Momentum coupling at laser ablation of liquids in a porous matrix

The main problems at laser impact on liquids are energy dissipation and splashing, leading to poor performance even after application of special tricks like viscosity increase, thin films, cavities or droplets formation. We studied the laser ablation of liquids, including energetic ones, confined by porous matrix made of sintered titanium powder. We have compared the liquid-filled targets (ethanol, kerosene, nitromethane) momentum coupling coefficient dependency on laser fluence with the same unfilled target. Filling a porous target with a liquid may have both positive and negative effects depending on impact regime. Porous matrix prevents heat and mass losses characteristic to bulk solid and liquid targets. Momentum coupling coefficient doubled at porous target density increase by 6% only with ethanol filling, and at least tripled at ca. 22% density decrease as compared to a bulk target. Filling of porous matrices with energetic liquids leads to improvement of laser thrust generation due to combination of heat and splashing losses substantial reduction and chemical energy release. (paper)