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KAGRA MIR (Scattering)
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HomareAbe - 09:48, Monday 25 July 2022 (3045)Get code to link to this report
Mistake in calibration of scattering measurements
Abe, Dan,

We noticed a mistake in the calibration step in the scatter measurement.
We assumed that the camera was receiving all of the light emitted from the integrating sphere, when in fact it was receiving only 0.43%.
This reduces the result for all scattered light to 0.43%.
In other words, the 7/22 result is 4~7%*4.3*10^(-3)= 1.7~3.0*10^(-2)% ,instead of 4~7%.
(The reason for the wide range of values is that the intensity of the scattered light has an angular dependence.)

This means that the scattered light is about 170~300ppm.
KAGRA MIR (Polarization)
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MarcEisenmann - 19:35, Friday 22 July 2022 (3044)Get code to link to this report
corrected AZTEC #1 birefringence

Following the solved issue of PSD saturation, I computed again calibration parameters (see figures 1 to 3).

Then, I computed polarization map with input polarization s (figure 4) and 15 deg (figure 5).

From these measurements, I could compute delta n and theta (figure 6) as well as polarization conversion losses (figure 7).

The 2 methods to estimate these losses agree well with each other and show losses at about 0.74 % !

We will fine tune the mirror rotation angle (seems we still have an offset about 2.37 deg or 4.65 arc length cord).

Images attached to this report
3044_20220722123120_calibmeasurement.png 3044_20220722123124_calibparameters.png 3044_20220722123127_iscalib.png 3044_20220722123522_pol0.png 3044_20220722123525_pol15.png 3044_20220722123529_dntheta.png 3044_20220722123535_conversionloss.png
KAGRA MIR (Scattering)
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HomareAbe - 11:23, Friday 22 July 2022 (3043)Get code to link to this report
Calculation of Aztec3 scattering
Abe, Dan

We calibrated IR camera sensitivity and analyze the scattering data.

According to our result, Aztec3 has 4~7% scattering for IR light.
Images attached to this report
3043_20220722040832_20220722094854.jpg 3043_20220722040900_countvsenergy.png
KAGRA MIR (Polarization)
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MarcEisenmann - 19:16, Thursday 21 July 2022 (3042)Get code to link to this report
PSD were saturating

Previous entries reported strange anti-correlation of s and p polarization power while not changing polarization.

Furthermore we had also s polarization power too constant while rotating the mirror.

Today I found out that the PSD were saturating despite neither the PSD displays nor the lockin-amplifier showing saturation.

This is because I forgot to reduce the laser power after checking the beam parameter with the razor blades.

The power is now decreased from 14 mW to 1.6 mW.

I redid the calibration measurement and started measurement with rotated sample and s polarization.

R&D (FilterCavity)
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NaokiAritomi - 16:25, Thursday 21 July 2022 (3041)Get code to link to this report
AA recovery

I found that green reflection for AA was misaligned a lot. I aligned steering mirrors for AA to make the green beam at the center of both QPDs. DC centering loop can be locked, but AA loop could not be locked. I checked AA setting and it was completely different from previous setting in elog2850 (Fig. 1). I brought it back to the previous setting and AA loop seems working now.

To check the IR alignment, I injected BAB to FC. I could not find BAB transmission, but I found BAB reflection from FC. I will maximize the BAB reflection and recover IR alignment soon.

Images attached to this report
3041_20220721092457_aaconfig.png
KAGRA MIR (Scattering)
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DanChen - 09:50, Thursday 21 July 2022 (3040)Get code to link to this report
Camera calibration for scattering measurement

With Homare Abe

Date: 2022/7/20

We performed a camera calibration measurement for the camera which we used to measure scattering of Aztec No3.

We used an integration sphere with a 1050nm LED (LED1050L2) input as a reference light, then we took pictures with conditions (distance, ISO, focal length etc) same as we took the Aztec sample.

We changed exposure time and took some data.

After the measurement, we converted the data to "count sum VS energy caught by the camera", which is attached here.
Now, we can convert picture data for Aztec No3 to energy or power.

Images attached to this report
3040_20220721025046_countvsenergy.png
KAGRA MIR (Polarization)
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MarcEisenmann - 19:50, Wednesday 20 July 2022 (3039)Get code to link to this report
Trial to rotate AZTEC #1

Marc, Michael, Yuhang

We checked the p polarization power after sample at its center while injecting s polarization and rotating the sample.

Result is attached to this entry.

Note that here, the positive rotation is opposite of positive rotation of the HWP. It means that we expect to see the minimum of p polarization power around -41.5 deg.

We indeed find a minimum around this position and started new measurement with the mirror rotated by -46.5 degrees.

During this measurement we found out that we have 2 beams on each port of the PBS on the readout part (maybe due to birefringence induced beam splitting).

Images attached to this report
3039_20220720124840_samplerotation.png
KAGRA MIR (Polarization)
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MarcEisenmann - 19:38, Wednesday 20 July 2022 (3038)Get code to link to this report
AZTEC #1 birefringence

We measured AZTEC #1 polarization with 0 deg (or s polarization), 15 and 45 deg polarization angle at the injection (see figures 1 to 3).

From the measurements with 0 and 45 deg input polarization angle, I could compute delta n and theta (figure 4) and s to p polarization losses (figure 5).

From this last figure, we can see a good agreement of losses between the direct measurement with the computation from delta n and theta.

This was not the case for the measurement with 15 deg input polarization angle and investigation are on-going.

The bad news is that theta is not uniform inside the central area of the mirror. This means that there is no rotation of the sample that will decrease the s to p polarization losses inside this area.

Images attached to this report
3038_20220720123334_pol0.png 3038_20220720123340_pol15.png 3038_20220720123346_pol45.png 3038_20220720123352_dntheta45.png 3038_20220720123356_s2ploss45.png
KAGRA MIR (Scattering)
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HomareAbe - 20:05, Tuesday 19 July 2022 (3037)Get code to link to this report
Current status of scattering measurement
Abe, Dan,

We could see IR scattering light.(See fig.)
Scattered light was visible only in the center of substrate.
We measured again in another angle.
Scattered light was visible in same position.

So we believe that internal scattered light does not have a strong angular dependence.

We start calibration for IR measurement.
We will use 1050nm LED.
We will use an optical table outside clean room. Please don't touch these components.
Images attached to this report
3037_20220719130311_img0008.jpg 3037_20220719130344_dsc0332left12m.jpg 3037_20220719130357_20220719183235.jpg
R&D (FilterCavity)
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NaokiAritomi - 16:22, Tuesday 19 July 2022 (3036)Get code to link to this report
Improvement of nonlinear gain

To check the alignment of green from OPO at GRMC, I put a PD at GRMC reflection for green from OPO (Fig. 1). The cursor 2 at 11.2mV shows the offset. Fig. 1 would show the green alignment to OPO is fine.

Then I measured nonlinear gain with BAB maximum. After some alignment of green to OPO, nonlinear gain with 25 mW green reached 5. This is consistent with theoretical nonlinear gain of 5.1 with 80mW OPO threshold, but lower than 6.8 which is the value one year ago in elog2577. The current setting is as follows.

green power (mW) 0 25
OPO temperature (kOhm) 7.13 7.13
p pol PLL frequency (MHz) 230 160
BAB maximum (mV) 286 1420
Nonlinear gain 1 5
Images attached to this report
3036_20220719092624_img9228.jpg
R&D (FilterCavity)
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NaokiAritomi - 15:57, Tuesday 19 July 2022 (3035)Get code to link to this report
FC locked stably

I scanned BS alignment and green beam can be found in FC transmission. I aligned input mirror with picomotor so that the green reflection overlaps with the injection. After I aligned end mirror, green flash can be found and FC locked stably!

KAGRA MIR (Polarization)
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MarcEisenmann - 21:48, Friday 15 July 2022 (3034)Get code to link to this report
preparation of AZTEC #1 birefringence measurement

Marc, Matteo

We removed the AZTEC #5 from the translation stage and installed 2 razor blades.

They are at 120 mm (for the vertical cut) and 122 mm (for the horizontal cut) of the last steering mirror on the injection path.

We realigned the probe beam and reached 0.003 deg and 0.005 deg angle of incidence for vertical and horizontal respectively.

We realigned the PBS and our photodetectors, tuned the QWP and HWP.

S polarization is best for 3.1 deg of the HWP. The best p polarization is reached by moving the HWP angle by -45 deg.

We did the calibration as for #3.

A bit strange result was that s and p polarization power fluctuations were anti-correlated suggesting that the input polarization was fluctuating.

Touching a bit the laser fiber I could generate such anti-correlation. One possible explanation for this could be that the fiber is now touching/resting on the scattering black box foil which might be moving due to the air flow (?).

In any case, we could get some reasonable calibration factors but we will further investigate this issue.

Finally, we started polarization measurement with s polarization at the input.

KAGRA MIR (Absorption)
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MarcEisenmann - 21:41, Friday 15 July 2022 (3033)Get code to link to this report
AZTEC #5 absorption

Report about AZTEC #5 absorption.

Absorption is about 140 ppm/cm

Interestingly, it is the only sample with so visible crystalline structure defects (see yz map).

It also had largest scattering area (visible with our probe laser) compared to the other samples.

Images attached to this report
3033_20220715144036_xy1.png 3033_20220715144040_xy2.png 3033_20220715144044_xy3.png 3033_20220715144050_xz.png 3033_20220715144054_yz.png
R&D (FilterCavity)
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MichaelPage - 13:34, Thursday 14 July 2022 (3032)Get code to link to this report
OPO replacement - green output vs infrared injection

Yuhang and Michael

We checked the output of green power vs injected infrared for the new OPO. A variable ND filter was placed along the path and then the power meter was used just before the OPO for IR and just after for green. Figure 1 shows the IR vs green profile and the efficiency of green generation. Note that the efficiency is P_green/P_IR^2. In Matteo's thesis figure 5.7, the efficiency of a PPKTP SHG IR to green conversion is found to be about 2.3 /mW, vs 0.4 /mW here. But, we are using an OPO cavity with an incoupling mirror that has 20% reflectivity for green, whereas an SHG cavity should be completely transmissive for green.

For whatever reason, the power reading with the variable ND filter in place didn't seem very stable. But when we removed it to do a couple of high power measurements, it was more stable.

 

The green beam shape also looks good (figure 2).

Images attached to this report
3032_20220714063425_opogreenir220713.jpg 3032_20220714063432_greenoutputshape20220713175923.jpg
KAGRA MIR (Scattering)
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MarcEisenmann - 11:57, Thursday 14 July 2022 (3031)Get code to link to this report
AZTEC #3 IR scattering rough upper limit

Before removing #3 of the birefringence measurement setup I measured the incident and transmitted IR power  at normal incidence.

From this measurement, I estimated a rough upper limit of scattered power to be 1 % but note that we had power fluctuations at about 4% during this measurement.

While this value is not precise at all, it is far below the green scattered power (supposedly between 10 and 30 % ; hopefully elog will follow for this measurement)

It means that the scattered power is strongly decreasing with the wavelength.

KAGRA MIR (Scattering)
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HomareAbe - 09:56, Thursday 14 July 2022 (3030)Get code to link to this report
Current status of scattering measurement
Abe, Dan, Ikeda

We changed IR laser and the camera which can receive IR light for IR measurement.
2days ago, we take picture of Aztec3 sample and we can see 4 scattering lights.

The light on the most right is front surface scattering.
The light seen third from the right is back surface scattering.
The light seen forth from the right(most left) is back reflection light.
About second one, we are discussing.

Yesterday, we installed beam profiler in clean room and measured new laser.
The result is like this.

The beam size is large. We will put some collimator lens.
Images attached to this report
3030_20220714024007_omega.png 3030_20220714024654_20220712aztec3.jpg 3030_20220714024659_20220712aztec3internal.jpg
KAGRA MIR (General)
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MarcEisenmann - 17:15, Wednesday 13 July 2022 (3029)Get code to link to this report
AZTEC #1 and beam profiler brought to pci clean room

Abe, Ikeda, Marc

Today we brought the beam profiler from ATC clean room to the PCI clean room.

We also brought AZTEC #1 from ATC to PCI cleanroom and reapplied first contact to one of the surface.

KAGRA MIR (Absorption)
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MarcEisenmann - 15:40, Tuesday 12 July 2022 (3028)Get code to link to this report
AZTEC #5 absorption started

Marc, Matteo

We checked the 1.5 inch absorption and got expected values.

We installed #5 and did a long z scan to find the 2 surfaces at 26.3 mm and 114.7 mm making z_center = 71 mm.

From this measurement we could also see absorption about 200 ppm/cm...

In any case we started XY measurement at Z_center.

KAGRA MIR (General)
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MarcEisenmann - 22:08, Monday 11 July 2022 (3027)Get code to link to this report
Preparation of AZTEC #5 absorption measurement

I removed #3 without rotating it : Please don't touch the holder nor the mirror as we need to precisely mark the c-axis orientation

I realigned and characterized with razor blades both the probe and pump beam as reported in figures 1 and 2.

Note that the x axis of these figures is somewhat random (just corresponds to translation stage z position with the razor blades installed)

I got good values of AOI, beam sizes and crossing point.

I measured the surface reference sample :

Pin = 29.6e-3
ac = 0.4355
dc = 4.28
acdc = 0.10175
R = 15.625 /W
(3% change wrt # absorption)
filename = 'Mon, Jul 11, 2022 8-40-39 PM'
 
xyz = 327.093,119.965,35
ziu = 68
Pin = 29.6e-3
ac = 0.4355
dc = 4.28
acdc = 0.10175
R = 15.625 /W
(3% change wrt #1 absorption)
filename = 'Mon, Jul 11, 2022 8-40-39 PM'
 
xyz = 327.093,119.965,35
ziu = 68
 
Then I measured the bulk reference sample : 
 
AC_bulkref =0.0839
DC_bulkref = 5.05
P_in = 29.8e-3
ACDC = 0.0166
P_t = 16.3e-3
 
z1 = 32.2
z2 = 35.4
z_center = 33.2
 
R_bulk = 0.7242 cm/W
filename = 'Mon, Jul 11, 2022 9-05-35 PM'
 
Also got good values wrt previous measurements
 
I installed the 1.5 inch sapphire sample, realigned the DC with ziu = 65.49 mm.
I did a long z scan with Pt = 5.51W (Mon, Jul 11, 2022 9-47-22 PM)
 
Finally, I started a XY measurement with 10 mm radius at z_center = 28.7 mm, x = 327.093 mm and y = 119.965 mm.
 
 
AC_bulkref =0.0839
DC_bulkref = 5.05
P_in = 29.8e-3
ACDC = 0.0166
P_t = 16.3e-3
 
z1 = 32.2
z2 = 35.4
z_center = 33.2
 
R_bulk = 0.7242
filename = 'Mon, Jul 11, 2022 9-05-35 PM'
Pin = 29.6e-3
ac = 0.4355
dc = 4.28
acdc = 0.10175
R = 15.625 /W
(3% change wrt # absorption)
filename = 'Mon, Jul 11, 2022 8-40-39 PM'
 
xyz = 327.093,119.965,35
ziu = 68Pin = 29.6e-3
ac = 0.4355
dc = 4.28
acdc = 0.10175
R = 15.625 /W
(3% change wrt # absorption)
filename = 'Mon, Jul 11, 2022 8-40-39 PM'
 
xyz = 327.093,119.965,35
ziu = 68
Images attached to this report
3027_20220711150819_20220711beamaoi.png 3027_20220711150824_20220711beamparam.png
KAGRA MIR (Polarization)
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MarcEisenmann - 14:20, Monday 11 July 2022 (3025)Get code to link to this report
Comment to Measurement of losses as a function of mirror rotation (Click here to view original report: 3020)

We did measurement with input polarization angles of 0 deg, 15 deg and 30 deg.

We computed delta n and theta from them.

Especially, we found that theta = 1.6 deg in the center of the mirror.

This is exactly the value we expected from the HWP rotation angle.

We will use this rotation of the mirror for the polishing.

Images attached to this comment
3025_20220711072052_finalrotdntheta.png