Recently, high power IMC output with misaligning PRM is often used and sometimes IMC is kept locking with high power over night, which results in making HPBD hot,
So, I discussed with uchiyama-san and decided to add the safety function in the IMC guardian.

If hitting 10W beam for 8 and 24 hours, HPBD temperature becomes 350K and 370K, respectively.
So, I set the threshold at 365K as shown in fig1.

From now, if the HPBD temperature exceeds 365K, IMC lock will be lost once to make IMC output smaller.

Note:

During the work, I noticed we have two ZERO_SERVOOFFSET state with the same index.
Since this state is not used, I didn't change them but it would be better to renew the IMC guardian.

Since the satellite box was replaced, we haven't observed any glitches. Very good. We'll keep our eyes on it until the next maintanance day.

[Takano]

We tuned the demodulation phase of REFL51 in the same way as klog 36990.

We injected the excitation at 50 Hz in SRCL1_EXC when SRMI was locked using 1f signals and measured the ASD. The demodulaiton was tuned so that the peak at 50 Hz in REFL51Q was minimised. The phase was changed from -60 to -85.

Yes, that's one typo; I removed 0 unintentionally.

Another typo exists here:

> Next, we changed the PRCL error signal from REFL45I to POP17I, because in RSE, REFL45I is used for CARM and POP17I for PRCL.

Not POP17I but POP45I.

>~7 deg rotated from the optimal angle, according to Ushiba-san

Not ~7 degs but 70 degs if I remembered correctly.

[Takano, Tanaka, Fujimoto, Saito]

To improve the mode matching between the main laser beam and the sub-laser beam incident on the RFPD, the optical path length of the sub-laser was adjusted. The resulting mode-matching ratio was approximately 76%. The alignment was performed using two irises, and the RFPD was installed. The alignment of the main laser was then finely adjusted to maximize the beat signal amplitude, and the polarization of the sub-laser was also optimized. As a result, the beat signal level increased from -58.67 dBm in the previous measurement (klog:36974) to -45.59 dBm.
 

• In klog:37004, the waist positions of the two beams differed by 352 mm. Therefore, part of the optical setup was modified to increase the optical path length of the sub-laser by approximately 350 mm. The beam profiles of both the main laser and the sub-laser were then measured at locations far from the beam waist on both sides of the waist, and fitting was performed (Figure 1). The green and orange curves represent the fitting results for the main laser, while the red and blue curves represent those for the sub-laser. The origin of the coordinate system is defined at the beam sampler where the two beams are combined.

  The waist positions and waist radii obtained from the fitting are summarized below.

  Main Laser

  x-direction: Waist position = -220.1 ± 3.7 mm, Waist radius = 0.0577 ± 0.0006 mm
  y-direction: Waist position = -170.7 ± 7.6 mm, Waist radius = 0.0674 ± 0.0014 mm
  →Average: Waist position = -195.4 mm, Waist radius = 0.0626 mm

  Sub-Laser

  x-direction: Waist position = -522.6 ± 1.5 mm, Waist radius = 0.0929 ± 0.0003 mm
  y-direction: Waist position = -522.6 ± 6.3 mm, Waist radius = 0.1077 ± 0.0015 mm
  →Average: Waist position = -522.6 mm, Waist radius = 0.1003 mm

  The waist position and waist radius of the main laser, which should not have changed, were found to differ significantly from the values reported previously. In klog:37004, the fitting had been performed using measurements taken only after the waist, which likely resulted in a large fitting error. If the sub-laser waist position is assumed to be -172.6 mm while all other parameters are taken from the present measurement, the calculated mode-matching ratio is 62%. Therefore, the mode-matching ratio of the optical setup in klog:37004 was likely around 62%, rather than the previously estimated 5%.

  Since the waist positions were still offset by 327.2 mm, part of the optical setup was modified again to reduce the sub-laser optical path length by approximately 325 mm. The beam profiles of the main laser and sub-laser were then measured only at locations far beyond the waist. The waist radii were fixed to the values obtained in Figure 1, and fitting was performed only for the waist positions (Figure 2). The green and orange curves represent the fitting results for the main laser, while the red and blue curves represent those for the sub-laser. The origin is again defined at the beam sampler where the two beams are combined.

  The fitted waist positions are summarized below.

  Main Laser

  x-direction: Waist position = -199.0 ± 13.1 mm
  y-direction: Waist position = -148.7 ± 14.8 mm
  →Average: Waist position = -173.9 mm

  Sub-Laser

  x-direction: Waist position = -133.0 ± 10.4 mm
  y-direction: Waist position = -194.1 ± 3.9 mm
  →Average: Waist position = -163.6 mm

  Using these results, the mode-matching ratio was calculated to be approximately 76%.
   

• Next, two irises were installed, and the alignments of both the main laser and sub-laser were adjusted so that the beams passed through both irises. A 50 mm focal-length lens used to focus the beams onto the RFPD, the steering mirror located immediately before the RFPD, and the RFPD itself were then installed. The current optical layout is shown in Figure 3.
   

• When both beams were directed onto the RFPD using the steering mirror, the DC output was -4.825 V. When only the main laser beam was incident on the RFPD, the DC output was -54.88 mV. The optical power incident on the RFPD was approximately 19 μW for the main laser and 1.638 mW for the sub-laser. After confirming the presence of the beat signal, the alignment of the main laser was finely adjusted to maximize the beat signal amplitude. In addition, the polarization of the sub-laser was adjusted using a HWP to further maximize the beat signal (Figure 4). As a result, the beat signal level increased from -58.67 dBm in the previous measurement (klog:36974) to -45.59 dBm. Furthermore, the beat signal amplitude exhibited very little fluctuation over time.

I intentionally changed the Pcal-X beam position by moving the pico motors and checked the response in the QPD signals.
(ETMX was in the LOCK_ACQUISITION state during this work.)

TCam images were taken before and after the pico-motor movement.

A detailed analysis of the QPD response will be performed later.

I modified the guardian to change the nominal PSL HWP angle from 148 to 152 so that IMC output becomes 1W when HWP is at nominal angle.

(Remote) R. Takahashi, Nakagaki, Ikeda

This work is related to K-Log #37013.
We replaced the PR3 satellite box.

[Details]
1. We measured the forward voltage at the end of the conversion cable connected to the feedthrough.
   There was no significant change in the values, and all measurements were normal.

IM H3

(Reference value)IM H1

2. Next, we replaced the satellite box.
We placed the new satellite box (S1604893) on top of the old satellite box (S1504430) and reconnected the DSUB cables from the old box to the new one.
H2 and H3 were connected to the replacement satellite box.Fig.1
 

Detail

The first trial

First, we started using 1f signals for locking the DRMI. The signals were as follows:

• PRCL: REFL 45I
• MICHL POP 17Q
• SRCL: POP 17I

The gain settings of them were decided as follows:

• PRCL: Measured the relative gain between REFL 45I and REFL 135I when PRMI was locked using 3f signals. Multiplied the factor by the gain for PRMI 3f locking.
• MICH and SRCL: Estimated the relative gain from SRMI to DRMI using Finesse simulation as shown in Fig. 1 (15 for MICH and -17 for SRCL). Multiplied the factors by the gains for SRMI 1f locking.

The initial guess of the appropriate gains and the actual gains after tuning are as follows:

We built these gains beforehand and set triggers to trigger the output when POP90 and AS34 buildups exceeded a certain level. With these configurations, we could hold the interferometer in a good position for ~1 sec (Fig. 1).

Second trial

Next, we changed the PRCL error signal from REFL45I to POP17I, because in RSE, REFL45I is used for CARM and POP17I for PRCL. We tried w/o and w/ triggers, but we could not lock the DRMI, even tweaking the gains. The situation got worse. 

We noticed that the PRCL feedback was incredibly small, more than 2 orders of magnitude smaller than the others, so we increased the gain of PRCL, but the stability didn't change significantly. We decided to use REFL135I, which is used for PRMI3f lock, to control PRCL instead of REFL45I. The PRCL gain for the new signal was chosen to maintain the overall gain from POP17I to REFL135I. Soon after changing the signal, we could lock the DRMI in 26 seconds (Fig. 2). Something was wrong with POP17I.

Tuning gains, changing signals

Then we started further tuning of the gains and selecting the signals. We tried replacing POP17Q (1f) with REFL51Q (3f) for MICH control, and it seemed that 3f was better than 1f.  We also tried replacing POP17I (1f) with REFL51I (3f) for SRCL control, but in this case, 1f seemed better than 3f.

The final configuration of the selected signal, the control gain, and the upper and lower thresholds for each DOF are shown below:

With these conditions, we could lock DRMI in> 5 minutes (Fig. 3). We could barely measure the open-loop transfer function of each DoF, as attached (Fig.4 for PRCL, Fig. 5 for MICH, Fig. 6 for SRCL). Probably because of control instability, the measurement data have lower coherence, so it is not clear exactly what they looked like.

Issues

As reported here, the buildup of AS34 would be more than 5, whereas it is currently 0.5-0.6. It could be that the current locking point is not what we want due to the incorrect signs of the gains and the offset in the error signals. However, the POP90 buildup looked good (it's almost 1, as expected), suggesting the SRCL might be controlled at a weird point. On the other hand, the buildup during DRMI swings reached ~2 and never reached 5. It could be due to poor alignment of SRMI, but I'm not sure.

Another issue is the coupling between the DoFs. The open-loop transfer functions looked very weird in shape, especially in the 10s of Hz, and we suspect the couplings are the cause. At least, we know the demodulation phase of REFL51I is far from optimal (~7 deg rotated from the optimal angle, according to Ushiba-san). We have to tune the phase in SRMI or DRMI, and also tune the control gain again.

Fig.1 is OSEM signal timeseries in last night. The interval between cursors shows the duration when PR3 was in PAY_FLOAT state. As you can see, There seems to be the noisy timing and the quiet timing. 

In the noisy timing, the glitch occurres per 1-2 mins (fig.2). If this becomes noisy at once, the situation continues several hours.  On the other hands, any glitch seems to not occured over several hours if it is in quiet timing (fig.3).

Quick checks on the QPD signals at Pcal-X Rx module.

I checked the signals from a QPD that had been temporarily placed in the Pcal-X Rx module yesterday.
At that time, the Pcal beam had not yet reached the Rx module, so the QPD had not been properly aligned.

I requested ETMX to go to the LOCK_ACQUISITION state and switched Pcal-X to high-power mode.
A clear signal was observed in the QPD sum channel (Fig. 1).

I also moved the setpoints of ETMX TM pitch and yaw.
Although small responses were seen in the QPD X and Y signals, no clear position response was observed (Fig. 2).

After the above checks, the ETMX TM pitch and yaw setpoints were returned to their original values.

[YamaT, Oshino, Nakagaki, Hayakawa, Sawada, M.Takahashi, Omae, Yamaguchi, Ikeda]

K1IOO1 was restored at approximately 16:00 on June 2, 2026.

Details
A new 120-meter HIB cable and a 150-meter MTP cable were installed between the computer room and the K1IOO1 rack.
The HIB cable was replaced, and the restoration of K1IOO1 was successfully completed.
The MTP cable will be retained as a spare. If the HIB cable becomes unusable in the future, it can be used by switching to a V2 IO chassis.

[Takano, Tanaka, Fujimoto, Saito]

The beam profiles of the main laser beam and the sub-laser beam incident on the RFPD were measured and fitted. The resulting mode-matching ratio was approximately 5%.

• The RFPD and the 50 mm focal-length lens placed immediately before it were removed. The beam profiles of both the main laser beam and the sub-laser beam were then measured downstream of the beam sampler where the two beams are combined. The fitting results are shown in Figure 1. The green and orange curves represent the fitting results for the main laser beam, while the red and blue curves represent those for the sub-laser beam. The origin of the coordinate system is defined at the beam sampler where the two beams are combined.

  The waist positions and waist radii obtained from the fitting are summarized below.

  Main Laser

  x-direction: Waist position = -611.3 ± 79.7 mm, Waist radius = 0.1246 ± 0.0120 mm
  y-direction: Waist position = -504.6 ± 98.5 mm, Waist radius = 0.1450 ± 0.0199 mm
  → Average: Waist position = -558.0 mm, Waist radius = 0.1348 mm

  Sub-Laser

  x-direction: Waist position = -194.3 ± 14.7 mm, Waist radius = 0.0944 ± 0.0031 mm
  y-direction: Waist position = -217.6 ± 19.2 mm, Waist radius = 0.1101 ± 0.0045 mm
  → Average: Waist position = -206.0 mm, Waist radius = 0.1023 mm

  The mode-matching ratio between the two beams is given by 4×R_1×R_2/((Z_1-Z_2)^2+(R_1+R_2)^2), where Z_x and R_x (x=1,2) are the waist position and Rayleigh range of each beam, respectively. Using the average waist positions and waist radii obtained from the fitting, the mode-matching ratio was calculated to be approximately 5%.

[Hirose, Tanaka, Takano Ushiba, 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.
The agreement between these two values is consistent with theoretical expectation.
From these results, 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 agreement of the two measurement results is 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.

Ushiba, Takano, Fujimoto, Hirose, Tanaka

## Abstract

We found that PR3 IM OSEM H3 has large gilitch frequently. This glitch shakes PR3 largely, more than 10 urads and disturbs PRMI/SRMI lock.

## Details

As reported in klog36978, PR3 moved largely again during today's commissioning.

First, GAS LVDT signals seem to become glitchy at this moment. We turned off only GAS controls and monitored the local sensor signals. Although GAS LVDT signal seems to be not changed, PR3 moved largely (fig.1). So GASs are not gulity.

Second, We turned off TM OLDAMP controls after restoring GAS controls. Similarly, PR3 moved largely (fig.2). So, TM oplev seems to be innocent.

Third, we turned off IM DAMP. Actually, we requested PR3 guardian to be the PAY_FLAOT state. Then, we found that IM OSEM H3 has large glitch, ~10 cnts? in the view from K1:VIS-PR3_IM_OSEMINF_H3_OUT (fig.3). This time, TM oplev seems to be stable(fig.4). IM OSEM H3 seems to be used for IM DAMP T and Y. We turned on the PAYLOAD controls (actually we requested the guardian to be LOCK_ACQUISITION) and then we turned off the IM DAMP T and Y. In this state, TM OLDAMP started oscillate 1.15 Hz. Except for this 1.15 Hz oscillation, PR3 seems not to move largely (fig.5). 

Finally, we closed the laser shutter in order to confime whether this glitches are caused by the scattered light from IFO. The glitch is still in the OSEM signals even though the laser shutter was closed (K1:PSL-BEAM_SHUTTER = 0) (fig.6). This indicates this glitch comes from OSEM itself.

According to OSEM2EUL matrix, the coefficient from DGS cnts to urad? in Y direction is 5.8. So This 10 cnts glitch is relavant with ~58 urad.  

OSEM giltch seems to appear in only one direction, that is in negative direction in K1:VIS-PR3_IM_OSEMINF_H3_OUT. we suspect that somethin ex. OSEM LED intensity? or LED current? gets weak.

We left PR3 in the PAY_FLOAT state overnight to check how frequent this glitch occurrs.

> The sequence stopped at INCREASE_LCS_POW_FOR_OMC. At that time, the IMC TRANS output stayed around 8.1 W.

I fixed a bug in the INITIAL_ALIGNMENT guardian, and also changed the way to increase the input power. Now the guardian monitors the input power and increases it until it exceeds 8.5 W.

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.