Carbon monoxide laser systems using optical fiber beam delivery

Considerable attention has been given in recent years to the potential for medical and light industrial applications based upon the use of carbon monoxide lasers. Significant progress has been made in the development of CO laser sources to address these applications, both in terms of diffusion-cooled devices and kilowatt scale lasers employing convective flow techniques. In addition, one of the advantages often claimed for the use of the 5-6-µm spectral region over the more commonly used carbon dioxide laser technology at 10 µm is the suggestion that effective laser power delivery, using optical fibres, will be easier to accomplish at the lower wavelength. In this paper, we describe advances in both diffusion-cooled and fast flow CO laser technology, as well as a comparison of the characteristics of hollow and solid core optical fibers as the basis for the design of 5-µm laser systems. Previous work has shown that diffusion-cooled, carbon monoxide lasers may be operated without cryogenic cooling to produce intermediate laser power (>100 W) in multimode beams, based on the use of the waveguide slab geometry. Here, we report the application of the hybrid (waveguide-unstable) resonator format in a transverse RF discharge excited waveguide slab configuration to produce high quality CO laser beams (M² < 1.2) at the 80 W cw power level from a 40-cm-long device, again without cryogenic cooling and without gas flow. In parallel work, a compact (table top) fast axial flow RF discharge excited CO laser, with cryogenic cooling, has been operated at the kilowatt cw power level with good beam quality. Each of these lasers has been used as the input radiation source in an experimental arrangement incorporating precision alignment of the fiber and launch optics, and the ability to measure both fibre transmission losses and input/output transverse beam intensity profiles. We report the results of an experimental assessment of the transmission characteristics of candidate 5-µm fiber waveguides. Included in this study have been both solid core chalcogenide glass fibers and hollow (air core) metal fibers. The latter have been fabricated to have a dielectric inner surface, which for one fiber type is germanium (n = 4), and for the other (Fiberlase Inc.) is a silver halide (n = 2.2). The fibers are also compared in terms of maximum power handling capability, the impact of fiber bending and material toxicity.