waveform is the most efficient way to achieve intense electric fields. Here, electron bunches of 50 fC from a flat copper photocathode are accelerated from rest to tens of eV by a microjoule THz pulse with peak electric field of 72 MV/m at 1 kHz repetition rate. We show that scaling to the readily-available GV/m THz field regime would translate to monoenergetic electron beams of ~100 keV.

    View details for DOI 10.1038/srep14899

    View details for Web of Science ID 000363284200001

    View details for PubMedID 26486697

    View details for PubMedCentralID PMC4613671

  • Terahertz-driven linear electron acceleration NATURE COMMUNICATIONS Nanni, E. A., Huang, W. R., Hong, K., Ravi, K., Fallahi, A., Moriena, G., Miller, R., Kaertner, F. X. 2015; 6: 8486


    The cost, size and availability of electron accelerators are dominated by the achievable accelerating gradient. Conventional high-brightness radio-frequency accelerating structures operate with 30-50 MeV m(-1) gradients. Electron accelerators driven with optical or infrared sources have demonstrated accelerating gradients orders of magnitude above that achievable with conventional radio-frequency structures. However, laser-driven wakefield accelerators require intense femtosecond sources and direct laser-driven accelerators suffer from low bunch charge, sub-micron tolerances and sub-femtosecond timing requirements due to the short wavelength of operation. Here we demonstrate linear acceleration of electrons with keV energy gain using optically generated terahertz pulses. Terahertz-driven accelerating structures enable high-gradient electron/proton accelerators with simple accelerating structures, high repetition rates and significant charge per bunch. These ultra-compact terahertz accelerators with extremely short electron bunches hold great potential to have a transformative impact for free electron lasers, linear colliders, ultrafast electron diffraction, X-ray science and medical therapy with X-rays and electron beams.

    View details for DOI 10.1038/ncomms9486

    View details for Web of Science ID 000364941100001

    View details for PubMedID 26439410

    View details for PubMedCentralID PMC4600735

  • Theory of terahertz generation by optical rectification using tilted-pulse-fronts OPTICS EXPRESS Ravi, K., Huang, W., Carbajo, S., Nanni, E. A., Schimpf, D. N., Ippen, E. P., Kaertner, F. X. 2015; 23 (4): 5253–76


    A model for terahertz (THz) generation by optical rectification using tilted-pulse-fronts is developed. It simultaneously accounts for in two spatial dimensions (2-D) (i) the spatio-temporal variations of the optical pump pulse imparted by the tilted-pulse-front setup, (ii) the nonlinear coupled interaction of THz and optical radiation, (iii) self-phase modulation and (iv) stimulated Raman scattering. The model is validated by quantitative agreement with experiments and analytic calculations. We show that the optical pump beam is significantly broadened in the transverse-momentum (kx) domain as a consequence of its spectral broadening due to THz generation. In the presence of this large frequency and transverse-momentum (or angular) spread, group velocity dispersion causes a spatio-temporal break-up of the optical pump pulse which inhibits further THz generation. The implications of these effects on energy scaling and optimization of optical-to-THz conversion efficiency are discussed. This suggests the use of optical pump pulses with elliptical beam profiles for large optical pump energies. Furthermore, it is seen that optimization of the setup is highly dependent on optical pump conditions. Trade-offs in optimizing the optical-to-THz conversion efficiency on the spatial and spectral properties of THz radiation are discussed to guide the development of such sources.

    View details for DOI 10.1364/OE.23.005253

    View details for Web of Science ID 000350872700135

    View details for PubMedID 25836558

  • From incoherent to coherent x-rays with ICS sources Nanni, E. A., Graves, W. S., Moncton, D. E., Khounsary, A. M., MacDonald, C. A. SPIE-INT SOC OPTICAL ENGINEERING. 2015

    View details for DOI 10.1117/12.2196891

    View details for Web of Science ID 000366305100004

  • Direct Machining of Low-Loss THz Waveguide Components With an RF Choke IEEE MICROWAVE AND WIRELESS COMPONENTS LETTERS Lewis, S. M., Nanni, E. A., Temkin, R. J. 2014; 24 (12): 842–44


    We present results for the successful fabrication of low-loss THz metallic waveguide components using direct machining with a CNC end mill. The approach uses a split-block machining process with the addition of an RF choke running parallel to the waveguide. The choke greatly reduces coupling to the parasitic mode of the parallel-plate waveguide produced by the split-block. This method has demonstrated loss as low as 0.2 dB/cm at 280 GHz for a copper WR-3 waveguide. It has also been used in the fabrication of 3 and 10 dB directional couplers in brass, demonstrating excellent agreement with design simulations from 240-260 GHz. The method may be adapted to structures with features on the order of 200 μm.

    View details for DOI 10.1109/LMWC.2014.2303161

    View details for Web of Science ID 000345903500008

    View details for PubMedID 25821412

    View details for PubMedCentralID PMC4374357

  • The Fifteenth Special Issue on High-Power Microwave Generation IEEE TRANSACTIONS ON PLASMA SCIENCE Greenwood, A. D., Lehr, F., Nanni, E. A. 2014; 42 (6): 1481
  • Electron Acceleration in a Single-cycle Terahertz Field Huang, W., Nanni, E. A., Ravi, K., Wong, L., Hong, K., Kaertner, F. X., IEEE IEEE. 2014
  • Dynamic nuclear polarization at 700 MHz/460 GHz JOURNAL OF MAGNETIC RESONANCE Barnes, A. B., Markhasin, E., Daviso, E., Michaelis, V. K., Nanni, E. A., Jawla, S. K., Mena, E. L., DeRocher, R., Thakkar, A., Woskov, P. P., Herzfeld, J., Temkin, R. J., Griffin, R. G. 2012; 224: 1–7


    We describe the design and implementation of the instrumentation required to perform DNP-NMR at higher field strengths than previously demonstrated, and report the first magic-angle spinning (MAS) DNP-NMR experiments performed at (1)H/e(-) frequencies of 700 MHz/460 GHz. The extension of DNP-NMR to 16.4 T has required the development of probe technology, cryogenics, gyrotrons, and microwave transmission lines. The probe contains a 460 GHz microwave channel, with corrugated waveguide, tapers, and miter-bends that couple microwave power to the sample. Experimental efficiency is increased by a cryogenic exchange system for 3.2 mm rotors within the 89 mm bore. Sample temperatures ≤85 K, resulting in improved DNP enhancements, are achieved by a novel heat exchanger design, stainless steel and brass vacuum jacketed transfer lines, and a bronze probe dewar. In addition, the heat exchanger is preceded with a nitrogen drying and generation system in series with a pre-cooling refrigerator. This reduces liquid nitrogen usage from >700 l per day to <200 l per day and allows for continuous (>7 days) cryogenic spinning without detrimental frost or ice formation. Initial enhancements, ε=-40, and a strong microwave power dependence suggests the possibility for considerable improvement. Finally, two-dimensional spectra of a model system demonstrate that the higher field provides excellent resolution, even in a glassy, cryoprotecting matrix.

    View details for DOI 10.1016/j.jmr.2012.08.002

    View details for Web of Science ID 000310765000001

    View details for PubMedID 23000974

    View details for PubMedCentralID PMC3965575

  • A 250 GHz gyrotron with a 3 GHz tuning bandwidth for dynamic nuclear polarization JOURNAL OF MAGNETIC RESONANCE Barnes, A. B., Nanni, E. A., Herzfeld, J., Griffin, R. G., Temkin, R. J. 2012; 221: 147–53


    We describe the design and implementation of a novel tunable 250 GHz gyrotron oscillator with >10 W output power over most of a 3 GHz band and >35 W peak power. The tuning bandwidth and power are sufficient to generate a >1 MHz nutation frequency across the entire nitroxide EPR lineshape for cross effect DNP, as well as to excite solid effect transitions utilizing other radicals, without the need for sweeping the NMR magnetic field. Substantially improved tunability is achieved by implementing a long (23 mm) interaction cavity that can excite higher order axial modes by changing either the magnetic field of the gyrotron or the cathode potential. This interaction cavity excites the rotating TE(₅,₂,q) mode, and an internal mode converter outputs a high-quality microwave beam with >94% Gaussian content. The gyrotron was integrated into a DNP spectrometer, resulting in a measured DNP enhancement of 54 on the membrane protein bacteriorhodopsin.

    View details for DOI 10.1016/j.jmr.2012.03.014

    View details for Web of Science ID 000307414500020

    View details for PubMedID 22743211

    View details for PubMedCentralID PMC3405196

  • Low-loss Transmission Lines for High-power Terahertz Radiation JOURNAL OF INFRARED MILLIMETER AND TERAHERTZ WAVES Nanni, E., Jawla, S., Shapiro, M. A., Woskov, P. P., Temkin, R. J. 2012; 33 (7): 695–714


    Applications of high-power Terahertz (THz) sources require low-loss transmission lines to minimize loss, prevent overheating and preserve the purity of the transmission mode. Concepts for THz transmission lines are reviewed with special emphasis on overmoded, metallic, corrugated transmission lines. Using the fundamental HE(11) mode, these transmission lines have been successfully implemented with very low-loss at high average power levels on plasma heating experiments and THz dynamic nuclear polarization (DNP) nuclear magnetic resonance (NMR) experiments. Loss in these lines occurs directly, due to ohmic loss in the fundamental mode, and indirectly, due to mode conversion into high order modes whose ohmic loss increases as the square of the mode index. An analytic expression is derived for ohmic loss in the modes of a corrugated, metallic waveguide, including loss on both the waveguide inner surfaces and grooves. Simulations of loss with the numerical code HFSS are in good agreement with the analytic expression. Experimental tests were conducted to determine the loss of the HE(11) mode in a 19 mm diameter, helically-tapped, three meter long brass waveguide with a design frequency of 330 GHz. The measured loss at 250 GHz was 0.029 ± 0.009 dB/m using a vector network analyzer approach and 0.047 ± 0.01 dB/m using a radiometer. The experimental results are in reasonable agreement with theory. These values of loss, amounting to about 1% or less per meter, are acceptable for the DNP NMR application. Loss in a practical transmission line may be much higher than the loss calculated for the HE(11) mode due to mode conversion to higher order modes caused by waveguide imperfections or miter bends.

    View details for DOI 10.1007/s10762-012-9870-5

    View details for Web of Science ID 000305216600003

    View details for PubMedID 23162673

    View details for PubMedCentralID PMC3498493

  • Mode Content Determination of Terahertz Corrugated Waveguides Using Experimentally Measured Radiated Field Patterns IEEE TRANSACTIONS ON PLASMA SCIENCE Jawla, S. K., Nanni, E. A., Shapiro, M. A., Woskov, P. P., Temkin, R. J. 2012; 40 (6): 1530–37


    This work focuses on the accuracy of the mode content measurements in an overmoded corrugated waveguide using measured radiated field patterns. Experimental results were obtained at 250 GHz using a vector network analyzer with over 70 dB of dynamic range. The intensity and phase profiles of the fields radiated from the end of the 19 mm diameter helically tapped brass waveguide were measured on planes at 7, 10, and 13 cm from the waveguide end. The measured fields were back propagated to the waveguide aperture to provide three independent estimates of the field at the waveguide exit aperture. Projecting that field onto the modes of the guide determined the waveguide mode content. The three independent mode content estimates were found to agree with one another to an accuracy of better than ±0.3%. These direct determinations of the mode content were compared with indirect measurements using the experimentally measured amplitude in three planes, with the phase determined by a phase retrieval algorithm. The phase retrieval technique using the planes at 7, 10, and 13 cm yielded a mode content estimate in excellent agreement, within 0.3%, of the direct measurements. Phase retrieval results using planes at 10, 20, and 30 cm were less accurate due to truncation of the measurement in the transverse plane. The reported measurements benefited greatly from a precise mechanical alignment of the scanner with respect to the waveguide axis. These results will help to understand the accuracy of mode content measurements made directly in cold test and indirectly in hot test using the phase retrieval technique.

    View details for DOI 10.1109/TPS.2012.2190105

    View details for Web of Science ID 000305153900006

    View details for PubMedID 25264391

    View details for PubMedCentralID PMC4175724

  • THz Dynamic Nuclear Polarization NMR IEEE TRANSACTIONS ON TERAHERTZ SCIENCE AND TECHNOLOGY Nanni, E. A., Barnes, A. B., Griffin, R. G., Temkin, R. J. 2011; 1 (1): 145–63


    Dynamic nuclear polarization (DNP) increases the sensitivity of nuclear magnetic resonance (NMR) spectroscopy by using high frequency microwaves to transfer the polarization of the electrons to the nuclear spins. The enhancement in NMR sensitivity can amount to a factor of well above 100, enabling faster data acquisition and greatly improved NMR measurements. With the increasing magnetic fields (up to 23 T) used in NMR research, the required frequency for DNP falls into the THz band (140-600 GHz). Gyrotrons have been developed to meet the demanding specifications for DNP NMR, including power levels of tens of watts; frequency stability of a few megahertz; and power stability of 1% over runs that last for several days to weeks. Continuous gyrotron frequency tuning of over 1 GHz has also been demonstrated. The complete DNP NMR system must include a low loss transmission line; an optimized antenna; and a holder for efficient coupling of the THz radiation to the sample. This paper describes the DNP NMR process and illustrates the THz systems needed for this demanding spectroscopic application. THz DNP NMR is a rapidly developing, exciting area of THz science and technology.

    View details for PubMedID 24639915

  • Microwave field distribution in a magic angle spinning dynamic nuclear polarization NMR probe JOURNAL OF MAGNETIC RESONANCE Nanni, E. A., Barnes, A. B., Matsuki, Y., Woskov, P. P., Corzilius, B., Griffin, R. G., Temkin, R. J. 2011; 210 (1): 16–23


    We present a calculation of the microwave field distribution in a magic angle spinning (MAS) probe utilized in dynamic nuclear polarization (DNP) experiments. The microwave magnetic field (B(1S)) profile was obtained from simulations performed with the High Frequency Structure Simulator (HFSS) software suite, using a model that includes the launching antenna, the outer Kel-F stator housing coated with Ag, the RF coil, and the 4mm diameter sapphire rotor containing the sample. The predicted average B(1S) field is 13μT/W(1/2), where S denotes the electron spin. For a routinely achievable input power of 5W the corresponding value is γ(S)B(1S)=0.84MHz. The calculations provide insights into the coupling of the microwave power to the sample, including reflections from the RF coil and diffraction of the power transmitted through the coil. The variation of enhancement with rotor wall thickness was also successfully simulated. A second, simplified calculation was performed using a single pass model based on Gaussian beam propagation and Fresnel diffraction. This model provided additional physical insight and was in good agreement with the full HFSS simulation. These calculations indicate approaches to increasing the coupling of the microwave power to the sample, including the use of a converging lens and fine adjustment of the spacing of the windings of the RF coil. The present results should prove useful in optimizing the coupling of microwave power to the sample in future DNP experiments. Finally, the results of the simulation were used to predict the cross effect DNP enhancement (ϵ) vs. ω(1S)/(2π) for a sample of (13)C-urea dissolved in a 60:40 glycerol/water mixture containing the polarizing agent TOTAPOL; very good agreement was obtained between theory and experiment.

    View details for PubMedID 21382733

  • Recent Progress at MIT on THz Gyrotron Oscillators for DNP/NMR Temkin, R. J., Barnes, A. B., Griffin, R. G., Jawla, S., Mastovsky, I., Nanni, E. A., Shapiro, M. A., Torrezan, A. C., Woskov, P. P., Koch, M. IEEE. 2011
  • 330 GHz Helically Corrugated Waveguide Woskov, P. P., Nanni, E. A., Shapiro, M. A., Jawla, S. K., Hummelt, J. S., Temkin, R. J., Barnes, A. B., Koch, M. IEEE. 2011
  • Design of a 527 GHz gyrotron for DNP-NMR spectroscopy Jawla, S., Nanni, E., Shapiro, M., Mastovsky, I., Guss, W., Temkin, R., Griffin, R., Koch, M. IEEE. 2011
  • Optimization of THz Wave Coupling into Samples in DNP/NMR Spectroscopy Nanni, E. A., Barnes, A. B., Matsuki, Y., Woskov, P. P., Corzilius, B., Griffin, R. G., Temkin, R. J., IEEE IEEE. 2010
  • Amplification of Picosecond Pulses in a 140 GHz Gyro-TWT Nanni, E. A., Kim, H. J., Shapiro, M. A., Woskov, P. P., Temkin, R. J., IEEE IEEE. 2010