Flexible waveguides for transmission of IR radiation and surgical applications

Infrared (IR) radiation emitted by lasers is a very important tool in surgery applications. This type of laser energy is used for cutting and soldering of tissues, cauterization, evaporation of growths, opening blocked passages and others. The most important lasers which give radiation in the mid-IR region are the CO₂ laser (λ = 10.6 μm), CO laser (λ = 5 mm) and the Er-YAG laser (λ = 2.94 μm). In our laboratory a plastic, flexible, hollow waveguide suitable for mid-IR energy transmission was devised. This waveguide is used successfully in surgery. The waveguide is made of a plastic tube covered internally with a thin metal layer (Ag) and a dielectric overlayer (AgI). A theoretical ray model was also developed which has described quantitatively the propagation of radiation through the waveguide under straight and bent trajectories. The thickness and index of refraction of the dielectric layer is the essential parameter which determines the attenuation of transmitted energy through the waveguide. Powers up to 50 watts of CO₂ laser can be transmitted through these waveguides for bending radii down to 2.5 cm.