Electronic system for modulating THz radiation at Novosibirsk free electron laser: possible applications and technical aspects

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 developed and implemented the approach allowing one to create THz macropulses at NovoFEL with any repetition rate and almost any individual pulse length. The proposed electronic modulation system is based on a periodic shift of the phase of electron bunch injection. Such a shift suppresses lasing and forms macropulses from quasi-continuous radiation of NovoFEL. The system is directly embedded into the electronic infrastructure of NovoFEL and can be triggered directly on user stations.

In order to characterize the modulation system, series of macropulses with different durations from 10 to 400 μs were measured for three available frequency ranges. Using the rising and falling edges of typical macropulses the calculations of the gain and total losses were done for three optical resonators. The use of short macropulses was exemplified for time-resolved EPR spectroscopy. The heating of a copper(II) complex by the absorbed THz radiation and its subsequent thermal relaxation were measured.

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