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.

Figure 1

(a) Measured photocurrent dependence vs intensity, verifying a three-photon process. The inset illustrates the various channels of electron emission, both coherent and incoherent. (b) Measured interferometric two-pulse 3PP-correlation trace for 27 fs laser pulses, indicating that at the surface of the film, the electron pulse duration is $\le 27\mathrm{f}\mathrm{s}$.

Figure 2

Experimental kinetic energy distribution of the femtosecond electron pulses.

Figure 3

(a) Calculated electromagnetic field distribution for coupling between a 27 fs pulse and SP waves in a 50 nm Ag film. (b) Electron trajectories, as calculated by the UPAS code, demonstrate the quivering motion of electrons placed in the SP enhanced electromagnetic pulse. (c) Calculated trajectory and (d) velocity components of a solitary 0.3 keV electron, which illustrate the net gain of energy of the electron in the presence of the ponderomotive potential of the SP.

Figure 4

Experimental (circles) and calculated (solid line) kinetic energy distributions of the SP-assisted femtosecond electron pulse generation. The inset shows the angular (in-plane) distribution of the electron pulses as calculated by UPAS.

Figure 5

Calculated kinetic energy distribution of SP-assisted femtosecond electron pulse generation. In this case, the peak SP electric field is a factor of 5 times higher than that used to simulate the data of Fig. 4.