Participaint: Aritomi, Chienming, Eleonora, Shurong and Yuhang

Today we achieved the lock of OPO on both p and s pol. The method is to lock OPO with p-pol (PDH signal goes to PZT of OPO) and then use PLL to lock s-pol to p-pol. Actually, before locking PLL we made sure the p and s both resonant inside OPO with peak overlaping.

The tricky part is to lock PLL as following:

1. We found that the frequency diffrerence of p and s is ~360MHz while the main laser current is 1.4A. However, this frequency increased ~420MHz after we increased main laser current to 1.8A.

2. Locking PLL for 420MHz is not possible. According to datasheet, we can provide VCO frequency only below 400MHz. At this moment, we decided to not use optimal temperature(optimal is 7.2kOm) but use 7.171kOm.

3. We investigated quite a long time and found we can use the built in divider to lock beatnote smaller than 400MHz. Since the phase detector can hold frequency only below 104MHz(also from datasheet), so we can divide signal and make it smaller than 104MHz. Then we can use reference frequency to compare with it.

4. As we have already mentioned in the last entry, we can only lock one side of PLL. We further found that we can change the sign of correction signal inside PLL board. We need to find the good comnbination of correction signal sign and the original frequency side(lower or higher than locking frequency). However, we were think if there is a way to change the offset of correction signal and make it have both positive and negitive signal.

After locking PLL, it is easy to lock OPO. The locking parameters are single-pol low-pass at 300Hz, gain of 100 and invert for SR560.

The locking parameters are single-pol low-pass at 30Hz, gain of 2 for SR560.(for GRMC)

I did the simulation about how much green we can produce now. The temperature we lock is 7.171kOm. The green we produce should be 90% of the peak value. However, the green production will be even smaller if we consider the overlap of p and s is not perfect.