Transmission of kilowatt-class CO_2 laser light through dielectric-coated metallic hollow waveguides for material processing

We have measured the transmittance of 3-kW CO(2) laser light through Ge-coated Ag hollow waveguides. The basic characteristics such as transmissivity, bending loss, and output-beam properties are described. A maximum laser power of 2.6 kW was delivered through a straight hollow waveguide that was 1.7 mm in diameter and 2 m long. Furthermore, 4-m-long waveguides were fabricated by joining two waveguides. Finally, preliminary experiments on welding steel plates were done with the light transmitted through the waveguide. Although the focusing properties of the output beam should be improved for practical laser processing, this type of waveguide is promising for high-power CO(2) laser-light transmission.