Tracing attosecond electron emission from a nanometric metal tip

Solids exposed to intense electric fields release electrons through tunnelling. This fundamental quantum process lies at the heart of various applications, ranging from high brightness electron sources in d.c. operation(1,2) to petahertz vacuum electronics in laser-driven operation(3-8). In the latter process, the electron wavepacket undergoes semiclassical dynamics(9,10) in the strong oscillating laser field, similar to strong-field and attosecond physics in the gas phase(11,12). There, the subcycle electron dynamics has been determined with a stunning precision of tens of attoseconds(13-15), but at solids the quantum dynamics including the emission time window has so far not been measured. Here we show that two-colour modulation spectroscopy of backscattering electrons(16) uncovers the suboptical-cycle strong-field emission dynamics from nanostructures, with attosecond precision. In our experiment, photoelectron spectra of electrons emitted from a sharp metallic tip are measured as function of the relative phase between the two colours. Projecting the solution of the time-dependent Schrodinger equation onto classical trajectories relates phase-dependent signatures in the spectra to the emission dynamics and yields an emission duration of 710 +/- 30 attoseconds by matching the quantum model to the experiment. Our results open the door to the quantitative timing and precise active control of strong-field photoemission from solid state and other systems and have direct ramifications for diverse fields such as ultrafast electron sources(17), quantum degeneracy studies and sub-Poissonian electron beams(18-21), nanoplasmonics(22) and petahertz electronics(23).

Automated summary

Solids exposed to intense electric fields release electrons through tunnelling, which plays a vital role in various applications. In this study, we use two-colour modulation spectroscopy to uncover the suboptical-cycle strong-field emission dynamics from nanostructures, with attosecond precision. By measuring the photoelectron spectra and matching the quantum model to the experiment, we determine the emission duration of 710 +/- 30 attoseconds. These results have implications for ultrafast electron sources, quantum degeneracy studies, nanoplasmonics, and petahertz electronics.