Investigation of glow discharge of gas in hollow-core fibers

For the purpose of constructing novel waveguide gas lasers based on hollow-core fibers, we carried out a series of discharge experiments and succeeded in obtaining sustained glow discharge of gas in a 150-mu m-inner-diameter (i.d.) hollow-core fiber with the length of 13.7 cm and in a 50-mu m-i.d. hollow-core fiber with the length of 2.9 cm by using longitudinal direct current excitation. A flash glow is also observed in hollow-core photonic bandgap fiber with 20-mu m i.d. and 2.6-cm length. Initial measurements of current-voltage (I-V) characteristics have been carried out for fibers of various hollow-core sizes filled with various gases at different pressures. Theoretical I-V characteristics are presented and compared with experimental results. Gas discharges in miniature-bore hollow-core fibers were found to exhibit unique characteristics that are different from the traditional larger-bore-diameter tubes. The glow-discharge spectrum of helium gas in a 150-mu m-i.d. and 8-cm-length hollow-core fiber is also presented.