KAGRA MIR (Polarization)
MarcEisenmann - 17:11, Wednesday 22 September 2021 (2688)
AZTEC sample measurement started

Today I tried to check if I could improve the shielding of the PBS transmission photodiode but it seemed to be already fine like this.

Then, following Simon advices, I tweaked both QWP and HWP at the DC photodiode (s pol) minimum.

In the end, the s pol  is minized for HWP = 46 degrees.

 

I took some values of AC and DC in different configurations :

 

without laser

AC= 0.6 V
DC = 0.065 V with lockin = 0.2 uV (sensitivity 30uV)
DC = 0.076 V with lockin = 0.007 mV (sensitivity 1mV)

with laser (~30 mW ie HWP1 = 20 deg) & HWP = 46 deg


AC= 607 V
DC = 0.099 V with lockin = 0.01 uV (sensitivity 1mV)

with AZTEC sample :


AC= 378 V
DC = 0.326 V with lockin = 0.032 uV (sensitivity 30uV)

The AZTEC sample orientation is the same as for the absorption measurement (black dot at the top).

I used the AC (p pol) to find the AZTEC sample center and got Y_center = 327.72 mm and Y_center = 122.825 mm. I didn't tune the Z position which is now 53mm.

The measurement started with Median filter  = 1, average filter = 0, wait time = 500 ms, map radius = 20 mm and step size = 0.1 mm and HWP = 46 degrees (ie p pol maximum).

The measurement should last 4h30. But before leaving PCI room I touched by mistake the lockin sensitivity... so one or two points might be wrong...

I will start other polarizations over the holidays.

Comments related to this report
MarcEisenmann - 21:45, Friday 24 September 2021 (2689)

There might have been some issue with this measurement as after 35h it did not finished..

Today Yuhang kindly went to PCI to reset the parameters (sensitivity = 1 mV for both lockin amplifiers and input A for the one connected to the PC).

We restarted the measurement with HWP = 46 deg (ie incident polarization is p).

The measurement finished and I started with HWP = 91 deg (ie incident polarization s)

Analysis to follow.

MarcEisenmann - 00:31, Wednesday 29 September 2021 (2692)

I did a series of measurements while changing the polarization angle by 90 degrees.

I did not recorded the required max/min of s and p polarizations to have accurate calibrations of the measurements.

So today I restarted measurements with incident p pol, s pol and started a 30 degrees polarization angle measurement.

However, there was another WIndows update... As it is not possible (yet?) to fully control the 2 lockin amplifiers from remote, I can not restart the measurement for today.

Furthermore, the HWP2 controller is not recognized by the software after acting strangely in the past days (only jog by 1 degree otherwise it resets the current angle to 0 and still move by 1 degree...)

 

For the new measurement a possibility could be to start by an absorption measurement before switching to birefringences ones.

This would assure 100 % that the orientation of the sample during all measurements is the same.

MarcEisenmann - 09:23, Wednesday 29 September 2021 (2693)

This morning I put back the correct lockin parameters.

 

I started a measurement so that the polarization angle is close to 45 degrees.

This time, a new trouble with the HWP appeared : I can change the polarization angle (quite visible from the relative change of the p pol and s pol photodiodes) but the value on the angle value on the Kinesis software does not change.

I'll investigate this issue after all required measurements for this sample are finished.