Time-resolved study of a laser-induced surface plasma by means of a beam-deflection technique
1988; American Institute of Physics; Volume: 64; Issue: 5 Linguagem: Inglês
10.1063/1.341657
ISSN1520-8850
AutoresE. Heidecker, J. H. Schäfer, J. Uhlenbusch, Wolfgang Viöl,
Tópico(s)Laser Design and Applications
ResumoA fast-beam deflection technique is used to investigate the transient behavior of a laser-induced surface plasma generated by CO2-laser pulses of 2-kW average power near an aluminum surface in various protective gas atmospheres, with a typical pulse energy of 3.3×10−2 J, a pulse repetition rate of 60 kHz, and an average peak power per pulse of 30 kW, corresponding to an intensiy of 6×1012 W/m2. As a laterally probing beam, a cw 10-W CO2 laser is used, whose beam is focused into a small volume in front of the surface. The electrons of the laser-induced plasma passing this volume diffract the cw CO2 laser beam, and the resulting beam deflection is determined by means of a partially absorbing CaF2 wedge in connection with a fast infrared detector. The evaluation of beam deflection 0.15 cm above the surface renders a maximum electro density of 2×1023 m−3 for a surrounding argon atmosphere and 0.7×1023 m−3 for pure helium. Additives of O2 reduce the attainable electron density even more. No plasma can be detected below a threshold of, say, 10 mJ energy per laser pulse. It is verified that high electron density as in the case of argon shields the surface against the incoming CO2 laser pulses so that material processing, such as welding, is rather poor. Better welding results are achieved in helium-oxygen mixtures.
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