i tried to find the optimum combination of L/2 and L/4 together with optimizing the alignment trough the high power PC which we wanna use for the pulsing of the laser.
The polarizer i use is a glan-laser polarizer from Karl Lambrecht with an extinction ration of about 10^5. Without the PC the remaining power in reflection is ~360uW out of 26W (~1:72000).

Screenshot 1 shows the remaining beam:

With the PC in the path and optimized alignment the remaining power is ~130mW, shape of the remaining beam shown in screenshot 2: