The propagation of short-pulse lasers through underdense plasmas at ultra-high intensities (I≥1019 W/cm) is examined. The pulse evolution is found to be significantly different than it is for moderate intensities. The pulse breakup is dominated by leading edge erosion and plasma wave wake formation rather than from Raman forward scattering type instabilities. A differential equation which describes local pump depletion is derived and used to analyze the formation and evolution of the erosion. Pulse erosion is demonstrated with one dimensional particle in cell (PIC) simulations. In addition, two dimensional simulations are presented which show pulse erosion along with other effects such as channeling and diffraction. Possible applications for plasma based accelerators and light sources are discussed.

The collisional heating rate of a fully ionized plasma driven by a strong electromagnetic pump wave is re-examined both analytically and with two-dimensional particle-in-cell (PIC) simulations. The high frequency conductivity model of Dawson and Oberman [J. Dawson and C. Oberman, Phys. Fluids 5, 517(1962)] is extended for the case in which the quiver velocity vo=eElmwo is much larger than the thermal velocity Vth and its equivalence to the results of Silin [V. P. Silin, Sov. Phys. JETP 20, 1510(1965] is shown. The Dawson and Oberman model is reduced to two-dimensions for comparison with the PIC simulations. Excellent agreement between the theory and the simulations for volvth~l is obtained. However, when volvth~l and the excursion amplitude xo=eElmw; is larger than the Debye length AD, the simulations show enhancements in the collision frequency from the theory. A possible mechanism for this enhancement is provided.

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Recent changes in the manner of performing hohlraum drive experiments have significantly advanced the ability to diagnose, understand and control the x-radiation flux ͑or drive͒ inside a laser heated hohlraum. Comparison of modeling and data from a very broad range of hohlraum experiments indicates that radiation hydrodynamics simulation codes reproduce measurements of time dependent x-radiation flux to about Ϯ10%. This, in turn, indicates that x-ray production and capsule coupling in ignition hohlraums will be very close to expectations. This article discusses the changes to experimental procedures and the broad variety of measurements and tests leading to these findings.