We succeeded in obtaining gas discharge in 250, 150, and 50μm bore-diameter hollow-core fibers by using longitudinal
DC excitation. Stable glow discharges of at least several minutes were observed for these hollow-core fibers, and a flash
glow was also observed for a hollow-core capillary with a diameter of ~20μm. Breakdown of helium and argon gases in
a 26.2cm-length 250μm-inner-diameter hollow-core fiber was achieved with a voltage of less than 30kV. Breakdown
voltages of helium and argon gases were measured for various bore-sizes, fiber-lengths, and a pressure range of from
below 1 to 50 Torr. Experimental results deviated from previous theoretical models and further theoretical and
experimental investigations are needed to understand the unique characteristics of gas-discharge in miniature capillaries
with bore-diameter below 250μm.
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-V)
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.
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