Femtosecond tunable-wavelength photoassisted cold field emission

We demonstrate photoassisted cold field emission (PFE) from a tungsten tip induced by tunable-wavelength low-power femtosecond laser excitation. The emission current from the apex of the (310)-oriented single-crystalline emitter is shown to linearly depend on the incident laser power, while the effective work function is reduced by the respective photon energy. Our results promote the implementation of the linear regime in laser-triggered cold field emission for ultrafast transmission electron microscopy.