[Hirose, Tanaka, Takano, Fujimoto]

Abstract

We performed the phasing of AS34-I during PRMI 3f lock.
As a result, AS34-I improved from ~0.14 to ~0.18. The value measured with SRMI (f1 resonant) was also ~0.18, which is theoretically consistent.
From these resuls, the AS34-I value expected for DRMI is estimated to be ~5.8.

Details

While PRMI was locked with the 3f signals, we adjusted the demodulation phase so as to minimize AS34-Q:

     K1:LSC-AS-PDA2-RF34-PHASE-R: -90 -> -126

With this adjustment, AS34-I in PRMI with 1.1 W input power improved from ~0.14 to ~0.18.

In addition, AS34-I was also measured to be ~0.18 when SRMI was locked with f1 resonant.
For PRMI and SRMI, the theoretical transmissivity of the f1 sidebands to AS34 are 3.0% and 3.1%, respectively, assuming PRM reflectivity of 90%, MI reflectivity of 14% for f1, SRM reflectivity of 85%, and ideal Schnupp asymmetry, PRCL, and SRCL.
Since the two transmittances are almost the same, the above measurement results are consistent with the theoretical expectation.

The expected transmissivity of f1 to AS when DRMI is locked is 97%.
Therefore, AS34-I in DRMI is expected to be amplified by a factor of about 32 compared to SRMI, resulting in an expected AS34-I value of ~5.8 for DRMI.

With Jiahui Xiong

Today, we checked the circuit and cabling for the QPD readout at Pcal-X.

First, we checked the circuit diagram: DocDB 9608 . From the diagram, this circuit seems to provide the 15 V power supply to the PDQ80A and to convert the QPD signals, X, Y, and Sum, from single-ended signals to differential signals.

Then we checked the setup at the Pcal-X area, and found the cable connecting the PDQ80A and the D-sub 9-pin connector.
We also tried to check the actual circuit, but it was difficult to remove the cables, so we could not directly inspect the inside of the circuit box.

However, after connecting the PDQ80A, we could confirm that the QPD signals were visible in the Pcal real-time model. Therefore, the basic signal readout seems to be working.

Although the alignment was not available today, we fixed one PDQ80A behind the mirror inside the Rx module as a temporary setup.

If possible, we would like to align the ETMX suspension tomorrow morning and adjust the position of QPDs.

I'm afraid that currently SMI ADS doesn't work welo, so DO NOT USE SRMI for aligning SRM until we confirm it works well. Instead, the conventional SRY ADS is fine for SRM alignment.

I offloaded the F3 GAS with the FR using the standalone stepper driver.

We compared two GIF animations (titled BEAM SPOT and MIRROR): one generated from two images acquired on 2026/04/22 (see 36793), in which the beam spot position was shifted, and another generated from two images acquired on 2026/06/01 (see 36984), in which the mirror position was changed. For the characteristic speckle-like structures indicated by the red circles, no apparent motion is observed in the BEAM SPOT, whereas a clear vertical displacement is observed in the MIRROR animation. This indicates that these structures are associated with the mirror.

With Shingo Hido

Summary

We performed the initial alignment for Xarm, Yarm, and OMC.

There were two points to be noted during the work:

• First, the IMC lost lock a few times. Most of the lock losses were recovered automatically, but once the IMC did not recover by itself. In that case, we manually changed the PZT offsets to recover the IMC lock, and then gradually returned all PZT offsets to 75.
• Second, the initial alignment sequence once stopped at INCREASE_LCS_POW_FOR_OMC. At that time, the IMC TRANS output stayed around 8.1 W. The PSL HWP had reached 169, while the REFL HWP was 152.266, slightly different from the target value. It is possible that the final fine adjustment of the HWP did not complete properly in that trial. After retrying the sequence, it passed this state and the alignment was completed.

Detials

Preparation

Before starting the initial alignment, we did the following checks and preparations.

• SRM and PRM were set to MISALIGNED.
• We confirmed that all Type-A suspensions could reach the LOCK_ACQUISITION state.
• The GRX and GRY shutters were open.
  • TR-GRX power was about 1.
  • TR-GRY power was about 1.
• PLLX and PLLY were confirmed to be in PLL_LOCKED.
• FIBX and FIBY were in SAFE due to the known DGS issue, but we proceeded.

Xarm alignment

For Xarm, the IX TCam image looked strange, possibly because of a different zoom or field of view. Therefore, we decided not to rely on the IX TCam image.

We requested the following states one by one:

• IRX_LOCKED
• GRX_LOCKED_WITH_IRX
• ALIGNING_XARM

During this process, the IMC lost lock about two times, but it seemed to recover automatically.

At ALIGNING_XARM, the GRX power was about 0.92, which was slightly low. We manually adjusted ITMX and ETMX as follows:

(IX-P, IX-Y, EX-P, EX-Y) = (9.4, -10.9, -12.0, -11.3) -> (8.4, -12.1, -12.8, -11.3)

After this adjustment, the GRX power increased to about 0.98. The IRX power stayed around 1.0.

Then we requested:

• RECORD_GOOD_VALUES_XARM
• OFFLOAD

Yarm alignment

For Yarm, we requested the following states one by one:

• IRY_LOCKED
• GRY_LOCKED_WITH_IRY
• ALIGNING_YARM

The alignment looked good, so we proceeded without manually adjusting the BS.

Then we requested:

• RECORD_GOOD_VALUES_YARM
• OFFLOAD

OMC alignment

For the OMC alignment, we first requested:

• IRY_LOCKED_FOR_OMC
• ENGAGE_OMMT2_TRANS_CENTERING
• ALIGNING_TO_OMC

The lock was lost during this process. We tried again by requesting:

• IRY_LOCKED_FOR_OMC
• ENGAGE_OMMT2_TRANS_CENTERING

but the lock was lost again, and this time the IMC did not recover automatically.

To recover the IMC, we manually changed the PZT offsets based on the DOF outputs.

• For DOF4-P:
  • The output had been around 23, but it was around -7.
  • We increased PZT1-P from 75 to 104.
• For DOF5-P:
  • The output had been around -46, but it was around -71.
  • We increased PZT2-P from 75 to 100.
• For DOF4-Y:
  • The output had been around -30, but it was around 0.
  • We started changing PZT1-Y from 75 toward 45.
  • During this adjustment, the IMC locked.
• DOF5-Y was not adjusted.

After that, IO reached PROVIDING_STABLE_LIGHT. We waited for a while and then gradually returned all PZT offsets to 75.

After the recovery, we requested IRY_LOCKED_FOR_OMC again. The IMC immediately lost lock once, but recovered automatically. The system soon reached IRY_LOCKED_FOR_OMC.

Then we requested:

• ENGAGE_OMMT2_TRANS_CENTERING

The sequence stopped at INCREASE_LCS_POW_FOR_OMC. At that time, the IMC TRANS output stayed around 8.1 W. We checked the HWP values and found:

PSL HWP  = 169REFL HWP = 152.266

The REFL HWP was still 0.266 away from the expected value, so the final fine adjustment may not have completed properly.

We retried the sequence again. Then, the sequence passed this state. In the successful trial, the HWP values were:

PSL HWP  = 169REFL HWP = 152

Then we requested:

• ALIGNING_TO_OMC

The OMC transmitted power, OMC-TRANS_DC_SUM_OUT16, reached about 30.5. The ground motion became somewhat noisy during this process, but it calmed down after a while, and the guardian state was successfully reached.

Finally, we requested:

• RECORD_GOOD_VALUES_OMC

The initial alignment up to OMC was completed.

[Fujimoto, Tanaka, Takano]

We could lock DRMI with a mixture of 3f and 1f signals. Currently, the lock is unstable, and it keeps locking up for several minutes. Further investigation is necessary.

• Fig. 1: When DRMI was locked
• Fig. 2: DRMI got unstable due to a glitch (probably the control instability)
• Fig. 3: measured OLTF for PRCL
• Fig. 4: measured OLTF for PRCL
• Fig. 5: measured OLTF for PRCL
• Fig. 6: Filter settings
• Fig. 7: Trigger settings 

The details will be reported later.

Summary

The modulation phase of POP17 was optimised using SRMI.

Detail

For a long time, we haven't tuned the demodulation phase of POP17. We optimised it by checking the POP17I and POP17Q signals when SRMI was locked using them (POP17I for SRCL and POP17Q for MICH).

We injected the excitation signal at 50 Hz, which would be outside of SRCL control band, at K1:LSC-SRCL1_EXC, and measured the ASD of SRCL_IN2 and MICH_IN2. We should not see any signal in MICH, i.e. POP17Q, so we changed the demodulation phase of POP17 and minimised the excess noise in MICH_IN2. Fig. 1 shows the results of the optimisation; the injected noise in MICH_IN2 was minimised when the modulation phase was set to -141 deg (by default it was -137 deg).

[Ushiba, Tanaka, Fujimoto, Saito]

Following klog:36974, we attempted to achieve lock by adding an integrator to the low-pass filter, but locking was not successful. We also tried changing the feedback sign, changing the frequency relationship between the main laser and the sub-laser, and using the low-pass filter of SR560 instead of Moku:Lab. However, none of these approaches resulted in lock acquisition. In addition, the measured beat signal amplitude was approximately 0.2 mVpp, whereas the value predicted from the laser powers was approximately 0.1575 V, representing a large discrepancy. Therefore, in the next experiment, we plan to investigate the alignment, mode matching, and polarization conditions to determine whether the beat signal amplitude can be increased.
 

• First, a 10 kHz low-pass filter was applied, and the gain was gradually increased. Oscillation occurred once the gain exceeded a certain level. We then inserted an integrator with a corner frequency of 1 Hz while keeping the gain just below the oscillation threshold and tested whether lock could be achieved. However, no behavior indicating that the beat frequency was being pulled toward the LO frequency was observed. In addition, when the integrator was enabled, the beat frequency was observed to move further away from the LO frequency. We also changed the feedback sign and tested both cases in which the sub-laser frequency was higher than and lower than the main laser frequency, but lock could not be achieved in any configuration. Furthermore, we attempted to use the low-pass filter of an SR560 instead of Moku:Lab and varied the gain, but lock acquisition was still unsuccessful.
   

• In addition, when the gain was increased with the 10 kHz low-pass filter in place, the frequency of the error signal at the onset of oscillation was approximately 900 kHz. When the beat signal was observed on the oscilloscope, its amplitude exhibited temporal fluctuations, and the measured frequency was also approximately 900 kHz. This amplitude-modulated signal disappeared when the sub-laser beam was blocked, but remained unchanged when the main laser beam was blocked. The same 900 kHz signal was also observed on the spectrum analyzer. Its level was approximately -43 dB with the noise eater turned off and decreased to approximately -80 dB when the noise eater was turned on. However, changing the state of the noise eater did not enable lock acquisition.

• The beat signal amplitude, converted from the spectrum analyzer reading in dBm, was approximately 0.2 mVpp. At present, the sub-laser power incident on the RFPD is approximately 1.78 mW, while the main laser power is estimated to be approximately 17 μW. Since the responsivity of the RFPD (1611FS-AC) is approximately 525 V/W, the expected beat signal amplitude is (525V/W)×2√(1.78×10^−3×17×10^−6) which is approximately 0.1575 V. This predicted value is about 788 times larger than the measured amplitude. Therefore, in the next experiment, we plan to investigate the alignment, mode matching, and polarization conditions to determine whether the beat signal amplitude can be increased.

[Kimura and Yasui]
 On the afternoon of June 1, we filled two helium compressors (EYC P-53 and EYC P-55) with G-1 grade helium gas to a pressure of 15 bar.
As a result, maintenance work on the EYC cryocooler for the radiation shield has been completed.

[Kimura, Yasui, Tanaka (Edwards) and Okada (Edwards)]
 On the morning of June 1, two Edwards technicians conducted an inspection of the Gamma ion pump power supplies used on the X and Y arms.
This inspection involved connecting a high-resistance dummy pump to the power supply’s high-voltage terminals and verifying that the voltage (~6 kV) and current (~60 μA) were being output stably. (Photos 1~3)
As a result, it was confirmed that the five Gamma ion pump power supplies used on the X and Y arms were operating without issues.
 Subsequently, the Edwards technicians inspected the Gamma ion pump power supply at the X-end that had generated an error. (k-log 36915)
(Photos 4~5)
No loose connections were found in the wiring forming the interlock.
Therefore, it was decided to monitor the situation for the time being.

YamaT-san, Nakagaki-san, Ikeda

> The standalone stepper motor driver for the F3 GAS didn't work. 
We migrated from k1script1 to k1script0 (K-Log #36747), but due to the same issue described in K-Log#36803, we are unable to establish a connection.
As a temporary workaround, the Standalone (IX) stepper motor has been moved to k1script1, and the configuration has been modified so that it can operate there.

Details

Just before starting the work, an earthquake occurred. There were also some aftershocks during the work. The earthquake was likely around seismic intensity 3 near Niigata. In addition, the ground motion was relatively large today.

Preparation

As a preparation, we misaligned SRM and PRM to avoid unwanted resonances. We also confirmed that all Type-A suspensions could go to the LOCK_ACQUISITION state.

The GRX and GRY shutters were opened. The GR transmission was about 0.7 for X-arm and about 1 for Y-arm.

An aftershock occurred at around 06:09.

X-arm alignment

Before starting the guardian-based initial alignment, we slightly moved PR3 to increase the GRX transmission.

The PR3 opticalign values were adjusted to increase the GRX transmission.

After that, we requested IRX_LOCKED. Then we requested GRX_LOCKED_WITH_IRX, but the lock was lost. The IMC did not recover automatically, so we worked on the IO alignment.

We requested PROVIDING_STABLE_LIGHT in the IO guardian and adjusted the PZTs. For example, we changed the PZT1 pitch offset. The original value was 75, and we tried 102 because the corresponding input value was about 27 when the alignment was good. We looked for sudden changes and tried to bring the corresponding degrees of freedom back to the previous good values.

We adjusted by using PZT{1,2}_{P,Y}. After recovering the IMC lock, we waited for the ASC to engage. Finally, the PZT value was returned to 75.

After the IO was recovered, we continued the X-arm alignment using the initial alignment guardian. In the ALIGNING_XARM state, we manually moved ITMX and ETMX while checking the transmission. And completed the Xarm alignment.

Y-arm alignment

We then started the Y-arm alignment. During the Y-arm alignment, we slightly moved BS to improve the alignment.

OMC alignment

For the OMC alignment, we first turned off the GR beams and requested IRY_LOCKED_FOR_OMC. Then we requested ENGAGE_OMMT2_TRANS_CENTERING, followed by ALIGNING_TO_OMC.

During the alignment, K1:OMC_TRANS_DC_SUM_OUT16 increased to about 33 and became stable. The alignment became stable, although the change was not very large.

After that, we requested RECORD_GOOD_VALUES_OMC.

SRY alignment

Finally, we tried the SRY alignment. We requested ALIGNING_SEY and adjusted SRM, referring to the procedure in klog 36967.

Since the alignment did not look good, we set the guardian to DOWN and manually moved SRM. We adjusted SRM while watching K1:LSC-AS_PDA1_DC_OUT_DQ and the POP camera.

We then requested ALIGNING_SRY again and adjusted the SRM opticalign values so that the oplev values became close to the previous good oplev values. We tried ALIGNING_SRY once more, but SRY could not be locked.

The failure to complete the SRY alignment might have been due to the relatively large ground motion today, including the earthquake and aftershocks.

Summary

The X-arm, Y-arm, and OMC alignments were completed. We also tried the SRY alignment, but it could not be completed.

[Yokozawa, Chen, Hirose]

We performed initial alignment procedures.

The X-arm, Y-arm, and OMC alignments were completed. We also tried to align SRY, but it could not be completed.

There was an earthquake just before starting the work, followed by some aftershocks. The ground motion was relatively large today, and this likely made the SRY lock difficult.

Details will be reported later.

SRMI was also locked with 3f signals (REFL 51I for SRCL, REFL 51Q for MICH) under the same conditions. It should be noted that the demodulation phase of REFL51 was optimised not for sensing SRCL & MICH signals, but for avoiding glitches when IR flashes at REFL table. This may cause weird phase rotation of the measured open loop transfer functions, as attached (Fig. 1 for MICH, Fig. 2 for SRCL). For stable locking of SRMI and DRMI, the phasing work seems necessary.

[Fujimoto, Takano]

Summary

We noticed that the previous locking point of SRMI was not as intended, somewhere very weird. Finally, we found the good locking point, where MICH is at the dark fringe and the f1 sidebands are on resonance in the SRC.

Detail

Once we thought that we could lock SRMI (see here), but after further discussion, we concluded that this locking point was not as expected, because the AS34 buildup was -0.04, whereas we observed it can reach ~ 0.9. After several trials and errors, we found out the optimal conditions for locking it at the point we wanted: MICH is at the dark fringe and the f1 sidebands are on resonance in SRC (Fig. 3). We implemented the appropriate servo settings in the VERTEX guardian. We could lock SRMI by requesting it. The measured open loop transfer functions are as attached (Fig. 1 and Fig. 2).

During the trial, we noticed that PR3 often moved quite largely, sometimes more than 10 urad. It looked like big glitches pushed it. These glitches sometimes unlocked the interferometers during the initial alignment (Fig. 4).

Attached figures show the latest open-loop transfer functions of PRCL and MICH in PRMI 3f locked after changing the REFL HWP angle. The overall gain of each loop was tuned to match the old measurement.

[Takano, Dan, Hirose, Saito]

Following klog:36916, we continued our attempts to achieve PLL lock. We tested both flat filters and low-pass filters. Although loose locking was achieved, we were unable to add an integrator while maintaining lock. In addition, we were unable to measure the open-loop transfer function successfully.
 

• First, we confirmed the beat signal between the sub-laser beam and the beam coming from the interferometer. Next, the 100 kHz low-pass filter after the mixer was replaced with a 1.9 MHz low-pass filter. A control filter was then implemented using Moku:Lab, and lock acquisition was attempted by matching the LO frequency to the beat signal frequency. For a flat control filter, the system appeared to be most stable with a gain of -10 dB. Increasing or decreasing the gain from this value resulted in poor locking performance. For a low-pass control filter, higher gains could be used compared to the flat-filter case while maintaining lock. However, as the cutoff frequency was reduced, lock acquisition became increasingly difficult.

  The control filters and corresponding beat signals are shown below. In the filter screenshots, the red trace represents the error signal and the blue trace represents the feedback signal.

  Flat filter with a gain of -20 dB (Photo 1), corresponding beat signal (Photo 2)
  Flat filter with a gain of -10 dB (Photo 3), corresponding beat signal (Photo 4)
  Flat filter with a gain of 0 dB (Photo 5), corresponding beat signal (Photo 6)
  Low-pass filter with a gain of 0 dB and a cutoff frequency of 100 kHz (Photo 7), corresponding beat signal (Photo 8)
  Low-pass filter with a gain of 40 dB and a cutoff frequency of 10 kHz (Photo 9), corresponding beat signal (Photo 10)
  Low-pass filter with a gain of 30 dB and a cutoff frequency of 1 kHz (Photo 11), corresponding beat signal (Photo 12)

  In addition, we attempted to add an integrator while the system was locked using either the flat filter or the low-pass filter. However, the lock was lost after the integrator was enabled. Since the integrator cutoff frequency was set directly to a relatively high value such as 1 kHz, it is possible that the lock could have been maintained if the integrator had been introduced gradually, starting from a much lower frequency. We also attempted to measure the open-loop transfer function while the PLL was locked in order to determine the UGF. However, we were unable to obtain a successful measurement.

[Takano]

Summary

Many updates on the initial alignment for DRMI were made. They are implemented in the initial alignment guardian, but no documents for them have been written so far. Also, PRMI ADS problem was solved (I hope).

Detail

When we tried SRMI locking, it seemed that the alignment to AS port looked bad. Until then, we aligned the beam up to OMMT1 using the OMMT2 trans QPD, but left the alignment to OMC as is. We already have the guardian state for the alignment to OMC using OMMT2 and OSTM, but they didn't work because the power after the SRM is now attenuated by 15%. To fit the guardian to the current situation, we added new states for OMC alignment, including OMMT1 alignment using the OMMT2 trans QPD.

The revised procedure is as follows:

1. Lock one of the arm cavities (Y arm is easier, because normally we align the beam to OMC after Yarm alignment)
   1. Set PRM to MISALIGNED_BF in order to increase the input power later
   2. Because of this, these states are different from the normal IR_LOCKED state, in which PRM is in MISALIGNED_FOR_LOCK_ACQ state.
2. Increase the input power to 8.5 W while keeping the arm cavity locked
   1. When the input power is 8.5 W, OMC transmission is 30 mW.
   2. The HWPs on both PSL table and REFL table are rotated in iterations. When the input power is increased, the power going to REFL PD gets increased; to compensate for this change, the HWP on REFL table is rotated.
3. Engage OMMT2 transmission QPD control loop for OMMT1 alignment
4. Lock OMC and engage OMC QPD control loop for OMMT2 and OSTM loop

These actions were written in INITIAL_ALIGNMENT guardian.

While locking OMC, we faced the guardian error again, which was once reported here. The previous procurement didn't work well unfortunately, but YamaT-san finally found a solution and now it's resolved.

After OMC alignment, I tried to lock PRMI, but it failed even with a decent alignment (POP90I buildup of 0.5). Looking at the error signal, REFL51Q had an offset. I subtracted the dark offset, but still an offset of 2.6 was there. I subtracted it manually by adding an offset in MICH1 filter, then I could lock PRMI, but ADS for it didn't work. Through many many investigations, I found that the angle of REFL HWP was different: when ADS for PRMI worked well, the angle was 125; when it did not, it was 146. The angle depended on which guardian we called to lock PRMI; when we didn't use INITIAL_ALIGNMENT guardian, the angle was 125 and ADS worked successfully, but INITIAL_ALIGNMENT guardian set the HWP angle to 146 when it was called. I changed the guardian so that we set the angle to 125 initially, then we could successfully engage the ADS loop for PRMI. This also removed the REFL51Q offset and PRMI was locked more easily than before.