Komori, Fujimoto, Ootaki, Iizuka, Tanaka

As reported in the original post, FNCs could be locked because DGS outputs for woofer PZTs were turned off and woofers were applied with 75 V offsets manually due to the k1ioo1 trouble in this May (klog36959). We restored the situation to that before the trouble. Fig.1 shows each PZT driver status for each PZT. We found that tweeter PZT were applied with ~135 V. According to Hirose-san, at that time, she also applied the tweeters with 75 V manually. Then, she did not turned off the DGS outputs for tweeters. So after the recovery of k1ioo1, tweeters were applied with manual offsets + DGS ouputs. So we restored the manual offsets to 0 about all of PZTs. After that, we turned on DGS outputs for woofer PZTs. Fig. 2 show the PZT driver status after our work.  Fig. 3 shows the timeseries of X or Y GR laser power at each fiber output on POP or POS. Around -5m, we performed the above work. GR Y power was restored (and improved) but the GRX was decreased. Therefore, we tweaked the alignment of the PZT mirror just before the fiber coupler (Gr M25 in PSL optical layout). Then, we restored the GRX power.

After coming back to Mozumi, we confirmed FNCs could be locked with guardians. FNCs could be locked (Fig.4). On the other hands, the fringe sizes of FNCs, especially FNC X seem to be lower than before (Fig.5). So we need to restore them. In this status, FNC X can keeps the lock ~2 hours and FNC Y can keeps the lock more than 4 hours.

Sorry. I'm talking about not ALS_DARM "lock" but the ALS_DARM "sensor". You measured the TFs from EX actuators to ALS_DARM sensor, K1:LSC-ALS_DARM_OUT. This ALS_DARM sensor has a pseudo CP filter to mimic an IR DARM responce. For example,  in the PRFPMI case, There is the CP filter, which is labeled as "CP_PRFPMI", in FM2 of this filter bank. In other words, for RSE, you need a filter corresponding to the ALS_DARM_OUT filter bank that is matched to the RSE CP because RSE CP differs from PRFPMI CP. My question is: Have you performed that operation?

But, even if that operation wasn't performed, it's very good to know that the actuators themselves have not changed since PRFPMI.

thank you for measuring. i have one question. do you compensate the DARM cavity pole for RSE in this measurements? because RSE cavity pole should be changed from PRFPMI one. 

If my memory is correct, DGS outputs for woofers are turned off due to IOO RTPC trouble in this May ( https://klog.icrr.u-tokyo.ac.jp/osl/?r=36959 ). Strictly speaking, now wonders are applied 75 voltages manually. And DGS offsets are set to 0.

We need to enter PSL and to restore them

[kTanaka, Hirose]
This work is continued from klog37323. We replaced the PZT mirror mounts for REFL QPD3 and AS QPD2.

• We checked the spare PZT mirror mounts and found two spares. We used them for the replacement. We also ordered additional PZT mirror mounts to keep enough spares.
• For AS QPD2, we could not see the beam even with a sensor card. We tried to rotate the HWP to increase the power at QPD2, but the HWP did not work properly. We asked Ikeda-san to repair the HWP (klog37328). To continue the work before the HWP repair, we increased the IMC transmission power to 8.5 W. Then, we replaced the PZT mirror mount for AS QPD2 and adjusted the beam alignment.

Next step

• Run the DC centering loops for the RF QPDs(ASQPD2 and REFLQPD3).
• Measure the WFS sensing matrix.

K.Tanaka-san, Hirose-san, Ikeda(remote)

Tanaka-san reported that the AS HWP was not rotating. 
Upon investigation, we identified two issues. After correcting them, we confirmed that the HWP operates properly.

1. When using an HWP without an encoder, the number of steps corresponding to one degree must be set in `K1:SYS-HWP_IFO_AS_CT_PER_DEG_{P,N}`.
   However, the value was set to zero, resulting in a division-by-zero error.

2. Fractional angle values had previously been enabled for other HWPs equipped with encoders, and the same change was mistakenly applied to the AS HWP.
   As a result, the motor-control code failed to process the fractional value correctly, preventing the motor from rotating.

[Corrective Actions]
1. A temporary value of 150 was set to prevent the division-by-zero error.
   [medm] sitemap → SYS → HWP OVERVIEW → count2degree

2. The code was modified so that fractional values are not used for the AS HWP.
   /opt/rtcds/userapps/release/sys/k1/scripts/medm_hwp_calib.sh
   Before:

   Fractional values were used.
   After:

   Fractional values are no longer used.

After implementing the above corrective actions, we confirmed that the HWP rotates properly.
To ensure accurate angle control, the value described in Item 1 should be properly calibrated.
 

B: ~detchar/Segments/K1-GRD_SCIENCE_MODE/K1-GRD_SCIENCE_MODE_EDGE_3SEC_O4{a,c}.xml

Invalid calibration related to causality of reconstruction filters.

C: ~detchar/Segments/K1-CAL_HOFT_NOT_OK/K1-CAL_HOFT_NOT_OK_O4c.xml

Invalid calibration related to improper calibration measurements.

It was officially moved from test space (see also klog#37280).

This issue was occurred only during O4c.

D: ~detchar/Segments/K1-DAQ_IPC_ERROR/K1-DAQ_IPC_ERROR_MARGIN_3SEC_O4{a,c}.xml

Invalid DAQ-ed data due to data loss on MX stream.

After the ITMY work, I investigated the SRM ADS phasing in some situations. This time, I locked DRMI with 1f and engaged PRM and IMMT2 ADSs. I found that the demod. phase of SRM dithering seems to be flipped with or without resG filters at corresponding frequecies of ADS in SRCL control loop. I summerized the phasing in each situation as below table. I'm not sure of the exact reason why the signe flip occured for now (A2L coupling? If A2L coupling is caused by the flip, the L conponent has the opposite sign from Angle conponent and the size is twice? SRCL control is reduced the L component to small enough?). However, the value itself seems to be reproducible if we measure it with good coherence, more than 0.9.   

As reported in klog37321, ITMY Yaw fluctuation around 0.1 Hz seems to be correlated with the drop on buildup sideband power in PRC and SRC. So I started to investigate the ITMY Yaw local control.  At last, I implemented a 0.13 Hz resG filter in FM5 of MN_OLDAMP_Y to suppress the 0.13 Hz fluctuation in ITMY TM oplev. Thanks to the implementation, AS34 seems to become more stable than before.

## What we did

As reported in klog37321, ITMY Yaw fluctuation around 0.1 Hz seems to be correlated with the drop on buildup sideband power in PRC and SRC. So I started to investigate the ITMY Yaw local control. 

As Ushiba-san commented in this morning, at first, we investigated whether MN OLDAMP caused the gain peaking or not. we measured the TF from EXC to IN1 of K1:VIS-ITMY_MN_OLDAMP_Y. For the reference, we also measured the TF of ITMX. Fig.1 shows the results, ITMY TFs in the left panel and ITMX TFs in the right panel. Both TFs from EXC to IN2 of ITMX and ITMY seem to have the same performace and there seems not to be gain peaking around 0.1 Hz. Also, Fig.2 shows the spectra of ITMY and ITMX oplev signals. the peaks around 0.1 Hz in ITMY Yaw oplev seems to be about 2 times larger than the ITMX one. From these points, we assumed that the disturbance for ITMY is lareger than the ITMX one.

I measured the ITMY and ITMX oplev spectra in each suspension state to check whether the some controls disturbs TM or not. Fig.3 and 4 shows the results of ITMY and ITMX, respectively. Compared ITMY with ITMX, (This time, when the suspensions were in the TWR_FLOAT state, Both ITMX and ITMY TM oplevs seemed to be the almost edge of the sensor area. So I adjusted both beam positions of thier oplevs to hit on the center of sensors by using MN_OPTICALIGNs.) I found that there was a 0.13 Hz peak only in ITMY Y when suspensions were the TWR_FLOAT state, which is no control state. According to Okutomi-san's simulation (JGWdoc), This peak maybe caused by #6 Y whole chian 3rd mode or #7 Y whole chian 4th mode. Anyway, the peak may be the cause of the larger disturbance than ITMX, I thought.

Then, I implemented the resG filter labeled "resGtest" in FM5 of ITMY_MN_OLDAMP (fig5). Fig.6 shows the measured OLTF of the loop after the implementation. Fig.7 shows the spectrum of ITMY TM Yaw oplev after the implementation. As you can see, the 0.13 peak is well damped.

Then, we locked DRMI with 1F with this ITMY.  Fig.8 shows the time-series of AS34, POP90, ITMY P and Y. Thanks to this, AS34 RMS seems to be smaller drastically. Fig.9 and Fig. 10 show the time series of DRMI LSC error/feedbacks before and after the implementation. Many glitches are seen in the LSC error/feedbacks, especially MICH and SRCL before the implementation. These glitches were caused by the 70-80 Hz oscillation due to degradation of the buildup power. However, after today's work, no glitches are seen in the error/feedbacks. Finally, Fig, 11 shows the coherences between the buildup power and ITMY oplev. Solid lines show the one after today's work, dash lines show before the work. I succeeded in reducing the coherence between buildup and ITMY Y motion.

Thanks to this, DRMI seems to become more stable than before.

[Aritomi, Hirose, Tanaka(remote)]
This work is continued from klog37320.

Summary

Following the previous investigation, we measured the optical power in front of the QPDs at the REFL, POP, and AS ports. We also investigated the cause of the QPD2 YAW PZT issue at the AS port and measured the optical power budget along the AS optical path.
We performed this measurement during the DRMI, but we haven't yet calibrated the power coming into the REFL, POP, and AS ports.

Result

REFL port

The optical power in front of each WFS was measured as follows:
 

A beam dump had been placed in front of WFS3. We removed the dump and instead installed a beam dump to absorb the reflection from the QPD.

By steering BS PZT1, we confirmed that the optical power toward the WFS1 and WFS2 directions was nearly identical.

POP port

The measured optical power was as follows:

The dark level, measured by blocking the beam, was approximately 0.09 μW.

AS port

During the previous investigation, the QPD2 YAW PZT actuator did not respond.

The actuator configuration is

• 3-channel PZT driver outputs → SMA cables → REMO cables → mirror mounts for QPD1 PIT, QPD1 YAW, and QPD2 PIT
• 1-channel PZT driver output → SMA cable → REMO cable → mirror mount for QPD2 YAW

We performed a series of cable and driver swap tests to identify the faulty component.

• The 1-channel PZT driver connected to the QPD2 YAW actuator showed only "3 V", indicating an abnormal condition.
• Connecting the PIT cable to the 1-channel driver resulted in approximately "75 V", confirming that the 1-channel driver itself is functioning properly.
• Connecting the YAW cable to the 3-channel driver still resulted in "3 V", suggesting that the problem is located downstream of the YAW cable.
• Connecting the YAW cable to the mirror mount PIT caused the PZT driver output to change normally, indicating that the cable is not faulty.
• Finally, connecting the PIT cable to the mirror mount YAW still resulted in "3 V", confirming that the mirror mount YAW actuator is faulty.

Therefore, the QPD2 YAW problem was identified as originating from the mirror mount YAW actuator rather than the PZT driver or cables.

The measured optical power at the AS port was
 

A half-wave plate (HWP) is installed upstream of the AS QPD path. Considering the measured power at the QPDs, especially the low power at AS QPD2, the current HWP angle may be reducing the power sent to the QPD path too much. We should first recalculate the expected optical power at the AS port when the BS is misaligned. Based on the calculated power, the optimal HWP angle should be reconsidered to provide sufficient power to the QPDs while maintaining an appropriate power distribution to the other AS port photodetectors.

In addition, Tanaka-san measured the dark offset of the digital output for the AS port PD2 and updated the digital offset value accordingly. This calibration removes the DC offset of the PD2 signal and provides a more appropriate baseline for subsequent measurements and control.

Next step

• Perform the calculation and comparison of the measurement result.
• Insert the calibration(cnt->mW) on AS PDs.
• Replace the faulty mirror mount YAW actuator for AS QPD2.
• Perform the DC centring loop for REFL QPD3
• Measure the sensing matrix for WFS on DRMI

Hirose, Tanaka

DRMI LSC oscillated at 70-80 Hz whenever POP90 and AS34 power decreased.

In pararell of Hirose-san's work in klog37320, I looked into the trend of build up sideband powers and the oplev signals. Fig.1 shows the time series of the build up sideband power (K1:LSC-POP_PDA2_R90_I_ERR_DQ, K1:LSC-AS_PDA2_R90_I_ERR_DQ), and mirror oplevs' signals (K1:VIS-{IMMT2,PRM,BS,SRM}_TM_WIT_{L,P,Y}_DQ). The drop rate of build up power seems to be about 0.1 Hz. It seems to be close to the Type B IM YAW resonant frequency. According to the time series, ITMY, SRM and BS seems to oscillate at around 0.1 Hz

I measured the coherences between POP90/AS34 power fluctuations and mirror alignment fluctuations. Thanks to the stable lock of DRMI, (almost 3 hours), we could measure it with long time. Fig. 2 shows the result. There seems to be large coherences around 0.1 Hz between AS34 and ITMY L, Y, SRM Y, PRM P, Y, IMMT2 P. Basically, SRM, PRM, IMMT2 are controlled by ADS. So it maybe fine. On the other hands, ITMY seems to has larger coherence than ITMX. So we need suppress the ITMY Yaw motion.

There seems to be some concerns. 

1. coherence around 1-2 Hz between PR3 alignments and AS34. I'm not sure of the reason why PR3 alignment has coherence with only AS34. One of the possiblities is the SRCL alignment is not good rather than the PRCL alignment.
2. the coherence around 0.2-0.3 between SR3 and AS34.
3. coherence peak around 0.45 Hz between AS34 and PR mirrors' motions and BS L (Type Bp resonant?)
4. broad coherence bump from 7 Hz to 70 Hz between PRM L and AS34 (PRCL control?)

Anyway, we need to modify the suspensions' local controls

[Aritomi, Tanaka, Hirose]

This work is a continuation of klog37318. We try to perform WFS for DRMI. So we start the preparation for WFS.

Our goal is to improve the alignment by switching the alignment control from ADS to WFS while the interferometer is in the DRMI1f lock state (with ADS IMMT2, PRM, SRM).

As a preparation for the WFS commissioning, we introduced dark offsets for the DC, I, and Q signals of the WFS QPDs. The applied offset values are summarized in Fig. 1-4.

After introducing the offsets, we enabled the DC centering loops(Fig. 5).  We created the ENGAGE_WFSDC_DRMI" state pathing DRMI ADS on the ASC_LOCK guardian. However, the error signal of AS_QPDA2 Yaw showed no response to the PZT feedback, suggesting that the signal path may not be properly connected. In addition, REFL_QPDA3 appears to receive little or no light.

We also performed a rough excitation of the BS to obtain preliminary responses.(Fig. 6)

For the next session, we will first check the cabling of AS_QPDA2 Yaw and REFL_QPDA3, and then repeat the measurements after confirming that the signals are properly connected.

## Summary of 2026.07.31 and 2026.08.04 works

(2026.07.31)

We redesigned ADSs for DRMI. First, we decided the dither frequency in order to solve the degeneracy betwen other DoFs. We prepared the frequency set per 2 Hz, which is above 1 Hz, typical suspension's resonant frequency, 4.125, 6.125, ...., 30.125, 32.125 Hz. This is because we want to see the sideband from alignment fluctuation until 0.5 Hz around one dither frequncy. So it is necessary to set the frequncy interval between each dither frequency which is used as PIT and YAW of one mirror.

Then, we measured the spectra of POP90 and AS34 with no exciations to look for the frequency region, which the only noise floor is in. There are some peak in the region from 14 Hz to 20 Hz in POP90. From this results, we decided the frequencies for ADSs as below. This time, we decided to use POP90 for PRM, BS, IMMT2 dithering and to use AS34 for SRM dithering.

• BS PIT: 22.125 Hz, YAW: 24.125 Hz
• PRM PIT: 4.125 Hz, YAW: 6.125 Hz
• SRM PIT: 26.125 Hz, YAW: 28.125 Hz
• IMMT2 PIT: 30.125 Hz, YAW: 32.125 Hz

We implemented the bandpasse filter at each corresponded frequency to K1:ADS-{PIT,YAW}_{IMMT2, PRM, SRM, BS}_DEMOD_SIG filter bank. and performed the phasing for each signal from alignment dither. This time, we decided the dither amplitude so that the sidelobe around the dither frquency could be seen largely enough.

After that, we implemented the 1.5 Hz cutoff lowpass filter, comb filter for corresponding frequency and its harmonics, and 2 Hz notch for the beat note between PIT and YAW in K1:ADS-{PIT,YAW}_{IMMT2, PRM, SRM, BS}_DEMOD_SIG_I, which is a filterbank for a demodulated signal.

Then, we tried to engage ADSs. PRM seems to work because POP90 increased and there seems to be harmonics of diter frequency, 8.25 Hz and 12.25 Hz in POP90. IMMT2 and SRM seems to work but their harmonics could not be seen in POP90 and AS34, respectively.

On the other hands, BS ADS seems not to work. ADS loop itself can be close but the POP90 and AS34 power decreased on engaging ADS.

During the work, we modified the ENGAGE_ADS_FOR_DRMI in order to engage current ADSs except for BS (I hope Hirose-san will report soon).

(2026.08.05 work)

In daytime, DRMI lock was too unstable to proceed the ADS. We suspected the seismic motion around 0.1 Hz disturbed the lock because the 0.1 Hz seismic motion got 1- order larger than the one in last Friday (klog37313) and BS and SRM IM YAW motion at 0.14 Hz, which is IM YAW resonant frequency, seems to become 1-order larger due to the large micro seismic. We implemented the resG filter for 1.4 Hz of FM5 in K1:VIS-BS_TM_OLDAMP_YAW, which was already implemented. It seems to reduce the Yaw motion at 0.14 Hz. However, DRMI lock was still unstable.

We observed two kinds of lock loss pattern in daytime. One is the oscillation at 20-30 Hz. Sometimes, DRMI LSC began oscillated at some frequency between 20-30 Hz. We measured the OLTFs. But the phase margins around their frequncies of DRMI LSC loop seem to be large enough even if the only overall gain was changed by some reasons. So something might change not only gain but also the phase of loop. Moreover, this oscilltion kicked the ADS, especially IMMT2 and SRM because their dither frequencies are close to oscillation frequencies and this kick changed the alignment them largely and often made the relock difficult.

Another pattern is the sudden lock loss. Sometimes, POP90 and AS34 dropped to 0 within less than 1 second. At that moment, any alignment seem to be not changed

In night time, DRMI lock seemed to become stable for some reason. Especially, DRMI was stable without ADS rather than with ADS. I attempted some trials to improve the stabilty, inclunding to review of ADSs.

• Decoupling the PRM motion from MICH error signal.
  • As reported in klog, I tried to decouple the PRM length motion from the MICH error signal with the same procedure of PRM-to-SRCL. I remeasured the MICH eror signal response when PRM length displacement was excited, including to the reprocebility of the check of PRM-to-SRCL decoupling factor.
  • I applied the obtained decouplig factor for PRCL-to-MICH but it seems not to work.
  • I also confirmed the decoupling factor of PRM-to-SRCL seemed to be almost the same. It seems to be good.
• Review of DRMI ADS
  • Since DRMI was stable without ADS rather than ADS, I reviewed the ADS
    • PRM
      • If PRM actuators is not optimized in terms of eular DoFs or if the beam spot on PRM is off from the center, the alignment excitation couples to length motion. On the other hands, if cavity length is tuned, this length motion should not be seen at the dither frequency. But if not so, the length fluction also contaminates in the alignment signal. Current DRMI lock is performed with some offsets in their error signals. But these offsets are not optimized. Therefore, I started to check whether the cavity length tunes or not by exciting the length.
      • I excited the PRM L displacement from K1:VIS-PRM_TM_ISCINF_L_EXC at the PRM PIT dither frequency, 4.125 Hz. Although PRCL control UGF is ~30 Hz, I could see the length excitation in POP90 and PRCL error signal. In this state, I changed the PRCL1 offset from -4.7 by 0.5 step. When the offset value was 0, the peak of PRM Length excitaiton disappeared from POP90 though it was in the PRCL error signal.
      • In this state, I switched the excitation from length to alignments and performed the phasing for PRM ADS again. Also, I found that the CLKGAIN = 30 cnts seems to be large enough to see the sidelobe. The phase seems to be almost the same. By the way, I tried to implement the resG filter for dither frequency in PRCL but the phasing is not changed.
    •  IMMT2
      • Also, as for IMMT2,  I performed the phasing. Before this, I found that there was the small peak at 30 Hz in POP90 without excitation. So I changed the PIT dither frequency from 30.125 Hz to 34.125 Hz. As for YAW, the domod phase was not changed so much (~several degrees)
    • I implemented ADSs of PRM and IMMT2 after re-phasing Then, POP90 are slightly improved (fig.1). The harmonics peaks of PRM dither frequencies (PIT -> 8.25 Hz, Yaw -> 12.25 Hz) also got slightly bigger (fig.2). 
    • SRM
      •  As Aritomi-san and Yokozawa-san already reported in klog37315, SRM phasing value seems to be not reproducibiltiy, the phase easily changed more than 90 degrees. 
      • I implemented the resG filter for SRM dither frequencies in the SRCL loop but the situation seems to be not changed.
      • Also, I tried to tune SRCL as the same procedure of PRCL but the AS34 fluctuation seems to be too large to adjust the offset.

During ADS work, we found that there was no anti-aliasing filter in AS34 and there was also no lowpass filter in normalization filter. we implemented them. (klog37314) 

### Next

• investigate SRM and BS ADS good configuration
• (give up ADS and move to WFS for DRMI?)

We measued the current TM coils' status with the health check script. Fig.1,2,3,4 show the results. They seem to be healthy compared with 2024.Dec. results by Takahashi-san in klog31919.

## (2026.08.05 early moring work)

I tried to implemented the subtraction of the PRM motion from the MICH error signal accoriding to the previous work in the original post.

The PRM coupling in MICH from of fig. 2 in original post is 0.45 (180 deg). However, the coherence seems not to be good, less than 0.7 unlike the PRCL-to-SRCL case. Anyway, I implement the value -0.45*10*(-1, phase =180 deg) as LSC_INPUT_MTRX. Also, the offset value in MICH1 was adjusted, -7.5 +4.7/10*4.5 = -9.6. In this situation, we can lock DRMI but the MICH error signal spectra and coherence MICH-to-PRCL seems to be not changed. So it seems not to work.

[Kenta, YamaT]

This is yesterday's work.

Add 16kto2k filter for AS34 at PD filterbank
When we checked all RF PDs to trace the signal path for the future calibration work, we found POP90 has "16kto2k" filter at FM9 of PD filterbank but AS34 doesn't. These two PDs are used for power normalization in LSC and the reference signal of ADS. Sending AS34 without AA filter to 2kHz ADS model makes aliasing noise on the error signal of ADS, so we added same "16kto2k" filter at FM9 of AS34 PD filterbank. According to the comparison plot of AS34 signal with and without AA on k1ascads, AA filter makes ~2 times improvement of noise floor around 30Hz (near dither frequency). Orange curve in Fig.1 represents original AS34_I on k1lsc. Green and blue curves represents AS34_I on k1ascads with and without AA filter, respectively. Note that, blue curve (without AA) is simulated one with original signal and offfiline signal processing (simulated filterbank, phase rotation, power normalize and decimation) because there is no proper DQ channel on k1ascads for checking aliasing noise and I forgot to take a spectrum data befor applying AA.

Add LP1 before power normalization of error signals
We also noticed MICH and SRCL error signal were divided by raw (non-lowpassed) AS34_I as the power normalization. (PRCL error signal is divided by low-passed POP90_I.) Since this implementation seemed to simply introduce noise derived from high-frequency components, we also added "LP1" filter (same as POW_NORM_POP90_I_FILT) at FM1 of POW_NORM_AS34_I_FILT.