Imaging the Nonlinear Plasmoemission Dynamics of Electrons from Strong Plasmonic Fields

Abstract

We use subcycle time-resolved photoemission microscopy to unambiguously distinguish optically triggered electron emission (photoemission) from effects caused purely by the plasmonic field (termed "plasmoemission"). We find from time-resolved imaging that nonlinear plasmoemission is dominated by the transverse plasmon field component by utilizing a transient standing wave from two counter-propagating plasmon pulses of opposite transverse spin. From plasmonic foci on flat metal surfaces, we observe highly nonlinear plasmoemission up to the fifth power of intensity and quantized energy transfer, which reflects the quantum-mechanical nature of surface plasmons. Our work constitutes the basis for novel plasmonic devices such as nanometer-confined ultrafast electron sources as well as applications in time-resolved electron microscopy.

Nonlinear Plasmonic Photoelectron Response of Ag(111)

“…Furthermore, above the bulk plasmon resonance, we find that the longitudinal bulk plasmon mode is excited and a two-quantum decay unexpectedly generates a spectroscopic feature, which appears only for ħw≧ħwp, where photoelectrons from EF are excited to Ef=2ħωp. Similar nonlinear plasmon-induced photoemission has recently been invoked in space-and time-resolved photoemission electron microscopy [62] of plasmonic nanostructures up to fifth order of the plasmon field when exciting Au at moderate powers with an ultrafast Ti:sapphire laser oscillator [63].…”

Frontier nonequilibrium materials science enabled by ultrafast electron methods

“…There is now a diversity of ultrafast electron sources and instrumentation available, including home-built keV systems, modified commercial TEMs, and RF-photoguns/MeV electron-beam instrumentation that originally found their use filling the storage ring at synchrotron facilities or driving x-ray free-electron lasers (XFELs). These instruments cover a wide range of electron energy from 10 s of eV to MeV and have provided for ultrafast versions of many conventional electron-based scattering, imaging, and spectroscopy method beyond those previously described (e.g., low-energy electron diffraction (LEED), 22 reflection high-energy electron diffraction (RHEED), 23 electron energy-loss spectroscopy (EELS), 24 photoemission electron microscopy (PEEM), 25 and other techniques).…”

“…Ultrafast electron diffuse scattering (UEDS) methods, for example, have provided unprecedented, direct access to the momentum-dependent couplings between carrier and phonon systems, and within the phonon system itself. A review of this approach highlights from the recent literature that is the focus of the article by Dürr et al 31 Ultrafast photoemission electron microscopy (uPEEM) has recently provided remarkable access to plasmon dynamics at nano-femtospatial resolution, 25 and the article by Dai et al 32 demonstrates an extension of these methods to imaging surface plasmon polaritons and coupled vectorial electromagnetic wave-charge density polarization fluctuations.…”

The 2021 ultrafast spectroscopic probes of condensed matter roadmap

“…This feature aided, for example, in the investigation of the so-called plasmoemission, where electrons are emitted from a metal surface in a nonlinear process purely by the absorption of SPPs, without an involved light field. By using energy-resolved PEEM, different orders of plasmoemission could be separated [144] (figures 15(a)-(c)).…”