I checked the IR mode matching to filter cavity and improved it. The injected BAB was 440uW.

We must check TEM00 power and injected BAB power at the same time to confirm the mode matching.

Mode matching before improvement: 77%

Mode matching after improvement: 94%

I replaced a 50% pick off BS (BSW11) with 20% one (BSS11).

I checked the reflectivity of them. For BSW11, injection, transmission, reflection powers were 74uW, 42uW, 31uW, respectively. So the reflectivity is 42%.

For BSS11, injection, transmission, reflection powers were 375uW, 293uW, 72uW, respectively. So the reflectivity is 19%.

Both are consistent with the reflectivity for p pol in their specification.

Marc and Yuhang

We have put two lenses for OPO mode matching telescope. They are LA1422 and LA1608, exactly the lenses suggested from simulation in elog2486.

After putting lens, we checked with sensor card and found the beam waist is about 5 holes after the second lens. This agrees with simulation.

According to the calibration factors in elog1874, I plotted all our suspended mirrors oplev signal.

As shown in the attached figure, bascially all mirrors pitch or yaw have bascially the same behavior. But there is an expectation of PR yaw.

Marc, Michael, and Yuhang

Yesterday, we made some measurement of FDS with WFS based AA.

The measurement is flat until almost 30Hz. We have also seen more than 1dB squeezing from 30 to 60Hz. However, the high frequency squeezing level was only 2dB (can not be higher by changing LO phase). This is very different from what we understood.

Anyway, I tried to use the old code to fit FDS. The fit agrees well with some measurements, but not for all. As shown in the attached figure, especially the measurement which should have squeezing at high frequency couldn't be fit by the code.

We need to investigate more about this result.

Marc, Michael and Yuhang

We tried to tilt the lenses of homodyne to reduce back scattered noise at low frequency. However, it seems it didn't work.

After the improvement of IRPS, we confirmed that there is not amplitude noise or beam jittering noise from the LO. So the input mirror feedback loop really reduced the back scattered noise.

Note: to close input mirror feedback loop, we had to improve the gain of the old loop.

We made a few more comparison yesterday. The noise and reduction is shown in the attached figures. From this measurement, the reduction of back scattered noise is not the same at all frequencies.

Marc, Yuhang

We checked the BAB transmission and locking accuracy when AA loop is closed or open.

In the case of BAB transmission, AA makes the signal worse below 100Hz.

But, in the case of BAB locking accuracy, AA seems to make the DC value better. After integrating at all frequency, AA actually makes locking accuracy better.

Today we received two viewports of EY TM OpLev.

I placed them inside ATC cleanroom as in figure 1 with :

left : EY TM OpLev viewport, Inner shield, -X +Y side, dirty surface up

right : EY TM OpLev viewport, Inner shield, +X +Y side, dirty surface up

I left them under their protective cover as in last figure.

I have some questions.

What is the meaning of the fit in the histograms? Do you have a reason to fit with specific distributions/densities or do you want to find a systematic pattern?

Marc and Yuhang

We have also checked one week data (from 2021/04/25/3pm to 2021/05/01/3pm)

We made two plots, the first plot includes all the data in this week. But the second plot excluded the last part of the data. This is because an earthquake might happen around the end of the one week data. This makes we see a peak in the first plot. 

To compare different mirrors angular drift, we calculated RMS value of data and summarized them as the attached table. [unit: urad]

From this table, we see PR pitch moved the most. But INPUT pitch also moved a lot. However, END pitch didn't move as large as PR and INPUT pitch. Since PR, INPUT and END have the same configuration, their difference in pitch drift indicates that this is not a design problem.

We know that temperature change influences mirrors drift. But PR, BS, and INPUT are all in the TAMA central room, they should have the same temperature change. But they didn't show the same drift. Form the airconditioner location, PR chamber is almost facing an air conditioner, which may cause temperature related problem. To confirm this is not the fault of air conditioner, we plan to switch off it for one or two days during weekends to check.

According to the OPLEV signal calibration value in elog1874, I plotted the four suspended mirrors drift during a time scale of one day(from 2021/05/12 1pm to 2021/05/13 1pm JST).

In figure 1, all four suspended mirrors are compared. It is very clear that PR pitch has a far larger angular drift compared with other mirrors.

The PR mirror changed by 100urad pk-pk during one day. Considering the distance from PR to END mirrors, the 1e-4*300 = 3e-2 m = 3cm.

Other mirrors other DOF changed by 10urad pk-pk during one day, which is ten times smaller than PR pitch.

Considering this measurement result, I think we should make beam pointing loop act on PR mirror.

Abe, Marc

Following the 3 maps measurements we performed again the bulk calibration where this time we moved the imagining unit by 0.32 mm in order to compensate the thickness difference between surface and bulk reference samples. We got the following result (also see last figure of this entry) :

AC_bulkref = 0.0731;
DC_bulkref = 4.164;
ACDC = 0.01755;
P_in = 29.5e-3;
P_t = 13.3e-3;
T_bulkref = P_t/P_in;
abs_bulkref = 1.04;
R_bulk = AC_bulkref/(DC_bulkref*sqrt(T_bulkref)*P_in*abs_bulkref) = 0.852 cm/W

Using this new calibration factor and using :

P_t = 6.25 W;
P_in = 7.322 W;

the absorption of this sample seems to be around 60 ppm/ cm for all 3 maps (see attached figures)

Today we will double check the bulk calibration as the change was quite larger than expected.

Abe, Marc

We modified the analysis to better estimate the mean and standard-deviation of absorption measurements.

The corrected results are attached to this entry.

Today I will remove the first contact that we applied on this sample and cross-checked if it affected the absorption measurement.

[Aritomi, Yuhang]

First we measured nonlinear gain again. We measured BAB transmission from OPO. When we used 40mW green, we decreased CC1 gain from 2 to 1. 

The measured nonlinear gain is 18.5 with 40.9 mW green while the theoretical value should be g = 1/(1-sqrt(40.9/80))^2 = 12.3. We don't know why they are different.

We found an oscillation in FC lock with green injection of 27mW and FC gain of 1.3. The green injection power was larger so we decreased FC gain from 1.3 to 1.

We measured CCFC with 40.9 mW pump green and 50% pick off. Fig 1 shows the CCFC error signal with some demodulation phase and Fig 2 shows CCFC calibration signal when CCSB are off resonance and CC1 is scanned. The amplitude of CCFC calibration signal is 524mVpp which is 10 times larger than before.

We will try with 20% pick off and thorlabs BSS11 seems good for BS (20% reflection for p pol).

The measurement performed during the golden week were using too low power (I_laser =3A ie P_laser~3.5W) that made it hard to really acquire signals.

The measurements have been restarted with higher power (I_laser=6A ie P_laser~8W?).

We'll have to check carefully the incident and transmitted power after the measurements.

Today I putted first contact on one side of the SHINKOSHA evaluation plate.

We'll remove and clean the other side tomorrow.

Thank you.

I have updated the absorption value using the bulk calibration measured just after removing this sample (see elog 2480) and the corrected absorption is 302 +/- 108 ppm.

Yuhang and Michael

We finished setting up the modulators.

Set up and aligned FI: 5.15 mW transmission, 5.54 mW incident (92.96% tranmission vs Thorlabs 92% specification)

Set up HWP and PBS to check vertical polarisation required for EOM: 5.17 mW transmit, 0.03 mW reflect, 5.35 mW incident (PBS), 5.97 mW incident (HWP)

Set up EOM: 5.63 mW transmission, 6.04 incident. 

At this point the power meter was seen to be not particularly reliable for alignment, since it seems to register too much power at the edge of the detector compared to the center. The EOM was centered by using the IR detector card and seeing that the beam passes through the center. Then, we added AOM.

Afterwards, we measured the beam profile coming out of the modulators. In 2421, the beam profile was measured coming from the lens that was previously fixed on the bench, as indicated in that entry. From that measurement I used a beam waist of 150 µm with position z = 0 defined by the position of the last preset lens. However, that beam waist was an average of the horizontal and vertical beam waist measurements, which were quite different. But perhaps that could have also been due to the alignment of the beam on the beam profiler, which in 2425 was seen to be off centered in the measurements close to z = 0. Using Jammt with Thorlabs lens database, an f = 100 mm lens placed at z = 0.125 m gives a waist of 218 µm at z = 0.272 (figure 1). However, as mentioned in 2482, the lenses shown were slightly adjusted in order to properly level the beam at 76 mm height. So the prediction may not be completely accurate anymore.

The measured beam profile is shown in figure 2. The predicted beam seems to be a bit too far forward and too large.

Readjusting the mode matching telescope with a waist of 193 µm at 13.3 cm with respect to the f = 100 mm lens gives the result shown in figure 3. The spacing between the two modematching lenses (f = 40 mm and f = 75 mm), as well as the space from the f = 75 mm to the OPO waist should still be sufficient.

Yuhang and Michael

We just did some adjustments to the beam using the lenses shown, to make sure the beam is travelling at about 76mm height along the screw hole line. It rises by about 1mm over ~50cm of travel. The mounts have also been adjusted to match the beam height.

This work will be on hold while the KAGRA ETMY is being cleaned.

Nice results!

It seems that Shinkosha still has its main feature: the prominent spider-web absorption.

But the absorption is really high this time.