NI ring adjustment

This morning (with Laura, Maurizio and G. Vajente) we tried to improve the NI ring. According to NI laser changed, the beam out of the laser is not a good TEM00. Indeed, after the AOM, it is possible to notice an halo around the main beam. Moreover, the beam is astigmatic before the AXICON.
At first, we tried to improve the contrast of the ring, by putting an iris after the AOM to get rid of the junk in the beam. It did not help at all.
So, we decided to decrease the astigmatism of the beam by mis-centering L2, translation in the horizontal direction. We managed to change the shape of the beam, at least as much as it can be seen with the cards. We then realigned the beam on the AXICON to get a better ring.
Figure 1 shows the ring as it was before these operations and figure 2 shows the ring after the activity. It seems that we managed to get some improvement. With the Tor Vergata CO2 beam profiler, maybe a better result could have been achieved.