Development of a Waveguide FEL Seeded in the 1–3 THz Range for Microbunching Experiment at the Neptune Laboratory

IFEL and FEL techniques can be used to modulate an electron beam on the scale of the radiation wavelength. However, the lack of a high power radiation source in the 100–300 μm range hinders the progress on THz IFEL microbunching. In this paper, we discuss microbunching of an electron beam using a single‐pass FEL seeded with a low power THz pulse generated by frequency mixing of CO2 laser lines in a GaAs nonlinear crystal. A narrowband THz seed source is pumped by a dual beam TEA CO2 laser and can be tuned in the 1–3 THz range. The THz radiation is guided through a hollow waveguide inside the planar FEL undulator driven by a photoinjector. By using a time‐dependent FEL code GENESIS 1.3, we optimized the undulator parameters and analyzed the dynamics of the modulated electron beam. By using a ∼ 8 MeV electron beam with a peak current of 40 A and a ∼1kW THz seed with wavelength 200 μm, the energy modulation up to 1.3% can be achieved in a ∼1.8‐m long undulator with a constant period of 2.7 cm. At present, th...