Transient chirp reconstruction of an ultrafast electron beam via a tightly focused chirped laser pulse

Controlling particle beam phase space is essential for producing high-quality, ultrashort electron beams (e-beams) in plasma-based accelerators. Diagnosing the rapidly evolving transient energy chirp during early acceleration remains challenging. We propose what we believe to be a novel method using tightly focused and chirped laser pulses to reconstruct the chirp profile. By analyzing conditions for enhancing divergence modulation and leveraging intrinsic phase correlations in phase space, precise chirp reconstruction is achieved. Additionally, temporal delay between the laser and e-beam is determined via Fourier analysis of the divergence modulation. This method enables attosecond-level precision laser streaking for relativistic ultrashort e-beams, offering a powerful tool for ultrafast electron dynamics diagnosis.