Small-diameter hollow waveguides based on silver-clad stainless steel tube for infrared laser light transmission

We have fabricated hollow waveguides based on a silver-clad stainless steel tube for delivery of infrared (IR) laser light such as Er-YAG and CO 2 laser light. The silver-clad layer's inner wall was polished to a mirror-smooth state. A thin silver iodide (AgI) layer was formed by iodination of the layer's inner surface to enhance reflection of the propagating IR light at the inner wall of the hollow waveguide. The waveguide's inner and outer diameters are 0.4 and 0.6 mm, respectively. Since this type of metallic hollow waveguide has high mechanical strength and heat resistance, it seldom fractures or melts. Moreover, it has such a small diameter that it can be bent flexibly. We have experimentally fabricated a 1-m-long hollow waveguide with a 0.24 μm thick inner AgI layer, which is optimum thickness for Er-YAG laser light transmission. The transmissions of Er-YAG laser light were 64% and 60% under a straight condition and a 90° bend with a 7.5-cm radius condition, respectively. By optimizing the thickness of the inner AgI layer according to the propagating light's wavelength, CO 2 laser light can also be transmitted effectively though the hollow waveguide.