@article{KlennerAugustinSchaeferetal.2006,
  author    = {J{\"u}rgen Klenner and J{\"u}rgen Augustin and Andreas Sch{\"a}fer and Walter Greiner},
  title     = {Photon-photon interaction in axial channeling},
  journal   = {Physical review A},
  volume    = {50},
  number    = {2},
  pages     = {1019 -- 1026},
  url       = {http://link.aps.org/abstract/PRA/v50/p1019},
  year      = {2006},
}