Divergence gating towards far-field isolated attosecond pulses

Abstract

Divergence gating, a novel method to generate far-field isolated attosecond pulses (IAPs) through controlling divergences of different pulses, is proposed and realized by relativistic chirped laser-plasma interactions. Utilizing various wavefronts for different cycles of incident chirped lasers, reflected harmonics with minimum divergences are obtained only at the peak cycle when plasma targets are adjusted to proper distances from foci of lasers. Therefore, the corresponding attosecond pulse is isolated in far field due to much slower decay during propagation than others. Confirmed by three-dimensional numerical simulations, millijoule-level sub-50 as IAPs with intensity approaching 1016 W cm-2 (1017-1018 W sr-1) are obtained by our scheme, where low-order harmonics can be preserved.