Fluence homogenization of a 240 J-diode-laser pump system for a multi-pass solid state laser amplifier

Within the POLARIS project multi-pass amplification to the 10 joule level for a femtosecond CPA laser system has been achieved by diode-pumping an Yb doped fluoride-phosphate glass disk with a total energy of 240 J. The collimated light of 40 diode stacks is focussed onto a circular area of the glass disk with a diameter of 18 mm. A two-sided ring shaped setup is used for axially symmetric pumping. We developed a computer aided optimization routine for the positioning of single pump foci to gain a smooth homogeneously distributed, top-hat shaped pump profile. The homogeneity of the pump light distribution was improved substantially by this new method.