Tunable THz radiation source from dielectric loaded waveguide excited by nonrelativistic electron bunch trains

We propose a novel scheme to generate a tunable narrow-band THz radiation. In this scheme, a train of laser pulses with THz repetition rate is used to drive a photocathode direct current (DC) gun, leading to the emission of a train of electron bunches. The electron bunch train is subsequently accelerated by the gun field and applied to selectively excite one of the modes in the dielectric loaded waveguide (DLW) structure, which is located downstream the DC gun. Thanks to the tunability of the repetition rate of laser pulses and the gun voltage, a tunable narrow-band THz radiation source can be obtained. This proposed source has the advantages of compactness, robustness and relatively high power.

Figure 1

Cross section draw of the proposed scheme.

Figure 2

Dispersion curves of the first four order modes (black lines) and electron beam lines with different energies.

Figure 3

Electron beam simulation results: (a) the evolutions of rms beam size along the longitudinal position; (b)the cross section distribution state and (c) the coherence factor of the electron beam at the DLW entrance position when the initial time spacing $\mathrm{\Delta }\tau =8.2\mathrm{ps}$ and gun voltage is 100 kV.

Figure 4

Beam radius evolutions along the longitudinal DLW position.

Figure 5

Simulated electric field strength at $r=0.40\mathrm{mm}$, the corresponding spectrum calculated by Fourier transform, and the pulse power distribution along the longitudinal position. (a) The coherence factor is resonant at ${\mathrm{TM}}_{01}$ mode ($\mathrm{\Delta }\tau =\frac{1}{0.1236\mathrm{THz}}=8.09\mathrm{ps}$) and the beam energy is 200 keV; (b) The coherence factor is resonant at ${\mathrm{TM}}_{01}$ mode ($\mathrm{\Delta }\tau =\frac{1}{0.2434\mathrm{THz}}·2=8.2\mathrm{ps}$) and the beam energy is 100 keV.

Figure 6

The same as that of Fig. 5, when the coherence factor is resonant at ${\mathrm{TM}}_{02}$ mode ($\mathrm{\Delta }\tau =\frac{1}{0.3842\mathrm{THz}}·2=5.2\mathrm{ps}$) and the beam energy is 150 keV.