Hardware
Spectrometer Development
We have developed many EPR-spectrometers allowing us to push the boundaries of EPR beyond the capabilities of commercial instrumentation. We have implemented high speed (12GSa/s) arbitrary waveform generators (AWGs) to enable ultrawide-band (up to 5GHz) excitation and detection at both X and Q-Band. Through custom software we are able to precisely control the pulse shapes used and compensate for resonator effects and implement advanced digital detection filtering.
In recent years, we have included an additional AWG with lower sampling rates for shaped/chirped radio-frequency pulses into one of our AWG-based setups. This enables us to create both mw and rf pulses in ENDOR experiments of any shape and gives us optimal control over the spin system of interest. We showed that this system boosts the sensitivity of standard ENDOR experiments, but also unlocks the door to more advanced ENDOR experiments.
We are also investigating how the expansion of 5G and satellite communication into the Ka-Band unlocks new low-cost components that can trickle down to EPR. In this direction we are developing a new low-cost EPR spectrometer built around the 30-31GHz satellite communication band.
Selected publications:
- Doll, A. & Jeschke, G. Wideband frequency-swept excitation in pulsed EPR spectroscopy. Journal of Magnetic Resonance 280, 46–62 (2017)
- Stropp, J., Wili, N., Nielsen, N. C. & Klose, D. Increased sensitivity in electron–nuclear double resonance spectroscopy with chirped radiofrequency pulses. Magn. Reson. 6, 33–42 (2025)
People: Hugo Karas, Julian Stropp, Daniel Klose, Gunnar Jeschke
Resonator Development
In parallel to our spectrometers we have regularly developed new resonators to complement our commercial ones. We have developed pulse Q-Band resonators unlocking larger sample volumes or ultrawide-bandwidths. Additionally, we have designed and manufactured a Q-Band cw resonator for 3mm sample tubes allowing the exact same sample to be measured at multiple frequencies, which is especially helpful for highly air-/moisture-sensitive, unstable catalytic samples.
We have also developed custom high temperature X-Band cw resonators, improving the quality factor and temperature stability.
Selected publications:
- Tschaggelar, R. et al. Cryogenic 35GHz pulse ENDOR probehead accommodating large sample sizes: Performance and applications. Journal of Magnetic Resonance 200, 81–87 (2009)
- Tschaggelar, R. et al. High-Bandwidth Q-Band EPR Resonators. Appl Magn Reson 48, 1273–1300 (2017)
- Fischer, J. W. A. et al. Design and performance of an oversized-sample 35 GHz EPR resonator with an elevated Q value. Magn. Reson. 5, 143–152 (2024)
People: Julian Stropp, Rene Tschaggelar, Oliver Oberhänsli, Daniel Klose
Operando Catalysis
We developed a dedicated setup for in-situ and operando EPR investigation of heterogeneous catalysts under working conditions. We perform experiments both under gas flow and in batch, at high temperature (up to 500°C), high pressure (up to 10 bar) and in vacuum. We use special home-built water-cooled resonators with stable performance at high temperature. The gas flows are controlled by a series of mass flow controllers (MFCs) with a gas pulse control system enabling modulation excitation spectroscopy with phase sensitive detection. The resonator is coupled with a mass spectrometer (MS), which allows the detection of reaction products during the operando experiments. We also implemented the contact-free conductivity measurement through the detection of off-resonance changes of the Q factor, which can be detected in parallel with the EPR measurements.
The same setup is also used for different experiments, for instance for EPR/MS monitoring of thermally-induced depolymerization.
Selected publication:
- Fischer, J. et al. Current Developments in Operando Electron Paramagnetic Resonance Spectroscopy. Chimia 78, 326–332 (2024).
People: Katja Raue, Mikhail Agrachev