Absorption and Transport Effects Induced in Plasmas by the Interaction of Electrons with Laser Speckles.

We show that the ponderomotive force associated with laser speckles can scatter electrons in a laser-produced plasma in a manner similar to Coulomb scattering. Analytic expressions for the effective collision rates are given. The electron-speckle collisions become important at high laser intensity or during filamentation, affecting both long- and short-pulse laser intensity regimes. As an example, we find that the effective collision rate in the laser-overlap region of hohlraums on the National Ignition Facility is expected to exceed the Coulomb collision rate by 1 order of magnitude, leading to a fundamental change to the electron transport properties. At the high intensities characteristic of short-pulse laser-plasma interactions (I≳10^{17}  W cm^{-2}), the scattering is strong enough to cause the direct absorption of laser energy, generating hot electrons with energy scaling as E≈1.44(I/10^{18}  W cm^{-2})^{1/2} MeV, close to experimentally observed results.