Temporal Broadening of Attosecond Pulse Trains Induced by Multi-Band inference in Solid-State High-Order Harmonic Generation

The mechanism underlying high harmonic generation (HHG) in gases has been well clarified, characterizing attosecond pulse trains (APT) in the time domain, significantly advances the synthesis of isolated attosecond pulse (IAP). However, the complexity of HHG in solid obstacles IAP separation. Here, we use time-dependent density functional theory (TDDFT) to investigate the multiband mechanism of APT in solid state with bulk silicon as prototype. Our research unveils that: 1. The temporal characteristics of APT can be characterized by the occupation of electrons in different energy bands. 2. Due to the temporal occupation difference caused by optical transition allowed (or forbidden) by symmetry between different conduction bands and valence bands, a harmful phase shift in harmonics emission to APT for extracting IAP occurs. Our findings not only shed light on the mechanisms behind solid-state HHG but also provide new avenues to control APT to generate IAP.