Participaint: Chienming, Shurong and Yuhang

Today Chienming and Shurong aligned the SHG, GRMC and OPO. There are some coments from them.

1. The alignment of SHG was always degraded by the constantly shifting of the second Faraday isolator.

2. There are two higher order modes of SHG cannot be removed. We guess these two modes come from some inherent mismatch inside SHG. We also found the bad shape of green beam comes from the cut of this green beam by the edge of SHG housing. However, as Chienming suggested, the side of beam is trivial compared with center. And we also found it is fine for filter cavity locking. So we guess it is fine.

3. Chienming put small spacers for the FI just after SHG. The purpose is to move the point(diffracting the light) to the edge of the beam.

4. GRMC and OPO were aligned to the best situation by Chienming and Shurong.

After that we found the beam was shifted. I guess this is because of the align of beam done by Chieming. Anyway, we recover the green beam direction by using BS before 100mm lens. Then we changed the AOM driving amplitude, the value now is -6.4dBm. It used to be -10dBm. This change of driving amplitude was suggested by Chienming. We increase driving amplitude and look at AOM first order power. We stop when we found the maximum. At that time, it became -6.4dBm. We can see from the attached figure. The zero order now is not round.

However, we still can see the beam seems to be cut by AOM. But Chienming suggested to check this beam with a much lower power(like what we have before, 8mW). But anyway, we cannot see this structure when there is only zero order going inside AOM.

So tomorrow we can do

1. Check the first order of AOM with lower power

2. Try to align filter cavity to see flash

Figure: (1and2: BAB inside OPO. 3and4: SHG. 5and6: GRMC 7:AOM situation of beam shape when amplitude maximized 8:AOM RF driving amplitude)