Nishino,

2024.10.28 (see TF5)

I locked all degrees of freedom and measured the speed transfer function for the first time.

The total loss is estimated as 150 ppm.

I checked alignment of ppol to OPO. It was a bit bad (maybe 80% mode matching, fig 1). I realigned to 86.2% (fig 2). It seems in the past the alignment of ppol to OPO was never really that critical anyway.

Since the laser was just activated, the ppol lock was not so stable - this is normal for about 2 hours after laser activation. ppol PLL quite regularly unlocks and relocks when the laser is warming up but it seems to go back to normal after a while.

There is some odd behaviour where sometimes if I touch the steering mirrors a small amount there is an extra mode which flashes on and off. Normally the main ppol mode isn't that sensitive to the steering mirror tuning. Also in transmission of OPO I can see some flashing on the sensor card, displaced about 5mm in yaw from the TEM00 mode.

I looked a bit at BAB and it seems also ok, maybe just a small tweak. But I didn't touch it or take a picture yet.

There has been a long running issue with IRMC lock ever since the main laser EOM was switched from 15 MHz to 88.3 MHz. Before, the error signal was acquired with a TAMA 15 MHz resonant PD but we since switched to a Thorlabs PDA05CF2 broadband RFPD with 75 MHz linewidth. From old logs, the error signal was about 1Vpp before the change and decreased to 100 mV after changing to new modulation scheme. However, the SHG underwent the same change and only saw a factor of 4 decrease in error signal. Initially I though there was some issue with weak IRMC modulation or demodulation signal due to weakening local oscillator synthesis from DDS, but the SHG uses the same mod/demod electronics and works mostly fine so that isn't the main problem.

We currently inject about 2.5 - 3 mW IR to IRMC with the goal of about 2 mW transmission on resonance. So off resonance about 3 mW makes it to IRMC REFL, which is a bit much for the PD. For whatever reason, at some point there was a weak ND filter Thorlabs ND03A, which resulted in a base level of > 5 V on the reflection spectrum (fig 1). With the PD close to saturation, the side spikes of the PDH signal become very small (fig 2). I changed the ND filter to Thorlabs ND1 which is what it was a while ago, which gives a base level of about 2.0 V and dip of 1.3 V (fig 3). This makes the error signal have the usual PDH shape but it also became quite small, ~ 70 mVpp.

I checked the PDH sidband amplitude by manually putting the IRMC near resonance (servo scan amplitude zero and PZT HVD offset adjusted to make the reflection signal drop by 1.3 V). I could see the 88 MHz sideband from IRMC REFL RF was about -27 dBm. I sent it to a spare RF amplifier port on the rack +18 dB and could see that the sideband was amplified to maximum -8 dBm. The error signal becomes 400 mVpp (fig 4). I adjusted the cable length a bit to improve the demodulation phase and now the IRMC can automatically lock quite stably. IRMC transmission is about 2.16 mW.

For now this is reasonable to operate. There is some issue with the servo electronics that is reducing the signal. One fix we discussed a while ago with Yuhang and Pierre Prat is to replace resistor R33 in the servo schematic (feedback resistor of an inverting op amp) with a ten times higher resistance to increase the op amp gain 10x. Also I think we could use a *slightly* weaker ND filter on IRMC REFL RF. Could also make an 88 MHz resonant PD but maybe that's too much effort. For now it's fine, we still have spare RF amplifier ports so we don't need to mess with it until we need those for other things.

Next:

• measure IRMC tansfer function and optimise UGF
• recover BAB alignment to OPO and homodyne
• optimise green alignment to OPO via BAB nonlinear gain

[Shalika, Katsuki]

Both hydrogel and force gauge are on translation stage. We moved the force gauge up using the actuator on translation stage.See Fig 1 and Fig 2.

hydrogel is 8-9cm in length and 1.5mm thick. Each measurement take 2:30 mins

The laser is at center

0.26 N

C:\Users\atama\Dropbox\Cell Birefringence\Measurement data\hydrogel\Force gauge v2\Fri, Oct 25, 2024 4-02-01 PM.txt

0.28

C:\Users\atama\Dropbox\Cell Birefringence\Measurement data\hydrogel\Force gauge v2\Fri, Oct 25, 2024 4-06-13 PM.txt

0.30

C:\Users\atama\Dropbox\Cell Birefringence\Measurement data\hydrogel\Force gauge v2\Fri, Oct 25, 2024 4-09-53 PM.txt

0.32 N

C:\Users\atama\Dropbox\Cell Birefringence\Measurement data\hydrogel\Force gauge v2\Fri, Oct 25, 2024 4-13-41 PM.txt

0.34 N

C:\Users\atama\Dropbox\Cell Birefringence\Measurement data\hydrogel\Force gauge v2\Fri, Oct 25, 2024 4-18-30 PM.txt

0.36

C:\Users\atama\Dropbox\Cell Birefringence\Measurement data\hydrogel\Force gauge v2\Fri, Oct 25, 2024 4-22-30 PM.txt

0.38

C:\Users\atama\Dropbox\Cell Birefringence\Measurement data\hydrogel\Force gauge v2\Fri, Oct 25, 2024 4-26-43 PM.txt

0.40

C:\Users\atama\Dropbox\Cell Birefringence\Measurement data\hydrogel\Force gauge v2\Fri, Oct 25, 2024 4-30-35 PM.txt

0.42 N

C:\Users\atama\Dropbox\Cell Birefringence\Measurement data\hydrogel\Force gauge v2\Fri, Oct 25, 2024 4-34-02 PM.txt

0.44

C:\Users\atama\Dropbox\Cell Birefringence\Measurement data\hydrogel\Force gauge v2\Fri, Oct 25, 2024 4-37-43 PM.txt

0.46

Fri, Oct 25, 2024 4-41-56 PM

0.48

C:\Users\atama\Dropbox\Cell Birefringence\Measurement data\hydrogel\Force gauge v2\Fri, Oct 25, 2024 4-46-00 PM.txt

0.50

C:\Users\atama\Dropbox\Cell Birefringence\Measurement data\hydrogel\Force gauge v2\Fri, Oct 25, 2024 4-50-26 PM.txt

we moved the hydrogel laterally--the beam is not in center

0.51

C:\Users\atama\Dropbox\Cell Birefringence\Measurement data\hydrogel\Force gauge v2\Fri, Oct 25, 2024 4-54-17 PM.txt

0.48

C:\Users\atama\Dropbox\Cell Birefringence\Measurement data\hydrogel\Force gauge v2\Fri, Oct 25, 2024 4-59-40 PM.txt

0.46

C:\Users\atama\Dropbox\Cell Birefringence\Measurement data\hydrogel\Force gauge v2\Fri, Oct 25, 2024 5-03-11 PM.txt

0.44

C:\Users\atama\Dropbox\Cell Birefringence\Measurement data\hydrogel\Force gauge v2\Fri, Oct 25, 2024 5-06-56 PM.txt

0.42

C:\Users\atama\Dropbox\Cell Birefringence\Measurement data\hydrogel\Force gauge v2\Fri, Oct 25, 2024 5-11-10 PM.txt

0.40

C:\Users\atama\Dropbox\Cell Birefringence\Measurement data\hydrogel\Force gauge v2\Fri, Oct 25, 2024 5-17-25 PM.txt

0.38

C:\Users\atama\Dropbox\Cell Birefringence\Measurement data\hydrogel\Force gauge v2\Fri, Oct 25, 2024 5-21-26 PM.txt

0.36

C:\Users\atama\Dropbox\Cell Birefringence\Measurement data\hydrogel\Force gauge v2\Fri, Oct 25, 2024 5-24-52 PM.txt

0.34

C:\Users\atama\Dropbox\Cell Birefringence\Measurement data\hydrogel\Force gauge v2\Fri, Oct 25, 2024 5-29-02 PM.txt

0.32

C:\Users\atama\Dropbox\Cell Birefringence\Measurement data\hydrogel\Force gauge v2\Fri, Oct 25, 2024 5-32-51 PM.txt

The hydrogel maybe is a bit dry. So, the 0.32 was the minimum the translation stage could move.

We moved the hydrogel laterally to another side.

0.32

C:\Users\atama\Dropbox\Cell Birefringence\Measurement data\hydrogel\Force gauge v2\Fri, Oct 25, 2024 5-41-43 PM.txt

0.36

C:\Users\atama\Dropbox\Cell Birefringence\Measurement data\hydrogel\Force gauge v2\Fri, Oct 25, 2024 5-45-22 PM.txt

we stop coz the force change by itself.

The analysis done only for the 2nd hydrogel (the one which was measured after the first one broke). The point with force 0N is omitted, since the actual 0N should be the point of start of seeing the force change. The birefringence was measured at 2 points

Fig1:Birefringence vs Force of point 1

Fig 2: Diattenuation vs Force  of point 1

Fig 3:Birefringence vs Force of point 2

Fig 4: Diattenuation vs Force  of point 2

The number plotted is the median obtained from the data at each force value.

Update 1: I changed the plot becauase I had previously overconverted rad to rad, assuming it was degrees.

Update 2: Added Error bar to fitted data

with BS removed, I aligned the BB1EO3 at 45 degree. This is to check if Polarization ray tracing analysis is correct for coatings. 

LC goes from 0-3.5V with 0.1V step and 100 averaging

C:\Users\atama\Dropbox\LC-Experiment\Measurement Data\Birefringence Measurements\Coating measurement\BB1-E03\20241022\Tue, Oct 22, 2024 3-37-46 PM.txt

[Katsuki, Shalika, Marc]

1.5 mm hydrogel, recipe same as previous. The error on force can be ±0.01 N. The measurement is taken in transmission of LC without BS. 

20 avg, 0.5V-3V with 0.25V

0 N

C:\Users\atama\Dropbox\Cell Birefringence\Measurement data\hydrogel\Force gauge v2\Mon, Oct 21, 2024 5-15-53 PM.txt

0.28 N

C:\Users\atama\Dropbox\Cell Birefringence\Measurement data\hydrogel\Force gauge v2\Mon, Oct 21, 2024 5-22-16 PM.txt

0.31 N

C:\Users\atama\Dropbox\Cell Birefringence\Measurement data\hydrogel\Force gauge v2\Mon, Oct 21, 2024 5-27-33 PM.txt

0.36 N

C:\Users\atama\Dropbox\Cell Birefringence\Measurement data\hydrogel\Force gauge v2\Mon, Oct 21, 2024 5-31-40 PM.txt

0.41 N

C:\Users\atama\Dropbox\Cell Birefringence\Measurement data\hydrogel\Force gauge v2\Mon, Oct 21, 2024 5-36-20 PM.txt

hydrogel broke -- Also, there could be an issue of hydrogel breaking due to it getting dried. So, reduced to 10 avg for faster measurement.

0 N

C:\Users\atama\Dropbox\Cell Birefringence\Measurement data\hydrogel\Force gauge v2\Mon, Oct 21, 2024 5-44-04 PM.txt

0.28 N

C:\Users\atama\Dropbox\Cell Birefringence\Measurement data\hydrogel\Force gauge v2\Mon, Oct 21, 2024 5-47-38 PM.txt

0.30 N

C:\Users\atama\Dropbox\Cell Birefringence\Measurement data\hydrogel\Force gauge v2\Mon, Oct 21, 2024 5-50-56 PM.txt

0.37 N

C:\Users\atama\Dropbox\Cell Birefringence\Measurement data\hydrogel\Force gauge v2\Mon, Oct 21, 2024 5-54-23 PM.txt

0.42 N

C:\Users\atama\Dropbox\Cell Birefringence\Measurement data\hydrogel\Force gauge v2\Mon, Oct 21, 2024 5-58-02 PM.txt

0.45

C:\Users\atama\Dropbox\Cell Birefringence\Measurement data\hydrogel\Force gauge v2\Mon, Oct 21, 2024 6-02-41 PM.txt

0.51

C:\Users\atama\Dropbox\Cell Birefringence\Measurement data\hydrogel\Force gauge v2\Mon, Oct 21, 2024 6-06-23 PM.txt

we moved the translation stage by (23.2-20.2) cm

0.51 N

C:\Users\atama\Dropbox\Cell Birefringence\Measurement data\hydrogel\Force gauge v2\Mon, Oct 21, 2024 6-12-19 PM.txt

0.45 N

C:\Users\atama\Dropbox\Cell Birefringence\Measurement data\hydrogel\Force gauge v2\Mon, Oct 21, 2024 6-15-46 PM.txt

0.42 N

C:\Users\atama\Dropbox\Cell Birefringence\Measurement data\hydrogel\Force gauge v2\Mon, Oct 21, 2024 6-20-16 PM.txt

0.37 N

C:\Users\atama\Dropbox\Cell Birefringence\Measurement data\hydrogel\Force gauge v2\Mon, Oct 21, 2024 6-23-50 PM.txt

0.31 N

C:\Users\atama\Dropbox\Cell Birefringence\Measurement data\hydrogel\Force gauge v2\Mon, Oct 21, 2024 6-27-47 PM.txt

0.28 N

C:\Users\atama\Dropbox\Cell Birefringence\Measurement data\hydrogel\Force gauge v2\Mon, Oct 21, 2024 6-31-09 PM.txt

0 N

C:\Users\atama\Dropbox\Cell Birefringence\Measurement data\hydrogel\Force gauge v2\Mon, Oct 21, 2024 6-34-17 PM.txt

Input without any sample

C:\Users\atama\Dropbox\Cell Birefringence\Measurement data\hydrogel\Force gauge v2\Mon, Oct 21, 2024 6-37-59 PM.txt

Nishino

In my calculation, the best PCC round-trip phase is 1) when the transmittance light from ETM gets maximum AND 2) monitoring the transmittance light from the PCM, the relative angle between the signal and main beam becomes pi/4. 

Adjusting the PCC angle to meet 1) and the signal beam angle to meet 2) condition by hand, I obtained the result shown in Fig. 2). Red is the speed state and blue is the position state. Somehow it behaves weird at high-frequencies but taking their ratio (green) it could be fitted well with a model. I guess the photo-detetor calibration went wrong for some reason.

I rotated BS to align the arrows with the beam propagation direction. 

BS Font face

C:\Users\atama\Dropbox\LC-Experiment\Measurement Data\Birefringence Measurements\Beam Splitter Calibration\20241006\front_refl\Tue, Oct 8, 2024 5-18-51 PM.txt

C:\Users\atama\Dropbox\LC-Experiment\Measurement Data\Birefringence Measurements\Beam Splitter Calibration\20241006\front_trans\Tue, Oct 8, 2024 6-59-48 PM.txt

The large birefringence(23 deg) in reflection was confusing. So, alignment was improved more. Redid measurement in reflection of BS front face. 

C:\Users\atama\Dropbox\LC-Experiment\Measurement Data\Birefringence Measurements\Beam Splitter Calibration\20241009\front_refl\Wed, Oct 9, 2024 10-26-57 PM.txt

I mounted mirror(BB1EO3 sample 1) in the transmission of the BS front face. The mirror is aligned to obtain reflection at optimal position. Then I flipped BS. This was to ensure that in case the BS moved, I can understand that its from BS flipping and not mirror misalignment. After flipping BS, the beam maintained its position after reflection from coating. We don't care about the reflection from the back face of the BS anymore. 

Polarization states generated with BS back face transmission:

C:\Users\atama\Dropbox\LC-Experiment\Measurement Data\Polarization states\20241010\Thu, Oct 10, 2024 4-20-30 PM.txt

In the reflection of the mirror, after BS:

C:\Users\atama\Dropbox\LC-Experiment\Measurement Data\Birefringence Measurements\Coating measurement\BB1-E03\20241010\Thu, Oct 10, 2024 5-40-42 PM.txt

Also, the measurement takes only 1 hour. Maybe it improved sometime from labview modifications. I never noted the time of measurements after the 1st labview was made, which was taking rather 2 hrs. 

Nishino,

I measured transfer functions of the speed and position meter. The PCC is not locked but just scan the PCM to minimize and maximize the transmittance light which is a consequence of interference between the first and second circulation light. 

The result is shown in the figure. Blue is the position state and red is speed state. Their ratio is fitted with a function with a cavity loss of 500 ppm. 

with 1 mm step size, 14mm radius

Input = ['Fri, Oct 11, 2024 11-36-41 AM.txt', 'Fri, Oct 11, 2024 1-34-57 PM.txt' , 'Fri, Oct 11, 2024 2-13-44 PM.txt' , 'Fri, Oct 11, 2024 2-51-14 PM.txt' , 'Fri, Oct 11, 2024 3-41-43 PM.txt' , 'Fri, Oct 11, 2024 4-52-41 PM.txt']

iLM/LMA ; white dot placed on top toward laser source

Output = ['Fri, Oct 11, 2024 11-40-34 AM.txt' , 'Fri, Oct 11, 2024 1-36-56 PM.txt', 'Fri, Oct 11, 2024 2-17-22 PM.txt' , 'Fri, Oct 11, 2024 2-53-16 PM.txt' , 'Fri, Oct 11, 2024 3-46-31 PM.txt' , 'Fri, Oct 11, 2024 4-55-02 PM.txt']

AZTEC 30mm number 1 (number is attributed randomly by me).

Output = ['Tue, Oct 15, 2024 10-21-16 AM.txt' , 'Tue, Oct 15, 2024 9-45-08 AM.txt' , 'Fri, Oct 11, 2024 9-05-53 PM.txt' , 'Fri, Oct 11, 2024 8-26-53 PM.txt' , 'Fri, Oct 11, 2024 7-53-34 PM.txt', 'Fri, Oct 11, 2024 7-17-27 PM.txt']

AZTEC 30mm number 2 (number is attributed randomly by me).

Output = ['Tue, Oct 15, 2024 12-03-02 PM.txt' , 'Tue, Oct 15, 2024 1-20-44 PM.txt' , 'Tue, Oct 15, 2024 2-01-50 PM.txt' , 'Tue, Oct 15, 2024 2-40-34 PM.txt' , 'Tue, Oct 15, 2024 3-27-17 PM.txt' , 'Tue, Oct 15, 2024 4-20-30 PM.txt']

Nishino,

This is a result on 2024/10/11.

I measured the open loop transfer function (OLTF, Fig.1) of the GR lock loop. The filter funtions are measured independently (Fig. 2 and 3).

Setting of SR560 (Fig. 5) and Moku (Fig. 6):

SR560: 0.3 Hz, first order low pass, gain=10000

Moku PID:  I=2.87 kHz, DS=25.0 dB

The inferred optical gain (not optical gain itself but A*H) is plotted in Fig. 4. From this result, I reduced the overall gain just by -2 dB, then the modified OLTF looks like Fig. 7, with UGF=2 kHz and phase margin=20 degrees.

Nishino,

This is a result on 2024/10/10.

I measured the open loop transfer function (OLTF, Fig.1) of the GR lock loop. The filter funtion and actuator efficiency is measured independently (Fig. 2 and 3, Fig. 4 is their sum).

Setting of SR560 (Fig. 7) and Moku (Fig. 8):

SR560: 3 Hz, first order low pass, gain=100

Moku PID: P=10 dB, D=4.118 kHz, DS=13.0 dB

The inferred optical gain is plotted in Fig. 5. From this result, I modified the shape of filter by Moku PID controller as:

P = 10 dB, D = 20 dB, DS = 8 kHz.

Then the modified OLTF is plotted in Fig. 6 with UGF=4 kHz and phase margin=50 degrees.

It seems there is some issue with all elogs made before the server change. They are looking weird. For instance https://gw-elog.mtk.nao.ac.jp/osl/index.php?r=3342

Due to this issue, sometimes the search filter fails, because it is unable to find the word(since it looks strange). The issue happens only if I search and go to the elog. Perhaps not if I go directly without searching through keyword option. 

I made a mistake in measuring the BS. I rotated only 90deg. It was supposed to be rotated by 180 deg.

I designed some adapters between force gauge and hydrogel holders.

They're 3D printed with help of Kanzawa-san and models are saved in the dropbox/mount and holder folder.

The birefringence obtained is Fig 1. Since there were too few points (112/6050) after filtering. I will re take measurements. 

The diattenuation vs. Displacement is as in Fig 1. Doesn't change with increasing displacement. 

The birefringence of BS changed from 17deg to 10 deg after alignment tuning. See the picture for its Jones matrix (Fig1) and birefringence (Fig2). As you can see the JM doesn't have -ve sign any more in the real parts, and is closer to identiy matrix.

The condition on physical realizablity had error bar of 1E-4 (to lower two peaks on BS birefringence).

Polarization ray tracing to correct coordinate systems seems correct. Perhaps can tune BS alignment a bit more. 

Owing to the spurious 17deg of circular retardation observed in BS birefringence characterisitics after correction using Polarization ray tracing, I redid calibration.

1. First it seems the alignment was off by 0.2 cm before the BS. I corrected this using the last steering mirror before the LC path. The beam height is now 7.5cm all along. The alignment was also checked with BS and was slightly(0.1cm) tuned to obtain good alignment in its reflection. 

2. The BS is removed. LC voltage changes from 0-3.5V with 0.1V step and 100 avg.

Polarization states without BS:

C:\Users\atama\Dropbox\LC-Experiment\Measurement Data\Polarization states\20241004\Fri, Oct 4, 2024 6-35-14 PM.txt

3. The BS is rotated by 180 degrees to measure its back face.

Polarization states after relfection from back side of BS:

C:\Users\atama\Dropbox\LC-Experiment\Measurement Data\Birefringence Measurements\Beam Splitter Calibration\20241006\back_refl\Sun, Oct 6, 2024 5-32-19 PM.txt