X-band (9 GHz) Electron Paramagnetic Resonance station at the NovoFEL facility: sensing the spin dynamics induced by high-power THz pulses
- Dr. Sergey VEBER
- Dr. Sergey VEBER (International Tomography Center SB RAS)
Large-scale facilities such as neutron research reactors, synchrotron light sources and free electron lasers offer natural science experimentalists the opportunity to perform unique experiments which determine the cutting edge of experimental data accessible. Novosibirsk Free Electron Laser (NovoFEL) was originally developed to fit the requirements of physicists, chemists and biologists  and featured ultrawide range of radiation wavelength (THz, far- and mid-IR ranges) and very high average power (up to 400 W at 70 cm-1). International Tomography Center SB RAS is constructing two user stations at NovoFEL aiming to utilize the unique radiation applied to the field of molecular magnetism: SQUID magnetometer station and continuous-wave (CW) and Time-Resolved (TR) X-band (9 GHz) Electron Paramagnetic Resonance (EPR) station.
In this work we present the current status of CW and TR EPR station at NovoFEL. The detailed layout of the experimental user station is shown and discussed. While the CW and TR EPR X-band (9 GHz) spectrometer used is almost the same as in many EPR laboratories, it was built in the NovoFEL beamline and allows performing the unique EPR experiments with simultaneous irradiation of the sample by common UV-vis and exceptional NovoFEL light. For this purpose, multimodal THz waveguide allowing to fed NovoFEL radiation directly into the EPR resonator is used. Laser radiation of NovoFEL is passed through the collimator based on two off-axis parabolic mirrors which compress the beam diameter by a factor of 15 adjusting it to the aperture of THz waveguide used in EPR spectrometer. Mechanical optical chopper is used to decrease the average power by a factor of 100 to the safety level while keeping the maximum accessible peak power. Passed through the collimator and optical chopper, the NovoFEL radiation can be readily directed to the sample into EPR resonator. Different detection schemes of experiments conditioned by the initial time profile of NovoFEL radiation, optical chopper modulation and the capability (CW and TR) of EPR spectrometer used are discussed. Special attention is drawn to the heat effect and its practical use for the temperature-modulated detection of very broad EPR spectra .
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 S.L. Veber et.al., Journal of Magnetic Resonance, 2018, 288, 11–22
Acknowledgements: This work has been supported by the Russian Science Foundation (no. 17-13-01412).