Dark current measurement for InGaAs QPDs (OSI FCI-InGaAs-Q3000) has been done using Keithley 2450 and Frank's diode test kit. Frank's setup uses various custom instruments which are no longer exist, therefore the kit was used only for switching between the segments.

The diodes were serialized as 81, 82, 83, 84, continuing the numbering for the OMC QPDs. The numbers are engraved at the side and the back of the diode cans.

Overall, the QPDs nominally indicated the usual dark current level of <10nA.
SEG1 of #82 showed a lower voltage of reverse breakdown but this is not a critical level.
#83 showed variations between the segments compared to the uniform characteristics of #81 and #84.

Dark current of the HQE PD and other PDs were measured.

- The HQE PDs were loaded on the new PD transportation cages (Attachment 1)
The PDs are always shorted by a clean PD plugs. The PD element is still capped with Kapton seals.

- The assignment of the container/slot and the PDs are as follows

- The measurement has been done with KEITHLEY sourcemeter SMU2450.

- The result is shown in Attachment 2. Most of the PDs show the dark current of ~3nA at 15V bias. C1-05 and C1-07 showed higher dark current at high V region. We should avoid using them for the aLIGO purpose. I hope they are still OK at low bias V if there is no noise issue (TBC). You can not read the PD names on the plot for the nominal ones, but that's OK as they are almost equivalent.

- As a comparison, the dark current of a C30655 (serial #10) was measured. Considering a DC current due to an anbient light (although the PD was covered), the dark current of the HQE PD seems double of C30655.

- Taking an advantage of having the setup, I took the same measurement for the Laser Comp. PDs in ATF. I gave the identification as #1 and #2. #1 has full-length legs while #2 has trancated legs. As Zach reported before, they showed significantly high dark current. (Attachment 3)

Transfered for RGA scan

B4 (C1-05) -> F1
C1 (C1-07) -> F2

[Camille, Thejas]

We repeated Zygo measurements (using the same setup and method as below) for curved mirrors sn07, sn11, sn12, sn18, sn19, sn25, sn26, and sn30.

sn11 and sn25 still show a large spread in angular measurements (see attached.) This is attributed to the low decentering values for these two mirrors (0.072mm and 0.158mm, respectively).

Attached here with are relevant plots.

The dimensions of a high QE PDs was measured as well as the ones for C30665. (Attachment 4, Unit in mm)
They seemed to be very much compatible.

The PDs came with the designated case (Attachment 1). The bottom of the case has a spongy (presumably conductive) material.

Diodes have no window. Each came with an adhesive seal on it. (Attachment 2)
There is a marking of a serial at the side.

I opened one (Attachment 3). The sensitive area looks just beautiful. The seal was reapplied to avoid possible contamination.

Quantum efficiencies of the C30665GH diodes were measured. 

- The diode was biased by the FEMTO preamplifier.

- Diode Pin 1 Signal, Pin 2 +5V, Pin 3 open

- Preamp gain 10^3 V/A

- Beam power was measured by the thorlabs power meter.

PD #1
Incident: 12.82 +/- 0.02 mW
Vout: 9.161 +/- 0.0005 V
PD Reflection (Prompt): 0.404 mW
PD Reflection (Total): 1.168 mW

PD #2
Incident: 12.73 +/- 0.02 mW
Vout: 9.457 +/- 0.0005 V
PD Reflection (Prompt): 0.364 mW
PD Reflection (Total): 0.937 mW

PD #3
Incident: 12.67 +/- 0.02 mW
Vout: 9.1139 +/- 0.01 V
PD Reflection (Prompt): 0.383 mW
PD Reflection (Total): 1.272 mW

PD #4
Incident: 12.71 +/- 0.02 mW
Vout: 9.3065 +/- 0.0005 V
PD Reflection (Prompt): 0.393 mW
PD Reflection (Total): 1.033 mW

PD #5
Incident: 12.69 +/- 0.02 mW
Vout: 9.1071 +/- 0.005 V
PD Reflection (Prompt): 0.401 mW
PD Reflection (Total): 1.183 mW

PD #6
Incident: 12.65 +/- 0.02 mW
Vout: 9.0310 +/- 0.01 V
PD Reflection (Prompt): 0.395 mW
PD Reflection (Total): 1.306 mW

PD #7
Incident: 12.67 +/- 0.02 mW
Vout: 9.0590 +/- 0.0005 V
PD Reflection (Prompt): 0.411 mW
PD Reflection (Total): 1.376 mW

PD #8
Incident: 12.63 +/- 0.01 mW
Vout: 9.0790 +/- 0.0005 V
PD Reflection (Prompt): 0.420 mW
PD Reflection (Total): 1.295 mW

PD #9
Incident: 12.67 +/- 0.02 mW
Vout: 9.2075 +/- 0.0005 V
PD Reflection (Prompt): 0.384 mW
PD Reflection (Total): 1.091 mW

PD #10
Incident: 12.70 +/- 0.01 mW
Vout: 9.0880 +/- 0.001 V
PD Reflection (Prompt): 0.414 mW
PD Reflection (Total): 1.304 mW

PD #11
Incident: 12.64 +/- 0.01 mW
Vout: 9.2861 +/- 0.0005 V
PD Reflection (Prompt): 0.416 mW
PD Reflection (Total): 1.152 mW

PD #12
Incident: 12.68 +/- 0.02 mW
Vout: 9.3650 +/- 0.001 V
PD Reflection (Prompt): 0.419 mW
PD Reflection (Total): 1.057 mW

PD #13
Incident: 12.89 +/- 0.01 mW
Vout: 9.3861 +/- 0.001 V
PD Reflection (Prompt): 0.410 mW
PD Reflection (Total): 1.047 mW

PD serial number
 1 - 0782
 2 - 1139
 3 - 0793
 4 - 0732
 5 - 0791
 6 - 0792
 7 - 0787
 8 - 0790
 9 - 0781
10 - 0784
11 - 1213
12 - 1208
13 - 1209

{
  {1, 12.82, 9.161, 0.404, 1.168},
  {2, 12.73 , 9.457, 0.364 , 0.937} ,
  {3, 12.67 , 9.1139, 0.383 , 1.272 },
  {4, 12.71 , 9.3065, 0.393 , 1.033 },
  {5, 12.69, 9.1071, 0.401 , 1.183 },
  {6, 12.65, 9.0310, 0.395 , 1.306} ,
  {7, 12.67, 9.0590, 0.411 , 1.376} ,
  {8, 12.63 , 9.0790, 0.420 , 1.295} ,
  {9, 12.67 , 9.2075, 0.384 , 1.091} ,
  {10, 12.70, 9.0880, 0.414 , 1.304 },
  {11, 12.64 , 9.2861, 0.416 , 1.152} ,
  {12, 12.68 , 9.3650, 0.419 , 1.057} ,
  {13, 12.89 , 9.3861, 0.410 , 1.047}
};

Diode testing

o Purpose of the measurement

- Test Si QPDs (C30845EH) for ISC QPDs Qty 30 (i.e. 120 elements)

- Test InGaAs PDs (C30665GH) for OMC Qty 10 (i.e. 10 elements)

o Measurement Kit

- Inherited from Frank.

- Has relays in it.

- D0 and D1 switches the measurement instrument connected to an element

- D2 and D3 switches the element of the QPDs

- Digital switch summary

d0 d1 0 0 - ln preamp
d0 d1 1 0 - dark c
d0 d1 0 1 - omc preamp
d0 d1 1 1 - impedance

d2 d3 0 0 - A x x x
d2 d3 1 0 - C x o x
d2 d3 0 1 - B o x o
d2 d3 1 1 - D o o o

- The universal board in the box is currently configured for C30845.
  Pin1 - Elem A. Pin3 - B, Pin7 - C, Pin9 - D, Pin 12 - Case&Bias

o Labview interface

- Controls NI-USB-6009 USB DAQ interface and Agilent 82357B USB-GPIB interface

o Dark current measurement

- Borrowed Peter's source meter KEITHLEY 2635A

- For C30845GH the maxmum reverse bias is set to -20V. This drops the voltage of the each element to the bias voltage.

o Spectrum measurement

- The elements are connected to FEMTO LN current amp DLPCA-200.

- Bias voltage is set to +10V. This lifts up the outside of the amplifier input to +10V.

o Impedance measurement

- Agilent 4395A at PSL lab with impedance measurement kit

- For C30845GH the maxmum reverse bias is set to -15V. This drops the voltage of the each element to the bias voltage.

- Calibration: open - unplug the diode from the socket, short - use a piece of resister lead, 50Ohm - a thin metal resister 51Ohm

- Freq range: 30-50MHz where the response of the cables in the setup is mostly flat.

- Labview VI is configured to read the equivalent circuit parameters in the configuration "D" (series LCR).

- Labview fails to read the series resistance. This was solved by first read the equiv circuit param and then read it with Sim F-CHRST.
  F-CHRST does nothing on the parameters so the second request successfully acquires the first ones.

- For the dark noise measurement, the lid of the die-cast case should also contact to the box for better shielding. This made the 60Hz lines almost completely removed, although unknown 1kHz harmonics remains.

- The precise impedance of the setup can not be obtained from the measurement box; the cable in between is too long. The diode impedance should be measured with the impedance measurement kit.

- With the impedance measurement kit, the bias voltage of +5V should be used, in stead of -5V.

- diode characteristics measured at 10-100MHz

- Typical impedance characteristics of the diodes

Excelitas (Perkin-Elmer) C30665GH Rs=9Ohm, Cd=220pF, L=0~1nH (Vr=5V)

Excelitas (Perkin-Elmer) C30642G Rs=12Ohm, Cd=100pF, L=~5nH (Vr=5V) longer thin wire in a can?

Excelitas (Perkin-Elmer) C30641GH Rs=8Ohm, Cd=26pF, L=12nH (Vr=5V) leg inductance? (leg ~30mm)

- PD serial

C30665GH, Ls ~ 1nH

  1 - 0782 from PK, Rs=8.3Ohm, Cd=219.9pF
  2 - 1139 from PK, Rs=9.9Ohm, Cd=214.3pF
  3 - 0793 from PK, Rs=8.5Ohm, Cd=212.8pF
  4 - 0732 from PK, Rs=7.4Ohm, Cd=214.1pF
  5 - 0791 from PK, Rs=8.4Ohm, Cd=209.9pF
  6 - 0792 from PK, Rs=8.0Ohm, Cd=219.0pF
  7 - 0787 from PK, Rs=9.0Ohm, Cd=197.1pF
  8 - 0790 from PK, Rs=8.4Ohm, Cd=213.1pF
  9 - 0781 from PK, Rs=8.2Ohm, Cd=216.9pF
10 - 0784 from PK, Rs=8.2Ohm, Cd=220.0pF
11 - 1213 from the 40m, Rs=10.0Ohm, Cd=212.9pF
12 - 1208 from the 40m, Rs=9.9Ohm, Cd=216.8pF
13 - 1209 from the 40m, Rs=10.0Ohm, Cd=217.5pF

C30642G, Ls ~ 12nH

20 - 2484 from the 40m EG&G, Rs=12.0Ohm, Cd=99.1pF
21 - 2487 from the 40m EG&G, Rs=14.2Ohm, Cd=109.1pF
22 - 2475 from the 40m EG&G glass crack, Rs=13.5Ohm, Cd=91.6pF
23 - 6367 from the 40m ?, Rs=9.99Ohm, Cd=134.7pF
24 - 1559 from the 40m Perkin-Elmer GH, Rs=8.37Ohm, Cd=94.5pF
25 - 1564 from the 40m Perkin-Elmer GH, Rs=7.73Ohm, Cd=94.5pF
26 - 1565 from the 40m Perkin-Elmer GH, Rs=8.22Ohm, Cd=95.6pF
27 - 1566 from the 40m Perkin-Elmer GH, Rs=8.25Ohm, Cd=94.9pF
28 - 1568 from the 40m Perkin-Elmer GH, Rs=7.83Ohm, Cd=94.9pF
29 - 1575 from the 40m Perkin-Elmer GH, Rs=8.32Ohm, Cd=100.5pF

C30641GH, Perkin Elmer, Ls ~ 12nH

30 - 8983 from the 40m Perkin-Elmer, Rs=8.19Ohm, Cd=25.8pF
31 - 8984 from the 40m Perkin-Elmer, Rs=8.39Ohm, Cd=25.7pF
32 - 8985 from the 40m Perkin-Elmer, Rs=8.60Ohm, Cd=25.2pF
33 - 8996 from the 40m Perkin-Elmer, Rs=8.02Ohm, Cd=25.7pF
34 - 8997 from the 40m Perkin-Elmer, Rs=8.35Ohm, Cd=25.8pF
35 - 8998 from the 40m Perkin-Elmer, Rs=7.89Ohm, Cd=25.5pF
36 - 9000 from the 40m Perkin-Elmer, Rs=8.17Ohm, Cd=25.7pF

Note:
  1mm Au wire with dia. 10um -> 1nH, 0.3 Ohm
20mm BeCu wire with dia. 460um -> 18nH, 0.01 Ohm

The 40m Bake Lab's Dirty ABO's OMEGA PID controller was borrowed for another oven in the Bake Lab, so I have had to play with the tuning and parameters to recover a suitable bake profile. This bake is pictured below (please excuse the default excel formatting).

I have increased the ramp time, temperature offset, and thermal mass within the oven; after retuning and applying the parameters indicated, the rate of heating/cooling never exceeds .5°C/min.

The ABO is controlled by a different temperature readout from the data logger used to collect data; the ABO readout is a small bead in contact with the shelf, while the data logger is a lug sandwiched between two stainless steel masses upon the shelf. I take the data logger profile to be more physically similar to the heating experienced by an optic in a gluing fixture, so I feel happy about the results of the above bake.

I plan to add the data source file to this post at my earliest convenience.

Follow up on OMC elog 379

I was able to obtain the following (dark blue) bake profile, which I believe is adequate for our needs.

The primary change was a remounting of the thermocouple to sandwich it between two stainless steel masses. The thermocouple bead previously was 1) in air and 2) close to the oven skin.

Dmass borrowed the LB1005 servo amp from the OMC lab.
It happened this week although it seems still January in his head. Got it back on Mar 24th

The A2 and C2 mirrors have been sent to Josh Smith at Fullerton for the scatterometer measurement.

First Contact kit (incl. Peek Sheets)
Manasa borrowed the kit on Feb 7. Got it back to the lab.

http://nodus.ligo.caltech.edu:8080/Cryo_Lab/799

(KA: Returned upon H1OMC building)

I wondered why the black glass beam dumps looked not as shiny as before. It was in fact a layer of dusts (or contaminants) accumulated on the surface.
The top part of the internal surface of the black glass was touched by a piece of lens tissue with IPA. The outer surface was already cleaned. IPA did not work well i.e. Required multiple times of wiping. I tried FirstContact on one of the outer surface and it efficiently worked. So I think the internal surfaces need to be cleaned with FC.

This is not an OMC related and even not happening in the OMC lab (happening at the 40m), but I needed somewhere to elog...

E1400445 first look

LIGO DCC E1400445

Attachment 1: Record of the original state

Attachment 2: Found one of the SMA cable has no shield soldering

EGE&G 2mm photodiode angle response measured by Sam T1100564-v1

Linearity of the EOM driver was tested. This test has been done on Nov 10, 2015.

- Attachment 1: Output power vs requested power. The output start to deviate from the request above 22dBm request.

- Attachment 2: Ctrl and Bias voltages vs requested power. This bias was measured with the out-of-loop channel.
The variable attenuator has the voltage range of 0~15V for 50dB~2dB attenuation.

Therefore this means that:

- The power setting gives a voltage logarithmically increased as the requested power increases. And the two power detectors are watching similar voltages.

- And the servo is properly working. The control is with in the range.

- Even when the given RF power is low, the power detectors are reporting high value. Is there any mechanism to realize such a condition???

Qs' were estimated with a lorentzian function (eye fit)

Current LHO EOM (final version, modulation depth measurement 2018/4/5)
f0=9.1MHz, Q=18
f0=45.38MHz, Q=46
f0=118.05MHz, Q=30

Prev LHO EOM (RF transmission measurement 2018/4/13)
f0=9.14MHz, Q=53
f0=24.25MHz, Q=55
f0=45.565MHz, Q=62;

3IFO EOM (RF transmission measurement 2018/4/23)
f0=8.627MHz, Q=53
f0=24.075MHz, Q=60
f0=43.5MHz, Q=65

The circuit models for the 3IFO EOM (before mods) were made using LISO.
Then the modification plan was made to make it a new LLO EOM.

Impedance data, LISO model, Mathematica files are zipped and attached at the end.

https://awiki.ligo-wa.caltech.edu/wiki/EOM_Mount_Stability

Here is a summary of the events of the last week, as they relate to EP30-2.

1) I lost the EP30-2 syringes that had been ordered for the OMC, along with the rest of the kit.

• Corrective action: Found in the 40m Bake Lab garbing area.
• Preventative action: log material moves and locations in the OMC elog
• Preventative action: log EP30-2 moves and locations in PCS via location update [LINK]
• Preventative action: keep EP30-2 kit on home shelf in Modal Lab unless kit is in use

2) The EP30-2 syringes ordered for the OMC Unit 4 build from January had already expired, without me noticing.

• Corrective action: Requested LHO ship recently-purchased EP30-2 overnight
• Preventative action: log expiration dates in OMC elog
• Preventative action: begin purchasing program supported by logistics, where 1 syringe is maintained on hand and replaced as it expires

3) LHO shipped expired epoxy on Thursday. Package not opened until Monday.

• Corrective action: Requested LHO ship current EP30-2 overnight, this time with much greater scrutiny (including confirming label indicates not expired)
• Preventative action: Packages should be opened, inspected, and received in ICS or Techmart on day of receipt whenever possible.

4) Current, unopened syringe of EP30-2 has been received from LHO. Expiration date is 22 Jan 2020. Syringe storage has been improved. Kit has been docked at its home in Downs 303 (Modal Lab) (see attached photo, taken before receipt of new epoxy).

Current Status: Epoxy is ready for PZT + CM subassembly bonding on Monday afternoon 23 September.

EP30-2 bonding setup

EP30-2 gluing test

This post captures the curing timeline followed by OMC PZT Assys #9 and #10.

Source file posted in case any updates or edits need to be made.

The following is the current status of the epoxies used in assembly of the OMC (excerpt from C1900052)

Re-purchasing efforts are underway and/or complete

• DONE
  • Masterbond EP30-2 currently located in Downs 303, Modal Lab (see image)
    • ( WILL EXPIRE JANUARY 2020 )
    • ( tracked using THIS PCS LINK https://services.ligo-la.caltech.edu/Inventory/history.php?recid=1582&invtype=cit_noncap )
  • Electronic Materials Inc Optocast 3553-LV procured via PCard, will arrive today 22 October
    • plan to track using PCS is WIP
• WIP
  • Epoxy Pax EP-1730-1 quoted and requisitioned, PO is WIP

Firstly, the excess epoxy was removed using a cleaned razor balde

Secondly, EP30-2 epoxy was applied at the exterior edges of the beam dump.
Interior of the V were glued at two points. This is to keep the gap away from being trapped

Here is the result of the gluing. Some epoxy was sucked into the gap by capillary action.
I believe, most of the rigidity is proivded by the bonds at the edges.

A carpenter has come to install the eyeware storage and hooks for the face shields.

OMC SN002 = Former LHO OMC which CM1 was destroyed by the lock loss pulse in 2016. This OMC needs to be optically tested before storage.

The test items:

• [done] FSR measurement with offset PDH locking (FM->AM conversion)
• [done] FSR/finesse measurement with the EOM RFAM injection
• [done] TMS measurement with input miaslignment and the trans RFPD misalignment: with no PZT offset
• [done] TMS measurement with input miaslignment and the trans RFPD misalignment: with PZT offsets
   
• PZT response
• Mirror cleaning
• Power budget
• Diode alignment: shim height
• PD/QPD alignment

3rd OMC FSR / Finesse measurement

RF AM was injected by detuning a HWP.

[Camille Koji]

We quickly measured the basic parameters of the OMC as is.

=== FSR ===
Used the technique to find a dip in the transmission transfer function (TF) with offset locking + phase modulation. The FSR was 264.79003MHz = The cavity length of 1.13219 [m] (requirement 1.132+/-0.005 [m])

=== TMS ===

Used the technique to find the peaks in the trans TF with phase modulation + input misalignment + trans PD clipping.
TMS_V: 58.0727 / TMS_H: 58.3070 => TMS/FSR V:0.219316 H:0.220201

This makes the 9th-order modes nicely avoided (Attachment 1). A slightly longer FSR may makes the numbers close to the nominal.

=== Spot positions ===

The image/video capture board turned out not functional with the new Apple silicon mac. We decided to use a small CCD monitor and took a photo of the display.

All the spots are within the acceptable range. The scattering on CM2 was particularly bright on the CCD image and also in the image with the IR viewr.

The spot on FM1/2 are right at the expected location. The spot on CM1 is 0.5mm low and 0.7mm inside (left). The spot on CM2 is ~0.25mm too high and 0.3mm outside.
(Attachment 2, a small grid is 1 mm/div)

== Transmission ==

We made a quick simplified measurement (Attachment 3).

Assuming the reflectivity of the matched beam to be ~0, the mode matching is M=1-(59.2e-3-(-6.5e-3))/(3.074-(-6.5e-3))=0.979
==> The power of the coupled mode is M x 21.28mW = 20.83 mW
The measued transmission was 19.88 mW
==> The OMC transmission (total) was 0.954 (4.5% loss)

This number is not too bad. But the spot on CM2 has too bright scattering. Next week, we want to check if swapping CM2 may improve the situation or not.

[Camille Koji]

We replaced CM2 with a PZT mirror subassembly serialized by PZT "13" (Attachment 1).
This made the transmission increase to 96.x%. Therefore the quick measurement of FSR and TSM were done. Also more careful measurement of the transmission was done.

Next time

== Alignment ==

• CM2 was replaced from PZT "12" to PZT "13".
• The resulting position of the cavity spot were all over 1mm too "+" (convention T1500060 Appendix C).
• So we decided to rotate CM2 by 1mrad in CW. This was done with (-) micrometer of CM2 "pushed" by 20um (2 rotational div).
• The resulting spot positions were checked with CCD. (Attachment 2). The spot positions seemed to be within +/-1mm from the center as far as we can see from the images. (good)
• CM2 spot looks much darker. CM1 spot is almost invisible with a CCD and also an IR viewer. FM1/2 spots were nominal bright level. (Looks OK)

== Quick measurement of the transmission ==

Transmission: 20.30 mW
Reflection Voltage (locked): 65.0 mV
Reflection Voltage (unlocked): 3.094 V
Reflection Voltage (dark): -6.5 mV
Incident Power: 21.64 mW

---> Mode matching 1-0.023 / Pcoupled = 21.14 / OMC Transmission 0.96

96% transmission is not the best but OK level. We decided to proceed with this mirror combination.

== Quick measurement of FSR/TMS ==

FSR: 264.7837MHz
TMS_V = 58.2105MHz
TMS_H = 58.1080MHz

The HOM structure (with PZT Vs = 0) is shown in Attachment 3. 9th order modes look just fine. The excplicit coincidence is 19th order 45MHz lower sideband. (Looks good)

== Transmission measurement ==

The raw measurements are shown in Attachment 4. The processed result is shown in Attachment 5.
We found that data set 2 has exceptionally low transmission. So we decided to run the 4th measurement excluding the set 2.

Over all OMC loss
Set1: 0.029 +/- 0.014
Set3: 0.041 +/- 0.0014
Set4: 0.038 +/- 0.001

--> 0.036 +/- 0.004
(0.964 Transmission)
 

1. FSR was adjusted and measured with "the golden arches" technique again.

FSR = 264.8412 MHz +/- 1400Hz => Lcav = 1.13197 m. (nominal 1.132m)

2. Transverse mode spacings for the vertical and horizontal modes were measured.

TMS/FSR = 0.218144 (V) / 0.219748 (H)

This is almost perfect!

The 19th-order lower sideband hit the resonance. Next step is to glue some of the flat mirrors.

[Koji, Jeff, Zach, Lisa]

We glued a test PZT-mirror assembly last week in order to make sure the heat cure of the epoxy does not make any problem
on the glass-PZT joints. The assembly was sent to Bob for the heat treatment. We received the assembly back from Bob on Wednesday.

We noticed that the assembly after the heat cure at 100degC had some voids in the epoxy layer
(looking like the fused silica surface was only 70% "wetted" by the epoxy).
The comparison of the assembly before and after the heat treatment is found in the slideshow at the bottom of the entry.

Initially our main concern was the impact to the control and noise performance.
An unexpected series resonance on the PZT transfer function and unwanted noise creation by the imperfect bonding may terribly ruin the IFO sensitivity.
In reality, after repeated poking by fingers, the PZT-prism joint was detached. This isn't good at all.
Note that there is no sign of degradation on the glass-glass joint.

We investigated the cause of this like:
- Difference of thermal expansion (3ppm/C PZT vs 0.55ppm/C fused silica)
- Insufficient curing of epoxy by UV (but this is the motivation of the heat cure)

Our resolution up to this point is to switch the glue to EP30-2. This means we will go through the heat cure test again.
Unfortunately there is no EP30-2 in stock at Caltech. We asked MIT to send us some packets of EP30-2.

Hardness of the epoxies is another concern. Through the epoxy investigation, we learned from Noliac that the glue for the PZT
should not be too hard (stiff) so as not to constrain the deformation of the PZT. EP30-2 has Shore D Hardness of 75 or more,
while Optocast UV epoxy has 88, and EPOTEK Epoxies, which Noliac suggested for gluing, has ~65. This should also be
confirmed by some measurement.  We will also ask Master Bond if they have information regarding the effect of curing
temperature on the hardness of the epoxy.  EP30-2 can be cured anywhere between RT and 200F (it's service range is up to 300F).
However, the entire breadboard, with the curved mirror sub-assemblies, will need to be baked at 110C to cure the UV Bond epoxy. 
We hope that exposure to relatively higher temps doesn't harden the EP30-2. The EP30-2 data sheet recommends an epoxy
thickness of 80-120 microns which is much thicker than we would like.

We also don't have a way tocontrol the thickness; though we could add glass spheres to the epoxy to control the thickness.
The thickness of the EP30-2 used to bond the metal wire guide prism on the core optics is much thinner at 15-25 microns.

Mode matching:

I attempted to fit the data taken by Koji of the beam spot precession at the CCD in order to find the location of the curvature bottom in terms of its distance (d) and angle () from the centre of the mirror. This was done using the method described in a previous similar measurement  and Section 2.1.3 of T1500060.

Initially, I attempted doing a circle_fit on python as seen in Attachment 1, and even though more points seem to coincide with the circle, Koji pointed out that the more appropriate way of doing it would be to fit the following function:

since that would allow us to measure the angle more accurately; is the anti-clockwise measured angle that the curvature bottom makes with the positive x direction.

As seen on the face of the CCD, x is positive up and y is positive right, thus, plotting it as the reflection (ref. Attachment 2) would make sure that  is measured anti-clockwise from the positive x direction.

The distance from the curvature bottom is calculated as 

r: radius of precession on CCD screen (value obtained from fit parameters, uncertainty in this taken from the std dev provided by fit function)

R: radius of curvature of the mirror 

L: Distance between mirror and CCD

R = 2.575  0.005 m (taken from testing procedure doc referenced earlier) and L = 0.644  0.005 m (value taken from testing doc, uncertainty from Koji)

	d (mm)	(deg)
C7	0.554  0.004	-80.028  0.005
C10	0.257  0.002	-135.55  0.02
C13	0.161  0.001	-79.31  0.06

Steve and I visited Margot to have a training session for application of First Contact on optics.

- Make "thick" layer of first contact. It becomes thin when it gets dried.

- Apply more FC once a peek sheet is placed on the FC

- Wait for drying (~15min)

- Rip off the FC layer by pulling a peek tab. Make sure the ionized N2 is applied during ripping.

- Margot has a Dark Field Microscope. We checked how the dusts are removed from the surface.
There are many dusts on the mirror even if they are invisible. First Contact actually removes
these dusts very efficiently. Margot told us that even carbonhydrates (like finger prints) can be removed by FC.

Conclusion: Good. First contact did not damage the coating surface, and reduced the loss

- Construct a cavity with A1 and C2

- Measure the transmission and FWHM (of TEM10 mode)

- Apply First Contact on both mirrors

- Measure the values again

Transmission:

2.66 +/- 0.01 V -> 2.83  +/- 0.01 V

==> 6.3% +/- 0.5 % increase

FWHM of TEM10:

Before: (66.1067, 65.4257, 66.1746) +/- (0.40178, 0.38366, 0.47213) [kHz]
After: (60.846, 63.4461, 63.7906) +/- (0.43905, 0.56538, 0.51756) [kHz]

==> 5.1% +/- 2.7% decrease

Question: What is the best way to measure the finesse of the cavity?

Data can be found in DCC document T2300050. 

On Friday. Camille and I measured the flatness of the flat mirror.  Tilt values (without subtracting tilt) were less than 100 nm and PV across the surface was about 50 nm. 

This checks that the flat mirror surface distortions are not contributing to the systematic deviations in our measurement of curvature minimum with varying the fiducial clocking angle. The deviations in the data show a far more disagreement between Y-Tilt of different clocking angles than the X-Tilt. 

- The floor of the room was cleaned and waxed!

- Sticky mats are placed! Now we require shoe covers!

- Work benches are being built. One unit is done.

- The other is half done because the table top has chippings.

T&Rs of the B mirrors and some of the E mirrors are measured.

I found that these BSs have high loss (1%~3%) . As this loss will impact the performance of the squeezer
we should pick the best ones for the DCPD path. B5, B6, and B12 seems the best ones.

Mirror | P_Incident   P_Trans     P_Refl      | T             R             loss          |
       | [mW]         [mW]        [mW]        |                                           |
-------+--------------------------------------+-------------------------------------------+
B1     | 13.80+/-0.05 7.10+/-0.05 6.30+/-0.05 | 0.514+/-0.004 0.457+/-0.004 0.029+/-0.005 |
B2     | 14.10+/-0.05 6.50+/-0.05 7.15+/-0.05 | 0.461+/-0.004 0.507+/-0.004 0.032+/-0.005 |
B3     | 13.87+/-0.05 7.05+/-0.05 6.55+/-0.05 | 0.508+/-0.004 0.472+/-0.004 0.019+/-0.005 |
B4     | 13.85+/-0.05 6.78+/-0.05 6.70+/-0.05 | 0.490+/-0.004 0.484+/-0.004 0.027+/-0.005 |
B5     | 13.65+/-0.05 6.93+/-0.05 6.67+/-0.05 | 0.508+/-0.004 0.489+/-0.004 0.004+/-0.005 |
B6     | 13.75+/-0.05 6.70+/-0.05 6.92+/-0.05 | 0.487+/-0.004 0.503+/-0.004 0.009+/-0.005 |
B7     | 13.83+/-0.05 7.00+/-0.05 6.60+/-0.05 | 0.506+/-0.004 0.477+/-0.004 0.017+/-0.005 |
B8     | 13.90+/-0.05 6.95+/-0.05 6.68+/-0.05 | 0.500+/-0.004 0.481+/-0.004 0.019+/-0.005 |
B9     | 13.84+/-0.05 6.95+/-0.05 6.70+/-0.05 | 0.502+/-0.004 0.484+/-0.004 0.014+/-0.005 |
B10    | 13.97+/-0.05 6.98+/-0.05 6.72+/-0.05 | 0.500+/-0.004 0.481+/-0.004 0.019+/-0.005 |
B11    | 13.90+/-0.05 7.05+/-0.05 6.70+/-0.05 | 0.507+/-0.004 0.482+/-0.004 0.011+/-0.005 |
B12    | 13.90+/-0.05 6.98+/-0.05 6.78+/-0.05 | 0.502+/-0.004 0.488+/-0.004 0.010+/-0.005 |
-------+--------------------------------------+-------------------------------------------+

Mirror | P_Incident   P_Trans         P_Refl       | T            R             loss          |
       | [mW]         [uW]            [mW]         | [ppm]                                    |
-------+-------------------------------------------+------------------------------------------+
E4     | 13.65+/-0.05 0.0915+/-0.0005 13.50+/-0.05 | 6703+/-44ppm 0.989+/-0.005 0.004+/-0.005 |
E12    | 13.75+/-0.05 0.0978+/-0.0005 13.65+/-0.05 | 7113+/-45    0.993+/-0.005 0.000+/-0.005 |
E16    | 13.90+/-0.05 0.0975+/-0.0005 13.30+/-0.05 | 7014+/-44    0.957+/-0.005 0.036+/-0.005 |
-------+-------------------------------------------+------------------------------------------+

Since the previous measurement showed too high loss, the optical setup was checked.
It seemed that a PBS right before the T&R measurement setup was creating a lot of scattering (halo) visible with a sensor card.

This PBS was placed to confirm the output polarization from the fiber, so it was ok to remove it.

After the removal, the R&T measurement was redone.
This time the loss distributed from 0.2% to 0.8% except for the one with 1.3%. Basically 0.25% is the quantization unit due to the lack of resolution.

At least B7, B10, B12 seems the good candidate for the DCPD BS.

The AR reflection was also measured. There was a strong halo from the main reflection with an iris and sense the power at ~.5mm distance to separate the AR reflection from anything else. Now they are all somewhat realistic. I'll elog the measurement tonight.

33.6 +/- 0.2 uW out of 39.10+/-0.05 mW was observed. The offset was -0.236uW.
This gives us the AR reflectivity of 865+/-5ppm . This meets the spec R<0.1%

Mirror | P_Incident   P_Trans      P_Refl       | T             R             loss          |
       | [mW]         [mW]         [mW]         |                                           |
---------------------------------------------------------------------------------------------
B1     | 39.10+/-0.05 19.65+/-0.05 19.25+/-0.05 | 0.503+/-0.001 0.492+/-0.001 0.005+/-0.002 |
B2     | 39.80+/-0.05 19.90+/-0.05 19.70+/-0.05 | 0.500+/-0.001 0.495+/-0.001 0.005+/-0.002 |
B4     | 39.50+/-0.05 19.70+/-0.05 19.30+/-0.05 | 0.499+/-0.001 0.489+/-0.001 0.013+/-0.002 |
B5     | 39.50+/-0.05 19.70+/-0.05 19.50+/-0.05 | 0.499+/-0.001 0.494+/-0.001 0.008+/-0.002 |
B6     | 39.55+/-0.05 19.50+/-0.05 19.95+/-0.05 | 0.493+/-0.001 0.504+/-0.001 0.003+/-0.002 |
B7     | 40.10+/-0.05 19.80+/-0.05 20.20+/-0.05 | 0.494+/-0.001 0.504+/-0.001 0.002+/-0.002 |
B8     | 40.15+/-0.05 19.80+/-0.05 20.20+/-0.05 | 0.493+/-0.001 0.503+/-0.001 0.004+/-0.002 |
B9     | 40.10+/-0.05 19.90+/-0.05 19.90+/-0.05 | 0.496+/-0.001 0.496+/-0.001 0.008+/-0.002 |
B10    | 40.10+/-0.05 19.70+/-0.05 20.30+/-0.05 | 0.491+/-0.001 0.506+/-0.001 0.002+/-0.002 |
B11    | 40.20+/-0.05 19.80+/-0.05 20.20+/-0.05 | 0.493+/-0.001 0.502+/-0.001 0.005+/-0.002 |
B12    | 40.20+/-0.05 19.90+/-0.05 20.20+/-0.05 | 0.495+/-0.001 0.502+/-0.001 0.002+/-0.002 |
---------------------------------------------------------------------------------------------

Total (excluding C2, C7, C8): 2.575 +/- 0.005 [m]

New results

C6: RoC: 2.57321 +/− 4.2e-05m

C7: RoC: 2.56244 +/− 4.0e−05m ==> Polaris mount

C8: RoC: 2.56291 +/− 4.7e-05m ==> Ultima mount

C9: RoC: 2.57051 +/− 6.7e-05m

Previous results

C1: RoC: 2.57845 +/− 4.2e−05m

C2: RoC: 2.54363 +/− 4.9e−05m ==> Josh Smith @Fullerton for scattering measurement

C3: RoC: 2.57130 +/− 6.3e−05m   

C4: RoC: 2.58176 +/− 6.8e−05m

C5: RoC 2.57369 +/− 9.1e−05m

Now it's enough for the first OMC (or even second one too).
Today's measurements all distributed in theta>0.5deg. Is this some systematic effect???
I should check some of the compeled mirrors again to see the reproducibility...

A1    Horiz Wedge    0.497039    +/-    0.00420005    deg / Vert Wedge     0.02405210    +/-    0.00420061    deg

A2    Horiz Wedge    0.548849    +/-    0.00419993    deg / Vert Wedge     0.05087730    +/-    0.00420061    deg
A3    Horiz Wedge    0.463261    +/-    0.00420013    deg / Vert Wedge     0.00874441    +/-    0.00420061    deg
A4    Horiz Wedge    0.471536    +/-    0.00420011    deg / Vert Wedge     0.01900840    +/-    0.00420061    deg
A5    Horiz Wedge    0.458305    +/-    0.00420014    deg / Vert Wedge     0.00628961    +/-    0.00420062    deg

B1    Horiz Wedge    0.568260    +/-    0.00419988    deg / Vert Wedge    -0.00442885    +/-    0.00420062    deg
B2    Horiz Wedge    0.556195    +/-    0.00419991    deg / Vert Wedge    -0.00136749    +/-    0.00420062    deg
B3    Horiz Wedge    0.571045    +/-    0.00419987    deg / Vert Wedge     0.00897185    +/-    0.00420061    deg
B4    Horiz Wedge    0.563724    +/-    0.00419989    deg / Vert Wedge    -0.01139000    +/-    0.00420061    deg
B5    Horiz Wedge    0.574745    +/-    0.00419986    deg / Vert Wedge     0.01718030    +/-    0.00420061    deg
E1    Horiz Wedge    0.600147    +/-    0.00419980    deg / Vert Wedge     0.00317778    +/-    0.00420062    deg
E2    Horiz Wedge    0.582597    +/-    0.00419984    deg / Vert Wedge    -0.00537131    +/-    0.00420062    deg
E3    Horiz Wedge    0.592933    +/-    0.00419982    deg / Vert Wedge    -0.01082830    +/-    0.00420061    deg

-------

To check the systematic effect, A1 and B1 were tested with different alignment setup.

A1    Horiz Wedge    0.547056    +/-    0.00419994    deg / Vert Wedge    0.0517442    +/-    0.00420061    deg
A1    Horiz Wedge    0.546993    +/-    0.00419994    deg / Vert Wedge    0.0469938    +/-    0.00420061    deg
A1    Horiz Wedge    0.509079    +/-    0.00420003    deg / Vert Wedge    0.0240255    +/-    0.00420061    deg

B1    Horiz Wedge    0.547139    +/-    0.00419994    deg / Vert Wedge    0.0191204    +/-    0.00420061    deg



 

The Glasgow polarizer was passed to Kate on Dec 17, 2015.

Black and Decker Glue Baking Oven came back to the OMC lab on Aug 10, 2020, Georgia had lent the unit for the SAMS assembly/testing.

Short conclusion:

The roundtrip cavity length for the H1 OMC was adjusted to be 1.145m
instead of 1.132m such that the 19th HOMs of the lower sideband do not get resonant together with the carrier.

Background:

The purpose of the OMC is to transmit the carrier TEM00 mode while anything else is rejected.
As the optical cavity has infinite numbers of resonant modes, what we practically do is to select
the roundtrip accumulated gouy phase so that low order higher order modes for the carrier
as well as the sidebands (including the TEM00 modes).

The nominal round trip length of the OMC is 1.132m. The curvature of the mirror is 2.575m.
The nominal ratio between the TMS and FSR is 0.218791 and 0.219385 (TMS_V/TMS_H= 0.9973)
for the vertical and horizontal modes. This split comes from the non-zero angle (~4deg) of incidence on the curved mirrors.

In reality, the TMS/FSR ratio depends on the true curvature of the mirror. More importantly, astigmatism
of the mirror changes the difference of the ratios for the vertical and horizontal modes.

The mirror astigmatism can either reduce or increase the split. between the TMSs. For example,
the L1 OMC showed the TMS/FSR ratio of (0.218822, 0.219218) for the vertical and horizontal modes.
TMS_V/TMS_H is 0.9982 which is 0.18% from the unity. This suggests, roughly to say, that 0.27% of the
astigmatism coming from the AOI of 4deg was partially compensated by the mirror astigmatism. This was lucky.

Something unlucky happened to the case for the first choice of the H1OMC curved mirrors.
TMS_V/TMS_H is 0.990 which is indeed 1% away from the unity. This actually caused some problem:
As the modes spreads too wide, the 19th modes became unavoidable. (see the picture below)

           Red - carrier, Blue - upper sideband (+45MHz), Green - lower sideband

After the replacing one of the PZT assembly with another one, 1-TMS_V/TMS_H went down to 6%.
But still the 19th mode is on resonance. In order to shift the 19th mode from the resonance, the cavity length
had to be changed more than the range of the micrometer.

Simple simulation:

Attached Mathematica file calculates expected mode structure when the curved mirror position is
moved by DL (then the total roudtrip length changes 4*DL). This tells us that the 19th mode is
moved from the resonance by giving DL=-0.003 or DL=0.0025.

It was impossible to make the cavity short enough as the gluing fixture interferes with the curved mirror.
In fact, it was also impossible to make the cavity long enough as it was. Therefore PEEK shims with
the thickness of 1.5mm was inserted.

Result:

The FSR and TMS were measured with the longer cavity. 50V was applied to PZT1.

FSR: 261.775MHz
TMS_V: 57.575MHz
TMS_H: 57.880MHz

=> Cavity round trip length of 1.1452m
=> TMS/FSR = {0.219941, 0.221106}

The 19th modes for the lower sidebands are successfully moved from the carrier resonance.
The first accidental resonance is the lower sideband at the 28th order modes.

H1 OMC Cavity side optics was glued on the breadboard

Curved mirror gluing

- Applied the UV glues to CM1/CM2 prisms.

- Checked the spot positions on the curved mirrors

- Apply 50V to CM1

- Measure the FSR and TMS while the cavity was locked.

FSR: 261.70925MHz
TMS_V: 57.60500MHz
TMS_H: 57.94125MHz

=> Cavity round trip length of 1.1455m
=> TMS/FSR = {0.220111, 0.221395}

First accidental resonance is the lower sideband at 28th order modes.

Carrier 9th-order HOM: 2.9~7.6 line width away
Upper Sideband 13th-order HOM: 14.1-20.7 LW away
Lower Sideband 19th-order HOM: 3.3-13.1 LW away

- As this result was satisfactory, the UV illumination was zapped. It did not change the alignment. The cavity was kept locked during the illumination.

Peripheral optics gluing

- QPD path BS/Steering Mirrors were glued
- DCPD path BS was glued

The UV glue was applied to the optics.
Then the optics were placed on the breadboard along with the fixture.

Placed the dummy QPD/DCPD mount with the alignment disks.
The horizontal positions of the spots were well with in the horizontal range of the mounts.
 The UV illumination was zapped. Checked the alignment again and no problem was found.

Preparation of 3rd OMC for the use in H1

New DCPD(T) = B1-01
DCPD(T) = DCPDA: extracted and accomodated in CAGE-A SLOT1

New DCPD(R) = B1-16
DCPD(R) = DCPDB: extracted and accomodated in CAGE-A SLOT2

The Invar Mounting Blocks were glued on the breadboard.

Serial number #1/2/5/6/7/8 -> I1 OMC cable side

Serial number #9/10/11/12 -> H1 OMC cavity side

Since the middle of September, the optical tests of H1 OMC were took place.
Here is summary of the progress.

TEST1: FSR/FINESSE measurement before applying First Contact
TEST2: Power budget

MIrror cleaning with First Contact

TEST3: FSR/FINESSE measurement after First Contact application
TEST4: Power budget

TEST5: N/A

TEST6: HOM measurement @PZT V=0
TEST7: HOM measurement @PZT V=0-200

TEST8: DC response of the PZT
TEST9: AC response of the PZT

TEST10: PD/QPD alignment / output check