Progress toward a novel hollow-core fiber gas laser

We report the progress toward a novel waveguide gas laser based on hollow-core light guiding capillaries and hollowcore photonic bandgap (PBG) fibers. Since Smith reported the first waveguide He-Ne laser at 0.633μm with a 20cm length of 430μm-diameter-bore glass-capillary-tubing in 1971, no smaller size waveguide gas laser has ever been constructed. Conventional hollow waveguide theory reveals that small bore size tubes suffer greater waveguide loss which hinders the construction of smaller size waveguide gas lasers. Hollow-core PBG fibers guide light through PBG effect that is different from grazing incidence mechanism of traditional simple hollow waveguides, and PBG fibers with a loss of below 0.5dB/m have been demonstrated at various wavelengths including 633nm. This indicates that we may construct waveguide gas lasers with such hollow-core PBG fibers. We carried out a series of experiments and succeeded in discharging gases contained within 250μm, 150μm and 50μm bore diameter hollow-core light guiding capillaries or fibers. Stable glow discharge of at least several minutes was observed for these waveguides. A flash glow was also observed from a hollow-core capillary with a diameter of ∼20μm. Initial measurements of current-voltage (I-Y) characteristics have been carried out for various tube sizes filled with various gases at different pressures. Theoretical IV characteristics are also presented and compared with experimental results. Discharging miniature waveguide bore tubes was found to exhibit unique characteristics that are different from the traditional larger diameter tubes.