This morning, I found that the PMC transmission power had often decreased (Fig. 1), and that the beam image on the PMC REFL camera had glowed at that moment (Fig. 2). This indicates that a mode hop occurred. This phenomenon seems to have lasted for the last three days, i.e. since last Friday (Fig. 3). Therefore, the current IR temperature does not seem suitable in terms of the mode hop.
The temps in the PSL room are cooler by ~ 0.1~0.3 C than before. So, anyway, I changed the target temp of the precision cooler from 20.90 to 21.10 around 20:32.
(Tanaka, Miyakawa)
We changed the IR crystal temperature from 41.05 degrees (Fig.1) to 39.23 degrees (Fig.2), and we did not change the green crystal temperature. Last week's measurement result for IR temperature shows that around 41 degrees stays close to the edge of the mode, and around 39 degrees stays at the middle of the slope with the same frequency. With these temperatures, we see no modehop on the PMC transmitted light anymore.
Additionally, we looked at the actual voltage going to the wideband EOM using an oscilloscope when IMC was locked. Maximum voltages were slightly over +/-40V at ~5kHz (Fig. 3,4), and they showed up every ~10 seconds. We saw no over 50V signal. The current limit of the RF HV amp is +/-100V, so we can say that it has enough range.
