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The paper presents the results on investigations and development ofmultichannel CO2 lasers with diffusion cooling of active medium excited by discharge of audio-frequency alternating current. Various methods of improving the laser beam quality and energy efficiency have been considered and experimentally tested. MULTICHANNEL INDUSTRIAL CO2 LASERS DEVELOPMENTBy now, a number of models of multichannel industrial CO2 lasers (MTL) with diffusion cooling, up to 5 kW power, active medium excitation by AC discharge has been developed in the NICTL RAN. These lasers are distinguished by design simplicity, 1ow-cost production and operation, high compactness. The multibeam structure enables wide variation of energy profile on the workpiece surface by focusing with simple spherical optics. High beam uniformity renders these lasers indispensable in heat treatment, alloying, surfacing [1 3].A disadvantage of the MTL is a comparatively large output beam aperture at relatively high beam divergence, specified by the diameter of a single discharge tube. This disadvantage poses difficulties to beam delivery and renders its fine focusing impossible. Though, as will be given below, the problem of wideaperture beam transportation may be overcome by applying beam compactizators of special design. Generation of low-divergence beam requires synchronization of the MTL individual heads. Some synchronization methods and the results of pursued studies are presented below.A multibeam concept of technological laser was first suggested and realized in papers [4 6], when the first model of IGLAN laser with DC discharge excitation was constructed. The IGLAN-3 laser comprises a bunch of 37 glass DC discharge tubes, each having 10 mm inner diameter, for 360 cm total length of active medium and 94 mm aperture of output beam.In 1979, another modification of the MTL [7] was suggested by the Kurchatov Insthute, wherein the electrodeless capacitor AC discharge of audio4requency was used for active medium excitation and a 2 kW scale model of multibeam laser was produced [8]. The new pumping method proved extremely promising, enabling at once a body of merits as against the active medium excitation by DC discharge current: -losses elimination in active ballast resistors to increase the laser technical efficiency; -operating voltage reduction with concurrent increase of working pressure; -simplificationof gas discharge unit design, improvement of its producibility and reliability; -removal of electrodes from the discharge region, thus eliminating erosion and oxidation processes, decrease of working mixture deterioration; more compact laser head design.The long-term research and development work performed in the NECTL RAN resulted in production of an up-to-date industrial technological MTL-2 CO2 laser having 2 kW rated mean power and intended substantially for heat treatment of materials [2, 3]. MTL-2.5 AND MTL-4 LASERSThe MTL-2.5 and MTL-4 models have been developed having 2.5 and 4 kW rated mean power, respectively. Note that the MTL-4 model has practical...

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