title: Moving focus in the propagation of ultrashort laser pulses in air.
abstract: The long light filaments generated in air by powerful ultrashort laser pulses, previously attributed to self-channeling, were investigated by use of gigawatt pulses from a Ti:sapphire chirped-pulse-amplification laser system. A filament contained only a small fraction of the pulse energy and always ended at the diffraction length of the beam (~100 m), independently of the pulse energy. These features are explained by the moving-focus model, which is presented as an alternative to the self-channeling model. Computer simulations involving ionization of the air also support the moving-focus model.
authors.forename: A
authors.initials: A
authors.lastname: Brodeur
authors.forename: C Y
authors.initials: CY
authors.lastname: Chien
authors.forename: F A
authors.initials: FA
authors.lastname: Ilkov
authors.forename: S L
authors.initials: SL
authors.lastname: Chin
authors.forename: O G
authors.initials: OG
authors.lastname: Kosareva
authors.forename: V P
authors.initials: VP
authors.lastname: Kandidov