Optical gain measurements at 10.6 µm in an 80 µm hollow-core slab waveguide

N
2
, when externally excited in a gas discharge and mixed with CO
2
+He in a planar metallic waveguide with plate separation less than 80μm, has produced an active laser medium with gain in excess of 17 dB/m. These results demonstrate that an active medium capable of sustaining oscillation can be produced in a waveguide with core dimensions suitable for distributed feedback at 10.6μm. Results are reported for both longitudinal and transverse gas flow configurations.