To measure the laser output profile is not actually that easy, although measured values are not so terrible.
Make sure the PBS you used is not BK7, but Fused Silica.
It would be nicer if you don't need to use transmissive optics for the measurement.
i.e. Put a fused silica AR-coated window and use the reflection.
BK7 windows may not work. BK7 has more than x10 CTE compared with Fused Silica. (7.5 ppm/K vs 0.55 ppm/K).
The absorption may also be higher.