Beam generation and beam shaping for a 1.5 kW diffusion-cooled annular CO2 laser

A diffusion-cooled CO2-laser with an output power of 1.5 kW was developed and set up with a coaxial RF-excited discharge. The laser beam is extracted by a resonator with helical mirrors, which is stable in the radial direction and unstable in the azimuthal direction. Without any beam transformation this laser emits a general astigmatic beam with an elliptical power density distribution, which is rotating in a plane perpendicular to the beam axis while propagating. Also, the beam shows hard edge diffraction effects due to the hybrid unstable/stable design of the resonator. In order to make the beam applicable to standard materials processing applications a beam shaping device has to be used to transform the general astigmatic beam into one of more rotational symmetry. The resulting beam has a times-diffraction-limited factor M2=1.5.