Pierre, Aritomi, Eleonora, and Yuhang
After we used the new base plate for mirror mount, we measured the optomechanical transfer function yesterday. (Later we realize that we lock with a bandwidth of only around 100Hz. We saw ~1kHz resonance oscillation when we tried to increase gain)
Today, Pierre designed the new CC1 locking servo. While we have the same problem of ~1kHz oscillation. We could only lock with a bandwidth of 200Hz which is reasonable. I realize only now that we should have this 1kHz oscillation problem. With the locking bandwidth of 200Hz, we could measure the open loop transfer function. The measurement result is shown as attached figures.
| Frequency of peak | Description |
| 661Hz | This is different from the resonance around 500Hz we found before. |
| 1048Hz | This peak shows up and disappears from time to time. But when we see oscillation, we always see 1kHz. |
There is no particular explanation of why we have this new 1kHz peak. And this peak height is around 20dB. This height of peak makes the system very unstable.
Notice: we could measure open loop transfer function with servo and network analyzer again. The reason is we connect network analyzer power with ground floated.
