Accessing precisely the phase variation of electronic wave-packet (EWP) provides unprecedented spatiotemporal information of the microworld. A radial interference pattern at near-zero energy has been widely observed in experiments of strong-field photoionization. Here we report an experimental and theoretical investigation of this low-energy interference structure (LEIS) in mid-infrared laser fields. We clarify that the LEIS arises due to the soft-recollision mechanism, which was previously found to play a pivotal role in producing the pronounced low-energy structure. Specifically, the LEIS is induced by the interference between direct and soft-recollision EWPs launched within a 1/18 laser-cycle time scale in our experiments. Our result opens a promising new avenue for retrieving the structure and dynamics of EWPs in atoms and molecules with attosecond time resolution.

精确访问电子波包 (EWP) 的相位变化可提供前所未有的微观世界时空信息。在强场光电离实验中广泛观察到接近零能量的径向干涉图案。在这里，我们报告了中红外激光场中这种低能量干涉结构 (LEIS) 的实验和理论研究。我们澄清了 LEIS 是由于软碰撞机制而产生的，以前发现该机制在产生明显的低能量结构中起着关键作用。具体来说，LEIS 是由我们实验中在 1/18 激光周期时间尺度内发射的直接和软反撞 EWP 之间的干扰引起的。