Characterization of the Absorption Wave Produced by CO2 Laser Ablation of a Solid Propellant

摘要

A requirement for efficient pulsed laser propulsion from ground to LEO is the achievement of a specific impulse of up to 800 s at a jet efficiency of at least 50%. With CO2 laser radiation at pulse lengths in the range of 10 microseconds and polymers as propellant these numbers cannot be attained by classical laser ablation. Also, the blending of the polymers with various metal powders did not improve the situation. Obviously, the major reason for the impossibility to deposit enough energy in a sufficiently small volume are severe absorption losses in gases building up during the laser pulse in front of the target surface. Energy, that is dissipated in this region, does not improve the generation of a pressure force on the target and is therefore lost for thrust production. It was the aim of this research to get firstly an idea of the losses as a function of the incident energy, the environmental conditions (standard pressure air or vacuum), and the ablated material (POM with and without metal content). Secondly, the expansion of the ablation products and the build-up and spreading of the absorption zone in front of the propellant surface have been observed.