For the first time, we have measured the momentum coupling coefficient and plasma expansion velocity (specific impulse) in the femtosecond region, over a laser intensity range from ablation threshold to thirty times threshold. These measurements extend the laser pulsewidth three orders of magnitude relative to previous reports. We studied several pure metals and three organic compounds as targets. The organic compounds were exothermic polymers specifically developed for the micro-laser plasma thruster, and two of these used "tuned absorbers" rather than carbon particles for the laser absorption function. The metals ranged from Li to W in atomic weight. We measured time of flight profiles for ions and found dramatic two-temperature distributions for some conditions. Specific
impulse reached record values for this type of measurement and ablation efficiency was near 100%.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.