A carbon nanotube based electron source with 0.3eV energy spread and an unconventional time delay

Conventianal metal tip based laser-driven electron source is normally constrained by a trade-off between energy spread and pulse duration due to optical-field-induced free electron acceleration, making it challenging to overcome the current state of the art electron source with over 1 eV energy spread and hundreds of femoto second (fs) duration. Here, we report an unconventional delayed emission in a one-dimensional carbon nanotube (CNT) based electron source. By utilizing a special pump-probe approach, we apply 7 fs laser pulses to the CNT emitters and observe free electron emission tens of fs after the pulse. This delayed emission resulted in a substantial reduced energy spread to approximately 0.3 eV and an electron pulse duration of about 13 fs. Through time-dependent density functional theory calculations, we find that this is driven by the interplay of collective oscillations and electron-electron interactions. Our results may provide a promising technology for the cutting-edge ultrafast electron sources.