Figure l a shows the spot diagram measured after wavefront precorrection just before a full energy shot . The red circle presents the 100 prad diameter spatial filter hole (the hole is removed during the wavefront correction process). We can clearly see that some stray rays may potentially touch the edges of the hole. The spot diagram measured on a 18,5 kJ, 5 ns shot (figure 1 b) presents a much better wavefront. No stray rays are present around the hole and the RMS angular spot diagram is 18,5 prad (compared to the 100 prad spatial filter).