High power lasers for industrial applications necessitate easy handling and ability to be subjected to fast movements. Thus, small volume and weight for these devices without prejudicing their accuracy of beam-fire and their integrity during the time is required. Solid state crystal Nd :YAG lasers were consequently considered. An important aspect under high power irradiation, is the system of mirrors of the cavity that must reflect back towards the laser active crystal source a sufficient radiant energy to activate laser pumping. At the same time the material of these mirrors must not degrade in short times (in the sense of industrial applications) and be sufficiently able to dissipate the produced heat. Ceramics are obvious candidates in particular alumina ceramic. After the test concerning the reflectivity of a wide range of white materials, it was realized that alumina ceramic is up to now the better and about which current technology allows easy manufacture of these mirrors. Certain rules must be followed to prepare white alumina mirrors able to maintain for sufficiently long times their reflectivity such as sintering at suitably high temperature in reducing atmosphere using very pure corundum-like spheroidal grains, correct granulometry of the utilized powders and treatment of the surface with a specific porcelain-like glaze before firing.
1. introduction
The utilization in the industrial field of apparatus that depends upon laser devices as the heart of their activity is rapidly increasing as their technological evolution improves. Lasers are now commonly used in training devices to reach the highest precision possible on the positioning of pieces during their machining. This is currently a particularly important technology on robotized working and assembly lines. Lasers are also utilized by the electronics industry to help in mass production on the surface of machining pieces, microwelding, micromelting or localized chemical transformation (these reactions are carried out under a suitable gaseous atmosphere and are induced solely by laser-beam radiation at a specific wavelength). In many cases, a laser beam is also utilized to obtain straight, thin and burrless cuts on ceramics (e.g. on alumina substrates in the thick-film electronic industry) or on metals (e.g. in the steel plate coils industry). In every kind of application the result obtained depends on the laser power. To cut slabs, the requested power of the utilized laser increases as the thickness of the slab increases.
Up to now the most used laser source for highpower industrial application was the CO 2 laser. The CO2 laser is already available for average power in excess of 10 kW. Recently, a growing interest has been shown in industrial processes involving high averagepower solid-state lasers, mainly lasers that use a large