The attached figure shows a summary of the current situation IMMT2-PRM-PR2. How do you think about the next step??
[Nakagaki, Tomura, Kamiizumi, Hirose]  Thank you very much for helping with the hard work, Nakagaki-san, Tomura-san, Kamiizumi-san.
We did cabling for the WFSf3.
Cables were routed between mini-racks and IOO0 racks, IOO1 racks, and the REFL optical table. We did not connect them together.
The details are summarised in the PDF file.
Future plans
Systematic uncertainties on BS transmission and reflectivity measurements were estimated.
Updated results are:
Ts=51.9 +/- 0.2 (stat.) +/- 0.2 (sys.) % for s-pol
Rs=47.7 +/- 0.2 (stat.) +/- 0.2 (sys.) % for s-pol
Tp=77.7 +/- 0.6 (stat.) +/- 0.2 (sys.) % for p-pol
Rp=21.8 +/- 0.2 (stat.) +/- 0.2 (sys.) % for p-pol
Here, uncertainties from the incident angle and the polarization angle are considered.
It seems that they are not responsible for Rs being to low and Rp being too high, compared with the design.
Incident angle error:
- BS and the incident beam was not aligned perfectly to have the incident angle of 45 deg. BS was in SAFE state.
- BS reflected beam was not going though the viewport at the gate valve between BS and ITMY. The beam spot was off by ~15 cm over 3.3 m distance. From this, we have estimated that the incident angle error is about 50 mrad (3 deg).
- Left panel of Attachment #1 is the reflectivity from the coating design, extracted from JGW-T1503347. The middle panel is the zoomed plot around 1064 nm.
- From this, we can estimate the incident angle dependence as follows.
- Reflectivity can be written as
R = R0 + dR/dtheta * dtheta
where theta = theta_in/n_eff is the incident angle inside the coating with an refractive index of n_eff (we used n_eff=1.7).
Slight change in theta_in introduces effective coating thickness change, which is equivalent to the laser wavelength change of
dlambda = lambda/cos(theta+dtheta) - lambda/cos(theta)
= lambda/cos^2(theta)*sin(theta)*dtheta
Therefore,
dR/dtheta_in = dR/dlambda*dlambda/dtheta*dtheta/dtheta_in
= dR/dlambda*lambda*1/cos^2(theta)*sin(theta)*1/n_eff
- From the coating design, dR/dlambda is -7e-3 %/nm for s-pol and -3e-4 %/nm for p-pol.
- From the equations above, this gives dR/dtheta is -4e-2 %/deg for s-pol and -2e-3 %/deg for p-pol (Right panel of Attachment #1).
- 50 mrad gives dR of 0.1% for s-pol and 0.006% for p-pol.
Polarization angle error:
- When the polarization angle from s-pol is phi, the measured R will be
R = Rs*cos(phi)**2 + Rp*sin(phi)**2
- If phi had an error of 5 deg, dR will be 0.2% for s-pol and p-pol.
- It is hard to explain Rs being too low by ~2%, just from the polarization angle error.
Discussions:
- Combined systematic uncertainties are 0.2% for all.
- Rs seems to be too low and Rp seems to be too high, compared with the design.
- The other source of error could be from the offset of the power measurements from the ambient light.
- We could also try aligning the polarization angle by maximizing (for s-pol) or minimizing (for p-pol) BS transmission.
Takano, Hirata, Akutsu; following 29282.
Afternoon, we checked beam dumps, and ghost beams caught by them in IFI and IMM chambers, and all seemed ok so far. The detailed check will be done next week.
The attached figure shows a summary of the current situation IMMT2-PRM-PR2. How do you think about the next step??
Hirata, Akutsu; following 29723.
We found that the main light beam location at the aperture of PR2 HR mid baffle was almost centered when centering the beam spot on PR2 (to precisely put, PR2 HR target). This means PR2 HR mid baffle is dislocated with respect to the main (forward) beam, unfortunately. My conlusion is that this baffle needs to move about 5 mm in the minus Y direction next week.
As discussed in the morning, we were worried if the current light beam was not be clipped at the aperture of PR2 HR mid baffle. So we started with checking the aperture edge with the Miyakawa-san's IR camera, and no shining in IR found. However, at the same time, we found that the beam passed through the very center (or even shifted in the minus Y direction slightly) of the aperture (Fig. 1).
Nominally, the input beam to PR2 should pass through 6.3 mm shifted in the plus Y direction with respect to the center the aperture of PR2 HR mid baffle (JGW-T1910200-v4). Otherwise the light beam reflected at PR2 toward PR3 would be clipped at this aperture. Because we have not yet determined the "nice" alignment of PR2, we could not make this light beam so far, unfortunately. So we could not check if this reflected beam would be clipped here or not. At any rate, if the input beam would be centered, or in other words, off-centered about 6.3 mm in the minus Y direction with respect to PR2 HR mid baffle, this document says that the reflected beam would be clipped, as the 2.8-sigma edge of this reflected beam is only 4.6mm away from the aperture edge.
So, we need to move PR2 HR mid baffle 6.3 mm (or let's say ~ 5mm) in the minus Y direction.
The drawback of this move is: the invac POP-POM is on the same suspended breadboard as that for PR2 HR mid baffle. When this baffle moves, the balance of the breadboard might be affected, and the alignment of invac POP-POM may also vary slightly. The invac POP-POM is steering (1) POP_FORWARD and (2) GRX to PR3, so both of them should be affected. In short, we have to repeat Day 1 work for GRX, and Day 2 work for POP_FORWARD later. Our hope is that the suspended breadboard does not have vertical springs, so the balance variation might be very small, altough this means no vertical vibration isolation for the stuffs on this breadboard.
Anyway, moving PR2 HR mid baffle will be done in the next week. Hirata-san found several tools used in the past to move this. For reference, see 19291.
[Shimasue, Takano, Michimura]
BS transmission for s-pol is a bit too high, which might be because BS is not aligned (it is now in SAFE state).
We might need to measure them again once BS and ITMs are aligned.
What we did:
- Followed the procedure in klog 29275 for measuring the BS transmission.
- For BS reflection, we opened an ICF203 flange labeled HY-2-1 (Attachment #1) so that we can stick the power meter (Thorlabs S310C) from the hole (Attachment #2).
Results:
- The table below summarizes the results
polarization | incident power | BS transmitted power | BS reflected power |
s-pol | 38.224 +/- 0.061 mW | 19.832 +/- 0.087 mW | 18.248 +/- 0.088 mW |
p-pol | 36.931 +/- 0.067 mW | 28.696 +/- 0.211 mW | 8.062 +/- 0.062 mW |
- By calculating T = (BS transmitted power) / (incident power) and R = (BS reflected power) / (incident power), transmission and reflectivity were estimated.
Discussions:
- We noticed that the beam reflected by BS is not going through the viewport at the gate valve. We then realized that BS is not in ALIGNED state, but in SAFE state.
- This means that the incident angle to the BS might be off by 50 mrad (~15 cm over 3.3 m distance).
- The measurent tells that AR reflectivity is small enough compared with the measurement uncertainties.
Next steps:
- Estimate the effect of incident angle from the wavelength dependence from the design.
- Re-do the measurements with BS and ITMs aligned.
[Shimasue, Takano, Michimura]
They are consistent with the design (see, also, klog 29269 and JGW-T1503347)
What we did:
- Assembled a tripod setup for injecting the probe beam at IMC REFL area. We had a hard time collimating the beam for a few meters with the beam size smaller than the aperture of the power meter (Thorlabs).
- The injection bench consists from the laser source -> steering mirror -> Glan laser prism (rotated so that it transmits most of the beam, which was mostly s-pol) -> HWP -> f=-75 mm lens -> steering mirror -> Glan laser prism (rotated to define the polarization of the probe beam) -> f=300 mm lens (Attachment #1)
- Put the power meter head on a stick so that we can stick it inside the BS chamber (Attachment #2) to measure the power of transmitted beam. IR card was also put in front of the power meter head to find the beam.
- Brought these setup to the BS area, and put the tripod setup for injecting the probe beam between BS and PR2 chambers.
- The alignment of the incident beam, both in pitch and yaw was tuned by eye by centering the beam on BS.
- Measured the incident power at the injection bench, after the last lens (Attachment #3), and the transmitted power at the back of BS (Attachment #4) by holding the power meter on stick by hand. The stick was rested on a ground and/or some vacuum structures so that the head will be stable.
- The polarization of the probe beam was tuned by eye by rotating the second Glan laser prism (OptoSigma GLPB2-10-25.9SN-7/30). When the white line is vertical, it is s-pol and when horizontal, it is p-pol. The HWP was tuned to maximize the probe beam power.
Results:
- The table below summarizes the results
polarization | incident power | BS transmitted power |
s-pol | 44.98 +/- 0.75 mW | 22.87 +/- 0.18 mW |
p-pol | 42.44 +/- 0.54 mW | 33.21 +/- 0.52 mW |
- By calculating T = (BS transmitted power) / (incident power), BS transmission was estimated.
Discussions:
- The measured values are consistent with the coating design shown in JGW-T1503347.
- The incident angle was tuned within a few mrad (beam centering error of a few cm over injection bench to BS distance of 3.3 m).
- Mis-tuning of the incident angle by a few mrad can be converted into laser wavelength mis-tuning of a few 0.1 %.
- According to the coating design in JGW-T1503347, HR reflectivity and AR reflectivity does not depend very much on laser wavelength, and probably we will be still be limited by the uncertanties in the power measurement, even if we tune the incident angle more carefully.
Next steps:
- Measure reflectivity by sticking a power meter from the ICF203 flange between BS and ITMY.
- Re-do the measurements after aligning ITMs. Use ITM reflection to more carefully align the probe beam to the BS so that the incident angle will be the same with the main beam. (But this is probably uncesessary considering the uncertainties of the power measurement)
- Estimate systematic uncertainties from the polarization orientation of the incident beam, the incident angle etc.
[Shimasue, Takano, Michimura]
BS transmission for s-pol is a bit too high, which might be because BS is not aligned (it is now in SAFE state).
We might need to measure them again once BS and ITMs are aligned.
What we did:
- Followed the procedure in klog 29275 for measuring the BS transmission.
- For BS reflection, we opened an ICF203 flange labeled HY-2-1 (Attachment #1) so that we can stick the power meter (Thorlabs S310C) from the hole (Attachment #2).
Results:
- The table below summarizes the results
polarization | incident power | BS transmitted power | BS reflected power |
s-pol | 38.224 +/- 0.061 mW | 19.832 +/- 0.087 mW | 18.248 +/- 0.088 mW |
p-pol | 36.931 +/- 0.067 mW | 28.696 +/- 0.211 mW | 8.062 +/- 0.062 mW |
- By calculating T = (BS transmitted power) / (incident power) and R = (BS reflected power) / (incident power), transmission and reflectivity were estimated.
Discussions:
- We noticed that the beam reflected by BS is not going through the viewport at the gate valve. We then realized that BS is not in ALIGNED state, but in SAFE state.
- This means that the incident angle to the BS might be off by 50 mrad (~15 cm over 3.3 m distance).
- The measurent tells that AR reflectivity is small enough compared with the measurement uncertainties.
Next steps:
- Estimate the effect of incident angle from the wavelength dependence from the design.
- Re-do the measurements with BS and ITMs aligned.
Systematic uncertainties on BS transmission and reflectivity measurements were estimated.
Updated results are:
Ts=51.9 +/- 0.2 (stat.) +/- 0.2 (sys.) % for s-pol
Rs=47.7 +/- 0.2 (stat.) +/- 0.2 (sys.) % for s-pol
Tp=77.7 +/- 0.6 (stat.) +/- 0.2 (sys.) % for p-pol
Rp=21.8 +/- 0.2 (stat.) +/- 0.2 (sys.) % for p-pol
Here, uncertainties from the incident angle and the polarization angle are considered.
It seems that they are not responsible for Rs being to low and Rp being too high, compared with the design.
Incident angle error:
- BS and the incident beam was not aligned perfectly to have the incident angle of 45 deg. BS was in SAFE state.
- BS reflected beam was not going though the viewport at the gate valve between BS and ITMY. The beam spot was off by ~15 cm over 3.3 m distance. From this, we have estimated that the incident angle error is about 50 mrad (3 deg).
- Left panel of Attachment #1 is the reflectivity from the coating design, extracted from JGW-T1503347. The middle panel is the zoomed plot around 1064 nm.
- From this, we can estimate the incident angle dependence as follows.
- Reflectivity can be written as
R = R0 + dR/dtheta * dtheta
where theta = theta_in/n_eff is the incident angle inside the coating with an refractive index of n_eff (we used n_eff=1.7).
Slight change in theta_in introduces effective coating thickness change, which is equivalent to the laser wavelength change of
dlambda = lambda/cos(theta+dtheta) - lambda/cos(theta)
= lambda/cos^2(theta)*sin(theta)*dtheta
Therefore,
dR/dtheta_in = dR/dlambda*dlambda/dtheta*dtheta/dtheta_in
= dR/dlambda*lambda*1/cos^2(theta)*sin(theta)*1/n_eff
- From the coating design, dR/dlambda is -7e-3 %/nm for s-pol and -3e-4 %/nm for p-pol.
- From the equations above, this gives dR/dtheta is -4e-2 %/deg for s-pol and -2e-3 %/deg for p-pol (Right panel of Attachment #1).
- 50 mrad gives dR of 0.1% for s-pol and 0.006% for p-pol.
Polarization angle error:
- When the polarization angle from s-pol is phi, the measured R will be
R = Rs*cos(phi)**2 + Rp*sin(phi)**2
- If phi had an error of 5 deg, dR will be 0.2% for s-pol and p-pol.
- It is hard to explain Rs being too low by ~2%, just from the polarization angle error.
Discussions:
- Combined systematic uncertainties are 0.2% for all.
- Rs seems to be too low and Rp seems to be too high, compared with the design.
- The other source of error could be from the offset of the power measurements from the ambient light.
- We could also try aligning the polarization angle by maximizing (for s-pol) or minimizing (for p-pol) BS transmission.
[Kimura, M. Takahashi and Sawada (Hokuto)]
In preparation for crane inspection of the EYA clean booth,
the duct side flange of EYA and the flange on the duct side opposite it were temporarily closed with stainless steel plates.
See attached photos.
To ease the removal of the temporary flange, the temporary flange is fixed with low adhesive tape.
When removing the temporary flange on the duct side of the EYA, care must be taken with the wiring directly under the duct side flange of the EYA.
[Kimura and Ueda (SKS) ]
On the morning of April 18, a vacuum leak test was performed on the reclosed flanges around the IYC and IYA.
The results of the vacuum leak test confirmed that the reclosed flanges did not leak more than 1x10^-11Pam^3/s.
[Kimura and Ueda (SKS)]
The pressure of the X-arm increased rapidly.
Please confirm attached graph.
This was probably due to the effect of opening GVitmx and GVetmx.
Therefore, after discussing with Uchiyama, we started TMP (X-2, X-10,X-15, X-21) for X-arm and stopped the Ion pumps.
To prevent condensation on the Ion pump power supply, the high voltage of the Ion pump power supply was turned off and the power switch was turned on.
Aso, Ikeda, Hirata, Takano, Akutsu; following 29261.
Confirmed the aligned light beam POP_FORWARD reached two QPDs on the POP table, but mostly clipped at a steering mirror on the POP table. So not yet centered to these QPDs. The work is still on the way.
Yesterday we tweaked IMMT1 and 2 with their oplev setpoint in yaw to their limits. So, we were worried if the actual beam might be off-centered at IMMT2. So, we started with checking this. Before that, we called PROVIDING_STABLE_LIGHT
to IO Guadian to make IMC with LSC and ASC. In addition, we also set IMC ASC gain to zero (following Ushiba-kun's suggestion) tentatively from MEDM so that we were able to walk across the light beam to IMMT1T without disturbing the aligned IMC. Then, we found that the spot on IMMT2 was seemingly mis-centered somehow (difficult to see it due to the fact that it is located in the deep of the chamber and the surface is protected with the black shield). So, we re-considered our plan. At this point, the new plan was to (1) reset the setpoint values of IMMT1 and 2 to the values before yesterday, (2) check the IMMT2 centering, and if not good, adjust with IMMT1 setpoint, (3) align IMMT2 to center the spot on PR2 with setpoint, and (4) adjust PRM centering with its traverser.
When reset IMMT1 setpoint, the beam centering at IMMT2 seemed ok (Fig. 1) , so we simply left the IMMT1 setpoint as reset value. Then, we tweaked IMMT2 to bring the beam spot at the center of PR2 (precisely, its HR target); Fig. 2. With this situation, we checked the beam spot postion at PRM (both at AR (Fig. 3) and HR (Fig. 4) with the relevant targets; these AR and HR spot locations were almost the same), and it was 5-mm off-centered in the minus Y direction.
5-mm would be too large for the PRM traverser to move. The demerit of using the traverser are (1) the small movable limit itself as already mentioned, (2) we need to adjust oplevs otherwise we would lose ALIGNED state of PRM (ALIGNED state would be useful to control a suspension with its setpoint values), (3) even though "ALIGNED" can be obtained, this would not mean the beam reflected at PRM could reach REFL, and (4) at any rate, PRM mid baffles do not follow the move of the main suspension chain of PRM. On the other hand, considering the RoC of PRM is ~460 m (kagra wiki), 5-mm off center might be acceptable or easily to be compansated.
So, we determined to modify the original plan mentioned above: (4) -> not adjust PRM traverser, but adjust mid baffles for PRM later.
The PRM AR mid baffle seemingly caught two (known) ghost beams from PRM already. In this sense, this mid baffle would be also ok. But in fact, looking at the aperture of the PRM AR mid baffle, the aperture edge seemed shining with IR (Fig. 5; taken from a location between IFI and IMM with the Miyakawa-san's IR camera; two ghost beam spots at IMMT1's shield can be also seen, and they may come from IFI...). This shining might be due to the main beam's slight clipping. JGW-T1910659-v2 shows where these ghost beams and main beam would come at PRM AR mid baffle, and from these nomial locations, it would not be strage at all that this clipping might happen in the current situation: the main beam is shifted with respect to the aperture in the minux Y direction about 5 mm, while this document says the 2.8 sigma radius of this main beam should be nominally 4.8 mm away from the edge. So we will adjust the AR (and HR for balancing?) mid baffle position later. See also Fig. 6; also compare with 20797 and 21654.
Anyway, apart from the slight clipping at this PRM AR mid baffle, the main beam would be well aligned. Then, we detached the duct connecting the POP table and PR2 chamber to see the PR2 transmission IR beam, or POP_FORWARD. Fortunately we confirmed that this beam was somehow reaching relevant two QPDs (Fig. 7). We also confirmed this with QPDs SUM count variation. But we also found that this beam was 90%-ly clipped at a steering mirror just after the periscope (Fig. 8). It seemed no simple way to resolve this clipping...
[Shimasue, Michimura]
We are preparing a setup for BS transmission and reflectivity measurements around IMC REFL area.
Background:
BS is designed and measured to have 50:50 transmission and reflectivity for s-polarization (Ts=49.96%, JGW-T1503347).
But the BS transmission and reflectivity for p-polarization are unknown (Designed to have Tp=80% or so, AR for p-pol a few %, JGW-T1503347).
To understand what is going on in the IFO for p-pol, we are planning to measure them with an another laser source during this vent.
What we did:
- Assembled a tripod setup with a bread board to install laser source (Attachment #1)
- Assembled a laser injection bench on the bread board (Attachment #2, now resting on IMC REFL table)
- Assembled a tripod setup with a bar to hold a power meter to measure the incident power to the BS and BS reflected/transmistted powerr (Attachment #3)
- We are planning to stick this power meter to ICF203 flanges between BS and ITMX or ITMY (Attachment #4 and #5)
[Takahashi, Ikeda]
We took pictures of the space between the SUS blocks with the fiber scope in the OMM chamber. We could see gaps around all the bellows that we could access. We could not access the 2-1, 2-3, and 3-3 bellows.
To align GRX and find the good alignment of PR3, we first opened GVs between IX/EX and X arm.
Then, I tweeked PR3 alignment to maximize the GRX PD output, which is aligned just before the vacuum evacuation (klog29131).
After finding the good alignment, we checked the single GRX beam position on ITMX.
Figure 1 and 2 show the Tcam photos with GRX before the earthquke and now.
Though current beam seems slightly shifted from the beam before the earthquake, the amount of shift is not so large and maybe acceptable.
So, we didn't move the POMs yesterday.
After confirming these things, works in the Akutsu-san's reports followed.
Please see the original report in 2019 (klog 9555).
Ushiba, Aso, R. Takahashi, Shimasue, Ikeda, Hirata, Akutsu; Ref: 16954.
Our objective is to finalize stuffs in IFI, IMM, and PRM chambers, which will be closed in the nex week. The finalization include main beam alignment and alignment relevant ghost beams to beam dumps. Today GRX path was confirmed. Alignmenf of the input IR beam axis to POP_FORWARD through PR2 and PRM is still on the way (we are at proceder #5 shown below).
Refer to Fig. 1.
After FC works (29254), PRM, PR2, PR3, and their BBs were released as planned. For PR3 release, as unfortunately as usual, PR3 was largely tilted and the oplev lost. The alignment was tentatively adjusted with picomotors. Fortutenately PR3 oplev came back, but one of the PR3 OSEMs would be about saturated. Because PR3 Guradian was able to reach ALIGNED, today we accepted this situation at this point. Later we need to adjust PR3 suspension manually.
Opening GRX shutter, and sweeping PR3, GRX transmission was immediately found at TMSX. The would mean that letting PR2 BB releasing/sitting might not so affect POP-POM alignment. This is good news. Also, the GRX spot at ITMX seemed almost the same as the one taken some days ago when the interferometer was nice alignment (the detail of this point will be separately reported by Ushiba-kun?)
Putting a PR2 HR target, we checked GRX spot on this target, and it was not so bad (mostly centerd but slightly shifted), so we left it as was. See Figs. 2 and 3. Then detaching the PR2 HR target, and putting a PR3 HR target, we also checked GRX spot on this target. As written in the above planned procedure, this was just for confirmation; we could not do anything on this spot (Figs. 4 and 5). By the way, when you would insert the target, the suspension should not be at ALIGNED state, as oplev and/or OSEMs might be affected by your beam cut or light illumination. If you are very much careful, you may be able to live with ALIGNED state, though.
Then we started iteration of the IR beam from IMC. As mentioned above, to IO Guardian, we called PROVIDING_STABLE_LIGHT, which means that the input beam axis is fixed to the sub-local area around IMC, and IMMT1T QPD was used as one of references. One should not cut the beam to IMMT1T to keep this alignment control. The iteration is: (1) check PR2 HR target and IR spot on it, and adjust the IR spot on it with IMMT2, (2) check PRM AR target and IR spot on it, and adjust the IR spot on it with IMMT1. (3) Repeat from (1) until the situation converges. But, for some reason, repeating several times, the situation was not so converged. Even more, before converging, for IMMT1 and IMMT2, the oplev range and/or coil actuator range both reached limits. We may start with taking care of these tomorrow morning.
To align GRX and find the good alignment of PR3, we first opened GVs between IX/EX and X arm.
Then, I tweeked PR3 alignment to maximize the GRX PD output, which is aligned just before the vacuum evacuation (klog29131).
After finding the good alignment, we checked the single GRX beam position on ITMX.
Figure 1 and 2 show the Tcam photos with GRX before the earthquke and now.
Though current beam seems slightly shifted from the beam before the earthquake, the amount of shift is not so large and maybe acceptable.
So, we didn't move the POMs yesterday.
After confirming these things, works in the Akutsu-san's reports followed.
[Kimura, M. Takahashi and Sawada (Hokuto)]
On the morning of Apr. 17, one failed helium compressor (Xfs) at IXC was replaced due to a suspected IXC failure.
(klog28051)
This compressor is the compressor for IXC's duct shield cooling cryo-cooler.
The removed compressor will be repaired.
[Kimura and Ueda (SKS) ]
On the morning of April 17, a vacuum leak test was performed on the closed flanges around IXC and IXA.
The vacuum leak test results showed a large leak of more than 3.9 x10^-9 Pam^3/s at the +Y side flange of the cross tube.
Since this leak affects the cooling of the mirror, it is necessary to repair the leak by pressurizing the vacuum chamber to atmospheric pressure.
High purity air with a low dew point was arranged for pressurization.
[Araki (KEK) and M. Takase]
We finished surveying the V-type Chamber (IYV) after pumping down on Apr. 17.
Could you please tell us when is the last measurement? before the Noto earthquake?
If so many positions are contacted, I am afraid that the optical table rotation angle may change because of the friction forces at these contacting points.
I checked the condition of the stack partially with an inspection mirror in the IFI and IMM chamber. I could see gaps between the SUS blocks much enough to prevent touching.