With Dan Chen, Yuli Liang, Jinshui Tian

We continued the work from the previous day. (37183)

Before starting the work, we recorded the alignment of the current YPcal laser using the previously prepared reference setup.

We reduced the power of the main beam path of new laser using HWP before performing the alignment work.

We aligned the beam from the new laser and successfully extracted it from the Tx module.

At the end of the work, we turned on the current laser and checked the beam position on the RxPD. 

No significant change was observed, indicating that the installation and alignment work had not affected the alignment of the existing laser.

I collected the high-power coil driver (HPCD) from EYV (S1604763) and brought it back to Mozumi.

According to Saito-kun, HV amp (x10) was directly connected to the laser PZT input for the PLL lock. According to my past experiences, the direct connection tends to excite PZT at high frequency.

To solve this problem, we inserted a passive LPF that is set as one of the filters for the control servo between the PZT input and the HV. According to my memory, 10Hz ?? LPF and 100kHz?? LPF were used as one of the control filters. So what I can suggest is to set a passive LPF btw the PZT and the HV, and remove the same LPF in the control filters. I have a ponoma case and a film condenser (400V?) in my room.

Another concern is that the UGF at 10kHz for the PLL control might to excite some resonances of the PZT as in the main laser frequency stabilization servo.

I performed the initial alignment Xarm, Yarm, OMC, PRMI and SRY.

[Aritomi, Ushiba, Tanaka, Saito]

The sub-laser was injected into SRY, and the PLL was engaged while the LO frequency was swept to scan the beat signal. Using the maximum hold function of the Moku:Lab spectrum analyzer, the SRY transmitted power was recorded as a function of frequency. Because the slopes on the two sides of the resonance peak were different, the data were fitted both with and without a linear background offset. The two fitting methods yielded resonance frequencies differing by approximately 47.9 kHz. If this difference is regarded as the fitting uncertainty, it is comparable to the measurement uncertainty reported previously (klog:37191). The PLL UGF was then reduced to narrow the beat-signal linewidth, and the measurement and fitting procedure was repeated. However, the fitted resonance frequencies with and without a linear background offset differed by approximately 143 kHz, indicating that the fitting uncertainty was not improved. To achieve more accurate fitting, it will likely be necessary to suppress fluctuations in the beat-signal amplitude and reduce the influence of higher-order modes.

• The sub-laser was injected into SRY, the PLL was engaged, and the beat signal was observed using the RFPD installed at OMC REFL. The LO frequency was then swept to scan the beat signal. The maximum hold function of the Moku:Lab spectrum analyzer was used to obtain the transmitted power of SRY as a function of beat frequency (Fig. 1). In Fig. 1, the orange trace represents the maximum-hold spectrum, while the red trace shows the instantaneous beat signal. The data between 163.5 MHz and 164.0 MHz were fitted using Φ=A*f−B,P_t​=C/(1+D(sin(Φ/2))^2), where f is the beat frequency. The fitted resonance frequency was 163.7443 ± 0.0017 MHz. However, as shown in Fig. 1, the slopes on the two sides of the resonance peak were asymmetric, and the fitted curve did not perfectly reproduce the measured data. Based on a suggestion from ChatGPT that a linear background should be included for such asymmetric data, the data were also fitted using Φ=A*f−B,P_t​=C/(1+D(sin(Φ/2))^2)+E*f+F, where E and F represent the linear background terms (Fig. 3). This fit yielded a resonance frequency of 163.7922 ± 0.0057 MHz. The fit including the linear background appears to reproduce the measured data better than the fit without the background. However, the resonance frequencies obtained from the two fitting methods differ by approximately 47.9 kHz. Therefore, if this difference is regarded as the fitting uncertainty, it is comparable to the uncertainty obtained in the previous measurement (klog:37191).
• Next, an attempt was made to perform the PLL using the SRMI signal, but the PLL could not be locked. The SRM gain was also increased while measuring SRY, but no noticeable improvement was observed. The SRM gain was then restored to its original value, and the PLL UGF was reduced in order to narrow the beat-signal linewidth and thereby improve the acquisition of the maximum-hold spectrum during the LO frequency sweep. The UGF was reduced by changing the gain of the Moku:Lab filter from 0 dB to −40 dB. The LO frequency was swept again, and another transmission spectrum of SRY was obtained (Fig. 4). The data between 165.6 MHz and 166.4 MHz were first fitted without a linear background, yielding the result shown in Fig. 5. The fitted resonance frequency was 166.0614 ± 0.0055 MHz. The same data were then fitted with a linear background, as shown in Fig. 6, resulting in a resonance frequency of 166.204 ± 0.049 MHz. As in the previous measurement, the fit including the linear background appears to reproduce the measured data more accurately. However, the resonance frequencies obtained with and without the linear background differ by approximately 143 kHz, indicating that the fitting uncertainty was not improved. These results suggest that achieving more accurate fitting will require suppressing fluctuations in the beat-signal amplitude and reducing the influence of higher-order transverse modes.

[Jinshui Tian, Yuli Liang, Dan Chen]

On 2026/07/09, we updated the Pcal Reconstruction model for both EX and EY so the output Pcal beam position is consistent with the calculation in the paper: Performance of the KAGRA photon calibrators during the fourth joint observing run with LIGO and Virgo - IOPscience.

We deployed the updated model files into the production environment via k1ctr27 (replacing the original files) and confirmed the GRD and SDF statuses.

We then recompiled, installed, and restarted the front-end models as follows:
EX Model (k1ex0):

ssh k1ex0
cdscode 
make k1calex 
make install-k1calex 
startk1calex

EY Model (k1ey0):

ssh k1ey0
cdscode 
make k1caley
make install-k1caley
startk1caley

From ndscope, observable value steps were noted on the following channels:
EX Channels: K1:CAL-PCAL_EX_A_X_MON & K1:CAL-PCAL_EX_A_Y_MON at GPS: 1467955200 s
EY Channels: K1:CAL-PCAL_EY_A_X_MON & K1:CAL-PCAL_EY_A_Y_MON at GPS: 1467956800 s

We plan to calculate and compare the pre- and post-update channel data tomorrow.
 
 

[ Yasui, Oshino,  Nakagaki ]

We have installed a system to monitor the open/closed status of the manual gate valve between PRM and PR3.
The open/closed status is provided via the following PVs:

K1:VAC-GV_PR3_OPEN
K1:VAC-GV_PR3_CLOSE

These have also been added to the `VAC_OVERVIEW` MEDM screen.

Since we were unable to test the valve in the closed position today, we will conduct that test at a later date.

Because the LPD values went down in these days, Pcal GRD went to FAULT state today.
I think this is caused by the instability in the laser source.

So I changed the threshold value from 3.3 to 3.0.

I compared the spectra in the IRM damper servo ON/OFF again. The IP was excited in yaw with the IP actuators. The servo gain was increased from 1.5 to 2. Although the peak around 60 mHz was damped by the servo, the RMS reduction was small due to the resonance at 160mHz.

I collected the high-power coil drivers (HPCDs) from IXV (S1604827) and IYV (S1706250) and brought them back to Mozumi.

[Tanaka, Hirose, Fujimoto, Saito]

Following the same procedure as in the previous measurement (klog:37185), the lengths of PRY, SRY, and SRX were measured. The differences between the measured and design values were 0.6 ± 1.2 cm for PRY, 1.5 ± 1.3 cm for SRY, and 2.8 ± 1.6 cm for SRX. Therefore, the PRY measurement is consistent with the design value within the measurement uncertainty of 1.2 cm, whereas the differences for SRY and SRX exceed their respective uncertainties, suggesting that their actual lengths may differ from the design values.
 

• As in the previous measurement (klog:37185), the sub-laser was injected into PRY, SRY, and SRX, the PLL was engaged, and the beat signal was observed with the RFPD installed at OMC REFL. The minimum and maximum frequencies at which the beat-signal amplitude reached its maximum were measured. The results are summarized below.

  PRY
  Minimum    Maximum
  161.501 MHz    161.583 MHz
  138.351 MHz    138.485 MHz (assuming ±67 kHz around 138.418 MHz)
  −140.999 MHz    −140.865 MHz (assuming ±67 kHz around −140.932 MHz)
  −161.783 MHz    −161.649 MHz (assuming ±67 kHz around −161.716 MHz)
  SRY
  Minimum    Maximum
  161.371 MHz    161.492 MHz
  140.6095 MHz    140.7305 MHz (assuming ±60.5 kHz around 140.67 MHz)
  −141.0055 MHz    −140.8845 MHz (assuming ±60.5 kHz around −140.945 MHz)
  −161.7595 MHz    −161.6385 MHz (assuming ±60.5 kHz around −161.699 MHz)
  SRX
  Minimum    Maximum
  −160.384 MHz    −160.244 MHz (assuming ±70 kHz around −160.314 MHz)
  −140.65 MHz    −140.51 MHz (assuming ±70 kHz around −140.58 MHz)
  162.316 MHz    162.456 MHz (assuming ±70 kHz around 162.386 MHz)
  140.33 MHz    140.47 MHz (assuming ±70 kHz around 140.400 MHz)

  During the measurements, the sub-laser temperature was changed significantly when switching the beat frequency from +160 MHz to −160 MHz. Under these conditions, the beat frequency observed at OMC REFL fluctuated much more frequently, suggesting that the fluctuations become significant until the sub-laser temperature stabilizes. In addition, after switching from +140 MHz to −140 MHz during the SRY measurement, the frequency fluctuations did not subside. However, when the MCE feedback was enabled during the subsequent SRX measurement, the fluctuations were noticeably reduced. This suggests that fluctuations of the main laser also contribute to the beat-frequency instability.
   

• For each cavity, the midpoint between the measured minimum and maximum frequencies was calculated and divided by the corresponding FSR calculated from the design lengths of 64.9265 m (PRY), 64.9264 m (SRY), and 68.2562 m (SRX). The resulting values were rounded to the nearest integers, and the measured frequencies were fitted with the linear function AN+B, where A and B are fitting parameters and N is the corresponding integer. The fitting results are as follows.

  PRY (Fig. 1)
  A = 2.30892 ± 0.00044 MHz
  B = −0.091 ± 0.030 MHz
  SRY (Fig. 2)
  A = 2.30818 ± 0.00046 MHz
  B = −0.136 ± 0.030 MHz
  SRX (Fig. 3)
  A = 2.19520 ± 0.00051 MHz
  B = −0.076 ± 0.035 MHz

  Since A corresponds to the FSR, the cavity lengths obtained from the fitted FSR values are

  PRY
  Fitted length: 64.921 ± 0.012 m
  Design length: 64.9265 m
  Difference (Fitted − Design): −0.6 ± 1.2 cm
  SRY
  Fitted length: 64.941 ± 0.013 m
  Design length: 64.9264 m
  Difference (Fitted − Design): 1.5 ± 1.3 cm
  SRX
  Fitted length: 68.284 ± 0.016 m
  Design length: 68.2562 m
  Difference (Fitted − Design): 2.8 ± 1.6 cm

  Therefore, the measured PRY length is consistent with the design value within the measurement uncertainty of 1.2 cm. In contrast, the differences between the measured and design values for SRY and SRX exceed their respective uncertainties, suggesting that their actual cavity lengths may differ from the design values.

ETMX went to PAY_TRIPPED at 13:56 JST due to glitches on MN V1 photosensor (Fig.1).

ETMX was in MISALIGNED (STATE_N=1400) and all payload control was disengaged, so it's not caused by the local control.
Similar glitches appeared several times before going to PAY_TRIPPED (Fig.2).
This situation is similar to klog#29475 (ITMX_MN_V1), klog#31522 (ETMY_MN_V1), and klog#32077 (ETMY_MN_V2).
If glitches will appear again, it might be better to stop using ETMX_MN_V1.

Pictures: link

[Saito, Tanaka, Fujimoto]

Abstract

We performed a PRX length measurement using the beat signal between the main laser and the auxiliary laser in OMC REFL.
As a cross-check of the data analysis, I analyzed the data independently from Saito-kun. In this entry, I show my results.
Please refer to Saito-kun’s klog entry (klog #37185) for the details of the measurement.

From my analysis, the measured PRX length is consistent with the design value within the measurement uncertainty of 1.3 cm, and this is consistent with Saito-kun's result:

• L_PRX_design = 68.2560 m
• L_PRX_measured = 68.267(13) m
• Difference between measurement and design: (1.1±1.3) cm

Details for analysis

Design values for PRX

The design values for PRX are as follows:

• L_PRX_design = 68.2560 m
• FSR_PRX_design = 2.19609 MHz

Measured beat frequency

We measured the beat frequencies between the main laser and the auxiliary laser when the auxiliary laser was resonant in PRX at four different frequency regions: around -160 MHz, -140 MHz, +140 MHz, and +160 MHz.

For the +140 MHz and +160 MHz cases, we measured the frequency range where the maximum could not be clearly distinguished, and estimated the center values and error bars from that range.

For the -140 MHz and -160 MHz cases, due to time constraints, we did not perform this range measurement. Instead, we used the frequencies that seemed to correspond to the maxima as the measured points. For their error bars, we used the uncertainty obtained from the +140 MHz measurement, which was 0.064 MHz.

The results are summarized in the table below:

Fitting results

I plotted the beat frequency as a function of the FSR index and fitted the data with a linear function, a*x+b, where x is the FSR index.

Fig. 1 shows the measured data points and the fitted line.

The fitting model and the obtained parameters are as follows:

• Model: a*x+b
• Results:
  • a = 2.19575(40) MHz
  • b = -160.376(47) MHz

Results for the FSR and PRX length

The fitted parameter (a) directly gives the FSR of PRX.
The PRX length calculated from this FSR is as follows:

• FSR_PRX_measured = 2.19575(40) MHz
• L_PRX_measured = 68.267(13) m
• L_PRX_design = 68.2560 m
• Difference between measurement and design:
  L_PRX_measured - L_PRX_design = (1.1±1.3) cm

Therefore, within the measurement uncertainty of 1.3 cm, the measured PRX cavity length is consistent with the design value.

[Tanaka, Fujimoto, Saito]

To observe the beat signal with the RFPD installed at OMC REFL, the vertical axis of the spectrum analyzer was set to a linear scale, and the number of frame averages was increased to make the peak height and frequency easier to identify. During the observation, the beat frequency occasionally shifted toward lower frequencies, sometimes as often as once every few seconds. The No. 3 sub-laser used in this experiment (as identified in the JGW DOC documentation) is known to exhibit frequency-noise events that increase its RMS frequency noise approximately once every 5 s to 2 min, and the occurrence rate closely matched that of the observed beat-frequency shifts. Therefore, these frequency shifts are considered to originate from the frequency noise of the sub-laser. The beat-signal amplitude also fluctuated, which is believed to be caused by fluctuations of PRX. Accordingly, when the beat signal was stable, the LO frequency was varied, and the minimum and maximum frequencies at which the beat-signal amplitude reached its maximum were measured around 160 MHz, 140 MHz, −160 MHz, and −140 MHz. Fitting these measurements yielded a PRX length of 68.27 ± 0.01 m, compared with the design value of 68.2563 m.
 

• The sub-laser was injected into PRX, the PLL was engaged, and the beat signal was observed with the RFPD installed at OMC REFL. The objective was to determine the minimum and maximum frequencies at which the beat-signal amplitude reached its maximum. For this purpose, the vertical axis of the spectrum analyzer was set to a linear scale, and the number of frame averages was increased to improve the visibility of the peak height and frequency. By varying the PLL LO frequency, both the resonance point (Fig. 1) and the anti-resonance point (Fig. 2) were observed. At the anti-resonance point, however, the beat-signal peak appeared to split into two peaks.
   
• During the measurements, the beat frequency occasionally shifted toward lower frequencies, sometimes as often as once every few seconds. The beat signal in the PLL path exhibited the same frequency shift. Initially, fluctuations of the Moku:Lab LO signal were suspected, so the LO source was switched from the Moku:Lab to the function generator that had originally been used. However, no change was observed. Fluctuations of the main laser were also considered, and an additional control loop was applied to suppress them, but this likewise produced no improvement. On the other hand, the No. 3 sub-laser used in this experiment (as described in the JGW DOC documentation) is known to exhibit frequency-noise events that increase its RMS frequency noise approximately once every 5 s to 2 min, and the occurrence rate closely matched that of the observed beat-frequency shifts. Therefore, the observed frequency shifts are considered to originate from the frequency noise of the sub-laser. The beat-signal amplitude also fluctuated, which is believed to be caused by fluctuations of PRX.
   

• Therefore, when the beat signal was stable, the LO frequency was varied, and the minimum and maximum frequencies at which the beat-signal amplitude reached its maximum were measured around 160 MHz, 140 MHz, −160 MHz, and −140 MHz. Negative frequencies correspond to the case where the sub-laser frequency is lower than the main-laser frequency. The measured values are listed below.

  Minimum    Maximum
  162.363 MHz    162.442 MHz
  140.366 MHz    140.494 MHz
  −140.683 MHz    −140.555 MHz (assuming ±0.064 MHz around −140.619 MHz)
  −160.435 MHz    −160.307 MHz (assuming ±0.064 MHz around −160.371 MHz)

  The midpoint between the minimum and maximum frequencies was then calculated for each measurement. Each midpoint was divided by the FSR calculated from the PRX design length of 68.2563 m. The resulting values were rounded to the nearest integers, and the measured frequencies were fitted with the linear function AN+B, where A and B are fitting parameters and N is the corresponding integer. The fitting results are shown in Fig. 3 and are summarized below:

  A = 2.1957 ± 0.0004 MHz
  B = −0.08 ± 0.03 MHz

  Since A corresponds to the FSR, the PRX length calculated from the fitted FSR is

  Fitted PRX length: 68.27 ± 0.01 m
  Design value: 68.2563 m

With Jinshui Tian, Yuli Liang

We are preparing for the installation of the Ncal system. As part of this preparation, we checked the installation area and confirmed the tools, space, and cable routing needed for the pylon and Ncal installation work.

The following items were checked at the site:

• We placed the full-scale drawing of the pylon at the planned installation location. No serious issue was found. We also measured the distance to nearby structures, and the closest clearance was about 3 cm.
• We confirmed that a lifter, Bishamon, is available at the Xend.
• We checked the possible location for hanging a chain block. The floor of the mezzanine level was inspected for this purpose.
• We confirmed that the parts of the gantry crane exist at the site. However, we probably will not use it for the actual installation work.
• We took site photos of the possible routes for the signal cables and power cables.

The site photos will be shared later.

[Fujimoto, Kenta, Saito, YamaT]

We laid cables on the AS table to connect Moku to the DGS network.

Only one UTP cable had been laid from the OMC fire alarm rack to the k1ctr6@OMC and laying a new cable from the OMC fire alarm rack requires an aerial work platform and schedule coordination with technical staffs. So I installed a new unmanaged switch in the workstation cart and split the DGS LAN to k1ctr@OMC and Moku@AS-table as shown in attached figures.

This implementation is not suitable for permanent equipment. So it will be removed after finishing recent PRCL/SRCL works. If DGS wired LAN will be permanently required around AS table, make a request in advance so we can coordinate schedules with technical staffs for laying a new cable between the OMC fire alarm rack and the AS table.