  A novel mechanism of efficient second harmonic generation in domain wall
series is reported. By employing angle modulation, obvious intensity peaks of
second harmonic appear at specific incident angles utilizing the continuous
laser source of 200mW, and the single-pass conversion efficiency comes up to
5%/W only through dozens of domain walls. It can be shown that the phenomenon
is caused by coherent superposition of Cherenkov second harmonics (CSH)
generated by different domain walls, which is a novel mechanism totally
distinguished from Quasi-phase-matching (QPM).
