X- and Q-band EPR with cryogenic amplifiers independent of sample temperature

Vidmantas Kalendra; Justinas Turčak; Jūras Banys; John J L Morton; Mantas Šimėnas

doi:10.1016/j.jmr.2022.107356

X- and Q-band EPR with cryogenic amplifiers independent of sample temperature

J Magn Reson. 2023 Jan:346:107356. doi: 10.1016/j.jmr.2022.107356. Epub 2022 Dec 9.

Authors

Vidmantas Kalendra¹, Justinas Turčak², Jūras Banys², John J L Morton³, Mantas Šimėnas⁴

Affiliations

¹ Faculty of Physics, Vilnius University, Sauletekio 3, LT-10257 Vilnius, Lithuania; Amplify My Probe Ltd., London NW1 1NJ, UK.
² Faculty of Physics, Vilnius University, Sauletekio 3, LT-10257 Vilnius, Lithuania.
³ London Centre for Nanotechnology, University College London, London WC1H 0AH, UK; Dept. of Electronic & Electrical Engineering, University College London, London WC1E 7JE, UK.
⁴ Faculty of Physics, Vilnius University, Sauletekio 3, LT-10257 Vilnius, Lithuania. Electronic address: mantas.simenas@ff.vu.lt.

PMID: 36516664
DOI: 10.1016/j.jmr.2022.107356

Abstract

Inspired by the success of NMR cryoprobes, we recently reported a leap in X-band EPR sensitivity by equipping an ordinary EPR probehead with a cryogenic low-noise microwave amplifier placed closed to the sample in the same cryostat [Šimėnas et al. J. Magn. Reson.322, 106876 (2021)]. Here, we explore, theoretically and experimentally, a more general approach, where the amplifier temperature is independent of the sample temperature. This approach brings a number of important advantages, enabling sensitivity improvement irrespective of sample temperature, as well as making it more practical to combine with ENDOR and Q-band resonators, where space in the sample cryostat is often limited. Our experimental realisation places the cryogenic preamplifier within an external closed-cycle cryostat, and we show CW and pulsed EPR and ENDOR sensitivity improvements at both X- and Q-bands with negligible dependence on sample temperature. The cryoprobe delivers signal-to-noise ratio enhancements that reduce the equivalent pulsed EPR measurement time by 16× at X-band and close to 5× at Q-band. Using the theoretical framework we discuss further improvements of this approach which could be used to achieve even greater sensitivity.

Keywords: Cryoprobe; EPR; LNA; Noise; SNR; Sensitivity.