Spatially variable retardation plate for beam brightness enhancement in a high-power laser

We present a simple and robust method for brightness enhancement, efficiently transforming a radially polarized LG (0,1)(*) mode into a nearly Gaussian beam of much higher quality. We use for this a spatially variable retardation plate and a spatial filter. The analysis shows that the transformation yields an increase in brightness by a factor of 3.4. In the experiment, we transformed a high-power Nd:YAG radially polarized (0,1)(*) LG beam with power of 70 W and M(2)=2.6 into a nearly Gaussian beam with M(2)=1.36. This resulted in brightness enhancement by a factor of 2.6.