title: Time dependence of fast electron beam divergence in ultraintense laser-plasma interactions.
abstract: We report on the measurement and computer simulation of the divergence of fast electrons generated in an ultraintense laser-plasma interaction (LPI) and the subsequent propagation in a nonrefluxing target. We show that, at Iλ(2) of 10(20) Wcm(-2)μm(2), the time-integrated electron beam full divergence angle is (60±5)°. However, our time-resolved 2D particle-in-cell simulations show the initial beam divergence to be much smaller (≤30°). Our simulations show the divergence to monotonically increase with time, reaching a final value of (68±7)° after the passage of the laser pulse, consistent with the experimental time-integrated measurements. By revealing the time-dependent nature of the LPI, we find that a substantial fraction of the laser energy (~7%) is transported up to 100 μm with a divergence of 32°.
authors.affiliation: The Ohio State University, Columbus, Ohio 43210, USA.
authors.forename: K U
authors.initials: KU
authors.lastname: Akli
authors.forename: M J
authors.initials: MJ
authors.lastname: Storm
authors.forename: M
authors.initials: M
authors.lastname: McMahon
authors.forename: S
authors.initials: S
authors.lastname: Jiang
authors.forename: V
authors.initials: V
authors.lastname: Ovchinnikov
authors.forename: D W
authors.initials: DW
authors.lastname: Schumacher
authors.forename: R R
authors.initials: RR
authors.lastname: Freeman
authors.forename: G
authors.initials: G
authors.lastname: Dyer
authors.forename: T
authors.initials: T
authors.lastname: Ditmire