LAUSR

Photoemission driven by ultrafast optical fields enables spatiotemporal control of electron motion with extremely high precision. Here, we present a quantum model for ultrafast photoelectron emission from a dc-biased surface induced by laser pulses of arbitrary duration, ranging from subcycle to continuous wave, by solving the time-dependent Schr\"odinger equation exactly. The single formulation is valid from photon-driven electron emission in low intensity optical fields to field-driven emission in high intensity optical fields. We find the emitted charge per pulse oscillatorily increases with pulse repetition rate, due to varying coherent interaction of neighboring laser pulses. For a well-separated single pulse, our results recover the experimentally observed vanishing carrier-envelope phase sensitivity in the optical-field regime. We also find that applying a large dc field to the photoemitter is able to greatly enhance the photoemission current and in the meantime substantially shorten the current pulse.