title: Dynamic nuclear polarization by frequency modulation of a tunable gyrotron of 260GHz.
abstract: An increase in Dynamic Nuclear Polarization (DNP) signal intensity is obtained with a tunable gyrotron producing frequency modulation around 260GHz at power levels less than 1W. The sweep rate of frequency modulation can reach 14kHz, and its amplitude is fixed at 50MHz. In water/glycerol glassy ice doped with 40mM TEMPOL, the relative increase in the DNP enhancement was obtained as a function of frequency-sweep rate for several temperatures. A 68 % increase was obtained at 15K, thus giving a DNP enhancement of about 80. By employing λ/4 and λ/8 polarizer mirrors, we transformed the polarization of the microwave beam from linear to circular, and achieved an increase in the enhancement by a factor of about 66% for a given power.
authors.affiliation: École Polytechnique Fédérale de Lausanne, Institute of Condensed Matter Physics, CH-1015 Lausanne-EPFL, Switzerland. Electronic address: dongyoung.yoon@epfl.ch.
authors.forename: Dongyoung
authors.initials: D
authors.lastname: Yoon
authors.affiliation: École Polytechnique Fédérale de Lausanne, Institute of Condensed Matter Physics, CH-1015 Lausanne-EPFL, Switzerland.
authors.forename: Murari
authors.initials: M
authors.lastname: Soundararajan
authors.affiliation: École Polytechnique Fédérale de Lausanne, Institute of Condensed Matter Physics, CH-1015 Lausanne-EPFL, Switzerland.
authors.forename: Philippe
authors.initials: P
authors.lastname: Cuanillon
authors.affiliation: Centre de Recherches en Physique des Plasmas, Station 13, École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne-EPFL, CH-1015 Lausanne, Switzerland.
authors.forename: Falk
authors.initials: F
authors.lastname: Braunmueller
authors.affiliation: Centre de Recherches en Physique des Plasmas, Station 13, École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne-EPFL, CH-1015 Lausanne, Switzerland.
authors.forename: Stefano
authors.initials: S
authors.lastname: Alberti
authors.affiliation: École Polytechnique Fédérale de Lausanne, Institute of Condensed Matter Physics, CH-1015 Lausanne-EPFL, Switzerland.
authors.forename: Jean-Philippe
authors.initials: JP
authors.lastname: Ansermet
keywords: Circular polarization; DNP; Frequency modulation; Gyrotron; Millimeter waves; TEMPOL