Anomalous photoemission from Ag(100) in the femtosecond regime

Abstract

We investigate the nonlinear photoemission from a silver monocrystal with femtosecond laser pulses in a wide range of photon energies (0.8 eVϽhϽ6.3 eV). Electrons with high kinetic energy are observed in all cases of nonlinear photoemission and at intensities much smaller than 1 GW/cm 2 . In the infrared, the electron distribution resembles a decreasing exponential, the tail extending up to tens of eV. At hϭ3.1 eV such exponential distribution coexists with the Fermi-Dirac distribution due to two-photon emission. An explanation in terms of nanosize protuberancies, heated by localized surface plasmons cannot be ruled out, but alternative pictures, however speculative, are worth being considered.

Electron emission from films of Ag and Au nanoparticles excited by a femtosecond pump-probe laser

“…Although resonant absorption by coupling of the exciting light to localized plasmon modes of the particles is certainly present and leads to an enhancement in the electron yield, 16 this process does not determine the shape of the curves in Fig. 6.…”

Terahertz-pulse emission through excitation of surface plasmons in metallic nanostructures

“…42,43 The nonlinear photoelectric effect is enhanced by surface roughness 43,59 and by the excitation of surface plasmons, for example, in metal films on prisms 60-64 or on gratings. [65][66][67] The work function of gold and silver is 5.3 eV and 4.7 eV respectively.…”

“…It is well known that gold and silver metal films irradiated with ultrashort visible laser pulses can exhibit the multiphoton photoelectric effect. 42,43 If terahertz emission in such metal films were related to the multiphoton photoelectric effect, one might expect an approximately sixth-order dependence of terahertz fluence on input power at 800 nm as the work function of gold and silver is ~5 eV. 44 The metal surfaces used were not crystallographically flat and surface roughness can effectively lower the work function.…”

Spin-resolved photoelectron spectroscopy using femtosecond extreme ultraviolet light pulses from high-order harmonic generation

“…However, the mechanism for the acceleration of the photoelectrons to high kinetic energies is still under debate. 56,57,61 Since the NIR pump-induced photoelectrons also affect the XUV probe-induced electrons via Coulomb repulsion, they create an additional space-charge contribution which varies with the delay ∆t between pump-and probe-pulse. We investigated the interaction between the pump-and the probe-generated electron clouds using Cu(001) spectra measured for different ∆t with the femtosecond HHG source at 5 kHz in BDM.…”

“…The latter fact points to a crucial role of the sample quality and surface roughness. 14,56,57 As the underlying physical process for the generation of these photoelectrons, usually thermally assisted multiphoton photoemission is considered 58-60 for the laser peak power range that we use. However, the mechanism for the acceleration of the photoelectrons to high kinetic energies is still under debate.…”