After looking at the availability of the cores in Japan, and switching to iron powder cores. I came up with the modified design (attached).

The impedance matching is relatively well, from previous design. I don't want to go above 1kV for now. I don't want arcs flying. 

I optimized the design of the RF circuit to have better inductor and use transformer to do impedance matching. The core material can be 43. The fig shows more detail about the plan. 

For imepdance matching, the resonant part impedance is 44kohm. To better take into account this value, the Q of the circuit should be first measured.

Since, sqrt(44E3/200) = 15. Therefore, the input transfomer should have turns ratio 1:15. 

Reference materials:

To decide the core material you can use:   https://toroids.info/

and to know how to make RF transformer, use: https://youtu.be/41q0eVpNN8k?si=fb9kXypXaEAJZAcn

[Marc, Shalika, Tsuzuki]

We set up a long term measurement over the week-end without sample (but its holder present) and p-polarized light.

We'll take 1 spectrum / hour.

We also took temperature and humidity sensor from TAMA FC (TSP01) that will provide temperature of the light source, integrating sphere together with temperature and humidity from the table were is located the spectrophotometer.

They will be measured every 900s.

Tsuzuki-san already performed such measurement last year with unpolarized light that showed strong correlation between background transmission and temperature.

Just to add that the first HWP is slightly tilted so that the reflected beam (~1mm size from sensor card) is at the side of the laser aperture.

The beam sampler was actually replaced by a 2 inch polarizing beam splitter from CVI (TFP-1064-PW-2037).

The previous issue with power control was solved by tuning it closer to its Brewster angle (56deg) allowing to change the transmitted power from 16 to 370mW (maximum power at 2A).

We reduced the laser current to 2A to prevent potential damage of this 30years old laser following Akutsu-san recommendation.

Here is the report of the laser characterization for the cavity experiment (effect of birefringence on alignment strategy of crystalline cavity)

-Laser nominal specification :

reference : LightWave 126-1064-500

serial number : 204

Manufactured date : July 1994

Maximum power : 2W

-Control specification: 

name : LightWave 125/126

serial number : L-7-2001-6

First the relation between the electric intensity provided by the controler and the optical power at the output of the laser has been characterized. The data and the linear fit made with a least square method can be found on the figure 1. The measurent has been done at 26cm from the laser aperture without optical layout between both.

Then we installed a half wavelength plate and a beam sampler in order to controle the power that will be injected in the future optical system. The first optics are know installed, the actual setup can be seen on the figure 2

From this setup, we measured the beam radius as a function of the postion from the lens. The lens is used to focus the beam as the beam radius was too large for the beam profiler aperture, its focal lens is 100mm. Simulation work will be necessary to recover the real beam radius from the laser aperture and will presented in a future logbook or as a reply of this one. The beam radius as a function of the distance from the lens can be seen on the figure 3. The measurement has been done for two radius in two orthogonal directions. The parameter found are :

For Ww(d)

w0 = 263.72 ± 32.54 um

z0 = 11.51 ± 0.08 cm

zr = 1.29 ± 0.18 cm 

For Wv(d)

w0 = 278.19 ± 2.68 um

z0 = 11.86 ± 0.09 cm

zr = 1.03 ± 0.19 cm

With Ww and Wv the beam radius in two orthogonal direction keping the notation used by the beam profiler software. 

I changed the LC tank circuit, inductor to 470uH. These are the old inductors in elec shop. I couldn't understand why my resonant frequency shifted from 2.1Mhz to 1.63MHz. First I took it as some drift in pockel cell capacitance. But, then I tried to find the specs of the inductor. (It's bad!!)

The self resonance frequency of the inductor is 2.4Mhz. It's literally near my resonant freq. I was not expecting it to be this low. If we use such inductor near their self resonant freq, all forms of parasitic capacitance will affect my circuit. This explains also why my circuit could only achieve half of the desined modulation. The radial leaded inductor stored in elec shop are not good for RF applications. Being so close to self resonance freq can lead to degraded quality factor as well.

I found specs of some from coilcraft, and their self resonance freq is 210Mhz. Some inductor like this will solve the issue. There are some chip based inductors in elec shop, I will check their specs. 

Fig 1 is the circuit currently. The opamp used is EL2099CT. 

File 2 is datasheet of 470uH from elec shop. 

by rotating the polarization before a pbs or a tilted beam sampler we should be able to tune the reflected (or transmitted) power.

However the typical change we saw (0.3%) is far lower than expected.

Why should the power change when you rotate HWP? The polarization from laser is perfectly linear. So, all you do when you rotate hwp is rotate polarization. The power can be rather controlled with a rotating polarizer. 

Another issue is that the separate temperature vi was not on.

hence all temperature are 0 on the measurements file..

[Clement, Marc]

Yesterday, Shalika and Clement found a spare laser controller nearby TAMA input laser bench that seemed to work properly.

We tried to use it but the current range is between 1.4A to 2.6A.

Clement made power vs current graph that will be uploaded soon.

While the laser manual specifies a waist 5cm after the laser head aperture, it seems to be more around 15cm.

We started to install a power controller (rotating HWP + tilted beam sampler) but somehow the reflected power is almost independent of HWP angle.

We replaced the beam sampler by a TFP polarizing beam splitter and got similar result...

We added a QWP after the HWP and got same result.

Note that we're using (for the first time) a high power power meter head found in PCI (S145).

Today I tried to measure the sample only with p-pol from calibration.

The input polarization is set by rotating the polarizer (spol = 358deg, ppol = 88deg).

It seems I made a mistake in saving the no sample measurement before the sample...

The strange features seen in sample transmission spectrum with ppol is also visible without sample.

More analysis to follow.

The spectrophotometer is off.

[Marc, Tsuzuki]

In the past years we made several measurements with ATC spectro-photometer which showed more or less good agreement with PCI measurement at 1064nm.

One suspect for discrepancy was the unpolarized light of the spectrophotometer.

We purchased a broadband polarizer and started measurement today.

Tsuzuki-san explained me how to operate the spectrophotometer and me made our first trial measurement with Shinkosha 50 30 3 sample.

We have to do calibration-> no sample -> s pol & sample -> p-pol & sample -> no sample measurement.

In current settings (220->2050nm, 0.1nm step and low scanning speed), it takes about 46mn per measurement.

One think we didn't considered for this 1st trial is the fact that initial calibration/background measurement are made with s-pol while later one are made with p-pol.

Last measurement is now on-going but at first glance it seems that s and p pol transmission is far more different than what I was expecting....

maybe misalignment of the sample or polarizer could be an issue..

The spectrophotometer will be kept on during the night.

[Clement, Marc, Shalika]

We went to ATC clean room to take the laser.

First, we removed the seiden F sheet at the entrance that was placed to protect the clean room during the repair work.

Note that due to this work, the room (outside the clean room) is extremely dirty.

We reinstalled the sticky mat and took both laser, laser controller and 2 power supplies.

Also, there seems to be optics with first contact, might be worth to reapply first contact to remove it.

Some paper is also inside the clean room which could affect its cleanliness.

[Marc, Shalika]

After some debugging (related to issue in saving data) here are the results.

Fig 1 is the control test (likely Arylamide). It does not match that well with previous measurements...

Fig 2 is all newly tested hydrogel.

There is clear issue with ktk693, likely due to slipping of hydrogel during the measurement.

Maybe also issue with ktk697 (large error bar in birefringence).

[Akutsu, Marc]

Akutsu agreed to lend us the lighwave laser that was at some point used to prepare the replacement of TAMA opo.

Yesterday we tested it. Indeed, the power supply of the laser controller being broken, its is now powered by an external power supply directly connected to the +/-5V/ground pins of the controller.

The 2 power supply are locked and OVP/OCP (over voltage/current protection) settings at around 17V/10A and set parameters around 1A/5.1V.

When at 5.0V provided, the laser was stuck at 'warming up'

It will be moved today to BIGFOOT lab.

We installed the 2nd shelf by taking some easy insert washers from the cable holders.

New washers should arrive on Friday with some spares.

[Hirata, Marc]

after cleaning all parts, we assembled one of the 2 new hanging shelves.

It can hold up to 50kg with a safety factor 2.

We ordered new washers needed to assemble the second one.

Assembly documents are stored in the red desk.

all other parts are on the CO2 experiment table.

I switched TAMA air conditioning to cooling.

I also turn on computer fan in the previous storage room but temperature is still around 27degC...

[Katsuki, Marc]

Measurements goal is to better understand what structure is responsible for positive or negative birefringence.

ktk*** indicates the number of the hydrogel (not its composition)

-------------------

*negative control (acrylamide)

C:\Users\atama\Dropbox\Cell Birefringence\Measurement data\hydrogel\ktk703\Wed, Apr 9, 2025 11-35-04 AM.txt

*ktk693

C:\Users\atama\Dropbox\Cell Birefringence\Measurement data\hydrogel\ktk693\Wed, Apr 9, 2025 1-29-48 PM.txt

at 0.37N I forgot to change the force(0.34 ->0.37)

*ktk697

C:\Users\atama\Dropbox\Cell Birefringence\Measurement data\hydrogel\ktk697\Wed, Apr 9, 2025 3-44-57 PM.txt

at 0.41N gel was broken

*ktk699

C:\Users\atama\Dropbox\Cell Birefringence\Measurement data\hydrogel\ktk699\Wed, Apr 9, 2025 4-40-39 PM.txt

at 0.42N gel was broken

*without sample

C:\Users\atama\Dropbox\Cell Birefringence\Measurement data\hydrogel\without_gel\Wed, Apr 9, 2025 5-27-39 PM.txt

I had re-executed the code. I don't see the dot anymore. 

I had increased the limitation on filtering by putting limits on (value + uncertainity), instead of having lower limit (value-uncertainity)