Measuring Attosecond Electron Pulses with Coherent Nonlinear Thomson Scattering*

Attosecond-duration electron pulses can potentially enable new scientific discoveries on the frontier research area of ultrafast dynamics. However, current conventional methods for measuring attosecond-duration of electron pulses, such as coherent transition radiation and Smith-Purcell radiation, are inapplicable in the important low energy region. We show that nonlinear Thomson scattering is a robust solution to this problem, and can in principle provide even zeptosecond resolution (10$^{\mathrm{-21}}$ s). The pulse duration is revealed by features of the radiation spectrum due to coherent scattering by tightly bunched electrons. The limits and robustness of this method, as well as considerations for its application in realistic experimental conditions, will be discussed in detail.