title: Spatially resolved measurements of laser filamentation in long scale length underdense plasmas with and without beam smoothing.
abstract: The onset of filamentation, following the interaction of a relatively long (τ(L)≃1  ns) and intense (I(L)≃5×10(14)  W/cm(2)) laser pulse with a neopentane filled gas bag target, has been experimentally studied via the proton radiography technique, in conditions of direct relevance to the indirect drive inertial confinement fusion scheme. The density gradients associated with filamentation onset have been spatially resolved yielding direct and unambiguous evidence of filament formation and quantitative information about the filamentation mechanism in agreement with previous theoretical modelings. Experimental data confirm that, once spatially smoothed laser beams are used, filamentation is not a relevant phenomenon during the heating laser beams propagation through typical hohlraum gas fills.
authors.affiliation: School of Mathematics and Physics, The Queen's University of Belfast, United Kingdom.
authors.forename: G
authors.initials: G
authors.lastname: Sarri
authors.forename: C A
authors.initials: CA
authors.lastname: Cecchetti
authors.forename: R
authors.initials: R
authors.lastname: Jung
authors.forename: P
authors.initials: P
authors.lastname: Hobbs
authors.forename: S
authors.initials: S
authors.lastname: James
authors.forename: J
authors.initials: J
authors.lastname: Lockyear
authors.forename: R M
authors.initials: RM
authors.lastname: Stevenson
authors.forename: D
authors.initials: D
authors.lastname: Doria
authors.forename: D J
authors.initials: DJ
authors.lastname: Hoarty
authors.forename: O
authors.initials: O
authors.lastname: Willi
authors.forename: M
authors.initials: M
authors.lastname: Borghesi