Quantum wavefunction reconstruction by free-electron spectral shearing interferometry

We propose a novel spectral method for reconstructing quantum wavefunction of an electron pulse, free-electron spectral shearing interferometry (FESSI). We employ a Wien filter to generate two time-delayed replicas of the electron wavepacket and then shift one replica in energy using a light-electron modulator driven by a mid-infrared laser. As a direct demonstration, we numerically reconstruct an ultrashort electron pulse with a kinetic energy of 10 keV. FESSI is experimentally feasible and enables us to fully determine distinct orders of spectral phases and their physical implications, providing a universal approach to characterize ultrashort electron pulses.