Abstract
In most laser materials processing applications, a shorter wavelength laser is eagerly desired to enhance the efficiency and the quality of the process, because the shorter wavelength laser light results in higher surface absorption (Fresnel absorption) and/or in lower absorption loss through the laser-induced plasma. Currently, only CO2 laser can be practically Used at high laser power levels (>10 kW) but its long wavelength of 10.6 μm limits the process efficiency and quality in many applications. For example, at highPower levels, deep penetration, high- quality welding can not be obtained with a CO2 laser because the plasma absorption disturbs the energy coupling considerably. Because the plasma absorption (the inverse bremsstrahlung absorption) varies approximately as the square of the laser wavelength, plasma-related problems can be significantly reduced or overcome if the 5-μm-band CO laser is used. Higher processing efficiencies have been reported in cutting and surface treatment, Where the energy coupling may be dominated by the Fresnel absorption.1-3 Potential fiber-based beam delivery is another advantage of the CO laser.4 Although multikilowatt 1.06-μm Nd:YAG lasers are now commercially available, their operating efficiency and beam quality still need to be improved for widespread use at high-power levels.
© 1996 Optical Society of America
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