hrvatski

Plasma plumes generated by laser ablation of capillaries

Through laser ablation of a capillary wall it is possible to generate two plasma plumes with different physical characteristics. One plume is mainly generated by the outer part of the laser beam missing the capillary and hitting the front surface of the target, while the other is generated inside the capillary by the part of the laser beam that enters the capillary. The laser beam is then guided through the capillary by grazing-incidence reflections at the wall. If it is intense enough, the plasma is generated inside the capillary. The plasma then expands from the capillary openings into the surrounding space thus producing two plasma plumes. We report here the results of experiments on laser ablation of aluminum capillaries 1--2 mm in length and 0.5 mm in diameter. Ruby laser pulses (1 kJ/cm2 on target, 15 ns FWHM) were focused into a capillary in such a way that the beam waist diameter was approximately equal to the capillary diameter. It turns out that the front plasma plume is very similar to the plume generated by laser ablation of a solid target surface while the plume observed behind the capillary is much less dense and a lot colder then the front one. However, it is still dense enough to be usable in attempts to use such plasmas in thin film deposition processes. The possibility to reduce the presence of droplets in thin films using such a plasma source is currently being evaluated.

PACS: 5250J: Plasma production and heating by laser beams

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