Laser Ablation - From Picoseconds to Microseconds

October 20, 2000 - 12:00pm
Bldg. 90
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Laser ablation is used in many applications, such as for the fabrication of new materials (nanomaterials, catalysts, superconductors), chemical analysis, medical surgery, semiconductor lithography, and many others. However, the fundamental mechanisms describing laser ablation are not established. Laser ablation involves processes that occur over several orders of magnitude in time. Understanding these processes is vital to optimizing this technology for these applications and for discovery of new applications. The basis of this research is to elucidate the fundamental mechanisms underlying laser ablation processes. This work investigates the laser induced plasma properties using picosecond time-resolved shadowgraphs, interferograms and spectroscopic measurements. Electron emission from target surface with an electron density on the order of 1020 cm-3 was the first process, which induces breakdown of air. The longitudinal expansion of this plasma was suppressed due to the development of a strong space-charge field. After electron emission, mass is removed from the target on the nanosecond scale. The electron number density and temperature of this mass plasma were deduced by measuring emission-line broadening. On the microsecond time scale, phase explosion occurs and large (> mm) particles are ejected. Time resolved shadowgraph images show that the rapid increase in crater depth at the threshold corresponds to large size droplets leaving the surface.

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