Participants : Yuefan, Eleonora

We prepare the set up to characterize the reflected beam from the FC. In the final configuration we will need to take a part of the reflected beam to send it to the quadrants for the AA.

At present the green FI reflects about 4.5 mW which are attenauted in order to send only 150 uW to the PD used for the filter cavity lock. (150 uW corresponds to a DC output of 88 mV )

Up to now we used a set of optical densities just placed on the bench to attenuate the power and today we changed them with two "mirror shaped" optical densities  ( ND 1 and ND 0.5)  which we coud directly screw on the last lens before the PD, making the setup more stable.

Since the beam height is only 3.8 cm,  we prepere a periscope to be installed before the PD. The lower mirror of the telecope should be a BS which trasmit at least 3% to the PD and send the rest to the quadrants.  Since we couldn't find any suitable mirror we could not perform the beam characterization with the FC cavity locked. We will do it as soon as we can get the mirror for the green.

Pic 1 and 2 show the periscope we assembled.

We remark that there won't be a lot of space to put quadrants and galvo in that area of the bench, so the desing has to be studied carefully.