title: A cryogenic receiver for EPR.
abstract: Cryogenic probes have significantly increased the sensitivity of NMR. Here, we present a compact EPR receiver design capable of cryogenic operation. Compared to room temperature operation, it reduces the noise by a factor of ≈2.5. We discuss in detail the design and analyze the resulting noise performance. At low microwave power, the input noise density closely follows the emission of a cooled 50Ω resistor over the whole measurement range from 20K up to room temperature. To minimize the influence of the microwave source noise, we use high microwave efficiency (≈1.1-1.7mTW(-1/2)) planar microresonators. Their efficient conversion of microwave power to magnetic field permits EPR measurements with very low power levels, typically ranging from a few μW down to fractions of nW.
authors.affiliation: Department of Physics, TU Dortmund University, Otto-Hahn-Str. 4, D-44221 Dortmund, Germany. Electronic address: rysard.narkovic@uni-dortmund.de.
authors.forename: R
authors.initials: R
authors.lastname: Narkowicz
authors.affiliation: Max-Planck Institute for Chemical Energy Conversion, Stiftsraße 34-36, D-45470 Mülheim a.d. Ruhr, Germany.
authors.forename: H
authors.initials: H
authors.lastname: Ogata
authors.affiliation: Max-Planck Institute for Chemical Energy Conversion, Stiftsraße 34-36, D-45470 Mülheim a.d. Ruhr, Germany.
authors.forename: E
authors.initials: E
authors.lastname: Reijerse
authors.affiliation: Department of Physics, TU Dortmund University, Otto-Hahn-Str. 4, D-44221 Dortmund, Germany.
authors.forename: D
authors.initials: D
authors.lastname: Suter
keywords: Cryogenic receiver; Planar microresonators; Sensitivity; Signal-to-noise ratio