LASERS FOR MATERIALS PROCESSING - SPECIFICATIONS AND TRENDS

An overview is given of the types of lasers dominating the field of la ser materials processing. The most prominent lasers in this field are the CO2 and the Nd:YAG laser. The domain of CO2 lasers is applications which demand high laser powers (up to 30 kW are available at present) , whereas the domain of Nd:YAG lasers is micro-machining applications. In the kilowatt range of laser output power, the two types of lasers are in competition. New diffusion-cooled CO2 laser systems are capable of output laser powers of several kilowatts, with good beam qualities , while still being quite compact. The output power and beam quality o f Nd:YAG lasers has been improved in recent years, so that Nd:YAG lase rs are now an alternative to CO2 lasers even in the kilowatt range. Th is is especially true for applications that demand optical fibre trans mission of the laser beam, which is possible with Nd:YAG laser light b ut not with the longer-wavelength light emitted by CO2 lasers. The mai n problem in solid-state lasers such as Nd:YAG is the thermal lensing effect and damage due to thermal stresses. In order to reduce thermal loading, cooling has to be enhanced. Several alternative geometries ha ve been proposed to reduce thermal loading and, by this, thermal lensi ng effects. There are now slab and tube geometries which allow much hi gher output powers than the conventionally used laser rods. A very new scheme proposes a thin slab whose cooled side is also used as one of the laser mirrors, so that thermal gradients occur mainly in the direc tion of the beam propagation and not perpendicular to it, as is the ca se in the other geometries. As well as CO2 and Nd:YAG lasers, semicond uctor laser diodes are very promising for direct use of the emitted li ght or as pump sources for Nd:YAG and other solid-state lasers. When p ackaging together thousands of single laser diodes, output powers of s everal kilowatts can be realized. Major problems are collimation of th e highly divergent laser beams and cooling of the laser diode bars.