Laser filament shattering of distilled water and seawater droplets

Understanding laser-droplet interactions is relevant to medical and machining applications. Additionally, laser filaments produced by high peak power femtosecond lasers have been proposed as a tool to clear a path through a fog or cloud, and in long range applications in communication and remote sensing. The existing body of work has explored the interaction of a filament with a single aerosol and with a cloud of aerosols. Aerosol sizes are typically within 10-100 μm. Raindrops and seawater droplets are much larger, with diameters on the scale of ~1 mm. For filaments generated by a near infrared femtosecond laser, the intensity full-width at half maximum is well known to be ~150 μm, surrounded by a millimeter scale energy reservoir. Therefore, it can be expected that the interaction of a filament with an aerosol versus a raindrop would be affected by the relative size of the obstruction compared to the filament size. In this experiment, we investigate interactions of filaments with distilled water and seawater droplets of millimeter scale diameters. We present results on the laser energy required to induce shattering in the droplet. The early timescale dynamics of the droplet deformation and shattering are also examined and compared for distilled water and seawater. No filament reformation was observed following interaction with a droplet. This work builds on the knowledge of filament-aerosol interactions to better understand how larger droplets, such as raindrops or seawater drops, affect filament propagation.