Large-Angle Electron Diffraction Structure in Laser-Induced Rescattering from Rare Gases

We have measured full momentum images of electrons rescattered from Xe, Kr, and Ar following the liberation of the electrons from these atoms by short, intense laser pulses. At high momenta the spectra show angular structure (diffraction) which is very target dependent and in good agreement with calculated differential cross sections for the scattering of free electrons from the corresponding ionic cores.

Figure 1

(a) Schematic showing the relative sizes of the momentum vector of a returning electron with maximal energy and the momentum shift which this electron will receive from the laser field after recollision, at $8.3\times {10}^{13}\mathrm{W}/{\mathrm{cm}}^2$. (b) Experimental electron momentum image from a 7 fs pulse of this intensity on the background gas of water vapor and hydrocarbons.

Figure 2

Density plots of electron momentum spectra at different laser intensities for 7 fs pulses on Xe. The intensities (in units of ${10}^{13}\mathrm{W}/{\mathrm{cm}}^2$) and corresponding values of $p_0$ (in a.u.) are, respectively, (a) 4.18, 0.74; (b) 5.8, 0.86; (c) 7.1, 0.95; (d) 8.3, 1.03. The white circles show the inner edges of the regions from which the differential cross sections were extracted (see text).

Figure 3

Experimental angular distributions extracted from the data of Fig. 2. The solid lines show the theoretical calculations of differential cross sections for free electrons scattered in the backwards direction from ${\mathrm{Xe}}^{+}$. The momenta of the backscattering electrons, $p_0$, are, from top to bottom, 1.03, 0.95, 0.86, and 0.74 a.u. The vertical scale is the theoretical one in atomic units, and the data have been normalized to roughly match the theory.

Figure 4

(a) Experimental angular distributions for background, Ar, Kr, and Xe at $8.3\times {10}^{13}\mathrm{W}/{\mathrm{cm}}^2$. (b)–(d) Background-subtracted and normalized angular distributions, compared to theoretical differential cross sections (in a.u.) for backscattering of 14.4 eV free electrons ($p_0=1.03\mathrm{a}.\mathrm{u}.$).