Since OPO is finally closed, the next step is to characterize the intra-cavity losses. This is important for us because we are suspecting some of the optical losses are from OPO (current estimated loss budget for FDS). So this is an important step to understand the loss budget in the frequency dependent squeezing experiment.

I modified a bit the code to see the difference of measurement for different OPO intra-cavity losses.

Now, the laser is injected from the crystal side of OPO. I did a simulation of this case as Fig. 1. In this case, we will miss the information of OPO reflection. The blue and orange curves overlap for reflection.

If laser is injected from in-coupling mirror, as shown in Fig.2, we find that although decay time is not enough to indicate optical losses. We can extract losses from reflection signal.

So we will rotate OPO next week and inject laser from the in-coupling mirror side.