Flexible Hollow-Core-Waveguides for CO_2-lasers potential and limitations as beam guiding systems for medical applications -

摘要

In contrast to Nd:YAG-lasers no amorphous material is existing which can be used as flexible solid optical fiber for far infrared wavelength as it is emitted by CO_2-lasers. This is resulting in some disadvantages regarding beam guiding and handling, e. g. reduced motion flexibility and accessibility, relative large and stiff devices for beam guiding. It is well known that beam guiding by hollow waveguide structures is possible in principle. Main problems in the development and realisation of such kind of beam guiding systems have been limitations in transfer efficiency, flexibility, length and diameter. A possible technical solution for the medium-power range is basing on flexible silica capillaries which are coated inside with a double layer system out of silver (metallic) and silverjodid (dielectric) using a chemical deposition process. These capillaries can actually be produced with inner diameter between 0,5 mm - 2 mm and a length up to 13 m, covered by a mechanical protection out of acrylic material. The optical principle of the hollow-core-waveguides (HCW) is presented as well as some first results regarding their influence on the transported beam. So investigations will be presented for instance showing the attenuation depending on different parameters of the waveguide system. In addition to that it will be shown that, because of the influence on the wave front and of the numerical aperture, the focussability of a laser beam is reduced but nevertheless the transmitted beam can be focussed to small diameters. The principle usability as well as the limits of flexible HCW in the medium power range, which is typically used in medical applications, will be demonstrated by the presented results.