Air Pressure Effect on Propulsion with Transversly Excited Atmospheric CO2 Laser

The assessment of energy partition between air and solid propellant has been conducted using a transversely excited atmospheric CO2 laser. The experiments were performed by focusing output pulses of the laser (200-ns pulsewidth at 10.6-µ mw avelength and ∼10.6-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 to the momentum due to the breakdown on the target surface. At pressures exceeding 10 torr, the coupling to the target due to air breakdown dominates the ablation.