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

: Habich, U.; Heursch, A.; Plum, H.-D.; Poprawe, R.

Kudryashov, A.V.; Galarneau, P.:
Laser resonators
Bellingham: SPIE, 1998 (SPIE Proceedings Series 3267)
ISBN: 0-8194-2706-3
Conference Laser Resonators <1998, San Jose/Calif.>
Fraunhofer ILT ()
aberration; carbon compounds; gas laser; laser beam; laser cavity resonator; laser material processing; laser mirror; laser stability; light diffraction; ring 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.