High repetition rate coherent terahertz synchrotron radiation via self-amplified energy modulation

Coherent terahertz (THz) radiation sources based on a storage ring hold a significant future for generating high average power terahertz radiation, as the electron beam possesses a high revolution frequency. We propose a novel scheme to generate a high repetition rate coherent THz radiation leveraging the energy modulation self-amplification technology. In this scheme, utilizing the interaction of external intensity-modulated laser pulses with the electron beam can lead to a customized manipulation of the electron beam, such as a periodic longitudinal density modulation with a submillimeter scale for coherent THz radiation. Positively, it can propel the repetition rate when the peak power requirement of an external laser system is decreased. Thus, we employ a self-modulation method to enhance the initial weak energy modulation induced by the laser directly. In the meanwhile, the use of self-modulation can bypass the limitation that the bandwidth of a long modulator should be smaller than that of the external wideband laser source, which is necessary to shape the intensity envelope flexibly. The one-dimensional analytical description of electron longitudinal dynamic during the self-modulation process is given, which confirms the effective enhancement of the modulation at THz band. Three-dimensional time-dependent simulation results based on the parameters of Hefei light source-II show that the coherent THz radiation pulses with a repetition rate of 10 kHz can be generated.

Figure 1

(a) Scheme for generating high repetition rate THz CSR; (b) the specific layout of the self-modulation section.

Figure 2

The maximal bunching factor (blue line) and modulation amplitude (green line) versus the external seed laser power with (solid line) or without (dotted line) self-amplification process. The bunching factor of the narrow spectrum is peaked at $f_m=1\mathrm{THz}$.

Figure 3

Longitudinal phase space. Without self-amplification process at (a) submillimeter scale and (c) laser wavelength scale; with self-amplification process at (b) submillimeter scale and (d) laser wavelength scale. The pulse energy of the seed laser is 0.4 mJ with a 40 MW peak power.

Figure 4

The maximal bunching factor versus the external seed laser peak power with (solid line) or without (dotted line) self-amplification process for two cases of $f_m=1\mathrm{THz}$ (blue lines) and 3 THz (red lines).

Figure 5

(a) The longitudinal phase space of the electron beam is plotted for turn 0 (blue), 500 (green), and 20 000 (red); (b) The fractional energy spread evolution of the modulated beam after radiation for 100 000 turns. The pulse energy of the seed laser is 0.4 mJ with a 40 MW peak power.