To confirm the result of loss and phase noise, I measured squeezing and anti squeezing with different loss. The way to inject additional loss is to put HWP in squeezing path and rotate the polarization. The loss can be estimated by measuring the visibility. I assumed mode matching is 99% during this measurement.

I fitted squeezing level with 3 variables which are injected squeezing and loss and phase noise. The result is injected squeezing = 16.3dB, loss = 25%, phase noise = 23.8 mrad. This is consistent with previous loss and phase noise measurement.

According to the beam parameter of entry 1046 and the telescope design from yuefan(entry 1564), I simulated the beam situation again. But it seems not the same with yuefan simulation. But anyway I checked the robust for the NF telescope. The FF telescope is quite different from yuefan design, I will confirm with yuefan what makes this difference. And do the robustness check soon.

Difference one: the distance from L1 to NF quadrant is 0.535 (in my case) and 0.65 (in yuefan case)

Difference two: I used the same distance with yuefan design, but the gouy phase is 87.277(in my case) and 90.2(in yuefan case)

Notice: from the simulation, the beam size for FF quadrant (if I use yuefan design) is 2.179mm (radius). This is 2 times larger than the requirement. We should also check this.

I confirmed with yuefan that we are using the same initial beam parameter. Also, yuefan told me we have a tolerance of several degrees for the gouy phase. So I think with our hand we can have a precision within 1 cm, and in this case, it should be fine if we don't use the first lens on the rail. However, if we consider the distance estimation error from lens1 to NF quadrant PD, we may have another 1cm of error. In this case, maybe we should use rail.

Or we can just measure the beam parameter with beam profiler after BS and find out where is the beam waist. Then put quadrant PD in the position of the waist.

Or we can tell if we are seeing the decoupled motion of cavity by looking at the output signal of quadrant PD. Then we can decide the position of quadrant PD.

The components until the second layer were installed, and also 50:50 BS was installed. (attached picture 1 and 2) I also adjusted the lens and mirror position and angle, so that the beam is going as straight as possible.

Actually, I would like to measure the beam after BS to confirm everything is fine, but I broke the screw of beam profiler. I tried to replace the broken screw but seems not possible. (attached picture 3 and 4 are broken screw)

We could also just replace the mount. Up to now, I couldn't find a suitable mount. (See attached picture 5, 6 and 7)

Figure 5: sigma waveplate mount(originally we were using this)

Figure 6: connection part of the beam profiler

Figure 7: the wave plate mount(we usually use on bench, we have a lot but seems not suitable)

Simon

With the recent recalibration of the PCI, I took another XY-map at the center in longitudinal direction. The results are attached as png pictures.
Compared with the results of the measurements before, we can see that the mean value of the absorption coefficient is much lower now (all given in ppm/cm):

The numbers in parentheses are those for the older measurements but with the recalibrated bulk-reference value. Note that for the "Center" value of the most recent measurement the absorption coefficient would increase to 177 if using the old reference value.

It would be of course better to see the measured mean-values also for the other Z-positions but I don't know whether there is time.

Attached is also a map in YZ-direction, taken at X = 398 (also the center). It clearly shows an increase in absorption toward the outgoing surface (smaller Z) and oriented on the left-hand side (the map shows the situation as seen from above the test-mass with the incoming surface on the bottom).
The mean value within the relevant region (the substrate without the surface) is 148 ± 115 ppm/cm.

1. I found there was no space for the AA first steering mirror, so I moved the steering mirror, lens and PD for FC lock closer to FI. The situation is shown in the first attached figure.

2. The BS now we are using for splitting GR reflection is coated for IR since we don't have GR BS. We decided to order BST10, and hopefully it will arrive next week.

3. The periscope for rising up GR reflection is done for a beam height of 206.4mm. (attached figure 2)

4. The three steering mirror and one lens on the bench is prepared. (attached figure 3)

Simon

(This is the report of the last two days activities)

I finished the recalibration of the PCI were I slightly adjusted the position of the pump-beam and used (now) the correct way of the surface calibration sample.

R_surf = AC_surfref/(DC_surfref*P_in*abs_surfref) = 17.2 [1/W]
where AC_surfref = 0.48V, DC_surfref = 4.07V, P_in = 0.031W and abs_surfref = 0.22

R_bulk = AC_bulkref/(DC_bulkref*sqrt(T_bulkref)*P_in*abs_bulkref) = 0.784 [cm/W]
where AC_bulkref = 0.09V, DC_bulkref = 4.8V, T_bulkref = 0.55, P_in = 0.031W and abs_bulkref = 1.04/cm

Both values indicate that the AC/DC ratio is higher than before and hence, the crossing-point is indeed more at the pump beam's waist.

After the calibration, I changed back to the spare ETMY and made a scan along Z (c-axis) where you can see some interesting structures both in AC and phase at around Z=55 and Z>90 (see attached screenshot).

We measured squeezing spectrum with 40mW green. Turbo pump is OFF. Squeezing level is 5.62dB and a bit lower than yesterday. Spectrum at 100Hz region seems clear when turbo pump is OFF.

Aritomi and Yuhang

Green injection power to filter cavity: 12mW

Green reflection power from the filter cavity (measured from the FI extraction point)(filter cavity unlock): 5mW (we loss a lot)

This reflection is separated into two parts:

          1. To FC lock PD: 3.5mW(FC unlock) 2.3mW(FC lock)

          2. To auto-alignment: 0.9mW(FC unlock) 0.6mW(FC lock)

Notice: the green power was measured with a power meter and it fluctuates a lot. So the number reported above is value roughly located in the middle of this fluctuation range.

So the BS is splitting reflection with ratio 20:80 (R:T). Also there is a ghost beam and it is roughly 0.1mW. It would be nice that we can have a 90:10 BS to replace. Because we only need less than 0.3mW for filter cavity lock.

[Matteo, Eleonora]

We reinstalled the second ADC PCie into the standalone after it was taken out because of the timing-box issue.

The standalone PCie slots are piled up in vertical are (from the bottom):

1) ADC1 

2) ADC2

3) DAC

4) empty

We connected the new timing box to ADC2 and the real time model was restarted without problems.

We installed one of the two new BNC2dsub box in the clean room (to be used for AA signals) and we connected the cables from to the AA module which is in the standalone rack.

Now the situation is:

ADC0  

-16 channel in the standalone rack (used for local control)

-16 channel in the clean room. (4 used for FC lock signals, 12 available for AA)

ADC1

-16 channel in the clean room. (available for AA)

-16 channel possibly available by installing an additional BNC2dsub box

Now we need to test if ADC2 can correctely acquire signals. I need to modify the real time model to do this.

Pic1: modules on the standalone rack in the corner of TAMA central area

Pic2: modules on the rack in the clean room

Since we had problem of saturation, I decreased again the power of LO. Then the measurement of visibility if consistent with the two homodyne PDs. But they are not exactly the same.

We are still having the resonance issue of CC2. As we reported, we could lock CC2 wih bandwidth of kHz. However, sometimes if the resonance is excited by some random vibration. We have resonance at 3.2kHz. This limits our CC2 bandwidth. For example, sometimes we could only lock it with bandwidth of 400Hz(first picture shows this). The resonance is shown in the attached picture if we increase the gain.

Aritomi and Yuhang

I attach here the plot of SQZ, Anti-SQZ and shot noise level. These are used for entry 1571 for the estimation of loss and phase noise.

Aritomi and Yuhang

In the beginning of yesterday's recovery of squeezing measurement, we measured LO spectrum with homodyne and found lots of peaks at the low frequency region. We checked the clipping and the centering of beam on homodyne PD. It was fine.

However, since we recognized that the frequency of 24.5Hz comes from scroll pump. And 20Hz comes from clean room fan. The 13.5Hz peak comes from bench horizontal mode. We decide to put back the board wihch is taken away because the demodstration requirement we had on Monday. After that, the measurement of LO spectrum becomes very clean.

Maybe the balance of weight on top of bench helps to remove the bench horizontal mode peak. And the board isolate the sound wave propogates to the mirrors and PDs. These help to remove peaks. But the source of peaks at 16Hz, 18Hz and 33.8Hz are still unknown.

Simon

(This is report from Yesterday)

I inspected the OSTM mirror substrate by my eyes in the TAMA clean-room (absorption bench) to make sure that there are no major damages (pictures attached).
So far, it looks good. I packed the substrate again and left it in the shelf in the anteroom.

[Yuhang, Eleonora]

Today we worked on the recovery of the FC after summer break. We recovered easily the alignment towards the end mirror but once we aligned the input we couldn't find any flash.

Since from the signal we suspected a saturation of the stanford research used to amplify oplev signals in the end, we went to check and we found a major water leakage in the end room.

The floor below and around the vacuum chamber (which is a bit lower with respect to the rest of the room) was completely covered with water (~1cm deep).

While switching on and off the air conditioner we observed that a discrete amount of water started to drop from it along and wall, reaching the floor. We suspect that the drain system of the air condition is not working properly.

We tried to dry the water with some paper but a part of the water is still there. 

Anyway we decided to go on with the recovery: we zeroed the oplev signal, so that the stanford where not saturating anymore and we could close the loop properly. Than we realigned the end mirror, found the flashes and lock the cavity.

To realign the end mirror, we did the usual trick that is to let the beam pass through the second target hole and look for the reflection from the end mirror on the back of the second target. 

Tomorrow we will remove the remaining water and ask Takahashi-san if he can check with us the air conditioner.

As suggested by Matteo, our squeezing measurement issue can be related to homodyne. The idea is to check the visibility of homodyne by using two PD of homodyne and compare them. To check the visibility, I used BAB and IRMCtra to make the beat note. For the BAB maximum transmission, the new PLL locking frequency I got today is 315MHz (without green).

For homodyne PD close to IRMC:

BAB is 500mV

LO is 1.835V

In this case, I found PD is saturated. So I put an OD 0.5 filter in front of IRMC. After this, LO becomes 644mV.

The beat note is shown in the attached figure 1. In this case, visibility is 90.37%

For homodyne PD far from IRMC(everything is the same apart from this PD):

BAB is 498mV

LO is 647mV

The beat note is shown in the attached figure 2. We could see that it is saturated. This is strange because this PD should have the same response with the other. Or we should not use this homodyne in this way because it is designed to use both PD at the same time. Anyway, we should investigate if this is a problem or not.

Today I checked the alignment of SHG, GRMC, OPO, IRMC and homodyne.

Among them, only OPO and homodyne is misaligned. So every misalignment is related to OPO.

Homodyne visibility is measured as 90.37%. (The situation of homodyne will be reported in the following entry)

Fig.1 SHG spectrum

Fig.2 GRMC spectrum

Fig.3 OPO p-pol spectrum

Fig.4 OPO p-pol spectrum(after alignment improvement)

Fig.5 IRMC spectrum

Fig.6 OPO CC spectrum

Fig.7 OPO BAB spectrum

Fig.8 OPO BAB spectrum(after pitch alignment improvement)