Lisa, ChrisW, Jamie, Arnaud, Kiwamu

We locked the PRMI with the 1f signals at a CARM offset of 1-2 kHz. The goal is to hand it over to the 3f after the CARM offset passes approximately 1 kHz at which the arm cavities resonate with the 2f sidebands. However, we didn't get a real progress tonight. We will continue studying this configuration.

What we did:

• We aligned TMSX by using the usual baffle diodes technique.
• This resulted in a small beatnote at the ALS diff broadband PD. So I realigned the beatnote.
• The SHG was found to be somewhat low. So I realigned the crystal. Now the power at 532 nm is about 0.024 mW according to the monitor diode. This is a factor of two improvements. Good. The comm beatnote is now at -1 dBm at the PFD monitor.
• We had a difficulty in engaging ALS diff.
  • This turned out to be due to new L2P filters in UIM of ETMY that Aranud put in today. Although the filter is more accurate, the impulse response in pitch was the killer when the DIFF loop is being engaged. So we went back to the legacy filters. This fixed the problem.
  • Also, the DC bias of ETMX ESD had an opposite sign. This prevented us from going to a high UGF. So we flipped it back to 125 kcnts as usual.
• There was a high-cavity-motion time in which we were not able to hold the green PDH for 1 min due to the PDH actuation range.
• We started using the slow feedback onto ETMs.
  • Since the guardian codes tend to clear the length history, this produced large kick on ETMs every time when it looses the lock.
  • We commented out the sentences which clear the history in order to reduce the kick.
  • Also, I changed ALS-X(Y)_ARM filters because the PDH autolocker was clearing the history by toggling the first two filters. Right now these filters are intentionally left empty such that the autolocker does not clear the history.
• At some point, we noticed that the cavity stay locked without the slow feedback. So we stopped using the slow feedback.
• After some struggling to align the PRMI, we managed to start the real experiments.
• I tried CARM offsets of 1 kHz and 2 kHz. These worked just fine.
  • While holing the PRMI with the 1f signals, I tried to approach the resonance by reducing the CARM offset to see how it behaves.
  • In the case of the 2 kHz offset, it dropped the lock when the offset was about 1.5 kHz.
  • In the case of the 1 kHz offset, it dropped the lock when the offset was about 900 Hz. Both lock losses seem to be associated with high frequency contamination. I didn't take a close look yet.