Recent advances on microstructured optical fiber allow the demonstration of hollow-core PBG fibers with core diameters ranging from 5microm to 50pm. The attenuations of these fibers are much smaller than that predicted from the conventional hollow waveguide theory, indicating that special waveguide designs (e.g. hollow PBG fiber and hollow Bragg fiber) can help to obtain small waveguide losses. With these novel hollow-core fibers, compact and flexible fiber gas lasers may be constructed.;We have investigated, theoretically and experimentally, the various issues related to the construction of a fiber gas (e.g. He-Ne) laser. Theoretical investigations include: waveguide losses of different type of hollow-core fibers, various cavity configurations and cavity configuration for achieving optimal couplings, bending losses of hollow-core fibers, population inversions in small bore size hollow-core fibers, gas flow dynamics in hollow-core fibers, and breakdown characteristics. Experimental studies include: design of vacuum system, longitudinal DC discharge experiments, current-voltage characteristic of gas discharge in hollow-core fibers, spectrum measurements, and exploring of optimized design of laser structure.;We succeeded in obtaining gas discharge in 250, 150, and 50 microm inner-diameter (i.d.) hollow-core fibers by using longitudinal direct current excitation. Stable glow discharges of at least several minutes were observed for these hollow-core fibers. A flash glow was also observed for a hollow-core fiber with an i.d. of ∼20 microm. Breakdown of helium and argon gases in a 26.2cm-length 250microm-i.d. hollow-core fiber was achieved with a voltage of less than 30kV.;All the results of theoretical and experimental investigations indicate that it should be possible to construct hollow-core fiber gas lasers with an inner diameter of 250microm or less. The successful demonstration of miniature fiber gas lasers would open doors for many new applications such as rotation sensing and flow measurement.
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