Unveiling Photoinjection Dynamics

Strong-field ionization, leading to the formation of electron wave packets, is central to attosecond science. In solids, valence electrons can be promoted to conduction bands via multiphoton absorption or interband tunneling induced by a strong laser field. The highly nonlinear nature of this process confines photoinjection to sub-half-cycle time intervals (for linearly polarized fields). Furthermore, for few-cycle pulses, photoinjection can be largely confined to a single half cycle of the electric field [1]. These properties are central to ultrafast techniques such as nonlinear photoconductive sampling [2] and solid-state TIPTOE [3], which enable optical-field-resolved measurements with a petahertz bandwidth [4]. Advancing these techniques requires a deeper understanding of photoinjection dynamics. Key questions remain: What is the duration of a sub-half-cycle photoinjection event? How many carriers are photoinjected by each half-cycle? And what are the optimal conditions for single subfemtosecond photoinjection within feasible optical waveforms?