Naoki, Nutsinee, Daniel
We installed all the optics for PMC and locked the PMC with p-polarization. We will lock the PMC with s-polarization and align SHG, CLF, seed next week.
First we put a HWP before PMC and changed the beam to the p polarization since the p-pol has much lower finesse in PMC and it is easy to align. The HWP angle is 152 for p-pol and 108 for s-pol.
We aligned two steering mirrors before PMC. Fig. 1 and 2 show the PMC trans (blue) and refl (red) with PMC scan. The mode matching is 93% and the refl dip reaches 88% from the maximum.
We found that the label of the pick off mirror before PMC REFL PD says R=5% for s-pol, but it was actually R=90% for s-pol and R=70% for p-pol. The PMC REFL power is ~30mW and more than 20mW was injected to PMC REFL PD, which is a lot. So we replaced this mirror with the mirror which is R=8% for s-pol and R=1% for p-pol.
Then we adjusted the demod phase of PMC PDH signal and locked the PMC with p-pol. The UGF is 1.3 kHz and phase margin is 67 deg as shown in Fig. 3. We accepted the SDF related to PMC as shown in Fig. 4.
Note that we will have 20 times more optical gain with s-pol because of higher finesse. Also we will have 8 times more power at PMC REFL PD with s-pol because of the pick off mirror. So we need to reduce the gain by 160 with s-pol to have the same UGF as p-pol.
After the pick-off mirror swap with 34mW input we have ~2mW hitting the PMC Refl. DC readout reads 75mW. The HWP before the PMC is set to s-pol at the moment.
Attached an updated picture of the SQZT0 table. All the optics are in.
The PMC PZT trigger has the PMC TRANS PD wired to channel 1 and PMC REFL to channel 2.
The DC readback of PMC_REFL is saturating and the gain adjust is broken due to a missing ground wire in the controls of aux concentrator 11 (which pegs the adjustable gain to 40dB).
Nevertheless, we were able to engage the guaduan to lock the PMC using the dip in reflection.