OMC Unit 4 Build Machined Parts are currently located in Stephen's office. See image of large blue box from office, below.

Loaned item D1100855-V1-00-OMC08Q004 to Don Griffith for work in semi-clean HDS assy.

This includes mass mounting brackets, cable brackets, balance masses, etc. For full inventory, refer to ICS load Bake-9527 (mixed polymers) and Bake-9495 (mixed metals).

Inventory includes all items except cables. Plasma sprayed components with slight chipping were deemed acceptable for Unit 4 use. Cable components (including flex circuit) are ready to advance to fabrication, with a bit more planning and ID of appropriate wiring.

More explicit insights into the inventory for the Unit 4 build. Image of inventory included below.

Machined Parts:

• New fabrication = Contents of Storage-11112 are consistent with upgrade ECR.
• Old leftovers = Storage-9482 and Storage-9483 .

Cable Components:

• Hughes Circuits made us Kapton flex circuits. These have not been processed in any way.
• Rich had supplied a spool of Gore 4-conductor in-vacuum wire (see below image). I returned the sppol for Rich but it is living in Downs and available for use.
• PEEK cable ties were damaged during bake, and will be replaced by SYS inventory.

Retrofit/Repair Capabilities:

• Aluminum reinforcement brackets D1600316
• Glass reinforcement brackets (Edmund Optics 45-072 and 45-071)

ref: E1900034 and other associated documents.

Backscattering reflectivity of the 3rdOMC was measured.

Attached: Measurement setup

1) A CVI 45P 50:50 BS was inserted in the input beam path. This BS was tilted from the nominal 45 deg so that the reflection of the input beam is properly dumped.
This yielded the reflectivity of the BS deviated from 45deg. The measured BS reflectivity is 55%+/-1%.

2) The backward propagating beam was reflected by this BS. The reflected beam power was measured with a powermeter.

3) The powermeter was aligned with the beam retroreflected from the REFL PDH and the iris in the input path. The iris was removed during the measurement
as it causes a significant scatter during the measurement.

4) While the cavity was either locked or unlocked, no visible spot was found at the powermeter side.

The input power to the OMC was 14.6mW. The detected power on the powermeter was 66.0+/-0.2nW and 73.4+/-0.3nW with the cavity locked and unlocked, respectively.
This number is obtained after subtraction of the dark offset of 5.4nW.

Considering the reflectivity of the BS (55+/-1%) , the upper limit of the OMC reflectivity (in power) is 8.18+/-0.08ppm and 9.09+/-0.09ppm for the OMC locked and unlocked respectively. Note that this suggests that the REFL path has worse scattering than the OMC cavity but it is not a enough information to separate each contribution to the total amount.

Impact on the OMC transmission RIN in aLIGO:

- The obtained reflectivity (in power) was 8ppm.
- For now, let's suppose all of this detected beam power has the correct mode for the IFO.
- If the isolation of the output faraday as 30dB is considered, R=8e-9 in power reaches the IFO.
- The IFO is rather low loss when it is seen as a high reflector from the AS port.
- Thus this is the amount of the light power which couples to the main carrier beam.

When the phase of the backscattered electric field varies, PM and AM are produced. Here the AM cause
the noise in DC readout. Particularly, this recombination phase is changing more than 2 pi, the fringing
between the main carrier and the backscattered field causes the AM with RIN of 2 Sqrt(R).

Therefore, RIN ~ 2e-4 is expected from the above of backscattering.

Now I'm looking for some measurement to be compared to with this number.

First, I'm looking at the alog by Zach: https://alog.ligo-la.caltech.edu/aLOG/index.php?callRep=8674

I'm not sure how this measurement can be converted into RIN. Well, let's try. Zach told me that the measured value is already normalized to RIN.
He told me that the modulation was applied at around 0.1Hz. The maximum fringe velocity was 150Hz from the plot.
At 100Hz, let's say, the RIN is 2e-6 /rtHz. The fringe speed at 100Hz is ~70Hz/sec. Therefore the measurement stays in the 100Hz freq bin
only for delta_f/70 = 0.375/70 = 5.3e-3 second. This reduces the power in the bin by sqrt(5.3e-3) = 0.073.

2e-6 = 2 sqrt(R) *0.73 ==> R = 2e-10

This number is for the combined reflectivity of the OMC and the OMC path. Assuming 30dB isolation of the output Faraday
and 20% transmission of SRM, the OMC reflectivity was 5e-6. This is in fact similar number to the measured value.

If I look at the OMC design document (T1000276, P.4), it mentions the calculated OMC reflection by Peter and the eLIGO measurement by Valera.
They suggests the power reflectivity of the order of 1e-8 or 1e-7 in the worst case. This should be compared to 8ppm.
So it seems that my measurement is way too high to say anything useful. Or in the worst case it creates a disastrous backscattering noise.

So, how can I make the measurement improved by factor of 100 (in power)

- Confirm if the scattering is coming from the OMC or something else. Place a good beam dump right before the OMC?

- Should I put an aperture right before the power meter to lmit the diffused (ambient) scatter coming into the detector?
  For the same purpose, should I cover the input optics with an Al foil?

- Is the powermeter not suitable for this purpose? Should I use a PD and a chopper in front of the OMC?
  It is quite tight in terms of the space though.

- Any other possibility?

Presence of the misaligned SRM (T=20%) was forgotten in the previous entry.
This effectively reduces the OMC reflectivity by factor of 25.

This is now reflected in the original entry. Also the argument about the power spectram density was modified.

Backscatter measurement ~ 2nd round

Summary

- The backscatter reflectivity of the 3rd OMC is 0.71 ppm

- From the spacial power distribution, it is likely that this is not the upper limit but the actual specular spot from the OMC,
propagating back through the input path.

Improvement

- The power meter was heavily baffled with anodized Al plates and Al foils. This reduced many spourious contributions from the REFL path and the input beam path.
  Basically, the power meter should not see any high power path.

- The beam dump for the forward going beam, the beamsplitter, and the mirrors on the periscope were cleaned.

- The power meter is now farther back from the BS to reduce the exposed solid angle to the diffused light

- The REFL path was rebuilt so that the solid angle of the PD was reduced.

Backscattering measurement

- P_in = 12.3 +/- 0.001 [mW]

- R_BS = 0.549 +/- 0.005

- P_back = 4.8 +/- 0.05 [nW] (OMC locked)       ==> R_OMC(LOCKED) = 0.71 +/- 0.01 [ppm]

- P_back = 3.9 +/- 0.05 [nW] (OMC unlocked)   ==> R_{OMC(UNLOCKED)} = 0.57 +/- 0.01 [ppm]

Note that the aperture size of Iris(B) was ~5.5mm in diameter. 

V-dump test

- Additional beam dump (CLASS A) was brought from the 40m. This allowed us to use the beam dump before and after the periscope.

- When the beam dump was placed after the periscope: P = 0.9+/-0.05nW

- When the beam dump was placed before the periscope: P=1.0+/-0.1nW

===> This basically suggests that the periscope mirrors have no contribution to the reflected power.

- When the beam dump was placed in the REFL path: P=2.1+/-0.1nW

Trial to find backward circulating beam at the output coupler

The same amount of backreflection beam can be found not only at the input side of the OMC but also transmission side.
However, this beam is expected to be blocked by the beamsplitter. It was tried to insert a sensor card between the output coupler
and the transmission BS, but nothing was found.

In order to see if the detected power is diffused light or not, the dependence of the detected light power on the aperture size was measured.
Note that the dark offset was nulled during the measurement.

IRIS B
aperture   detected
diameter   power
[mm]       [nW]
 1.0        1.1
 2.5        2.6
 4.25       4.0
 5.5        4.6
 8.0        5.3
 9.0        6.1
11.0        6.3
15.0        7.0

We can convert these numbers to calculate the power density in the each ring. 
(Differentiate the detected power and aperture area. Calculate the power density in each ring section, and plot them as a function of the aperture radius)

This means that the detected power is concentrated at the central area of the aperture.
(Note that the vertical axis is logarithmic)

If the detected power is coming from a diffused beam, the power density should be uniform.
Therefore this result strongly suggests that the detected power is not a diffused beam but
a reflected beam from the OMC.

According to this result, the aperture size of 2.6mm in raduis (5.5mm in diameter) was determined for the final reflected power measurement.

The OMC went into the oven at around 2PM on Thursday. It will be baked at 80degC for 48 hours.
The RGA result will be obtained on Monday.

Link to the ICS entry

OMC is back from the oven today.

To Do:

Optical tests

• Cleaning
• Power Budget
• FSR measurement
• TMS measurement
• TMS measurement (with DC voltage on PZTs)
• PZT DC response
• PZT AC response
• QPD alignment
• DCPD alignment
• First Contact

Backscattering test

Cabling / Wiring

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

Vibration test

Packing / Shipping

We have measured the dimensions and mass of the OMC glass plates/breadboards:

• ^* orientation is relative to "front" face, i.e. long-short face with S/N on it, with S/N upright.
• Height measurements were made twice, once at each end.
• TMeasurements of 03, 05, 02, and 06 were done in the open in the OMC lab.  This was not thought to be too much of an issue since the plates
  are already covered with particulate matter from the tissue paper that they were wrapped in. 
  Measurements of 04 and 01 were done on the optics table, under the clean room enclosure.

Note by Koji:

• The scale of the bake lab was used. (Max 60kg, Min resolution of 1g)
• The dimensions were measured by a huge caliper which Jeff brought from Downs.
• S/N 01, 03, 04 look pretty similar. They should be the primary candidates.

25 March (Mon):

Inspect the test PZT assembly

• => Give it to Bob. (done)

Glue topside components (done)

• Clean up the table for the gluing work.
• Prepare the transport fixture on the table.
• Glass breadboard
  • Pick breadboard #1 (cf. [ELOG 27])
  • Wipe the entire glass breadboard with IPA
  • Place the breadboard in the fixture (check which is the upper side)
• Gluing
  • Set the gluing template on the breadboard.
  • Place all of the glass components on the plate (just for confirmation)
  • Wipe (locally) both surfaces to be glued.
  • Apply glue on the component to be glued
  • Align the components in the template. Use the cantilever pusher if necessary.
  • Illuminate UV
  • Repeat the above process for all of the components.
• Close the transport fixture and wrap with Al foil

26 March (Tue):

- Curved mirror characterization (Koji, done)

- Input optics for the cavity locking (Zach)

Faraday, BB EOM, Resonant EOM, AOM, MZ

27 March (Wed)

- AOM drift investigation (Lisa, Zach)

- Cavity input optics ~ Fiber coupling (Zach)

Action Items

• Glue curved mirror sub-assys.
• R&T measurement

28 March (Thu):

• Rebuild the bottom template in the lab
• Place the bottom template on the OMC
• Glue the PZTs on the mounting prisms (x2)
• Glue the curved mirrors on the PZTs (x2)
• R&T measurement
• Placing optics on the OMC breadboard
   
• Better coupling to the fiber
• Matching to the OMC cavity

29 March (Fri):

Start gluing bottom side: Set 4 cavity mirrors and 1 HR mirror
   and try to resonate beam.  Glue when OK.

Place BS and DCPD mounting brackets.  Glue when OK.
Friday: Place QPDs and rest of optics.  Glue when OK.

WB 1 April

• Testing at CIT
  
  • Transmission / Coupling / Loss
  • FSR / TMS
  • Power dependence
  • PZT position dependence
  • Back scattering
  • Openloop TF
  • PZT TF
  • Noise measurement
• Epoxy cure bake at CIT
• Retest at CIT
  
  • ditto

WB 8 April or after

• Packing
• Shipping - Shipping box?
• Optical Testing at LLO (2 days anticipated)

WB 18 March

• Diode test
  
  • Dark current / Dark noise / Impedance
  • Quantum Efficiency test (but with glass)
  • Diode given to Bob for cleaning
• Research possible issue of UV light on 1064 HR coating
  
  • ~ppm order loss increase after depositing 3J/cm^2 in 8 hours (i.e. same order to our illumination but in 10s for us)
  • Sent an e-mail to Ke-Xun Sun -> So far, no reply.
• Glue test of PZT+prism+curved mirror with UV bond epoxy 
  
  • Done. Found some handling issues on the fixture.
• Preparation of N2 line:
  
  • Done

Action items:

• Bake test at 100°C for 1 hour at CIT 
  
  • Will be done on 25 Mon-26 Tue at Bob's lab
• Curved mirror characterization
• R&T measurement

The OMC cables #4 arrived on Feb 3rd. (See Attachment)

This shipment included two DCPD cables and two QPD cables. It means that the direct wiring from the PZT to the mighty mouse connectors was not included in the shipment.

Inspection

Updated ICS (Shipment-12578) and moved those parts to Storage-9482.

Inspection showed the following:

• Serial numbers matched the packing list
• SN S1301807: We observed some discoloration on the Gore wire close to one cable termination. [Attachment 1]
  • greenish tint
  • appeared to be superficial
  • slight removal observed when gently wiped with an IPA soaked AlphaWipe ("red wipe")
  • did not follow the helical of the teflon sheath
  • recommend additional inspection when Unit 4 build is resumed
• Cables were returned to the box labeled "OMC Cables" in the south cabinets in the OMC lab.

Observations for aLIGO OMC Unit 4 Build

An ICS Record Navigator search of onboard OMC cables reveals the following quantities appear to have been fabricated for aLIGO.

• D1300371 = Qty 3
• D1300372 = Qty 5
• D1300374 = Qty 3
• D1300375 = Qty 5

The leftover cables are all of the long variety (D1300372, D1300375), and the received quantities make sense. 3 aLIGO OMC assemblies used quantity 3 of each cable, leaving the remaining cables which had been stored at LHO:

• D1300372 = Qty 2
• D1300375 = Qty 2

The received cables from LHO may apparently be used interchangably, and the extra slack (~ 5", compared to the D1300371, D1300374 part numbers) should be managable.

Next Steps for aLIGO OMC Unit 4 Build

We will move forward in fabricating Unit 4 with the received cables from LHO, despite their extra length.

To complete the Unit 4 on board cable set (refer to OMC_Lab/203), we will need to crimp pins onto the PZT leads, and we need to find, clean, and bake quantity 1 4 pin mighty mouse connector.

• PZT leads terminate crimp pins inserted into Glenair Mighty Mouse 803-003-07M6-4PN-598A (per OMC_LAB/203, record navigator)
• Cable bracket interface to OMCS is Glenair Mighty Mouse 803-003-07M6-4PN-598A (per D1300376-v3).

I will ask Chub to see if there are any Class A spares of the PZT termination connector already on hand.

- QPD mount aligned, QPD output checked
  The spots are with 100um from the center of the diodes. [ELOG Entry (2nd photo)]

- TMS/FSR dependence on the PZT V
  Shows significant dependence on the PZT voltages
  It seems that the curvartures get longer when the voltages are applied to the PZTs.
  The effect on these two PZTs are very similar. The dependence is something like
  (TMS/FSR) ~ 0.219 - 1e-5 V
  May cause resonance of the higher-order modes (like 13th order of the 45MHz sidebands) at a specific range of the PZTs.
  We can't change anything any more, but the impact needs to be assessed

- DC response of the PZTs [ELOG Entry]
  PZT voltages were swept. Observed multiple fringes during the sweep.
  The data to be analyzed.

- AC response of the PZTs [ELOG Entry]
  PZT1 and PZT2 well matched. The first resonance at 10kHz.

- Open loop TF of the servo
  The UGF more than ~30kHz.

- Cleaning of the main optics with First Contact
  Done. Visible scattering seen with an IR was reduced, but still exist.
  All four cavity mirrors have about the same level of scattering.
  Each scattering is a group of large or small bright spots.
  It's actually a bit difficult to resolve the bright spots with the IR viewer.

- Raw transmission: i.e. Ratio between the sum of the DCPD paths and the incident power
  May 8th (before the baking):      0.918
  May 8th (First Contact applied): 0.940 (improved)
  Jun 2nd (after the baking):         0.927 (worse)
  Jun 2nd (First Cotact applied):   0.964 (improved)

- TMS/FSR/Finesse change before/after cleaning [ELOG Entry]
  Just a small change from the parameters before the bake.
  No quantitative difference.

  Method:
  BB EOM produces the AM sidebands together with the PM sidebands.
  Ideally, the PM sidebands does not produce the signal at the transmission, the output is dominated by the AM component.
  This is only true when there is no lock offset. In reality the curve is contaminated by the PM-AM conversion by the
  static offset or dynamic deviation of the locking point. So I had to take the central part of the TF and check the
  dependence of the fit region and the finesse.

  Before the cleaning: Finesse 396.9
  After the cleaning: Finesse 403.8

To Do

- Placement of the DCPD housings
- Through-put test with DCPDs
- Transmission dependence on the incident power
  (although the max incident is limited to ~35mW)

- Application of the first contact for the surface protection

[Joe, Phillip, Koji, Stephen]

*draft post, please add anymore info if I missed something*

• made initial alignment of the cavity. To do this we used the periscope mirrors to aim the incoming beam at the centre of the first mirror and second (1st curved mirror) mirror. Using the micrometers (initial positions was 0.20mm), we moved the first curved mirror so that it hit the third mirror. We then used a combination of the periscope and first curved mirror movements to start seeing 2 or 3 round trips. micrometer was set to roughly 0.11mm. We then only used  periscope mirrors to align the beam into the cavity.
• We set up a wincam at the transmission of the cavity. This was a useful was of seeing what mode was being transmitted through the cavity. We walked the beam with the periscope mirrors until we saw flashes of the TM00 mode.
• Once the cavity was transmitting TM00 modes, we started to lock it. Once it was locked we looked at the the spot positions of beam on the mirrors. Phillip looked with an IR viewer and could see that the spots were too high on both the curved mirrors
• We set up a CCD to capture an image of this. Two post holders have been left in place for easy movement of the CCD.

General notes about working with this set up. The lens on the CCD can come off quite easily, as you just change how much its screwed on to change the focus. Care should be taken that you don't know the template with this as well, as the camera is quite close to the template (and near the edge of the bench!). Also be mindful of the PZT wires, as they can pull the mirrors out of position.

Attachment 1 shows the position of the spots on the mirrors A14 and PZT11. The spots are about 3mm ish from the centre of the curved mirror in the vertical and horizontal direction. 

Attachment 2 sketch of mirror positions.

Attachment 3 shows the postion of the spot on PZT13. The spot is less near the edge than on PZT11, but its still 2mm ish from the centre of the curved mirror in both directions.

To move the beam horizontally we can use the alignment matrix in appendix C of T1500060. However since we don't have control over the pitch of the mirrors, moving the spots down could require us to inspect the glass breadboard/prisms for dust. We suspect that PZT could be the culprit, as we could not see newtonian rings between its base and the glass breadboard. One way to test this idea is just to clean the bottom of the PZT with acetone, and see if that improves the spot position. If we don't have to do any work to realign it, then this was not the issue.

Koji pointed out that the spot in attachment 1 is very near the edge of the optic, so shifting the beam horizontally could also fix the vertical issue. 

The spot on CM1 was found displaced by 3.4mm (horiz.) and 3.0mm (vert.) in the upper right direction looking from the face side.
The spot on CM2 was found displaced by 1.2mm (horiz.) and 1.8mm (vert.) in the upper left direction looking from the face side.

The drawing on the left side of the attachment shows the estimated misalignment when we think they all come from the curved mirrors.
As for the yaw misalignment, CM1 and CM2 were 3.9mrad and 5.6mrad rotated (misaligned) in CW, respectively.
As for the pitch misalignment, CM1 and CM2 has 1.7mrad (narrowing) and 3.5mrad (widening), respectively. We have no adjustment for this.
Let's say if this comes from the dusts on the bottom of the prisms, CM1 has ~17um one, and CM2 has ~35um one beneath them. The question is if we can believe this or not? This should be checked with the Newton fringes we can see at the bottom of the prisms.

L1 OMC is back on the table for the action next week.

The OMC came back to the table again.

No obvious change is visible: no crack, no delamination

The OMC was fixed on the table and the beam was aligned to the cavity

[Joe, Koji, Liyuan, Philip, Stephen]
Work done on 16.04.2019

Finishing assembly of transport box
Assembly worked fine except for the clamping structure to clamp the lid of the transport box to the bottom part.
It seemed that some of the plastic of these clamps became brittle during the baking. The plastic was removed and the
clamps where wiped clean. It appears that the clamps can't be locked as they should. Still the transport box should be fine
as the long screws will mainly clamp the two parts together.

Preparing the transport box to mount the breadboard
The lid of the the transport box was placed upside down and clamped to the table. All peak clamping structures where pulled back as far as possible.

Preparation and cleaning of the breadboard
We unpacked the breadboard and found lots of dust particles on it (most likely from the soft paper cover which was used). We used the ionized nitrogen gun
at 25 psi to get rid of the majority of particles and cross-checked with a bright green flash light before and after blowing. The second stage of cleaning was done
below the clean room tent and included the wiping of all surfaces. The breadboard was then placed into the prepared lid of the transport box and clamped with peak
screws.

Unpacking of the template
The previously cleaned template was unpacked while the last layer of coverage was removed below the cleanroom tent.

Template adjustment on the breadboard
All peak screws of the clamping structure of the template where removed. The template was placed onto the breadboard only seperated by peak spacers.
All peak screws have been inserted for horizontal clapming. A calipper was used to measure the distance of each edge of the template to the edge of the
breadboard. For documentation the labeled side of the bradboard (facing away from the persons on the pictures) of the upside down breadboard is defined to 
be the south side, continuing clockwise with west, north and east. First rough alignment was done by shifting the template on the breadboard and then the 
peak screws where used for fine tuning. The caliper values measured where:
North   C 8.32mm     E 8.52 mm     W 8.41 mm
East     C 8.08 mm
South   C 8.32 mm
West    C 8.02 mm
(E indicating east side position, W indicating west side position and C indicating center position)

The OMC mode matching sled was fixed on the nominal part of the table. Then the OMC was located at the nominal position marked by three poles.

The input periscope was adjusted to have the input beam roughtly centered on the OMC QPDs. This made the beam from FM2 aligned to the missing CM1, and the beam just went through the hole of the mounting prism. Very promising!

I wanted to use the new (modified) mirror gluing fixture to hold a curved mirror on the mounting prism. It turned out that the fixture was neither cleaned nor assembled. I will ask Downs Team to help me to get the cleaned and assembled fixtures.

Meanwhile, I just reused the original gluing fixture upside down in order to proceed cavity alignment and locking. (Attachment 1)
In fact, once the mirror is placed on the mounting prism, the cavity started to flash without further alignment. I thank for the very precise (repeatable) alignment of the OMC optics and PD/QPDs.

The next steps are initial cavity locking, more alignment, and mode matching.

The OMC cavity was locked. The alignment was precisely adjusted. The mode matching was optimized by the lens positions. The reflection during the lock is ~0.01 compared to the full reflection on non-resonance, meaning the mode matching is ~99%. The error signal was maximized (i.e. demod pahse was adjusted) by sweeping the modulation frequency. Note that the EOM is broad band. The modulation freq chosen today was 34.6MHz.

Some notes:

- The error signal has not been preamplified at all yet. Because of this, the reflection is very much sensitive to the input offset.

- The OMC needs wind shield to prevent from the noise caused by air turbulance.

- The laser PZT was actuated via the Thorlabs HV amp. Otherwise, the thermal path needs to be configured.

- One of the CCD monitor is dead. Needs more replacement.

- All the electronics should be moved to the rack. This required long BNC and SMA cables.

- The optical table needs cleaning.

3rd OMC power budget (2014/7/2)

Input power: 34.8mW

REFLPD dark offset:  -7.57mV
REFLPD unlocked: 6.22 V
REFLPD locked: 110mV

Transmitted Power: 16.8mW (T) and 15.9mW (R)
CM1 transmission: 0.176mW
CM2 transmission: 0.181mW

Cavity Finesse: 399.73

Junk light: 0.64mW (out of 34.8mW)
Coupled beam: 34.16 mW (out of 34.8mW)
Mode Matching: 0.982
Cavity reflectivity: 467ppm
Loss per mirror in ppm: 63.8ppm
Cavity transmission (for TEM00 carrier): 0.957

FM1: R = 0.992277, T = 7659.46
FM2: R = 0.992277, T = 7659.46
CM1: R = 0.999895, T = 41.5461
CM2: R = 0.999893, T = 42.7309

Compare the above number with the best result obtained during the alignment trials

Input power: 34.4mW

REFLPD dark offset:  -7.5mV
REFLPD unlocked: 5.99 V
REFLPD locked: 104mV

Transmitted Power: Total 32.7mW (T+R)
CM1 transmission: 0.194mW
CM2 transmission: 0.194mW

Cavity Finesse: 400

Junk light: 0.631mW (out of 34.4mW)
Coupled beam: 33.77 mW (out of 34.4mW)
Mode Matching: 0.982
Cavity reflectivity: 255ppm
Loss per mirror in ppm: 39.7ppm
Cavity transmission (for TEM00 carrier): 0.968

[koji,philip,joe,liyuan,stephen]

need to add spot positions.

Mirrors: PZT11,PZT22, A14, A5

Mode matching = 97.72%

15.66-> 15.30mW coupled.

~100uW for QPD

->15.2mW in cavity

Trans = 14.55mW -> 95.7% transmission

The flat mirrors were the ones with the most scattering, so we thought about how to improve it. We tried to move the first flat mirror by pushing it with our finger so that he beam would move along the optic. We tried this a couple of times, however the second time we moved it we lost our alignment and could not retrieve it. We looked at the mirror and we could see quite a lot of newtonian rings. We could see a small fibre on the glass bread board. We cleaned the optics base and the gbb, and we could get the alignment back. The beam was aligned to the cavity, the spots no longer hit the centre of the CM2. 

We measured the power budget again.

mode matching = 1-47/2680 = 0.9824, 98.2% mode matching

same p_normalise so

15.66-> 15.34mW coupled.

~15.24mW in cavity

transmission = 14.45, so 94.8% transmission.

Koji noticed that FM1 wasn't touching the template correctly, so he re-aligned the cavity.

Afternoon session - UV Bonding (E1300201-v1 procedure 6.4.4 "Gluing" using procedure in section 7.2 "UV Gluing")

Wiped down UV PPE, UV Illuminator, and UV Power Meter

Applied Optocast 3553-LV Epoxy to sample fused silica optics, to test quantity of glue needed and to become familiar with the process and tools. Philip and Joe each created a successful bond. Joe's had 3 visible spots in the bulk of the bond. Acetone was used to scrub some residue of epoxy from the surface near the OD, which was likely cured. Short duration exposure (seconds) to acetone at the perimeter of the bond did not yield any weakening of bond.

While test pieces were bonded, Koji was making some adjustments to the cavity alignment in preparation for gluing of the steering mirror BS1.

Koji noticed that the spring clamp was causing pitch in the BS1 mirror, so he recommended that we utilize the "restrain by allen key" technique to load the mirror during curing.

Once aligned, we tried taking the BS1 mirror out of the template and then putting it back. We did this twice and both times the cavity needed realigning (with the curved mirrors as well as the input steering periscope). Why is this? Since the mirror was touching the template it should not have become misaligned right? Maybe the template moves slightly? I think before glueing in the cavity mirrors we should find out why probably? Koji took a look and claimed that a few optics may have been unconstrained. 

Planning between Koji and Joe led to placement of 5 drops of epoxy on the BS1 surface, to match the bonding area. At this point we noticed that the template was not secured very well, by poking down on it we could see it move. This might explain why we are becoming misaligned very easily. Once the prism was back on the board, Koji used allen keys to move around the prism. This was done until we could align it again (i.t looked too pitched). The beam was aligned back into the cavity, and the UV light was used to cure the bond. The reflected DC when locked was

• pre-cured = 47mV
• cured = 55 mV

so it looks ok still.

Spot positions were inferred from the photos

On Feb 16, Camille and I attampted at locking the OMC cavity. It was quick to re-align the beam to the cavity (by using only the fine adjustment of the output fibre couple). This was done by looking to minimize the power reflected from the cavity and observing the mode shapes on the CCD. After we achieved locking we placed the lid of the OMC back and turned off the laser. 

As performed in the ELOG 202, the PZTs of the OMC 002 were tested.

DC response was measured by sweeping each PZT with 0-150V triangular voltage at 11Hz. Acquire 0.2sec of the tie series using an oscilloscope to get the PDH error, cavity transmission, and the sweep signal.

The voltage where the tranmission peaks were observed were fitted were recorded. One fringe corresponds to the displacement of 532nm. So the displacement and the applied volatagewere fitted witha linear function.

This gave the PZT response for PZT1 and PZT2 to be 14.9nm/V and 14.4nm/V.

AC response was measured with SR785. The PZT was shaken with 1~50mVpp signal with the DC offset of 5V while the OMC was locked with the feedback to the laser fast PZT. The transfer function from the applied PZT voltage to the servo output were measured. The closed loop TF was also measured to remove the effect of the servo control.  The DC levels of the responses were calibrated using the values above.

The beam height in the cavity became totally different from the previous one and the shims needed to be much thicker than before. This is probably because of the alignment of the newly-glue curved mirror.

As the beam height is 2~2.5mm higher, two shims need to be stacked. The preliminary check of the heights using the alignment disks (dummy PDs) suggested the following combinations.

QPD1(SHORT)  D1201467-03 (SN 007) + D1201467-03 (SN 008) (2.0 mm + 2.0 mm = 4 mm)
QPD2(LONG)   D1201467-01 (SN 001) + D1201467-01 (SN 002) (1.5 mm + 1.5 mm = 3 mm)
DCPD1(TRANS) D1201467-02 (SN 006) + D1201467-03 (SN 005) (1.75mm + 2.0 mm = 3.75 mm)
DCPD2(REFL)  D1201467-02 (SN 002) + D1201467-03 (SN 006) (1.75mm + 2.0 mm = 3.75 mm)

This resulted that the fixing button head socket screws for the PD housings to be replaced from 5/16" to 7/16". Stephen kept CLASS A spare screws from Jeff's time.

For the DCPD alignment, a cap-removed Excelitas 3mm InGaAs PD is used. -> This needs to be returned to the PD stock next time.

- DCPD1 was aligned using the zoomed CCD image (Attachment 1). Once the beam is aligned, the angle was tweaked to have the reflection nicely dumped by the glass beam dump (Attachment 2).

- DCPD2 was aligned too. (Attachment 2/3)

- The two housings were fastened by a torque wrench at 2 inch lb.

Next step:

Continue with the QPDs. The QPD amp was already set.

Notes:
The cable of the CCD monitor has a problem -> need to check what's wrong
The servo box probably have large offset at the output stage or somewhere (but not input stages).

QPD#              QPD1       QPD2
Housing#          #004       #008
Diode#            #44        #46
Shim              (see OMC ELOG 323)
-------------------------------------
Power Incident    252.3 uW  266.0 uW
Sum Out           174.2 mV  176.0 mV   +0.3
Vertical Out      + 4.7 mV  +19.0 mV   +0.2
Horizontal Out    -16.1 mV  - 8.0 mV   +0.0
SEG1              -52.4 mV  -53.  mV   -0.1
SEG2              -37.6 mV  -47.  mV   -0.1
SEG3              -41.8 mV  -34.  mV   -0.1
SEG4              -43.7 mV  -36.  mV   -0.1
-------------------------------------
Spot position X   +39   um  +15. um  (positive = more power on SEG1 and SEG4)
Spot position Y   - 8.1 um  -56. um  (positive = more power on SEG3 and SEG4)
-------------------------------------
Responsivity[A/W] 0.69      0.66
Q.E.              0.80      0.77
-------------------------------------

Arrangement of the segments
View from the beam
/ 2 | 1 X
|---+---|
\ 3 | 4 /

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

I(w,x,y) = Exp[-2 (x^2 + y^2)/w^2]/(Pi w^2/2)

(SEG_A+SEG_B-SEG_C-SEG_D)/(SEG_A+SEG_B+SEG_C+SEG_D) = Erf[sqrt(2) d/w]

d: distance of the spot from the center
w: beam width

There was a concern that the transmission from CM1 has additional fringes. The shape of the transmitted beams from CM1, CM2, and FM2 (main) werecaptured with WinCamD.
Indeed CM1 and CM2 have the fringes, but it does not exist in the main transmission. So it seems that the fringes are associated with the curved mirrors. But how???

Belated entry: OMC(004) FSR / Finesse measurement (May 3rd, 2023)

1) FSR measurement with offset locking (Attachment 1)
FSR: 264.8003 +/- 0.0007 [MHz]
Cavity roundtrip length: 1.132146 +/- 0.000003 [m]

2) RFAM Injection (Attachment 2)

• Placed a PBS before the OMC
• Placed an HWP before the above PBS
• HWP before the EOM was rotated

FSR: 264.794 +/- 0.001 [MHz]
Cavity roundtrip length: 1.132174 +/- 0.000005 [m]
Finesse: 369 +/- 1

Note that the finesse looks lower than expected from the transmission.

Belated entry: OMC(004) FSR / Finesse measurement (Jun 13th, 2023)

RFAM Injection (Attachment 1)

FSR: 264.7939 +/- 0.0004 [MHz]
Cavity roundtrip length: 1.132173 +/- 0.000002 [m]
Finesse: 381.3 +/- 0.4

Note that the finesse still looks lower than expected from the transmission.

Belated entry: OMC(004) PZT Slow scan / freq response measurements (May 10/11/17, 2023)

PZT DC scan measurement showed that CM1 had a significantly larger response than the usual PZT responses, and CM2 has the one significantly less. The measurements were repeated and the same result was confirmed.

 Curiously enough, the AC response didn't show a significant difference between the two PZT responses.
Further investigation showed that CM2 shows a similar response to CM1 at low voltage, but has a reduction of the response at high V (like >100V).

So there is something strange with CM2.

Meanwhile, CM1 actuation shows much larger angular coupling and also increased cavity loss.
Therefore, CM1 should be used for the shutter function, and CM2 for the OMC servo.

QPD#              QPD1       QPD2
Housing#          #008       #009
Diode#            #62        #70
Shim              2.50mm 05  0.75mm 08   (see D1201467)
-------------------------------------
Power Incident     76.5 uW   71.5 uW
Sum Out            49.0 mV   50.2 mV
Vertical Out      -16.0 mV    8.2 mV
Horizontal Out    - 2.4 mV   -3.6 mV
SEG1              - 8.2 mV  -16.2 mV
SEG2              - 8.0 mV  -13.0 mV
SEG3              -15.1 mV  - 9.5 mV
SEG4              -17.4 mV  -11.5 mV
-------------------------------------
Spot position X   + 8   um  +33   um  (positive = more power on SEG1 and SEG4)
Spot position Y   +81   um  -52   um  (positive = more power on SEG3 and SEG4)
-------------------------------------
Responsivity[A/W] 0.64      0.70
Q.E.              0.75      0.82
-------------------------------------

Arrangement of the segments
View from the beam
/ 2 | 1 X
|---+---|
\ 3 | 4 /

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

I(w,x,y) = Exp[-2 (x^2 + y^2)/w^2]/(Pi w^2/2)

(SEG_A+SEG_B-SEG_C-SEG_D)/(SEG_A+SEG_B+SEG_C+SEG_D) = Erf[sqrt(2) d/w]

d: distance of the spot from the center
w: beam width

We are going to use A5 and A14 for FM1 and FM2. (The role of these two can be swapped)

The reason for the selection is the better perpendicularity among the available prisms.

A11 has the best perpendicularity among them. However, the T didn't match with the others. The pair of A5 and A14 has a good matching with small compromise of the perpend.

The attachment is the excerpt from T1500060.

We are going to use B6 for the DCPD BS (BS2), and B1 for the QPD BS (BS3). Their role can not be swapped.

B6 has the best loss among the available ones, while the perpendicularity is not so critical due to the short arm.

B1 has the OK perpendicularity, while the loss is also moderately good.

The attachment is the excerpt from T1500060 with some highlighting.

We are going to use E6, E9, E11, and E14 for BS1, SM1, SM2, and SM3. They (and E18) are all very similar.

The attachment is the excerpt from T1500060 with some highlighting

D1200105 SN006 was selected as the breadboard for OMC(004).
The reason is the best parallelism among the unused ones.

The attached is the excerpt from T1500060 with the #006 highlighted.

[Stephen Koji]

The baking of the PZT subassemblies was more complicated than we initially thought.

The four PZT subassemblies were placed in the air bake oven A. We meant to bake the assemblies with the ramp time of 2.5h, a plateau of 2h at 94degC, and slow ramp down.

The oven controller was started and the temperature has been monitored. The ramping up was ~20% faster than expected (0.57degC/min instead of 0.47degC/min), but at least it was linear and steady.

Once the temperature reached the set temperature (around t=120min), the temperature started oscillating between 74 and 94degC. Stephen's interpretation was that the PID loop of the controller was not on and the controller falled into the dead-bang mode (=sort of bang-bang control).

As the assembly was already exposed to T>70F for more than 2.5hours, it was expected the epoxy cure was done. Our concern was mainly the fast temperature change and associated stress due to thermal expansion, which may cause delamination of the joint. To increase the heat capacity of the load, we decided to introduce more components (suspension balance weights). We also decided to cover the oven with an insulator so that the conductive heat loss was reduced.

However, the controller thought it was already the end of the baking process and turned to stand-by mode (i.e. turned off everything). This started to cause rapid temp drop. So I (Koji) decided to give a manual heat control for mind cooling. When the controller is turned off and on, it gives some heat for ramping up. So the number of heat pulses and the intervals were manually controlled to give the temp drop of ~0.5degC/min. Around t=325, the temperature decay was already slower than 0.5degC/min without heat pulse, so I decided to leave the lab.

We will check the condition of the sub-assemblies tomorrow (Fri) afternoon.

[Koji Stephen]

The four PZT sub-assemblies were glued in the gluing fixtures. There were two original gluing fixtures and two additional modified fixtures for the in-situ bonding at the repair of OMC(002).

- Firstly, we checked the fitting and arrangements of the components without glue. The component combinations are described in ELOG 329.
- Turned on the oven toaster for the cure test (200F).
- Then prepared EP30-2 mixture (7g EP30-2 + 0.35g glass sphere).
- The test specimen of EP30-2 was baked in the toaster oven. (The result shows perfect curing (no stickyness, no finger print, crisp fracture when bent)
- Applied the bond to the subassemblies.
- FInally the fixtures were put in airbake Oven A. We needed to raise one of the tray with four HSTS balance weights (Attachment 2).

[Stephen, Shruti, Koji]

We worked on the gluing of the PZT sub-assy (#9 and #10) along with the designed arrangement by Shruti (OMC ELOG 374).

The detailed procedures are described in E1300201 Section 6.2 PZT subassembly and Section 7.3 EP30-2 gluing.

We found that the PZTs, which were debonded from the previous PZT sub assy with acetone, has some copper wires oxidized. However, we confirmed that this does not affect the conductivity of the wires, as expected.

The glue test piece cooked in the toaster oven showed excellent curing. GO SIGNAL

Stephen painted the PZT as shown in Attachment 1.

The fixtures were closed with the retaining plate and confirmed that the optics are not moving in the fixtures.

At this point, we checked the situation of the air-bake oven. And we realized that the oven controller was moved to another vacuum oven and in use with a different setting.

Stephen is going to retrieve the controller to the air bake oven and test the temp profile overnight. Once we confirm the setting is correct, the PZT sub assys will be heat cured in the oven.  Hopefully, this will happen tomorrow. Until then, the sub-assys are resting on the south flow bench in the cleanroom.

Friday: [Stephen, Koji]

As the oven setting has qualified, we brought the PZT assys in the air bake oven.

Monday: [Stephen, Shruti, Koji]

We brought the PZT assys to the clean room. There was not bonding between the flexture and the PZT subassy (Good!). Also the bonding o at each side looks completely wetted and looks good. The package was brought to the OMC lab to be tested in the optical setup.

[Koji Stephen]

(Friday afternoon) We retrieved the PZT sub-assemblies to the clean room.

We started removing the ASSYs from the fixtures. We noticed that some part of the glass and PZT are ripped off from the ASSY and stuck with the fixture. For three ASSYs (except for #9), the effect is minimal. However, ASSY #9 has two large removals on the front surface, and one of the bottom corners got chipped. This #9 is still usable, I believe, but let's avoid to use this unit for the OMC. Individual inspection of the ASSYs is posted in the following entries.

This kind of fracture events was not visible for the past 6 PZT sub-ASSYs. This may indicate a few possibilities:
- More rigorous quality control of EP30-2 was carried out for the PZT ASSY bonding. (The procedure was defined after the past OMC production.) The procedure leads to the strength of the epoxy enhanced.
- During the strong and fast thermal cycling, the glass was exposed to stress, and this might make the glass more prone to fracture.

For the production of the A+ units, we think we can avoid the issues by modifying the fixtures. Also, reliable temperature control/monitor technology should be employed. These improvements should be confirmed with the bonding of spare PZTs and blank 1/2" mirrors before gluing any precious components.

Sub-ASSY #10

Attachment #1: Mounting Block SN021

Attachment #2: PZT-Mounting Block bonding looks just excellent.

Attachment #3: The other side of the PZT-Mounting Block bonding is also excellent.

Attachment #4: The mirror-PZT bonding also look excellent. Some barrel fracture is visible at the lower left of the mirror.

Sub-ASSY #7

Probably the best glued unit among the four.

Attachment #1: Mounting Block SN001

Attachment #2: PZT-Mounting Block bonding looks completely wet. Excellent.

Attachment #3: The other side of the PZT-Mounting Block bonding. Also looks excellent.

Attachment #4: Overall look.

Attachment #5: The mirror-PZT bonding also look excellent. The mounting block surface has many EP30-2 residue. But they were shaved off later. The center area of the aperture is clear.

Attachment #6: A small fracture of the mirror barrel is visible (at 7 o'clock).

Sub-ASSY #8

Probably the best glued unit among the four.

Attachment #1: Mounting Block SN007

Attachment #2: Overall look.

Attachment #3: Some fracture on the barrel visible.

Attachment #4: It is visible that a part of the PZT removed. Otherwise, PZT-Mounting Block bonding looks pretty good.

Attachment #5: The other side of the PZT bonding. Looks fine.

Attachment #6: Fractured PZT visible on the fixture parts.

Attachment #7: Fractured glass parts also visible on the fixture parts.

Attachment #8: MIrror bonding looks fine except for the glass chip.

Sub-ASSY #9

The most fractured unit among four.

Attachment #1: Mounting Block SN017

Attachment #2: Two large removals well visbile. The bottom right corener was chipped.

Attachment #3: Another view of the chipping.

Attachment #4: PZT-mounting block bonding look very good.

Attachment #5: Another view of the PZT-mounting block bonding. Looks very good too.

Attachment #6: Fractures bonded on the fixture.

Attachment #7: Front view. The mirror-PZT bonding look just fine.

[Koji, Philip]

Today we tested the functionality of the four remaining PZTs (11,12,13 and 22) .  Each PZT was placed within a collimated 500um beam.
Roughly half of the beam was blocked by the PZT. The PZT and a PD then acted as shadow sensor. Each PZT was tested with 0 and
150 V. The resulting power change then could be converted into a displacement of the PZT using the beam diameter.

The open light value for each of these tests was 3.25 V.

PZT 11:
0 V supply voltage     --> 1.717 V on PD
150 V supply voltage --> 1.709 V on PD
delta = 0.008 V

PZT 12:
0 V supply voltage     --> 1.716 V on PD
150 V supply voltage --> 1.709 V on PD
delta = 0.007 V

PZT 13:
0 V supply voltage     --> 1.702 V on PD
150 V supply voltage --> 1.694 V on PD
delta = 0.008 V

PZT 22:
0 V supply voltage     --> 1.770 V on PD
150 V supply voltage --> 1.762 V on PD
delta = 0.008 V

0.008 V --> 0.24% change in power on PD --> about  3.8 um displacement assuming no light which is blocked
by the PZT is hitting the PD.

We further started to drive all four PZTs over night with 100 V (half of their range) at 100 Hz.
We additionally display the impedance to ensure none of them degrades.

All four PZTs seem to be connected to Teflon coated wires. It needs to be checked if these
fulfill the vacuum compatibility requirements.

Attachment 1: Shadow sensor setup for the PZT displacement test

Attachment 2: PZT endurance test. 4 PZTs were shaken at once.

Attachment 3~5: Function generator setup 100Hz, 3.5Vpp 1.75Voffset (meant be displayed for 50Ohm load)

Attachment 6: The above setting yields 7Vpp unipolar signal @Hi-Z load

Attachment 7: The output was monitored with a 1/10 probe with the PZTs connected. This shows 10Vmax 0Vin -> Good. This photo was taken at 17:35.

Attachment 8: The test is going well @9:15 next day. (t=15.7hours = 5.6Mcycles)

Attachment 9: The test went well. The modulation was stopped @15:35. (t=21hours = 7.6Mcycles)