Laser Propulsion with Liquid Propellants Part II: Thin Films

Thin films of a liquid propellant have been studied as a potential way to boost thrust for laser propulsion applications. A TEA CO2 laser with 300 ns pulse width was operated at up to 20 J pulse energy to produce irradiances at the target on the order of 1–1200 MW/cm2 to ablate various systems of thin films on Delrin® substrates. In this study, time‐resolved force sensors and ICCD imaging techniques were used to determine how an addition of thin liquid films to solid substrates affects propulsive properties such as momentum coupling coefficient, specific impulse, and internal efficiency. Transparent (hexane) and absorbing (ethanol and water) thin films were formed above Delrin® substrates for the laser system operating at 10.6 μm. Thickness effects on the hexane‐Delrin® system will be examined. An analysis will be made of the possible routes for force generation, and the general properties, benefits, and shortcomings of liquid thin film structures will be summarized with regard to laser propulsion.