Coherent high-order harmonic generation by sawtooth-like laser fields.

We theoretically investigate the high-order harmonic generation driven by sawtooth-like laser fields. It is found that the coherence of the high-order harmonic spectrum could be controlled by adjusting the sawtooth shape parameter α (0 ≤ α ≤ 0.5). With proper α, the intensity of the high-order harmonic spectra come from the electrons with long trajectories can be greatly weakened and the harmonic photons in the plateau burst with high coherence in a broad frequency range. Selecting these harmonics, a phase-stabilized attosecond pulse train with regular pulse structure could be obtained.