title: Characterization of high-intensity laser propagation in the relativistic transparent regime through measurements of energetic proton beams.
abstract: Experiments were performed to investigate the propagation of a high intensity (I approximately 10(21) W cm(-2)) laser in foam targets with densities ranging from 0.9n(c) to 30n(c). Proton acceleration was used to diagnose the interaction. An improvement in proton beam energy and efficiency is observed for the lowest density foam (n(e)=0.9n(c)), compared to higher density foams. Simulations show that the laser beam penetrates deeper into the target due to its relativistic propagation and results in greater collimation of the ensuing hot electrons. This results in the rear surface accelerating electric field being larger, increasing the efficiency of the acceleration. Enhanced collimation of the ions is seen to be due to the self-generated azimuthal magnetic and electric fields at the rear of the target.
authors.affiliation: Blackett Laboratory, Imperial College, London SW7 2AZ, UK.
authors.forename: L
authors.initials: L
authors.lastname: Willingale
authors.forename: S R
authors.initials: SR
authors.lastname: Nagel
authors.forename: A G R
authors.initials: AG
authors.lastname: Thomas
authors.forename: C
authors.initials: C
authors.lastname: Bellei
authors.forename: R J
authors.initials: RJ
authors.lastname: Clarke
authors.forename: A E
authors.initials: AE
authors.lastname: Dangor
authors.forename: R
authors.initials: R
authors.lastname: Heathcote
authors.forename: M C
authors.initials: MC
authors.lastname: Kaluza
authors.forename: C
authors.initials: C
authors.lastname: Kamperidis
authors.forename: S
authors.initials: S
authors.lastname: Kneip
authors.forename: K
authors.initials: K
authors.lastname: Krushelnick
authors.forename: N
authors.initials: N
authors.lastname: Lopes
authors.forename: S P D
authors.initials: SP
authors.lastname: Mangles
authors.forename: W
authors.initials: W
authors.lastname: Nazarov
authors.forename: P M
authors.initials: PM
authors.lastname: Nilson
authors.forename: Z
authors.initials: Z
authors.lastname: Najmudin