Nowadays laser-plasma-based wakefield accelerators are capable to deliver GeV-level femtosecond electron bunches crucial for emerging applications in medicine, industry, and fundamental science. Many of these applications critically require the precise characterization of the accelerated electron bunch as well as the plasma wakefield that largely affects the bunch's quality, there advanced diagnostics of such highly transient, microscopic bunch and field structures are highly demanded. In this talk, we will introduce our recently developed technique named as femtosecond relativistic electron microscopy (FREM), which has been demonstrated to be a powerful tool for probing the fine structures of highly nonlinear plasma waves and accelerated electron bunch with very high spatiotemporal resolution. Here our talk will focus on two very recent observations we have got using FREM related to shock-front induced electron injection and all-optical staging, both showing very interesting features that have not been directly revealed yet during experiment. We anticipate that these results will significantly advance the understanding of the complex laser-beam-plasma dynamics important for optimizing plasma accelerators in real time.
 

laser-driven wakefield; beam-driven wakefield; femtosecond relativistic electron microscopy