40m QIL Cryo_Lab CTN SUS_Lab CAML OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop
  ATF eLog, Page 29 of 58  Not logged in ELOG logo
ID Date Authorup Type Category Subject
  2490   Mon Mar 9 13:13:02 2020 KojiLab InfrastructureHVACHVAC work concluded for today

Last Friday, I found the HEPA units on the squeezer table were not on. I turned them on at "SLOW".


  2491   Mon Apr 6 18:35:48 2020 KojiSummaryGeneralWest Bridge flooding Apr 6th

West Bridge flooding Apr 6th due to rain in the night

Looks like the first responder was Calum. The attached photos were sent from him.


Attachment 1: image2.jpeg
Attachment 2: image1.jpeg
  2492   Mon Apr 6 18:38:50 2020 KojiUpdateGeneralWest Bridge flooding Apr 6th

To check the status of all the labs, I went to WB. There was no ongoing water leakage in the labs.

Attachment 1: The subbasement was completely dry.

Attachment 2: Upon the lab inspection, I took PPE from the OMC lab. This was intended to prevent me to pick up anyone's anything and you to pick up my anything.

Attachment 3: The EE shop has no problem

Attachment 4: Cryo Lab. No problem.

Attachment 5: Crackle Lab. No problem, but a lot of dead cockroaches on the floor!

Attachment 6: OMC Lab. No problem.

Attachment 7: C.Ri.Me Lab. Gabriele has already checked the status in the morning. And I found no problem. Didn't bother to turn on the light.

Attachment 8: CTN Lab. No problem.

Attachment 9: QIL Lab. The floor was mostly dry. Did someone wipe the floor?

Attachment 10: Some water drip was found in front of the workbench.

Attachment 11: It comes from the ceiling.

Attachment 12: Left a trash box to catch future possible leak.

Attachment 13/14: TCS Lab. No problem found.

Attachment 15: As per Aidan's request, the instruments were moved to the North-East area of the room to avoid future possible leak.

Attachment 1: 20200406143251_IMG_9618.jpg
Attachment 2: 20200406143856_IMG_9621.jpg
Attachment 3: 20200406143932_IMG_9622.jpg
Attachment 4: 20200406144014_IMG_9623.jpg
Attachment 5: 20200406144119_IMG_9626.jpg
Attachment 6: 20200406143837_IMG_9620.jpg
Attachment 7: 20200406144413_IMG_9633.jpg
Attachment 8: 20200406144522_IMG_9635.jpg
Attachment 9: 20200406144648_IMG_9639.jpg
Attachment 10: 20200406144730_IMG_9643.jpg
Attachment 11: 20200406144752_IMG_9644.jpg
Attachment 12: 20200406144942_IMG_9645.jpg
Attachment 13: 20200406145125_IMG_9646.jpg
Attachment 14: 20200406145127_IMG_9647.jpg
Attachment 15: 20200406145347_IMG_9652.jpg
  2493   Mon Apr 6 19:01:21 2020 KojiUpdateGeneralWest Bridge flooding Apr 6th

Additional notes:

I did not see anyone in the building.

Attachment 1/2: Our labs have no sticker/paper to indicate any disinfection of the room. (Make sense)

Attachment 3: Most of the basement offices have the notes to indicate disinfection.

Attachment 4/5: Our offices have no notes.

Attachment 1: 20200406151420_IMG_9653.jpg
Attachment 2: 20200406151428_IMG_9654.jpg
Attachment 3: 20200406151459_IMG_9655.jpg
Attachment 4: 20200406151633_IMG_9656.jpg
Attachment 5: 20200406151709_IMG_9658.jpg
  2521   Fri Nov 20 18:47:42 2020 KojiSummaryGeneralPermenant exchange of TED200C(QIL) and TED200C(2umECDL)

I moved the brand new TED200C on the workbench to Crackle for 2um ECDL (permanently)
The TED200C temp controller used in the 2um PD test setup will stay there (permanently)


  2522   Fri Nov 20 18:49:43 2020 KojiSummaryGeneralInstrument loan

FEMTO DLPCA200 low noise preamp (brand new)

Keithley Source Meter 2450 (brand new) => Returned 11/23/2020

were brought to the OMC lab for temporary use.

  2526   Tue Dec 22 15:20:14 2020 KojiSummaryGeneralInstrument loan

Is the reverse bias programmable? FEMTO has a bias trimmer on it. It's useful in the usual application, but for automation, the configuration of the input becomes cumbersome.

  2572   Thu May 20 16:57:32 2021 KojiElectronicsGeneralKeithley Source Meter returned to Downs

I've returned the Keithley Source Meter unit
- The unit (Keithley 2450?2460?)
- A power cable
- A pair of banana clips
- the transistor test fixture & triax cable/connectors

Attachment 1: P_20210520_154439.jpg
Attachment 2: P_20210520_154505.jpg
Attachment 3: P_20210520_154523.jpg
  2589   Wed Jun 16 17:17:12 2021 KojiUpdateGeneralI2 cell

I was searching an I2 (Iodine) cells back to the days of the laser gyro.

I found a likely box at a very tricky location. Took the photos and returned to this tricky place.

2021/Jul The box was moved to the OMC lab (KA)

Attachment 1: P_20210616_170104.jpeg
Attachment 2: P_20210616_170038.jpeg
Attachment 3: P_20210616_170021.jpeg
  2603   Thu Jul 15 23:34:17 2021 KojiSummaryTempCtrlTemprerature Log for cooling down / warming up

[Stephen Koji Radhika]

Stephen and Radhika worked on the cooling down and warming up of the cryostat with the cold head RTD attached using a spring-loaded screw. No other configuration changes compared to QIL/2599. Here are the temperature log plots. Photos of spring clamped RTD are outstanding, but the clamp is the same as the workpiece pictured in QIL/2599/Attachment 12.

Attachment 1: temp_log_cooldown_20210709_1747.pdf
Attachment 2: temp_log_warmup_20210712_1315.pdf
  2604   Thu Jul 15 23:37:53 2021 KojiSummaryCryo vacuum chamberBonding work for the prep of the preliminary suspension test

[Stephen / Koji]

Bonding work for the prep of the preliminary suspension test

- 1" sq mirror-ish polished SUS piece was bonded to a face of the silicon mass. We chose the location right next to a line on the barrel. (Attachment 1)

- The mass was flipped with two more same thickness pieces used for the spacers to keep the mass horizontal.

- A pair of an OSEM and dumbbell-magnet was brought from the 40m (courtesy by Yehonathan). The magnet was glued on the mass at the opposite position of the attached mirror because the optical ports are going to be arranged to share an axis. A piece of cryo varnish was also painted with a piece of cigarette paper at the center of the mass so that we can attach an RTD. (Attachment 2)

Next Things To Do (Attachment 3)

  • Vent the chamber
  • We will move an optical port to the opposite position of the other port.
  • A DB9 feedthru is going to be installed.
  • Suspension
    • Move the sus frame in the chamber
    • Suspend the mass
  • Sensor arrangement
    • Set up the oplev
    • Hold the OSEM at the height of the magnet
    • Set up a camera to observe the magnet-OSEM clearance
    • We improvise the DB crimping sockets so that we can electrically connect the OSEM (optional)
  • Pump down / cool down the chamber
    • The main target of the cooling is to check the cooling capability of the test mass mainly with radiative cooling.
    • An optional target is to observe the misalignment as a function of the temperature -
      • -> Oplev signals are to be connected to CDS / check if CDS is logging the data
    • Check if the OSEM/magnets survive the thermal cycle
    • If possible we can try to actuate the OSEM / check the LED/PD function at the cryo temp
Attachment 1: P_20210715_170102-1.jpg
Attachment 2: P_20210715_172218-1.jpg
Attachment 3: experiment_plan.pdf
  2605   Fri Jul 16 23:28:24 2021 KojiSummaryCryo vacuum chamberSus Test Work 07/16/2021

[Stephen Koji]

We started cooling down of the test mass.


- Stephen vented the chamber at 2PM. An optical port was moved to see the OSEM from the back.

OSEM wiring

- Brought DSub crimp sockets from the 40m. We picked up 3x 1m LakeShore WCT-RB-34-50 (twisted silver-plated copper, 34 AWG with Teflon insulation). The ends of the wires were dangled so that crimping is possible. A single wire resistance was measured to be ~1Ohm at room temp. (Attachment 1)

- OSEM pin out / backside view (cable going down) (Attachment 2)

|   o   o   o |
| o   o   o   |                 Wire
  ^ ^ ^ ^ ^ ^---PD K        ---- R3
  | | | | |-----PD A        ---- B3
  | | | |-------LED A       ---- B2
  | | |---------LED K       ---- R2
  | |-----------Coil End    ---- B1
  |-------------Coil Start  ---- R1

Twisted Pair 1: (R1&B1) with 1 knot  at the feedthru side
Twisted Pair 2: (R2&B2) with 1 knot  at the feedthru side
Twisted Pair 3: (R3&B3) with 1 knot  at the feedthru side

Dsub feedthru in-air pinout (Mating side)

    1  2  3  4  5
\ o  o  o  o  o /
 \ o  o  o  o  /
   6  7  8  9

Pin1 - Coil Start
Pin6 - Coil End
Pin2 - LED K
Pin7 - LED A
Pin3 - PD A
Pin8 - PD K

Pin1-6 R=16Ohm
Pin2-7 Diode V (with Fluke) 1.18V (Pin2 black probe / Pin7 red probe)
Pin3-8 Diode V (with Fluke) 0.7V (Pin3 red probe / Pin8 black probe)

- OSEM pin out / backside view (cable going down)

Suspension installation (Attachment 3)

- The sus frame was moved into the chamber

- We measured the test mass dimension before installation: L 3.977" D 4.054"

- The attached mirror size is 1"x1" made of SUS #8 (?)

- The mass was suspended. The height / rotation of the mass was adjusted so that the reflecting mirror is visible from the oplev window and also the OSEM magnet is visible from the OSEM window.

- The OSEM was placed on an improvised holder. (Attachment 4)

Oplev installation

- ...Just the usual oplev installation. Adjusted the alignment and the return beam hits right next to the laser aperture. This beam was picked off by a mirror and steered into a QPD. (Attachments 5/6)

- The lever arm length is ~38" (960mm) -- 9" internal / 29" external
- The oplev signal is shaking so much and occupying ~50% of the full scale. Added a lens with f=250 to make the beam bigger, but the improvement was limited.

Pumping down

- Started ~8:30PM?

DAQ setup

- Wired 3 BNC cables from the table to the DAQ rack. CHX/Y/S are connected to ADC16/1718ch.

- The real-time processes seemed dead. Looked at [QIL ELOG 2546] to bring them up. TIM/DAQ error remains, but the data stream seems alive now. Leave it as it is.


- Temp Logging started. Filename: temp_log_cool_down_20210716_2255.txt

- Cryocooler turned on. ~10:55PM

- Confirmed the cold head temp was going down. The cold head temp is 75K at 0:30AM

OSEM photo

- An example photo was taken from the rear window. The attempt with 40m's Canon failed. Attachment 7 was taken with KA's personal compact camera with a smartphone LED torch. The gap between magnet and OSEM is highly dependent on the view axis. So this is just a reference for now.

Attachment 1: 20210716170727_IMG_0719.jpeg
Attachment 2: 20210716174712_IMG_0723.jpeg
Attachment 3: 20210716195953_IMG_0726.jpeg
Attachment 4: 20210716200005_IMG_0728.jpeg
Attachment 5: 20210716200224_IMG_0734.jpeg
Attachment 6: 20210716200112_IMG_0733.jpeg
Attachment 7: 20210716234113_IMG_0742.jpeg
  2606   Sat Jul 17 00:55:41 2021 KojiSummaryCryo vacuum chamberTemp Log 210716_2255

Temperature log for the first 2 hours (Attachment 1)

I wonder why the temperatures displayed on CTC100 and the ones logged are different...?


Attachment 1: temp_log_cool_down_20210716_2255.pdf
  2609   Mon Jul 19 17:21:19 2021 KojiSummaryCryo vacuum chamberTemp Log 210716_2255

Temp Log on Jul 19 2021 17:20

I wonder what is the heat transfer mode for the test mass right now. Radiative? or Conductive through the wires?


Attachment 1: temp_log_cool_down_20210716_2255.pdf
  2610   Tue Jul 20 11:33:52 2021 KojiSummaryCryo vacuum chamberA cooling model (Temp Log 210716_2255)

A naive cooling model was applied to the cooling curve.
A wild guess:

- The table temp is the same as the test piece temp as measured on 2021/7/9
- The inner shield temp is well represented by the table temp
- The specific heat of Si is almost constant (0.71 [J/(g K)] between 300K~200K

Radiative cooling:
The curve was hand-fitted by changing the emissivity of the inner shield and the silicon mass. I ended up having the same values for these to be 0.15.
Surprisingly well fitted!

Conductive cooling:
The conductive cooling through the wire does not fit the cooling curve, although the quantitative evaluation of the wire conductivity needs to be checked carefully.

Stephen shared attachments 2 and 3, which contain insights on the wire used to hang the Si mass. .017" diameter Music Wire from California Fine Wire, 2004 vintage, borrowed from Downs High Bay.

Attachment 1: cooling_model.pdf
Attachment 2: IMG_9390.JPG
Attachment 3: IMG_9391.JPG
  2611   Tue Jul 20 17:28:30 2021 KojiSummaryCryo vacuum chamberA cooling model (Temp Log 210716_2255)

Updated the model the latest log data with cooling prediction

  • The radiative cooling is expected to be the dominant cooling mode.
  • It will take ~3 more days to reach 123K. We don't need to wait for it.
  • For more informative temp data, we need the temperature of the inner shield and the table.

  • We know the cold head temp from the measurement. For the prediction, the constant cold head temp of 65K was assumed.
  • The table temp was estimated using conductive cooling model + linear empirical dependence of the conductivity on the temp
  • The constant specific heat of the silicon mass (0.71 J/K/g) was assumed. This may need to be updated.
  • The radiative cooling is given from Stefan–Boltzmann law with the emissivity of 0.15 for both the shield and the mass.
  • The conductive cooling of the test mass was estimated using: Wire diameter 0.017" (=0.43mm), 4 wires, length of ~10cm (guess), no thermal resistance at the clamps (-> upper limit of the conductive cooling)

Radiative cooling already gives us a good agreement with the measured temp evolution for the test mass. The conductive cooling is not significant and does not change the prediction.

Updated the plot with the new data (2021/7/21 12:30PM)

Attachment 1: cooling_model.pdf
  2613   Wed Jul 21 14:53:28 2021 KojiSummaryGeneralJul 17, 2021: Canon camera / small silver tripod / macro zoom lens / LED ring light borrowed -> QIL

See https://nodus.ligo.caltech.edu:8081/40m/16250

  2614   Wed Jul 21 21:05:59 2021 KojiSummaryCryo vacuum chamberTest mass cooling (2021/07/16 ~ 2021/07/21)

[Stephen and Koji for discussion / Koji for the execution]

1. Temperature Trend

See [QIL ELOG 2611] for the updated temp log and the cooling model.

Considerations for the next cycle:
-> How can we accelerate the cooling? It seems that the table cooling is conduction limited. Improve the cold head connection.
-> We want to move the RDTs
-> How can we improve radiative cooling?

2. Oplev Trend (Attachment 1)

Sum: The beam has been always on the QPD (good). See also Attachment 2

X&Y: In the first few hours the beam drifted in -X and then +X while Y had slow continuous drift in +Y. ~11hours later sudden drift in -Y and totally saturated. Also -X saturation observed @~16hrs. Again +Y drift was seen @~25hrs. The totally saturated in -X and +Y.
They may be related to the drift of various components with various cooling time scale.

Visual check: ~2mm shift in X&Y is visually observed. Attachment 2

-> How can we quantify the drift? What information do we want to extract?

3. OSEM and the magnet

The magnet is intact. And the suspension seemed still free after cooling (Attachment 3)
Significant misalignment was not visible. No visible damage by cooling was found. The coil is alive and the PD/LED are also intact. Fluke showed that they are still diodes, but their function was not checked.

The coil resistance changed from 16Ohm -> 4.2Ohm. For the 16Ohm, 2 Ohm was from the wire. Let's assume we still have 2Ohm overhead -> The coil R changed from 14->2.2. This corresponds to the coil temperature of the order of ~100K. This is not so crazy.

Some actuation current was applied to the magnet. For this test, the oplev was realigned.
First, some ~300mA current pulses were applied to the coil. The ringdown of the yaw mode was visible. Then the DC current of 100mA was applied. This didn't make visible change on the spot position but the data showed that there was a DC shift.

-> We prefer to have a softer suspension for the next test.

4. CTC100 logging

During the cooling we kept having inaccurate data logged compared with the displayed data on the screen of CTC100.
As soon as the cooling logging was stopped, telneting to CTC100 was available. So, I telnetted to the device and sent the data transfer command ("getOutput"). Surprisingly, the returned values agreed with the displayed values.
So my hypothesis is that somehow the data strings are buffered somewhere and gradually the returned values get delayed. From the behavior of the device, I imagined that the fresh telnet connection gives us the latest data and there is no buffering issue.

So I tweaked the data logging code to establish the telnet connection every time the values are asked. The connection is closed after the every data acquisition. I like this as we can also make the test connection between each data acquisition points, although I have not tried it yet. The code is in the same folder named ctc100_controller_v2.py

5. Heating

Now I thought that I did all I wanted to do this evening, so the heater was turned on at ~20:50, Jul 21. The heating power saturated at 22W, which is the set limit.

Attachment 1: oplev_trend.png
Attachment 2: 20210721201333_IMG_0765.jpeg
Attachment 3: 20210716234113_IMG_0742.jpeg
Attachment 4: Screenshot_from_2021-07-21_20-19-09.png
  2615   Thu Jul 22 22:03:45 2021 KojiSummaryCryo vacuum chamberTest mass heating in progress (2021/07/21 ~ 2021/07/23)

- Temperature Log updated 2021/7/23 12:00 Heating Ended

- Assuming reaching the room temp at ~30hrs and heating power saturated at 22W: Predicted heat injection 30*3600*22 = ~2.4MJ

Update from Stephen
- Note that we can check logging accuracy against the snapshot (timestamp 20210723_1113).
If my math is correct, this would be time = 37.35 38.35 hours

Update from KA
=> The corresponding time in sec is 138060 sec
The raw data line for the corresponding time is:

138016.839614, 295.805, 306.678, 302.518, 312.401, 0.000, 0.000, -0.001, 0.621, 0.622, 1.429, 0, 0, NaN, NaN, NaN
The values on the photo 295.806, 306.677, 302.518, 312.401 ==> Well matched. Victory!

Attachment 1: IMG-9395.jpg
Attachment 2: temp_log_warmup_20210721_2052.pdf
  2616   Fri Jul 23 20:53:40 2021 KojiSummaryGeneralJul 17, 2021: Canon camera / small silver tripod / macro zoom lens / LED ring light returned / ELectronics borrowed

[Returned] Brought one HAM-A coil driver (D1100687 / S2100619) and one Satellite Amplifier (D1002818 / S2100741) from the 40m

Also brought some power cables.

Brought ~1m of 0.0017" (~43um) misical wire. This will make the tension stress be 341MPa. The safety factor will be ~7.


Attachment 1: P_20210723_212158.jpg
  2617   Sun Jul 25 21:45:46 2021 KojiSummaryCryo vacuum chamberAbout the radiation heat transfer model

The following radiation cooling model well explained the cooling curve of the test mass (until ~150K)

\dot{Q}=0.15 A\,\sigma (T_{\rm SH}^4-T_{\rm TM}^4)

where dQ/dt is the heat removed from the test mass, A is the surface area of the test mass, \sigma is the Stefan-Boltzmann constant, T_SH and T_TM are the temperatures of the surrounding shield and the test mass.

Can we extract any information from this "0.15"?

I borrowed "Cryogenic Heat Transfer (2nd Ed)" by Randall F. Barron and Gregory F. Nellis (2016) from the library.
P.442 Section 8.5 Radiant Exchange between Two Gray Surfaces can be expressed by Eq 8.44

\dot{Q} = F_e F_{1,2} \sigma A_1 (T_2^4-T_1^4)

where T_i is the temperature of objects 1 and 2. For us, OBJ1 is the test mass and OBJ2 is the shield. A1 is the surface area of A1. F_1,2 is the view factor and is unity if all the heat from the OBJ1 hits OBJ2. (It is the case for us.)

F_e is an emissivity factor.

The book explains some simple cases in P 443:

Case (a): If OBJ2 is much larger than OBJ1, F_e = e_1 where the e_i is the emissivity of OBJi. This means that the radiated heat from OBJ1 is absorbed or reflected by OBJ2. But this reflected heat does not come back to OBJ1. Therefore the radiative heat transfer does not depend on the emissivity of OBJ2.

Case (b): If OBJ1 and OBJ2 has the same area, \frac{1}{F_e} = \frac{1}{e_1} + \frac{1}{e_2} -1. The situation is symmetric and the emissivity factor is influenced by the worse emissivity between e1 and e2. (Understandable)

Case (c): For general surface are ratio,  \frac{1}{F_e} = \frac{1}{e_1} + \left(\frac{A_1}{A_2}\right)\left(\frac{1}{e_2} -1 \right ). OBJ2 receives the heat from OBJ1 and reradiates it. But only a part of the heat comes back to OBJ1. So the effect of e2 is diluted.

For our case, OBJ1 is the Si mass with DxH = 4in x 4in, while the shield is DxH = 444mm x 192mm. A1/A2 = 0.12.
We can solve this formula to be Fe=0.15. e1 = (0.147 e1)/(e2-0.0178).

Our inner shield has a matte aluminum surface and is expected to have an emissivity of ~0.07. This yields the emissivity of the Si test mass to be e1~0.2

How about the sensitivity of e1 on e2? d(e1)/ d(e2) = -0.95 (@e2=0.07).

Can Aquadag increase the radiative heat transfer?

Depending on the source, the emissivity of Aquadag varies from 0.5 to 1.
e.g. https://www.infrared-thermography.com/material-1.htm / https://www.mdpi.com/1996-1944/12/5/696/htm

  • Assuming Aquadag's emissivity is ~1
    • If only the test mass is painted, F_e increases from 0.15 to 0.39 (x2.6)
    • If the inner shield is also painted, F_e increases to 1, of course. (pure black body heat transfer)
    • If shield panels are placed near the test mass with the inner surface painted, again F_e is 1.
  • Assuming Aquadag's emissivity is ~0.5
    • If only the test mass is painted, F_e increases from 0.15 to 0.278
    • If the inner shield is also painted, F_e increases to 0.47.
    • If shield panels are placed near the test mass with the inner surface painted, F_e is 0.33 assuming the area ratio between the test mass and the shield panels to be unity.

It seems that painting Aquadag to the test mass is a fast, cheap, and good try.

  2618   Mon Jul 26 01:30:42 2021 KojiSummaryCryo vacuum chamberPrep for the 2nd cooling of the suspension

Updated Jul 26, 2022 - 22:00


  1. Reconstruct the cryostat
    1. [Done] Reinstall the cryo shields and the table (Better conductivity between the inner shield and the table)
    2. [Done] Reattach the RTDs (Inner Shield, Outer Shield)
      -> It'd be nice to have intermediate connectors (how about MIllMax spring loaded connectors? https://www.mill-max.com/)
    3. Reattach the RTD for the test mass
  2. Test mass & Suspension
    1. [Done] Test mass Aquadag painting (How messy is it? Is removal easy? All the surface? [QIL ELOG 2619]
    2. [Done] Suspension geometry change (Higher clamping point / narrower loop distance / narrower top wire clamp distance -> Lower Pend/Yaw/Pitch resonant freq)
    3. [Done] Setting up the suspension wires [QIL ELOG 2620]
    4. [Done] Suspend the mass
  3. Electronics (KA)
    1. [Done] Coil Driver / Sat Amp (Power Cable / Signal Cables)
    2. Circuit TF / Current Mon
    3. [Done] DAC wiring
    4. [Done] Damping loop
  4. Sensors & Calibration (KA)
    1. [Done] Check OSEM function
    2. [Done] Check Oplev again
    3. Check Oplev calibration
    4. [Done] Check Coil calibration
    5. Use of lens to increase the oplev range
    6. Recalibrate the oplev
  5. DAQ setup (KA)
    1. [Done] For continuous monitoring of OSEM/OPLEV
  2619   Mon Jul 26 22:49:00 2021 KojiSummaryCryo vacuum chamberAquadag painting

[Stephen Koji]

We decided to paint the silicon test mass with Aquadag to increase the emissivity of the test mass.

Stephen brought the Aquadag kit from Downs (ref. C2100169) (Attachment 1)

It's a black emulsion with viscosity like peanut butter. It is messy and smells like squid (Ammonium I think) (Attachment 2)

We first tried a scoop of Aquadag + 10 scoops of water. But this was too thin and was repelled easily by a Si wafer.
So we tried a thicker solution: a scoop of Aquadag + 4 scoops of water. (Attachment 3)

The thicker solution nicely stayed on the Si wafer (Attachment 4)

We want to leave the central area of the barrel unpainted so that we can put the suspension wire there without producing carbon powder. (Attachment 5)
1.5" from the edge were going to be painted. The central1" were masked.

The picture shows how the Si test mass was painted. The test mass was on a V-shaped part brought from the OMC lab. The faces were also painted leaving the mirror, while the place for RTD, and the magnet were not painted. (Attachment 6)

It looked messy while the painting was going, but once it started to dry, the coating looks smooth. It's not completely black, but graphite gray. (Attachment 7)

After the test mass got dry, another layer was added. (Attachment 8)

Then made it completely dry. Now the mask was removed. Nice! (Attachments 9/10)

Attachment 1: 20210726164254_IMG_0768.jpeg
Attachment 2: 20210726164530_IMG_0769.jpeg
Attachment 3: 20210726164225_IMG_0766.jpeg
Attachment 4: 20210726164957_IMG_0772.jpeg
Attachment 5: 20210726173608_IMG_0774.jpeg
Attachment 6: 20210726174523_IMG_0775.jpeg
Attachment 7: 20210726182715_IMG_0783.jpeg
Attachment 8: 20210726192042_IMG_0784.jpeg
Attachment 9: 20210726192837_IMG_0790.jpeg
Attachment 10: 20210726192853_IMG_0791.jpeg
  2620   Wed Jul 28 00:59:47 2021 KojiSummaryCryo vacuum chamberThe test mass successfully suspended

[Stephen Koji]

While Stephen worked on the RTD reattachment, I worked on the suspension part.

- First of all, we found that the magnet was delaminated from the silicon mass (Attachment 1). It was bonded on the test mass again.

- The suspension frame was tweaked so that we have ~max suspension length allowed.

- The first attempt of suspending the mass with steel wires (0.0017" = 43um dia.) failed. Stephen and I went to downs and brought some reels.

- I chose the wire with a diameter of 0.0047" (= 119um) (Attachment 2). ~8x stronger! The suspension was successfully built and the mass is nicely sitting on the 4 strain releasing bars (improvised effort). (Attachments 3/4)

We can install the suspension in the chamber tomorrow (today, Wed)!


Attachment 1: P_20210727_154143.jpeg
Attachment 2: P_20210727_190356.jpeg
Attachment 3: P_20210727_190426.jpeg
Attachment 4: P_20210727_190543.jpeg
  2621   Thu Jul 29 00:42:38 2021 KojiSummaryCryo vacuum chamberThe test mass successfully suspended

[Stephen Koji]

Road to cooling down

  • The suspension with the test mass was installed in the chamber again
  • Looking at the oplev beam, we jiggled the wire loop position to adjust the alignment approximately.
  • The oplev beam was aligned more precisely.
  • We intentionally kept the OSEM at the "fully-open" position, while it is still close to the magnet so that we can have some actuation.
  • The coil driver was tested before closing the chamber, but it did not work.
    The coil itself was still intact, and the mirror was responding to the coil current if the coil current of ~100mA was applied from a bench power supply with the current ~100mA).
    So the problem was determined to be external.
  • Once we were satisfied with the oplev/OSEM conditions, the inner and outer lids were closed. Then the chamber was closed.
  •  Started pump down.
  • Started cooling down @18:30 / started temp logging too. Log filename: temp_log_cool_down_20210728_1830.txt

The photos were uploaded to Google Photo of WB labs.

The coil driver issue was resolved:

  • It was necessary to take care of the enable switch. Made a DB9 short plug for this purpose.
  • The output R was 1.2K (i.e. 2.4K across the + and - outputs). We needed ~10x more to see visible motion of the mass
  • e.g. The internal gain of the driver is x1.1. If we connect 5VDC input across the diff input of the driver yields, +11V shows up across the outputs of the final stage.
    If the R across the coil is ~100Ohm, we get ~100mA.
  • Soldered 6 x  330Ohm (1/8W) in parallel to 1.2K R_out. -> This ended up 51.5Ohm x2 across the coil. Each R=330 consumes ~1/10W. ->OK

Checking the DAQ setup / damping loop

  • DAQ setup
    • ADC: QPD X->FM16 / Y->FM17 / S->FM18 / OSEM-> FM19
    • DAC: CH11 -> Coil Driver In
  • Connected FM16 and FM17 to the coil drive by setting C4:TST-cdsMuxMatrix_12_17 and C4:TST-cdsMuxMatrix_12_18 to be 1.0
  • It was not obvious if the coil could damp the rigid body modes.
    • Actating the magnet caused Yaw motion most. Some Pitch motion too.
    • Configured FM16 and FM17 for the damping loop.
      • Filter Bank #1: [Diff0.1-10]  Zero 0.1Hz / Pole 10Hz
      • Filter Bank #10: [Anti Dewht]  Zero 1&200Hz / Pole 10&20Hz
    • Tried various damping gain. The mass was moving too much and the proper gain for the damping was not obvious.
    • So, the initial damping was obtained by shorting the coil at the coil in of the sat amp unit. (Induced current damping)
    • Once the test mas got quieter, it was found that -0.01 for FM16 could damp the yaw mode. Also it was found that +0.1 for FM17 could damp the pitch mode. (But not at once as the filters were not set properly)
  • TF measurement for calibration
    • The beam was aligned to the QPD
    • The test mass was damped by using the damping loops alternately 
    • Taken a swept sine measurement Filename: OSEM_TF_210729_0243.xml
      Recorded the time, saved the data, and took a screenshot
      • This measurement was taken @T_IS=252K / T_TM=268K @t=8hr (2:30AM), Rcoil=15.6Ohm
    • Second measurement Filename: OSEM_TF_210729_2147.xml
      • @T_IS=172K / T_TM = 201K @t=27.5hr (10PM), Rcoil=10Ohm
    • 3rd measurement Filename: OSEM_TF_210730_1733.xml
      • @T_IS=116K / T_TM = 161K @t=47hr (5:30PM), Rcoil=?
    • 4th measurement Filename: OSEM_TF_210731_2052.xml
      • @T_IS=72K / T_TM = 134K @t=75hr (9:30PM), Rcoil=6.0Ohm


  • The Satellite amp brought from the 40m is used as-is.
  • The initial OSEM reading was 8.8V, this corresponds to ~30000cnt.
  • As the OSEM was cooled, this number was increasing. To avoid the saturation, a voltage divider made of 4x 15kOhm was attached. I didn't expect to have the input impedance of the AA filter (10K each for the diff inputs), this voltage divider actually made 18.24V across POS and NEG output to be 5.212V to the AA fiter. So the voltage division gain is not 0.5 but 0.2859.
  • This made the ADC range saved, but we still have a risk of saturating the PD out. If this happens. The PD TIA gain will be reduced before warming up.
    -> The TIA and whitening stages use AD822, and the diff output stage uses AD8672. AD822 can drive almost close to rail-to-rail. AD8672 can drive upto ~+/-14V.

There was not enough time for the QPD calib -> Tomorrow

  2622   Thu Jul 29 13:11:17 2021 KojiSummaryCryo vacuum chamberCooling progress: Update

The current cooling curve suggests that the radiative cooling factor Fe (black body =1) increased from 0.15 to 0.5.

Update: The test mass temp is reaching 200K at ~27hrs. cf previously it took 50hrs
Update: The test mass temp is 170K at ~41.5hrs.

OSEM illumination & photodetector efficiency has been kept increasing @41.5hrs

Attachment 1: temp_log_cool_down_20210728_1830.pdf
Attachment 2: cooling_model1.pdf
Attachment 3: cooling_model2.pdf
Attachment 4: OSEM_cooling.pdf
  2625   Fri Jul 30 12:22:56 2021 KojiSummaryCryo vacuum chamberCooling curve comparisons

In all aspects, the latest cooling shows the best performance thanks to better thermal connection, thermal isolation, and the black paint.

- The cold head cooling is faster and cooler

- The inner shield cooling is faster

- The test mass cooling is faster

Attachment 1: comparison_cold_head.pdf
Attachment 2: comparison_inner_shield.pdf
Attachment 3: comparison_test_mass.pdf
  2628   Fri Jul 30 18:18:21 2021 KojiDailyProgressCDSConnecting CTC100 to EPICS/rtcds system

[Radhika, Koji]

During the process, we corrected the channel labeling for RTD #3/#4. So  for a few first data points, the numbers for the workpiece and the outer shield were swapped.

  2629   Sun Aug 1 22:22:00 2021 KojiSummaryCryo vacuum chamberCooling update

The test mass temperature indicates 121K@100hr but there seemed a few sensor glitches for the test mass (𝛥=-4.2K) and the inner shield (𝛥=-0.43K).
So the actual test mass temperature could be 125K.

The temp was read to be 119K@114hr (Attachment 1)

There was very little cooling capability left for the test mass (Attachment 2)

The OSEM reading is now stable @12.3V (Attachment 3)

The raw temp data and the minimal plotting code are attached (Attachment 4)

Attachment 1: temp_log_cool_down_20210728_1830.pdf
Attachment 2: cooling_meas.pdf
Attachment 3: OSEM_cooling.pdf
Attachment 4: cooldown_210728.zip
  2632   Mon Aug 2 21:51:37 2021 KojiDailyProgressCDSConnecting CTC100 to EPICS/rtcds system

The legit way to restart st.cmd is

systemctl restart CTC100
  2633   Tue Aug 3 23:56:00 2021 KojiDailyProgressCryo vacuum chamberWarmup started 02 August

- Confirmed the heating stopped in the evening -> The heater was deactivated @~23:00

- Made some measurements and checks - the oplev spot was approximately on the center of the QPD before warming up. Now it is ~4mm above the center (note that the QPD size is 0.5" in dia) (Attachment 2). This corresponds to ~2mrad misalignment.

- Dismantled the OSEM electronics and power supply from the table. The electronics were salvaged into the OMC lab -> to be returned to the 40m.

- A 2" Al mirror package was brought to the OPLEV periscope so that the gold mirror (too thin) can be replaced. (Attachment 1)

Attachment 1: P_20210804_000247.jpg
Attachment 2: P_20210803_235421.jpg
  2642   Wed Aug 11 18:00:19 2021 KojiDailyProgressCryo vacuum chamberCooldown model fitting for MS

How about incorporating radiative and conductive terms from the object at 300K?


  2645   Sun Aug 15 00:33:15 2021 KojiSummaryCryo vacuum chamberAquadag painting on the inner shield

[Stephen Koji]

We applied Aquadag painting on the inner side of the inner shield.

  • Upon the painting work, we discussed which surfaces to be painted. Basically, the surface treatment needs to be determined not by the objects but by the thermal link between the objects.
    • We want to maximize the heat extraction from the test mass. This means that we want to maximize the emissivity factor between the test mass and the inner shield.
    • Therefore the inner barrel surface of the inner shield was decided to be painted. The test mass was painted in the previous test.
    • For the same reason, the lid of the inner shield was painted.
    • It is better to paint the cold plate (table) too. But we were afraid of making it too messy. We decided to place the painted Al foil pieces on the table.
    • The outer surface of the inner shield and the inner surface of the outer shield: Our outer shield is sort of isolated from the cold head and the steady-state temp is ~240K. Therefore we believe that what we want is isolation between the inner and outer shields. Therefore we didn't paint these surfaces. (note that in Mariner and beyond, the outer shield will be cooled, not isolated, and the radiative link to the outer shield would be strong by design)
    • I believe that this is not the ideal condition for the inner shield. We need to model the cryo stat heat load and take a balance between the isolation and the conduction between the outer shield and the cold head so that we gain the benefit of the outer shield as a "not so hot" enclosure.
  • OK, so we painted the inner barrel of the inner shield, the lid of the inner shield, and some Al foils (shiny side).
  • Stephen made the Aquadag solution. The solution was 2 scoops of Aquadag concentrate + 6 scoops of water, and the adhesion/runniness test was done on a piece of aluminum foil.
  • The barrel and the lid were painted twice. Attachment 1 shows the painting of the inner shield cylinder. Attachment 2 shows a typical blemish which necessitates the second coat.
  • To accelerate the drying process, we brought the heat gun from the EE shop --> (update - returned to EE shop, see Attachment 3)
  • We took some photos of the process. They are all dumped in the QIL Cryo Vacuum Chamber Photo Dump album in the ligo.wbridge account.
Attachment 1: IMG_9636.JPG
Attachment 2: IMG_9632.JPG
Attachment 3: IMG_9646.JPG
  2740   Mon Mar 28 18:00:43 2022 KojiSafetyCleanlinessLab flooding

Flood photo album: https://photos.app.goo.gl/BZAG8DyQzFVTfMNz6 (This link is read-only who has no access to the account)


  2743   Wed Mar 30 16:25:06 2022 KojiSafetyCleanlinessLab flooding

Muddy Waters is not new, but if the facility can fix it we'd take it.


  2826   Thu Jan 12 11:50:20 2023 KojiHowtoGeneralHow to move the large engine hoist through the narrow door

How to move the large engine hoist through the narrow door

See http://nodus.ligo.caltech.edu:8080/Mariner/122

  2871   Tue Jun 13 14:02:17 2023 KojiSummaryGeneralOrganizing subbasement storage cage

Storage organizing session Jun 13, 2023
I'm posting the log here because there is no other appropriate place to post.
JC, Shruti, Aaron, Yahonathan, and Rana worked on organizing the WB SB storage cage.

  • The left half was cleared at the beginning
  • Wire shelving was built in the cage
  • Placed the heavy vacuum stuff at the bottom, then placed the electrical instruments on the shelf. We still have a lot of space to put. Victory! (Attachment 1)
  • We have some items to be transported to the 40m, including a picomotor driver that would be used for the 40mBHR (Attachment 2)
  • We found a potential clean room table set. Bring the set to the 40m so that we can use it once the large optical table is removed. (Attachment 3)
  • The previous bottom wooden pallet was removed. We will toss it. (Attachment 4)

Action Item:
Having one or two flat/piano dollies in the cage would be great.

Attachment 1: PXL_20230613_191826685.jpg
Attachment 2: PXL_20230613_191841771.jpg
Attachment 3: PXL_20230613_191853574.jpg
Attachment 4: PXL_20230613_191903191.jpg
  178   Thu Jul 16 15:01:48 2009 Koji & Connor LaserPSLRazor Blades!


Since the beamscan is in a questionable state of scanny goodness, Koji advised that I do some razor blade occlusion power measurements of the beam and then fit an erf to it to find the waist. I took data with the tinker toys pictured below.

I will compare these results with some beamscans results to verify (hopefully) that the beamscan is outputting useful results, not lies.


Actually, it would be nicer if we have a calibrated micrometer screw for the thread.
Connor and I tried to make another set of the razor blade arrangement with a micrometer.
We put it on the PSL optical table. Please use it.

  2029   Sun Feb 21 22:02:01 2016 Koji Antonio,MiscPD QEPD window removal few notes

Rich removed the window from PD on Friday. The basics steps for the removal are the following:


0. PD in a socket, it helps;

1. In the beginning you open the screws on the cutter up so they just hold the photodiode;

2. Make a light little line first at desired height and make sure that it is a circle and not a helix;

3. You do not want to go start right away full force on it, you want to make tiny little incremental cuts. Eventually it just falls apart;


Attachment 2: Screen_Shot_2016-02-21_at_8.34.43_PM.png
  2012   Thu Feb 4 21:23:31 2016 KojiNMiscPD QEPreparation of some components

I prepared some basic optics for a PD QE enhancement experiment.

Specifically, two half wave plates, a PBS, a BS, a PD mount, and a stage for the PD mount are prepared.

The PD mount has a glued connector for PDs for replacing them easily.

The sage for the PD mount has three micrometers for moving PDs accurately to three axes.


A male pin assignment for a DC power supply of a circuit for the PD is confirmed.

As shown in the following image, #1 pin, #2 pin, and #5 or #9 pin should be connected to +15 V, -15 V, and GND, respectively.

Male pin assignment for the DC power supply of the circuit for the PD


In addition, for aligning the optics, a CCD camera and a lens for the camera are also prepared.

All things are placed on an optical bench without being aligned.


I will align the optics and test the PD circuit and the camera with laser light.

  2013   Fri Feb 5 21:06:14 2016 KojiNMiscPD QEInitial alignment of optics

To pick off adequate laser power for our PD QE enhancement experiment, the first HWP in front of the laser was rotated.

The inititial angle of the first HWP was 48 degree.

For measuring the laser power, some optics were aligned as shown in the following figure using a CCD camera.

In this figure, the beam dump #1 is placed for dummping the laser for the other expetiment that is made on the same optical bench as the PD QE experiment, and the Irises are placed for dumping unnecessary light.

I plan to place HWPs and PBSs additionally and to measure the polarization and the laser power at the beginning of next week.

Current optical setup.
  2014   Tue Feb 9 00:00:11 2016 KojiNMiscPD QEMeasurement of a beam profile

For measuring  a current beam profile, the setup as shown in Fig. 1 was prepared.

At first, laser powers at Point 1 and 2 were measured and the results were

* at Point 1: 17.71 mW

* at Point 2: 16.15 mW

The difference may be come from the loss of HWP #2 and the beam damped by Iris.

(Laser power just in front of the Iris cannot be measured because of the space constraint.)

Then the beam profile was measured as shown in Fig. 2.

The measurement was perfomed from 0 cm to 25.4 cm (11 points) and in the measurement the angles of HWP #1 and #2 were 48.1 degree and 22.4 degree, repsectively.

(The zero point is set after the PBS as shown in Fig. 1.)

As shown in Fig. 2, the beam profile, in especially y-direction, seems to be a bit strange.

This is condiered to be an effect of a kind of saturation, but this is a just guess.

The measured data and the fitted curves are shown in Fig. 3. 

Fig. 1 Current setup.
Fig. 2 Beam profile measurement.
Fig. 3. Measured data and fitted curves.


Attachment 3: BeamAfterPBS.pdf
  2015   Wed Feb 10 00:17:31 2016 KojiNMiscPD QEAlignment of the single mode fiber and re-measurement of the beam profile

The beam measued yesterday was very elliptic.

Thus, for obtaining a round beam, we decided to use a single mode fiber.

The single mode fiber was aligned with KojiA's instruction.

(There is the specific method in the last of this log)

As a result, the obtained mode matching ratio was 64.5%. (Input power for the fiber was 18.7 mW, and output power of the fiber was 12.07 mW.)

Then, the setup as shown in Fig. 1 was prepared.

In this setup, the beam profile after the single mode fiber was measured as shown in Fig. 2.

When Fig. 2 is observed, there is still a kind of lines in the y-direction and we consider it comes from the problem of camera.

The measured data and fitted curves are shown in Fig. 3.(Zero point of the distance was set at the position of the collimator #2)


Specific method to align the single mode fiber

1. place the collimator #1 at the focal point of the laser

2. align the laser light (IR light) to the collimator #1 roughly with steering mirror

3. unset the collimator #2 and set a fiber illuminator instead of the collimator #2

4. at just after the Iris #2, align the laser from the fiber illuminator (Red light) to the IR light with knobs of the collimator #1 holder.

5. at just before the collimator #1, align the IR light to the Red light with the steering mirror #1

6. repeat step 4. and 5. a few times

7. unset the fiber illuminator and confirm the IR laser is ouput from the collimator #2. (If the IR light cannot be observed, go back to step 3.)

8. set a power meter after the collimator #2

9. maximize the IR light power using yaw knobs of the collimator #1 holder and the steering mirror #1

10. maximize the IR light power using pitch knobs of the collimator #1 holder and the steering mirror #1

11. repeat step 9. and 10.

12. If a good mode matching ratio can be obtained, this fiber alignment is finished. If the good mode matching ratio cannot be obtained, change the Lens #1 and re-start from step 1.

Fig. 1 current setup.
Fig. 2 Screen of the beam profiler.
Fig. 3 Measured data and fitted curves of the beam profile.


  2016   Thu Feb 11 00:03:24 2016 KojiNMiscPD QEBeam Adjustment

For adjusting the beam, the setup was prepared as shown in Fig. 1.

Our taget is 80 um beam waist in radius as shown in Fig. 2.

(Please note that the axes of Fig. 1 and Fig. 2 do not have the same zero point.)

The waist position is not much took care to if the position can be accessed easily.

In our simulation using the beam measured yesterday, when the lens #2 (f=-200 mm) and the lens #3 (f=150 mm) are placed at z = 0.260 m and z = 0.474 m, respectively, the target radius could be obtained at z = 0.74 m.

However, in this setup we cannot obtain the target beam and the waist size seemed to be larger and the waist position seemed to be farther.

Thus the lenses were moved iteratively.

Finally, the lens #2 and #3 are placed at z = 0.114 m and z = 0.483 m, respectively, and the measured beam is as shown in Fig. 3.

(The beam profiler seemed to be saturated. Thus the additional ND filter (O.D.=4.0) is put and the saturation seemed to be extinguished as shown in Fig. 4.)

As a result, the beam waist radius and the beam waist position are 86 um and z = 0.750 m (for the x-direction) and 89 um and z = 0.750 m (for the y-direction), respectively.

These parameters can still be improved by refining the positions of the lens #2 and #3.

Fig. 1 Current setup.
Fig. 2 Target beam.
Fig. 3 Measured data and fitted curves of the beam profile.
Fig. 4 Screen of the beam profiler.


  2017   Thu Feb 11 23:54:48 2016 KojiNMiscPD QEPolarization measurement

For measuring the polarization, the setup as shown in Fig. 1 was prepared.

The angle of the HWP #2 was 30 degree.

Rotating the angle of the HWP #3, I measured the laser power with a power meter and a PD.

And I fitted the measured data to the function, f(\theta) = a \sin^2(2(\theta-\phi)\pi/180)+b.

Here \theta is the angle of the HWP #3.

The result was shown in Fig. 2 and the paremeters were determined as

(with the power meter) a = 7.965 +/- 0.0005 mW, b = -0.002 +/- 0.003 mW, phi = -40.65 +/- 0.01,

(with the PD) a = 1373 +/- 3, b = -1 +/ 2, phi = 40.52 +/- 0.03. 

Accoding to this result, the S-pol. and the P-pol are obtained at 40.6 degree and 85.6 degree of the angle of the HWP #2, respectively.

And the calbration constant of the PD from voltage to power is determined roughly as 5.8*10^(-3) W/V. (Systematic errors have not yet been concerned.)

Fig. 1 Current setup.
Fig. 2 Measure data and fitted curves.


  2018   Sun Feb 14 01:04:07 2016 KojiNMiscPD QEMeasurement of PD reflectivities and PD efficiencies for P-pol. and S-pol.

According to the polariztion measurement, we found that the laser is not linear polarization.

Thus the QWP #2 was placed after collimator #2 as shown in Fig. 1 and the linear polarization laser was obtained.

Then the PD, C30665GH, with the glass window was set on the PD mount and placed at the center of the rotational stage as shown in Fig. 1.

The PD position is 5 cm after the beam waist and, at this position, the beam sizes in x-direction and y-direction are 215 um and 210 um, respectively.

In this setup, there are two reflected lights which may be come from the glass window and the PD.

Changing the laser incident angle to the PD, I measured the PD reflectivities and the PD efficiencies for P-pol. and S-pol.

The results are shown in Fig. 2 and Fig. 3.

The reason why the measurement end before the tasty part like ~40deg is that the beam is clipped.

Possibly, the light may already be clipped at ~25deg.

The alignment, i.e. the centering of the light to the PD, was optimized before the measurement as possible as we could.

The measurement was done only by rotating the rotational stage, i.e. I didn't use the steering mirror.

(Perhaps, I should use the steering mirror for optimizing the alignment at every angle.)

The incidnet power was 11.4 +/- 0.1 mW.

I meausred the powers of the one light, the other light (with the Iris #3), and the two lights (without the Iris #3) at all incident angles.

The errors in Fig. 2 is determined by the error of the measured incident and reflected light power. The position dependency on the power meter is not took into consideration.

When the PD responsivity for 1064 nm and the PD calibration constant (W/V) are 0.78 A/W and 5.8*10^(-3) W/V (see elog:2017), respectively, is assumed, the PD EQE is about 0.9 between -30 degree and 40 degree in the incident angle, according to

 Q = \frac{I \ h\ c}{\phi\ n\ e\ \lambda},

where I is the photocurrent, h is Planck's constant, c is the speed of light, phi is the incident power, n is the index of refraction of air, e is the elementary electronic charge, and lambda is the wavelength of the laser.

For calibrating the output voltage to EQE, the electric current must be known but, so far, I don't know the resistance in the photo detector circuit because the circuit is not made by myself. Thus I must investigate the circuit.

This is why I used "0.78 A/W" and "5.8*10^(-3) W/V" to estimate the current for a moment. The calibration constant "5.8*10^(-3) W/V" is determined without taking the errors, such as the position dependency on the power meter, the fluctuation of the laser light and so on, into consideration. (Of course, this is a problem.)

The errors in Fig. 3 is determined by the error of the reading error of the oscilloscope and the incident power. The position dependency on the power meter is not took into consideration.

Fig. 1 Current setup.
Fig. 2 Reflectivities for P-pol. and S-pol. between -25 degree and 30 degree in the incident angle. "Beam 1+2" means the measured power of the both reflected light and "Beam1+Beam2" means the sum of  "Beam1" and "Beam2".
Fig. 3 PD output voltage for P-pol. and S-pol. in the wide incident angle.


  2019   Tue Feb 16 23:51:31 2016 KojiNMiscPD QERe-measurement of the PD efficiencies for P-pol. and S-pol.

We aligned the single mode fiber again and We obtained the linear polarization without QWP as shown in Fig. 1.

P-pol. and S-pol. are able to be obtined at 34.8 deg and 81.0 deg in angle of HWP #3, respectively.

Then, We checked the PD read-out circuit and the circuit diagram is shown in Fig. 2.

Important resistanve values are as follows:

R4 = 20.2 Ohm, R5 = open, R11 = 1.000 kOhm, R16 = 9.82 kOhm, R7 = 50.2 Ohm.

In this circuit, the current generated by PD (I_PD) can be calibrated from the DC output voltage (V_out) using the following equation:

I_{\rm PD} = \frac{R_{11}}{R_4(R_{11}+R_{16})}V_{\rm out} = 4.57\times10^{-3} \left( \frac{V_{\rm out}}{1 {\rm V}}\right)

(In other words, the trans-impedance of the readout circuit is 219 Ohm.)

After that, we measured the DC output voltage at every 10 deg in the incident angle with the window glass as shown in Fig. 3.

The PD position is 5 cm after the beam waist and, at this position, the beam sizes in x-direction and y-direction are 215 um and 210 um, respectively.

The incident angle is determined with +/- 0.5 deg error by following way:

step1 (in this step, PD is alomost perpendicular to the beam) seeing reflected light from the PD, we centerd the beam to the PD using the steering mirror. 

step2 We miscenterd the beam to the border of the PD, and checked the incident angle seeing the reflected light. The incident angle was 0.5 deg (-0.5 deg in the opposite side.) Then the beam was re-centerd to the PD by the steering mirror.

step3 The PD is tilted by the rotational stage (the angle of the stage is called "alpha"), and, if the beam is miscenterd, we centerd the beam to the PD using steering mirror (the angle caused by the steering mirror is called "beta"). Thus the incident angle is "alpha + beta"

step4 Without touching the steering mirror, the PD is rotated to be perpendicular to the beam (i.e. "alpha" became 0 deg).

step5 We checked whether the beam is still on the PD or not (in today's measurement, the beam is on the PD in this step). If the beam is on the PD, the incident angle at step3 is estimated as follows,

alpha - 0.5 < alpha + beta (incident angle) < alpha + 0.5 (degree)

Therefore, the incident angle is determined with +/- 0.5 deg error.

We are going to measure again the reflectivity tomorrow with this method.

Fig. 1 Current setup.
Fig. 2 Readout circuit diagram.
Fig. 3 Measured DC output and EQE.


Attachment 3: D980454-00(QE).pdf
D980454-00(QE).pdf D980454-00(QE).pdf
Attachment 4: D980454-00(QE)_2.pdf
Attachment 5: D980454-00(QE).pdf
D980454-00(QE).pdf D980454-00(QE).pdf
  2020   Thu Feb 18 08:12:53 2016 KojiNMiscPD QERe-measurement of the reflectivities and the EQEs of the PD for S-pol and P-pol

The reflecrivities and the EQEs of the PD (C30665GH, with the glass window) for S-pol and P-pol were measured at every 10 deg in incident angle as shown in Fig. 1 and Fig. 2.

In this measurement, for alignmnet the steering mirror was used and it was confirmed that the beam was not clipped.

The EQE is obtained from the DC output voltage which was read from the oscilloscope using the following equation (see also elog2019):

{\rm EQE} = \frac{I_{\rm PD}hc}{\phi ne\lambda} = 5.32 \times 10^{-3} \left( \frac{V_{\rm out}}{1 {\rm V}} \right) \left( \frac{1{\rm W}}{\phi} \right),

where I_PD is the photocurrent, V_out is the DC output voltage, h is Planck's constant, c is the speed of light, phi is the incident power, n is the index of refraction of air, e is the elementary electronic charge, and lambda is the wavelength of the laser.

Fig. 1 Measured reflectivities for P-pol and S-pol.
Fig. 2 Determined EQEs for P-pol and S-pol.


Attachment 1: QE3.pdf
Attachment 2: QE_ll.pdf
  2022   Fri Feb 19 00:01:36 2016 KojiNMiscPD QERe-measurement of the reflectivities and the EQEs of the PD for S-pol and P-pol

I calculated IQEs using the measured EQEs and reflectivities and the following formula:

{\rm IQE} = \frac{{\rm EQE}}{1-R-T},

where R is the reflectivity of the PD, and T is the transmittance of the PD.

Here T is assumed to be zero and the scattering loss is ignored as you said.

The obtained IQEs are shown in Fig. 1.


Also the EQE, IQE, and reflectivity at a few angles near the angle where the EQE goes maximum for the P pol were measured as shown in Fig. 2 and Fig. 3.

The angle where the EQE goes maximum for the P pol is -51 deg.

So far, in these plots, the systematic errors because of the power meter are not considered.


And I replaced the figures with the figures having larger fonts.

Fig. 1 Measured EQEs and IQEs.
Fig. 2 Measured reflectivities around -51 deg.
Fig. 3 Measured EQEs and IQEs around -51 deg.

QE_Ref_P.txt QE_Ref_S.txt


Attachment 1: IQE.pdf
Attachment 2: Ref.pdf
Attachment 3: QE_Ref_P.txt
# angle(deg) 3beams(mW) error DCout(V) error
# incident power is 11.7 +/- 0.2 mW
-80.    4.6     0.1     0.14    0.02
-75.    3.52    0.02    1.02    0.02
-70.    1.24    0.02    1.58    0.02
-60.    0.627   0.002   2.04    0.02
-50.    0.244   0.002   2.12    0.02
-40.    0.410   0.002   2.10    0.02
-30.    0.512   0.002   2.04    0.02
-20.    0.851   0.002   1.98    0.02
... 13 more lines ...
Attachment 4: QE_Ref_S.txt
# angle(deg) 3beams(mW) error DCout(V) error
# incident power is 11.7 +/- 0.2 mW
-80.   6.61     0.03    0.04    0.02
-75.   6.17     0.03    0.52    0.02
-70.   5.29     0.02    0.98    0.02
-60.   3.40     0.02    1.42    0.02
-50.   1.85     0.02    1.70    0.02
-40.   1.78     0.02    1.84    0.02
-30.   1.372    0.004   1.90    0.02
-20.   1.293    0.004   1.92    0.02
... 13 more lines ...
Attachment 5: AroundPeak.txt
angle(deg) inc.pow.(mW,P) error Ref(mW,P) error DCout(V,P) error inc.pow.(mW,S) error Ref(mW,S) error DCout(V,S) error
-47 11.64 0.03 0.173 0.003 2.02 0.01 11.54 0.03 1.92 0.03 1.70 0.01
-49 11.46 0.02 0.375 0.004 1.99 0.01 11.60 0.03 2.12 0.04 1.66 0.01
-51 11.67 0.03 0.282 0.003 2.04 0.01 11.61 0.03 2.36 0.03 1.64 0.01
-53 11.56 0.02 0.325 0.003 2.00 0.01 11.35 0.03 2.59 0.04 1.56 0.01
-55 11.62 0.02 0.518 0.003 1.97 0.01 11.53 0.02 2.86 0.04 1.51 0.02
Attachment 6: QE2.pdf
  2023   Fri Feb 19 00:39:24 2016 KojiNMiscPD QEFirst QE measurement with the reflector

QEs (with the glass window) with the reflector were measured as shown in Fig. 1.

The radius of curvature of the reflector is 25 cm and the reflector was placed at a distance of 5 cm from the PD.

At the reflector position, the beam size is 403 um in x-direction and 391 um in y-direction.

And, at the PD position, the beam size of the light reflected by the reflector is 435 um in x-direction and 422 um in y-direction.

When Fig. 1 is observed, the QEs in S-pol are less enhanced than that in P-pol.

This is because there are a few lights which are reflected by the PD and have almost the same power, in other words in this measurement only one or two beams are re-input to the PD by reflector.

In fact, we can see the two peak output voltages of the PD when the reflector are rotated in the yaw direction.

Fig. 1 Measured enhenced and not enhanced QEs.


Attachment 1: QE_enh.txt
# angle(deg) enh.vol(V,P) error vol(V,P) error enh.vol(V.S) error vol(V,S) error
-15. 2.12    0.01    1.94    0.01    2.12    0.01    1.94    0.01
-30. 2.12    0.01    2.00    0.01    2.08    0.01    1.88    0.01
-45. 2.12    0.01    2.08    0.01    1.92    0.01    1.76    0.01
-60. 2.10    0.01    2.04    0.01    1.62    0.01    1.46    0.02
Attachment 2: QE_enh.pdf
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