I checked the TM transfer functions in a vacuum. The IP setpoints were reset to the original (-164 to -550 for L and -24 to -50 for T), so the Length Oplev was also aligned. The transfer functions were consistent with the references.

I checked the IM transfer functions in a vacuum. They were the same as the recent situation in the vacuum (the DC gain is smaller than the reference, except for L and H1).

I checked the GAS transfer functions in a vacuum. They were consistent with the references.

I checked the IP transfer functions in a vacuum. IDAMP signals are not treated well, so please see the LVDT responses in BLEND signals. The resonant frequencies of the IP were 63mHz for L, 74mHz for T, and 0.32Hz for Y, respectively.

EYC1F temperature seemed to have decreased by 2 C degrees for 2 months.

I increased the heater power as follows,

• Delonghi 0 -> 1.2kW
• Sunrise 1 : 900W -> 1.2kW
• Sunrise 2: 600W -> 1.2kW

[Tanaka, Hirose, Saito]

We confirmed that the Moku:Lab was operating properly. We also set up the system so that the local oscillator frequency could be continuously adjusted while monitoring the beat signal frequency. Although various types of filters were tested, the control system unfortunately did not function.
 

• Following the previous attempt (klog:36845), we continued working on the PLL. First, to verify that the Moku:Lab was functioning correctly, we connected its output to its input and confirmed that a constant voltage applied at the output was observed unchanged at the input. Next, we confirmed that the error signal was properly output when passed through a flat (0 dB) filter.
  We then split the beat signal into two using a power splitter and used an additional Moku:Lab as a spectrum analyzer to continuously monitor the beat signal, allowing us to match the local oscillator frequency accordingly. Observing the mixed beat signal and local oscillator signal on the Moku:Lab oscilloscope, we saw that the amplitude of the error signal fluctuated and its frequency also varied (Photo 1). The red line represents the error signal, and the blue line represents the feedback signal. In this state, we applied various filters, including flat, high-pass, and low-pass filters, but no significant change in the error signal amplitude was observed. We also attempted to measure the open-loop transfer function; however, it did not appear that any meaningful measurement was obtained. Therefore, it is likely that feedback was not properly established. In addition, since the feedback signal amplitude was limited to a maximum of ±1 V, it may have been too small to achieve lock. It may be necessary to amplify the signal using an SR560 or a similar device before feeding it back to the laser PZT.

[mTakahashi, Yasui]

We tried a nitrogen purge to promote H2O removal.
9:37 9.3e-1 Pa
9:44 stopped the dry pump
9:58~ N2 purge
10:09 8.8e3 Pa
10:12 started the dry pump
13:14 24 Pa(SRM), 9.2e-2 Pa(OMMT)
13:15 GVommt open->14Pa(SRM), 12Pa(OMMT)
13:16 started the TMP
So far, the pressure has decreased faster than in the previous trial on April 24.
It took 1 hour 8 minutes to reach 4e-4 Pa from 1e-2 Pa this time, whereas it took 10.5 hours last time.  The nitrogen purge seems to have been effective.

[Tanaka, Saito, Hirose]

Yesterday, as preparation for klog36845, we performed the initial alignment of Xarm and Yarm. Then, we noticed that the feedback signal for the OPLEV control of the PITYAW on SR3 had changed significantly compared to the previous Yarm flash. We confirmed that it has been specifically moved to 4/23 PM1:50JST(fig1). When we performed Lissajous the PITYAW on SR3 so that Yarm would flash again, the optimal YAW value had changed from -9 urad to 55 urad(55urad: fig2).

[Tanaka, Hirose, Saito]

We constructed the PLL control system in which a feedback signal was generated using a mixer, a local oscillator, a SR560, and a Moku:Lab, and fed back to the PZT of the sub-laser. Unfortunately, the control system did not function successfully.
 

• Since the previous observation of the beat signal (klog:36835), the sub-laser had remained on with its temperature kept at 31.57 ℃. Under this condition, a beat signal was observed; however, its amplitude changed significantly, and its frequency drifted by about 5 MHz over approximately one minute. Because the frequency was close to 0 Hz and the range over which it could be further reduced was limited, we increased the sub-laser temperature to 31.60 ℃ to raise the beat signal frequency to about 112.1 MHz (Photo 1). Next, this beat signal and a local oscillator signal (112.1 MHz, 10 dBm) were input to the mixer to generate an error signal. The mixer output was then fed into the SR560, where it was amplified and passed through a first-order low-pass filter with a cutoff frequency of 1 MHz. The output of the SR560 was subsequently input to the Moku:Lab, where an integrator was applied using a PID controller (Photo 2). The output of the Moku:Lab was connected to the PZT of the sub-laser, and the overall gain was varied. However, the error signal did not decrease, and no change was observed in the feedback signal. The error signal amplitude was 1.090 V; however, when the local oscillator frequency was set to 90 MHz, it became 409.5 mV, and at 80 MHz, it became −154.0 mV, indicating that it varied with the local oscillator frequency (Photo 3). On the other hand, changing the temperature of the sub-laser did not result in any noticeable change in the error signal amplitude. This suggests that the signal being treated as the error signal may in fact be a different signal. It is also possible that the Moku:Lab was operated incorrectly.

[R.Takahashi, Washimi, Kimura, Yasui, M.Takahashi, Sawada]

We reinstalled the geophone pods. Additionally, we adjusted the tilt of the FLDACCs. The feedback signals to the proof mass(COILOUTF) became smaller: +12200 to +1400 for H1, +12500 to -500, and -4900 to +2200 in count, respectively.

I checked the IM transfer functions again at 10Pa. The DC gain was smaller than the reference a little (1~2dB).

I checked the TM transfer functions after closing the top flange. The Length Oplev was not aligned well, so the DC gain of the transfer function for L was smaller than the reference.

I checked the GAS transfer functions after closing the top flange. They were consistent with the references.

I checked the IP transfer functions after closing the top flange. IDAMP signals are not treated well (just summation of ACC+FLDACC+LVDT), so please check the LVDT responses in BLEND signals. The resonant frequencies of the IP were 63mHz for L, 74mHz for T, and 0.32Hz for Y, respectively.

I checked the IM transfer functions after closing the top flange. They are consistent with the references except for L and H1 (the DC gain is 3dB larger than the reference due to the replacement of the satellite box).

With H.Yamaguchi, M.Onishi, S.Matsuo

We transported the new Pcal-Y laser from Toyama University to Y-end.
For access to Y-end, we used the Mozumi entrance.

The laser is currently placed under the duct near the EYA chamber.

I checked the signals of the IM OSEMs during the pump down. Just after starting the pressurization from 2.0Pa, the signals in count rapidly increased in 1 min.

[Tanaka, Hirose, Saito]

We matched the polarization of the sub-laser beam to that of the beam coming from the interferometer. Next, we increased the power of the beam coming from the interferometer by opening the iris. Then, we adjusted the alignment so that the sub-laser beam overlapped with the beam coming from the interferometer at the mirror just before the RFPD. As a result, we were able to observe the beat signal between the beam coming from the interferometer and the sub-laser beam.
 

• First, we checked the polarization of the sub-laser by inserting a PBS after the FI and found that it was mostly P-polarized. Since the beam coming from the interferometer is S-polarized, we installed a HWP after the FI and used the PBS to adjust the polarization to S-polarization. Next, the iris used for alignment had been partially closed; by opening it, the power of the beam coming from the interferometer incident on the RFPD increased from about 2 μW to about 15 μW. Then, with both the beam coming from the interferometer and the sub-laser beam incident on the RFPD, we found that their spot positions differed at the mirror just before the RFPD. We adjusted the alignment so that the sub-laser beam overlapped with the beam coming from the interferometer. At this time, observing the DC output of the RFPD with the oscilloscope on Moku:Lab, we found an offset of about 12 mV; the beam coming from the interferometer contributed about 29 mV and the sub-laser beam about 83 mV. Next, we attempted to observe the beat signal using the spectrum analyzer on Moku:Lab. When we set the sub-laser temperature to 31.57 ℃ to match the main laser frequency, a beat signal was observed (Photo 1). The amplitude of the beat signal fluctuated significantly, and its frequency changed by about 3.5 MHz over the course of approximately one minute.

[Kimura and Yasui]

 Attached is the residual gas distribution during the SRM build-up test using the Qmass installed in the OMMT.

Since the pressure inside the Qmass analysis tube exceeded 1×10² Pa, the Qmass measurement was interrupted at 12:45 p.m. due to the interlock mechanism.