## Abstract
- I measured the TF of RF amp of POP WFS2 with electronical signal and with AM laser. Their results are consistent with QPS design and Shomode-san's previous measurement.
- I tried to do the phasing about each segment of both WFS. WFS1 phasing is succeeded, and the phase difference between segment 1 and the others is removed. However, WFS2 phasing failed because the in-phase demod signal from segment 4 has strange fluctuation so the relative phase between segment 1 and segment 4 also fluctuates. So Today, I had no time to investigate the cause of this issue. I will investigate later...
## What I did
### TF measurement of WFS2 RF amp
- I measured the TF of WFS2 in the same manner in klog21025. I put these results in /kagra/Dropbox/Measurements/IFO/ASC/IRQPD/POP/TF. Each file name convention is below
- TEST port to RF{17, 45} SEG{1,2,3,4}: MokuFrequencyResposeAnalyzerData_20220615_{hhmmss}_pop_qpd2_rf{17, 45}_test2seg{1,2,3,4}
- AM laser to RF{17, 45} SEG{1,2,3,4}: MokuFrequencyResposeAnalyzerData_20220615_{hhmmss}_pop_qpd2_rf{17, 45}_am2seg{1,2,3,4}
- The gain around the target frequency is a gentle curve, on the other hand, the gain at the other frequency is dipped. Fig.1 and 2 are ones of the results in TEST to RF17 seg 4 and in AM to RF17 seg 4
### POP WFS phasing
- I did the phasing for POP WFSs in the same manner in klog21025. Firstly, I measured the relative phase difference of each segment of RF17 and RF45 WFS1 using a 100 Hz beat signal. Fig. 3, and 4. are the relative phase difference before phasing of RF17 and RF45 WFS1. Fig. 5 and 6. are the ones after the phasing of RF17 and RF45. As you can see, the phase difference seems to be around 0. Fig. 7. and 8 are the medm screen of demod phase of each RF WFS after phasing.
- Then, I tried to do the phasing for POP WFS2. However, I failed it due to the phase difference between segment 4 and segment 1. I found that the amplitude of the demod signal from segment 4 largely fluctuated (fig. 9) and the relative phase difference varies the amplitude. This phenomenon was observed for both RF17 and RF45 demodulated signals. On the other hand, we also looked at the same signal in WFS1, where phasing was successful, but no such phenomenon was observed. (fig. 10)
- At this time, I confirmed that the beam was hitting the center of the QPD and that all wiring was not loose.
- Since I did not have enough time today, I did not check upstream of the digital system. I plan to investigate the cause of the problem in the upstream section in the future.
