Technical aspects and possible applications of the THz radiation electronic modulation system of NovoFEL

The Novosibirsk Free Electron Laser (NovoFEL) facility is able to produce high-power tunable laser radiation in quasi-continuous mode in the terahertz (THz) frequency range. The ability to save the peak power of this radiation together with the possibility to control radiation time is of great importance in a number of experiments. In this work we propose the approach suitable for radiation modulation of free electron lasers based on recuperation design, which is based on periodic phase shift of electron bunches with respect to radiation stored in optical cavity. THz macropulses in the range of several microseconds (limited by quality factor of the optical resonator and FEL gain) to several hundred microseconds can be generated by this approach in three different frequency ranges of NovoFEL, i.e. mid-IR (~1100 cm⁻¹), far-IR (~200 cm⁻¹), and THz (~40 cm⁻¹). The macropulse repetition rate is controlled by an external trigger. For each of three available frequency ranges the typical rise and decay of the macropulse were measured and interpreted. The possible applications of short THz macropulses with the maximum available peak power were shown by time-resolved electron paramagnetic resonance (EPR) spectroscopy.

This work was supported by the Russian Science Foundation 17-13-01412.