Rescattering for Extended Atomic Systems

Laser-driven rescattering of electrons is the basis of many strong-field phenomena in atoms and molecules. Here, we will show how this mechanism operates in extended atomic systems, giving rise to effective energy absorption. Rescattering from extended systems can also lead to energy loss, which in its extreme form results in nonlinear light-induced trapping. Intense-laser interaction with atomic clusters is discussed as an example. We explain fast electron emission, seen in experimental and numerically obtained spectra, by rescattering of electrons at the highly charged cluster.

Figure 1

Schematic picture of the scattering process. The upper part shows the electron’s momentum, the lower part the potential and the value of the electric field (assumed to be homogeneous in space) as a function of time, respectively.

Figure 2

Kinetic energy distribution of electrons $S(E)$, i.e., number of electrons with an energy between $E-\delta E/2$ and $E+\delta E/2$ whereby $\delta E=0.03E_{\mathrm{pond}}$, for two laser pulses of 400 fs duration (full width at half maximum of a Gaussian pulse) and peak intensities of $1\times {10}^{15}\mathrm{W}/{\mathrm{cm}}^2$ (a) and $5\times {10}^{15}\mathrm{W}/{\mathrm{cm}}^2$ (b), respectively. Shown are the results for three different cluster sizes ${\mathrm{Xe}}_{135}$, ${\mathrm{Xe}}_{1151}$, and ${\mathrm{Xe}}_{9093}$, respectively. The first two are shifted upwards for better visibility. Each set of points is fitted (solid lines) by an exponential curve according to Eq. (12). Note that the energy scale is given by the corresponding ponderomotive energy $E_{\mathrm{pond}}$.

Figure 3

Electron energies as a function of the ponderomotive energy $E_{\mathrm{pond}}$ from various clusters. The solid symbols show $E_{\mathrm{kin}}$ for experiments (red or gray) and microscopic calculations (blue or dark gray): ${\mathrm{Ag}}_{1000}$ (square, [25]), ${\mathrm{Ar}}_{1700}$ and ${\mathrm{Ar}}_{33000}$ (diamonds, [27]), ${\mathrm{Xe}}_{1151}$ and ${\mathrm{Xe}}_{9093}$ (circles, Fig. 2). The corresponding estimates $\Delta E$ from the rescattering model (10) are shown by open symbols.