The fitting results for PRX and PRY in klog:37458 are shown below.
The measurement data are saved in the following Dropbox folders:

All files/Dropbox KAGRA/Measurements/IFO/PRCL/PRCL_OMMT2_REFL_beat_signal_PZT_sweep/2026_09_04_PRX
All files/Dropbox KAGRA/Measurements/IFO/PRCL/PRCL_OMMT2_REFL_beat_signal_PZT_sweep/2026_09_04_PRY
 

• PRX
  Fig. 1: Around 1.6 GHz, without a linear background. Using the data from 1591.51 MHz to 1592.0 MHz, the fitted peak frequency was 1591.7750(12) MHz.
  Fig. 2: Around 1.6 GHz, with a linear background. Using the data from 1591.51 MHz to 1592.0 MHz, the fitted peak frequency was 1591.8014(56) MHz.

  Fig. 3: Around 800 MHz, without a linear background. Using the data from 807.62 MHz to 808.15 MHz, the fitted peak frequency was 807.8942(17) MHz.
  Fig. 4: Around 800 MHz, with a linear background. Using the data from 807.62 MHz to 808.15 MHz, the fitted peak frequency was 807.8842(49) MHz.

  Fig. 5: Around -800 MHz, without a linear background. Using the data from 821.12 MHz to 821.59 MHz, the fitted peak frequency was 821.3504(11) MHz.
  Fig. 6: Around -800 MHz, with a linear background. Using the data from 821.12 MHz to 821.59 MHz, the fitted peak frequency was 821.3352(35) MHz.

  Fig. 7: Around -1.6 GHz, without a linear background. Using the data from 1563.29 MHz to 1563.82 MHz, the fitted peak frequency was 1563.5494(14) MHz.
  Fig. 8: Around -1.6 GHz, with a linear background. Using the data from 1563.29 MHz to 1563.82 MHz, the fitted peak frequency was 1563.5525(32) MHz.
   

• PRY
  Fig. 9: Around 1.6 GHz, without a linear background. Using the data from 1599.85 MHz to 1600.57 MHz, the fitted peak frequency was 1600.1828(18) MHz.
  Fig. 10: Around 1.6 GHz, with a linear background. Using the data from 1599.85 MHz to 1600.57 MHz, the fitted peak frequency was 1600.1637(33) MHz.

  Fig. 11: Around 800 MHz, without a linear background. Using the data from 810.32 MHz to 810.95 MHz, the fitted peak frequency was 810.6120(14) MHz.
  Fig. 12: Around 800 MHz, with a linear background. Using the data from 810.32 MHz to 810.95 MHz, the fitted peak frequency was 810.5939(29) MHz.

  Fig. 13: Around -800 MHz, without a linear background. Using the data from 816.67 MHz to 817.23 MHz, the fitted peak frequency was 816.9934(28) MHz.
  Fig. 14: Around -800 MHz, with a linear background. Using the data from 816.67 MHz to 817.23 MHz, the fitted peak frequency was 817.0274(72) MHz.

  Fig. 15: Around -1.6 GHz, without a linear background. Using the data from 1596.96 MHz to 1597.66 MHz, the fitted peak frequency was 1597.3557(27) MHz.
  Fig. 16: Around -1.6 GHz, with a linear background. Using the data from 1596.96 MHz to 1597.66 MHz, the fitted peak frequency was 1597.4093(82) MHz.

[Fujimoto, Ye, Saito]

We adjusted the HWP and polarizer to obtain clean peaks and acquired beat signal data for PRX and PRY. After fitting the data, the deviations from the design values were 0.926(22) cm for PRX and 0.043(52) cm for PRY. Compared with the previous measurements before moving the lens to improve the mode-matching ratio (klog:37260), which gave deviations of 0.677(11) cm for PRX and -0.107(46) cm for PRY, both results are slightly different.

We also calculated the PRC length and the Schnupp asymmetry from the PRC. Using the Schnupp asymmetry calculated from the SRC in klog:37455, we then calculated the Schnupp asymmetry by taking a weighted average of the two values. The results were as follows:

PRC length: 66.59625(28) m
Schnupp asymmetry calculated from the PRC: 3.338630(565) m
Schnupp asymmetry from the weighted average:
3.33884(48) m when SRY was measured with the HWP scale at 14 and the polarizer scale at 295
3.33839(47) m when SRY was measured with the HWP scale at 59 and the polarizer scale at 250

Compared with the previous measurements before moving the lens to improve the mode-matching ratio (klog:37260), which gave a PRC length of 66.59425(24) m, a Schnupp asymmetry calculated from the PRC of 3.337640(473) m, and a Schnupp asymmetry from the weighted average of 3.33791(45) m, the PRC length is slightly different. However, there is no inconsistency between the Schnupp asymmetry calculated from the PRC and that calculated from the weighted average.
 

• To acquire the beat signal data for PRX, we first turned off the main laser and adjusted the alignment of the sub-laser. We then turned on the main laser and adjusted the alignment to the RFPD. When we checked the beat signal with the HWP scale at 82 and the polarizer scale at 50 using a spectrum analyzer, the peak was not clean (Photo 1). We therefore rotated the HWP and polarizer. The peak became clean when the HWP scale was set to 70 and the polarizer scale was set to 254. We then acquired data around 1.6 GHz (Photo 2), 0.8 GHz (Photo 3), -0.8 GHz (Photo 4), and -1.6 GHz (Photo 5).
   
• Similarly, for PRY, we first turned off the main laser and adjusted the alignment of the sub-laser. We then turned on the main laser and adjusted the alignment to the RFPD. We set the HWP scale to 16 and the polarizer scale to 117 to obtain clean peaks, and acquired data around 1.6 GHz (Photo 6), 0.8 GHz (Photo 7), -0.8 GHz (Photo 8), and -1.6 GHz (Photo 9).
   

• We then fitted the obtained PRX and PRY data with and without a linear background. I will post the fitting results for the individual peaks later. From the peak frequencies obtained from the fits and their uncertainties, we calculated the minimum and maximum values within the uncertainty ranges. We then took the overall minimum and maximum values from both fitting models, with and without a linear background, as the uncertainty range. The following data were therefore used to determine the PRX and PRY lengths.

  PRX
  Minimum (MHz)    Maximum (MHz)
  1591.7738    1591.8070
  807.8792    807.8958
  -821.3516    -821.3318
  -1563.5557    -1563.5479

  PRY
  Minimum (MHz)    Maximum (MHz)
  1600.1604    1600.1846
  810.5910    810.6133
  -817.0346    -816.9907
  -1597.4175    -1597.3530

  We set the FSR index of the data around -1.6 GHz to 0. For each pair of nearby peak frequencies, we calculated the frequency difference and divided it by the design value of the FSR. We then rounded the resulting value to the nearest integer to determine the FSR index. We fitted the measured peak frequencies as a function of the FSR index using the linear function AN+B, where A and B are fitting parameters and N is the FSR index.

  The fitting results were as follows.

  PRX (Fig. 1)
  A: 2.1957810(72) MHz
  B: -1563.5483(38) MHz

  PRY (Fig. 2)
  A: 2.308691(19) MHz
  B: -1597.363(21) MHz

  Since A corresponds to the FSR, we calculated the PRX and PRY lengths from the fitted values of A. The results were as follows.

  PRX
  Fitted length: 68.26556(22) m
  Design value: 68.2563 m
  Difference from the design value (fitted length − design value): 0.926(22) cm

  PRY
  Fitted length: 64.92693(52) m
  Design value: 64.9265 m
  Difference from the design value (fitted length − design value): 0.043(52) cm

  Compared with the previous measurements before moving the lens to improve the mode-matching ratio (klog:37260), which gave deviations of 0.677(11) cm for PRX and -0.107(46) cm for PRY, both results are slightly different.
   

• We also calculated the PRC length and the Schnupp asymmetry from the PRC. Using the Schnupp asymmetry calculated from the SRC in klog:37455, we calculated the Schnupp asymmetry from the weighted average as follows.

  PRC
  Calculated value: 66.59625(28) m
  Design value: 66.5914 m
  Difference from the design value (calculated value − design value): 0.485(28) cm

  Schnupp asymmetry calculated from the PRC
  Calculated value: 3.338630(565) m
  Design value: 3.3298 m
  Difference from the design value (calculated value − design value): 0.8830(565) cm

  Schnupp asymmetry
  When SRY was measured with the HWP scale at 14 and the polarizer scale at 295:
  Weighted average: 3.33884(48) m
  Design value: 3.3298 m
  Difference from the design value (weighted average − design value): 0.904(48) cm

  When SRY was measured with the HWP scale at 59 and the polarizer scale at 250:
  Weighted average: 3.33839(47) m
  Design value: 3.3298 m
  Difference from the design value (weighted average − design value): 0.859(47) cm

  Compared with the previous measurements before moving the lens to improve the mode-matching ratio (klog:37260), which gave a PRC length of 66.59425(24) m, a Schnupp asymmetry calculated from the PRC of 3.337640(473) m, and a Schnupp asymmetry from the weighted average of 3.33791(45) m, the PRC length is slightly different. However, there is no inconsistency between the Schnupp asymmetry calculated from the PRC and that calculated from the weighted average.

The fitting results for the SRY measurements in klog:37455, with the HWP scale at 14 and the polarizer scale at 295, and with the HWP scale at 59 and the polarizer scale at 250, are shown below.

The measurement data are saved in the following Dropbox folders:

All files/Dropbox KAGRA/Measurements/IFO/SRCL/SRCL_OMMT2_REFL_beat_signal_PZT_sweep/2026_09_01_SRY_hwp14_pol295
All files/Dropbox KAGRA/Measurements/IFO/SRCL/SRCL_OMMT2_REFL_beat_signal_PZT_sweep/2026_09_01_SRY_hwp59_pol250
 

• HWP scale: 14, Polarizer scale: 295

  Fig. 1: Around 1.6 GHz, without a linear background. Using the data from 1611.21 MHz to 1612.42 MHz, the fitted peak frequency was 1611.809(10) MHz.
  Fig. 2: Around 1.6 GHz, with a linear background. Using the data from 1611.21 MHz to 1612.42 MHz, the fitted peak frequency was 1611.766(45) MHz.

  Fig. 3: Around 800 MHz, without a linear background. Using the data from 810.37 MHz to 811.56 MHz, the fitted peak frequency was 810.962(11) MHz.
  Fig. 4: Around 800 MHz, with a linear background. Using the data from 810.37 MHz to 811.56 MHz, the fitted peak frequency was 810.993(45) MHz.

  Fig. 5: Around -800 MHz, without a linear background. Using the data from 845.47648 MHz to 846.683146 MHz, the fitted peak frequency was 846.1233(96) MHz.
  Fig. 6: Around -800 MHz, with a linear background. Using the data from 845.47648 MHz to 846.683146 MHz, the fitted peak frequency was 846.033(45) MHz.

  Fig. 7: Around -1.6 GHz, without a linear background. Using the data from 1655.6 MHz to 1656.77 MHz, the fitted peak frequency was 1656.233(13) MHz.
  Fig. 8: Around -1.6 GHz, with a linear background. Using the data from 1656.6 MHz to 1656.77 MHz, the fitted peak frequency was 1656.2322(79) MHz.
   

• HWP scale: 59, Polarizer scale: 250

  Fig. 9: Around 1.6 GHz, without a linear background. Using the data from 1599.24 MHz to 1600.04 MHz, the fitted peak frequency was 1599.5509(77) MHz.
  Fig. 10: Around 1.6 GHz, with a linear background. Using the data from 1599.24 MHz to 1600.04 MHz, the fitted peak frequency was 1599.507(11) MHz.

  Fig. 11: Around 800 MHz, without a linear background. Using the data from 789.2 MHz to 789.96 MHz, the fitted peak frequency was 789.4894(61) MHz.
  Fig. 12: Around 800 MHz, with a linear background. Using the data from 789.2 MHz to 789.96 MHz, the fitted peak frequency was 789.449(11) MHz.

  Fig. 13: Around -800 MHz, without a linear background. Using the data from 814.0 MHz to 814.82 MHz, the fitted peak frequency was 814.4756(78) MHz.
  Fig. 14: Around -800 MHz, with a linear background. Using the data from 814.0 MHz to 814.82 MHz, the fitted peak frequency was 814.541(15) MHz.

  Fig. 15: Around -1.6 GHz, without a linear background. Using the data from 1582.56 MHz to 1583.35 MHz, the fitted peak frequency was 1583.0282(66) MHz.
  Fig. 16: Around -1.6 GHz, with a linear background. Using the data from 1582.56 MHz to 1583.35 MHz, the fitted peak frequency was 1583.0585(99) MHz.

We analyzed the SRY data obtained in klog:37440. The deviation from the design value was 2.168(80) cm when the HWP scale was 14 and the polarizer scale was 295, and 2.319(71) cm when the HWP scale was 59 and the polarizer scale was 250. Compared with the previous measurement (klog:37393), which gave a deviation of 2.385(42) cm from the SRY design value, the result with the HWP scale at 59 is consistent, while the result with the HWP scale at 14 appears to be slightly different. Both results differ more significantly from the result before moving the lens to improve the mode-matching ratio (klog:37250), which gave a deviation of 1.757(50) cm from the design value.

Using the SRX result from klog:37450, we also calculated the SRC length and the Schnupp asymmetry. The SRC lengths were 66.61778(45) m for the HWP scale of 14 and polarizer scale of 295, and 66.61853(41) m for the HWP scale of 59 and polarizer scale of 250. The Schnupp asymmetries calculated from the SRC lengths were 3.339390(904) m and 3.337880(825) m, respectively. Compared with the previous measurement (klog:37393), which gave an SRC length of 66.61828(92) m and a Schnupp asymmetry calculated from the SRC of 3.33605(185) m, both SRC lengths are consistent, while the Schnupp asymmetry with the HWP scale at 14 appears to be slightly different. Compared with the results before moving the lens to improve the mode-matching ratio (klog:37260), which gave an SRC length of 66.61409(70) m and a Schnupp asymmetry calculated from the SRC of 3.34023(139) m, both SRC lengths are slightly different, while the Schnupp asymmetry with the HWP scale at 59 appears to be slightly different.
 

• We fitted the SRY data obtained in klog:37440 with and without a linear background. I will post the fitting results for the individual peaks later. From the peak frequencies obtained from the fits and their uncertainties, we calculated the minimum and maximum values within the uncertainty ranges. We then took the overall minimum and maximum values from both fitting models, with and without a linear background, as the uncertainty range. The following data were therefore used to determine the SRY length.

  HWP scale: 14, Polarizer scale: 295
  Minimum (MHz)    Maximum (MHz)
  1611.7206    1611.8190
  810.9479    811.0371
  -846.1329    -845.9886
  -1656.2458    -1656.2199

  HWP scale: 59, Polarizer scale: 250
  Minimum (MHz)    Maximum (MHz)
  1599.4960    1599.5586
  789.4376    789.4956
  -814.5555    -814.4679
  -1583.0683    -1583.0217

  We set the FSR index of the data around -1.6 GHz to 0. For each pair of nearby peak frequencies, we calculated the frequency difference and divided it by the design value of the FSR. We then rounded the resulting value to the nearest integer to determine the FSR index. We fitted the measured peak frequencies as a function of the FSR index using the linear function AN+B, where A and B are fitting parameters and N is the FSR index.

  The fitting results were as follows.

  HWP scale: 14, Polarizer scale: 295 (Fig. 1)
  A: 2.307939(29) MHz
  B: -1656.230(13) MHz
  HWP scale: 59, Polarizer scale: 250 (Fig. 2)
  A: 2.307886(26) MHz
  B: -1583.043(22) MHz

  Since A corresponds to the FSR, we calculated the SRY length from the fitted value of A. The results were as follows.

  HWP scale: 14, Polarizer scale: 295
  Fitted length: 64.94808(80) m
  Design value: 64.9264 m
  Difference from the design value (fitted length − design value): 2.168(80) cm
  HWP scale: 59, Polarizer scale: 250
  Fitted length: 64.94959(71) m
  Design value: 64.9264 m
  Difference from the design value (fitted length − design value): 2.319(71) cm

  Compared with the previous measurement (klog:37393), which gave a deviation of 2.385(42) cm from the SRY design value, the result with the HWP scale at 59 is consistent, while the result with the HWP scale at 14 appears to be slightly different. Both results differ more significantly from the result before moving the lens to improve the mode-matching ratio (klog:37250), which gave a deviation of 1.757(50) cm from the design value.
   

• Using the SRX result from klog:37450, we calculated the SRC length and the Schnupp asymmetry as follows.

  HWP scale: 14, Polarizer scale: 295
  SRC
  Calculated value: 66.61778(45) m
  Design value: 66.5913 m
  Difference from the design value (calculated value − design value): 2.648(45) cm

  Schnupp asymmetry calculated from the SRC
  Calculated value: 3.339390(904) m
  Design value: 3.3298 m
  Difference from the design value (calculated value − design value): 0.9590(904) cm

  HWP scale: 59, Polarizer scale: 250
  SRC
  Calculated value: 66.61853(41) m
  Design value: 66.5913 m
  Difference from the design value (calculated value − design value): 2.723(41) cm

  Schnupp asymmetry calculated from the SRC
  Calculated value: 3.337880(825) m
  Design value: 3.3298 m
  Difference from the design value (calculated value − design value): 0.8080(825) cm

  Compared with the previous measurement (klog:37393), which gave an SRC length of 66.61828(92) m and a Schnupp asymmetry calculated from the SRC of 3.33605(185) m, both SRC lengths are consistent, while the Schnupp asymmetry with the HWP scale at 14 appears to be slightly different. Compared with the results before moving the lens to improve the mode-matching ratio (klog:37260), which gave an SRC length of 66.61409(70) m and a Schnupp asymmetry calculated from the SRC of 3.34023(139) m, both SRC lengths are slightly different, while the Schnupp asymmetry with the HWP scale at 59 appears to be slightly different.

The fitting results for the individual peaks after changing and then restoring the SRX length in klog:37450 are shown below.

The measurement data are saved in the following Dropbox folders:

All files/Dropbox KAGRA/Measurements/IFO/SRCL/SRCL_OMMT2_REFL_beat_signal_PZT_sweep/2026_09_03_SRX_moved
All files/Dropbox KAGRA/Measurements/IFO/SRCL/SRCL_OMMT2_REFL_beat_signal_PZT_sweep/2026_09_03_SRX_restored
 

• After changing the SRX length
  Fig. 1: Around 1.6 GHz, without a linear background. Using the data from 1630.48 MHz to 1631.57 MHz, the fitted peak frequency was 1630.9316(29) MHz.
  Fig. 2: Around 1.6 GHz, with a linear background. Using the data from 1630.48 MHz to 1631.57 MHz, the fitted peak frequency was 1630.9322(38) MHz.

  Fig. 3: Around 800 MHz, without a linear background. Using the data from 789.76 MHz to 790.84 MHz, the fitted peak frequency was 790.2061(23) MHz.
  Fig. 4: Around 800 MHz, with a linear background. Using the data from 789.76 MHz to 790.84 MHz, the fitted peak frequency was 790.2147(25) MHz.

  Fig. 5: Around -800 MHz, without a linear background. Using the data from 798.46 MHz to 799.51 MHz, the fitted peak frequency was 799.0342(30) MHz.
  Fig. 6: Around -800 MHz, with a linear background. Using the data from 798.46 MHz to 799.51 MHz, the fitted peak frequency was 799.0380(41) MHz.

  Fig. 7: Around -1.6 GHz, without a linear background. Using the data from 1588.38 MHz to 1589.78 MHz, the fitted peak frequency was 1589.2838(23) MHz.
  Fig. 8: Around -1.6 GHz, with a linear background. Using the data from 1588.38 MHz to 1589.78 MHz, the fitted peak frequency was 1589.2831(38) MHz.
   

• After restoring the SRX length
  Fig. 9: Around 1.6 GHz, without a linear background. Using the data from 1608.77 MHz to 1609.66 MHz, the fitted peak frequency was 1609.0959(28) MHz.
  Fig. 10: Around 1.6 GHz, with a linear background. Using the data from 1608.77 MHz to 1609.66 MHz, the fitted peak frequency was 1609.0650(63) MHz.

  Fig. 11: Around 800 MHz, without a linear background. Using the data from 796.61 MHz to 797.44 MHz, the fitted peak frequency was 796.9280(26) MHz.
  Fig. 12: Around 800 MHz, with a linear background. Using the data from 796.61 MHz to 797.44 MHz, the fitted peak frequency was 796.898(10) MHz.

  Fig. 13: Around -800 MHz, without a linear background. Using the data from 835.71 MHz to 836.57 MHz, the fitted peak frequency was 836.2367(26) MHz.
  Fig. 14: Around -800 MHz, with a linear background. Using the data from 835.71 MHz to 836.57 MHz, the fitted peak frequency was 836.2598(71) MHz.

  Fig. 15: Around -1.6 GHz, without a linear background. Using the data from 1577.79 MHz to 1578.53 MHz, the fitted peak frequency was 1578.1716(42) MHz.
  Fig. 16: Around -1.6 GHz, with a linear background. Using the data from 1577.79 MHz to 1578.53 MHz, the fitted peak frequency was 1578.168(10) MHz.

[Fujimoto, Ye, Saito]

After Takahashi-san and Ushiba-san changed the length of SRX (klog:37449), and again after they restored the length, we acquired beat signal data around 1.6, 0.8, -0.8, and -1.6 GHz. We then calculated the SRX length. The deviations from the design value were 3.050(11) cm after the length was changed and 3.127(42) cm after the length was restored. Comparing the result after restoring the length with the previous measurement (klog:37393), which gave a deviation of 3.01(18) cm from the design value, we consider the results to be consistent. However, the result differs slightly from the result before moving the lens to improve the mode-matching ratio (klog:37260), which gave a deviation of 2.80(13) cm. According to klog:37449, the SRX length decreased by 1 mm after the length was changed. The two measurements also show that the SRX length decreased by approximately 1 mm after the length was changed. Therefore, we confirmed that this measurement method can detect changes in the cavity length.
 

• After Takahashi-san and Ushiba-san changed the SRX length (klog:37449), we removed the mirror that had been placed in the optical path to the RFPD at the reflection port of OMMT2 in the previous measurement (klog:37445). We then injected the light into the RFPD and adjusted the alignment to maximize the DC output. Next, we injected the sub-laser with the HWP scale set to 82, corresponding to S-polarization. We observed the beat signal with a spectrum analyzer and rotated the polarizer to maximize the beat signal. The scale reading was then set to 50. We acquired data when the beat signal was around 1.6 GHz (Photo 1), 0.8 GHz (Photo 2), -0.8 GHz (Photo 3), and -1.6 GHz (Photo 4).
   
• After Takahashi-san and Ushiba-san restored the SRX length, we adjusted the alignment to maximize the DC output of the RFPD. When we checked the beat signal around 1.6 GHz, the peak appeared to be split into two peaks (Photo 5). We therefore turned off the main laser and adjusted the alignment of the sub-laser. However, the alignment already appeared to be sufficiently optimized, and there was almost no change. We then turned the main laser back on and checked the beat signal again. The peak had become clean, so we acquired data when the beat signal was around 1.6 GHz (Photo 6), 0.8 GHz (Photo 7), -0.8 GHz (Photo 8), and -1.6 GHz (Photo 9).
   

• We fitted the data around each peak with and without a linear background. I will post the fitting results for these peaks later. From the peak frequencies obtained from the fits and their uncertainties, we calculated the minimum and maximum values within the uncertainty ranges. We then took the overall minimum and maximum values from both fitting models, with and without a linear background, as the uncertainty range. The following data were therefore used to determine the SRX length.

  After changing the length
  Minimum (MHz)    Maximum (MHz)
  1630.9283    1630.9360
  790.2038    790.2172
  -799.0422    -799.0312
  -1589.2869    -1589.2793

  After restoring the length
  Minimum (MHz)    Maximum (MHz)
  1609.0587    1609.0987
  796.8883    796.9306
  -836.2669    -836.2342
  -1578.1785    -1578.1583

  We set the FSR index of the data around -1.6 GHz to 0. For each pair of adjacent peak frequencies, we calculated the frequency difference and divided it by the design value of the FSR. We then rounded the resulting value to the nearest integer to determine the FSR index. We fitted the measured peak frequencies as a function of the FSR index using the following linear function AN+B where A and B are fitting parameters and N is the FSR index.

  The fitting results were as follows.

  After changing the length (Fig. 1)
  A: 2.1951014(35) MHz
  B: -1589.2804(34) MHz

  After restoring the length (Fig. 2)
  A: 2.195077(14) MHz
  B: -1578.1721(92) MHz

  Since A corresponds to the FSR, we calculated the SRX length from the fitted value of A. The results were as follows.

  After changing the length
  Fitted length: 68.28670(11) m
  Design value: 68.2562 m
  Difference from the design value (fitted length − design value): 3.050(11) cm

  After restoring the length
  Fitted length: 68.28747(42) m
  Design value: 68.2562 m
  Difference from the design value (fitted length − design value): 3.127(42) cm

  Comparing the result after restoring the length with the previous measurement (klog:37393), which gave a deviation of 3.01(18) cm from the design value, we consider the results to be consistent. However, the result differs slightly from the result before moving the lens to improve the mode-matching ratio (klog:37260), which gave a deviation of 2.80(13) cm.
  According to klog:37449, the SRX length decreased by 1 mm after the length was changed. The two measurements also show that the SRX length decreased by approximately 1 mm after the length was changed. Therefore, we confirmed that this measurement method can detect changes in the cavity length.

[Ushiba, Takahashi]

We moved three SR mirrors to change SRCL. Each setpoint for the IP L LVDT was changed by +200 [um]. SRCL was decreased by 1mm in Total. Moving order was SR3, SRM, and SR2. After changing the setpoints, GRY was locked and aligned. The setpoints for the Oplev yaw were changed from 37 to 31 for SR3 and from -49 to -45 for SR2. Changed values are summarized below. Oplev L was different from IP L by a factor of 2. After the length measurements, all setpoints were recovered.

Note that: OMMT1 equips LIGO-OSEMs, and the OSEMs are using LEDs, whose wavelength is nearly infrared (but not 1um), and the IR camera (without proper filtering) senses the infrared light clearly. Very brighter than stars which the IR camera can detect.

To distinguish the light source, it might be helpful to turn off the OSEM LEDs, if possible.

[Fujimoto, Ye, Saito]

To investigate whether the splitting of the peak observed in the previous measurement (klog:37440) was caused by mode splitting due to birefringence of the ITM substrate, we used an HWP and a PBS to separate the light into S- and P-polarizations and installed PDs to monitor the two signals. When we performed cavity scans using only the main laser or only the sub-laser, we confirmed that the resonance positions of the cavity scans were different between S- and P-polarizations in both cases. Therefore, we consider that the splitting of the peak was caused by mode splitting due to birefringence of the ITM substrate.
 

• In the previous measurement (klog:37440), to investigate whether the splitting of the peak was caused by mode splitting due to birefringence of the ITM substrate, we placed an additional mirror after the mirror at the reflection port of OMMT2. We then placed an HWP and a PBS after this mirror and installed two PDs to monitor both the reflected and transmitted light from the PBS (Photo 1).
   
• Next, we rotated the HWP so that the transmitted and reflected powers from the PBS were approximately equal. The scale reading was 56, and both powers were approximately 0.7 mW. This scale reading was similar to the value obtained when the polarization was rotated by 45 degrees in the previous measurement (klog:37440).
   
• We then turned off the main laser, removed the ND filter, and injected only the sub-laser in the S-polarization state. By sweeping the PZT with a triangular waveform, we confirmed that the resonance positions of the cavity scans were different between S- and P-polarizations (Photo 2). The orange line in Photo 2 shows the S-polarization signal, while the blue line shows the P-polarization signal. Since the relative shift reverses at the turning points of the triangular waveform, we consider that this is caused by mode splitting due to birefringence of the ITM substrate.
   
• Next, we turned off the sub-laser and used only the main laser. When we swept the SRM, we similarly observed a difference in the resonance positions between S- and P-polarizations (Photo 3). However, near each peak, the other polarization signal became smaller (Photo 4), suggesting that the S- and P-polarizations were not completely separated. We therefore rotated the HWP to see whether the two polarizations could be separated more completely, but there was no improvement. Therefore, the light appears to be elliptically polarized. The reason why this behavior was not observed when using the sub-laser is likely that the SNR was too low.

With Haio-san

We have checked some items for NAOJ asset check process.

Xend Pic
Yend Pic

[Fujimoto, Saito]

The issue of the low DC output from the RFPD reported previously (klog:37436) was resolved by reconnecting the cable. Next, an HWP was installed in front of the BS for the sub-laser, and the polarization was set to S-polarization. When the beat signal was observed, the peak was split into two. By rotating either the HWP in front of the BS or the polarizer in front of the RFPD, the relative amplitudes of the two peaks could be changed. Therefore, it appears that the P-polarization peak is also being observed simultaneously, and this is likely caused by birefringence in ITMY. The results of determining the SRY length from the beat signal data acquired while maximizing each of the two peaks will be posted later.
 

• First, to investigate the reason for the low DC output from the RFPD reported previously (klog:37436), we monitored the DC output of the RFPD with an oscilloscope and found it to be approximately 8 V. Since there was no problem with the signal amplitude and the fluctuations were not significant, we reconnected the RFPD to CDS, and the DC output was approximately 12500 counts, corresponding to approximately 7.6 V. Therefore, the connection may not have been good in the previous measurement (klog:37436).
   
• Next, an HWP was installed in front of the BS for the sub-laser (Photo 1), and the polarization was set to S-polarization using a PBS. The main laser was then turned off, and the sub-laser was aligned to SRY. When we observed the beat signal at -1.6 GHz, the peak was split into two (Photo 2). We then rotated the polarizer in front of the RFPD. This allowed us to decrease the amplitude of one peak while increasing that of the other. Similarly, rotating the HWP installed in front of the BS also allowed us to change the relative amplitudes of the two peaks. Therefore, although the sub-laser was initially set to S-polarization, the measured beat signal contains a P-polarization component. This is likely due to birefringence in ITMY.
   

• When the measurement was first performed with S-polarization, the HWP setting was 82. By changing the HWP setting to 14 and the polarizer setting in front of the RFPD to 295, we were able to maximize the peak that was smaller in the initial S-polarization measurement. We then acquired data at beat frequencies of 1.6 GHz (Photo 3), 0.8 GHz (Photo 4), -0.8 GHz (Photo 5), and -1.6 GHz (Photo 6). Next, we set the HWP to 59 and the polarizer in front of the RFPD to 250, which allowed us to maximize the other peak. We then acquired data in the same way at beat frequencies of 1.6 GHz (Photo 7), 0.8 GHz (Photo 8), -0.8 GHz (Photo 9), and -1.6 GHz (Photo 10). The amplitudes of the beat signals when each peak was maximized were approximately 931 μV for the peak that was larger in the initial S-polarization measurement and approximately 1.46 mV for the peak that was smaller. Thus, the two peak amplitudes differed by a factor of approximately 1.57. In addition, when the HWP setting was 14, we checked the polarization of the sub-laser using a PBS. The measured powers were approximately 476 mW for P-polarization and 513 mW for S-polarization. Finally, we removed the HWP, but the beat signal was still split into two peaks, similar to the observation in Photo 2.

  The result of determining the SRY length from the data analysis will be posted later.

Based on the information in K-Log #37433, an additional investigation was conducted to determine whether any AC alarms had occurred.
The IM Heater and CRY Stepper were checked, and AC input undervoltage protection (AC-FAIL) errors were found. After the inspection, all alarms were cleared.

For details about AC-FAIL, please refer to the following website: link

Based on these results, it is presumed that a momentary voltage drop occurred throughout, including the center area, rather than only at both ends, although the extent of the impact varied depending on each device’s threshold.

IM HEATER
EX: AC-FAIL error
EY: AC-FAIL error
IX: No error
IY: AC-FAIL error

CRY Stepper
EX: AC-FAIL error
EY: AC-FAIL error
IX: No error
IY: AC-FAIL error

For reference:

The equipment that can be controlled via the web interface uses the following two regulated DC power supplies.
The PWR401MH is equipped with AC input undervoltage protection (AC-FAIL).
The PMX70-1A does not have this function; therefore, it is assumed to have recovered automatically after the momentary power interruption.

A list of the equipment used is available on the following page:
https://gwwiki.icrr.u-tokyo.ac.jp/JGWwiki/KAGRA/Subgroups/DGS/Projects/IMHeater
 

[Ushiba, Fujimoto]

Abstract

Toward the PRC/SRC length measurement using P-pol., we implemented an SRY lock check and SRM ADS using POP DC instead of AS DC.
We confirmed that the modified configuration works properly in the VERTEX Guardian, ASC_LOCK Guardian, and INITIAL_ALIGNMENT Guardian.

Details

In the PRC/SRC length measurement using P-pol., the beam is extracted from the OMM chamber by a steering mirror after reflection from OMMT2. Therefore, the AS signal becomes unavailable.

As a result, the SRY lock check and the SRM ADS, which use AS DC, no longer work.
To address this, we implemented the SRY lock check and SRM ADS using POP DC instead of AS DC.

Modification of the SRY Lock Check Function

As shown in Fig. 1, we modified the is_src1f_locked() function in lsclib.py so that the lock check is performed using POP DC instead of AS DC.
This implementation was copied from the function used in is_prc1f_locked().

Modification of the SRM ADS

The SRM alignment had been performed so as to maximize AS DC in SRY.
Therefore, it does not work in the current configuration where the AS beam is blocked.

We therefore decided to engage the ADS using POP DC.

Fig. 2 shows ENGAGE_ADS_FOR_SRY in the modified ASC_LOCK.py.

The specific changes are as follows. The previous settings are kept as commented-out lines.

• TRG_MTRX: changed from AS DC to POP DC
• INMTRX: changed from AS DC to POP DC
• INF_GAIN: changed from -0.3 to -0.45

The reason for changing the gain from -0.3 to -0.45 is as follows.
From the time-series data during ADS using AS DC, shown in Fig. 3, the AS DC power was approximately 1.5 times larger than the POP DC power. Therefore, the gain was adjusted to compensate for this difference.

Fig. 4 shows the behavior of the relevant signals when the ADS was engaged.
After the ADS was engaged, the SRM moved, and both POP DC and REFL DC increased.

We confirmed that the modified configuration works properly in the VERTEX Guardian, ASC_LOCK Guardian, and INITIAL_ALIGNMENT Guardian.

Summary

We modified the Guardians so that the SRY lock check and SRM ADS can be performed using POP DC instead of AS DC.

This modification is only a temporary treatment. After the PRC/SRC length measurement with P-pol. is completed and the AS signal becomes available again, the configuration should be reverted to the previous one.

[Fujimoto, Yokozawa, Saito]

A mirror was installed inside the OMMT chamber so that the light reflected from OMMT2 would reach the optical table on the X+ side. The reflected light was then directed into the RFPD. However, the DC output was approximately 1.3 V, with fluctuations in the signal also observed. Since the DC output was several volts when the RFPD was placed at OMC REFL, the position of the RFPD will be fine-tuned next time to maximize the DC output, and the condition of the RFPD will also be investigated.
 

• First, a mirror was installed inside the OMMT chamber so that the light reflected from OMMT2 would reach the optical table on the X+ side (Photo 1). The beam was then lowered using a periscope, and the optical power was measured to be approximately 12 mW. An ND filter with OD = 1.0, a mirror, a lens with a focal length of 50 mm, and the RFPD were then installed. The optical power measured just before the RFPD was approximately 1.5 mW. Next, a rotatable polarizer was placed in front of the lens (Photo 2), and the polarizer angle was adjusted to maximize the optical power. The measured power was approximately 1.0 mW. The BNC cable that had been used for the OMC REFL PD was then connected to the DC output of the RFPD so that the signal could be monitored through CDS. The mirror alignment was adjusted to maximize the DC count, resulting in approximately 2200 counts, corresponding to approximately 1.3 V. When the RFPD was placed at OMC REFL and approximately 1 mW of light was injected, the DC output reached several volts after optimizing the mirror alignment. Therefore, it is likely that not all of the incident light is being coupled into the RFPD. Fluctuations in the signal were also observed. Next time, the position of the RFPD will be fine-tuned to maximize the DC output, and the condition of the RFPD will be investigated.

I checked the guardian and found that this filter was not implemented into the guardian, so this filter should be turned on manually at some point.
I also checked when the filter was turned on (fig1) and checked the klog around that  day but I could not find the related log.

If this filter is really necessary, it should be turned on again, and also be managed by the guardian.

I checked ETMX and ETMY suspensions by engaging local controls step by step.
There seems no serious issue and both suspensions can reach LOCK_ACQUISITION state without any problems.

[Nakagaki, Yasui]

I tried to turn off the heater on the 8K shield, but this power output was already 0W.

We checked the situation and found that the AC alarm was active on this power supply.

It appeart that the heater shut off due to a drop in the input valtage.

According to the temperature of the 8K shield top, the heater appeared to have stopped before 8:31(JST) on Aug 27.

Around this time we experienced a momentary power outage at this site.(klog 37420)

We checked the resistance of this heater and found no issues.

Anyway, we completed the pre-heating work.