EleonoraP, EleonoraC and Yuhang

We achieved the matching of the BAB (IR probe beam co-aligned with squeezing) into the filter cavity.

In order to align BAB into the FC, we mainly followed the IR alignment procedure we did more than one year ago (entry #646). The main steps of this procedure are to align the cavity for the green, recover the reference on PR chamber, maximize IR reflection from the input mirror, not to look for the beam on the first target and check instead the second target and the end camera.

However, since BAB is only 250uW, it is too weak to see. So we used the green pump to amplify it. The maximum green we can give is obtained setting the offset on the MZ control servo at 4.3 and at that time we have roughly 30mW of IR going to FC. This measurement of power is done while we scanned the green pump phase. So actually we are sending a repeated segment of a sine wave.

By using this 30mW and following the procedure above, we found the flashes of IR. Check attached video.

As you can see in the video, this beam is too bright so, in order to avoid saturation, we decide to reduce the power to around 10mW. In this case, we need to use temperature of 7.202 for OPO, MZ offset of 4.1 and lock p-pol PLL on 150MHz.

After achiving the alignment with the amplified BAB we confirmed that flashes cannot be seen without amplification. (BAB power ~250 uW)

Next steps are to optimize the matching and to use AOM to make green and IR both resonant.