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High Power Infrared Laser Beam AnalyzersJ. CHABLAT, D. GERBET, J.L. PARADISEtablissement Technique Central de l'Armement16 bis Avenue Prieur de la Cote d'Or, 94114 ARCUEIL - Cedex, FRANCEAbstractThe research teams at ETCA have designed and developed more than a dozen transportableanalyzers used to characterize high power CO laser beams at 10.6 µm and providing a realtime high rate space -time distribution of th6 beam at all points on a cross -section. Forexample, in a range of analyzers covering analysis fields up to 200 x 200 mm2, we havedeveloped equipment providing the following performance levels: for a field of 20 x 20 mm2,resolution of 0.4 mm on 50 lines, 50 images per second, and for a field of 5 x 5 mm2,resolution of 50 µm on 100 lines, 5 to 25 images per second, and permissible power of10 kW/mm2 for another.IntroductionFor industrial applications such as cutting, welding and surface treatments, high powerCO lasers have clearly demonstrated their possibilities for improving quality and produc-ti .Oity. Succinct knowledge of the intensity distribution in the beam is often sufficient,and usual methods such as imprints on Plexiglas or refracting bricks providing qualitativeindications averaged in time are satisfactory. If a more in -depth study of the laser -material interaction is required, it becomes necessary to specify the beam parameters(diameter, divergence, intensity profile, fluctuations).As of 1973, the ETCA has undertaken a research effort concerning characterization oflaser beams, leading to the development of a range of analyzers used both for characteriza-tion of sources and understanding of phenomena.Principle of analyzersThe principle used to carry out a space -time analysis of the intensity distribution ina laser beam consists of establishing a correspondence between an elementary analysiswindow located in the plane of the section studied with a photoelectric sensor onlyreceiving the energy crossing this elementary window for which it outputs an electricalsignal proportional to the energy. To analyze the entire section of the laser beam, it isnecessary to move the analysis window over the entire field. The dimensions of theelementary window are related to the desired spatial resolution.The method adopted consists of using a screen containing a hole forming the elementaryanalysis window. A collecting optical system transmits the flux passing through the hole tothe sensor. The average intrinsic attenuation of this analysis system is the ratio of thesurfaces of the analyzed field with respect to that of the analyzed hole (figure 1). |
