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Birefringence mitigation (General)
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MarcEisenmann - 20:58, Thursday 11 May 2023 (3248)Get code to link to this report
overhead shelf

The overhead sheld (ATS6) was delivered and assembled by Japan Laser people.

It is possible to move the hanging shelf and the cable management tray by unscrewing the bolts.

Be careful that there are other bolts inside the frame that need to be moved as well.

There are also extra bolts and smaller tube for the hanging shelf in a plastic bag taped to the optical table foot.

KAGRA MIR (Polarization)
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MarcEisenmann - 14:39, Thursday 11 May 2023 (3247)Get code to link to this report
Comment to PCI clean room cleaning towards birefringence measurement (Click here to view original report: 3245)

[Marc, Takahashi, Yoshizumi]

We removed the failling tape and replaced them with plastic ones.

The pre-clean room and clean room wall are now repaired.

KAGRA MIR (Polarization)
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MarcEisenmann - 11:59, Tuesday 02 May 2023 (3246)Get code to link to this report
alignment and calibration

[Marc, Munetake, Shalika]

We reconfigured the PCI for birefringence measurement.

First, we put back all required cables with the 6dB attenuators at the output of the PSD sum.

We tuned the laser power to 1.6mW (laser current = 1A and HWP rotated to 348deg.

We installed the razor blades and tuned the vertical and horizontal angle of incidence to about 0.006deg.

We realigned the readout part.

We tuned the QWP and HWP to minimize p pol in transmission with HWP = 351.2 deg.

We took 10mn of s and p polarization and got the attached calibration coefficients.

Images attached to this report
3246_20230502045947_calibration.png
KAGRA MIR (Polarization)
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MarcEisenmann - 11:55, Tuesday 02 May 2023 (3245)Get code to link to this report
PCI clean room cleaning towards birefringence measurement

[Marc, Shalika]

Following the several months with the too large scattering box, the wall of the PCI clean room are quite damaged...

We should definitely replace them.

We removed the box and several of the optics used for the scattering measurement.

Because of the damaged wall, the 'clean room' was quite dirty and we spent some time cleaning it up.

We install a new shelf in front of the PCI clean room entrance to store the scattering components

Comments related to this report
MarcEisenmann - 14:39, Thursday 11 May 2023 (3247)

[Marc, Takahashi, Yoshizumi]

We removed the failling tape and replaced them with plastic ones.

The pre-clean room and clean room wall are now repaired.

R&D (FilterCavity)
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RyutaroTakahashi - 13:56, Thursday 27 April 2023 (3244)Get code to link to this report
Comment to Dry-pump failed (Click here to view original report: 3216)

I started the SIP "N-S P8" near the south end. Applied voltag and current were changed as follows.

[Just after starting]

  N-S P8
Voltage [V] 5910
Current [mA] 0.8

[After 3 hours]

  N-S P8
Voltage [V] 5910
Current [mA] 0.4
Birefringence mitigation (General)
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ShalikaSingh - 20:00, Wednesday 26 April 2023 (3243)Get code to link to this report
Modifications for easy VI use
Overview: Minor modifications of VI for feasibility during real time use
 
1. The VI has a parameter called "comment". This helps us to understand what is the nature of our file. So, here you can input an extra parameter like rotation or your motive of measurement. Moving on, since we won't be rotating LC for birefringence measurements, we didn't add rotator control to our VI. Adding components decreased speed. So we made an extra component "comment" to save an extra parameter appended to our file.
 
2. Yesterday, when we were doing calibration measurements we had to switch off the controller(temp, voltage both) to save data for every unique rotation angle of LC (because only after switching off you can change the extra parameter in comments or create a new file). Switching off the VI every time and starting it back is extremely time-consuming as we need to wait several minutes before the temperature stabilized. To combat all these issues and easy long-term measurements for different parameters without switching off the VI, I removed the temperature controller's stop condition. Now, it's independent of the switch of the voltage controller and will turn off only when we exit the VI. This will make temperature control stable for the entire measurement.
 
3. Now we can save several sorts of data in the same file or even make new files without switching off the temperature control or camera. Also, you can change the "comment" during an ongoing measurement and it would save the new parameter as soon as you changed it. 
 
4. I removed voltage and temperature graphs, as the more visuals we have on the front panel the more tradeoff occurs with speed. Therefore, all the graph is now independent in a timed loop outside the main loop. This helped relax the speed. In programming, it's better to have two loops doing simple things rather than one loop doing too complicated and a lot of stuff. For extremely fast measurements, all these parameters do affect the speed. 
 
5. Previously, when we started saving 6 parameters VI slowed down a bit by 20Hz. As a matter of fact, all the new changes have been made in a way that our speed is not compensated and it still saves data at 80Hz.
Birefringence mitigation (General)
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MarcEisenmann - 15:17, Wednesday 26 April 2023 (3242)Get code to link to this report
LC fast axis direction as a function of applied voltage

[Marc, Shalika]

When we measured the polarization state with the polarization camera directly after the LC we could see that the azimuth angle seems to change a lot around the half-wave retardation voltage.

We tried to measure the fast axis direction by minimizing the transmitted power of the LC after a polarizer but the results were quite strange and not so consistent when repeated..

One possible explanation is that the power minimization was not precise enough to do by hand.

We decided to follow the procedure of [1] where we installed the output polarizer to be in cross-polarizer configuration and measured the transmitted power while appling a sawtooth voltage and rotating the LC from 0 to 360 deg with 10deg increment.

The resulting function is fitted for a given voltage by a sum of cosine with different orders, all as a function of (x-x0) where x is the rotation angle of the LC and x0 a possibly voltage-dependent offset that should correspond to the LC fast axis rotation as a function of the applied voltage.

By repeating this for every voltage we can get the attached figure where we found that the fast axis orientation is almost voltage independent (within 1deg).

 

[1] : Measurements of linear diattenuation and linear retardance spectra with a rotating sample spectropolarimeter David B. Chenault and Russell A. Chipman

Images attached to this report
3242_20230426081647_fastaxis.png
Comments related to this report
MarcEisenmann - 10:12, Tuesday 16 May 2023 (3253)

To measure the fast axis orientation we shuold have the 2 polarizers parallels and not crossed.

Birefringence mitigation (General)
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MarcEisenmann - 15:10, Wednesday 26 April 2023 (3241)Get code to link to this report
LC extinction ratio

[Marc, Shalika]

To measure the extinction ratio of our LC, we removed the polarizer and rotated the LC to measure the maximum and minimum of the transmitted power.

To be more precise, the transmitted power is normalized by the input power.

We repeated this measurement for several voltages applied to the LC as in the attached figure.

The errorbars are coming from the power fluctuations we measured.

The extinction ratio seems quite constant at all voltages at about 1.009+/-0.002

Images attached to this report
3241_20230426080936_extinctionratio.png
R&D (Roberts Linkage)
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KoheiMitsuhashi - 07:15, Monday 24 April 2023 (3238)Get code to link to this report
Estimated Q factor of Roberts Linkage after attached coil magnet actuator

Waht I did: estimated Q factor after attached coil magnet actuator.

I estimated Q factor of Roberts linkage after attached coil magent actuator.
This Robert linkages' resonant frequency is 0.67Hz.
When I estimated Q factor, I used the ring down curve from 2000s to 2500s(just Fig 2).
Estimated Q factor of Roberts linkages is 3.91×10^3.

Blue points are mesurement and red points are fitting.
Vertical axis is read out of photo seosor that can detect displacement, horizontal axis is time.
Fig 1 is over view of the ring down curve.
Fig 2 is the data that is used for estimating Q factor(2000s to 2500s).
Fig 3 is over view and fitting results.
Fig 4 is the ring down curve that is used for estimating Q factor and fitting results.
Fig 5 is also the ring down curve and fitting results from 2000s to 2020s.

Images attached to this report
3238_20230423164434_lawoverview.png 3238_20230423164441_lawmediam.png 3238_20230423164452_fittingoverview.png 3238_20230423164502_fittingmediam.png 3238_20230423164510_fittingdetail.png
R&D (Roberts Linkage)
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KoheiMitsuhashi - 07:14, Monday 24 April 2023 (3239)Get code to link to this report
Measured the transfer function form coil magnet actuator to photo sensor

What I did: measure the transfer function from coil magnet actuator to photo sensor.

I measured the Roberts Linkage's transfer function from coil magnet actuator to photo sensor.
First of all, I attached magnets on the suspended mass, and also set a coil.
Fig 1, 2, 3, 4 is a setup of coil magnet actuator.

When I measured the transfer function, the data was measured from 0.1Hz to 10Hz and also measured form 10Hz to 0.1Hz.
The reason is that a resonant osillation of Roberts linkage remained for a while, so I can't measured the trasfer function appropriately after passing throught the resonant frequency.

Fig 5 is the transfer function when I measured it from 0.1Hz to 10Hz.
Fig 6 is the transfer function when I measured it from 10Hz to 0.1Hz.
Fig 7 is combined one. 

Images attached to this report
3239_20230423181115_20230412135036.jpg 3239_20230423181208_20230412150926.jpg 3239_20230423181245_20230412150807.jpg 3239_20230423181256_20230412201845.jpg 3239_20230423181612_1hz.png 3239_20230423181619_transfrom10hz.png 3239_20230423181635_transcombine.png
Birefringence mitigation (General)
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MarcEisenmann - 21:34, Saturday 22 April 2023 (3237)Get code to link to this report
ambient light cover towards final characterization

[Marc, Shalika]

As our calibration and vi are now finalized we are now setting up our final calibration before starting birefringence measurement.

We made a black cover box from 2 un-used optical lever covers. We drilled one small hole for the laser input and another one for the several cables we need.

The ambient light from the power meter or the camera were reduced by a factor 100.

Birefringence mitigation (General)
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MarcEisenmann - 10:52, Friday 21 April 2023 (3236)Get code to link to this report
LC hysteresis

[Marc, Shalika]

Following the speed improvement of the LC voltage control we implemented a sine modulation of the voltage.

However, we found that the resulting retardance is different if the voltage is increasing or decreasing.

We decreased a lot both the sine freq and sampling freq and could resolve this issue.

This seems related to the LC different switching frequency when applying increasing or decreasing voltage with decreasing voltage being faster.

To mitigate this effect, we also implemented a decreasing sawtooth function and plan to mainly use this one for our future calibration and measurements.

R&D (FilterCavity)
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RyutaroTakahashi - 09:59, Thursday 20 April 2023 (3235)Get code to link to this report
Comment to Dry-pump failed (Click here to view original report: 3216)

I checked the voltage and curent in the SIPs today.

  N-S P5&6 N-S P7
Voltage [V] 5200 5930
Current [mA] 0.2 0.4
Birefringence mitigation (General)
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ShalikaSingh - 10:41, Wednesday 19 April 2023 (3234)Get code to link to this report
Increased Speed of measuring points per second

[Shalika, Marc]

 

OverviewThe speed of saving data/characterization is 80 Hz. 

 

Details:

 

We changed a "lot" of stuff. Techniquely we were removing everything one by one and seeing how they affected the speed. We did this with every single component in our VI. We were simultaneously optimizing speed by removing VIs which were not so important. Previously our speed was 8Hz, so we were acquiring 8 points per second. Now we have around 80 points per second, i.e 80Hz. 

 

Refer to Fig 1 for more details, but below are the most essential parts which helped optimize the speed. 

1. Temperature controller was extremely heavy. It doubled the speed when we removed it. We brought the control outside the main loop. 

2. We did the same with the Power meter and Polarization camera. 

3. And, we are now using global variables to access and save data in the main loop.  

Images attached to this report
3234_20230419033536_procedureforoptimizingcode.jpg
R&D (FilterCavity)
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RyutaroTakahashi - 16:32, Tuesday 18 April 2023 (3233)Get code to link to this report
Comment to Dry-pump failed (Click here to view original report: 3216)

I started the SIPs between the EM2 and the mid point in the south arm. The power supply #3 (DIGITEL 1500) drived "N-S P5" and "N-S P6", and the power suply #4 (DIGITEL MPC) drived "N-S P7". Applied voltag and current were changed as follows.

[Just after starting]

  N-S P5&P6 N-S P7
Voltage [V] 5000 5720
Current [mA] 20 4.4

[After 3 hours for P5&P6 or 1.3 hours for P7]

  N-S P5&P6 N-S P7
Voltage [V] 5200 5980
Current [mA] 0.6 0.8
Birefringence mitigation (General)
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ShalikaSingh - 18:07, Friday 14 April 2023 (3232)Get code to link to this report
MOD-IN operation tests
Overview: Testing the output of MOD-IN mode of KLC
 
Details:
 
We provided different voltages as the input to KLC and observed the output. It seems that the output in MOD-IN mode is highly inconsistent.
 
There are a lot of problems like,
1. It does not reach 25V all the time. Sometimes the maximum voltage is around 17V even if 5V is provided as input. 
2. It stops giving any output after some time. It behaves as if it's ON but is receiving 0V as input. 
3. The data resolution was changed by 1mV at the input. Despite this, the data resolution at the output was not so good (see Fig 1). 
4. Even switching frequency between 500-2500 Hz didn't give any improvements. 
5. Although I did the measurements after the warm-up time it didn't resolve any issues. 
 
Fig 1 will help better understand the above issues. Although Thorlabs recommended using this, it seems we need to further investigate how to properly utilize it. 
Images attached to this report
3232_20230414104522_modinoperation.png
Birefringence mitigation (General)
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ShalikaSingh - 20:50, Thursday 13 April 2023 (3231)Get code to link to this report
External Input to KLC for faster voltage sweep
Overview: Use "MOD-IN" port of KLC for faster switching between voltages
 
Details:
 
In order to produce polarization states extremely fast we wish to rapidly change/sweep the voltage across LC and so we chose to use "sine" for making the variations in labview. Although we removed most of the logic for the iteration using sine, we are still a bit limited by the voltage controller itself. 
 
Thorlabs advised to not use the normal V1 as input but rather use an external input.
 
So, I connected the output of one KLC(SN-38) to the "MOD IN" of another KLC(SN-52). Here the output voltage of the controller(SN-52) is set by the external input signal of the “MOD IN” port. The 0~5.0 V DC external input corresponds to the output voltage of 0 to ±25 Vrms. For visualization, I connected the output of SN-52 KLC to the oscilloscope.
 
The variation observed is as follows:
 
Mod In (In Volts Output (Cyc RMS) (in Volts)
0 0.09 
1 1
2 2.54
3 10.2
4 15.2
5 25.4
(It did behave randomly sometimes though. For example, it used to provide the same output irrespective of change in input)
 
This worked both with the Thorlabs application and Labview. I was able to integrate the same in our labview. See Fig 1 for a better understanding. The first plot in labview shows input voltage which is varied using the sine function. and the output is shown in the second plot.
 
Next Step:
Investigate issues with data resolution of this new output and check its consistency. 
Images attached to this report
3231_20230413134845_modinsinesweep.png
R&D (FilterCavity)
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RyutaroTakahashi - 11:33, Wednesday 12 April 2023 (3230)Get code to link to this report
Comment to Dry-pump failed (Click here to view original report: 3216)

I checked the voltage and curent in the SIPs today.

  N-S P1 N-S P2 N-S P3&4
Voltage [V] 5890 5980 5400
Current [mA] 0.45 0.83 0.88
R&D (FilterCavity)
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RyutaroTakahashi - 16:42, Tuesday 11 April 2023 (3229)Get code to link to this report
Comment to Dry-pump failed (Click here to view original report: 3216)

I started the SIPs between the NM2 and the mid point in the south arm. The power supply #1 (DIGITEL MPC) drived "N-S P1" and "N-S P2", and the power suply #2 (DIGITEL 1500) drived "N-S P3"(photo) and "N-S P4". Applied voltag and current were changed as follows.

[Just after starting]

  N-S P1 N-S P2 N-S P3&P4
Voltage [V] 5640 5510 5200
Current [mA] 4.3 9.6 5.4

 [Ater 2 hours]

  N-S P1 N-S P2 N-S P3&P4
Voltage [V] 5840 5810 5300

Current [mA]

0.6 1.4 1.7
Images attached to this comment
3229_20230411093759_img20230411115122.jpg 3229_20230411093823_img20230411135719.jpg 3229_20230411093902_img20230411135744.jpg
R&D (Speed meter)
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YoheiNishino - 15:47, Tuesday 11 April 2023 (3228)Get code to link to this report
Beam profile of the Mephisto laser

Yohei,

What I did:

I have measured the beam profiles of the Mephisto laser. I have used a f250 lens to focus the beam, then estimated its original q-parameters of the laser.

Result:

The measured beam parameters (Fig1).

  beam radius [mm] weist position* [mm] M-factor
x 0.510 535 1.05
y 0.460 505 1.08

* z=0 is set to 100 mm away from the laser head. See the yellow tape in the attached picture (Fig2).

The estimated original parameters of the laser.

  beam radius [mm] weist position* [mm]
x 0.161 -164
y 0.174 -176

The weist is 60-70 mm inside the laser head. The weist position is supposed to be 90 mm inside the laser head, but the estimated values suggest it's almost near the laser head. I don't know why it happens.

 

** Sorry but there is some error on the first figure.

Images attached to this report
3228_20230411083701_setup.jpg 3228_20230411083721_202304111.png 3228_20230411084746_setup.jpg