I took a Thorlabs 1064 VLP Faraday isolator (4.7mm aperture, max power 1.7 W) from the speed meter experiment to the KOACH clean room. We still need an appropriate power meter - we would like to inject up to 1 W into the SHG.

The voltage scan was performed for the measurement. The scans started from 0-25V for each LC with a resolution of 0.1V and were finished with 1-1.3V and 22-23V with 0.001V resolution for the 1st and 2nd LC respectively. 

I have rotated the mirror by 23 deg. The voltage scans were started for 0-25V range with  0.01V 0.1V (edited) resolution.

measurement file is here:

C:\Users\atama\OneDrive\LC-Experiment\Measurement Data\Coating measurement\BB1-E03\23 deg\Wed, Dec 13, 2023 1-20-43 PM.txt

MZ and GRMC

Lock was recovered with the nominal level of stabilized output power (power meter in transmission of GRMC says 26.5 mW green to OPO at 4.2 on the MZ offset dial, which is our usual setting).

I tried mode matching on each arm - 
PZT arm: 384 mV TEM00, 8 mV HOM, 96.9%
Non PZT arm: 364 mV TEMO00, 33.2 mV total HOMs, 91.6 %
 

After adjusting them together, then maximising the mode cleaner transmission using the MZ HVD offset (different control knob to the above), I get:
GRMC: 1.5 V TEM00, 68 mV HOMs, 95.76%
but one other time I got 720 mV, 72.4 HOMs, 90.9%
 

The power meter autoranging should be off. Maybe I am just a bit confused about the MZ scan. A bit of explanation for people not familiar, the MZ is not locked using PDH since it is not a cavity, rather it is just locked to some reference voltage controlled by MZ offset dial. When the LOCK switches are turned on, the GRMC scans across the free spectral range quickly and acquires lock first using the PDH sideband signal from GRMC reflection PD, then the MZ scans slowly and locks second using the signal from GRMC transmission PD to keep the transmitted green power at a stable level. Also, the interference condition of MZ using the HVD offset can be changed to reflect or transmit TEM00/HOM - we want it to transmit mostly TEM00 and reflect HOM into a rejected port. Anyway, I don't remember how slow is "slow" scan, but I don't think it should be causing the slow change of MZ mode matching on the timescale I saw. Either way, that is only an issue for measuring mode matching when not locked. The system locks and sends stabilized power to OPO so we can fix it later.

BAB to OPO

I recovered bright alignment beam mode matching to about the level it was during Yuhang's last visit, which is to say, ok but not great (~ 60%). I measured using power meter in transmission of OPO - it is quite hard to see the BAB transmission with OPO unlocked since it is injected from the HR side of the OPO, but there was a conveniently placed holder at just the right spot for the power meter. I tried to measure with homodyne but the IRMC started having some issue where it wouldn't lock to the correct point. We have been having issue with SHG and IRMC mutual lock ever since we switched to the single 88 MHz EOM to do all of the squeezer table modulations. We should decouple these two signals some time.

FC green lock

I turned on the FC length control servo inside the clean room and then tried to lock FC on green but was not successful.

I could fix 2 out 3 metric screws in the KAGRA mir box (spareETMY). the last screw was harder to fix and I didn't had the proper key so I did not fix it yet..

The spare screws are in the PCI pre-clean room

The IRMC was not too badly misaligned, just tweaking a bit the lens in front of it I could recover about 94% mode-matching.

Further improvement would require to tune the IRPS but it's not high priority for now so I left it like that.

Then, could smoothly lock it.

[ByeongJun, Marc, Michael]

The GR beam was realigned on BS chamber using PR picomotors, on 1st and 2nd target using BS picomotors.

We tuned END coils actuators to get the beam on the back of 2nd target.

Then, using IN picomotors, we recovered fundamental mode in transmission of FC.

To do :

offload END pitch (now 280 is sent to coil)

replace the quad box for the camera display close to DGS

recover remote control of 2nd target

I replaced the newfocus 5104 with Thorlabs BB1-E03 mirror.

Actually, when I first checked the beam centering, I noticed that the beam was not centered on the 5104 mirror. The beam at this instance was at the center of the camera.

So, even though I changed the mirror, it was made sure that the beam was incident at the center of mirror, and the reflection was at the center of the camera. In, this process only the mirror was moved. All other components were left undisturbed.

The LC voltage scan was done from 0-25V for both with 0.02 resolution.

measuerment data location
C:\Users\atama\OneDrive\LC-Experiment\Measurement Data\Coating measurement\BB1-E03-10\Fri, Dec 8, 2023 5-48-31 PM.txt

Edited:

measurement file is here:

C:\Users\atama\OneDrive\LC-Experiment\Measurement Data\Coating measurement\BB1-E03\0 deg

I confirmed the alignment of the green AOM.

The (lower left on electronics rack) function generator outputs from channel 1: 109.036 035 615 MHz, 5 dBm voltage, to + 18 dB RF amp -> 23 dBm to AOM.

I reduced the main laser current from 1.833 to 1.750 to make the green power consistent with previous values of AOM green power. I confirmed the alignment of the first order diffracted beam from the AOM to the subsequent iris and the green is now hitting the PR tank targets.

SHG green out: 284 mW
AOM in: 48.8 mW
AOM out (RF on): 46.0 mW
AOM out (RF off): 45.2 mW
Iris out (RF on): 22.1 mW
Iris out (RF off): < 10 uW

[Shalika, Marc]

In continuation of elog 3361, the coating was characterized and compensated as mentioned in the table.

First the beam was positioned to be incident at the center and the measurement was done with the rotator mount at 0º. For further investigation, we rotated the mirror by 20º. Several voltage scans were done, starting from 0-25V of both LCs with the resolution of 0.02V. The final scans were performed with the resolution of 1mV around points which provided us with the minimum values in azimuth and ellipticity of polarization. 

The combination of voltages at which the minimum for both azimuth and ellipticity were obtained is mentioned in the table below. 

The power meter was installed in GRMC transmission in order to align the MZ. First I blocked the PZT arm of the MZ and aligned using the MZ mirror and subsequent steering mirror to optimise mode matching from GRMC transmission. Then I blocked the non-PZT arm and aligned the MZ to GRMC again. Afterwards I adjusted MZ offset on the high voltage driver to get the intereference condition that outputs TEM00 from the main MZ path and TEM10 from the rejected path. Currently we have:

TEM00 1540 mV
HOMs 56, 32, 12 mV
Mode matching = 1540/1640 = 94%

One time I noticed the level of TEM00 slowly going down over a timescale of minutes. Adjusting the MZ offset brings it back to where it was. Maybe something is drifting slowly?

power before shg a bit higher than usual ~840mW

installed power meter in transmission of SHG

tuned to recover fundamental mode

actually the lens installed on rail just before SHG was not fixed. I tried to tune it a bit but it seemed that the initial position was quite good (48mm).

it was a bit hard to tune as when it is unscrewed it is also tilted. If needed, could spend time to have a finer tuning.

installed power meter in reflection of SHG (in reflection of 1st dichroic before beam dump)

further tuned alignment

tuned SHG modulation phase to 70deg (from 0deg) to recover the usual shape.

can see weak green in reflection and error signal seems half of usual ~1VpK

found out that temperature control of SHG and OPO was not turned on (actual temp was around 11kOhm)

after thermalisation recovered error signal ~2.4Vpk and could lock SHG.

Green power before EOM is ~247mW (also a bit larger than usual due to higher input laser power)

A bit strange thing is the GRMC refl pd has a quite strong noise at 100 Hz. It disappears when ceiling light is off though.

I tried, mostly just for my own amusement, to again align the SHG. The reflected beam overlaps the incident and I brought the power to a reasonable level by beam walking the two steering mirrors just before the cavity, but still no clear mode structure. I guess due to the temperature the z-direction mode matching is not good enough - the beam waist inside the nonlinear crystal cavities is very small and extremely sensitive to tuning. So I guess we just wait for the air conditioning to be fixed.

I replaced a faulty 3x2 power plug board that was making an uncomfortable crackling noise with a 6x1 board. The connected items are the homodyne power supply, power meter power supply and one other item.

[Katsuki, Marc]

without sample in direct reflection of BS : Mon, Dec 4, 2023 1-02-58 PM.txt

with ecoli box (beam going on top part) : Mon, Dec 4, 2023 1-08-10 PM.txt

with glass box : Mon, Dec 4, 2023 1-09-35 PM.txt

small cell dish : Mon, Dec 4, 2023 2-00-17 PM.txt

can see both azimuth and ellipticity change when applying more force with holder

small dishwith hydrogel : Mon, Dec 4, 2023 4-17-11 PM.txt

ecoli box  with hydrogel : Mon, Dec 4, 2023 4-21-00 PM.txt

glass box with hydrogel : Mon, Dec 4, 2023 4-26-43 PM.txt

More analysis will follow but it seems the container with smallest effect on birefringence is the glass box.

Used the old soleil-babinet compensator manual actuator to try to apply force to hydrogel.

pushed few milimeters and could see small changes in hydrogel birefringence but the actuator entered inside it so not really uniform force applied

added plastic plate just touching (8.xx) Mon, Dec 4, 2023 4-52-28 PM.txt

However, the plastic was not sturdy enough to apply force...

We will design a proper way to apply uniform force (surely 3D printed based on the plastic box which has same dimension has the glass one).

Despite all the tentatives to apply force, the hydrogel birefringence seemed quite constant when no more force was applied.

[Katsuki, Marc, Takahashi]

We moved the movable clean-booth on top of LC experiment to avoid dust contamination during the air conditioning replacement.

The hepa filter is not connected though

I tried to run some COMSOL simulations on the LC pc with too fine mesh which crashed the pc..

The measurement restarted with LC1 voltage between 0 to 25V with 10mV step; LC2 voltage between 1 to 3 V with same step.

filename is Fri,Dec 1, 2023 6-10-52 PM.txt saved in the same folder

[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.

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. 

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. 

[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.

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.