Transmission properties of rectangular hollow waveguides for CO(2) laser light

Transmission losses of two types of dielectric-coated rectangular waveguide are analyzed theoretically to transmit linearly or circularly polarized CO(2) laser light. When ZnS and PbTe are chosen as coating materials, waveguide losses are reduced by ~ 1 order of magnitude by increasing each pair of coating materials. Phosphor bronze rectangular waveguides with small aspect ratios and various cross sections, whose inner walls are coated with a single PbF(2) layer, are fabricated by using vacuum-evaporation and assembly techniques. Transmission losses of straight and bent waveguides are measured for coherent CO(2) laser light as well as for incoherent infrared lights. Straight waveguide losses of 0.1 dB/m including a coupling loss from a laser, are obtained at a 10.6-microm wavelength for 1-m-long and small-core waveguides.