Single longitudinal and transverse mode operation of a hybrid unstable resonator TE CO2 laser

Single-mode operation of an atmospheric-pressure TE CO2 laser is reported. Single longitudinal mode emission has been achieved by incorporating a low-pressure, transversely excited gain section in the same laser cavity as the atmospheric-pressure section. The effects of different resonator configurations on the system modal behavior have been investigated and it is shown that unstable resonators are particularly suitable for controlling the transverse mode structure with a complete coverage of the excited medium. With an unstable resonator configuration, formed by a metallic convex mirror and a plane diffraction grating, single longitudinal and single transverse mode output pulses with energy up to 2J have been produced on more than 40 lines of both the 9.4 micron and 10.4 micron bands.