Two-color laser driven enhanced electron emission from carbon nanotubes with long carrier lifetime

Ultrafast electron pulses generated using femtosecond lasers offer a direct means for investigating ultrafast processes, but the yield of electron emission remains a significant practical limitation. This study demonstrates a substantial enhancement in yield of electron emission from carbon nanotubes induced by two-color (ω + 2ω) pulses with an 80 MHz repetition rate and this enhancement is non-delay-dependent. Compared to the sum of photocurrents induced by each color pulse individually, the combined two-color pulses result in a remarkable enhancement in yield of electron emission by more than 25 times. We attribute this enhanced yield to carrier-assisted optical field emission: carbon nanotubes sustain high carrier concentration state under laser radiation thereby enhancing yield of electron emission. We propose the carrier migration emission model to provide a semi-quantitative description for the carrier-assisted optical field emission. This phenomenon introduces a new method for higher yield of ultrashort electron pulses from CNTs and paves the way for next-generation ultrafast electron emitters and on chip ultrafast optoelectronic device.