In the past days we have been working in order to improve the green beam shape at the end of the arm. 

1) We have realigned the optics on the bench many times in order to be well centered on the optics. After adding each optics we measured the beam and propagate it far (about 5-6 m) to check if we could notice any astigmatism.

2) We have tried to be as centered as possibile in the sferical mirror of the telescope and on the two gates between BS-NM2 and NM2-PIPE

3) We have change the telescope configuration for the grean beem in order to have longer focal length whit respect to the dimension of the beam on the lenses and avoid sferical aberations as much as possible.

In this condition we are able to have a beam which looks failry circular at the input of the pipe and also on the first target but which becomes very bad when observed on the  290 target. (The main effect is elongation in the orizontal direction). This video shows what we see on the far target while scanning the orizontal direction with the BS local controls.  While moving from one side to the other, at first we can observe some scattered light, than we don't see anything for a while and finally we see the beam on the target. Continuing the scan, the beam disapears and after another moment of darkness we can see again the scatterd light. From this I would say that what we observe is the direct beam and not its reflection on the pipe wall.

In order to better understand the evolution of the propagating beam we have put two steering mirrors at the level of the input mirror in order to send the beam in the corridor. (As steering mirrors we used to 5" mirrors used as PR ans END dummy mirrors, which should be both former TAMA PR mirrors with long RoC )

The beam at 300 m is shown in picure. It is moving a lot because of the air but it doesn't look elongated in the orizontal direction. There are no evident reasons why the beams propagating in the corridor and in the vacuum look so different. Here some hypothesis:

1) The air is affecting the propagation, masking the astigmatism observed in vacuum.

2) The steering mirrors are not flat enough and they modifiy the beam masking the astigmatism.

3) The astigmatism is introduced by the window at the input of the pipe and becomes evident only after a long propagation (on the target at 10 m the beam stil looks good) 

4) Effect due to possible multiple reflections from the target and the input window (it could be ruled out by looking at the beam reaching the end chamber) 

We remark that the beam on the target observed by the camera looks better than in reality. The same is true for the pictures taken to the green beam where small deviation from the circular shape are difficult to be apprieciated.