Cryogenic Q-band (35 GHz) probehead featuring large excitation microwave fields for pulse and continuous wave electron paramagnetic resonance spectroscopy: Performance and applications

Abstract

The construction and performance of a Q-band (35 GHz) cryogenic probehead for pulse electron paramagnetic resonance and continuous wave electron paramagnetic resonance measurements with down-scaled loop gap resonators (LGRs) is presented. The advantage of the LGR in comparison to TE 012 resonators lies in the large B 1 microwave (mw) fields that can be generated with moderate input mw power. We demonstrated with several examples that this allows optimal performance for double-quantum electron coherence, HYSCORE, and hyperfine decoupling experiments employing matched and high turning angle mw pulses with high B 1-fields. It is also demonstrated that with very low excitation power (i.e. 10–40 mW), B 1-fields in LGRs are still sufficient to allow short mw pulses and thus experiments such as HYSCORE with high-spin systems to be performed with good sensitivity. A sensitivity factor Λ rs of LGRs with different diameters and lengths is introduced in order to compare the sensitivity of different resonant structures. The electromagnetic field distribution, the B 1-field homogeneity, the E 1-field strength, and the microwave coupling between wave guide and LGRs are investigated by electromagnetic field calculations. The advantage and application range using LGRs for small sample diameters is discussed.