Mid-IR laser emission from a C2H2 gas filled hollow core fiber

We demonstrate what we believe is the first hollow fiber gas laser based on population inversion. A single-cell-defect Kagome fiber with a core diameter of about 40 microns was filled with a few torr of acetylene (¹²C₂H₂). Acetylene has absorption transitions in the attractive telecommunication C band region and recently lasing was observed at about 3 microns from a gas cell when optically pumped. Pumping the gas filled fiber (1.65 m) with micro Joule pulses from a 5-ns OPO resulted in the emission of two laser lines at 3123.2 nm and 3162.4 nm. The pump (-1521 nm) was in the guiding regions of the fiber (loss ~ 0.75 dB/m) while the laser output occurred in weakly guided modes (~ 20 dB/m). This laser combines attractive features of both fiber and gas lasers, such as the confinement of the pump and laser over long interaction lengths in a compact configuration, the many possible emission wavelengths of various gases, high damage threshold, and the potential for coherent beam combining of mutually incoherent pump sources. While this first laser demonstration used a pulsed pump, the gas filled fiber laser is particularly attractive for pumping with CW laser sources.