Microscopic Analysis of Large-Cluster Explosion in Intense Laser Fields

We present a three dimensional microscopic particle in cell code. The code models nanoplasmas in intense laser fields, taking account of all relevant microscopic interactions. Our simulation reveals the physical processes determining the laser induced explosion of large clusters with several 10 000 atoms.

Figure 1

(a) Energy spectra of ions emitted by an ${\mathrm{Ar}}_{10000}$ cluster after irradiation with an 100 fs FWHM (full width at half maximum) laser pulse, ${sin}^2$ pulse envelope, peak intensity $I=8\times {10}^{15}\mathrm{W}/{\mathrm{cm}}^2$, wavelength $\lambda =800\mathrm{nm}$. The laser field propagates in the $z$ direction and is linearly polarized in the $x$ direction. The solid and dotted lines refer to ion emission parallel and perpendicular to the laser electric field. (b) Electron energy spectrum for ${\mathrm{Ar}}_{10000}$ and ${\mathrm{Xe}}_{25000}$. The exponentially decaying part of the spectrum can be described by a single temperature that is 600 and 800 eV for the Ar and the Xe cluster, respectively.

Figure 2

This figure shows the $x\mathrm{\text{−}}y$ plane going through the cluster center: (1) charge state of ions versus position; (2) position of ions (red dots) and electrons (blue dots); (3) electric field at the position of the ions for the parameters of Fig. 1. (a) and (b) refer to the times of observation $t=-92.9\mathrm{fs}$, $-25.9\mathrm{fs}$, where $t=0$ marks the peak of the laser pulse. The laser intensities for (a) and (b) are $I=4.4\times {10}^{14}\mathrm{W}/{\mathrm{cm}}^2$ ($E=5.7\times {10}^{10}\mathrm{V}/\mathrm{m}$) and $I=6.7\times {10}^{15}\mathrm{W}/{\mathrm{cm}}^2$ $E=2.2\times {10}^{11}\mathrm{V}/\mathrm{m}$), respectively.

Figure 3

This figure shows the macroscopic electron current $J_x$ (1), as defined in the text, and the current of a single free electron (2) in the direction of the laser electric field. The currents were scaled to a similar size to facilitate comparison. The phase difference between a free electron current and a cluster current and the nonsinusoidal (nonlinear) contributions (corresponding to higher harmonics of the laser field) lead to laser dephasing heating (LDH) of the electrons.