title: Bright multi-keV harmonic generation from relativistically oscillating plasma surfaces.
abstract: The first evidence of x-ray harmonic radiation extending to 3.3 A, 3.8 keV (order n>3200) from petawatt class laser-solid interactions is presented, exhibiting relativistic limit efficiency scaling (eta approximately n{-2.5}-n{-3}) at multi-keV energies. This scaling holds up to a maximum order, n{RO} approximately 8{1/2}gamma;{3}, where gamma is the relativistic Lorentz factor, above which the first evidence of an intensity dependent efficiency rollover is observed. The coherent nature of the generated harmonics is demonstrated by the highly directional beamed emission, which for photon energy hnu>1 keV is found to be into a cone angle approximately 4 degrees , significantly less than that of the incident laser cone (20 degrees ).
authors.affiliation: Department of Physics and Astronomy, Queens University, Belfast, UK.
authors.forename: B
authors.initials: B
authors.lastname: Dromey
authors.forename: S
authors.initials: S
authors.lastname: Kar
authors.forename: C
authors.initials: C
authors.lastname: Bellei
authors.forename: D C
authors.initials: DC
authors.lastname: Carroll
authors.forename: R J
authors.initials: RJ
authors.lastname: Clarke
authors.forename: J S
authors.initials: JS
authors.lastname: Green
authors.forename: S
authors.initials: S
authors.lastname: Kneip
authors.forename: K
authors.initials: K
authors.lastname: Markey
authors.forename: S R
authors.initials: SR
authors.lastname: Nagel
authors.forename: P T
authors.initials: PT
authors.lastname: Simpson
authors.forename: L
authors.initials: L
authors.lastname: Willingale
authors.forename: P
authors.initials: P
authors.lastname: McKenna
authors.forename: D
authors.initials: D
authors.lastname: Neely
authors.forename: Z
authors.initials: Z
authors.lastname: Najmudin
authors.forename: K
authors.initials: K
authors.lastname: Krushelnick
authors.forename: P A
authors.initials: PA
authors.lastname: Norreys
authors.forename: M
authors.initials: M
authors.lastname: Zepf
mesh_terms: D005720:Gamma Rays; D007834:Lasers; D017785:Photons; D014965:X-Rays