Analysis and elimination of the distortion in electro-optic measurement of low-energy subpicosecond electron bunches

Electro-optic (EO) technique is widely used to characterize longitudinal profile of electron bunches. However, electron bunches with a low energy (∼MeV) and a short time duration (∼subpicosecond) cannot be well resolved by EO measurement, which leads to distortion. The convolution theorem is proposed to analyze this distortion in EO measurement. And the factors leading to the distortion are discussed, among which the divergent Coulomb field of electrons is the main one. Distortion elimination and reconstruction of electron bunch profiles from detected EO signals is an ill-posed inverse problem. This paper proposes an iterative Tikhonov regularization method to solve this inverse problem and to reconstruct electron bunch profiles from the EO signals detected by the EO measurement. The feasibility of our proposal is tested and numerically verified based on subpicosecond electron bunches with several MeV energy.