Lasers for materials processing: specification and trends

An overview is given of the types of lasers dominating the field of laser materials processing. The most prominent lasers in this field are the C02 and the Nd:YAG laser. The domain Of C02 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 C02 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 of Nd:YAG lasers has been improved in recent years, so that Nd:YAG lasers are now an alternative to C02 lasers even in the kilowatt range. This is especially true for applications that demand optical fiber transmission of the laser beam, which is possible with Nd:YAG laser light but not with the longer- wavelength light emitted by C02 lasers. The main 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 geometry's have been proposed to reduce thermal loading and, by this, thermal lensing effects. There are now slab and tube geometry's which allow much higher 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 direction of the beam propagation and not perpendicular to it, as is the case in the other geometry's. As well as C02 and Nd:YAG lasers, semiconductor laser diodes are very promising for direct use of the emitted light or as pump sources for Nd:YAG and other solid-state lasers. When packaging together thousands of single laser diodes, output powers of several kilowatts can be realized. Major problems are collimation of the highly divergent laser beams and coo l ing of the laser diode bars.