Since this tool processes real-time data via NDS, it allows us to apply filtering and arithmetic operations to the signals without affecting the actual control loop.
> /kagra/bin/ndscope-filter channel --corner f1 [f2]
can apply simple butterworth LPF, HPF (giving negative value for f1), or BPF to the channel as shown in Fig.1.

> /kagra/bin/ndscope-filter channel
(without --corner option) can apply any filter made by foton using the usual MEDM filter bank interface as shown in Fig.2. (At typing above command, viewer window, foton window, and MEDM screen are launched simultaniously.)

Since this interface uses dummy foton file (/tmp/ndscope-filter/*.txt) to generate filters and dummy EPICS channels (K2:***) for operation filterbank MEDM, so this mode also doesn't affect the real the real-time system (strictly speaking, DAQ load is increased when TPs are used).


By giving the secondary (A2) and subsequent (N1, D1, N2, and D2) channels, this tool can also provides
channle * N1 / D1 + A2 * N2 / D2
for the signals from each channel after filtering (channels not given are treated as 0.0 or 1.0 for A2 depending on D2 and 1.0 for others). It appears that setting the filter gain to a negative value allows for all four arithmetic operations.

Note that,
1) Different sampling rate between given channels makes run-time error because re-sampling function hasn't been prepared.
2) Both DQ and TP channels can be used but it may not work well for DQ channels that sampling rate are different from the model rate.

Fujimoto, Tanaka, Komori(remote)

We performed the sensor diagonalization check between L and others by oscillating IP L at 0.02 Hz. This time, SRM was in the PAY_FLOAT state. Then, we excited IP L by injecting sine wave at 0.02 Hz into setpoint of the IP L DC control (K1:VIS-SRM_IP_SET_L_EXC). We measured the spectra of TM oplevs and TFs from IP L DC control feedback to TM oplevs (fig.1). There seems to be a 0.02 Hz peak only in the L oplev. And the relative gain between L and P seems to be less than 0.1. Therefore, the L sensor seems to be well diagonalized.

Actually, we already measured the TFs from P (or Y) to others at P (or Y) resonant frequncies (P:~0.8 Hz, fig.2 and Y:~1 Hz, fig.3). According to these results, the coupling from P(Y) to L or the coupling from P(Y) to Y(P) seems to be several percentage or less. So they seems to be well diagonalized.

After that we performed coil balances between TM coils with these sensors. We followed the same procedure as klog36229. First, we balanced the coils H1 and H4 by decreasing Y motion first (fig.4), and the coils H2 and H3 second, then the pair H1 and H4 and the pair by decrasing P motion (fig.5). Fig. 6 shows each coil gain after the balance.   

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. 

[Tanaka, Komori, Fujimoto]

Abstract

We measured the PRX length using the TOF technique with the PRMI in the carrier-resonant configuration.
An unexplained 180-deg flip was observed in the measured optimal demodulation phase.
Although the origin of this flip is still unknown, assuming and correcting for this 180-deg offset gives the following result, which is consistent with the measurement by Saito-kun:

• L_{PRX} (this measurement): 68.254(13) m
• L_{PRX} (Saito-kun’s result: klog #37260): 68.26307(11) m
• L_{PRX} (design value): 68.2563 m
   

Details

In the previous PRX measurement using the TOF method (klog #37244), the PRMI was operated in a configuration where the carrier was anti-resonant and the f2 sidebands were resonant.
In this configuration, if the f2 modulation frequency deviates from an integer multiple of the PRCL FSR, the upper and lower f2 sidebands become detuned from the PRCL resonance.
This detuning rotates the demodulation phase and therefore introduces a systematic error in the TOF measurement.
To avoid this effect, we changed the PRMI configuration such that the carrier was resonant and the f2 sidebands were anti-resonant, and measured the PRX length using the TOF technique.

Modifying the VERTEX guardian for carrier-resonant PRMI

We modified the PRMI_1F_LOCKED state of the VERTEX guardian so that the PRMI could be locked in the carrier-resonant configuration.
The following changes were made:

• The sign of the PRCL gain was flipped.
• The magnitudes of the PRCL and MICH gains were adjusted.
• The lock check for PRMI_1F_LOCKED was changed to POP DC.

Fig. 1 shows screenshots of the lock behavior and the filter settings.

Optimal demodulation phase for carrier-resonant PRMI

We measured the optimal demodulation phase of the carrier-resonant PRMI using the same code as in the previous measurement with the sideband-resonant PRMI (klog #37244).
The PD used for the measurement was REFL PDA3 45.

Fig. 2 shows the measurement result. The obtained optimal demodulation phase was

• Optimal phase for carrier-resonant PRMI: 225.8(14) deg

For reference, the results from the previous sideband-resonant measurement are also listed below:

• Optimal phase for sideband-resonant PRMI: 117.80(52) deg
• Optimal phase for XARM: 230.140(48) deg

Data analysis and resulting PRX length

Let the optimal local oscillator for the carrier-resonant PRMI be

$\cos(\omega_\mathrm{m}t+\phi_\mathrm{PRMI})$

where $\phi_\mathrm{PRMI}$ is the optimal demodulation phase.
The optimal local oscillator for XARM is then

$\cos(\omega_\mathrm{m}t+\phi_\mathrm{XARM}) = \cos\left( \omega_\mathrm{m}t+\phi_\mathrm{PRMI} -\frac{2L_\mathrm{PRX}\omega_\mathrm{m}}{c} \right)$

so that the optimal phase changes by the phase accumulated over the PRX round-trip length.
In this measurement,

$\phi_\mathrm{PRMI}=225.8\pm1.4\,\mathrm{deg}$

and

$\phi_\mathrm{XARM} \equiv230.140\pm0.048\,\mathrm{deg} \quad (\mathrm{mod}\, 360\,\mathrm{deg})$

Taking into account the current f2 modulation frequency: f2=8*5.624365513 MHz, and the design PRX length L_PRX=68.2563 m, we expect

$\phi_\mathrm{XARM} = \phi_\mathrm{PRMI} -360\times20.49\,\mathrm{deg} \equiv \phi_\mathrm{PRMI}-176.4\,\mathrm{deg} \,(mod\,360\,\mathrm{deg})$

However, the measured result differs from this expectation by approximately 180 deg.
This discrepancy is much too large to be explained by an actual cavity-length error.
Furthermore, introducing an additional 180-deg correction makes the measurement agree well with the design value.
Therefore, it appears that an unexplained 180-deg phase flip is present somewhere in the measurement.
A Finesse simulation is discussed later in this klog, but the origin of this 180-deg flip could not be identified in the simulation either.

*In the following analysis, we therefore assume that an additional 180-deg phase flip is present for some unknown reason.
With this assumption,

$-\frac{2L_\mathrm{PRX}\omega_\mathrm{m}}{c} = (230.140(48)\,\mathrm{deg}-180\,\mathrm{deg}) -225.8(14)\,\mathrm{deg} -360\times20\,\mathrm{deg}$

which gives

$L_\mathrm{PRX}=68.254(13)\,\mathrm{m}$

Comparison with other results

The obtained PRX length is compared with the design value and Saito-kun’s result below:

• L_{PRX} (this measurement): 68.254(13) m
• L_{PRX} (Saito-kun’s result: klog #37260): 68.26307(11) m
• L_{PRX} (design value): 68.2563 m

These results are mutually consistent within the measurement uncertainties.

Finesse simulation

To investigate the unexplained 180-deg flip observed in this measurement, we first considered the possibility of an error in the analytical calculation.
We therefore simulated the optimal demodulation phases for the PRMI and XARM using Finesse and compared the results.
The design values were used for the cavity lengths and mirror reflectivities, and the current modulation frequency,f2=8*5.624365513 MHz, was used.
For the PRMI simulation, an effective ITM reflectivity of 0.85 was used to account for the birefringence of the ITM substrates.

The results are shown in Fig. 3. In the Finesse model, the RFPD was placed at the position of the EOM. Therefore, the absolute demodulation phases differ from those in the experiment. However, this does not matter here because only the relative phase difference is relevant.

The optimal demodulation phases obtained from the Finesse simulation were:

• XARM: 75.978 deg
• PRMI (carrier resonant): 252.299 deg
• Relative difference: -176.321 deg

Thus, as expected from the analytical calculation, the relative phase difference is approximately 180 deg.
Therefore, it is still unclear why the experimental result appears to contain an additional 180-deg flip.

In addition, the PRX length calculated from the relative phase obtained in the simulation is 68.2597 m, which differs by approximately 3.4 mm from the design value of 68.2563 m used in the simulation.
This difference is likely caused by the demodulation-phase shift arising from the fact that f2 is slightly detuned from the exact anti-resonance condition of the PRMI.
A systematic error of approximately this magnitude is therefore also expected to be present in the experimental result.

Summary and future work

In this TOF measurement using the carrier-resonant PRMI, an unexplained 180-deg phase flip was observed.
After applying a 180-deg correction, however, the resulting PRX length was consistent with Saito-kun’s result.
The precision of this method is much worse than that of Saito-kun’s beat-note measurement using an auxiliary laser.
In addition, applying the TOF method to the SR side is difficult. Therefore, there does not appear to be a strong need to continue this measurement at present.
If we want to further validate this measurement method, performing the same measurement for PRY would be a useful next step.
 

Komori, Fujimoto, Tanaka

We found that the IRX TRANS value (K1:LSC-TR_IRX_NORM_OUT_DQ) seems to be not zero, -0.1 when the PD was dark. Due to this, IRX power reached only 0.9 even though Xarm ADS was engaged during INITIAL ALIGNMENT. We measured the dark offset and subtracted it  by inserting the measured offset in K1:TMS-X_IR_PDA1_OFFSET. Then, we confirmed IRX power could reach almost 1 after Xarm ADS was engaged.

Also, Komori-san checked the beam spot on optics in the IR PD path on TMSX in this moring. According to him, all of beam spot on optics in the path seems to be each center of each optics.

After that, we centered the IR camera.

Komori, Fujimoto, Tanaka

We tried to improve the stability of DRMI 3F lock. Current DRMI 3f signals (maybe MICH?) seems to has a very narrow linear range. Due to this, if build up powers fluctuate by fluctuating length or alignment, it causes the lock loss. And also the good offset value seems to be changed by the alignment for some reasons. Therefore, obtaining and maintaining good alignment is necessary to keep the 3f lock for a long time.      

## What we did

Currently, DRMI 3f lock duraion seems to become short, at most several ten seconds. We observed a specific phenomenon before the lock loss that the AS34 and POP90 dropped suddenly and error signals moved largely. Fig 4 is one of examples on lossing the lock. We confirmed that we can hand over the 3f signal from the 1f signal for 1 DoF. Also we could handed over the 3f signals of PRCL and MICH at the same time. However, if we handed over the 3f signals to the 1f signals for SRCL and either one of other two, the sudden drop happens. So we assumed the coupling in 3f sensors between SRCL and others seems to be large. we moved the decoupling.

### Decoupling DRMI 3f sensors

First, we tried to subtract the PRM motion from SRCL and MICH 3f sensors. We measured the 3f sensors' responses when PRM was excited with the same manner in klog37312. We applied for LSC-{CARM,XARM,YARM}_IN1 as 3f sensors of PRCL, SRCL, and MICH, respectively. Fig.1 shows the ratio between PRCL1 and 3f sensors (CARM, XARM, YARM). the ratio between PRCL 1f and SRCL and MICH 3fs seems to become smaller than the one between PRCL 1f to PRCL 3f.  From the results, we obtained the matrix like Fig.2. And Fig.3 show the spectra of each sensor and coherences among them. There seems to be lower coherences of 3f sensors from 10 Hz to 100 Hz. 

### lock loss investigation

We used these decoupled sensors to lock DRMI 3f. The situation became slightly better. We can hand over the 3f signal from the 1f signals of PRCL and MICH /SRCL maybe thanks to this. However, we could not handed over the 3f signals of MICH and SRCL at the same time. According to this results, we assumed that some or all error signals has narrow linear range.

We swept the offset of the 3f signals one by one when we handed over the only one 3f signal to estimate the range roughly. We obtained the center value of the range and applied the value for the setpoint. Then, we tried to 3f locked. but the situation was not changed.

At last, Fujimoto-kun found that the MICH offset, which makes AS DC power minimum seems to be better. In this offset, 3F lock kept ~30 mins.  

### reproducibility of the offset

Next day, we tried to lock DRMI with 3f with the same offsets which were found by Fujimoto-kun. However, we failed the lock. And we found that MICH offset seems to be changed by the alignment, especially SRM.  Therefore, we need the method to obtain and maintain good alignments.

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?)