title: Self-shortening dynamics measured along a femtosecond laser filament in air.
abstract: The filamentation-induced temporal shortening of a 40 femtosecond pulse propagating in air is traced using impulsive vibrational Raman scattering and measurement of the power spectrum as a function of position along the propagation axis. The N2, O2, and H2O vibrational Raman responses reveal self-shortening of pulse features to 14 fs during the first filamentation cycle and to at least 9 fs in the second cycle. Spectral measurements further demonstrate that the coherent bandwidth generated in the region from 470 to 330 nm during the self-shortening process forms the ∼9  fs pulse.
authors.affiliation: Department of Chemistry, Temple University, Philadelphia, Pennsylvania 19122, USA.
authors.forename: J H
authors.initials: JH
authors.lastname: Odhner
authors.forename: D A
authors.initials: DA
authors.lastname: Romanov
authors.forename: R J
authors.initials: RJ
authors.lastname: Levis