40m QIL Cryo_Lab CTN SUS_Lab TCS_Lab OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop
 ATF eLog, Page 29 of 54 Not logged in
ID Date Author Type Category Subject
2613   Wed Jul 21 14:53:28 2021 KojiSummaryGeneralJul 17, 2021: Canon camera / small silver tripod / macro zoom lens / LED ring light borrowed -> QIL
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).

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]

• 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 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

OSEM LED/PD

• 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 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

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
178   Thu Jul 16 15:01:48 2009 Koji & Connor LaserPSLRazor Blades!

 Quote: 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.

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.

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.

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.

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.

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.)

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.

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.

D980454-00(QE).pdf

Attachment 3: D980454-00(QE).pdf
Attachment 4: D980454-00(QE)_2.pdf
Attachment 5: 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.

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.

AroundPeak.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.

QE_enh.txt

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
2024   Fri Feb 19 20:15:03 2016 KojiNMiscPD QEMeasurement of the reflectivity, EQE, and IQE of the PD without glass window

The glass window of the PD was removed and is placed in our shelf.

The reflectivity, EQE, and IQE of the PD were measured without the glass window as shown in following figures in the same setup as the measurements of the PD with glass window (see also elog2019, elog2020, and elog2022).

The laser power incident to the PD was 11.4 +/- 0.1 mW.

Attachment 1: Ref.pdf
Attachment 2: QE.pdf
Attachment 3: QE2.pdf
Attachment 4: Ref_QE_wow.txt
angle Ref(mW,P) error DC(V,P) error Ref(mW,S) error DC(V,S) error
-85 5.82 0.01 0.70 0.02 7.04 0.03 0.60 0.02
-80 4.05 0.02 1.34 0.02 4.72 0.01 1.22 0.02
-70 1.54 0.01 1.80 0.02 2.04 0.02 1.72 0.02
-60 0.532 0.002 1.98 0.02 .806 0.005 1.94 0.02
-50 0.197 0.002 2.06 0.02 0.408 0.002 2.02 0.02
-40 0.136 0.001 2.06 0.02 0.313 0.002 2.04 0.02
-30 0.217 0.001 2.06 0.02 0.363 0.001 2.06 0.02
-20 0.367 0.001 2.04 0.02 0.454 0.001 2.04 0.02
-10 0.480 0.001 2.02 0.02 0.504 0.001 2.02 0.02

... 11 more lines ...
Attachment 5: QE_cal3_NK.m
% EQE calculation
%V=input('input voltage (V): ');
filename='Ref_QE_wow.txt';
delimiterIn = ' ';

% filename1 = 'QE_Ref_P.txt';
% filename2 = 'QE_Ref_S.txt';
% filename3 = 'QE_enh.txt';

... 59 more lines ...
2025   Fri Feb 19 20:25:14 2016 KojiNMiscPD QEMeasurement of the enhanced QE of the PD without glass window

The enhanced QE of the PD without the glass window was measured in the same setup as elog2023.

Attachment 1: QE_enh.pdf
Attachment 2: QE_enh2.pdf
Attachment 3: QE_enh.txt
angle inc(mW,P) error DC(V,P) error enh(V,P) error inc(mW,S) error DC(V,S) error enh(V,S) error
-15 11.22 0.02 1.96 0.01 2.03 0.01 11.18 0.02 1.94 0.01 2.03 0.01
-30 11.12 0.02 1.98 0.01 2.02 0.01 11.12 0.02 1.96 0.01 2.02 0.01
-45 11.20 0.02 2.01 0.01 2.04 0.01 11.22 0.02 1.97 0.01 2.04 0.01
-60 11.29 0.01 1.94 0.01 2.04 0.01 11.20 0.02 1.88 0.01 2.03 0.01
-70 11.23 0.02 1.75 0.01 2.01 0.01 11.31 0.02 1.67 0.01 1.98 0.01
Attachment 4: QE_enh_ref.txt
angle inc(mW,P) error ref(mW,P) error inc(mW,S) error ref(mW,S) error
-15 11.42 0.01 0.434 0.001 11.44 0.01 0.487 0.001
-30 11.42 0.01 0.222 0.001 11.45 0.01 0.371 0.001
-45 11.40 0.01 0.143 0.001 11.46 0.01 0.348 0.001
-60 11.32 0.01 0.569 0.001 11.47 0.01 0.870 0.001
-70 11.23 0.01 1.58 0.01 11.27 0.01 2.06 0.01
Attachment 5: QE_enh_cal_NK.m
% EQE calculation
%V=input('input voltage (V): ');
filename='QE_enh.txt';
delimiterIn = ' ';

filename='QE_enh_ref.txt';
delimiterIn = ' ';

... 77 more lines ...
2027   Sun Feb 21 21:16:10 2016 KojiNMiscPD QEMeasurement of the enhanced QE of the PD without glass window

> My interpretation of this is that we get ~2% increase in the peak EQE for p-pol by doing the extra bounce. Is that correct? If so, its a pretty good result.

Your interpretation for the current result is collect. However, there are still several errors which aren't took into consideration, such as the error of the resistances and so on. Thus, for saying that the EQE is increased by about 2%, we must obtain more accurate data or analyse the results more preciselly.

> I wonder if you can do some more angles to see if there are any features in the angular dependence.

We plan to do a finer angular scan with the more accurate setup.

> It would also be interesting to modify the beam size to see if there is any change in the EQE. What is the estimated beam size now in the x & y directions? Does the reflected beam overlap the first beam? It would be good if the 2nd reflection from the PD can be steered to not go back into the fiber.

Actually, it is not easy to change the beam size immediatelly because the lenses and the PD are fixed. However, we plan to change the beam size for observing the BRDF. Thus in that time we will measure the EQE changing the beam size.

The estimated beam size of the first incident light on the PD is 215 um in the x direction and 210 um in the y direction, and the size of the second reflected light on the PD is 436 um in the x direction and 422 um in the y direction.

The second reflected light is aligned not to overlap the first incident light. However, so far, the distance of the two beams cannot not be measured because the second light is so weak that we cannot see.

> Is there a diagram with the reflector in place?

This is the diagram with the reflector.

> Is it possible to use the camera to take an image of the reflection from the PD? I wonder if its Gaussian or messy.

It's possible. We will measure the beam profile of the reflection light from the PD for confirming if the PD can be regarded to be well-polished and flat.

> What about repeating this experiment with the 1.5 micron laser now? Or maybe a HeNe where the IQE is lower?

For now, we don't have the plan to change the wavelength. Before the wavelength is changed, we would like to do the whole measurement includidng the noise estimation such as the back scattering noise. Once we establish the whole experimental method, we will change the wavelength and the PD.

Attachment 1: 2016_02_19_setup.pdf
2028   Sun Feb 21 21:53:04 2016 KojiNMiscPD QEMeasurement of the enhanced QE of the PD without glass window

If we want to check soon the EQE with a different beam size, we may want just to add (for a kind of quick check) an additional lens in the path without changing what we already have.

 Quote: > My interpretation of this is that we get ~2% increase in the peak EQE for p-pol by doing the extra bounce. Is that correct? If so, its a pretty good result. Your interpretation for the current result is collect. However, there are still several errors which aren't took into consideration, such as the error of the resistances and so on. Thus, for saying that the EQE is increased by about 2%, we must obtain more accurate data or analyse the results more preciselly. > I wonder if you can do some more angles to see if there are any features in the angular dependence. We plan to do a finer angular scan with the more accurate setup. > It would also be interesting to modify the beam size to see if there is any change in the EQE. What is the estimated beam size now in the x & y directions? Does the reflected beam overlap the first beam? It would be good if the 2nd reflection from the PD can be steered to not go back into the fiber. Actually, it is not easy to change the beam size immediatelly because the lenses and the PD are fixed. However, we plan to change the beam size for observing the BRDF. Thus in that time we will measure the EQE changing the beam size. The estimated beam size of the first incident light on the PD is 215 um in the x direction and 210 um in the y direction, and the size of the second reflected light on the PD is 436 um in the x direction and 422 um in the y direction. The second reflected light is aligned not to overlap the first incident light. However, so far, the distance of the two beams cannot not be measured because the second light is so weak that we cannot see. > Is there a diagram with the reflector in place? This is the diagram with the reflector. > Is it possible to use the camera to take an image of the reflection from the PD? I wonder if its Gaussian or messy. It's possible. We will measure the beam profile of the reflection light from the PD for confirming if the PD can be regarded to be well-polished and flat. > What about repeating this experiment with the 1.5 micron laser now? Or maybe a HeNe where the IQE is lower? For now, we don't have the plan to change the wavelength. Before the wavelength is changed, we would like to do the whole measurement includidng the noise estimation such as the back scattering noise. Once we establish the whole experimental method, we will change the wavelength and the PD.

2030   Mon Feb 22 23:51:18 2016 KojiNMiscPD QEBeam shape reflected by the PD

The beam shape reflected by the PD was measured.

The measurement was done 5 cm and 15 cm far from the PD at 15 deg, 45 deg, and 60 deg in incident angle.

(Please note that only at 15 deg, the measurement was done at 5 cm because of the space constraint.)

The results are shown in Figs. 1 and 2 and Tabs. 1 and 2.

When Figs. 1 and 2 are observed, the beam shape reflected by the PD looks still gaussian.

In the simulation, the beam size is estimated as, at 5 cm, 403 um in x-direction and 391 um in y-direction and, at 15 cm, 792 um in x-direction and 766 um in y-direction, respectively.

When Tabs. 1 and 2 are observed, the measured beam size looks not so different from the simulated one.

 15 deg 45 deg 60 deg 5 cm (6 cm) 470 um 406 um 411 um 15 cm 736 um 625 um 608 um

 15 deg 45 deg 60 deg 5 cm (6 cm) 522 um 489 um 491 um 15 cm 815 um 811 um 760 um

Attachment 1: BeamAt15deg15cm.pdf
Attachment 2: BeamAt45deg15cm.pdf
2031   Tue Feb 23 00:22:01 2016 KojiNMiscPD QERe-measurement of the QE of the PD without window glass

The QEs were measured again at every 10 deg incident angle.

The power meter to measure the incident angle was S401C (Thorlabs).

Output voltage was read by the degital multimeter 77 IV (Fluke).

The results are shown in Figs. 1--3.

(About the reflectivities, the data measured in elog2024 are used for now. Those data are obtained with S130C (Thorlabs. error is +/- 7%.))

In Fig. 3, the ratio of the enhanced QE and the not-enhanced QE is shown.

In these figures, the error of the S401C (3%), 77 IV (about 0.4% (depends on the measure value)), and resistances of the readout circuit (assumed to be 1%) are taken into consideration and they are assumed to be independent.

These results are consistent to the data we have measured by last week in the error.

Current errors of the EQEs in Figs. 1 and 2 about +/- 4% and they are mainly determined by the systematic error of the power meter.

Figure 3 claims that the QEs are improved with +/- 0.6% error using our new method.

Attachment 1: QE.pdf
Attachment 2: QE2.pdf
Attachment 3: QE3.pdf
Attachment 4: QE_enh.txt
angle inc(mW,P) error DC(V,P) error enh(V,P) error inc(mW,S) error DC(V,S) error enh(V,S) error
-10 11.45 0.3 1.914 0.007 2.000 0.007 11.48 0.3 1.915 0.007 2.003 0.007
-15 11.50 0.3 1.936 0.007 2.013 0.007 11.53 0.3 1.922 0.007 2.007 0.007
-20 11.56 0.3 1.950 0.007 2.010 0.007 11.62 0.3 1.939 0.007 2.012 0.007
-30 11.53 0.3 1.984 0.007 2.026 0.007 11.65 0.3 1.954 0.007 2.023 0.007
-40 11.55 0.3 2.001 0.007 2.029 0.007 11.58 0.3 1.968 0.007 2.029 0.007
-50 11.66 0.3 1.996 0.007 2.031 0.007 11.60 0.3 1.953 0.007 2.028 0.007
-60 11.67 0.4 1.938 0.007 2.030 0.007 11.68 0.4 1.888 0.007 2.026 0.007
-70 11.69 0.4 1.768 0.006 2.003 0.007 11.68 0.4 1.680 0.006 1.974 0.007
Attachment 5: Ref_QE_wow.txt
angle Ref(mW,P) error DC(V,P) error Ref(mW,S) error DC(V,S) error
-10 0.480 0.001 2.02 0.02 0.504 0.001 2.02 0.02
-15 0.434 0.001 2.02 0.02 0.487 0.001 2.02 0.02
-20 0.367 0.001 2.04 0.02 0.454 0.001 2.04 0.02
-30 0.217 0.001 2.06 0.02 0.363 0.001 2.06 0.02
-40 0.136 0.001 2.06 0.02 0.313 0.002 2.04 0.02
-50 0.197 0.002 2.06 0.02 0.408 0.002 2.02 0.02
-60 0.532 0.002 1.98 0.02 .806 0.005 1.94 0.02
-70 1.54 0.01 1.80 0.02 2.04 0.02 1.72 0.02
Attachment 6: QE_enh_cal_NK.m
%
filename='QE_enh.txt';
delimiterIn = ' ';

filename='Ref_QE_wow.txt';

phiP=A.data(:,2);

... 74 more lines ...
2033   Wed Feb 24 08:18:06 2016 KojiNMiscPD QESystematic error of the power meter (RM9, Ophir)

In the spec sheet, the systematic error of RM9 (power meter, Ophir) is 5%.

This is not very good.

However, the power meter was calibrated in the company at 808 nm wavelength and the deviation was 0.6%

This is very good.

If the 0.6% error could be applied to our power measurement, the systematic error would be improved.

Thus we inquired the error of RM9 to Ophir.

The answer was that the error is not 0.6% but is 5% at 1064 nm.

Attachment 1: RM9_RM9-PD_0.pdf
2034   Wed Feb 24 23:51:07 2016 KojiNMiscPD QETest of the BRDF measurement

For confirming if the BRDF of the PD (C30665GH) can be measured, the setup as shown in Fig. 1 is established.

For now, incident angle to the PD is 0 deg for simplicity.

The beam size on the PD (C30665GH) is estimated as 215 um in the x direction and 210 um in the y direction.

If the reflected light is incident to the lens, the light is focued at the PD (PDA100A).

For determining theta_s and aligning the lens, metal tube, and PD (PDA100A), the incident angle is set to theta_s/2 temporally and seeing the reflected light they are placed without PD.

Specifically, the reflected light is cented to the lens and the output of the tube.

After that, the PD (PDA100A) is placed and the incident angle is set to 0 deg.

The distance between lens and PD is 31 cm for theta_s>0, and 23 cm for theta_s<0.

These distances are determined by space constraint.

And also for space constraint, the BRDF cannot be measured at the theta_s beteween 40 and 80 deg.

The incident power is also measured by the PD (PDA100A).

The gain of the PD (PDA100A) was 0 dB at the incident power measurement and 70 dB at the scattered light power measurement.

The BRDF is obtained with folloing equation,

${\rm BRDF} = \frac{P_s}{P_i \cos \theta_i d\Omega} = \frac{P_s}{P_i \cos \theta_i (\pi r_l^2/d^2)}$,

where P_S is the power of the scatterd light, P_i is the power of the incident light, theta_i is the incident angle, dOmega is the solid angle of the detector, r_l is the radius of the lens, and d is the distance between the PD (C30665GH) and the lens.

With the setup and the method, the BRDF is measured for P-pol and S-pol as shown in Figs. 2 and 3.

The error of the Figs. 2 and 3 are determined by the systematic error of the PD and the distance error.

When Figs. 2 and 3 are observed, the BRDF looks to be able to be measured.

However the data quality can be improved.

Thus we are going to scan finer angles and change the incident angle from tomorrow.

Attachment 1: BRDF_mes.pdf
Attachment 2: BRDFat0deg.pdf
Attachment 3: BRDFat0deg2.pdf
Attachment 4: BRDFat0deg.txt
angle inc(V) zero sca(mV,P) sca (mV) zero dis(cm)
-90 5.43 0.026 330.0 336.9 328.7 23
-80 5.44 0.027 372.2 375.7 309.1 23
-70 5.44 0.026 295.8 295.1 292.9 23
-60 5.45 0.026 294.1 295.9 288.4 23
-50 5.43 0.027 289.1 288.9 285.2 23
-40 5.44 0.027 294.0 293.6 286.4 23
-30 5.44 0.026 296.3 292.8 282.1 23
-20 5.43 0.028 316.7 309.0 290.3 23
-10 5.44 0.026 366.4 365.7 292.9 23

... 4 more lines ...
Attachment 5: BRDF.m
% BRDF @ 0deg

filename='BRDFat0deg.txt';
delimiterIn = ' ';

G0=1.51*10^3; % V/A
EG0= 0.02; % %
G70=4.75*10^6; % V/A

... 25 more lines ...
2035   Fri Feb 26 10:00:18 2016 KojiNMiscPD QEBEDF measurement for wide angle

The BRDFs at 0 deg and 15 deg in incident angle were measured for the wide angle with the same way as elog2034 and Fig. 1 but finer scaning.

The results for P-pol and S-pol are shown in FIgs. 2 and 3.

It looks that there is no difference for polarization.

The tendency that the BRDF increases from -75 deg is consistent to the previous result of the BRDF measurement of the viewport used in LIGO.

Between -40 deg and -70 deg, we face the sensitivity limit of the PD (PDA100A). (In this range, the estimated power is 1 nW and the power range of the PDA100A is 500 pW in the specsheet.)

For comparing the two BRDF, the BRDF plot in which the BRDF at 15 deg incident angle is shifted by 30 deg is shown as Fig. 4.

In this plot, the BRDF for P-pol is picked.

It looks that there is no difference between 0 deg and 15 deg in incident angle from -40 deg to 40 deg.

Attachment 1: BRDF_setup.pdf
Attachment 2: BRDFat0deg_log.pdf
Attachment 3: BRDFat30deg_log.pdf
Attachment 4: BRDF_log_P.pdf
2036   Fri Feb 26 23:13:02 2016 KojiNMiscPD QEBRDF measurement around the peak

The BRDF of the PD (C30665GH) for 15 deg incident angle was measured arond the peak with the same was as elog2035 and elog2034 but with the additaional Iris as shown in Fig. 1.

For calculating the BRDF. the fomular in elog2034 is used.

(Please note that r_l becoms the radius of the Iris in front of the PDA100A and d becomes the distance between PD (C30665GH) and the Iris)

The Iris diameter is 3.5 mm.

There is no difference for polarization as the wider scan.

The result for p-pol is shown in Fig. 2 with the wider scan (the relsult of the elog 2034). This result was wrong.

There is a asymmetry around the -30 deg and the data around -35 deg are not consistent to the previous data.

We think these are come from the slight tilt of the Iris.

We will confirn that after tomorrow.

Attachment 1: BRDF_log.pdf
Attachment 2: BRDF_setup_fine.pdf
2037   Sun Feb 28 15:47:06 2016 KojiNMiscPD QEBRDF measurement around the peak

The result shown in the elog2036 looks not to consistent to the previous result.

Thus we checked the alignment of the Iris.

First, the effect of the tilt of the Iris was checked and it was found that the tilt effect is very small.

Second, we found that the center of the Iris was off from the center of the lens.

This off effect is dominant in the BRDF measurement.

The off was about 1 mm. However, the diameter of the Iris was 3.5 mm and 1 mm is about 30% and large to 3.5 mm.

Thus we re-align the Iris and measure the BRDF of the PD (C30665GH) at the 15 deg incident angle again as shown in Fig. 1.

Figure 1 shows that the new result is consistent to the previous wide range measurement in the error.

The reason why the error at -29 deg and -31 deg is very large is the effect of the main reflected beam.

The result that the new data arond peak and the previous wide range data are combined for p-pol and s-pol is also attached.

Note that the incident beam is at 0 deg and the angle is that we must take care in terms of the back scattering.

Attachment 1: BRDF_log_compare.pdf
Attachment 2: BRDF_log_all_wide.pdf
Attachment 3: BRDF_log_all_narrow.pdf
Attachment 4: BRDFat30deg.txt
angle inc(V) zero sca(mV,P) sca (mV) zero dis(cm)
-70 5.43 0.029 280.8 280.2 276.2 23
-60 5.44 0.030 280.3 282.1 271.8 23
-50 5.44 0.030 283.0 284.2 266.7 23
-45 5.45 0.029 311.5 317.2 267.2 23
-40 5.43 0.029 348.1 350.1 267.1 23
-35 5.44 0.029 468.6 470.1 263.9 23
-25 5.43 0.027 440.3 439.7 270.6 23
-20 5.43 0.028 349.5 349.1 278.6 23
-15 5.45 0.029 329.5 324.3 278.5 23

... 3 more lines ...
Attachment 5: BRDFat30deg_again.txt
angle inc(V) zero sca(mV,P) sca (mV) zero dis(cm) d(cm)
-35 5.44 0.029 276.5 276.5 261.4 23 0.35
-36 5.44 0.027 288.2 289.1 276.4 23 0.35
-37 5.43 0.028 293.6 291.3 280.5 23 0.35
-23 5.43 0.027 295.2 295.1 277.6 23 0.7
-25 5.43 0.030 290.2 287.2 283.2 23 0.35
2038   Mon Feb 29 08:19:53 2016 KojiNMiscPD QEMeasurement of the reflectivity, EQE, and IQE of the PD without glass window

The reflectivity of the PD (C30665GH) at 15 deg incident angle was measured precisely with PDA100A as shown in Fig. 1.

Ref_wow_again.txt

Attachment 1: Reflectivity.pdf
Attachment 2: Ref_wow_again.txt
angle inc(V) zero ref(V,P) ref(V,S) zero
-80 5.40 0.030 2.33 2.89 0.030
-70 5.42 0.030 0.919 1.205 0.029
-60 5.41 0.030 0.335 0.498 0.027
-50 5.42 0.030 0.141 0.262 0.027
-40 5.43 0.028 0.107 0.215 0.024
-30 5.42 0.029 0.153 0.241 0.021
-20 5.42 0.030 0.234 0.282 0.022
-15 5.43 0.030 0.271 0.301 0.023
-10 5.43 0.027 0.302 0.317 0.024

... 9 more lines ...
2039   Tue Mar 1 09:12:51 2016 KojiNMiscPD QEMeasurement of the BRDF with the Iris in the incident path

The BRDF at 15 deg incident angle with the Iris in the incident path was measured for p-pol with the same way as elog2034.

(Please note that, in this measurement, d is the distance between the PD (C30665GH) and the Iris in fron of the PDA100A.)

The setup is shown in Fig. 1.

The result is shown in Fig. 2.

Figure 2 indicates that the Iris reduced the BRDF by about 10 times.

Attachment 1: BRDF_setup.pdf
Attachment 2: BRDF_withIris.pdf
2040   Tue Mar 1 09:55:28 2016 KojiNMiscPD QEEstimation of the back scattering

In terms of the BRDF, the mount of the back scattering of our technique can be estimated using the result of elog2038 and elog2039.

In our new technique, there are two effect of the back scattering:

1. the first incident light effect,

2. the second reflection light effect.

If the reflector is placed on the 5 cm far from the PD, the two effect is estimated as follows.

The BRDF of the first effect is roughly estimated as 5*10^(-5) [1/st] form the result around 0deg of elog2039.

The BRDF of the second effect is roughly estimated as 1.5*10^(-4) (= 3*10^(-3) * 0.05) [1/st] from the result at 31 deg of elog2039 (2*10^(-3) [1/st]) and the reflectivity at 15 deg of elog2038 (0.05).

The Iris 1 diameter was 1.4 mm.

For confirming this estimation is reasonable, the back scattering effect was measured with the setup as shown in Fig. 1.

In this setup, the PBS and the QWP are used as a isolator.

The Iris 1 is place on the beam waist.

We measured with/without Iris 1 and with/without the reflector, i.e. in four pattern.

For calculating the BRDF, the formula in elog2034 is used.

For r_l, the Iris radius in front of the PDA100A (5.83 mm) is used and, for d, the distance between the PD (C30665GH) and the Iris in front of the PDA100A (35.56 cm) is used.

The result is shown in Fig. 2.

Taking the difference of the result between w/ Iris, w/o reflector and w/ Iris, w/ reflector, we can obtain the effect of the reflector, i.e. the second effect.

The difference is (1.0 +/- 0.8)*10^(-4) [1/st].

This is comparable of the upper estimation.

From these estimations, the second effect is larger by a factor of two or three.

However, considering the BRDF result arond the peak of elog 2039, we can reduce the second effect easily and dramatically by the reflector placed closer to the PD (e.g. 2.5 cm).

We will check this with more precise measurement.

Attachment 1: BackSca_setup.pdf
Attachment 2: BRDF_enh.pdf
Attachment 3: BRDF_enh2.txt
cond sca(mV) error zero(mV) dist(cm) d(cm)
incident power was 5.44 V (PDA100A gain 0 dB)
1 337.0 0.4 284.1 35.56 1.166
2 324.0 0.2 246.0 35.56 1.166
3 327.6 0.2 251.2 35.56 1.166
4 329.4 0.2 250.8 35.56 1.166

2041   Wed Mar 2 10:17:56 2016 KojiNMiscPD QEMeasurement of the BRDF with the Iris in the incident path

With the chopper, the BRDF at 15 deg incident angle with the Iris on the laser path was measured again.

This is because the BRDF with the Iris on the laser path was limited by the sensitivity even at the scattering angle very close to the peak (e.g. 35 deg).

The setup up is shown in Fig. 1.

The diameter of the Iris2 was 7 mm at -25, -27, and -33 deg, and was 3.5 mm at -29 and -31 deg.

In angles wider than -35 deg, the Irs 2 wad removed for obtaining larger light and the lens diameter is 1.905 cm.

We determined the choppwer frequency as 253 Hz, considering the PD dark noise.

The PD dark noise at 253 Hz is about 100 uV as shown in Fig. 2.

The peak value at 253 Hz is read and the value is calbrated to the voltage of the PD.

The calibration constant is determined cahnging the laser power and measureing the DC value of the PD (without chopper) and the peak value of the FFT analyzer and the constant is determined as 0.80 +/- 0.01. (from FFT to PD)

The result of the BRDF is shown in Fig. 3.

Attachment 1: BRDF_chopper_setup.pdf
Attachment 2: BRDF_with_chopper.pdf
Attachment 3: PD_darknoise.pdf
2042   Wed Mar 2 13:07:36 2016 KojiNMiscPD QEDistance between the 1st incident beam and the 2nd reflected beam

Using the setup for the measurement of the back scattering (in elog2040), the relative distance between the 1st incident beam and the 2nd reflected beam was measured.

First, the 1st incident beam position was detemined by aligning the reflector and overlapping the 2nd reflected beam on the 1st incidnet beam with the monitor of the value of the multimeter ("worst angle").

After that, the reflector was aligned onto the point that the back scattering is smallest and the relative angle of the knob of the reflector mount was noted ("best angle").

Using the value of the relative angle and some geometrical features of the mount, the relative reflector angle between "worst angle" and "best angle" was determined 0.4 degree, i.e. the incident angle to the reflector was 0.4 deg.

From this value, relative distance between the 1st incident beam and the 2nd reflected beam on the PD was determined 0.8 mm as shown in Fig. 1.

And the 1st incident beam and the 2nd reflected beam on the Iris was determined as 1.6 mm.

This means the main reflected beam was dumped by the Iris. (The Iris apature radius is 0.65 mm.)

The distance on the PD is designed as 1 mm.

The design value and the measured value is consistent.

For obtainning the design value, the 1st incident beam should be miscentered a bit more.

Attachment 1: Beam_Position.pdf
2043   Wed Mar 2 14:38:31 2016 KojiNMiscPD QEMeasurement of the reflectivity, EQE, and IQE of the PD without glass window

Using the improved reflectivity measurement, the IQE is calculated again (see also elog2031).

The QEs are calcurated with the same way as elog2020 and elog2022 and the results are shown in Figs. 1 and 2.

Figure 1 shows that, for p-pol, the not-enhanced EQE and the IQE are 0.90 +/- 0.03 and 0.94 +/- 0.04 at 15 deg, respectively.

Figure 2 shows that, for p-pol, the EQE is enhanced 4.0 +/- 0.4% and, between 30 deg and 50 deg, the EQE is enhanced almost up to the IQE.

Attachment 1: QE3.pdf
Attachment 2: QE_ratio2.pdf
2045   Sat Mar 5 01:42:02 2016 KojiNMiscPD QEMeasurement of the BRDF with the Iris in the incident path

The BRDF with Iris was measured with the chopper and FFT analyzer again because in the previous measuremt it is suspected that there may be a beam clip.

This time, the BRDF was measured after is is confirmed that the are no clipping using a IR view.

The result is shown in Fig. 1.

The error estimation has not yet be done.

The two data shown in Fig. 1 are consistent in the skirt ares by are not consistent arond the peak.

Thus, we checked the clipping effect by making a clip intentionally and measuring the BRDF at several point.

When there is a clip, the previous BRDF is reproduced.

There, we conclude that there was a clip in the previous measurement.

Attachment 1: BRDF_with_chopper.pdf
2047   Sun Mar 6 10:19:14 2016 KojiNMiscPD QEEstimation of the back scattering

(This is the work on Thursday.)

Background:

We observed large discrepancy of the back reflection between the values measured with a BS and estimated from the BRDF. The back-scattering from the PD (C30665GH) without the reflector measured in elog2040 (2*10^(-3) [1/sr]) was about 40 times larger than the value expected from the BRDF measurement (elog20455*10^(-5) [1/sr]). We thought this came from the ampbient light, scattering from other optics (e.g. PBS), and scattering from the chopper. We tried to measure the back reflection again with a refined setup.

What we did:

As the first attempt, for dumping the scattering light from the chopper, a "wall" to dump the light with the aluminum foil was mede and was placed between the lens and PBS as shown in Fig. 1. Before the wall was placed, the back reflection was about 162.6 mVrms (PDA100A gain 70dB). After the wall was placed, the back reflection was improved to about 82.5 mVrms (PDA100A gain 70dB).

Secondly, the chopper was tilted to reduce the direct reflection. Then the back reflection was reduced to about 3.48 mVrms (PDA100A gain 70dB).

Thirdly, we found that the incident beam was clipped at the incident Iris and the level was 0.4% in terms of the transmitted light power. (The Iris had been opened 1.2 mm in diameter.) The clip was small but could not be negligible. Thus we opened the Iris to 1.8 mm in diameter and the clip level was less than 0.1%, which is the detection limit of the degital multimater used to measure the output signal of the PD (C30665GH).

In order to obtain a reference calibration, we placed an HR mirror right before the target PD and measured the reflected power on the measurement PD (PDA100A).

All the numbers were measured with an FFT analyzer to read the peak value at the chopping frequency.

After that, we measured the back reflection with the same way as elog2040.

Measurement:

We measured the back scattering in following conditions:

1. d_ref = 5 cm, theta_ref = 0.8 deg, without the reflector,

2. d_ref = 5 cm, theta_ref = 0.8 deg, with the reflector,

3. d_ref = 5 cm, theta_ref = 1.7 deg, without the reflector,

4. d_ref = 5 cm, theta_ref = 1.7 deg, with the reflector,

5. d_ref = 2 cm, theta_ref = 4.3 deg, without the reflector,

6. d_ref = 2 cm, theta_ref = 4.3 deg, with the reflector,

where the paremeters are explanes in Fig. 2. In conditions 3--6, using the CCD camera, the primary incident beam on the PD aligned was  on 1 mm far from the boundary of the PD, i.e. the beam was aligned at 0.5 mm off from the center of the PD as shown in Fig. 2. (I'm sorry but in the condition 1 and 2 the beam position was unknown.) The theta_ref is determined as widely as we can keeping the output signal of the PD (C30665GH) maximum.

For calculating the BRDF. the fomular in elog2034 is used.

(Please note that r_l becoms the radius of the Iris in front of the PDA100A and d becomes the distance between PD (C30665GH) and the Iris)

The Iris diameter was 1.143 cm, the distance between PD (C30665GH) and the Iris, d, was 43.1 cm.

Result:

The measured value with HR mirror in front of the PD (C30665GH) was 2.400 Vrms (PDA100A gain was 0 dB.)

The voltages measured in the conditions were as follows (PDA100A gain was 70 dB).

1: 3.192 +/- 0.007mVrms

2: 27.3 +/- 0.01 mVrms

3: 3.347 +/- 0.004 mVrms

4: 3.786 +/- 0.008 mVrms

5: 3.881 +/- 0.009 mVrms

6: 3.846 +/- 0.007 mVrms.

The BRDF results are shown in Figs. 3 and 4.

The error estimation was not yet be done.

Discussion:

* Primary incident beam effect

When we see the values measured in the condtions 1, 3, and 5, the primary incident beam effect is about 8*10^(-4) [1/sr] which is still larger about 10 times larger than the expected value from the  BRDF measurement, 5*10^(-5) [1/sr].

This means that, for observing the back reflection of the primary incident beam, we must reduce the noise, i.e. the scattering which does not come from the PD.

* Secondary reflected beam effect

When we see the the gaps of the value between condition 1 and 2, between 3 and 4, and between 5 and 6, when theta_ref is made larger, the secondary reflection beam effect was reduced.

The difference between condition 3 and 4 is 1.1*10^(-4) [1/sr] and the expected secondary reflection light effect from the BRDF measurement was 0.8*10^(-4)  [1/sr].

They look consistent.

The difference between condition 5 and 6 can not be seen in current sensitivity and the expected secondary reflection light effect from the BRDF measurement was 1*10^(-5) [1/sr]

Thus it is reasonable that there is no difference between 5 and 6.

The difference between 3 and 5 is considered to come from the laser power drift.

Therefore, the secondary reflected beam effecte can be explained with the BRDF measurement.

Attachment 1: setup.pdf
Attachment 2: ref_ps.pdf
Attachment 3: Backscat.pdf
Attachment 4: BackScat2.pdf
2048   Mon Mar 7 15:34:46 2016 KojiNMiscPD QEBack reflection measurement with the chopper

Background:

We are still suffering from excess amount of back reflection compared with the predicted number from the BRDF measurement. Assuming this light is not coming from the target PD, we want to reduce the scattering from other optics. As an attempt, we decided to use a BS instead of the combination of a cube PBS and a QWP. This way we can reduce the number of the optics involved, particularly the PBS which may cause more scattering than others.

What we did:

The PBS and the QWP were removed, and then a 50:50 BS was inserted as shown in Fig. 1.

The distance between the target PD and Iris2 was measured to be 38.1 cm. The diameter of Iris2 was set to be 7 mm.

As a part of the calibration, the incident power on the target PD was measured using PDA100A (Gain 0dB). The measured value was 3.973 V with no chopper blocking the beam.

An HR mirror was then placed before the target PD to measure the reflected light power with the chopper still halted and the iris 1 is oped using PDA100A (Gain 0dB) which is placed at the position as shown in Fig. 1. It was measured to be 1.253 V. This means that the reflectivity of the BS is about 0.315. This reduction is considered to be the clipping at Iris1 as the returning beam has the bigger beam size (i.e. the iris worked as a sort of mode cleaner).

(==> There might be a misunderstanding because of my not clear explanation. So, I edited this paragraph again. KN)

Then, the chopper was started at 253 Hz. The reflected light from the HR mirror was measured using a FFT analyzer to be 642 mVrms (PDA100A gain 0 dB).
(==> mVrms? KA ==> mVrms. I fixed. KN)

Throughout the measurement, the opening of Iris1 was adjusted such that the clip level was less than 0.1% of the incident power (see also elog2047).This yielded the Iris1 diameter of 1.8 mm.

Finally, the back reflection was measured in the same way as elog 2040 , and also with Iris1 opend as much as possible.

Result:

The measured voltage with Iris1 with the diameter of 1.8 mm: 720 uVrms (PDA100A gain 70 dB)
==> This corresponds to the BRDF of 1.4 x 10-3 [1/sr].

The measured voltage with Iris1 completely open: 640 uVrms (PDA100A gain 70 dB)
==> This corresponds to the BRDF of 1.2 x 10-3 [1/sr].

These values are much (x40) larger than the BRDF value expected from the BRDF measurement (5x10-5 [1/sr], see also elog2045).
In fact, these are much (x2) larger than the ones with the PBS & the QWP (8x10-4 [1/sr], see also elog 2047).

(It is not so clear how these numbers were calculated. How these calibrations were used? How did you incorporate the BS transmissivity and reflectivity??? KA)

==> For calculating the BRDF, the fomular as shown elog2034 is used. Seeing the fomular, we need the ratio of the incident light power and the scattered (reflected, in this measurement) light power, the incident angle, and the solid angle. The ratio of the incident light power and the scattered light power can be obtained by taking the ratio of the measured voltage with the chopper as a part of the calibration, Vin (642 mVrms), and the measured voltage with Iris1 with the diameter of 1.8 mm (720 uVrms) or with Iris1 completely open (640 uVrms), Vsca, considering the difference of the PDA100A gain. In this calculation the BS reflectivity and transmissivity do not appear, see also Fig. 2. In addition, using the incident angle, 15 deg, and the solid angle from the PD(C30665GH) to the Iris2, 2.6x10-4 sr, the BRDF can be calculated.

And when the Iris was closed, the value was larger. This means that the Iris may make a scattering.
(==> This didn't make sense compared with the numbers above. KA ==> The numbers were written conversely. I fixed. KN)

[Ed.: KA]

Attachment 1: setup.pdf
Attachment 2: BRDF_cal.pdf
ELOG V3.1.3-