title: Direct imaging of the acoustic waves generated by femtosecond filaments in air.
abstract: We present time-resolved measurements of the gas acoustic dynamics following interaction of spatial single- and higher-mode 50 fs, 800 nm pulses in air at 10 Hz and 1 kHz repetition rates. Results are in excellent agreement with hydrodynamic simulations. Under no conditions for single filaments do we find on-axis enhancement of gas density; this occurs only with multifilaments. We also investigate the propagation of probe beams in the gas density profile induced by a single extended filament. We find that light trapping in the expanding annular acoustic wave can create the impression of on-axis guiding in a limited temporal window.
authors.forename: J K
authors.initials: JK
authors.lastname: Wahlstrand
authors.forename: N
authors.initials: N
authors.lastname: Jhajj
authors.forename: E W
authors.initials: EW
authors.lastname: Rosenthal
authors.forename: S
authors.initials: S
authors.lastname: Zahedpour
authors.forename: H M
authors.initials: HM
authors.lastname: Milchberg