As reported in elog2245, the AA noise level is in general higher than the noise of oplev from roughly 10Hz to 100Hz (looking at all Input/End pitch/yaw). This noise is suspected to come from PR/BS motion.

Therefore, the coherence check between PR/BS pitch/yaw excitation and AA signal was done. The result is shown in the attached figure 1-4. It can be seen that:

1. Compared with BS pitch excitation, all AA singals have high coherence between 10 and ~30Hz. (Fig 1)

2. Compared with BS yaw excitation, Input yaw shows the most coherence between several Hz to ~30Hz. (Fig 2)

3. Compared with PR pitch excitation, all AA signals have high coherence between ~30Hz to 100Hz. (Fig 3)

4. Compared with PR yaw excitation, Input yaw shows the most coherence between several Hz to ~30Hz. (Fig 4)

Besides, the AA signal with PR/BS local control loop open was also checked. The result is shown in the attached figure 5. It is clear that, the noise floor from ~10Hz to 100Hz becomes generaly lower. But there is no difference in End mirror yaw.

Later on, I found that all the filters disappear in foton.

Eleonora checked that we have archive file in the directory '/opt/rtcds/kamioka/k1/chans/filter_archive/k1fds'. The file used in foton is '/opt/rtcds/kamioka/k1/chans/K1FDS.txt'.

Then Shoda-san helped to check them. 'ls /opt/rtcds/kamioka/k1/chans/filter_archive/k1fds -all' was used to check the date of these files. The latest archived file in that directory was found to be 'K1FDS_201021_164656.txt' However, it was also shown in the terminal that this latest file has size of 3075 (usual size is 107155). We opened the file and found that the latest archived file is actually empty. In the end, we found  'K1FDS_201017_210326.txt' should be the latest useable file.

By using 'cp /opt/rtcds/kamioka/k1/chans/filter_archive/k1fds/K1FDS_201017_210326.txt /opt/rtcds/kamioka/k1/chans/K1FDS.txt', the filters are copied to foton. Now filters also work well!

When the transfer function is measured in diaggui, several choice could be used for measurement. Especially, when performing FFT measurement, there is 'Gaussian' and 'uniform' noise to be chosen. I checked today what is the difference of them.

I used Diaggui to generate these two noise as shown in the first figure. Then the spectrum of them was measured and shown in attached figure 2.

The conclusion is that both of them are white noise. But the 'Gaussian' noise is about twice the amplitude of 'uniform'.

It was figured out that there were two problems happened at the same time and caused this problem.

1. Instead of using 'make install-k1fds', I was using 'make install -k1fds'. By using correct command, the problem was solved.

2. One of the directory was full (/opt/rtcds/kamioka/k1/target/fb/log/old was as large as 18GB) . Then I couldn't make k1fds. By using 'sudo rm -r old', this problem was solved.

Tips:

To check if k1fds is running, command 'lsmod' could be used. After using it, if you see the name k1fds is listed on the left side in a certain column, it means k1fds is running.

To check the space used by different directory, 'du -h --max-depth=2 .' should be used.

Shoda and Yuhang

I found that the driving matrix of AA had large coupling last Friday. So I was thinking to make the driving matrix not seperate in pitch and yaw. It means to make the 2*2 matrix be a 2*4 matrix. For example, to control the yaw motion, there is not only signal coming from yaw but also from pitch.

Then I asked Shoda-san to modify the k1fds code. She helped me make the modification described as above.

But then, later on last Friday. By improving the driving matrix index with the separation of pitch and yaw, the pitch/yaw coupling becomes much better. So I decided by myself to modify it back.

However, after I modified it back. I found I couldn't make k1fds. The problem showed up as

gzip: stdout: Np space left on device.

make: ***[k1fds] Error 1

However, although this issue reased up, I was able to use control loops. So I didn't care about that.

Then, the day after, I found filters in foton disapeared. 

Eleonora and Yuhang

Firstly, we found that all the filters disappeared in foton (as shown in the attached figure 1).

Then we tried to restart standalone computer. However, after that, k1fds stopped working (as shown in the attached figure 2).

At the same time, we found that by using command 'df', /dev/sda1 shows 100% used (as shown in the attahed figure 3).

Eleonora tried to ssh standalone, and used command 'lsmod', and found there was no k1fds. She tried command 'startk1fds'. But it didn't work (see attached figure 4).

So probably the problem is connected with the full of /dev/sda1.

To check how AA affect input/end mirrors, I checked their oplev signals when AA loop is on/off.

From the measurement, the yaw motion of input/end mirrors is actually increased by AA loop.

0. Note that PR/BS local control is closed in this case.

1. The noise spectrum of AA is higher than oplev (from 10 to 100Hz)

2. The input pitch coupling to input yaw is visible.

To compare oplev and AA spectrum, the first step is to calibrate both of them. The calibration is done as follows:

1. Calibrate oplev signal. The oplev signal calibration method was developed by Eleonora and written in elog1874. 

2. Clibrate AA signal. The 4Hz sine wave was sent to Input/End pitch/yaw. By adjusting calibration factor of AA signal, AA's 4Hz peak was matched to oplev's peak. Then the calibration of AA signal was decided. The comparison is shown in the attached four figures.

unit: urad/counts

The first attached figure was the coupling (input pitch) situation before optimization.

The following figures show the coupling situation now.

According to the suggestion of Raffaele, I checked the diagonalized sensing signal (driving signal). I found there are quite a lot of coupling between each DOF. Therefore, I optimized the invertion matrix. After that, I also increase the gain of each loop.

New driving matrix:

New gain:

input yaw: 10

input pitch: 8

end yaw: 10

end pitch: 12

The comparison of new spectrum and old one is shown in the attached figure. We could see:

1. The coupling is bascially not visible in the spectrum.

2. The control bandwidth is increased.

3. The AA helps to reduce input mirror pitch motion to 2urad. Reduce input mirror yaw motion to 1urad.

4. The AA helps to reduce end mirror pitch motion to 1.2urad. Reduce input mirror yaw motion to 0.8urad.

As we concived that the mirror angular motion results in the difficulty of mode matching, this situation maybe improved by the AA control.

Calibration factor: The calibration was done by sending 4Hz with 5urad expected motion (driving magnitude is shown in elog2216). (I didn't consider yet the transfer function of pitch/yaw. Since 4Hz is not far from resonance frequency, the pendulum effect is temporary neglected.) Beside, looking at the noise spectrums, at 4HZ, there is not the effect of AA loop. Then I check the peak value at 4Hz. After subtracting the offset (value at 4Hz without excitation), the value is divided by 5urad. Then I get calibration factor. I use it to calibrate the spectrum measured from wavefront sensor.

The measurement result is shown in the attached figure. (REF0,1,2,3: AA loop on. REF4,5,6,7: electronic noise. Others: AA loop off. )

1. From this measurement, End mirror is moving less than Input mirror.

2. The RMS motions of Input mirror reach about 7urad for both pitch/yaw.

3. The RMS motions of End mirror reach about 2urad for both pitch/yaw.

4. The spectrum is well above the sensor noise.

5. The control bandwidth situation could also be seen from this measurement. The control in yaw direction has larger bandwidth and reach about several Hertz. The control in pitch direction has smaller bandwidth, but also reach about 1Hz.

6. It seems that the coupling from pitch to yaw is not small. The peaks in pitch (around 8-9Hz) is visible also in yaw.

The coherence in pitch direction is not very good in the last elog. Therefore, some new measurements were performed.

1. The first four figures are measured with gaussian noise excitation, resolution is 0.01Hz.

2. Figure 5 shows a measurement of END_yaw TF with uniform noise excitation. The measurement result is a bit different with guassian excitation.

3. I increase the input pitch gain from 0.3 to 2. The new TF is shown in figure 6.

The transfer functions of AA loop was measured with swipe sine method and reported in elog2230. But the signal at high frequency was not quite clear. Therefore, Eleonora suggested me to measure with fft method. The excitations were uniform noise and sent to each degree of freedom, their amplitude are

Note that if the excitation is not large enough, the coherence between these two signals will be exactly 1 at almost all the frequencies.

The measurement result is shown in the attached figures.

The air conditioner was switch to warm up mode last week. After that, I found green injection direction was changed a lot. The green beam references on the PR/BS chamber are fine (as shown in the figure 1). But the green beam was quite far from good height on the first target in the arm (as shown in the figure 2 and 3).

Therefore, I checked the PR/BS oplev signals (as shown in the figure 4). From this figure, we see that mainly PR pitch was moved a lot. Additionally, BS pitch also moved in the direction. This movement is so large, so I used picomotor to recover PR position.  After recovering PR pitch, BS was moved up with oplev. With good alignment, the green beam on the first target is shown in the figure 5 and 6. However, after locking FC, the GR DC tra was found to be only around 3000.

I checked green power before AOM, it was only about 30mW, but the nominal value should be 52mW. So I changed SHG temperature from 3.096 to 3.068. Note that 3.068 makes SHG have a local maximum green output, which gives 52mW before AOM. The AOM modulation depth is 5.5dBm, which gives 14.5mW injected into FC.

Besides, recently we have SHG output oscillation problem. This is due to the gain of SHG servo is smaller than 2.25. After I put the SHG servo gain back to 2.25, oscillation disappeared.

[Aritomi, Yuhang]

We measured CCFC RF noise (before demodulation after amplification).

Setting of spectrum analyzer: RBW: 300kHz,VBW: 10kHz

We used 50:50 BS to pickoff CCFC error signal and pump green power is 42 mW.

Note that CCFC and CCFC FC unlock were measured with max hold while others are normal setting. I think that's the reason why the floor noise level in CCFC and CCFC unlock are a bit higher than TAMA PD noise level.

What I did

In order to confirm the molecular layer formation at cryogenic temperature, I started another measurement with modified spacer.
The spacer has a slit to let residual gas molecules impinge on the folding mirror.
The incident angle is about 22.5 deg.
I installed it and pumped down.
Then I did some measurements to characterize the mirror property.

I turned on the cryocooler at 16:08.

Results

The finesse of the cavity was about 22000, which is better than before.
It seems that the beam hit the defect before.
At the defect, several tens ppm optical loss exists in folding mirror.

The frequency shift between p- and s-pol was about 20 MHz which is almost consistent with the theoretical calculation.
This measurement enables characterization of coatings.

Next step

I will monitor the finesse and splitting frequency for one or more weeks.

I monitored PR/BS oplev signal, INPUT/END AA correction signal, SHG transmission, Filter Cavity GR transmission, Filter cavity IR transmission, Filter cavity IR detuning and BS pointing for 200 minutes. The result is shown in the attached figure.

If we check the shape/peaks of FC IR detuning and BS pointing pitch, the correlation between them is quite obvious.

However, no clear correlation was found between PR/BS motion and INPUT/END correction, which could be due to the motion is always making effect with the combination of two mirrors.

In this measurement, we assumed that green power is 56mW and generated squeezing is 21 dB, but nonlinear gain was not optimized in this measurement and actual nonlinear gain (or generated squeezing) should be lower. I assume that generated squeezing is 16dB in this measurement and fitted the FDS measurement again (attached picture). In this case, homodyne angle changes from 0 deg to 90 deg and detuning is between 89-98 Hz. The detuning fluctuation might be better with CCFC.

[Aritomi, Yuhang]

We tried to measure FDS with CCFC with 42mW green. MZ offset is 4.5 and p pol PLL is 135 MHz for 42mW green. For 18mW green, MZ offset should be 4.2 and OD0.2 should be placed in pump injection path.

SR560 for CCFC: gain is 1000 and filter is 0.1Hz 1st order LPF.

We found that we can change the squeezing angle with CCFC, but with squeezing quadrature, the shot noise level is -123.8 dBm which is about 10 dB anti squeezing (attached picture). It seems CCFC makes the squeezing level worse a lot.