Attosecond nanoplasmonic streaking of localized fields near metal nanospheres

Collective electron dynamics in plasmonic nanosystems can unfold on timescales in the attosecond regime and the direct measurement of plasmonic near-field oscillations is highly desirable. We report on numerical studies on the application of attosecond nanoplasmonic streaking spectroscopy to the measurement of collective electron dynamics in isolated Au nanospheres. The plasmonic field oscillations are induced by a few-cycle near-infrared (NIR) driving field and are mapped by the kinetic energy of photoemitted electrons using a synchronized, time-delayed attosecond extreme ultraviolet (XUV) pulse. By a detailed analysis of the amplitudes and phase shifts, we identify the different regimes of nanoplasmonic streaking and study the dependence on particle size, XUV in streaking spectrograms photoelectron energy, and emission position. The simulations indicate that the near fields around the nanoparticles can be spatiotemporally reconstructed and may give detailed insight into the build-up and decay of collective electron motion.

Figure 1

Scheme for attosecond nanoplasmonic streaking of Au nanospheres employing few-cycle NIR pump pulses, attosecond XUV probe pulses, and the measurement of the kinetic energies of photoemitted electrons using a time-of-flight (TOF) spectrometer. The inset shows the field enhancement as calculated by Mie theory for $y=0$. Due to symmetry of the plasmonic field, the point of electron emission is uniquely defined by the angle $\alpha$.

Figure 2

(a) Phase shift $\Delta {\phi }_s$ and (b) maximum velocity shift as a function of electron energy $E_{\text{kin}}$ and Au sphere diameter $d$ obtained for a laser intensity of ${10}^{12}$ W$/{\text{cm}}^2$ and $\alpha =0^{\circ }$.

Figure 3

Streaking traces for emission positions $\alpha =0\text{--}{90}^{\circ }$ for 10 nm (a) and 100 nm spheres (b) and the respective electric fields acting on the photoelectrons (emitted at $t_e=0$ fs) as a function of time after photoemission, (c) and (d). The blue dashed lines show the plasmonic near field at the surface.

Figure 4

Simulated streaking spectrograms for 10 nm (a) and 100 nm (b) Au spheres. The red line shows the contribution of the $\alpha =0^{\circ }$ trajectories.