The fitting results for the individual PRY resonance peaks presented in klog:37209 are summarized below. The measurement data are stored in Dropbox → All files/Dropbox KAGRA/Measurements/IFO/PRCL/PRCL_OMC_REFL_beat_signal_LO_sweep/2026_07_14_PRY.

• Figure 1: Around 190 MHz, without a linear background. Using data from 186.5 MHz to 187.4 MHz, the fitted peak frequency is 186.9075 ± 0.0027 MHz.
  Figure 2: Around 190 MHz, with a linear background. Using data from 186.5 MHz to 187.4 MHz, the fitted peak frequency is 186.9512 ± 0.0049 MHz.
   
• Figure 3: Around 160 MHz, without a linear background. Using data from 163.4 MHz to 164.4 MHz, the fitted peak frequency is 163.8465 ± 0.0039 MHz.
  Figure 4: Around 160 MHz, with a linear background. Using data from 163.4 MHz to 164.4 MHz, the fitted peak frequency is 163.8930 ± 0.0044 MHz.
   
• Figure 5: Around 140 MHz, without a linear background. Using data from 131.05 MHz to 132.05 MHz, the fitted peak frequency is 131.4789 ± 0.0028 MHz.
  Figure 6: Around 140 MHz, with a linear background. Using data from 131.05 MHz to 132.05 MHz, the fitted peak frequency is 131.506 ± 0.010 MHz.
   
• Figure 7: Around −140 MHz, without a linear background. Using data from 115 MHz to 116 MHz, the fitted peak frequency is 115.5063 ± 0.0042 MHz.
  Figure 8: Around −140 MHz, with a linear background. Using data from 115 MHz to 116 MHz, the fitted peak frequency is 115.4978 ± 0.0068 MHz.
   
• Figure 9: Around −160 MHz, without a linear background. Using data from 156.6 MHz to 157.6 MHz, the fitted peak frequency is 157.0631 ± 0.0042 MHz.
  Figure 10: Around −160 MHz, with a linear background. Using data from 156.6 MHz to 157.6 MHz, the fitted peak frequency is 157.0710 ± 0.0098 MHz.
   
• Figure 11: Around −190 MHz, without a linear background. Using data from 189.1 MHz to 189.8 MHz, the fitted peak frequency is 189.3984 ± 0.0065 MHz.
  Figure 12: Around −190 MHz, with a linear background. Using data from 189.1 MHz to 189.8 MHz, the fitted peak frequency is 189.363 ± 0.018 MHz.

The fitting results for the individual SRY resonance peaks presented in klog:37209 are summarized below. The measurement data are stored in Dropbox → All files/Dropbox KAGRA/Measurements/IFO/SRCL/SRCL_OMC_REFL_beat_signal_LO_sweep/2026_07_14_SRY.

• Figure 1: Around 190 MHz, without a linear background. Using data from 186.4 MHz to 187.1 MHz, the fitted peak frequency is 186.8382 ± 0.0027 MHz.
  Figure 2: Around 190 MHz, with a linear background. Using data from 186.4 MHz to 187.1 MHz, the fitted peak frequency is 186.908 ± 0.022 MHz.
   
• Figure 3: Around 160 MHz, without a linear background. Using data from 165.6 MHz to 166.4 MHz, the fitted peak frequency is 166.0614 ± 0.0055 MHz.
  Figure 4: Around 160 MHz, with a linear background. Using data from 165.6 MHz to 166.4 MHz, the fitted peak frequency is 166.204 ± 0.049 MHz.
   
• Figure 5: Around 140 MHz, without a linear background. Using data from 130.96 MHz to 131.69 MHz, the fitted peak frequency is 131.4068 ± 0.0033 MHz.
  Figure 6: Around 140 MHz, with a linear background. Using data from 130.96 MHz to 131.69 MHz, the fitted peak frequency is 131.480 ± 0.012 MHz.
   
• Figure 7: Around −140 MHz, without a linear background. Using data from 126.8 MHz to 127.5 MHz, the fitted peak frequency is 127.0443 ± 0.0054 MHz.
  Figure 8: Around −140 MHz, with a linear background. Using data from 126.8 MHz to 127.5 MHz, the fitted peak frequency is 126.73 ± 0.47 MHz.
   
• Figure 9: Around −160 MHz, without a linear background. Using data from 159.1 MHz to 159.9 MHz, the fitted peak frequency is 159.4293 ± 0.0031 MHz.
  Figure 10: Around −160 MHz, with a linear background. Using data from 159.1 MHz to 159.9 MHz, the fitted peak frequency is 159.372 ± 0.016 MHz.
   
• Figure 11: Around −190 MHz, without a linear background. Using data from 189.1 MHz to 189.87 MHz, the fitted peak frequency is 189.3517 ± 0.0053 MHz.
  Figure 12: Around −190 MHz, with a linear background. Using data from 189.1 MHz to 189.87 MHz, the fitted peak frequency is 189.295 ± 0.024 MHz.

[Kimura and Yasui]
   On July 15, as part of maintenance work on the cryogenic cooling units, we set up two valve units for the radiation shield cryo-coolers (IXC P-53 and IXC P-55).
 The remaining tasks are filling the system with G-1 class helium gas up to 15 bar and performing leak tests on all connections.

Saito-kun,

Could you upload the overplot graphs of the raw data and the fitting functions similar to fig 2 and 3 in klog37201?

[Aritomi, Ushiba, Tanaka, Saito]

Sub-laser light was injected into the SRY, PRY, PRX, and SRX, and a PLL was established. The LO frequency was then swept to scan the beat signal. Using the maximum hold function of the Moku:Lab spectrum analyzer, transmission power as a function of frequency was recorded around 190 MHz, 160 MHz, 140 MHz, −140 MHz, −160 MHz, and −190 MHz. The data were fitted both with and without a linear background, and the maximum and minimum peak frequencies within the corresponding fitting uncertainties were determined. The cavity lengths were then calculated from these results. The differences between the measured cavity lengths and the design values were 0.15 ± 0.33 cm for PRY and 1.58 ± 0.82 cm for SRY. Therefore, the PRY measurement is consistent with the design value within its uncertainty of 0.33 cm, whereas the SRY measurement differs from the design value by more than the estimated uncertainty, suggesting that the actual cavity length may differ from the design value. The results for PRX and SRX will be reported after the analysis is completed.
 

• As in the previous measurement (klog:37201), sub-laser light was injected into the SRY, PRY, PRX, and SRX, and a PLL was established. The beat signal was observed using the RFPD installed at OMC REFL. The LO frequency was then swept to scan the beat signal. Using the maximum hold function of the Moku:Lab spectrum analyzer, transmission power as a function of frequency was measured around 190 MHz, 160 MHz, 140 MHz, −140 MHz, −160 MHz, and −190 MHz for each cavity. Here, negative frequencies correspond to the case where the sub-laser frequency was lower than that of the main laser.
   

• For the data near each resonance peak, fitting was performed both with and without a linear background, following the same procedure as in the previous analysis (klog:37201). From the fitted peak frequencies and their uncertainties, the maximum and minimum frequencies within the fitting uncertainty were determined. The overall uncertainty range was then defined as the largest and smallest values obtained from both fitting models. The following data were used to determine the PRY and SRY cavity lengths.

  PRY
  Minimum (MHz)    Maximum (MHz)
  186.9049    186.9561
  163.8426    163.8974
  131.4761    131.5159
  -115.5105    -115.4909
  -157.0807    -157.0589
  -189.4049    -189.3442
  SRY
  Minimum (MHz)    Maximum (MHz)
  186.8354    186.9305
  166.0559    166.2530
  131.4035    131.4918
  -127.2003    -126.2609
  -159.4324    -159.3557
  -189.3570    -189.2707
   

• From the measurement results, the midpoint between the minimum and maximum frequencies was calculated for each resonance. These midpoint frequencies were divided by the FSR calculated from the design cavity lengths (64.9265 m for PRY and 64.9264 m for SRY). 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 rounded integer. The fitting results were as follows.

  PRY (Fig. 1)
  A: 2.30865 ± 0.00012 MHz
  B: −0.0741 ± 0.0074 MHz
  SRY (Fig. 2)
  A: 2.30815 ± 0.00029 MHz
  B: −0.092 ± 0.021 MHz
   

• Since A corresponds to the FSR, the cavity lengths were calculated from the fitted values of A.

  PRY
  Measured cavity length: 64.9280 ± 0.0033 m
  Design value: 64.9265 m
  Difference (measured − design): 0.15 ± 0.33 cm
  SRY
  Measured cavity length: 64.9422 ± 0.0082 m
  Design value: 64.9264 m
  Difference (measured − design): 1.58 ± 0.82 cm

  Therefore, the PRY measurement is consistent with the design value within the uncertainty of 0.33 cm. In contrast, the difference between the measured and design values for SRY exceeds the estimated uncertainty, suggesting that the actual SRY cavity length may differ from the design value. The results for PRX and SRX will be posted once the analysis has been completed.

With Misato Onishi, Yuli Liang, Jinshui Tian

We installed 2 QPDs in Rx module on 7/14 for the Pcal beam monitoring.

And, I took Tcam data with changing Pcal beam positions by the pico PCAL_EY2 in the 7/15 morning.
The data will be analysed to check the QPD performance.

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.