X-band EPR setup with THz light excitation of Novosibirsk Free Electron Laser: Goals, means, useful extras

Electronic Modulation of THz Radiation at NovoFEL: Technical Aspects and Possible Applications

“…NovoFEL is equipped with a number of user stations representing different experimental techniques [16]. Among them, the EPR spectroscopy station allows for the detection of unpaired electrons in various materials and thus can be employed to study the influence of THz radiation onto their spin dynamics [3]. Over the past decades, a number of EPR techniques have been developed and widely used in physics, chemistry, and biology [16,17,18,19,20,21].…”

“…In most cases, the latter represents short-lived triplet states and radical pairs generated by the laser pulse of the ultraviolet–visible (UV-Vis) range (targeted processes are related to photochemistry). At the same time, THz-radiation of NovoFEL has much less energy quanta and is used to excite either vibrational bands of studied compounds [22] or high-energy EPR transitions [3] in high-spin systems with large zero-field splitting (targeted processes are related to spin system excitation) [23]. Regardless of the type of targeted processes, the absorption of THz light by the sample leads to its heating.…”

“…TR EPR experiments were carried out using an electronic modulation system, unless otherwise stated. A more detailed description of the experimental setup can be found elsewhere [3].…”

“…Although this is crucial for some applications [2], in most of the experiments, such high average power is excessive and thus should be attenuated. In particular cases, the use of short macropulses is required which allows one to keep the peak power very high, while the average one can be reduced significantly [3]. To fulfill these requirements without the use of external devices (e.g., mechanical optical choppers), one should be able to switch on and off the FEL lasing process.…”

Recent experiments at NovoFEL user stations

“…A one-color pump-probe setup was applied to research on the relaxation time in semiconductors with shallow donors at cryogenic temperatures [22]. The electron paramagnetic resonance station [23] enables exploration of the influence of high-power THz or mid-IR radiation on spin systems.…”