@article{1981,
  author = {Xiaoshi Zhang and A. Lytle and Tenio Popmintchev and Xibin Zhou and Henry Kapteyn and Margaret Murnane and O. Cohen},
  title = {Quasi-phase-matching and quantum-path control of high-harmonic generation using counterpropagating light},
  year = {2007},
  journal = {Nature Physics},
  volume = {3},
  pages = {270-275},
  month = {2007-09},
  issn = {1745-2473},
  doi = {10.1038/nphys541},
}