Abstract
The FB laser seems to be out of order. we will discuss the recovery plan.
Contents
Around 5AM, Ushiba-kun noticed that PMC could not be locked from the last night for over 6 hours, and no flashing in the PMC trans. At this moment,
- FB laser output of 19W was displayed. PMC REFL image of the GigE camera is OK. The transmitting light of the PMC could be faintly visible.
- PSL room temperature had no changes.
- The last unlock had no correlation to seismic noise enhancement cause by earthquakes.
So, firstly we suspected that the lock loss happened because of the control side events, such as some troubles in the PMC control including PZT itself.
We discussed what we should do among Ushiba-kun, Miyakawa-kun, Ikeda-san and Miyoki around 9AM via zoom1, and Miyakawa-kun decided to enter the PSL room to check thes present situation. The followings are waht Miyakawa-kun checked.
- Displayed values of the HV amp in the PSL room were OK.
- Turned off the HV amp, and disconnected the cable to the PZT at the output of the HV amp, then
- Check the resistance of PZT at the terminals on the PMC body. Over Mega-ohm was measured. ---> No problem.
- When he measured the resisstance of the PZT with a multi-meter, he observed the resistance increased up to over Mega-ohm for ~2 seconds. This means that the capacitance did exist at the measuring point. So coplete disconnection to the PZT path did not happen.
- Shorting between the PZT cables with a wire, then measured the resistance again. The resistance became over Mega-ohm again for ~ 5 seconds that is longer than the initial ~ 2 seconds.
- Touch the cables from the terminal to the PZT by finger, then measured the PZT resistance again. Over Mega-ohm was also measured.
- Check the resistance of PZT at the terminals on the PMC body. Over Mega-ohm was measured. ---> No problem.
- HV check
- Turned on the HV amp and check the voltage at its output. 150V was measured ---. No problem.
- Cable check
- Measured the resistance between the signal line and return line of the cable between the HV amp output and the terminal on the PMC, then no shoting was conffirmed.
- Reconnect the cables from the HV amp to the PZT again.
- Check voltage at the terminal on the PMC, then 150V was measured ---> No problem.
- Beam paths
- PMC trance beam was confirmed, not only just after the PMC but also the IMC REFL.
- A beam at the back of the mirror (named C) just beside the input mirror (named A) was confirmed.
- A beam at the back of the mirror (named D)just beside the output mirror (named B) was confirmed.
- So, misalignment of the A and D mirrors were possible. But no way to checck it.
- PZT scan again
- No flash was detected.
At this point we could not find any reason why the PMC cannot flash by the PZT scan.
Finally, Miyakawa-kun found the strange situation in the FB laser as,
- The seed laser was off (red indicator in the front pannel). However, the FB amp was on. In the control application in the PC showed, 19W at the FB output and 1.8W seed power.
However, this situation is the worst case that definetely would result in disorder of the FB laser. So, Miyakawa-kun reduced the current for the FB amp, then actually, the output power of the FB laser reduced and the GigE camera image of the PMC refl became smaller, then finally vanished when the current became zero.
After that Miyakawa-kun tried to recover the master laser, then it came back. At this point, the master laser power was dected in the controller application to be 1.5W. After that he increased the current of the FB amp. However, no output from the FBL. We tried the full process for the FB amp recovery, incuding the windos PC reboot. However, FBL output could not be recovered.
Finally, we suspected the disorder of the FBL.
Consideration
- Why the IR of 19W was emitted without no seed power?
- We expected the beam of the FBL did not come out when the seed light was off. however, it was emitted.
- Why the PMC flash vanished even if 19W laser was injected in to the PMC
- We suspected that the FBL became no-coherence light and multi-mode oscillation happened. So no way to resonate in the PMC?
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