Output beam propagation and beam quality from a multimode stable-cavity laser

The authors present experimental data for a high-power CO₂ laser which confirm the validity of a simple analysis for the beam divergence and beam quality of the output beam from a large-bore multimode stable-cavity laser oscillator. The multimode beam parameters can be accurately predicted from a simple theory using only the geometrical parameters of the stable resonator. The data also suggest that a laser of this type with a uniform gain profile across the tube bore oscillates preferentially in the highest order modes allowed by the laser cavity rather than, for example, equipartitioning the output power among all the allowed cavity modes