Electron collisions with laser speckles

We show that the ponderomotive force and electric field 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 and verified with numerical simulations of particles interacting with speckled lasers. The electron-speckle collisions become important in low-Z plasmas and at high laser intensity or during filamentation, affecting both the long- and short- pulse regimes. As an example, we find 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 an order of magnitude, leading to a fundamental change to the electron transport properties in the presence of intense lasers. At high intensities (>10¹⁸Wcm²) the scattering is fast enough to cause direct absorption of laser energy.