NAOJ GW Elog Logbook 3.2
The TMP in BS was replaced to STP-1003 on the 21st. After the one-day monitoring, I opened the gate valve on the pump. The pressure in the arm input was improved from 1.7x10-7 mbar to 8.5x10-8 mbar. Unfortunately the vacuum gauge on the BS is not working due to the over life-time.
We performed some tapping test in order to identify the resonances of the bench. On the attached plots x stands for the NS direction, y for the EW and z for the vertical.
- when tapping along NS we excited the 10,4 Hz peak (plot 3 shows the spectra during the tapping along the 3 directions)
- when tapping along EW we excited the 14,2 Hz peak (plot 4)
- when tapping along the vertical direction we excited a broad peak at 41.8 Hz and another broad bump around 84Hz, but not very clear (plot 5)
We also performed a switch off test of the fans over the SQZ bench. As you can see from plot 6, it doesn't seem to make any difference along the z direction
The last plot shows the FFTs of the accelerometers on the SQZ bench while excited and the ones of the seismometer on the floor. All 3 directions are shown together. It would be useful to compute the transfer functions between them.
In conclusion: 10,4 and 14,2 Hz are resonances of the SQZ bench, and the fan over it doesn't seem to create any excitation.
I checked the output voltage from the vacuum gauge and it was 0.2V.
This indicates that there is an error in the B-A gauge or the sensor.
I did degas, but this not change the situation.
One possible solution is to clean up the gauge.
Yaochin and Yuhang
The spectrum of BAB into AMC is as following. TEM00: 5.56V, Higher-order 1: 6.8mV, Higher order 2: 10.6mV.
So the matching is 5.56/(5.56+6.8e-3+10.6e-3) = 99.69%
Did you tune CC2 demodulation phase for each green power?
Yao-Chin and Yuhang
For the optimization of homodyne, we basically align again the homodyne. Including the matching of IRMC/AMC and OPO/AMC, the balance of homodyne, the beam height regulation.
The situation of IRMC/AMC matching is 99.95% while OPO/AMC is 99.7%.
The balance of homodyne now is done without aligning its BS but by aligning the lens before homodyne.
Benefit from not aligning homodyne BS, we could make squeezing go to homodyne flatly. Also, in this case, the balance of homodyne is easier.
After this work, we characterize squeezing again. We measured squeezing and anti-squeezing for power from 20mW to 60mW with an interval of 5mW. The result is shown in the attached first figure.
In the attached figure 2, we see there was a peak appearing. I need to mention that this peak appears after we did several measurements.
By fitting the squeezing and anti-squeezing, we could find out the loss and phase noise information. However, this time, the fitting and raw data has a larger discrepancy.
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I am sorry that I forgot to put the information about the Green power and demodulation phase.
| green pump power | MZ offset | OPO temperature | p-pol locking frequency | CC2 demodulation phase(sqz) | CC2 demodulation phase(asqz) |
| 20 | 4.1 | 7.166 | 175 | 75 | 160 |
| 25 | 4.2 | 7.167 | 175 | 90 | 170 |
| 30 | 4.3 | 7.18 | 175 | 100 | 175 |
| 35 | 4.4 | 7.18 | 175 | 120 | 170 |
| 40 | 4.5 | 7.19 | 180 | 120 | 160 |
| 45 | 4.6 | 7.19 | 170 | 125 | 155 |
| 50 | 4.7 | 7.19 | 150 | 125 | 160 |
| 55 | 4.8 | 7.195 | 150 | 125 | 155 |
| 60 | 4.9 | 7.2 | 150 | 135 | 155 |
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In the last attached figure, we can see the fit without considering the sqz-asqz for 55, 60mW.
Note: the anti-squeezing level is lower than the measurement did last week. This may come from the alignment issue of green pump.
Did you tune CC2 demodulation phase for each green power?
Yaochin and Yuhang
We found the two lenses before homodyne both have a scratch. One has scratch just in the center area. Another has a larger area scratched but not in the center.
The photo of the lens is shown in the attachment.
We will order new lenses.
I found that the vacuum gauge seemed to be working at relatively higher pressure level.
I vent a littele bit and started pumping down to see the behavior of vacuum gauge.
At some extent pressure, the gauge worked and the output voltage was not so strange.
The attached figure shows the pressure level (behavior of the gauge).
However, the voltage went crazy around 2*10-3 Pa and the display showed an error.
I checked the output voltage from the vacuum gauge and it was 0.2V.
This indicates that there is an error in the B-A gauge or the sensor.
I did degas, but this not change the situation.
One possible solution is to clean up the gauge.
Yaochin and Yuhang
In our lab, we have mainly three kinds of mirrors. One is from ALTECHNA, another is from LAYERTECH and the last is from Newport.
1. ALTECHNA mirror is the mirror we are basically using for squeezing injection to filter cavity. The company claim that it has a reflectivity of >99.5% for the HR side. And the surface quality is 20-10 SD. And wavefront distortion is lambda/8.
2. New port 5104 mirrors. From the website, reflectivity is >99.7%, wavefront distortion is lambda/10 and surface quality is 15-5 SD.
3. LAYERTECH. reflectivity is larger than 99.9%. We have only a few of them.
Yaochin and Yuhang
(Actually, we started to do this since last Friday)
After realizing the importance of this work, we started to move the two lenses between OPO and AMC. After reaching a matching level of 98.5%, we found the beam on the second lens is quite off-center. We know that this will cause the problem of astigmatism(see attached figure). So we should try to avoid this. However, actually, this is caused by the alignment of homodyne BS and dichroic mirror just after OPO.
For the homodyne BS, we adjust its pitch and yaw to balance homodyne. The consequence of this adjustment is that we need to tilt BAB in order to overlap it with LO.
For the dichroic after OPO, we forgot to change it back to flat after the characterization work of its loss. Then it may tilt the beam as well.
To correct these two things, we did again the check of beam flatness from OPO to homodyne. And at the same time, we changed the PBS after OPO to a normal mirror.
(This work is still going on)
Yaochin and Yuhang
We tried to match BAB to the filter cavity last Friday. However, we found the beam is quite misaligned. And we have a bad mode mismatch.
Later, we figured out that there are two different reasons causing this problem.
1. Change of Faraday isolator. The length of the old FI(IO-3-1064-VHP) is 114.3mm. The length of the new FI(FI-1060-5SC HP) is 58mm. This length difference is not negligible and will change the mode matching condition.
2. Change of lens1 position. This lens1 is the lens just after OPO transmission. It is the common lens for FIS and FDS path. After the installation of the new Faraday, the matching condition for FIS is changed a lot. To characterize FIS, we must move the common lens.
Anyway, we should first match BAB to AMC.
We will measure again the beam parameter and check the position of lenses after matching BAB to AMC.
The monitor indicates something wrong with the vacuum gauge...
Yao-Chin and Yuhang
We improved the matching between IRMC and AMC from 99.5% to 99.95%. As shown in the attached figure, you can find the TEM00 peak height(11V) and higher-order modes peak height(5.28mV).
[Matteo, Eleonora]
- We added a new DAC module both on the master model (k1x01) and slave model ( k1fds).
- We added a PCiexpresse DAC board to the last slot availabe on the standalone. Now we have 2 ADC and 2 DAC.
- We installed and powered an AI filter in the DGS rack. Only 8 channels are available. (Pic 1).
- We connected the DAC timing box to the DAC baord in the standalone. We could not connect the timing box to the AI filter because we miss the cable. (It will arrive tomorrow from Kamioka).
- We installed and powered a BNC to Dsub converter into the rack in the clean room. (Pic 2).
- We restarted the standalone and the model didn't show any problem.
We will test the signal from the new DAC as soon as we receve the missing cable.
I started pumping down this mornig and the pumps were working properly.
It seems that the vacuum gauge has a problem...
Although the pressure seemed decreasing, the pressure showen on the display was 9.8*10-1 Pa.
In addition to that, the output voltage from the ANELVA showed strange behavior.
Therefore I am suspecting the gauge has a problem.
Pengbo, Simon
On Friday (Nov. 15th) we reset the PCI system to do absorption measurements. The main purpose was basically to confirm the absorption maps with those Manuel measured before and to see whether the birefringence maps really do correlate with the absorption patterns.
The results can be seen attached. The map is quite similar to the "center"-map from Manuel and it the similarity of the patterns to the birefringence maps is obvious (elog 1843).
An interesting fact may be that the mean absorption coefficient is 77 ppm/cm which is ~30% smaller than the value Manuel has calculated from his' map. We are quite sure that this is due to the calibration factor we derived before starting the measurement.
This mornig the pressure was 9.8*10-1 Pa, though it was 5.0*10-3 Pa yesterday...
I am suspecting the residual water caused the problem.
I took a data during thus vacuum test.
The measured output voltage from ANELVA M-601GC has a relationship between the pressure which is described as
P = 102*V-12,
where P is the pressure and V is the output voltage.
I roughly checked the pressure using this relation and it was like 10-6 Pa, though the displayed pressure was ~10-3 Pa.
The output voltage was not correct for some reason,
I will check the measured voltage and do the test again without venting.
Yesterday I found a timed-out error on diaggui. DGS was restarted to reset timing syncronization
Yesterday, while testing an improveed filter for BS optical lever control, I found that, after closing the loop, there was an increese of the noise level in the spectrum (as I already observed in entry 1642), the level stayed high also after I open the loop and reset the filter. It went back to normal after I switch on and off the coildriver, but it got high again if I close the loop ( no matter whcih filter I use)
Pic1: blue curve open loop spectra before with normal noise level (YAW top/PIT bottom). Red curve closed loop spectra with increased noise.
I installed the another double-pass AOM — to be precise, I installed a lens, QWP, and mirror for composing double-pass AOM system.
The attached picture shows the installed optics.
The following is the procedure.
-
Adjusted the alignment to maximize the -1st order diffracted beam power.
The diffraction efficiency was about 85%. - Then put a lens (f=75mm) and QWP to collimate the beam.
- Put a mirror and adjusted the alignment to let the diffracted beam enter the AOM.
- Adjusted the alignment with two STMs and one end mirror by monitoring double-passed beam power.
- I got about 72% double-pass diffraction efficiency at the end.
I have not investigated the beam jitter of this system.
So I gonna measure the beam jitter with frequency scan and then install optics for ISS.
