Abstract
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.
Highlights
INTRODUCTIONPhotoelectron emission from metallic nanostructures due to ultrafast laser fields enables the spatiotemporal control of electron motion within femtosecond and nanometer scales [1,2,3,4,5,6], making it attractive to fundamental research and applications in ultrafast electron microscopy [7,8], diffraction [9,10], attosecond electronics [3,11,12], strong-field nanooptics [13], and nanoscale vacuum devices [14,15,16]
Based on the analytical formulation presented above, we provide an analysis of the photoelectron emission with different laser and dc fields
It is found that as T decreases, photoelectron emission is gradually confined to a smaller number of emission channels but with more electron yield, because of the decreasing frequency ratio between laser carrier ω and pulse repetition frequency ωE [Fig. 2(b)]
Summary
Photoelectron emission from metallic nanostructures due to ultrafast laser fields enables the spatiotemporal control of electron motion within femtosecond and nanometer scales [1,2,3,4,5,6], making it attractive to fundamental research and applications in ultrafast electron microscopy [7,8], diffraction [9,10], attosecond electronics [3,11,12], strong-field nanooptics [13], and nanoscale vacuum devices [14,15,16]. While there have been recent efforts to develop analytical quantum models for continuous-wave laser excitation [24,27,28,46], numerical simulations are typically implemented to study photoemission due to ultrashort pulse lasers. Fowler-Nordheim based models are widely used to calculate the photoemission rate [17,38,39], but it is only applicable in the strong optical-field regime. We construct a quantum analytical solution for ultrafast photoelectron emission from a dc-biased surface illuminated by few-cycle laser pulses (Fig. 1), by exactly solving the TDSE. Our solution is valid from the photon-driven regime to the optical-field-driven regime, and is applicable for arbitrary laser parameters (i.e., intensity, pulse duration, carrier frequency, and CEP), dc bias, and metal properties (i.e., work function and Fermi level). This work offers clear insights into the photoelectron energy distribution and spatiotemporal dynamics of electron emission under different driving electric fields
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