title: Plasma dynamics near critical density inferred from direct measurements of laser hole boring.
abstract: We have used multiframe picosecond optical interferometry to make direct measurements of the hole boring velocity, v_{HB}, of the density cavity pushed forward by a train of CO_{2} laser pulses in a near critical density helium plasma. As the pulse train intensity rises, the increasing radiation pressure of each pulse pushes the density cavity forward and the plasma electrons are strongly heated. After the peak laser intensity, the plasma pressure exerted by the heated electrons strongly impedes the hole boring process and the v_{HB} falls rapidly as the laser pulse intensity falls at the back of the laser pulse train. A heuristic theory is presented that allows the estimation of the plasma electron temperature from the measurements of the hole boring velocity. The measured values of v_{HB}, and the estimated values of the heated electron temperature as a function of laser intensity are in reasonable agreement with those obtained from two-dimensional numerical simulations.
authors.affiliation: Electrical Engineering Department, University of California Los Angeles, Los Angeles, California 90095.
authors.forename: Chao
authors.initials: C
authors.lastname: Gong
authors.affiliation: Electrical Engineering Department, University of California Los Angeles, Los Angeles, California 90095.
authors.forename: Sergei Ya
authors.initials: SY
authors.lastname: Tochitsky
authors.affiliation: SLAC National Accelerator Laboratory, Menlo Park, California 94025.|Lawrence Livermore National Laboratory, Livermore, California 94550.
authors.forename: Frederico
authors.initials: F
authors.lastname: Fiuza
authors.affiliation: Electrical Engineering Department, University of California Los Angeles, Los Angeles, California 90095.
authors.forename: Jeremy J
authors.initials: JJ
authors.lastname: Pigeon
authors.affiliation: Electrical Engineering Department, University of California Los Angeles, Los Angeles, California 90095.
authors.forename: Chan
authors.initials: C
authors.lastname: Joshi