title: Comment on "direct observation of laser filamentation in high-order harmonic generation".
abstract: We argue for a different physical interpretation of the results given in the recent Letter by Painter et al. [Opt. Lett.31, 3471 (2006)] in which an elongated Ti:saphire beam with two distinct waists is considered as direct evidence of laser filamentation. As the pulse power is well below the critical power for self-focusing, the authors pleaded for new examination of the n(2) value for He. A three-dimensional numerical modeling, using the published n(2) value for He, reproduces very well the measured data and invalidates the filamentation hypothesis.
authors.affiliation: National Institute for R&D Isotopic and Molecular Technologies, Donath 65-103, Cluj-Napoca, Romania. tosa@s3.itim-cj.ro
authors.forename: Valer
authors.initials: V
authors.lastname: Tosa
authors.forename: Chang Hee
authors.initials: CH
authors.lastname: Nam