@article{1968,
  author = {A. Lytle and X. Zhang and J. Peatross and Margaret Murnane and Henry Kapteyn and O. Cohen},
  title = {Probe of High-Order Harmonic Generation in a Hollow Waveguide Geometry using Counterpropagating Light},
  year = {2007},
  journal = {Physical Review Letters},
  volume = {98},
  month = {2007-03},
  issn = {0031-9007},
  doi = {10.1103/PhysRevLett.98.123904},
}