Resonator Design and Beam Quality of High Power YAG-Lasers

Conventional solid state lasers use flash lamps to pump a rod which is cooled only on its circumference. This leads to radial thermal gradients. Partly by thermal expansion but even more due to the thermal dependence of its refractive index, the rod behaves as an input power dependent thick intracavity lens. This influences the beam properties as illustrated in Fig.1. It shows measurements of a central cross section through the near and far field intensity distributions of a 300 W YAG laser with increasing input (and output) power. The measurements were made by means of a video camera and a video analyzer. The thick lines show the theoretical predictions which we will describe.