- A projectile was accelerated by irradiating an ablative target with a 300-J laser pulse in the air atmosphere at reduced pressures. It was found that resulting impulse was affected by the ambient air pressure. The influences of the laser fluence were investigated. The timeresolved measurement of the projectile acceleration has been tested using the VISAR (Velocity Interferometer with Any Reflector) method to clarify the characteristics of the impulse generation by laser ablation. © 2005 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.