Fig. 1. (Color online) The electromagnetic radiation waveform (red solid lines) in the wake at time and ; snapshots of the transverse current densities (blue dashed lines) and the electron densities (black dotted lines) are also plotted, where , . The filled red region indicates the incident laser.

Fig. 2. (Color online) The temporal waveforms of the radiation pulses observed at a fixed position at the right side of the simulation box in vacuum for three different laser intensities with initial plasma density (a) and the corresponding frequency spectra (b). Frequency spectra of the radiation produced with different plasma densities at a given laser amplitude are also plotted in (c).

Fig. 3. (Color online) The temporal evolution of the electromagnetic radiation emitted in the wake at three different laser intensities (a–c) and the corresponding frequency spectra (d), where .

Fig. 4. (Color online) The amplitude of the first pulse normalized by in the wake radiation (a) and its central frequency (b) versus the normalized laser strength , where .

Fig. 5. (Color online) 2D simulation results of wake radiation generation: (a) spatial distribution of electromagnetic radiation, (b) waveform of the radiation on the laser axis, and (c) frequency spectrum of the wake radiation, where and .

Fig. 6. The trajectory of a typical electron during and after the laser interaction in phase space (a) and the temporal evolution of its transverse momentum (b), where , . The inset in (b) shows the transverse momentum at a later time after the laser interaction.