[Aritomi, Yuhang]

We recovered the BAB alginment into OPO after removing second FI. The stability is also measured in the infrared path. As shown in the attached figure 1, it is quite stable(the fluctuation is only within 1%). From the experience, the stability is related to how well we align SHG. From the spectrum on the oscilloscpe we got after removing the second FI. And compare with the spectrum we got during Chienming is here. It is obvious that the alignment is worse than that time. So this stable infrared light is reasonable.

We also measured the green production efficiency, now it is 163/540.8=30%. This is lower than the effciency 35% when we have a better matching/alighnment. But still higher than the situation before Chienming came, at that time efficiency is only 20%. Although the efficiency is worse, but we have maximam 50mW going to OPO. While the threshold is 80mW for OPO. So we can use this power to observe a desirable level of squeezing. We can also increase the injection power to SHG if we want higher green power. So it should be fine with this alignment condition.

However, we found the parametric (de)amplification process has some abnormal behavior. If you check this video in the attached link, you can see the scanning peak has a roughly 50% of fluctuation(sorry I didn't take quite long time and this fluctuation doesn't have a clear frequency).  And seems there are two peaks they are competing with each other. Sometimes, the pump goes into one. Sometimes the other. Actually after we realize this problem, we start to check the fluctuation of infrared and green. They are as good as before. We also checked if we have mode hop. Even it is clear form the SHG scanning that we don't have this problem. After trying to change the temperature, we didn't find mode hop around our present situation. I also asked Chienming, he confirmed we didn't have this kind of fluctuation. But we didn't check the phase shifter, temperature control or some vibration. 

https://drive.google.com/open?id=1826D5cbTQ0ybPrw5KCKM0WpFTSIdkpUQ

Figure1: The statics of infrared beam(BAB) power.

Figure2: THe statics of green beam(before green EOM) power.

Figure3: SHG injection beam power.