Coating :

at 0 deg with 10 avg: C:\Users\atama\OneDrive\LC-Experiment\Measurement Data\Coating measurement\BB1-E03\20240606\0 deg\Sat, Jun 8, 2024 8-12-43 PM.txt

at 62 deg

10 avg:C:\Users\atama\OneDrive\LC-Experiment\Measurement Data\Coating measurement\BB1-E03\20240606\62 deg\Mon, Jun 10, 2024 12-22-38 PM.txt

100 avg: C:\Users\atama\OneDrive\LC-Experiment\Measurement Data\Coating measurement\BB1-E03\20240606\62 deg\Mon, Jun 10, 2024 9-26-34 AM.txt

I read a paper which said that Jones matrix measurement can be improved with more averaging. Although they measure a sample which was changing its properties in time. its quite different. But, still wanted to try to save with more averaging. So I did 100 averaging of each point. Also, had to take measurement again after amending flaws in the averaging./

So, I scan the LC voltage from 0-3.5V with 0.1V step.

Input file:

with 10 avg: C:\Users\atama\OneDrive\LC-Experiment\Measurement Data\Polarization states\20240607\Fri, Jun 7, 2024 10-13-20 AM.txt

with 100 avg: C:\Users\atama\OneDrive\LC-Experiment\Measurement Data\Polarization states\20240607\Fri, Jun 7, 2024 10-52-34 AM.txt

Output files of optics:

QWP:

at 0 deg with 10 avg C:\Users\atama\OneDrive\LC-Experiment\Measurement Data\Retarder\QWP\20240605\0 deg\Fri, Jun 7, 2024 3-13-11 PM.txt

at 62 deg with 10 avg: C:\Users\atama\OneDrive\LC-Experiment\Measurement Data\Retarder\QWP\20240605\62 deg\Fri, Jun 7, 2024 3-42-36 PM.txt

at 0 deg with 100 avg : C:\Users\atama\OneDrive\LC-Experiment\Measurement Data\Retarder\QWP\20240605\0 deg\Fri, Jun 7, 2024 1-30-40 PM.txt

at 62 deg with 100 avg: C:\Users\atama\OneDrive\LC-Experiment\Measurement Data\Retarder\QWP\20240605\62 deg\Fri, Jun 7, 2024 4-12-57 PM.txt

Coating BB1E03:

at 0 deg with 100 avg: C:\Users\atama\OneDrive\LC-Experiment\Measurement Data\Coating measurement\BB1-E03\20240606\0 deg\Fri, Jun 7, 2024 5-40-54 PM.txt

The STD has reduced to around 0.08 deg in azi and 0.03 in ell at around lc voltage of 0.9V (where the flip happens in sign and ell in wrapped). At all the other voltages of LC the std is 2e-3 deg ish in ell and azi both. 

The uncertainity was reduced by adding a wait time(1s) before the polarization camera is read and after lc voltage changes. From my understanding at this voltage of 0.9 ish V the lc molecules take more time to stabilize as compared to other voltages, which was giving rise to high std at just this voltage. Also, the ellipticity getting wrapped was giving rise to high std.

Now, the setup is ready to take measurement with better averaging and more averaging. I have left the setup to warm up. Will start measurement in an hour.  

[Logan, Marc]

We checked again SHG scan. Actually, we found that our HOMs were splitted in 2 due to mistuning of the input polarization.

This made our previous mode-matching estimation wrong. Retuning the HWP, we could properly recover the 91% mode-matching. It is not clear why the high order-mode that was spoiling 30% of mode-matching disappeared. Tuning the modulation phase and servo settings we could relock SHG. The DDS1 setting was saved.

We realigned MZ and GRMC and could also lock them without particular issue. Same for IRMC.

[Hugo, Marc, Shalika]

While trying to align the polarization camera on pci setup we found out that the power it measured was quite lower than expected.

We installed it on the translation stage to verify if the discrepancy was due to the beam size but whichever position gave similar result.

We also placed it on the LC beam that was used for birefringence compensation and Jones matrix measurement but still could see this discrepancy (we measure 75% of the real power).

This is true for vertical and horizontal linear polarization, elliptic, right/left circular polarization...

We are now discussing with Thorlabs support about this.

There were several issue related to data averging. The VI became too complicated due to unwise choices. modifications involved:

1. Previoulsy the averging and filling buffer was done in same labview. I separated both of them. Also made a subvi called delete buffer which resets the buffer before lc voltage is changed for new data.

2. removed PCI like complicated averging and now m using directly VI from NI for this. This made the labview very compact.

3. The only issue remains when the lc changes the azimuth from -45 to 45 kinda when the voltage is around 1V. The std is high at this point.

So, we have now a rather clean procedure

LC voltage change --->>>> create bufffer VI (initialized array of size equal to average order) --->>>> Fill Buffer VI by loading camera VI(number of times it loads is equal to averge order) --->>>> average VI (takes average of entire buffer) --->>>> Send data for saving --->>> delete buffer

On a good note: The VI datasaving speed is better now. With averging of 10th order the  data saving speed is 40Hz.

I did some check based on fiber equations that you can find on Thorlabs or Newport.

The fiber to the SHG is PM980 (polarization maintaining 980nm in-fiber wavelength) with a mode field diameter 6.6 um. This gives f/D = pi*MFD/(4 lambda) = 4.8. Thorlabs FC/ACP connector fiber collimators are sold with f = 2.0, 4.6, 7.5, 11.0, 15.3, 18.4mm focal lengths, giving input beam diameters D = 0.41, 0.94, 1.53, 2.26, 3.14, 3.8 mm. The clear apertures are 2.0, 4.9, 4.5, 4.4, 5.0, 5.5 mm. In retrospect, maybe I should have picked the f = 4.6mm. But it's maybe not super important. exp(-2*(r/w0)^2) = 0.00051 (510 ppm diffraction loss) for the current coupler. r > 2.7 w0 gives < 1 ppm diffraction loss.

We wish to investigate the correct relation between the ellipticity in degrees measured by thorlabs camera and the retardation of any sample, which is delta n.

For this I put polarizer and HWP after BS in the LC path. Then I tune the input polarization to be linear, i.e ell is 0 +/-0.1 aqnd azi is 0+/-0.04 deg respectively. I don't know the reason of the large fluctuation in ell.

Then I put QWP after them infront of the camera. Then I record the azimuth and ellipticity at various angles of the QWP. The QWP was mounted on rotator mount and the data was saved at various positions of the rotator.

filename:C:\Users\atama\OneDrive\LC-Experiment\Measurement Data\Retarder\QWP\20240605\Thu, Jun 6, 2024 10-12-20 AM.txt

the last column in file saved the angle of the rotator

[Logan, Marc]

Fixed amplifier and clock with kapton tape.

Seems clock and LNVR are quite hot  (no heatsink) maybe the reason for their degradation?

Recabled all DDS connections

SHG alignment : fundamental = 1.6V ; hom = 64+88mV ie 91.3% mode-matching. not sure why the previous spurious HOM diaspeared..

after some tweaking we got kind of similar values so it seems hard to further optimize without moving the matching lens.

IRMC fund = 320mV, hom = 32 + 18mV ie 87% mode-matching after alignment (only acting on lens) funad = 364mV and hom = 24mV ie 94% mode-matching

Logan, Michael

We found the source of the problem regarding beam size. Before the PBS there is a telescope consisting of two 100mm lenses but they were quite poorly centered. We took them out and adjusted the reference alignment to lie at 74mm height above the usual designated set of screw holes on the breadboard, then put in the lenses, both times centering them by recovering the reference alignment, approximately. After I fixed them, the beam waist moved a bit closer towards the source than before, but we could see from measurements of the beam divergence that now we have the beam diameter changing by approximately 150 um per screw hole of z displacement, going to and from the beam waist. The beam waist diameter is approximately 250-300 um, we didn't measure super precisely but it seems enough for the purpose of using modulators to the OPO.

Basically, always set a reference target before inserting optical components that require precise centering.

Next step is to construct the beam path to test the OPO. The beam size as is is probably fine for modulators but the beam size increases when going to the Korean Faraday isolator experiment. Guessing from Gaussianbeam.exe rough calculations and looking at the size of the sensor card, we can also get about 1.5mm diameter collimated beam from small fiddling of the mode matching telescope. I should check again what is the clear aperture of Korean FI but I suppose they can always put a lens before their periscope if they really need a smaller beam.

I originally designed some beam size parameters to put a 2.3mm diameter beam into the fiber SHG. However, the Taiwan New Years visitors used a completely different setup to what I wrote down. In some sense my design was not very good (I left the bare minimum of space for QWP/HWP/Faraday/Mode matching after the laser, for no good reason), although I asked a few people about it and no-one pointed out these issues. The 2.3mm beam diameter was a parameter given to me by Chien-Ming Wu for the fiber input, and given he used this type of fiber SHG before I just trusted him on the number. But it seems the people who set it up had other ideas. I need to check.

[Hugo, Marc, Shalika]

We installed the lens found by Shalika on 5cm tube attached to the camera.

We installed the camera and prepared alignment.

WIthout sample, the polarization was quite off pure s-polarized light so we started to optimize the input polarization. However, we were quickly limited by the 0.1deg rotation resolution of the HWP and QWP so we swapped their mount for higher manual precision ones. During this process, we found a small scratch at the edge of the HWP so we replaced it.

We started to tune the input polarization and achieved quite nice polarization with 0.01deg fluctuations in azimuth and ellipticity. However, it seems the camera alignment should be further optimized as we only have about 0.9mW reaching the camera (from the 1.6mW injected).

It truns out that there was some issue with the cooling tower on top of building 2 so the water being pumped was warm. I will do a standalone test next time the water supply to Matsuo-san lab can be turned off.

We wish to add polarization camera in the readout section on the PCI. We don't have a lot of space but do require a beam of divergence less than 2deg for camera and less than 3mm in diameter. 

For this we used the initial beam characteristics and chose a lens which could fit itself alongwith the camera in the readout.

At 2 cm after box The beam characteristics looks like shown here. 

At 0.5 cm after box  beam characteristics looks like shown here. 

so, we can probably add the F=100mm lens 2cm after the box starts. The farther we go the beam divergence and beam diameter incident on the camera will increase, which is not desirable in our case.

Overview: Tested the cryocooler operation with water supply to Matsuo-san lab shut off.

Conclusion (Hypothesis): Closing supply at Matuso-san lab may have cut off the supply to the GWSP cryocooler.

Details: I turned on the cryocooler at 8:27. The cryocooler turned off on it's own at 8:47. The following errors were displayed:

• Helium Temperature Err
• Water Temperature Err
• Water Flow Err

Observations: The cryocooler body was not hot. The helium supply tube was hot. The return supply tube was cold. The Temperature of both water supplies was normal. Note: All these temperature measurements are subjective to me holding the parts.

I am thinking that the water supply to our section was also cut off by the valve Matsuo-san shut.

Next: Confirm if the water is flowing into the cryooler.

Logan, Michael

We took out the Faraday isolator and set the beam profiler as a reference target. There was 2.7 mW incident. We set the Faraday isolator on a pedestal pillar and aligned it so that the beam profiler shape looks good, with no obvious HOM, and there is a decent amount of power, about 2.3 mW. Maybe not optimal transmission but good enough.

Then we checked the beam profile on the s-pol path. It is still doing that weird behaviour where ithe beam divergence coming out of the waist is about half the rate of beam convergence going into the waist, which applies to both the horizontal and vertical components. I don't know what is causing this, it doesn't seem to be the beam profiler since Hugo took it. I don't think it's anything to do with my Faraday technique since I just took it out of the box and I also did the Faraday for speed meter experiment and that is fine. There is one mode matching telescope before the PBS which seems a bit off centre but I feel like it's not enough to be causing the issue. The laser has a bit of difference between horizontal and vertical size but I think this was the same last time I did the OPO characterization. So I don't know what is causing the problem.

In some sense perhaps it is not important to find out either. That mode matching telescope was originally intended to make a 2.3mm collimated beam, so maybe we should just reset it to the original intention.

similar to elog 3581

we do stability check of setup before LC. The camera is place in the transmission of the mirror which steers the main beam to the QWP at the start of LC setup path.

filename C:\Users\atama\OneDrive\LC-Experiment\Measurement Data\Stability Check\Mon, Jun 3, 2024 5-20-28 PM.txt

The measurement will be started after an hour of switching on the laser.

from injection breadboard to blackbox 27 cm

from injection to readout breadboard 34 cm

last steering mirror to injection breadboard 5.5cm

size of camera 5.5 cm

beam after last steering mirror at 0

Also, In "Move read write with Cam" Vi there is a place where the lockin data was used to make the matrix for the map which is visible in the main VI. Since the previous configuration only allowed one input here, I only added ellipticity from the camera. Not sure how to introduce azimuth here on one single map.

In the averaging filter VI made copy of the previous filter 6 times to be able to filter Azimuth, Ellipticity, Power, S1, S2, S3. All of their output were added in cluster for ease of transfeering data from one Vi to another. In the Buffer filter file also I made the buffer for all variables.

The output of averaging filter was connected to the graphical displays on the main VI. The VI is perhaps ready for initial tests and for checking if everything was replaced in a proper manner. 

Tried to resolve labview crash/disappearing issue by

1. Tools>> Advanced>>Clear Compiled Object Cache

2. Windows Update

3. Added exclusion in windows defender for .vi programs