Participants: Eleonora, Manuel, Yuefan, Raffaele

Today we have worked on the injection of the beam, exiting the telescope, in the south arm cavity.

1) We have moved the 2" mirror telscope in the BS chamber 5 cm closer to the PR in order to have a distance of 272.5 cm between the two telescope mirrors. 

   distance  = f1 + f2  =  272.5 cm  where  f1 = 302.5 cm (see entry 419)  and f2 = -30 cm  (see entry 431)  

2) We have used a spare TAMA PR mirror (ROC of about 9 km, almost flat)  placed on a tripod, as steering mirror to send the beam in the corridor beside the pipe in order to check its features. We manage to send it into the end room and obseved its shape after 300 m. We remark that:

     a)  The beam is well collimated as it keeps roughly the same dimension after 300 m.

     b)  The beam moves a lot because of the air 

3)  We injected the green beam through the first viewport before NM2 chamber and tried to observe it on a target placed at 10 m,  without success. We changed the beam direction moving the yaw and the pitch of the last telescope mirror.

4) We injected a red beam in the viewport and we were easily able to make it impinge on the target at 10 m. We observed that, in order to be centered both on the target and on the viewport the beam has to start from a position about 4 mm higher than the green beam position (21.3 cm from the stack top plate)

Conclusion: It is not clear the reason why we cannot see the green beam on the target at 10 m. The only two possible reasons we could imagine are that we were not able to properly align the beam or that it is not enough transmitted by the viewports or by the temporary mirror installed in the NM2 chamber (a former LISM mirror ). Effects of a possibile antireflective coatings for the infrared light on the green light should be investigated.

Attached pictures:

1- Green beam at 150 m

2- Green beam at 300 m

3- Red beam impinging to the target at 10 m