Abstract
A new scheme to generate narrow-band tunable terahertz (THz) radiation using a variant of the echo-enabled harmonic generation is analyzed. We show that by using an energy chirped beam, THz density modulation in the beam phase space can be produced with two lasers having the same wavelength. This removes the need for an optical parametric amplifier system to provide a wavelength-tunable laser to vary the central frequency of the THz radiation. The practical feasibility and applications of this scheme are demonstrated numerically with a start-to-end simulation using the beam parameters at the Shanghai Deep Ultraviolet Free-Electron Laser facility (SDUV). The central frequency of the density modulation can be continuously tuned by either varying the chirp of the beam or the momentum compactions of the chicanes. The influence of nonlinear rf chirp and longitudinal space charge effect have also been studied in our article. The methods to generate the THz radiation in SDUV with the new scheme and the estimation of the radiation power are also discussed briefly.
Highlights
As has been widely used in radar, security, communication, medical imaging, etc., THz radiation has drawn a lot of attention all over the world
A new scheme of employing the echo effect previously observed in hadron accelerators was proposed [5] and experimentally tested [6] to generate high harmonics of free electron laser (FEL) radiation, and the bunching coefficients of this scheme were analyzed in detail [7] to give us a clearer picture of the mechanism behind it
The mechanism of allowing a chirped electron beam to interact with two lasers of the same wavelength can be explained as follows: the beam is modulated by the laser in the first modulator and generates energy modulation at wave number k0; the energy modulation is compressed to C1k0 with the compression of the whole beam; the modulated beam interacts with the laser again in the second modulator to produce a superimposed energy modulation; the energy modulation is converted to density modulation at wave number ðC1 − 1ÞC2k0 when the beam passes through the second dispersion
Summary
As has been widely used in radar, security, communication, medical imaging, etc., THz radiation has drawn a lot of attention all over the world. Providing the advantages of the echo-enabled harmonic generation FEL such as compact size, tunable frequency, etc., a method of using two lasers to modulate the electron beam to generate density modulation at THz frequency has been proposed and analyzed in Refs. The wave number of the beam density modulation will be compressed to k1 1⁄4 C1k0 and its high harmonics when the beam passes through the first dispersion section with small R56. After the beam passes through the second dispersion section, the energy modulation is converted into density modulation at the final wave number k 1⁄4 nC1C2k0 þ mC2k0, where n and m are nonzero integers.
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