Light propulsion of microbeads with femtosecond laser pulses

Milli-Joule, femtosecond laser pulses have been used to propel microbeads for the first time. The microbeads of three different materials ( iron, glass, and polystyrene) are used, weighting from 0.84 mg to 1.4 mg with a diameter range of 0.7-1.1 mm. Experimental parameters such as focused beam spot diameter, pulse energy, and pulse width are carefully varied to investigate their respective influences on the specific ablative laser propulsion. It is found that both the momentum coupling efficiency and the overall energy conversion efficiency from light energy to kinetic energy are greater for shorter laser pulses. A typical value of the momentum coupling efficiency of 5.0 dyne/W for iron beads is obtained. It is also evident that for metallic and non-metallic microbeads the momentum coupling efficiency has different variation tendencies versus the focused beam spot diameter. (C) 2004 Optical Society of America.