@article{10776,
  author = {J. Eberly},
  title = {Extended Two-Level Theory of the Exponential Index of Multiphoton Processes},
  year = {1979},
  journal = {Physical Review Letters},
  volume = {42},
  pages = {1049-1052},
  month = {Jan-04-1979},
  issn = {0031-9007},
  url = {http://link.aps.org/doi/10.1103/PhysRevLett.42.1049},
  doi = {10.1103/PhysRevLett.42.1049},
}