NAOJ GW Elog Logbook 3.2
[Takahashi, Aritomi, Marc, Yuhang, Michael]
Since the BS picomotors didn't work, we opened BS chamber and checked the picomotor. We found that BS was stuck at the stopper because we moved BS picomotor too much. After Takahashi-san adjusted suspension, BS picomotors worked well. Before we close the chamber, we aligned green. We moved PR to make the green beam at the center of BS and moved BS to make the green beam at the center of first target.
We also found that the BS oplev beam is hitting off center of BS. We tried to make it at the center of BS, but the reflection was hitting the pillar of BS suspension so we left it as it is.
Finally, we closed the chamber and started the evacuation.
Some notes for future alignment:
- We should not move picomotor ramdomly. We should move the picomotor little by little by looking at some references. We should not lose the green beam at the first target as much as possible.
- When we have the suspension or picomotor issue and open the chamber, we should make sure the green alignment at GV between BS/input and first target before closing the chamber.
- We should measure the oplev spectra/transfer function and each coil response before closing the chamber
[Aritomi, Marc]
At the beginning of today, the BS picomotor was working well. However, after some BS alignment, BS picomotor does not work again... We don't know the reason but maybe because we moved the BS picomotor too much. We need to open BS chamber again.
There were some mistakes in the analysis so these results are not correct.
I'm also starting to doubt the way we analyze our measurements so I'm thinking to speed up the installation of the Soleil-Babinet compensator for this characterization.
[Takahashi, Aritomi, Marc]
We replaced the two broken BS picomotors. After the replacement, we confirmed that the picomotors are working well. We started the evacuation of BS chamber. We will open GV between input/BS tomorrow.
This is a report of AZTEC #3 birefringence measurements where each map had for parameters : X_center = 400.735 mm, Y_center = 122.105 mm, Z_center = 70.275 mm, with 70 mm radius.
Birefringence characterization :
Figures 1 to 6 are the usual polarization measurements, 7 to 9 summarize informations about the stress tensors and delta n and theta distributions.
The sample seems quite uniform and is now a good candidate for KAGRA (it also had quite low absorption).
c axis orientation estimation :
In figure 10, I tried to compute from the mean output polarization the orientation of the sample c axis.
The mean output polarization is fitted by a sine square as a function of the input polarization where errorbars represent 1 sigma uncertainty.
From this fit, it seems that if we inject 50.23 deg input polarization we should have the same at the ouput.
In order to constrain a bit more the fit I am now doing a measurement with p polarization at the input and then will start the measurement at the polarization angle that should be conserved throughout the sample.
There were some mistakes in the analysis so these results are not correct.
I'm also starting to doubt the way we analyze our measurements so I'm thinking to speed up the installation of the Soleil-Babinet compensator for this characterization.
Marc, Matteo
We installed the AZTEC #3 on the translation stage.
We tuned the input laser power to have better SNR on the PSDs.
With about 2 mW power and 3 dB attenuator before the lockin amplifier we are roughly at half the PSDs saturation and about 0.6 V in the lockin-amplifier (saturation at 1 V).
Measurements on-going (one map is 5h40 and we need at least 6)
Following work in 2958, I had to tune the position of the input oplev tilt PSD to have enough space to move the shift PSD on its rail.
To perform decoupling between shift and tilt, I injected a line at 0.94 Hz (length mechanical resonance frequency) with 200 counts amplitude on input mirror length.
I moved the lens on the rail, for each position recenter the beam on the tilt PSD and measured the peak amplitude at 0.94 Hz.
Result is reported in fig 1.
It seems that for pitch, the ideal lens position should be about 12.2 cm while it should be about 11 cm for yaw.
For yaw, the peak was always present and as suggested by Matteo could be caused by the easy excitation of yaw when exciting length.
EDIT : corrected z units from mm to cm.
We put HWP with rotation mount before compensator and try to measure retardation of HWP as entry 2965.
We maximize p-pol power to rotate the HWP:
s = 19.9 mV
p = 648 mV
We rotate HWP and compensator to 45deg.(same direction)
we maximize p-pol power again and record value of the Vernier screw.
d = 6.84 mm
s = 766 mV
p = 16.8 mV
P-pol power was too low. It should be pure p-pol but p-pol power did not change even though we rotate the Vernier screw.
I think polarization direction was parallel to fast(slow) axis of compensator.
Retardation of HWP N_hwp is given by
N_hwp = 1-6.84/13.365
= 0.488
13.365 is calibration parameters measured in entry 2965.
Today with Matteo we removed AZTEC #1 and repeated bulk calibration (R = 0.5769 cm/W) which is compatible with before.
Then, I installed a steering mirror to make the pump beam goes to the birefringence imaging unit.
Using the 2 razors blades I measured the beam position on the last steering mirror of the injection unit.
Then I move the razor blade as far as possible in z and place it in either horizontal or vertical where the beam is located on the last steering mirror.
Note that during the horizontal position tuning it is important to make sure that the beam is still aligned into the power-meter.
I then tuned both horizontal (fig 1) and vertical (fig 2) to reach angles of incidence of 0.014 and 0.006 deg respectively.
This is more than a factor 30 below the KAGRA precision requirement on the c-axis orientation so it is fine.
I connected s polarization to AC and p polarization to DC. (ie old lockin amplifier).
I reduced the laser power to about 359 uW so that we have at maximum about 1V on the lockin amplifier.
I tuned QWP and HWP (0.1 deg precision) to inject linear polarization :
hwp = 336.2 deg (s pol)
AC_min = 355/1e6
DC_max = 9.86*1/10
hwp = 21.2 deg (p pol)
AC_max = 746000/1e6
DC_min = 2.98*0.1/10
The PSD is far from saturating so maybe we could increase a bit the pump laser power and add attenuators before the lockin amplifier.
We had some concerns with previous calibration of AZTEC #1 absorption measurements so we repeated the measurements.
With R = 0.5648 cm/W we have about 60 ppm/cm absorption which is compatible with previous estimation.
Abe, Marc
First we realigned the setup and tuned both HWP and QWP to inject s polarization.
With ceiling lights off we got :
hwp = 5.5 deg seems pure s s = 915mV p = 9.98 mV hwp = 320.5 deg s = 22.2 mV p = 805 mV
We installed the Soleil-Babinet compensator and tried to align it with auto-collimation.
However, while acting on the yaw steering screw, the retaining spring jumped outside the mount (even if we didn't felt any resistance or didn't reach the end of the screw range...)
Matteo helped us to reinstall it using the ones of an old mirror mount.
Once it was fixed, we could align the SBC without issue.
Tuning the SBC to reach maximal s polarization at the readout we measured :
s = 20.4 mV p = 652 mV
We can not reach as pure s polarization as before ...
Next step is to use the detent stop by 45 deg and use the Vernier screw to reach again pure s polarization, press the zero of this Vernier, move it again so to reach the next s polarization.
We measured d = 13.365 mm and got :
s = 21 mV p = 673 mV d is our calibration parameters and we can now use it to start measurements.
The beatnote can be seen with lower reference level (10dBm) as shown in the attached picture.
[Takahashi, Aritomi, Marc]
Since the BS pitch/yaw picomotors didn't move, we opened the BS chamber and checked BS suspension. All magnets are fine, but BS was touching the earthquake stopper so Takahashi-san adjusted the BS suspension.
However, BS pitch/yaw picomotors still don't move. We can hear the sound of picomotor, but the sound is smaller than usual. We also checked BS X/Y/Z picomotors. BS X/Z picomotors moved with usual large sound, but BS Y picomotor did not move without any sound.
To check if the problem is due to the picomotor itself or not, we disconnected the wire for BS yaw picomotor and connected it with a spare in-vac picomotor. The spare in-vac picomotor can be moved so the problem should be the picomotor itself. We have not checked the BS pitch picomotor, but we guess the problem would be the same. Since we have only one spare in-vac picomotor in TAMA, Takahashi-san will bring some spare in-vac picomotors from KAGRA and replace them next next Monday.
I found an old elog420 which also says that BS Y picomotor doesn't work.
I couldn't find the p-pol laser and sidebands on the spectrum analyser (figure 1). I made sure the DDS board was reset properly, the lasers had proper current and temperature, and the beam was going into the fiber. I also tried disconnecting and reconnecting p-pol cables that I could see. Maybe something is disconnected elsewhere?
CC seems ok (figure 2)
The beatnote can be seen with lower reference level (10dBm) as shown in the attached picture.
I changed the root password back to normal. For me it was just Linux paranoia to make the root password different but I guess it doesn't matter here.
Today I moved the clean booth that was in the storage room on the test setup for the Soleil-Babinet.
Indeed we want to install it later on the PCI setup and want to limit possible dust contamination.
All the optics that were below (seems to be TAMA mirrors) and screws, magnets, etc... are now inside the clean booth of the microscope.
The setup is now ready for calibration of the Soleil-Babinet and we plan to use pure s-polarization for this.
Marc Michael
Today we brought 2 SR560 to input oplev (one from the OPO test setup, one from the elec shop).
We reinstalled the shift PSD and a steering mirror on the rail and centered the PSD.
Note that the tilt PSD and its steering mirror are really close to the rail so the newly installed one have barely enough room to move.
Marc, Matteo, Michael
One possible reason for our very low coherence could be that we injected uniform noise with 4000 counts.
To improve both the driving and sensing it is actually better to inject noise through swept sine.
We did so with noise amplitude of 10000 counts and found that the length mechanical resonance at 0.9 Hz was strongly excited in every dof.
Either the noise is too strong, the PSD is at a wrong position or the driving matrix needs to be tweaked.
We are currently taking again this measurement with lower noise amplitude at 4000 counts.
Marc, Michael
We checked the END oplev SR560 and found out that the length oplev one was saturating.
We decreased the gain of all down to 1 and realigned all signals. After that we increased the gain back to 100.
For reference, the tilt PSD sum is about 4500 counts and shift PSD sum is about 3000 counts.
Marc, Michael
Because we are missing some SR560 now to check the input oplev we decided to check the end ones.
We recentered the beam on the PSD and confirmed the good condition by measuring the usual spectrum of the END oplev for pitch and yaw.
We tried to measure the TF between END mirror yaw excitation end the 3 dofs of the oplev.
However, we did not manage to have coherence about 0.1 between yaw excitation and yaw signal from the oplev.
We checked the coils and they are working fine.
We injected white noise from about 500 to 4000 counts amplitude but it did not change the coherence value.
We will try to check with excitation over longer duration.
We also tried to realign the length PSD but could not find proper values from MEDM.
We will try again this alignment removing the SR560 to avoid too large gain of the signal.
Marc, Michael
We checked the END oplev SR560 and found out that the length oplev one was saturating.
We decreased the gain of all down to 1 and realigned all signals. After that we increased the gain back to 100.
For reference, the tilt PSD sum is about 4500 counts and shift PSD sum is about 3000 counts.
Marc, Matteo, Michael
One possible reason for our very low coherence could be that we injected uniform noise with 4000 counts.
To improve both the driving and sensing it is actually better to inject noise through swept sine.
We did so with noise amplitude of 10000 counts and found that the length mechanical resonance at 0.9 Hz was strongly excited in every dof.
Either the noise is too strong, the PSD is at a wrong position or the driving matrix needs to be tweaked.
We are currently taking again this measurement with lower noise amplitude at 4000 counts.