title: Comment on "Generation of 10(11) contrast 50 TW laser pulses".
abstract: We argue for a different physical interpretation of the results given in the recent Letter by Chvykov et al. [Opt. Lett.31, 1456 (2006)] in which a double nonlinear crystal scheme for cross-polarized wave generation is analyzed. We discuss the most important factors that explain the origin of the two-crystal scheme's increased efficiency, namely, the Kerr lensing effect and a Gouy phase shift. The position and orientation of the second crystal relative to the first one are unambiguously defined; related effects are illustrated by already published works on the subject.
authors.affiliation: Laboratoire d'Optique Appliquée, ENSTA-Ecole Polytechnique-CNRS, 91761 Palaíseau Cedex, France. oliver.albert@ensta.fr
authors.forename: O
authors.initials: O
authors.lastname: Albert
authors.forename: A
authors.initials: A
authors.lastname: Jullien
authors.forename: J
authors.initials: J
authors.lastname: Etchepare
authors.forename: S
authors.initials: S
authors.lastname: Kourtev
authors.forename: N
authors.initials: N
authors.lastname: Minkovski
authors.forename: S M
authors.initials: SM
authors.lastname: Saltiel