Fujimoto, Tanaka. Komori(remote)

## Trial of DRMI 3f lock stability improvement by incraseing the DRMI LSC gains

We tried to improve the stability of DRMI 3f lock by incraseing the DRMI LSC gains. MICH gain increased to x3. PRCL 3f error signals seems to fluctuate around 4 Hz. So we engaged resG at PRM ADS frequencies(PIT:4.125 Hz, Yaw: 6.125 Hz). Thanks to this, Current lock duration of 3f lock is several ten mins.

After the transition to 3f, we measured OLTFs (fig.1: SRCL, fig.2:PRCL, fig.3:MICH). We found that PRCL and MICH OLTFs seems to become strange after the 3f transition. There seems to be coupling. According to klog37341, there seems not to be strange in OLTFs. The difference from klog37341 is the PRM decoupling. Then, we tried to decreasing the coupling by decreasing the 135I signal in MICH from -1.38 to -1. Then, MICH OLTFs seems to become better. So this is one of causes.  

## 3f lock check on flashing IR

We tried to check DRMI 3f lock can keep in flashing IR beam. We locked ALS DARM/CARM and shifted the CARM offset by inputting 500 cnts to K1:ALS-SUM_OFS_SLOWOUT_CALI_OFFSET, which was the same value as PRFPMI lock. Now, DRMI lock procedure is DRMI af locked at first, then, transitted to 3f signal. However, DRMI 1f lock acquisition when ALS CARM/DARM were locked seems to become more difficult than it when ETMs were misaligned. When we increased the offset to 1000 cnts, DRMI 1f lock acquistion became relative easy. So, the small IR flash in Arm cavities makes DRMI 1f lock acquistion difficult. Fig.4 shows the timeseries of the only one try by decreasing the CARM offset. However DRMI 3f locked were down even though there seems not to be flash.

## Coherence check among signals in DRMI 1f lock

Above that challenges, We decided to decreasing the coupling between 3f signals and to decreasing the fluctuation of length fluctuations. We measured the spectra and their coherences (fig.5 -13). we will check them tomorrow.