NAOJ GW Elog Logbook 3.2
Eleonora and Yuhang
We tried to measure filter cavity FIS with scanning LO phase to get squeezing and anti-squeezing level. But since the suspended mirrors are always moving a lot, we couldn't see the expected M shape.
Thank you for the measurement.
Can you add the fitting result of homodyne angle?
Eleonora and Yuhang
We fixed the CC2 demodulation phase and measure FDS during more than one hour.
During these measurement, filter cavity got unlock twice. Also, for the last measurement, we misaligned filter cavity yaw.
The detuning was stable within ~10min. Even without unlock, detuning changes and unlock almost doesn't change detuning if green is recovered. But detuning will change after a bit misalignment.
Thank you for the measurement.
Can you add the fitting result of homodyne angle?
This is my fitting result.
Aritomi, Eleonora and Yuhang
Today we monitored BAB PDH signal for more than one hour, which is taken by collecting filter cavity BAB reflection on an RF PD. During this time, filter cavity got unlock several times.
The orange color line is normalized PDH signal.
The cyan color line is PDH signal before normalization.
The dark blue color line is filter cavity control loop correction signal.
- We could see basically the PDH signal doesn't drift and it means the BAB is always on resonance. And there is fluctuation, by taking the pk-pk value of this thick line(let's say 8count pk-pk) and take calibration factor of 2Hz/count. We should have RMS locking accuracy of 11Hz. And this is roughly consistent with the measurement of locking accuracy spectrum which give result of 6Hz.
- We could see that in the middle, there is a time filter cavity got unlock, and normalized PDH has an offset from zero.
- There are many times filter cavity got unlock and everytime when it got lock again, the PDH went back zero again.
But we observed at least twice a strange behavior. The PDH becomes smaller and BAB transmission becomes also smaller while GR transmission is kept. After we tune AOM frequency, the BAB transmission was recovered and the detuning was changed a bit.
Earthquake of magnitude 7 occurred at 19:44 JST in the north of Hokkaido (https://www.jma.go.jp/en/quake/20200213104426395-13193432.html). Mirrors are shaking very much and the lock is difficult to recover.
By monitoring the long term drift of the supesnsions, we observed a ~24h cycle likey related to the temperature. It is especally visible in pitch. The "inversion points" are at about 5 am and 5 pm. Shorter period oscillations seem to appear in yaw.
Non normalized: 0.011 Hz/count
Normalized: 1.98 Hz/count
[Aritomi, Yuhang]
We locked FC with green and implemented dithering to be sure that alignment of FC is good. We locked IR off resonance (detuning is 1kHz). Unfortunately, today there was a large mode mismatch peak in AMC, which was ~50mV out of 1V. This becomes ~10% readout loss.
| MZ offset | green power (mW) | OPO temperature | p pol PLL (MHz) | CC2 demod phase (SQZ) (deg) | CC2 demod phase (ASQZ) (deg) |
| 4.2 | 17.4 | 7.163 | 190 | 185 | 260 |
| 4.3 | 21.2 | 7.175 | 200 | 185 | 260 |
| 4.4 | 25 | 7.175 | 200 | 195 | 255 |
| 4.6 | 32.6 | 7.2 | 215 | 200 | 255 |
| 4.8 | 39 | 7.2 | 200 | 195 | 250 |
| 5.2 | 50.5 | 7.22 | 200 | 200 | 250 |
| 4.8 (without OD 0.2) | 57 | 7.22 | 180 | 195 | 240 |
Measured loss is 40(1) % and phase noise is 30(5) mrad.
| Filter cavity loss | 94.5 ppm |
| Mode mismatch SQZ/FC | 0.072 |
| Mode mismatch SQZ/LO | 0.021 |
| FI phase noise | 76.5 mrad |
| FD phase noise | 5.2 pm (4.9 Hz) |
Calculation of FI phase noise:
K1:FDS-WFS2_DC_SEG1_OUT -> PDH IR
K1:FDS-WFS2_DC_SEG2_OUT -> IR TRA
K1:FDS-WFS2_DC_PIT_IN1 -> normalized PDH IR (i.e PDH IR/IR TRA)
Aritomi and Yuhang
| 4th Feb(in air) | 5th Feb(in air) | 6th Feb(in air) | 7th Feb (in air) | ||||
| injection | readout | injection | readout | injection | readout | injection | readout |
| 6.98% | 1.51% | 6.13% | 1.22% | 6.08% | 3.05% |
5.70% |
3.48% |
The loss measurement doesn't include intra-OPO loss (roughly 8%) in injection.
This measurement also doesn't include homodyne loss (roughly 4%), PD quantum efficiency (roughly 1%) in readout.
| 4th Fed (in vacuum) | 5th Feb (in vacuum) | 6th Feb (in vacuum) | 7th Feb (in vacuum) |
| 15.09% | 14.62% | 15.28% | 13.10% |
total loss:
| 4th Fed | 5th Feb | 6th Feb | 7th Feb |
| 36.58% | 34.97% | 37.41% | 35.28% |
[Aritomi, Yuhang]
| Filter cavity loss | 122 ppm |
| Mode mismatch SQZ/FC | 0.043 |
| Mode mismatch SQZ/LO | 0.024 |
| FI phase noise | 40.1 mrad |
| FD phase noise | 4.5 pm (4.2 Hz) |
[Aritomi, Eleonora, Yuhang]
Recently we couldn't lock FC and we thought it is due to strong wind, but today we found that green injection power was 11.5 mW which was a bit lower than usual. When we increased FC gain, FC locked. Then we changed SHG temperature from 3.078 to 3.09 and green injection power became 15.2 mW. We tuned the FC gain so that UGF of FC loop is 20kHz.
I am trying to align the TEM00 beam to the folded cavity.
In order to do that I am modifiying the beam path which allows us to align with 2 STMs which have some amount of separation distance.
Since a mount for folded cavity has not been delivered yet, I cannot clapm the cavity which withdraws me to play with silicon mirror.
So I am using tentative mirrors.
Tomorrow I will measure the beam profile and tweak the mode matching and consider about the output layout.
This entry is a log of yesterday's work.
I installed a number of mirrors in TEM00 path to inject the beam into the folded cavity only with sample mirror inside the chamber.
Then I install 2 mirrors inside the chamber for picking off the ''transmitted'' beam.
I confirmed that the transmitted beam can come back on the optical bench.
The next step is optimize the position of the folded cavity and mode matching.
Aritomi and Yuhang
Yesterday, the filter cavity is very stable (red curve). We took the spectrum and compared it with last friday (green curve).
The data is saved in desktop as TRA2.
Pengbo, Simon
The measurement on the P-pol input birefringence in TAMA#1 is finished. Please refer to the attached pictures.
As can be seen (again compared with the results of the former measurement, see elog entry 1807) we could decrease the number and epecially the strength of the disturbing vertical stripes. Of course, they are still present but note that the inhomogeneity level is quite low. Therefore, also weak remnants of polarization instabilities are easily visible.
| green power (mW) | 0 | 18 |
| OPO temperature (kOhm) | 7.164 | 7.164 |
| p pol PLL (MHz) | 240 (44) | 190 (38) |
[Aritomi, Yuhang]
I fitted the data from 70Hz to 800Hz. Compared with last week's measurement, produced SQZ increased from 7dB to 8.2dB since we optimized OPO temperature and p pol PLL. We found that today filter cavity is very stable and locking accuracy seems better than usual.
One thing we can try is to reduce LO if we can improve backscattering. Also we can try to reduce green power a bit more.
sqz_dB = 8.2; % produced SQZ
L_rt = 150e-6; % FC losses
L_inj = 0.20; % Injection losses
L_ro = 0.11; % Readout losses
A0 = 0.05; % Squeezed field/filter cavity mode mismatch losses
C0 = 0.05; % Squeezed field/local oscillator mode mismatch losses
ERR_L = 5e-12; % Lock accuracy [m]
ERR_csi = 80e-3; % Phase noise[rad]
Last Friday with the help of Lucia we modified end mirror damp loop to improve the performaces in pitch has I did for the input. It seemed good but after that the dithering was not working anymore. So I put back the previous filter and still it was not working. Finally I could make it work again by changing the sign of the loop (End part). Very strange.