Participants: Raffaele, Eleonora 

As reported in entry 649, while improving the IR aligment we realized that the power of the reflected beam was very small.  After some investigations we were able to see with the IR camera that the reflected beam was hitting a side of the inner part of the viewport. in order to avoid this we decide to slightly change the positon of the diachroic mirror SM2 (where green and IR recombine) in order to change the way the beam passes through the faraday.

We moved the yaw picomotor of SM2 several times (velocity 500, direction +), trying to recover the IR aligment with the two steering mirrors on the bench after each picomotor movement.

We did the following series of steps:

10, 10, 100, 300, 300, 600, 600 (Thursday) and 600,1000 (Friday)

Before the last movement (1000 steps) we were able to have a quite good alignment and a reflection between 11 and 12 mW  (the input was about 16 mW), nevertheless we were still able to see some IR scattered light inside the viewport.  After the last movement (1000 steps) the scatterd light was no more there but we were not able to recover a good aligment.

Sometimes, while recovering the aligment we had the impression that the matching was worsened (more LG modes), so we have changed the postion of the last IR lens different times in a range from 7 mm (original postion) to 22 mm.

Note that since we moved SM2, one of the two green references (the reflection from SM2) has changed accordingly. See attached picture.