Atmospheric aerosol clearing by femtosecond filaments

Abstract

Atmospheric aerosols, such as water droplets in fog, interfere with laser propagation through scattering and absorption. Femtosecond optical filaments have been shown to clear foggy regions, improving transmission of subsequent pulses. However, the detailed fog clearing mechanism had yet to be determined. Here we directly measure and simulate the dynamics of ~5 micron radius water droplets, typical of fog, under the influence of optical and acoustic interactions characteristic of femtosecond filaments. We find that for filaments generated by the collapse of collimated near-infrared femtosecond pulses, the main droplet clearing mechanism is optical shattering by laser light. For such filaments, the single cycle acoustic wave launched by filament energy deposition in air leaves droplets intact and drives negligible transverse displacement, and therefore negligible fog clearing. Only for tightly focused non-filamentary pulses, where local energy deposition greatly exceeds that of a filament, do acoustic waves significantly displace aerosols.

13 pages, 5 figures

References in corpus (6)

• Ultrashort filaments of light in weakly-ionized, optically-transparent media
• High repetition rate ultrashort laser cuts a path through fog
• Sensitivity of propagation and energy deposition in femtosecond filamentation to the nonlinear refractive index
• Self-guiding of long-wave infrared laser pulses mediated by avalanche ionization
• Molecular Quantum Wakes for Clearing Fog
• Air hydrodynamics of the ultrafast laser-triggered spark gap

Cited by in corpus (3)

• Opto-mechanical expulsion of individual micro-particles by laser-induced shockwave in air
• Time-Resolved Measurements of Cumulative Effects in Gas Dynamics Induced by High-Repetition-Rate Femtosecond Laser Filamentation
• Physics and technology of Laser Lightning Control