Abstract
Generation of tunable terahertz radiation based on the interaction of a frequency-chirped low power terahertz wave with a relativistic electron beam is proposed. The electron beam is first modulated temporally due to the ponderomotive force induced by the beat wave of two copropagating intense laser beams of slightly different frequencies. Then the electron beam interacts with a low-amplitude driver wave at terahertz frequency with a linear frequency chirping. A nonlinear transverse current density is driven that emits terahertz radiation at an up-shifted frequency with a relatively enhanced amplitude. The modulation process is analyzed theoretically by a complete set of fluid equations and considering the effects of both the electrons space-charge potential and the beat wave ponderomotive force. The initial density and energy of the electron beam are both optimized in order to improve the terahertz amplification process. The effect of the driver's frequency chirping, as well as the effects of the initial electron beam density and energy on the emitted terahertz radiation are investigated numerically. It is shown that the frequency chirping of the driver wave plays a key role in terahertz amplification. It is shown that there is an optimum chirp value for which the terahertz radiation is amplified significantly compared with the case without chirping. Moreover, transverse effects of the laser beams and the driver wave on the emitted terahertz radiation are also investigated.
Highlights
Terahertz radiation with widespread applications in science, technology, and medicine has attracted many scientists in the past few decades [1,2,3,4]
A mechanism of the terahertz radiation amplification by a laser-modulated relativistic electron beam interacting with a chirped-frequency low-amplitude driver wave at terahertz frequency was proposed
A uniform density relativistic electron beam has been modulated by the interaction with the beat wave of two lasers with different frequencies
Summary
Terahertz radiation with widespread applications in science, technology, and medicine has attracted many scientists in the past few decades [1,2,3,4]. The modulated electron beam emits radiation at terahertz frequency when interacts with a wiggler magnetic field [33] or surface plasma wave [34]. A uniform density electron beam is modulated with the ponderomotive force induced by the beat wave of two laser beams at slightly different frequencies. Thereafter, the modulated electron beam interacts with a chirped-frequency low-amplitude driver wave at terahertz frequency that drives a nonlinear transverse current of electrons. Such frequency-chirped terahertz waves could be practically generated by employing some modified photomixing schemes [40,41].
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