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The electron response of nanoplasmon and nanoplasma in the laser field is greatly important for improving the functionality and efficiency of many potential applications. However, how and under what conditions the nanoplasmon‐nanoplasma transition works remains poorly understood due to radiation damage and charge buildup. Utilizing the combined aerodynamic lens and velocity map imaging spectrometer, this transition mediated by different mechanisms are demonstrated, as verified by the distinct photoelectron momentum distributions from Cu nanoparticles. Initially the polarization‐dependent distributions emphasize the domination of surface emission driven by the plasmonic field. Subsequently the transition starts and the competition of volume‐multiphoton and thermionic emission plays the intermediate state dominating the transition process. Finally, a complete plasma is generated with the leading role of thermionic emission, which is confirmed by first observing the correlated electronic decay in metal nanoparticles. These findings bridge the gap between electron emission in nanoplasmonic and nanoplasma states and identify the mechanism‐specific contributions, which will offer general principles for designing nanostructure and laser fields to control electron excitation and emission in practice. [ABSTRACT FROM AUTHOR]

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 + 2 ω) 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 to increase the yield of ultrafast electron pulses from CNTs and paves the way for next-generation ultrafast electron emitters and on chip ultrafast optoelectronic device. [Display omitted] [ABSTRACT FROM AUTHOR]