A ns-Pulse Laser Microthruster

We have developed a prototype device which demonstrates the feasibility of using nsduration laser pulses in a laser microthruster. Relative to the ms-duration thrusters which we have demonstrated in the past, this change offers the use of any target material, the use of reflection-mode target illumination, and adjustable specific impulse. Specific impulse is adjusted by varying laser intensity on target. In this way, we were able to vary specific impulse from 200s to 3, 200s on gold. We used a Concepts Research, Inc. microchip laser with 170mW average optical power, 8kHz repetition rate and 20ttJ pulse energy for many of the measurements. Thrust was in the 100nN - 1 range for all the work, requiring development of an extremely sensitive, low-noise thrust stand. We will discuss the design of metallic fuel delivery systems. Ablation efficiency near 100% was observed. Results obtained on metallic fuel systems agreed with simulations. We also report time-of-flight measurements on ejected metal ions, which gave velocities up to 80km/s.