AI 中文总结
本研究采用太赫兹横向偏转腔结合偶极磁铁，实现了激光尾场加速电子束纵向相空间的高分辨率诊断，揭示了能量窗口参数对束团时长的调控规律，为优化压缩电子束提供了策略。
AI 中文摘要
飞秒相对论电子束是超快动力学的关键探针，其脉冲时长直接限制了可实现的时间分辨率。激光尾场加速（LWFA）可提供这类电子束的小型化源，但注入诱导的能散使得束团压缩对非线性纵向输运敏感，因此亟需直接测量纵向相空间（LPS）。本研究采用太赫兹横向偏转腔（THz-TDC）结合偶极磁铁，重建经双弯消色差器（DBA）压缩的LWFA电子束团的非线性LPS，解析出与高阶纵向输运相关的特征C形分布。在平均能量约为4.55 MeV时，该诊断装置实现了1.8 fs的时间分辨率和6.0 keV的能量分辨率，对应相对能量分辨率为0.13%。对于约2.9%的可比能散，将传输能量窗口中心从4.574 MeV移至4.532 MeV，可使所选束团远离非线性LPS的低斜率区域，均方根束长从26 fs增至42 fs；当窗口中心保持在4.553 MeV附近时，将能散从2.0%增至4.4%，束长从27 fs增至44 fs。这些结果表明，最终束团时长由非线性LPS内传输能量窗口的位置和宽度共同决定，建立了指导优化DBA压缩LWFA电子束团的LPS策略，为未来高阶相空间校正提供了基础。
英文摘要
Femtosecond relativistic electron beams are key probes of ultrafast dynamics, and their pulse duration directly limits the achievable temporal resolution. Laser wakefield acceleration (LWFA) provides a compact source of such beams, but the injection-induced energy spread makes bunch compression sensitive to nonlinear longitudinal transport, motivating direct longitudinal phase space (LPS) measurements. Here, a terahertz transverse-deflecting cavity (THz-TDC) combined with a dipole magnet is used to reconstruct the nonlinear LPS of LWFA electron bunches compressed in a double-bend achromat (DBA), resolving a characteristic C-shaped distribution associated with higher-order longitudinal transport. At an average energy of approximately 4.55 MeV, the diagnostic achieves a temporal resolving power of 1.8 fs and an energy resolution of 6.0 keV, corresponding to a relative energy resolution of 0.13%. For comparable energy spreads of approximately 2.9%, shifting the transmitted energy-window center from 4.574 MeV to 4.532 MeV moves the selected beam away from a low-slope region of the nonlinear LPS and increases the root-mean-square bunch length from 26 fs to 42 fs; with the window center held near 4.553 MeV, increasing the energy spread from 2.0% to 4.4% lengthens the bunch from 27 fs to 44 fs. These results show that the final bunch duration is governed by both the position and width of the transmitted energy window within the nonlinear LPS, establishing an LPS-guided strategy for optimizing DBA-compressed LWFA electron bunches and providing a basis for future higher-order phase-space correction.
Comments9 pages, 5 figures; submitted to Physical Review Applied
