Broadband flexible waveguides for free-electron laser radiation.

We refined flexible waveguides previously developed for CO(2) and Er:YAG laser radiation to transmit free-electron-laser (FEL) radiation. One can tune this laser over several segments of the radiation spectrum. This laser has a high peak power of as much as 10 MW with pulse energy of as much as 100 mJ. We made the waveguides of either Teflon or fused-silica tubes internally coated with metal and dielectric layers. We optimized the internal coatings specifications for transmission of various radiation wavelengths in the mid-IR range and enabled transmission of high-peak radiation. We performed experiments in three major FEL sites in the United States over a more than 1-year period when we measured and examined various characteristics of transmission. We used the analysis of these experiments as feedback to further improve these waveguides. The good preliminary results encourage us to invest more effort to further develop these waveguides until a suitable waveguide is obtained for this type of laser and make possible its introduction to the medical field where its characteristics can be exploited in surgical applications.