Logan, Michael

We planned out a simple setup to mode match into the OPO (beam size 25.5 um before placement). We place f = 40 at z = 65 in and f = 75 at z = 71.6 in (screw holes relative to laser head). The beam size is then ~ 25um at z = 79, a slightly more comfortable spacing than last time the OPO was tested (maybe 5 cm extra). We have enough space to put both steering mirrors after the lenses and then put a 50/50 BS between the lenses to send to reflection PD (PDA05CF2 RFPD was used last time).

We checked using the mode matching telescope that the beam waists are approximately the correct places and the waist after f = 40 is about the right size (~40 um). Then we tried to optimize the mode matching at z = 79 but couldn't get below ~ 40 um radius.

We inserted Newport 4003 Resonant IR EOM somewhere down the line (aligned with 94% transmission). Since it is coming out of the reflection of a PBS (s-pol) I didn't add a HWP. Perhaps it added a bit more optical path length than I expected, I didn't check carefully in the clean room. From online search afterwards, the crystal is 4 cm long and made of Mg:LiNbO3 with a 25 C 1064 nm refractive index of 2.15. So it adds an extra ~ 4.5 cm (1.8in) of optical path and the initial positioning was a bit too far forward.

I'm not entirely sure if we have to lock, or if we even can lock before the Taiwan people arrive, but we might as well leave the EOM there anyway and see if we can lock by July 16. At the very least we should try to visualize good mode matching of the order used in the current OPO ( >  91% BAB to OPO). It is probably not worth the effort to test the loss using the AOM deflection method, since last time it was inconclusive due to the very fast ringdown. The only meaningful test of the new OPO loss will be inserting it into the squeezer.