Marc, Michael, Yuhang

Matteo ordered BSF10-C to pick off CCFC error signal from filter cavity reflected squeezing. This mirror should take about 2% power, which means small optical losses for not degrading squeezing field. Today, we replaced the old 50:50 BS with this BSF10-C. We report several check we did here.

1. By using BAB and power meter, we checked power splitting ratio of BSF10-C. Incident power is 325uW, reflected power is 7uW, transmitted power is 321uW. From this measurement, the power loss is about 1~2%.

2. We checked CCFC sideband. When 40mW green is incident inside OPO, we have CCFC sideband as figure 1.

3. We compared CCFC error signal before and after replacing beam splitter. Figure 2 (after) and 3 (before) show them. We could see that error signal becomes not usable after this replacement.

4. We tried to amplify CCFC signal from photodetector, we got new sideband as figure 4. But, as figure 5,  the demodulated error signal just became overall larger.

I also attach here, as the last figure, how much FDS level we expect when we use different pick-off beam samplers. But since we just want to demonstrate this technique, maybe the current 50% BS is enough to see squeezing and stabilized detuning.