5104 coating measurement

[ByongJun, Marc, Shalika]

we installed a newport mirror with 5104 coating in a rotable mount, placed it in transmission of the LC.

PS : this mirror has a scratch a its edge.

We moved the polarization camera in reflection of the BS and used it to align the mirror. The beam is centered on the mirror and its reflection reaches the camera center.

We started birefringence measurement with 0deg rotation.

Change in alignment of LCs

A change in alignment is done as opposed to the configuration mentioned in elog 3355. The first LC was placed at 45º with respect to it fast axis, i.e at 0.5º. Additionally, the second LC is kept at its fast axis position, i.e at 73.42º. 

Comment to polarization states generation (Click here to view original report: 3357)

Yes, the labview was modified to improve the speed. There was no update regarding this in elog because this elog page was down for several weeks. Several such updates were unreported because of regular malfunctioning of Elog. 

polarization states generation

[Marc, Shalika]

Following the 2 LCs alignment, Shalika reinstalled the 2 LCs and removed the output polarizers.

Then we started to take generate polarization states by varying each LC voltages from  0 to 25V with 15mV step; LC temperature is 30degC.

I just saw that the measurement finished (actually a bit earlier than expected : maybe cleaning the LabView improved slightly the speed?)

So I restarted measurement saved in the same folder with 10mV step.

SHG alignment

I tried realigning the SHG using the two dichroic mirrors just before the cavity (the one right next to it, and the one with the yellow sticker). By beam walking in both pitch and yaw I could only raise the level of IR refl from ~ 1.7 to ~ 3.7 V on the oscilloscope, but I couldn't see any strongly defined cavity modes. The residual beam coming from the SHG output along the green path at least goes through the (previous now unused) green EOM, so it doesn't seem hugely misaligned.

At one point I took a pciture on my phone and saw a lot of violet ghost beams. So I was concerned if the laser was doing anything strange. I checked the settings on the laser head - the current is 1.833 A (same as reference) and temperature is 23.36C (vs 23.105C on wiki). But then I took another photo on my ipad and I didn't see anything. So maybe it's just my phone.

I turned off the FC lasers afterwards.

LC2 fast axis

[Shalika, Marc]

Measurements of LC2 fast-axis angle were done. The data was taken in cross polarizer setting. 

We measured fast-axis at 73.42°±0.52°. The angle is quite deviated from previous measurement which can be accounted due to the partially unscrewed LC. 

The second LC was then set at -45° from its fast axis, i.e 28.42°.

A quick look at the system after a long time inactive

I took a quick look at the laser system. I let it warm up for about half an hour.

As expected even the first component in the line, the SHG, is quite misaligned. There are no clear reflection peaks in the cavity scan. The error signal looks quite distorted too (EPSOUT2). 815 mW of IR made it to the SHG entrance, so there is no problem with the laser system, although it seems a bit misaligned at the entrance. The SHG servo can be "locked" but it only outputs less than 20 uW of green. I should remember next time to compared reflection and transmission to the previous reference values, though they are a bit lower compared to recent measurements of SHG input and green output:
- IR incident (just before dichroic mirror) - 684 mW
- IR reflect (before ND2 on PD) - 87 mW
- Green output (just before green FI) - 237 mW

During Chien-Ming's last visit it was noted that the temperature of the laser casing was very warm. This time the temperature of the laser didn't do anything strange over an hour or so active.

I turned on some of the things that were powered off, including the squeezer related servo racks and the RF amps on the floor. I left off the filter cavity related electronics and green AOM RF driver.

I took a 6 port multiplug with an on/off switch to use for the homodyne power supply - it was from a box next to the tool area (somehow I can't upload images right now).

LC1 fast-axis

[Marc,Shalika]

We took measurements of LC1 fast-axis angle.

We installed LC1 and measured the power after a cross-polarizer for various rotation angles while varying the LC1 voltage from 0 to 25V.

What is a bit surprising is that the fast-axis direction seems to be more sensitive to applied voltages compared to previous measurement.

This is visible in the figure with all fits. to be uploaded when logbook is able to.

In any case we measured fast-axis at 45.49 +/- 0.69 deg which is compatible with previous estimation.

LC1 fast axis tuning

[Shalika, Marc]

The ellipticity after BS was ~0.31° and we weren't able to tune it to 0° and simultaneously keep azimuth after BS at 0°. The tuning was being done by Polarizer and HWP+QWP before BS. We finally decided to remove the polarizer. The tuning of ellipticity and azimuth after BS was then done using HWP and QWP (before BS) to have 0° in both ellipticity and azimuth of the light after BS, i.e. linearly polarized light was ensured. 

Now, we had to recheck if our LC's fast axis was in the required position. (The misalignments could have risen from various factors especially, months of non operational temperature control in tama and not using the system)

The final position of LC would be updated in upcoming elogs.

ATC Cryostat Cabling

I confirmed the wiring of the ATC cryostat on the vacuum and air side. There are 3 Brundy 48-pin ports at the bottom of the cryostat labelled A, B and C. I only checked B, but the terminology and cabling should (hopefully) be the same for the other 2. The cables in air and vacuum are bundeled in sets of 4 labelled B1- B12. The table below shows the pin layout.

 

Name (wire bundle)	Pins	Wire Order (Pin number to wire color)
		In Air	Vacuum
B1	A B C D	Red Red-Black White White-Black	Red Black Blue Yellow (I only checked B1 and B2 but it should be same for the rest)
B2	E F G H
B3	J K L M
B4	N P R S
B5	T U V W
B6	X Y Z a
B7	b c d e
B8	f g h i
B9	j k m n
B10	p q r s
B11	t u v w
B12	x y z aa

BS cal uncertainty

	Front Face				Back Face
Parameters	Position 1 (3345)	Position 2	Position 3	Position 4	Position 1 (3345)	Postition 2	Position 3	Position 4
Reflection (%)	56.5 ± 1.1	56.6 ± 1.7	56.5 ± 1.3	52.8 ± 1.4	47.7 ± 0.8	49.5 ± 1.7	52.6 ± 0.9	49.1 ± 1.3
Transmission (%)	40.8 ± 0.7	40.8 ± 1.5	40.8 ± 0.8	40.9 ± 1.7	40.7 ± 0.7	40.9 ± 1.1	40.8 ± 0.7	40.9 ± 1.3
Loss (%)	2.7 ±  1.7	2.7 ± 2.8	2.7 ± 1.9	6.2 ± 2.6	11.6 ± 1.5	9.6 ± 2.5	6.6 ± 1.6	9.9 ± 2.3
Input Azimuth  (°)	-0.014+/-0.009	-0.0190 ± 0.0017	-0.0316 ± 0.0017	0.0207 ± 0.0021	1.6018 ± 0.0023	0.0190 ± 0.0017	-0.0316 ± 0.0017	0.0207 ± 0.0021
Reflected Azimuth  (°)	1.4154 ±  0.0022	1.3606 ± 0.0019	1.1625 ± 0.0022	1.5322 ± 0.0023	-0.014+/-0.009	1.4733 ± 0.0017	1.2267 ± 0.0017	1.7301 ± 0.0020
Transmitted Azimuth  (°)	-0.060 ±  0.0027	-0.0654 ± 0.0028	-0.0775 ± 0.0017	-0.0226 ± 0.0017	-0.0939 ± 0.0020	-0.1036 ± 0.0018	-0.0658 ± 0.0021	-0.0360 ± 0.0019
Input Ellipticity  (°)	0.008+/-0.008	0.0178 ± 0.0013	0.0150 ± 0.0013	0.0133 ± 0.0019	0.008+/-0.008	0.0178 ± 0.0013	0.0150 ± 0.0013	0.0133 ± 0.0019
Reflected Azimuth Ellipticity(°)	-0.3969 ± -0.3969	-0.3626 ± 0.0015	-0.3650 ± 0.0025	-0.1964 ± 0.0019	-0.1469 ± 0.0026	-0.1577 ± 0.0017	-0.0142 ± 0.0018	-0.0392 ± 0.0020
Transmitted ellipticity  (°)	0.2928 ±  0.0028	0.2921 ± 0.0033	0.2977 ± 0.0032	0.3175 ± 0.0016	-0.0549 ± 0.0021	-0.0623 ± 0.0014	-0.0602 ± 0.0014	-0.0555 ± 0.0017

 

P.S

1. Front face = where laser is incident on BS in an ideal configuration, and back face means the face opposite to front face.

2. the folders are saved on pc with the corresponding position name as folder name in BS calibration. 

Fixing Electrostatic atuator

The electrostatic actuator dislodged during transportation and came off while disassembling the setup.
Yesterday, I fixed it with Epoxy.
I couldn't remove the old Epoxy (not sure what type), so I just bonded on top of it.
The curing time is 7-14 days, but it should be ready to move by tomorrow.

BS cal (front and back face)

[13/11/2023]

Due to the position of clamp there was trouble calibrating the back face of BS(from 3342). The mount was changed. Previously we had mounted two different BS on two different mounts. So, in brief this is the second BS.

The BS is mounted on a magnetic mount, so just the upper half of mount was rotated such that the actual position of beam on BS doesn't change. This was best suited to calibrate both front and back face of BS. Even though the BS was rotated to calibrate two faces, the path of transmission and reflection doesn't change. The parameters obtained are as follows:

Input azimuth: -0.014+/-0.009
Input ellipticity: 0.008+/-0.008
 

Parameters	Front face (center)	Back Face (Center)
Reflection (%)	56.5 ± 1.1	47.7 ± 0.8
Transmission (%)	40.8 ± 0.7	40.7 ± 0.7
Loss (%)	2.7 ±  1.7	11.6 ± 1.5
Reflected Azimuth (°)	1.4154 ±  0.0022	1.6018 ± 0.0023
Transmitted Azimuth (°)	-0.060 ±  0.0027	-0.0939 ± 0.0020
Reflected ellitpticity (°)	-0.3969 ± -0.3969	-0.1469 ± 0.0026
Transmittted ellipticity(°)	0.2928 ±  0.0028	-0.0549 ± 0.0021

 

Beam Splitter calibration (front face)

[10/11/2023]

The front face of BS was calibrated and the properties obtained were:

Comment to Electrical shutdown preparation (Click here to view original report: 3340)

Takahashi-san, Sato-san and Hirata-san recovered vacuum without issue.

I recovered LC, PCI and Filter Cavity mostly without issues.

However, the wifi antenna in TAMA storage seems to be broken.

Also, one of the power supply switch in FC clean room  (mainly used for homodyne power) is making a strange sound if I turn it on.

I will replace it

Electrical shutdown preparation

[Marc, Shalika]

Workstation in room 216/217 off

ATC clean room koach filter off

LC : everything's off

PCI : everything should be off. We could not reach the switch of HEPA filter of pre clean room so it is unplugged (accessible from the stairs)

FDS : everything should be off both inside clean room, all oplevs, coil drivers, DGS. End electronics also off. Vacuum was taken care of by Takahashi-san (?)

Also turned off the server/network switch in storage, the new DGS switch, DAC/ADC and network switch

 

Can not upload pictures but I took the reference levels of several components.

Realigning input beam

[Shalika, Marc]

The recent temperature fluctuations led to multiples changes in beam path(tilted), height and input polarization. The mirrors were tuned to make the beam follow one line and at a uniform height of 75 mm all along the table.

The HWP and QWP were tuned to input a polarization of 0°±0.01°(azimuth) and 0°±0.01°(ellipticity)

The input polarizer was then tuned to get 0°±0.02°(azimuth) and 0°±0.02°(ellipticity). The power after the polarizer was 0.832 mW.

removal of spare ETMY

[Aso, Marc, Rishabh]

We removed the spare ETMY and put it inside its container.

To do it safely we first removed a front supporting pillar that has to be reinstalled.

Maybe because of that, it was first not possible to move the translation stage upwards (the right motor while looking from the input side was not moving).

After some up/down motion it could move slowly without issue.

We could not find the 3 screws to fix the container lid. We  plan to manufacture new ones.

ATC Optical Table

After discussing with Akutsu-san, I disassembled the Al frame on the optical table in front of the AC unit.

The optics (Nikon camera, some beamsplitters and other items) on the other end of the optical table (away from the AC unit) are still there since I have to discuss what to do with them with someone (who?).

Please feel free to use this table.

Data acquisition updated

In labview, we now have average filtering implemented. So, we can average camera and power meter's data (using average order from 1-10) at the same voltage of LC. 

Also, as a modification of 3319, we can now do several iterations of the same file and even fix the resolution of data that should be used from the file.