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  25   Tue Oct 9 05:03:15 2012 KojiElectronicsGeneralOMC Test Electronics Setup


Attachment 2: electronics_setup.pdf
  70   Thu Mar 14 17:06:21 2013 KojiMechanicsGeneralOMC SUS work @LLO

EDIT (ZK): All photos on Picasa. Also, I discovered that since Picasa was migrated to Google+ only,
you no longer have the option to embed a slideshow like you used to. Lame, Google.

Photos sent from Zach



  277   Tue May 16 19:05:18 2017 KojiOpticsConfigurationOMC SN002 fix - temporary optics

Working on the SN002 OMC fix. Checked the inventory. I think I am using C8 mirror as the new temporary CM1 and PZT24 as the new temporary CM2.

  108   Thu Apr 11 15:10:22 2013 KojiGeneralGeneralOMC Progress

[Zach, Jeff, Koji]

- Jeff configured the bottom side template to have a nominal value
obtained from the solid works model. Note that the thickness of the
curved mirrors are 6mm in the model. He added 0.3mmx2 to the dimensions.

- Jeff located the template on the breadboard such that each side has
the same amount of hanging out.

- Micrometer values

  • The one closest to the input mirror (CM1) 0.07
  • The other one on CM1 0.24
  • The one closest to the output mirror (CM2) 0.17
  • The other one on CM2 0.30

0.17         0.07
0.30         0.24

- Now the template is ready to accept the OMC optics.


- Zach and Koji finished a series of measurements for the test OMC.

Modulation depth:

- We scanned the laser PZT and recorded the data.
CH1: Reflection DC
CH2: PDH Error
CH3: Transmission (Magnified)
CH4: Transmission

- We should be able to obtain the estimation of the modulation depth and the finesse from this measurement.

- Rough calculation of the modulation depth is 0.19


- Incident 16.3mW
- Transmission 15.1mW
- This gave us the raw transmission of 92.6%ish.
- The modulation depth of 0.19 corresponds to 1.8% of the incident power
- The carrier reflection is almost dominated by the mode mismatch. (Note: We did not have a good resolution for the refl beam)  =>3.2%

- In total:The incident useful carrier power was 15.4mW ==> Throughput 98%
- There is slight headroom to increase the transmission by cleaning the mirrors.


- As our AOM is not functioning now, phase modulation sidebands are injected with the BBEOM.
- In principle, we can't expect any signal at the transmission at around the FSR frequency.
- If we apply small locking offset, the split peaks appear at the FSR frequency. The frequency of the dip corresponds to the FSR.
- We probably can extract the finesse of the cavity from this measurement. Lisa is working on this.


- The same PM injection gives us the frequency of the HOMs.
- We found that our EOM can work until ~500MHz.
- We could characterize the cavity resonance structure more than a single FSR.

  1   Fri Jun 15 15:45:49 2012 KojiGeneralGeneralOMC Plan

LIGO Document G1200683-v1:
aLIGO OMC fabrication and testing plan

aLIGO OMC wiki

  382   Tue Oct 22 10:25:01 2019 StephenGeneralGeneralOMC PZT Assy #9 and #10 Production Cure Bake

OMC PZT Assy Production Cure Bake (ref. OMC elog 381) for PZT Assy #9 and #10 started 27 September 2019 and completed 28 September 2019. Captured in the below figure (purple trace). Raw data has been posted as an attachment as well.

We have monitored the temperature in two ways:

1) Datalogger thermocouple data (purple trace).
2) Checking in on temperature of datalogger thermocouple (lavender circles) and drive thermocouple (lavender diamonds), only during initial ramp up.

Comments on bake:

  • No changes were made to the tuning or instrumentation of the oven between the successful qualifying bake obtained on 26 September (ref. OMC elog 380). However, the profile seems to have been more similar to prior qualifying bake attempts that were less successful (ref. OMC elog 379), particularly as the oven seems to have ramped to an overtemperature state. I am a bit mystified, and I would like to see the oven tuning characterized to a greater extent than I have had time and bandwith to complete within this effort.
  • The maximum datalogger temperature was 104 °C, and the duration of the soak (94 °C or higher) was 68 minutes. This was in contrast to a programmed soak of 2.5 hours and a programmed setpoint of 84 °C.
  • The drive thermocouple did appear to be under-reporting temperature relative to the datalogger thermocouple, but this was not confirmed during the soak period. Neither thermocouple was calibrated as part of this effort.


Attachment 1: OMC_ABO_PZT_Curing_Bake_effort_201906_thru_201909.xls
Attachment 2: production_cure_bake_pzt_assys_9_and_10_20190927.png
  43   Thu Nov 29 21:18:23 2012 KojiOpticsGeneralOMC Mounting Prisms have come



  235   Thu Aug 20 01:35:01 2015 KojiElectronicsGeneralOMC DCPD in-vacuum electronics chain test

We wanted to know the  transimpedance of the OMC DCPD at high frequency (1M~10M).
For this purpose, the OMC DCPD chain was built at the 40m. The measurement setup is shown in Attachment 1.

- As the preamp box has the differential output (pin1 and pin6 of the last DB9), pomona clips were used to measure the transfer functions for the pos and neg outputs individually.

- In order to calibrate the measurements into transimpedances, New Focus 1611 is used. The output of this PD is AC coupled below 30kHz.
This cutoff was calibrated using another broadband PD (Thorlabs PDA255 ~50MHz).

Result: Attachment 2
- Up to 1MHz, the transimpedance matched well with the expected AF transfer function. At 1MHz the transimpedance is 400.

- Above 1MHz, sharp cut off at 3MHz was found. This is consistent with the openloop TF of LT1128.


Attachment 1: OMC_DCPD_Chain.pdf
Attachment 2: OMC_DCPD_Transimpedance.pdf
  236   Wed Aug 26 11:31:33 2015 KojiElectronicsGeneralOMC DCPD in-vacuum electronics chain test

The noise levels of the output pins (pin1/pin6) are measured. Note that the measurement is done with SE. i.e. There was no common mode noise rejection.

Attachment 1: OMC_DCPD_OutputNoise.pdf
  155   Thu Aug 22 15:34:03 2013 KojiOpticsGeneralOMC Cavity side gluing

[Koji Jeff]

o BS1, FM1, FM2 prisms were glued
=> This fixed the unstability of the OMC locking

o Checked the spot position on the curved mirrors.

The height of the template was measured to be 6.16mm.
Using a sensor card, the heights of the spots on the curved mirrors were measured to be 7.4mm (CM1) and 7.9mm (CM2).
This means that the beam is ~1.5mm too low.

When the post clamps were applied to the PZT assemblies, the spot positions moved up a little bit (7.9mm - CM1, 8.2mm - CM2).
This is still ~1mm too low.

We can accommodate this level of shift by the curved mirror and the prisms.
We'll try other PZT assemblies to see if we can raise the beam height.

  110   Sat Apr 13 21:06:02 2013 KojiOpticsGeneralOMC Bottom-side: cavity glued

[Jeff, Zach, Lisa, Koji]

Gluing of the cavity mirrors went very well!!!


- Checked if the cavity is still resonating. => Yes.

- Checked the FSR: 264.251MHz => 1.1345m
  2.5mm too long => Move each micrometer by 0.625mm backward

  Aligned the cavity again and checked the FSR: 264.8485MHz => 1.13194m
  TMS(V): 58.0875MHz => gamma_V = 0.219324
  TMS(H): 58.1413MHz => gamma_H = 0.219526
  the 9th modes of the carrier is 9.7-10.4 line width (LW) away from the carrier resonance
  the 13th modes of the lower f2 sideband are 9.2-10.2 LW away
  the 19th modes of the upper f2 sideband are 0.3-1.8 LW away
  We found that this coincidence of the resonance can be corrected by shortening the cavity round-trip by 0.5mm

- Spot positions (I)
The spots on the curved mirrors were ~1mm too much inside (FM side). In order to translate the cavity axis,
  MM2 and MM4 were pushed by θ
  θ/2.575 = 1mm ==> θ = 2.6 mrad
  The separation of the micrometers are ~20mm
  d/20mm = 2.6mrad ==> d = 52um

  1div of the micrometer corresponds to 10um => 5div = 50um

- Move the micrometers and adjusted the input steering to recover the alignment.

- In any case we were confident to adjust the FSR/TMS/spot positions only with the micrometers

BS1/FM1/FM2 gluing

- Aligned the cavity

- Glued BS1/FM1/FM2 one by one while the cavity resonance was maintained.
  FM2 was slipping as the table is not leveled well and the fixture was not supporting the optic.

  FSR: 264.964875MHz => 1.13144m (Exactly 0.5mm shorter!)
  TMS(V): 58.0225MHz => gamma_V = 0.218982
  TMS(H): 58.1225MHz => gamma_H = 0.219359
  the 9th modes of the carrier is 10.3~11.7 LW away
  the 13th modes of the lower f2 sideband are 7.4~9.3 LW away
  the 19th modes of the upper f2 sideband are 1.5~4.4 LW away

- Spot positions (II)
  Looked OK.

CM2 gluing

- Glued CM2. The mirror was supported from the back with allen keys.

FSR: 264.9665625MHz => 1.13144m
  TMS(V): 58.1275MHz => gamma_V = 0.219377
  TMS(H): 58.0813MHz => gamma_H = 0.219202
  the 9th modes of the carrier is 10.2~10.9 LW away
  the 13th modes of the lower f2 sideband are 8.5~9.4 LW away
  the 19th modes of the upper f2 sideband are 1.4~2.7 LW away

- Spot positions (III)
  Looked slightly off at CM2. Pushed MM2 by 4um.

CM1 gluing

- Glued CM1.

FSR: 264.964875MHz => 1.13144m
  TMS(V): 58.06625MHz => gamma_V = 0.219145
  TMS(H): 58.08625MHz => gamma_H = 0.219220
  the 9th modes of the carrier is 10.8~11.1 LW away
  the 13th modes of the lower f2 sideband are 8.2~8.6 LW away
  the 19th modes of the upper f2 sideband are 2.6~3.2 LW away

- Spot positions (final confirmation)
  Looked OK. 

Final measurement

- After everything was finished, more detailed measurement has been done.

- FSR&TMS (final)
FSR: 264.963MHz => 1.13145m
  TMS(V): 58.0177MHz => gamma_V = 0.218966
  TMS(H): 58.0857MHz => gamma_H = 0.219221
  the 9th modes of the carrier is 10.8~11.7 LW away
  the 13th modes of the lower f2 sideband are 7.3~8.6 LW away
  the 19th modes of the upper f2 sideband are 2.6~4.5 LW away

Final values for the micrometers

  • MM1: The one closest to the input mirror (CM1) 0.78mm
  • MM2: The other one on CM1 0.89
  • MM3: The one closest to the output mirror (CM2) 0.90
  • MM4: The other one on CM2 0.90

0.90         0.78
0.90         0.89


Attachment 1: Cav_scan_response_130412_Pitch.pdf
Attachment 2: Cav_scan_response_130412_Yaw.pdf
  387   Fri Dec 13 14:59:18 2019 StephenGeneralGeneralOMC Beam Dump Production Cure Bake

[Koji, Jordan, Stephen]

The beam dumps, bonded on Fri 06 Dec 2019, were placed in the newly tuned and configured small dirty ABO at the Bake Lab on Fri 13 Dec 2019.

Images are shared and references are linked below

Bonding log entry - https://nodus.ligo.caltech.edu:8081/OMC_Lab/386

Bake ticket - https://services.ligo-wa.caltech.edu/clean_and_bake/request/992/

OMC Beam Dump - https://dcc.ligo.org/LIGO-D1201285

Attachment 1: IMG_6080.JPG
Attachment 2: IMG_6079.JPG
  388   Wed Dec 18 21:54:53 2019 KojiGeneralGeneralOMC Beam Dump Production Cure Bake

The beamdumps were taken out from the oven and packed in bags.

The bottom of the V are completely "wet" for 17 BDs among 20 (Attachment 1/2).

3 BDs showed insufficient glue or delamination although there is no sign of lack of rigidity. They were separated from the others in the pack.

Attachment 1: P_20191218_160650_vHDR_On.jpeg
Attachment 2: P_20191218_160705_vHDR_On.jpeg
Attachment 3: P_20191218_160733_003.jpeg
  393   Mon Sep 28 16:03:13 2020 ranaGeneralGeneralOMC Beam Dump Production Cure Bake
are there any measurements of the BRDF of these things? I'm curious how much light is backscattered into the incoming beam and how much goes out into the world.

Maybe we can take some camera images of the cleaned ones or send 1-2 samples to Josh. No urgency, just curiosity.

I saw that ANU and also some labs in India use this kind of blue/green glass for beam dumps. I don't know much about it, but I am curious about its micro-roughness and how it compares to our usual black glass. For the BRDF, I think the roughnesss matters more for the blackness than the absorption.

  394   Mon Sep 28 16:13:08 2020 KojiGeneralGeneralOMC Beam Dump Production Cure Bake

According to the past backscatter test of the OMC (and the black glass beamdump: not V type but triangular type on a hexagonal-mount), the upper limit of the back reflection was 0.13ppm. https://nodus.ligo.caltech.edu:8081/OMC_Lab/209

I don't have a BRDF measurement. We can send a few black glass pieces to Josh.

  127   Tue May 14 19:06:00 2013 KojiCleanGeneralOMC Baking

The OMC is in the air bake oven now.


  325   Fri Apr 5 23:30:20 2019 KojiGeneralGeneralOMC (002) repair completed

OMC(002) repair completed

When the cable harness of OMC(004) is going to be assembled, the cable harness of OMC(002) will be replaced with the PEEK one. Otherwise, the work has been done.

Note that there are no DCPDs installed to the unit. (Each site has two in the OMC and two more as the spares)

More photos: https://photos.app.goo.gl/XdU1NPcmaXhATMXw6

Attachment 1: P_20190405_222401.jpg
Attachment 2: P_20190405_222509.jpg
Attachment 3: P_20190405_222529.jpg
  319   Tue Mar 19 17:30:25 2019 KojiGeneralCharacterizationOMC (002) Test items

OMC #002 Optical tests

  • FSR measurement (done, 2019/1/8-9, 2019/4/1)
  • TMS measurement (done, 2019/1/9)
  • TMS measurement (with DC voltage on PZTs) (done, 2019/1/10)
  • Cleaning (done, 2019/3/19)
  • Power Budget (done, 2019/3/19, 2019/4/1)
  • PZT DC response (done, 2019/3/27)
  • PZT AC response (done, 2019/3/27)
  • QPD alignment (done, 2019/4/5)
  • DCPD alignment (done, 2019/4/4)
  • Beam quality check (done, 2019/4/4)

(Backscattering test)

(Cabling / Wiring)

  • (Attaching cable/mass platforms)
  • (PZT cabling)
  • (DCPD cabling)
  • (QPD cabling)

(First Contact)
(Packing / Shipping)

  281   Fri Jun 23 01:58:11 2017 KojiOpticsGeneralOMC #002 Repair - CM1 gluing

[Alena, Koji]

Jun 21: Alena and Koji worked on gluing of the CM1 mirror on the OMC breadboard #002. This is an irregular procedure. Usually, the PZT mirror subassembly is prepared before the mounting prism is glued on the breadboard. In this occasion, however, a PZT and a mirror are bonded on an existing prism because only the damaged mirror and still functional PZT were debonded from the mouting prism.

For this purpose, the mirror and the PZT were fixed on the mounting prism with the modified fixture set (D1600338). The original PZT was reused, and the new mirror #8 was used. The alignment of the mirror was checked OK using the cavity beam before any glue was applied. The arrow of the CM mirror is facing up.

We mixed 8g EP30-2 (it was almost like 3~4 pushes) and 0.4g glass sphere bond lining. Along with EP30-2 procedure, the bond was mixed in an Al pot and tested with 200degF (~93degC) preheated the oven for 15min. The cured bond showed perfect dryness and crispness. The bond was painted on the PZT and the PZT was placed on the fixture. Then more bond was painted on the other side of the PZT. The mirror was placed in the fixture. The spring-loaded front plate was fixed, and the breadboard was left for a day. (Attachment 1~3)

Jun 22: The fixture was removed without causing any visible delamination or void. The attachment 4~6 show how wet the joint is (before baking). There were some excess of EP30-2, which bonded the fixture and the mounting prism as usual. The fixture was detached by prying the front piece against the rear piece with a thin allen key. Some of the excess bond on the mounting prism was removed by scratching.

The alignment of the cavity was checked with the cavity beam and it is still fine.

More photos can be found here: Link to Google Photos Album "OMC #002 Repair - CM1 gluing"

Attachment 1: IMG_0857.JPG
Attachment 2: IMG_0859.JPG
Attachment 3: IMG_0860.JPG
Attachment 4: IMG_0865.JPG
Attachment 5: IMG_0868.JPG
Attachment 6: IMG_0864.JPG
  223   Wed Feb 18 21:51:23 2015 KojiGeneralGeneralNotes on OMC Transportation Fixtures & Pelican

LLO has one empty OMC transportation fixture.

LHO has one empty OMC transportation fixture.

LHO has one OMC transportation fixture with 3IFO OMC in it.

LHO has the Pelican trunk for the OMC transportation. Last time it was in the lab next to the optics lab.

  301   Tue Jul 3 12:07:47 2018 Rich AbbottElectronicsCharacterizationNotes on 3rd IFO EOM

Attached please see my notes summarizing the models for the electrodes and inductors within the 3rd IFO EOM

Attachment 1: EOM_Analysis2.pdf
EOM_Analysis2.pdf EOM_Analysis2.pdf
  71   Thu Mar 14 22:18:23 2013 KojiGeneralGeneralNew loans for the diode test

ALL returned

Loan from ATF:

2 blue banana cables returned on Jun 4, 2013

BNC cable returned on Mar 21, 2013

TENMA triple power supply returned on July 17, 2015

From 40m:

4x GPIB cables returned on Mar 21, 2013

From EE shop:

red banana cables returned on Jun 4, 2013

  304   Tue Aug 7 15:43:12 2018 KojiElectronicsCharacterizationNew LLO EOM stuffed

[Rich, Dean, Koji]

Stuffed all inductors for the new LLO EOM. As the impedances were sensitive to the positions of the inductors in the housing, they were glued with a glue gun.
Also the lid of the housing significantly change the stray capacitance and lowers the resonant frequency (meaning lowers the Q too), we decided to tune the matching circuit without the lid.

The attached plots show the measured impedances. They all look well tuned and matched. We will prepare and perform the optical measurement at the 40m.

Attachment 1: P_20180806_154457.jpg
Attachment 2: impedance_eom.pdf
Attachment 3: impedance_eom_zoom.pdf
  75   Sat Mar 23 02:32:23 2013 KojiFacilityGeneralN2 cylinder delivered

Preparation for ionized N2 blow

- 99.9998% N2 cylinder delivered (ALPHAGAZ 2 grade by AIR LIQUIDE) ALPHAGAZ 2 [PDF]

- Filter and Arcing module already in the lab

- A brass regulator to be installed (Done - March 24)

- 50 ft air line already in the lab / needs to be wiped/rinsed (Done - March 24)

- Air line and filter installed (Done - March 24)

Attachment 1: P3233349.jpg
  353   Tue Apr 23 10:21:12 2019 JoeOpticsConfigurationMoving the spots to the centre of the curved mirrors

[Koji,Philip, Liyuan, Joe]


We moved the curved mirrors to these positions:

inner = 0.807mm

outer = 0.983 mm


inner = 0.92 mm

outer = 0.85 mm

To do this so that realignment was easier, we moved the screws in steps of 5um. We alternated which mirror we adjusted so that we could monitor with a wincam how well aligned the beam into the cavity was. We only moved the cavity mirrors a small amount so we could still see higher order mode flashes transmitted through the cavity (e.g.TM03 modes). We would then improve the input alignment, and then move the cavity mirrors some more. Once the mirrors were adjusted according to http://nodus.ligo.caltech.edu:8080/OMC_Lab/190422_195450/misalignment4.pdf the spot positions looked near the middle of the curved mirrors (using a beam card). We began beam walking but we ran  out of range of the bottom periscope screws in the yaw dof. We tried using the third screw to move the mirrror in both yaw and pitch, hopefully this will let move the mirror such that we can use the just the yaw screw. This screw also ran out of range, so we decided that the cavity needed a small adjustment.

The curved mirrors were moved slightly (>5um) and then we tried to get alignment. By using the fibre coupler translation stage, we move the beam side ways slightly, and then tried to get the periscope mirrors back to a position where the screws could move the mirrors. Once we had an ok alignment, we checked the beam. It looked like it was pretty close to the centre of the curved mirrors, which is where we wanted it to be.

We then tried locking the cavity, although the error signal was quite small. The adjusted the input offset and gain of the servo (there is apparently some problem to do with the input and output offsets). Once the cavity was locked we could make the final adjustments to aligning. We still ran out of range on the periscope. We decided to move the breadboard with the fibre coupler and mode matching lenses on it. Because we knew that the cavity was aligned such that the beam hits the centres of the curved mirrors, we could regain flashes quite quickly. We saw the error signal go down, but eventually this decrease was just to do with the beam clipping on the periscope mirrors. We moved the spot back to where we ok aligned, and slid the periscope so we were not clipping the mirror. This worked very well, and then optimised the alignment.

We then tried to improve the mode matching. 

We took photos of the spot positions (quite near the center) and made the detuned locking measurement. The fitting of the data (attachment 1) wsa 1.1318m (what error should we put here?).

I think the order we did things in was:

  • turning anti clockwise on the fibre coupler and misalign the diode, we measured the modespacing.
  • returned the alignment for the photodiode, and realign fibre couple.
  • miss align the photodiode horizontally, and then used fibre coupler to maximise the peak higher order mode peak height. We then used the PD again to make the peak height bigger.
Attachment 1: FSR_detuned_locking.pdf
Attachment 2: CM1_IMG_7702.JPG
Attachment 3: CM2_IMG_7704.JPG
  124   Mon May 13 14:49:35 2013 KojiMechanicsCharacterizationMounting Glass Bracket still broke with tightenin stress

[Koji / Jeff]

This is the elog about the work on May 9th.

We made two glass brackets glue on the junk 2" mirrors with the UV glue a while ago when we used the UV bonding last time.

On May 7th:

We applied EP30-2 to the glass brackets and glued invar shims on them. These test pieces were left untouched for the night
and brought to Bob for heat curing at 94degC for two hours.

On May 9th:

We received the test pieces from Bob.

First, a DCPD mount was attached on one of the test pieces. The fasteners were screwed at the torque of 4 inch lb.
It looked very sturdy and Jeff applied lateral force to break it. It got broken at once side of the bracket.

We also attached the DCPD mount to the other piece. This time we heard cracking sound at 2 inch lb.
We found that the bracket got cracked at around the holes. As the glass is not directly stressed by the screws
we don't understand the mechanism of the failure.

After talking to PeterF and Dennis, we decided to continue to follow the original plan: glue the invar shims to the brackets.

We need to limit the fastening torque to 2 inch lb.

  116   Thu Apr 18 11:43:59 2013 KojiGeneralGeneralMounting Glass Bracket Failure

[Jeff, Koji]

- While we were working on the optics alignment, one of the mounting brackets made of glass god tore apart into two when a holding screw was removed.
The glass component had a crack at the very middle of the part.

- We borrowed a setup for photoelastisity measurement from Garilynn. This is a set of polarizer configured to have cross polarization. If there is no photoerastisity
the image is colored in blue (somehow). When the polarization is rotated, the color is changed in red, yellow, or white.

- The cross polarizer was tested with a polycarbonate face shield for the UV protection. It seems doing its job.

- We took a set of photos to see any residual stress in a block. The entire inside of the channel is frosted glass so the technique didn't yield much.
In one orientation we did see stress near the ends but the orientation didn't allow us to see exactly where.

- We had 30 brackets and one OMC requires ten of them. This means that there was no spare and now we don't have enough.
  So we decided to spend more as test pieces.

- We tested three scenarios this afternoon. In all three cases both screws were snugged (estimate 0.5 in*lb) before torquing by a torque wrench with a dial meter.
  The divisions on the dial of the wrench are 1 in*lb. We were not so confident in the exact measurement but we felt good about the repeatability of the values.

  1. Duplicated the original mounting with the chamfers of the PEEK bar facing into the channel. Cracked as the torque wrench read 1 in*lb.
      Crack initiation at the first screw, starting along the longitudinal centerline.

  2. Turned the nut bar over so the flat side faced into the channel. Successfully torqued both screws to 1 in*lb and removed them.

  3. With a razor blade, made fairly large reliefs (countersinks) around the holes in the PEEK. Successfully torqued both screws first to 1 in*lb then 1.5 in*lb.
      The block did crack (again at the screw along the centerline) when the torque was ~1.9 in*lb.

It occurs to us that we need micro-compliance AND structural rigidity to distribute the load. The PEEK bars are small and particularly thin where the #4-40 helicoil holes are.
The load is probably concentrated way too much at the holes because it is too weak. Perhaps a good solution, among others, would be to use an aluminum nut plate
with a thin (.02") kapton or viton layer to give the micro-compliance. Additionally, a kapton layer could be used between the block and the aluminum shim,
though this one is probably to be avoided so as to ensure rigidity of the bolted assembly to the bench. Lastly, the nut bar should be shaped such that the area
around the holes and the end of the channel (pretty much the same area) are less stressed than the center portion. 

After the discussion with Peter and Dennis, we decided to reinforce the bonded glass piece with invar shims.
Each shim will be threaded such that we don't need to stress the glass piece any more. EP30-2 will be used as the glue.

  35   Thu Nov 8 13:24:53 2012 KojiOpticsCharacterizationMore wedge measurement

Horiz Wedge    0.497    +/-    0.004 deg
Vert Wedge      0.024    +/-    0.004 deg

Horiz Wedge    0.549    +/-    0.004 deg
Vert Wedge      0.051    +/-    0.004 deg

Horiz Wedge    0.463    +/-    0.004 deg
Vert Wedge      0.009    +/-    0.004 deg

Horiz Wedge    0.471    +/-    0.004 deg
Vert Wedge      0.019    +/-    0.004 deg

Horiz Wedge    0.458    +/-    0.004 deg
Vert Wedge      0.006    +/-    0.004 deg

Attachment 1: wedge_measurement_overall.pdf
wedge_measurement_overall.pdf wedge_measurement_overall.pdf wedge_measurement_overall.pdf wedge_measurement_overall.pdf wedge_measurement_overall.pdf
  243   Thu Sep 10 04:03:42 2015 KojiOpticsCharacterizationMore polarizer optics measurement (Summary)

Brewster calcite PBS (eLIGO Squeezer OFI)

Loss L = 3600 +/- 200ppm
Angular dependence: Attachment 1

In the first run, a sudden rise of the loss by 1% was observed for certain angles. This is a repeatable real loss.
Then the spot position was moved for the second run. This rise seemed disappeared. Is there a defect or a stria in the crystal?

Wave plate (eLIGO Squeezer OFI?)

Loss L = 820 +/- 160ppm
Angular dependence: Attachment 2

Initially I had the similar issue to the one for the brewster calcite PBS. At the 0 angle, the loss was higher than the final number
and high asymmetric loss (~2%) was observed in the negative angle side. I checked the wave plate and found there is some stain
on the coating. By shifting the spot, the loss numbers were significantly improved. I did not try cleaning of the optics.

The number is significantly larger than the one described in T1400274 (100ppm).

Thin Film Polarlizer (aLIGO TFP)

Loss L = 3680 +/- 140ppm @59.75 deg
Angular dependence: Attachment 3

0deg was adjusted by looking at the reflection from the TFP. The optics has marking saying the nominal incident angle is 56deg.
The measurement says the best performance is at 59.75deg, but it has similar loss level between 56~61deg.

Glasgow PBS

It is said by Kate that this PBS was sent from Glasgow.

Loss L = 2500 +/- 600ppm
Angular dependence: Attachment 4


Attachment 1: eLIGO_PBS.pdf
Attachment 2: HWP.pdf
Attachment 3: TFP.pdf
Attachment 4: Glasgow_PBS.pdf
  244   Wed Sep 23 17:49:50 2015 KojiOpticsCharacterizationMore polarizer optics measurement (Summary)

For the Glasgow PBS, the measurement has been repeated with different size of beams.
In each case, the PBS crystal was located at around the waist of the beam.
Otherwise, the measurement has been done with the same way as the previous entries.

Beam radius [um]  Loss [ppm]
 160              5000 +/-  500
 390              2700 +/-  240
1100              5300 +/-  700
1400              2500 +/-  600 (from the previous entry)
2000              4000 +/-  350

Attachment 1: Glasgow_PBS_spotsize.pdf
  65   Fri Mar 1 23:06:15 2013 KojiOpticsConfigurationMore perpendicularity test final

Perpendicularity of the "E" mirror was measured.

Mounting Prisms:
(criteria: 30arcsec = 145urad => 0.36mm spot shift)
SN  Meas.(div) ArcSec Spec.
10   0.3989    11.97   29    good
11   0.2202     6.60   16
16   0.1907     5.72    5
20  -0.591    -17.73    5
21  -2.378    -71.34   15

21  -1.7      -51.     15
01  -0.5      -15.     52
02  -2.5      -75.     48
06  -1.0      -30.     15
07   1.7       51.     59
12  -2.2      -66.     40
13  -0.3      - 9.     12
14  -2.8      -84.     27
15  -2.5      -75.     50
17   0.7       21.     48
22   2.9       87.    

Mirror A:
A1  -0.5      -15.     NA    good
A3   0.5       15.     NA
A4   0.9       27.     NA
A5   0.4       12.     NA
A6   0.1        3.
    NA    good
A7   0.0        0.
    NA    good
A8   0.0       
0.     NA    good
A9   0.0       
0.     NA    good
A10  1.0      
30.     NA    good
A11  0.3       
9.     NA    good
A12  0.1       
3.     NA    good
A13  0.0       
0.     NA    good
A14  0.6      
18.     NA    good

Mirror B:
B1  -0.9     
-27.     NA    good
B2  -0.6     
-18.     NA    good
B3  -0.9     
-27.     NA    good
B4   0.7      
21.     NA    good
B5  -1.1     
-33.     NA
B6  -0.6     
-18.     NA    good
B7  -1.8     
-54.     NA
B8  -1.1     
-33.     NA
B9   1.8      
54.     NA
B10  1.2       
36.     NA   
B11 -1.7     
-51.     NA
B12  1.1       
33.     NA

Mirror E:
E1  -0.8      -24.     NA    good
E2  -0.8      -24.    
NA    good
E3  -0.25     - 7.5   
NA    good
E4  -0.5      -15.     NA
E5   0.8       24.     NA    good
E6  -1.0      -30.     NA
E7  -0.2      - 6.     NA
E8  -0.8      -24.     NA
E9  -1.0      -30.     NA
E10  0.0        0.     NA
E11 -1.0      -30.     NA
E12 -0.3      - 9.     NA
E13 -0.8      -24.     NA
E14 -1.0      -30.     NA    good
E15 -1.2      -36.     NA

E16 -0.7      -21.     NA
E17 -0.8      -24.     NA
E18 -1.0      -30.     NA

  64   Wed Feb 27 18:18:48 2013 KojiOpticsConfigurationMore perpendicularity test

Mounting Prisms:
(criteria: 30arcsec = 145urad => 0.36mm spot shift)
SN  Meas.(div) ArcSec Spec.
10   0.3989    11.97   29    good
11   0.2202     6.60   16
16   0.1907     5.72    5
20  -0.591    -17.73    5
21  -2.378    -71.34   15

21  -1.7      -51.     15
01  -0.5      -15.     52
02  -2.5      -75.     48
06  -1.0      -30.     15
07   1.7       51.     59
12  -2.2      -66.     40
13  -0.3      - 9.     12
14  -2.8      -84.     27
15  -2.5      -75.     50
17   0.7       21.     48
22   2.9       87.    

Mirror A:
A1  -0.5      -15.     NA    good
A3   0.5       15.     NA
A4   0.9       27.     NA
A5   0.4       12.     NA
A6   0.1        3.
    NA    good
A7   0.0        0.
    NA    good
A8   0.0       
0.     NA    good
A9   0.0       
0.     NA    good
A10  1.0      
30.     NA    good
A11  0.3       
9.     NA    good
A12  0.1       
3.     NA    good
A13  0.0       
0.     NA    good
A14  0.6      
18.     NA    good

Mirror B:
B1  -0.9     
-27.     NA    good
B2  -0.6     
-18.     NA    good
B3  -0.9     
-27.     NA    good
B4   0.7      
21.     NA    good
B5  -1.1     
-33.     NA
B6  -0.6     
-18.     NA    good
B7  -1.8     
-54.     NA
B8  -1.1     
-33.     NA
B9   1.8      
54.     NA
B10  1.2       
36.     NA   
B11 -1.7     
-51.     NA
B12  1.1       
33.     NA

  260   Tue Apr 5 21:20:15 2016 KojiElectronicsCharacterizationMore dark noise measurement

All survived PDs have been measured.

Attachment 1: PD_dark_current.pdf
PD_dark_current.pdf PD_dark_current.pdf PD_dark_current.pdf PD_dark_current.pdf PD_dark_current.pdf PD_dark_current.pdf PD_dark_current.pdf PD_dark_current.pdf
  182   Thu Apr 17 21:39:25 2014 KojiOpticsGeneralMore alignment


- The cavity mirrors have scattering spots. The cavity alignment should have been scanned to find a cavity mode to have lowest loss possible.
  BTW, We only have horizontal dof for the alignment scan.

- After some struggle nice cavity mode was found. The cavity transmission was 96% for the ideally matched TEM00 carrier.

- It turned out that this imposed too much beam shift in the input beam (~2mm).

- This big shift induces a lot of trouble for the peripheral optics (PDs, QPDs, sterring mirrors).

- What should we do???


- The beam needed to go up between CM1 and CM2 to have the right spots on them. ("UP" is the input side of the OMC).

- This imposed the beam between FM1 and FM2 moved up. In other word, for the given alignment of the FMs by the template,
  We needed to hit the upper part of the FMs to have the spots on the CMs up.


- The above argument suggets that the nominal beam will give us the right spots on the CMs if we rotate the FMs.
  Of course this induces the spot move on the FMs. But this should not be the issue as the most of the loss seems to come from the CMs.

- How much misalignment show we give to the FMs? We want to shift the beam by 2mm on the CMs.
  The length of the optical lever is ~0.25m. Therefore the mialignment angle should be

  theta = 2e-3/2/0.25 = 4e-3 rad = 4mrad.

  The template pad has ~20mm separation. The thickness of the shim should be 20mm*4mrad = 80um

- Our aluminum foil seems to have the thickness of 30-40um. We can't have this minimum thickness on the template pad as there is not enough compression pressure
  => Just use a single layer of Al piece to shim the FMs.


- The shims were inserted at the upper pads of the FMs.

- Aligned the input beam and the CMs so that the spots on the CMs are approximately recovered.

- Measure the cavity power budget

Pin: 34.7mW
Refl PD: offset = -7.5mV, unlock = 6.07V, inlock = 89.7mV

Ptrans = 32.5mW

Ptrans(CM2) = 0.181mW
Ptrans(CM2) = 0.184mW

Assume finesse of 400


Pin: 34.7mW
Pjunk: 0.534mW
Pcoupled: 34.1mW

Mode matching: 98.5%

Cavity reflectivity in power: 0.00061
Cavity transmission in power: 0.951 (This is not a best number but acceptable.)
Loss per mirror: 75.4ppm

FM power refl/trans: 0.9923 / 7630ppm
CM1 power refl/trans: 0.999882 / 42.8ppm
CM2 power refl/trans: 0.999881 / 43.5ppm
Total roundtrip loss of the cavity (Loss + CM leakage): 388ppm


How much the input beam is away from the left wall of the OMC breadboard?

40.88mm from the template edge
  8.36mm between the template edge and the bread board
=> 32.52mm

How much should this number be? 32.94mm from the solidworks model => With in 0.5mm! Nice!


- Just in case plce all of the optics and check if the beam is delivered within the alignment range of the optics


  42   Mon Nov 26 01:40:00 2012 KojiOpticsCharacterizationMore RoC measurement

C1: RoC: 2.57845 +/− 4.2e−05m

C2: RoC: 2.54363 +/− 4.9e−05m

C3: RoC: 2.57130 +/− 6.3e−05m   

C4: RoC: 2.58176 +/− 6.8e−05m

C5: RoC 2.57369 +/− 9.1e−05m


==> 2.576 +/- 0.005 [m] (C2 excluded)

Attachment 1: RoC_measurement.pdf
RoC_measurement.pdf RoC_measurement.pdf RoC_measurement.pdf RoC_measurement.pdf RoC_measurement.pdf
  100   Mon Apr 8 11:11:37 2013 KojiOpticsCharacterizationMore Mirror T measurement

More Ts of the mirrors were measured.

A mirror specification:
Request: 8300+/-800 ppm
Data sheet: 7931ppm

C mirror specification:
Request: 50+/-10 ppm
Data sheet: 51.48ppm or 46.40ppm


Mirror | P_Incident P_Trans  P_Offset | T_trans
       | [mW]       [uW]     [uW]     | [ppm]
A1     | 10.28    82.9       -0.205   | 8.08e3
A2     | -----     -----     ------   | ------
A3     | 10.00    83.2       -0.205   | 8.34e3
A4     | 10.05    80.7       -0.205   | 8.05e3
A5     |  9.94    81.3       -0.205   | 8.20e3
A6     | 10.35    78.1       -0.205   | 7.57e3
A7     | 10.35    77.8       -0.205   | 7.54e3
A8     | 10.30    78.0       -0.205   | 7.60e3
A9     | 10.41    84.1       -0.205   | 8.10e3
A10    | 10.35    77.3       -0.205   | 7.49e3
A11    | 10.33    77.9       -0.205   | 7.56e3
A12    | 10.34    78.7       -0.205   | 7.63e3
A13    | 10.41    85.4       -0.205   | 8.22e3
A14    | 10.34    84.4       -0.205   | 8.18e3
C1     | 10.30     0.279     -0.225   | 48.9
C2     | -----     -----     ------   | ------
C3     | 10.37     0.240     -0.191   | 41.6
C4     | 10.35     0.278     -0.235   | 49.6
C5     | 10.40     0.138     -0.235   | 35.9 => PZT assembly #2
C6     | 10.34     0.137     -0.235   | 36.0 => PZT assembly #1
C7     | 10.37     0.143     -0.229   | 35.9
C8     | 10.41     0.224     -0.237   | 44.3
C9     | 10.36     0.338     -0.230   | 54.8
C10    | 10.39     0.368     -0.228   | 57.4
C11    | 10.38     0.379     -0.209   | 56.6
C12    | 10.28     0.228     -0.238   | 45.3
C13    | 10.36     0.178     -0.234   | 39.8


  308   Sun Sep 23 19:42:21 2018 KojiOpticsGeneralMontecarlo simulation of the phase difference between P and S pols for a modeled HR mirror

[Koji Gautam]

With Gautam's help, I ran a coating design code for an HR mirror with the standard quarter-wave design. The design used here has 17 pairs of lambda/4 layers of SiO2 and Ta2O5 (=34 layers) with the fused silica as the substrate to realize the transmission of tens of ppm. At the AOI (angle of incidence) of 4 deg (=nominal angle for the aLIGO OMC), there is no significant change in the reflectivity (transmissivity). With 95% of the case, the phase difference at the AOI of 4 deg is smaller than 0.02 deg for given 1% fluctuation (normal distribution) of the layer design and the refractive indeces of the materials. Considering the number of the OMC mirrors (i.e. 4), the total phase shift between P and S pols is less than 0.08 deg. This makes P and S resonances matched well within 1/10 of the cavity resonant width (360/F=0.9deg, F: Finesse=400).

Of course, we don't know how much layer-thickness fluctuation we actually have. Therefore, we should check the actual cavity resonance center of the OMC cavity for the polarizations.

Attachment 1 shows the complex reflectivity of the mirror for P and S pols between AOIs of 0 deg and 45 deg. Below 30 deg there is no significant difference. (We need to look at the transmission and the phase difference)

Attachment 2 shows the power transmissivity of the mirror for P and S pols between AOIs of 0 deg and 45 deg. For the purpose to check the robustness of the reflectivity, random fluctuations (normal distribution, sigma = 1%) were applied to the thicknesses of each layer, and the refractive indices of Silica and Tantala. The blue and red bands show the regions that the 90% of the samples fell in for P and S pols, respectively. There are median curves on the plot, but they are not well visible as they match with the ideal case. This figure indicates that the model coating well represents the mirror with the transmissivity better than 70ppm.

Attachment 3 shows the phase difference of the mirror complex reflectivity for P and S pols between AOIs of 0deg and 45deg. In the ideal case, the phase difference at the AOI of 4deg is 1x10-5 deg. The Monte-Carlo test shows that the range of the phase for 90% of the case fell into the range between 5x10-4 deg and 0.02 deg. The median was turned to be 5x10-3 deg.

Attachment 4 shows the histogram of the phase difference at the AOI of 4deg. The phase difference tends to concentrate at the side of the smaller angle.

Attachment 1: reflectivities.png
Attachment 2: transmission.png
Attachment 3: phase_diff.png
Attachment 4: phase_difference_histogram.png
  309   Thu Sep 27 20:19:15 2018 AaronOpticsGeneralMontecarlo simulation of the phase difference between P and S pols for a modeled HR mirror

I started some analytic calculations of how OMC mirror motion would add to the noise in the BHD. I want to make some prettier plots, and am adding the interferometer so I can also compute the noise due to backscatter into the IFO. However, since I've pushed the notebook I wanted to post an update. Here's the location in the repo.

I used Koji's soft limit of 0.02 degrees additional phase accumulation per reflection for p polarization.

  310   Thu Nov 1 19:57:32 2018 AaronOpticsGeneralMontecarlo simulation of the phase difference between P and S pols for a modeled HR mirror

I'm still not satisfied/done with the solution to this, but this has gone too long without an update and anyway probably someone else will have a direction to take it that prevents me spinning my wheels on solved or basic questions.

The story will have to wait to be on the elog, but I've put it in the jupyter notebook. Basically:

  • I considered the polarization-separated OMC in several configurations. I have plots of DARM referred noise (measured free-running and controlled noise for the current OMC, thermal theoretical noise curve, scattered light) for the case of such an OMC with one lambda/2 waveplate oriented at 45 degrees. This is the base case.
  • I also considered such an OMC with a lambda/2 both before and after the OMC, where their respective polarization axes can be arbitrary (I look at parameter space near the previous case's values).
    • I optimize the BHD angle to balance the homodyne (minimize the E_LO^2 term in the homodyne readout).
    • I then optimize the rotations of the lambda/2 polarization axes to minimize the noise
    • For the optimum that is closest to the base case, I also plotted DARM referred length noise.


It's clear to me that there is a way to optimize the OMC, but the normalization of my DARM referred noise is clearly wrong, because I'm finding that the input-referred noise is at least 4e-11 m/rt(Hz). This seems too large to believe. 

Indeed, I was finding the noise in the wrong way, in a pretty basic mistake. I’m glad I found it I guess. I’ll post some plots and update the git tomorrow. 

  305   Wed Aug 8 17:32:56 2018 Rich AbbottGeneralCharacterizationModulation Index Test Setup at 40m Lab

Attached is a block diagram of the test setup used in the 40m lab to measure the modulation index of the IO modulator

Attachment 1: 40mLabModIndexSetup.pdf
  306   Thu Aug 9 11:24:29 2018 KojiGeneralCharacterizationModulation Index Test Setup at 40m Lab

[Rich Koji]

The impedances of the new LLO EOM were measured with the beat note setup at the 40m PSL (as described in the previous ELOG entry.

At the target frequencies (9.1MHz, 24.1MHz, 45.5MHz, 118.3MHz), the modulation responses were (0.09, 2.9e-3, 0.053, 0.021) rad/V.

This corresponds to the requirement for the driving power as follows.

modulation depth 
required (LHO) [rad]
drive [Vpk]
drive [dBm]
    9.1 0.09 0.22 2.4 17.8
  24.1 2.9e-3   0.014 4.8 23.7
  45.5   0.053 0.28 5.3 24.5
118.3   0.021   0.010   0.48   3.6


Attachment 1: modulation_depth.pdf
Attachment 2: modulation_depth_zoom.pdf
  8   Wed Jul 18 23:20:13 2012 KojiOpticsCharacterizationMode scan results of ELIGO

Nic Smith sent me a bunch of elog lists where the results of the mode scan can be found.

From Nic:

There have been many mode scan analyses done at LLO:

We didn't do as much of this at LHO. At some point we were trying to figure out how the arm cavity mode was different from the carrier mode:


Here's a long mode scan that was done, and the data is attached to the elog, but none of the amplitudes are analyzed.

  95   Thu Apr 4 01:35:04 2013 KojiOpticsCharacterizationMode matching to the OMC cavity

The fiber output was matched with the lenses on a small bread board.
The detailed configuration is found in the following elog link.


  216   Tue Aug 5 13:03:25 2014 KojiGeneralGeneralMissing cable components

DCPD Connector Face: Qty2 https://dcc.ligo.org/LIGO-D1201276
QPD Connector Face: Qty2 https://dcc.ligo.org/LIGO-D1201282

PD faster: 92210A07 Qty 4: MCMASTER #2-56 x .25 FHCS

Spare DCPD

  179   Fri Feb 28 19:50:11 2014 KojiGeneralGeneralMisalignment ABCD matrix for the aLIGO OMC

Relationship between mirror misalignment and cavity mode shift was calculated.
The technique described in T0900647 by Sam Waldman was used.

The angles and displacement of the mirrors and beams are defined in the attached figure.

x1 = 0.893134 α + 1.10676 β + 1.32252 γ + 1.24619 δ
𝛳1 = 0.75864 α - 0.75864 β - 0.271075 γ + 0.271075 δ

x2 = 1.10676 α + 0.893134 β + 1.24619 γ + 1.32252 δ
𝛳2 = 0.75864 α + 1.24136 β - 0.271075 γ + 0.271075 δ

x3 = 1.32252 α + 1.24619 β + 1.1691 γ + 1.39962 δ
𝛳3 = -0.271075 α + 0.271075 β + 0.818668 γ - 0.818668 δ

x4 = 1.24619 α + 1.32252 β + 1.39962 γ + 1.1691 δ
𝛳4 = -1.24136 α - 0.75864 β - 0.271075 γ + 0.271075 δ

Assuming the flat mirrors are fixed:
If I want to move the x3 mirror up by 1mm without moving x4, the solution is
γ = -0.00197 mrad
δ = +0.00236 mrad

This yields:
x1 = +0.33mm, x2=+0.66mm, x3 = +1mm, x4 = 0mm

Attachment 1: misalignment.pdf
  101   Mon Apr 8 11:29:08 2013 KojiOpticsCharacterizationMirror/PZT Characterization links
  151   Fri Aug 16 15:31:17 2013 KojiOpticsConfigurationMirror list for OMC(002)


Cavity Mirrors

FM1 (input coupler): A9
FM2 (output coupler): A13
CM1 (curved mirror close to FM1): C9 (PZT ASSY #6 /  M6 /PZT21/C9)
CM2 (curved mirror close to FM2): C4 (PZT ASSY #4 / M11/PZT25/C4)

DCPD path

BS3 (BS for DCPDs): B10

QPD path

BS1 (input steering): E3
SM1 (steering mirror next to BS1): E5
BS2 (BS for QPD path): B9
SM2 (steering mirror next to BS2): E1
SM3 (steering mirror next to SM2): E2




  113   Tue Apr 16 09:43:58 2013 KojiOpticsConfigurationMirror list for L1OMC


Cavity Mirrors

FM1 (input coupler): A8
FM2 (output coupler): A7
CM1 (curved mirror close to FM1): C6
CM2 (curved mirror close to FM2): C5

DCPD path

BS3 (BS for DCPDs): B5 B7

QPD path

BS1 (input steering): E10
SM1 (steering mirror next to BS1): E12
BS2 (BS for QPD path): B3
SM2 (steering mirror next to BS2): E4
SM3 (steering mirror next to SM2): E16


  91   Mon Apr 1 18:17:01 2013 KojiOpticsGeneralMirror curvature center test

Locations of the curvature minimum on the OMC curved mirrors have been measured.


When a curved mirror is misaligned, the location of the curvature center is moved.
Particularly, our OMC mirror is going to be attached on the PZT and the mounting prism with the back surface of the mirror.
This means that a curved mirror has inherent misalignment if the curvature minimum of the curved mirror is shifted from the center of the mirror.
Since we have no ability to control mirror pitch angle once it is glued on the prism, the location of the curvature minima
should be characterized so that we can oush all of the misalignment in the horizontal direction.

Measurement technique:

When a curved mirror is completely axisymmetric (in terms of the mirror shape), any rotation of the mirror does not induce change on the axis of the refected beam.
If the curvature minimum is deviated from the center of the mirror, the reflected beam suffer precession. As we want to precisely rotate the mirror, we use the gluing
fixture for the PZT assembly. In this method, the back surface of the curved mirror is pushed on the mounting prism, and the lateral position of the mirror is precisely
defined by the fixture. As you rotate the mirror in clockwise viewing from the front, the spot moves in counter clockwise on the CCD.



Setup and procedure:

The mounting prism (#21) is placed on the gluing fixture. A curved mirror under the test is loaded in the fixture with no PZT.
i.e. the back surface is aligned by the mounting prism. The fixing pressure is applied to the curved mirror by the front plate
with spring loads. The mirror needs be pushed from the top at least once to keep its defined position in the fixture.
The incident beam is slightly slated for the detection of the reflected spot. The beam is aligned and hits the center of the mirror as much as possible.


The position of the spot on the CCD (WinCamD) is recorded, while the mirror is rotated 90deg at once. The rotation of the mirror is defined as shown in the figure below.
The angle origin is defined by the arrow mark of the mirror and rotated in clockwise being viewed from the front face. The mirror is rotated 540deg (8points) to check
the reproducibility.


Measurement result:

8 point for each mirror is fitted by a circle. The fitting result provides the origin and radius of the circle, and the angle correspond to mirror angle of 0deg.


d: distance of the curvature minimum and the mirror center (quantity to be delived)

D: distance of the prove beam spot from the center of the mirror

R: Radius of curvature of the mirror

theta_R: angle of incidence/reflection




The interesting consequence is that precession diameter (X-X') on the CCD does not depend on the spot position on the mirror.
This ensures the precision of the measurement. In the measurement, the radius of the precession (r = (X-X')/2) is obtained.


d = r R / (2 L)

Mirror name, distance[mm]
C1: 0.95
C3: 1.07
C4: 1.13
C5: 0.97
C6: 0.73
C7: 1.67
C8: 2.72
C9: 1.05
C10: 0.41
C11: 0.64
C12: 0.92
C13: 0.14

The angle to be rotated is depicted in the following plot for each mirror.


Attachment 5: curved_mirror_precession.pdf
  40   Sat Nov 17 02:31:34 2012 KojiOpticsCharacterizationMirror T test

Mirror T test

The mirror was misaligned to have ~2deg incident (mistakenly...) angle.

C1: Ptrans = 7.58uW, Pinc = 135.0mW => 56.1ppm

C1 (take2): Ptrans = 7.30uW, Pinc = 134.4mW => 54.3ppm

C2: Ptrans = 6.91uW, Pinc = 137.3mW => 50.3ppm

C3: Ptrans = 6.27uW, Pinc = 139.7mW => 44.9ppm

C4: Ptrans = 7.62uW, Pinc = 139.3mW => 54.7ppm

C5: Ptrans = 6.20uW, Pinc = 137.5mW => 45.1ppm

A1: Ptrans = 1.094mW, Pinc = 133.6mW => 8189ppm

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