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@ARTICLE{Lu:5853,
      author       = {Lu, W. and Nicoul, M. and Shymanovich, U. and Tarasevitch,
                      A. and Zhou, P. and Sokolowski-Tinten, K. and von der Linde,
                      D. and Masek, M. and Gibbon, P. and Teubner, U.},
      title        = {{O}ptimized {K} alpha x-ray flashes from
                      femtosecond-laser-irradiated foils},
      journal      = {Physical review / E},
      volume       = {80},
      number       = {2},
      issn         = {1539-3755},
      address      = {College Park, Md.},
      publisher    = {APS},
      reportid     = {PreJuSER-5853},
      pages        = {026404},
      year         = {2009},
      note         = {This work was supported by the Deutsche
                      Forschungsgemeinschaft (Contract No. SFB 616 and Grants No.
                      GI 300/3-1, No. TE 190/6-1, and No. So 408/6-3) and the
                      European Union (Marie-Curie-network FLASH).},
      abstract     = {We investigate the generation of ultrashort K alpha pulses
                      from plasmas produced by intense femtosecond p-polarized
                      laser pulses on Copper and Titanium targets. Particular
                      attention is given to the interplay between the angle of
                      incidence of the laser beam on the target and a controlled
                      prepulse. It is observed experimentally that the K alpha
                      yield can be optimized for correspondingly different
                      prepulse and plasma scale-length conditions. For steep
                      electron-density gradients, maximum yields can be achieved
                      at larger angles. For somewhat expanded plasmas expected in
                      the case of laser pulses with a relatively poor contrast,
                      the K alpha yield can be enhanced by using a
                      near-normal-incidence geometry. For a certain scale-length
                      range (between 0.1 and 1 times a laser wavelength) the
                      optimized yield is scale-length independent. Physically this
                      situation arises because of the strong dependence of
                      collisionless absorption mechanisms-in particular resonance
                      absorption-on the angle of incidence and the plasma scale
                      length, giving scope to optimize absorption and hence the K
                      alpha yield. This qualitative description is supported by
                      calculations based on the classical resonance absorption
                      mechanism and by particle-in-cell simulations. Finally, the
                      latter simulations also show that even for initially steep
                      gradients, a rapid profile expansion occurs at oblique
                      angles in which ions are pulled back toward the laser by hot
                      electrons circulating at the front of the target. The
                      corresponding enhancement in K alpha yield under these
                      conditions seen in the present experiment represents strong
                      evidence for this suprathermal shelf formation effect.},
      keywords     = {J (WoSType)},
      cin          = {JSC},
      ddc          = {530},
      cid          = {I:(DE-Juel1)JSC-20090406},
      pnm          = {Scientific Computing},
      pid          = {G:(DE-Juel1)FUEK411},
      shelfmark    = {Physics, Fluids $\&$ Plasmas / Physics, Mathematical},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000269637900082},
      doi          = {10.1103/PhysRevE.80.026404},
      url          = {https://juser.fz-juelich.de/record/5853},
}