title: Observation of spontaneous self-channeling of light in air below the collapse threshold.
abstract: We report the observation of the self-guided propagation of 120 fs, 0.56 mJ infrared radiation in air for distances greater than 1 m. In contrast with the known case of filamentation, in the present experiment the laser power is lower than the collapse threshold. Therefore the counterbalance between Kerr self-focusing and ionization induced defocusing as the stabilizing mechanism is ruled out. Instead, we find evidence of a process in which the transversal beam distribution reshapes into a form similar to a Townes soliton, with the particularity of a very high stability. We include numerical support for this conclusion.
authors.affiliation: Departamento de Fí sica Aplicada, Universidad de Salamanca, E-37008 Salamanca, Spain.
authors.forename: C
authors.initials: C
authors.lastname: Ruiz
authors.forename: J
authors.initials: J
authors.lastname: San Román
authors.forename: C
authors.initials: C
authors.lastname: Méndez
authors.forename: V
authors.initials: V
authors.lastname: Díaz
authors.forename: L
authors.initials: L
authors.lastname: Plaja
authors.forename: I
authors.initials: I
authors.lastname: Arias
authors.forename: L
authors.initials: L
authors.lastname: Roso