CO and CO2 laser beam guiding with silver halide polycrystalline fibers and hollow waveguides

Abstract

Silver halide polycrystalline infrared (PIR) fibers and hollow waveguides (HWGs) have high transmission at midinfrared wavelengths from 3 to 18 µm. Their applications include a flexible delivery of CO2 and CO laser power. We investigated transmission of PIR fibers and HWGs at different bending radii using CO2 laser radiation and studied the intensity distribution after the distal fiber. The PIR fibers show only a relatively weak decrease in transmission with increasing curvature 1/R or decreasing bending radius R. This is an advantage over hollow waveguides, where transmission decreases sharply with curvature. Disadvantages are high reflection losses at the PIR fiber end faces due to the high refractive index of 2.15 for wavelengths in the mid-infrared region. To reduce these losses, the surface of the fiber end faces must be treated with several special methods including microstructuring or coupling with an antireflective window. The measured near-field and far-field intensity distributions or beam profiles are highly inhomogeneous for both fiber types. For large core diameters of 0.9 or 1 mm, the beam profiles appear to be more homogeneous for the PIR fibers.