Effect of air pressure on propulsion with TEA CO2 laser

The assessment of energy partition between air and solid propellant has been conducted using a TEA CO, laser. The experiments were performed by focusing output pulses of the laser (200 ns pulsewidth at 10.6 mum wavelength and similar to10.6 J pulse energy) on aluminum targets mounted on a ballistic pendulum. Coupling coefficients and mass removal rates were determined as functions of air pressure, which varied from 1 atm to 3.5 mTorr. The data from both coupling coefficients and mass removal rates show that there is a sharp transition region ranging between 1.0 and 10 Torr. In this region the momentum imparted to the target via air breakdown appears comparable and, at higher pressures, dominating the momentum due to the breakdown on the target surface.