We discover long-lived (microsecond-scale) optical waveguiding in the wake of atmospheric laser filaments. We also observe the formation and then outward propagation of the consequent sound wave. These effects may be used for remote induction of atmospheric long-lived optical structures from afar which could serve for a variety of applications.
DOI:https://doi.org/10.1103/PhysRevA.90.021801
©2014 American Physical Society
Scheme of the experimental setup. A Ti:sapphire pulsed laser 1-cm-wide beam with 50 fs time duration, central wavelength of 800 nm, 1 mJ per pulse at 1 kHz repetition rate, is focused into a diameter of ∼100 μm, creating a filament of ∼12 cm in the free air. The probe beam is a weak 527-nm pulsed laser beam, with a duration time of 150 ns and repetition rate of 1 kHz, triggered by the femtosecond laser. The delay between the pulses is controlled electronically and can span a range of 1 ms. In the filament region, the probe and pump beams propagate in opposite directions. The “input” and “output” planes correspond to the probe pulse entrance and exit planes of the filament channel, respectively. An imaging system images the probe pulse at the input and output planes. In the experiment presented in Fig. 4, we insert a lens that focuses the probe beam to a diameter of ∼100 μm at the input plane. No focusing lens is used in the experiments presented in Figs. 2 and 3, hence the probe beam is approximately a plane wave.
Reuse & PermissionsOutward propagation of the acoustic pulse. Shown are the intensity structures of the probe beam (plane wave) at the output plane for delay times of Δ = (a) 2.9, (b) 4.1, (c) 5.3, (d) 6.5, and (e) 7.7 μs after the filamenting pulse. Here, Δ = 0 corresponds to the time delay for which the probe and pump pulses collide within the filament channel. (f) Radius of the leading crest vs delay time. The calculated angle of the line corresponds to a velocity of 333 ± 1 m/s.
Reuse & PermissionsLong-lived index change in the filament wake. Shown are the intensity patterns of the probe beam at the output plane, for delay times of Δ = (a) −0.04, (b) 0.08, (c) 0.16, (d) 0.26, (e) 0.36, (f) 0.46, (g) 0.65, (h) 0.85, and (i) 1.4 μs after the filamenting pulse.
Reuse & PermissionsLong-lived filament-induced ring-shaped waveguide. (a) Intensity structure of the focused probe beam at the input plane. (b) Intensity structure of the probe beam at the output plane when the pump beam is blocked, i.e., no filament is formed. In the absence of the filament, the probe beam exhibits considerable diffraction broadening. (c)–(h) Intensity structures of the guided probe beam at the output plane for delay times of Δ = (c) −0.04, (d) 0.08, (e) 0.16, (f) 0.26, (g) 0.36, and (h) 0.45 μs with respect to the filamenting pulse. (i) Radius of the acoustic wave (blue dots) and coupling efficiency (green triangles) as a function of time delay. The black line is a linear fit of the radius with slope corresponding to a velocity of 310 ± 9 m/s.
Reuse & PermissionsNumerical simulations of the filament wake. (a) Radial air density [ρ()] as a function of time delay. At the beginning (Δ = 0) the medium is homogeneous, i.e., . The density at the center ( = 0) initially becomes lower due to the sudden heating. The air moves outward radially, creating an acoustic wave with higher density. Regions with higher air density exhibit a positive refractive index change which forms a waveguide. Inset: Density profiles at time delays of Δ = 0 μs (dashed line) and μs (solid line) after the filamenting pulse. (b), (c) The first two guided modes of the refractive index structure formed in the wake of the filament.
Reuse & Permissions
