Fujimoto, Tanaka

We also performed the MICH actuator diagonalization by using 1f sensors with the same procedure as 3f sensors in klog37352, in order to check whether the diagonalization value by 1f sensors become the same as the value by 3f sensors. This time, we did not perform the 1f sensor diagonalization before the actuator diagonalization.

The values are summarized as below

• MICH to PRM: 0 -> -0.0425
• MICH to SRM: 0 -> 0.25
• MICH to BS: 1 (unchanged)

Also, we compared these ratios with the ratios of the actuator effeciecies measued by Length OPLEVs. According to suspensions' plant models in FM10 of {PRM,SRM,BS}_TM_OLDAMP, the actuator effieciencies @ 100 Hz are as below,

• BS @ 100 Hz: -171 dB (According to the model, the efficiency of BS is -168 dB. Since the BS is oriented at 45 degrees to the optical axis, its contribution to the optical path length is changed by a factor of 1/sqrt(2), corresponding to -3dB. Thus, the effective efficiency in terms of MICH is -171dB @ 100 Hz.)
• PRM @ 100 Hz: -143dB
• SRM @ 100 Hz: -157dB

From above the efficiecies, the ratio between BS and PRM efficiencies is -143dB - (-171dB) = 28 dB. The diagonalization ratio between BS and PRM is also 20*log10(1/0.0425) = 27dB. They seem to be almost consistent. Similarly, the ratio between BS and SRM efficiencies is -157dB - (-171dB) = 14 dB. The diagonalization ratio between BS and SRM is also 20*log10(1/0.25) = 12dB. They have 3dB discrepancy. 

We input these values in LSC OUTPUT MTRX and these value are implemented by the VERTEX guardian if the guardain are requested to DRMI_1F_LOCKED.

[Hirose, Tanaka, Ushiba, Komori (remote), Fujimoto]

Abstract

We performed the MICH diagonalization for the DRMI 3f lock again, this time with the POP17I removed from the MICH signal.
The OLTFs were still clean by the MICH diagonalization, but the lock duration was only a few minutes, unlike the previous lock.

Further investigation is necessary to understand the cause of the short lock duration.
Possible causes are:

• Interferometer misalignment (reproducibility may be improved by implementing the ADS loops for SRM and BS)
• Mis-diagonalization of MICH

Details

As Yokozawa-san pointed out, in the previous MICH diagonalization work (klog #37352⁠), POP17I was mistakenly sent to MICH with a factor of 2.06500.
This time, we turned off this POP17I path and performed the MICH diagonalization using only the 3f signals.
Since the procedure was the same as before, please refer to the previous klog for the details.

Removal of PRCL coupling

We excited PRM in the length direction above the control bandwidth and removed the PRCL signal from MICH and SRCL.
Fig. 1 shows the peaks after reducing the coupling from PRCL.
The factors were changed as follows.

• REFL135I_to_MICH: -1.38 ⇒ -1.139
• REFL135I_to_SRCL: 0.705 ⇒ 0.65

The coupling to MICH was reduced by about a factor of 4, and the coupling to SRCL was reduced by about a factor of 5.
These values were implemented in the guardian.

Removal of SRCL coupling

In the same way, we excited SRM above the control bandwidth and tried to remove the SRCL signal from PRCL and MICH.
However, as in the previous measurement, the coupling from SRCL was already sufficiently small, as shown in Fig. 2.
Therefore, we did not perform any further coupling reduction for SRCL.

Diagonalization of the MICH actuator

Fig. 3 shows the spectra when we diagonalized the MICH actuator by combining BS, PRM, and SRM.
The reference traces show the spectra when only BS was excited.

The OUTPUT_MTRX values to BS, PRM, and SRM used in this adjustment were as follows.

• BS: 15
• PRM: -0.61
• SRM: 5.35

With this adjustment, the coupling to SRCL was reduced by about a factor of 10, and the coupling to PRCL was reduced by about a factor of 80.

Using the ratios obtained here, we changed the MICH actuator settings in the OUTPUT_MTRX of LSC_OVERVIEW as follows.

• MICH_to_PRM: 0 ⇒ -0.04066
• MICH_to_SRM: 0 ⇒ 0.3566
• MICH_to_BS: 1.0 ⇒ 1.0 (unchanged)

These values were also implemented in the guardian.

OLTFs

After the sensor and actuator diagonalization described above, we measured the OLTFs of MICH, PRCL, and SRCL, and adjusted the overall gains.

Figs. 4, 5, and 6 show the OLTFs of MICH, PRCL, and SRCL after the gain adjustment, respectively.

The current overall gains and filters are as follows.

• MICH1 gain: 2.1 ⇒ 9.0
• PRCL1 gain: 2.0 ⇒ 2.0 (unchanged)
• SRCL1 gain: 1.4 ⇒ 2.0
• MICH2 roll-off: ELP500 ⇒ ELP100

As in the previous measurement, the OLTF shapes themselves were clean, and the strange-shape problem seen without the diagonalization was again resolved.

In addition, since the MICH output tended to be close to saturation, we changed the roll-off filter from ELP500 to ELP100 to reduce the RMS of the output.

Lock duration

Although the OLTFs were as clean as those obtained in the previous measurement, where POP17I was mixed into MICH, the lock duration was only a few minutes.

The cause of the short lock duration is still unclear, and further investigation is necessary.
Possible causes include:

• Mis-diagonalization of the sensors and/or actuators
• Strong dependence of the lock duration on the interferometer alignment (Currently, the ADS loops for SRM and BS have not yet been implemented for DRMI, so the alignment reproducibility is not good.)

The first possibility is briefly discussed below.

Discussion

Possible mis-diagonalization of the sensors and actuators

In this measurement, the following OUTPUT matrix elements were obtained as a result of the MICH actuator diagonalization.

• MICH_to_PRM: -0.04066
• MICH_to_SRM: 0.3566
• MICH_to_BS: 1.0

On the other hand, according to the suspension model checked by Ushiba-san, the actuator efficiencies at 100 Hz are:

• PRM: -143 dB
• SRM: -157 dB
• BS: -168 dB

From these values, the theoretically expected absolute values of the MICH actuator factors, including the correction for the 45-degree angle of BS, are:

• MICH_to_PRM (model): 0.0398
• MICH_to_SRM (model): 0.200
• MICH_to_BS (model): 1.0

The measured MICH_to_PRM factor is roughly consistent with the model prediction.
However, the measured MICH_to_SRM factor is about 1.8 times larger than the model prediction.

One possible reason is that the demodulation phase of REFL51I/Q was not well tuned, and the MICH signal leaked into REFL51I.

Therefore, it may be useful to assume that the values from the suspension model correctly produce a pure MICH actuator, and then use this actuator to phase REFL51I/Q. 

Plan for tomorrow

One possible plan is to implement the ADS loops for SRM and BS in DRMI in order to improve the alignment reproducibility.
This will help us check whether the lock duration depends strongly on the alignment.

Also, as mentioned in the discussion above, it may be useful to construct a pure MICH actuator using the theoretical values from the suspension model, or using the length oplev signals as suggested by Ushiba-san.
Then, we can use this pure MICH actuator to determine the sensor diagonalization.

[Shaojin, Washimi]

Today we finished the masurement at the X-end outside, and cleaned up out setup.

After that, we moved them and started at Mozumi area.

A check of package/module dependency for user Guardian codes on the new Guardian server was finished.
I'll be probably able to migrate the new server in next time.

-----
All user codes in userapps/release/*/{k1,common}/guardian/*.py were checked on the new environment.
- Some minor fixes in SyntaxError/Warning in Python3.13 were applied.
- Some missing packages/modules were newly installed on the new server.
- VIS_* Guardians were able to reach LOCK_ACQUISITION state.
- IO guardian was able to reach PROVIDING_STABLE_LIGHT state.
- Guardian nodes not directly related to IFO control e.g. SYS_* worked fine.

Hopefully, the Guardian server will be able to be migrated to the new system in next time

BTW, don't leave unnecessary codes in userapps/release/*/{k1,common}/guardian/.
Especially, don't put LIGO's user codes in {k1,common}.
Make {l1,h1} directory and put there, if you need LIGO's code as a reference.

I lost few hours to run common/guardian/OMC_LOCK.py which seems old H1 OMC guardian code.
Additional unnecessary packages to operate it became not to be removed from the new system due to dependency hell.
Maybe it's easier to re-install OS than to solve dependency hell for cleaning up unnecessary settings.
It's just an only reason why I couldn't complete the Guardian server migration today.

Thank you for your comment.
And I’m sorry, this is a mistake.

I think I probably forgot to remove this value after trying the 1f decoupling.
I checked and found that this value was also present during the 3f diagonalization, so redoing the diagonalization is necessary.

Fortunately, POP17I, rather than POP17Q, was being sent to MICH, so it does not seem that MICH was being locked with the 1f signal.

Abstract

For the DRMI LSC, I reduced the coupling from PRCL to the MICH signal and diagonalized the MICH actuator.
As a result, the strange shape of the 3f OLTFs reported previously was resolved, and cleaner OLTFs were obtained.
The lock duration was also improved, and the 3f lock was maintained for more than 11 hours (still locked now).

These settings have not yet been implemented in the guardian. I plan to implement them after they are reviewed by other commissioners.

Details

In the previous DRMI 3f lock, as reported in klog #37346⁠, the shapes of the PRCL and MICH OLTFs after the transition to 3f were strange.
This suggests that there was coupling between the degrees of freedom.
Therefore, for the DRMI 3f lock, I performed sensor diagonalization and actuator diagonalization and also adjusted the gains of the OLTFs.
During this 3f lock, the ADS loops for BS and SRM were turned off.

Removal of PRCL coupling

After locking the DRMI with the 3f signals, I used OSC1 in LSC_OVERVIEW with the following settings and excited PRM in the length direction above the control bandwidth.

• Amplitude: 6000
• Frequency: 230 Hz
• Injection point: PRM

In this state, I checked the peaks in the spectra of the PRCL, MICH, and SRCL error signals.
Then I adjusted the factor applied to REFL135I when constructing the MICH and SRCL signals, in order to remove the peaks.

Fig. 1 shows the peaks after reducing the coupling from PRCL. The factors were changed as follows.

• REFL135I_to_MICH: -1.38 ⇒ -0.75
• REFL135I_to_SRCL: 0.705 ⇒ 0.705 (unchanged)

The coupling to MICH was reduced by about a factor of 7, while the coupling to SRCL could not be reduced further.

In addition, especially for SRCL, the coupling seemed to have some alignment dependence.
In some cases, the coupling slightly increased as shown in Fig. 1, even though the factor was not changed.

Removal of SRCL coupling

In the same way as above, I excited SRM above the control bandwidth and tried to remove the SRCL signal from PRCL and MICH. However, as shown in Fig. 2, the coupling from SRCL was already sufficiently small.
Therefore, I did not perform any further coupling reduction for SRCL.

Diagonalization of the MICH actuator

Previously, only BS was used as the actuator for MICH. However, this also moves PRCL and SRCL.
Therefore, I adjusted the actuation so that only MICH is driven by moving PRM and SRM together with BS.

Specifically, I used OSC1 in LSC_OVERVIEW to drive BS, PRM, and SRM, and adjusted the factors so that the excitation appeared only in the MICH error signal.

The three reference traces in Fig. 3 show the spectra when only BS was excited with an amplitude of 6000 × 15.
The first three traces in the legend show the spectra after the factors were adjusted.

The OUTPUT_MTRX values from OSC1 to BS, PRM, and SRM used in this adjustment were as follows.

• BS: 15
• PRM: -0.6
• SRM: 5.1

With this adjustment, the coupling to SRCL was reduced by about a factor of 5, and the coupling to PRCL was reduced by about a factor of 50.

Using the ratios obtained here, I changed the MICH actuator settings in the OUTPUT_MTRX of LSC_OVERVIEW as follows.

• MICH_to_PRM: 0 ⇒ -0.04
• MICH_to_SRM: 0 ⇒ 0.34
• MICH_to_BS: 1.0 ⇒ 1.0 (unchanged)

OLTFs

After the sensor and actuator diagonalization described above, I measured the OLTFs of MICH, PRCL, and SRCL, and adjusted the overall gains.

Figs. 4, 5, and 6 show the OLTFs of MICH, PRCL, and SRCL after the gain adjustment, respectively.
The overall gains were changed as follows.

• MICH1 gain: 2.1 ⇒ 7.5
• PRCL1 gain: 2.0 ⇒ 2.0 (unchanged)
• SRCL1 gain: 1.4 ⇒ 2.0

With the previous settings, as reported in klog #37346⁠, the shapes of the 3f MICH and PRCL OLTFs were abnormal.
However, as shown in Figs. 4 and 5, probably thanks to the diagonalization performed this time, I obtained relatively clean OLTFs similar to those of the 1f lock.

Lock duration

Even after the sensor and actuator diagonalization and the corresponding setting changes, the DRMI remained locked with the 3f signals.
As shown in Fig. 7, the lock was maintained for more than 11 hours.

Screenshot of the current setup

Fig. 8 shows a screenshot of the current setup.

Summary and future work

This time, I diagonalized the MICH 3f sensor and the MICH actuator.

As a result, the shapes of the 3f OLTFs became cleaner, and the lock also seemed to be maintained more stably.

These settings have not yet been implemented in the guardian.
If these settings are confirmed to be appropriate, I would like to update the guardian settings accordingly.

In addition, the output of LSC-MICH_OUT_DQ was close to 100000 and seemed to be close to saturation.
Therefore, the roll-off filters or related settings should also be adjusted.

For ASC, the ADS loops for BS and SRM were not engaged this time, so they need to be also optimized.
And since the sensor coupling seemed to depend on the alignment, it may be necessary to do the diagonalization procedure described above again after introducing the ADS loops.

In parallel with working on these items, we would like to try the detuned-arm + DRMI 3f lock again.

Fujimoto-san, YamaT-san, Ikeda

Fujimoto-san reported that the IMC lock could not be restored because the PSL HWP was not rotating. The issue has now been resolved.

Investigation

At 20:04:11 JST on August 15, 2026, Guardian issued a command to rotate the PSL HWP. After the movement, the control PC was expected to send a callback to `k1script` to update the HWP position. However, the value was not updated, leaving the system in a state where the HWP was still considered to be in motion.
A similar issue occurred in K-Log #36869. However, the permissions were configured correctly this time, so the root cause was different.
According to YamaT-san’s investigation, the EPICS Gateway was temporarily unavailable at around the same time. Consequently, `k1script` failed to write to the EPICS channel.
Although the EPICS Gateway recovered after approximately 30 minutes, the HWP could not recover automatically. We therefore triggered the callback manually and restored the system.
 

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