Beam density modulation during emission under RF and laser fields

Free-electron beam-based devices are vital in numerous applications, such as telecommunication systems, satellite-based transmitters, radar, communication data links, and electronic countermeasures. These devices utilize the collective interaction between an electron beam and a circuit structure, to convert the energy of the electron beam into electromagnetic radiation. If we can generate an electron beam with direct density modulation during its emission, rather than modifying a continuous beam in an RF interaction region to achieve beam modulation, the performance of the devices for power amplification can be significantly enhanced [D.R. Whaley, et al, IEEE Trans. Plasma Sci. 30(3), 998–1008 (2002].

This work demonstrates various pulse shapes of pre-bunched electron beams emitted from a radio frequency (RF) cold cathode under different combinations of RF field and optical field (continuous-wave or pulsed), using an exact quantum model for photo-/field- emission [Y. Zhou and P. Zhang, J. Appl. Phys. 130(6), 064902 (2021)]. The profile of the produced emission current can be modulated by varying RF field (amplitude and frequency) and optical field (laser wavelength, laser intensity, pulse length). The emission current pulse amplitude, beam width, electron numbers per pulse, as well as the harmonic spectrum of the current pulse, are investigated in detail under various combinations of RF and optical fields.