Yuhang, Michael

From 2024-01-03 to 2024-01-05

We took the replacement OPO from the ATC cleanroom to TAMA and (finally) intended to replace it.

We decided to do a quick check for squeezing and afterwards just swap out the OPO. Since BAB, CC and ppol all end up being commonly aligned to the OPO via 2 steering mirrors after the recombination beam splitter, we decided we could just take it out, replace it and then recover the alignment with either of those beams. ppol is probably the most straightforward since it has its PD connected to one of the monitor channels on the OPO servo board. We should probably get a camera to check the shape of the SHG mode mismatch but for now we will just use transmission spectrum to align.

We drew lines around the old OPO to refer to exactly where to put it. After realigning the ppol reflection to itself we looked to scan the transmission spectrum, but the HVD would not turn on. After extracting the HVD -> OPO connection it turns out the HVD is fine, so the problem is somewhere in the electrical connection to the PZT. 

It seems the new OPO PZT is broken. So we had to put the old one back in. I accidentally burned a mark in the POM casing (the ppol laser is < 50 micron radius at the entry point of the OPO housing). After readjusting the alignment and mode matching of ppol to the old OPO, it was seen that the mode matching was improved by a small amount compared to the reference level shown on the wiki, so there is no issue with the crystal. There are two lenses on a ruler rail before the OPO - the positions before taking out the OPO were 170/264, and after replacing were 168/262, with 91.3% mode matching.

The old OPO PZT gives about 800 nF capacitance (about the same as the datasheet) while the new OPO doesn't give a reading.