Coherent Field Emission Upon Ultrafast Laser Irradiation of the Tip Plasmon

Abstract: Irradiation of sharp silver tips with femtosecond laser pulses leads to photoassisted coherent field emission without a static field. We reconstruct the time profile of the emission, and show that the process is entirely governed by the collective response of the tip plasmon and its field emission. Weak-field optical excitation leads to multiphoton absorption and field emission from the tip apex due to the enhanced local field. The attendant sharp field gradient ensures ponderomotive acceleration of emitted electrons and non-local light-matter interaction. The crossover regime in which simultaneous multiphoton absorption and optical field emission take place is evidenced by the time profile of electron emission correlation, laser power dependence, and polarization angle dependence of each harmonic current.