Carbon dioxide lasers

Abstract

The efficient use of high power lasers for material processing depends on several properties of the laser beam. First of all the intensity must reach at least a million Watts per cm² to achieve secure melting and evaporation of the workpiece, which are both necessary for nearly all production processes with lasers such as cutting, ablation, welding and coating. Secondly, the beam waist must have a diameter as small as a few tenths of a millimetre and the extension of the focused region, the so called Rayleigh length, must be at least several millimetres long to be able to obtain narrow processing paths and to achieve a reasonable depth of processing. To obtain this narrow beam waist and a low divergence, the radial beam mode must come as close as possible to the fundamental Gaussian distribution. Thirdly, the wavelength of the laser beam must be matched to the absorption properties of the workpiece material to avoid high reflectivity and to achieve an efficient production process. Therefore, for the treatment of metals, wavelengths up to one micrometre (μm) are most appropriate. Concerning the treatment of plastics, glass and similar materials, the wavelength of 10 μm is excellently suited. Finally, the overall power of the laser beam must be as large as possible, since for the treatment of thick workpieces the beam must be focused to a low divergence, what means in turn, that the beam waist diameter becomes rather large and therefore the necessary intensity mentioned above requires a high beam power.