Observation of few-cycle, strong-field phenomena in surface plasmon fields.

We present experimental evidence of the generation of few-cycle propagating surface plasmon polariton wavepackets. These ultrashort plasmonic pulses comprised of only 2-3 field oscillations were characterized by an autocorrelation measurement based on electron photoemission. By exploiting plasmonic field enhancement, we achieved plasmon-induced tunnelling emission from the metal surface at low laser intensity, opening perspectives for strong-field experiments with low pulse energies. All-optical electron acceleration up to keV kinetic energy is also demonstrated in these surface-confined, few-cycle fields with only 1.35×10(12) W/cm2 focused laser intensity. The experimental results are found to be in excellent agreement with the model.

Influence of the carrier-envelope phase of few-cycle pulses on ponderomotive surface-plasmon electron acceleration.

Control over basic processes through the electric field of a light wave can lead to new knowledge of fundamental light-matter interaction phenomena. We demonstrate, for the first time, that surface-plasmon (SP) electron acceleration can be coherently controlled through the carrier-envelope phase (CEP) of an excitation optical pulse. Analysis indicates that the physical origin of the CEP sensitivity arises from the electron's ponderomotive interaction with the oscillating electromagnetic field of the SP wave. The ponderomotive electron acceleration mechanism provides sensitive (nJ energies), high-contrast, single-shot CEP measurement capability of few-cycle laser pulses.

Femtosecond electron pulse gating using surface plasmons.

We present a theoretical investigation of a novel all-optical method for electron beam gating via ponderomotive surface plasmon (SP) interaction. Using femtosecond optical pulses, large electric field gradient SP waves are launched on the surface of a metal film and selectively gate an external electron beam. It is shown that this method can generate electron pulses having similar durations as the laser pulse. The ultrashort electron packets are highly directional and examination of their spatial distribution reveals a large degree of spatial microbunching. Angle-resolved energy spectra of the electrons reveal that their final velocities are highly correlated with exit angle. Furthermore, it is demonstrated that the SP gating technique can be utilized for temporal characterization of ultrashort electron pulses with durations <100 fs.

Generation of 0.4-keV femtosecond electron pulses using impulsively excited surface plasmons.

We demonstrate the generation of 0.4-keV, sub-27 fs electron pulses using low-intensity laser pulses from a Ti:sapphire oscillator through the excitation of surface plasmon waves on a time scale within the plasmon lifetime. Modeling of the ponderomotive electron pulse acceleration yields electron energy spectra that are in excellent agreement with the observed ones. Our work opens a doorway for time-resolved experimentation using low-power, high-repetition rate laser pulses.