Mode behaviour of a waveguide annular CO2 laser with a Talbot cavity

The annular geometry represents an interesting alternative to the slab format for diffusion cooled RF excited CO2 lasers. Typical draw backs of this scheme are related to the difficulties encountered in extracting a good quality beam [1] and in uniformly distributing the power in the discharge. Some effective solutions to the latter problem have recently been found [2,3], We have focused our attention to the former problem, experimentally testing the use of a Talbot cavity together with a phase-correcting mirror on the 100 W class annular laser described in Ref.[1]. The extraction efficiency obtained so far with this scheme is half that of a simple plane-plane guided resonator producing a multimode beam. The beam quality on the other hand appears sensibly enhanced.