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Development and optical absorption properties of a laser induced plasma during CO2-laser processing

Entwicklung und optische Absorptionseigenschaften des laserinduzierten Plasmas während der Bearbeitung mit dem CO2-Laser
: Bakowski, L.; Beyer, E.; Herziger, G.; Poprawe, R.

Schuöcker, D. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
Industrial applications of high power lasers. Proceedings
Bellingham/Wash.: SPIE, 1984 (Proceedings of SPIE 455)
ISBN: 0-89252-491-X
Conference "Industrial Applications of High Power Lasers" <1983, Linz>
Fraunhofer ILT ()
absorption; cw CO2-Laser; cw CO2-laser machining; Intensitätsrate; intensity level; laser induced plasma; laser welding; laserinduziertes Plasma; Laserschweißen; maschinelle Bearbeitung; optical absorption target; optisch; radiation; Strahlung; target; vaporisation; Verdampfung

Laser material processing is accompanied by a laser induced plasma in front of the target surface as soon as the laser radiation exeeds a certain critical intensity. For cw CO2-laser machining of metal targets the threshold for plasma onset is about 10 high 6 W/qcm. Critical condition for plasma generation at this intensity level is to reach evaporation temperature at the target's surface. At intensity levels exceeding 10 high 6 W/qcm the laser light is interacting with the laser induced plasm and then the plasma in turn interacts with the target. The absorptivity is no longer constant, but increases with increasing intensity of the incident radiation, so that the total amount of power coupled to the target is increasing. This holds up to asterrisk levels of 2 asterisk 10 high 7 W/qcm. Then the plasma begins to withdraw from the target surface, thus interrupting plasma-target interaction so that the laser power is no longer coupled into the target completely. The results of laser weldi ng (welding depth) in the intensity level of 10 high 6 I 10 high 7 W/qcm are governed by the product of incident intensity times focus radius, so that welding results are a measure to determine focus radius and laser intensity.