Propulsion pellets of different metal/salt (Zn/CaCO3) composition have been prepared. The impulse imparted to the pellet by the laser has been measured using two different methods: a torsion pendulum and a piezoelectric sensor. The dependence of the coupling coefficient, C-m, on the composition of the solid binary propellants in ablative laser propulsion has been investigated under different experimental conditions: in vacuum and at atmospheric pressure as well as with two different wavelengths, IR and UV. The composition of the Zn/CaCO3 propellant mixture that optimizes the coupling coefficient, C-m, has been determined. (C) 2010 Elsevier B.V. All rights reserved.