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  152   Fri Aug 16 16:36:19 2013 KojiOpticsGeneralOptics List

Link to the "Mirror/PZT Characterization links"

Breadboard

BB1 OMC(001) OMC
BB2 OMC(002) OMC
BB3 -
BB4 OMC(003) OMC

BB5 -
BB6 -

Mounting Prisms:

M01
M02
M06 OMC(002) CM1 (PZT ASSY #6)

M07
M10 OMC(003) CM1 (PZT ASSY #5)

M11 OMC(002) CM2 (PZT ASSY #4)
M12
M13 OMC(003) CM2
(PZT ASSY #3)
M14
M15
M16 OMC(001) CM1 (PZT ASSY #1)
M17
M20 OMC(001) CM2 (PZT ASSY #2)
M21
M22 

Mirror A:
A1  fOMC FM1
A2
  Fullerton for the scattering measurement
A3  fOMC FM2
A4 
A5 
A6  OMC(003) FM2
A7  OMC(001) FM2
A8  OMC(001) FM1
A9  OMC(002) FM1
A10
A11
A12 OMC(003) FM1
A13 OMC(002) FM2
A14 

Mirror B:
B1 
B2 
B3  OMC(001) BS2 (QPD)
B4 
B5  OMC(003) BS2 (QPD)
B6 

B7  OMC(001) BS3 (DCPD)
B8 

B9  OMC(002) BS2 (QPD)
B10 OMC(002) BS3 (DCPD)
B11

B12 OMC(003) BS3 (DCPD)

Mirror C:

C1 OMC(003) CM1 (PZT ASSY #5)
C2 Fullerton for the scattering measurement

C3 OMC(003) CM2 (PZT ASSY #3)
C4 OMC(002) CM2 (PZT ASSY #4)
C5 OMC(001) CM2 (PZT ASSY #2)
C6 OMC(001)
CM1 (PZT ASSY #1)
C7 fOMC CM1
C8 fOMC CM2 -> OMC(002) CM1 (PZT ASSY #6)

C9 OMC(002) CM1 (PZT ASSY #6) -> BURNT
C10 (Liyuan tested)
C11 (Liyuan tested)
C12 curvature untested, faux OMC CM2
C13 curvature untested

Mirror E:
E1  OMC(002) SM2
E2  OMC(002) SM3
E3  OMC(002) BS1
E4  OMC(001) SM2

E5  OMC(002) SM1
E6 
E7  OMC(003) BS1
E8  OMC(003) SM1
E9 

E10 OMC(001) BS1
E11
E12 OMC(001) SM1
E13 OMC(003) SM2
E14
E15
E16 OMC(001) SM3
E17 OMC(003) SM3
E18

PZT:
PZT11
PZT12
PZT13
PZT14 OMC(003) CM1 (PZT ASSY #5)
PZT15 OMC(003) CM2 (PZT ASSY #3)
PZT21 OMC(002) CM1 (PZT ASSY #6)
PZT22
PZT23 OMC(001) CM2 (PZT ASSY #2)
PZT24
PZT25 OMC(002) CM2 (PZT ASSY #4)
PZT26 OMC(001) CM1 (PZT ASSY #1)

 

 

  153   Fri Aug 16 17:21:38 2013 KojiGeneralGeneral[OMC002] Build started

[Jeff Koji]

The breadboard (SN2) was loaded on the transportation fixture.

The laser side template was installed and the cavity mirrors were placed.

The laser beam will be resonated in the cavity next week.

  154   Wed Aug 21 08:31:21 2013 KojiOpticsCharacterizationH1 OMC cavity alignment

Alignment of the H1 OMC cavity mirrors

- The cavity mirrors as well as the first steering mirror were aligned on the cavity side template.

- The locking of the cavity was not so stable as before. Some high freq (several hundreds Hz) disturbance makes the cavity
  deviate from the linear range. This can be mitigated by turning off the HEPA units but this is not an ideal condition.

- FSR and TMS were measured.

FSR: 264.305MHz
TMS(V): 58.057MHz
TMS(H): 58.275MHz

These suggest the cavity length L and f_TMS/f_FSR (say gamma, = gouy phase / (2 pi) ) as
L=1.1343 m        (1.132m nominal)
gamma_V = 0.219659    (0.21879 nominal)
gamma_H = 0.220484    (0.21939 nominal)


- the 9th modes of the carrier is away from the resonance 6-9 times of the line width (LW)
- the 13th modes of the lower f2 sideband are 11-15 LW away
- the 19th modes of the upper f2 sideband are 0.6-7 LW away

We still need precise adjustment of the gouy phase / cavity length, this was enough for the gluing of the flat mirrors

  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.

  156   Thu Aug 22 15:40:15 2013 KojiElectronicsConfigurationPZT endurance test

[Koji, Jeff]

Background

In response to the failure of one of the PZTs on L1OMC (LLO:8366), we have been taking place an endurance test of
the four PZT sub-assemblies in prior to their being glued on the glass breadboard.

According to the technical note by Noliac, the common mode of PZT failure is degradation of the impedance
due to cyclic actuation (like 10^7 times) with over voltage. Therefore our procedure of the test to actuate the PZTs
at least 10^7 times with half voltage of the nominal operating voltage (i.e. nominal 200V) and check the degradation
of the impedance.

Driving signal

For the driving of the PZT, a thorlabs HV amp is used. A source signal of 3.5Vpp with an offset of 1.7V is produced
by DS345 function generator. This signal turns to a sinusoidal signal between 0 and 100V in conjunction with the gain
of 15 at the HV amp.

The maximum driving frequency is determined by the current supply limit of the HV amp (60mA). The capacitance
of each PZT is 0.47uF. If we decide to cycle the signal for 4 PZTs in parallel, the maximum frequency achievable
without inducing voltage drop is 100Hz. This yields the test period of 28hours in order to achive 10^7 cycles.

P8214340.jpg

Initial impedance diagnosis

To check the initial state of the PZTs, a DC voltage of 100V was applied via 1kOhm output resistance.
(Note that this output resistance is used only for the impedance test.)
For each PZTs, both side of the resister showed 99.1V for all measurement by a digital multimeter.
Assuming the minimum resolution (0.1V) of the multimeter, the resistance of each PZT was more than 1MOhm before
the cycling test.

Failure detection

In order to detect any impedance drop of the PZTs, the driving signal is monitored on the oscilloscope via a 1:10 probe.
If there is any significant impedance drop, the driver can't provide the driving current correctly. This can be found
by the deviation of the driving voltage from the reference trace on the oscilloscope (below).

P8214337.jpg

Temperature rise

Because of the loss angle of the PZT capacitance, heating of the PZTs is expected. In order to check the temperature rise,
an IR Viewer (FLIR) was used. We did not take care of careful calibration for the PZT emissibity as what we want was a
rough estimation of the temperature.

Before the driving (LEFT) and at the equilibrium (RIGHT)
IR_0457.jpg
IR_0461.jpg

The temperature change of the PZT was tracked for an hour (below). Fitting of the points indicated that the temperature rise is 2.3degC and the
time constant of 446 sec. This level of temperature rise is totally OK. (Note that the fitting function was T = 27.55 - 2.31 Exp[-t/446.])

 

Results

DAY1:

Start driving
20:27 25.2 degC, status OK
20:33 26.7 degC, status OK
20:41 26.9 degC, status OK
20:48 27.6 degC, status OK
20:54 27.4 degC, status OK
21:10 27.4 degC, status OK
21:37 status OK
Stop driving

70 minutes of driving (i.e. 4.2x10^5 cycles) => no sign of degradation

DAY2:

Start driving
14:15, 24.5 degC, status OK
14:17, 26.0 degC, status OK
14:24, 27.0 degC, status OK
14:40, 26.8 degC, status OK
14:50, 26.8 degC, status OK
15:30, 26.8 degC, status OK
15:55 status OK
17:40 status OK
21:00 status OK (2.43Mcycles + 0.42Mcycles = 2.85Mcycles)
1d+12:00 status OK (7.83Mcycles + 0.42Mcycles = 8.25Mcycles)
1d+15:00 status OK (8.91Mcycles + 0.42Mcycles = 9.33Mcycles)
1d+18:40 status OK (10.23Mcycles + 0.42Mcycles = 10.65Mcycles)
Stop Driving

After 10.65Mcycles no sign of degradationwas found.

  157   Fri Aug 23 19:24:32 2013 KojiElectronicsConfigurationPZT endurance test (II)

The PZT tests were finished with the conclusion that the PZT won't be damaged with our expected usage.


This is another test of the PZTs to make sure small (~10V) reverse voltage does not break the PZTs.

Background

At the site, we decided to use one of the PZT, which is still alive, for the HV and LV actuation.
The HV actuation is limited to 0 to 100V while the LV actuation is 10Vdc with 1Vpp fast dithering.
This means that a reverse voltage upto 10.5V will be applied to the PZT at the worst case.

From the technical note this level of reverse voltage does not induce polarization of the PZT.
The test is to ensure the PZT is not damaged or degraded by this small reverse voltage.

Method

HV drive: Thorlabs HV amp (G=15) driven with DS345 function generator (3.5Vpp+1.7Vdc, 0.1Hz)
=> 0-100V @0.1Hz
=> The hot side of the potential is connected to the positive side of the PZT

LV drive: Phillips function generator (1Vpp+9.5Vdc@1kHz)
The driving frequency is limited by the current output of the function generator.
=> The hot side of the potential is connected to the negative side of the PZT

These drives shares the common ground.

Tests

Testing with spare PZTs 

Started @19:23 (Aug 23)
Stopped @20:15+2d (Aug 25, duration 48h52m)
17600cycles for the 0.1Hz drive.
176Mcycles for the 1kHz drive.

Checked the impedances of PZT1 and PZT2.

Apply 100Vdc via a 1kOhm resister, 0V detected across the 1kOhm resister
This is equivalent to the resistance of 1MOhm.

 

Testing with the PZT subassemblies

Started shaking of the four PZT assemblies @20:20 (Aug 25)
No impedance change observed @11:10+1d
No impedance change observed @15:30+1d
Stopped shaking of the four PZT assemblies @XXXX (Aug 26)

 

Wiring for the test

PZT_shaking.png

 

 

  158   Tue Aug 27 17:02:31 2013 KojiMechanicsCharacterizationSpot position measurement on the diode mounts

After the PZT test, the curved mirrors were aligned to the cavity again.

In order to check the height of the cavity beam, the test DCPD mount was assembled with 2mm shim (D1201467-3)
The spot position was checked with a CCD camera.

According to the analysis of the picture, the spot height is about 0.71mm lower than the center of the mount.

Attachment 1: DCPD1.png
DCPD1.png
  159   Thu Aug 29 02:52:50 2013 KojiOpticsCharacterizationH1OMC Curved Mirror Alignment

Cavity parameter was measured with 50V bias on PZT1 (CM1)

- PZT combination was changed: PZT1 #21 (PZT ASSY#6) / PZT2 #25 (PZT ASSY #4)

- 19th HOMs of the USB makes accidental resonance with the nominal cavity length.
  Because of the mirror astigmatism, HOMs spreads more than the design.
  In order to avoid these modes, the cavity length had to be moved from the nominal value (1.134m).

- The clearance between the fixture and the prism was limited. This prevents to shorten the cav length.
  The cavity length was made longer about 10mm.

-----

Cavity parameter obtained from the pitch misalignment

Free Spectral Range (FSR): 261.777947 +/− 0.000299 MHz
Cavity roundtrip length: 1.145217 +/− 0.000001 m
Lock offset: 1.636183 +/− 0.238442 kHz
Transverse mode spacing (TMS): 57.581950 +/− 0.000163 MHz
TMS/FSR: 0.219965 +/− 0.000001
Cavity pole (1st order modes, avg and stddev): 353.465396 +/− 0.657630 kHz
Finesse (1st order modes, avg and stddev): 370.302940 +/− 0.688585

Carrier 9th-order HOM: -8.1 line width away
Upper Sideband 13th-order HOM: 13.3 LW away
Lower Sideband 19th-order HOM: 2.2 LW away

-----

Cavity parameter obtained from the pitch misalignment

Free Spectral Range (FSR): 261.777106 +/− 0.000226 MHz
Cavity roundtrip length: 1.145220 +/− 0.000001 m
Lock offset: 0.215937 +/− 0.183434 kHz
Transverse mode spacing (TMS): 57.875622 +/− 0.000116 MHz
TMS/FSR: 0.221087 +/− 0.000000
Cavity pole (1st order modes, avg and stddev): 356.862001 +/− 0.448102 kHz
Finesse (1st order modes, avg and stddev): 366.776766 +/− 0.460598

Carrier 9th-order HOM: -4.1 line width away
Upper Sideband 13th-order HOM: 19.1 LW away
Lower Sideband 19th-order HOM: 10.8 LW away

-----

We could avoid hitting the 19th modes of the 45MHz sidebands.

First accidental hit is the 28th order modes of the lower sideband.

Red: Carrier
Blue: Upper sideband (45MHz)
Green: Lower sideband (45MHz)

Attachment 1: Cav_scan_response_130828_Pitch.pdf
Cav_scan_response_130828_Pitch.pdf
Attachment 2: Cav_scan_response_130828_Yaw.pdf
Cav_scan_response_130828_Yaw.pdf
  160   Thu Aug 29 18:55:36 2013 KojiMechanicsGeneralI1 OMC top side gluing (UV)

The glass components for the I1 OMC top side were glued by the UV glue.

Breadboard SN#4
Wire bracket SN#5/6/7/8

  161   Fri Aug 30 12:14:50 2013 KojiOpticsGeneralH1 OMC Cavity length adjustment

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.

P8284343.jpg

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.

Attachment 1: Gouy_FSR_130827.nb.zip
  162   Fri Aug 30 12:22:56 2013 KojiOpticsGeneralH1 OMC Cavity side UV gluing

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.

  163   Fri Aug 30 12:24:28 2013 KojiOpticsCharacterizationH1OMC Spot positions

Beam heights on the diodes

DCPD1: 14.459mm -> With 1.5mm shim, the beam will be 0.038mm too low.

DCPD2: 14.221mm -> With 1.25mm shim, the beam will be 0.026mm too low.

QPD1: 14.691mm -> With 1.75mm shim, the beam will be 0.056mm too low.

QPD2: 14.379mm -> With 1.5mm shim, the beam will be 0.118mm too low.

Attachment 1: DCPD1.png
DCPD1.png
Attachment 2: DCPD2.png
DCPD2.png
Attachment 3: QPD1.png
QPD1.png
Attachment 4: QPD2.png
QPD2.png
  164   Fri Aug 30 12:25:29 2013 KojiGeneralGeneralH1 OMC Invar mount gluing

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

Attachment 1: P8304368.JPG
P8304368.JPG
Attachment 2: P8304370.JPG
P8304370.JPG
  165   Tue Sep 3 17:03:25 2013 KojiGeneralGeneralH1 OMC gluing completed

[Koji Jeff]

H1 OMC All Gluing completed

5 Glue H1 beam dumps (UV)

4 glass wire brackets glued on the H1 topside (UV) SN: #9/10/11/12

6 Invar blocks glued on the H1 topside (EP30) SN: #13/14/15/16/18/19

  166   Wed Sep 4 22:22:54 2013 KojiGeneralGeneralH1 OMC wrapped and moved to the bake lab.

[Koji, Jeff]

We moved the H1OMC to the bake lab.

Chub set up the vacuum bake oven (Oven F) and running without the actual OMC.

We use low temperature (55degC) for the baking.

The actual OMC will be baked from tomorrow afternooon.

  167   Sat Sep 7 17:20:56 2013 KojiGeneralGeneralOMC/PD lab optical table wrapping

[Koji Jeff]

In order to prepare for the splinkler installation on the HEPA enclosure, the table with the optics was wrapped with Ameristat sheets.

Attachment 1: P9064377.JPG
P9064377.JPG
  168   Fri Sep 13 15:09:20 2013 KojiGeneralGeneralSprinkler installation: done

A sprinkler head was installed on the HEPA enclosure. The head is covered with a plastic cap.

Attachment 1: P9134379.jpg
P9134379.jpg
Attachment 2: P9134378.jpg
P9134378.jpg
  169   Mon Oct 14 13:40:16 2013 KojiOpticsCharacterizationH1 OMC Optical testing

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

 

 

  170   Mon Oct 14 15:50:55 2013 KojiOpticsCharacterizationH1 OMC Power budget

LHO OMC power budget

Date 2013/9/17 2013/9/17 2013/10/16 2013/10/22
Condition  Before the cleaning  After the cleaning  Confirmation  Confirmation
Input Power [mW]  35.2  35.4  34.54  34.9
REFLPD dark offset [V]  -0.00763  -0.00763  -0.00772  -0.000759
REFLPD unlocked [V]  0.0749 +/- 0.0005  0.067+/- 0.0005  0.0640+/-0.0005  0.0530+/-0.0001
REFLPD locked [V]  5.49 +/- 0.01  5.55+/-0.01  5.28+/-0.01  5.26+/-0.01
         
 Transmitted Power to DCPD1 (T) [mW]  16.5  16.4  16.1  16.0
 Transmitted Power to DCPD2 (R) [mW]  15.9  16.2  15.55  15.55
 FM2 transmission [mW]  32.4  32.9+/-0.1  -  -
 CM1 transmission [mW]  0.166  0.169  0.164  0.165
 CM2 transmission [mW]  0.165  0.169  0.158  0.162
 Input BS transmission [mW]  0.234  0.218  0.230  0.227
         
 Cavity Finesse  373.114  373.114  373.114  373.114
         
 Junk Light Power (Pjunk) [mW]  0.489  0.434  0.422  0.332
 Coupled beam power (Pcouple) [mW]  34.71  34.97  34.12  34.57
 Mode Matching (Pcouple/Pin) [mW]  0.986  0.988  0.988  0.990
 Cavity reflectivity in power  0.00115  0.00119  0.00136  0.00199
 Loss per mirror [ppm]  122  124  134  167
 Cavity transmission for TEM00 carrier
 0.933  0.932  0.927  0.913

 

Attachment 1: OMC_power_budget.pdf
OMC_power_budget.pdf OMC_power_budget.pdf OMC_power_budget.pdf OMC_power_budget.pdf
  171   Tue Oct 15 18:50:08 2013 KojiOpticsCharacterizationQPD alignment

1) Deburr the bottom surfaces of the QPD housings

2) Aligned the QPDs

 

QPD#              QPD1       QPD2
Housing#          #004       #008
Diode#            #44        #46
Shim              1.75mm 001 1.25mm 001

-------------------------------------
Power Incident    125.7 uW  126.4 uW
Sum Out            80.1 mV   78.9 mV
Vertical Out      + 3.4 mV    0   mV
Horizontal Out    -23.7 mV  -26   mV
SEG1              -15.6 mV  -13.2 mV
SEG2              -13.1 mV  -13.3 mV
SEG3              -29.0 mV  -26.4 mV
SEG4              -23.2 mV  -26.3 mV
-------------------------------------
Spot position X   -13   um  - 0.8 um  (positive = more power on SEG1 and SEG4)
Spot position Y   +93   um +107   um  (positive = more power on SEG3 and SEG4)
-------------------------------------

Responsivity[A/W] 0.64      0.62
Q.E.              0.74      0.73
-------------------------------------

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

  172   Wed Oct 16 19:16:29 2013 KojiOpticsCharacterizationPD alignment

 

 shim 1.5mm 001/002

  173   Tue Oct 22 17:17:59 2013 KojiGeneralGeneralH1OMC cabling

[Chub, Jeff, Koji]

We worked on the wiring and routing of the cables.

- The cables for the PZT was installed first.

- Pins for the mighty mouse connector were crimped on the PZT wires

- Checked the wiring diagram (D1300589) to find the pinouts.
  Pin1 of the mighty mouse is connected to PZT2+, Pin2 to PZT2-, PIn3 to PZT1+, and Pin4 to PZT1-

- Then QPD and PD cables are fixed on the cable harness.

- The QPD/PD cables are attached on the diode housings.

During this process one of the DCPD mounts moved. The fixing screws were not torqued enough.
This means that all of the FC layers need to be removed and the DCPD housing should be aligned again.

- We continued on the cabling. The cables were routed on the top (cable) side.

- Some of the cable pegs were tightened by PEEK cable ties.

- We found that Pin1 and Pin2 of the PZT cables were not intact anymore.

- We ask Chub to work on the PZT pins tomorrow. The PD alignment will be taken tonight or tomorrow.

  174   Wed Oct 23 02:45:07 2013 KojiGeneralGeneralPD realignment

DCPD2 got misaligned during the cable installation. The PD alignment procedure have been gone through again.

Cavity locking

- Removed the FC layers for the cavity related mirrors.

- Aligned and locked the cavity.

PD alignment

- Loosen DCPD2. Checked the reflection with a IR card. Checked the spot on the PD with an IR viewer.

- Finger-tight the screws. Check the reflection with the card again. Check the pot on the PD with a CCD.

- If the spot positions are not satisfactory repeat the process.

- If the spot positions are satisfactory, take pictures of the CCD image.

- Fixing screws for all of the PDs/QPDs were tighten by the torque driver with a torque od 1.75 inch lb.

PD QE measurements

- Measure the power incident on the PDs.

- Set up the transimpedance amp to check the photo current.

- PD1 (T side) 9.10+/-0.03 V 13.02 +/- 0.01W -> QE ~80%

- PD2 (R side) 8.70+/-0.01 V 12.53 +/- 0.01W -> QE ~80%

- These are not strange values considering the presence of the glass caps.

PZT polarity check

- The connections between the PZT electrodes and the pins were checked.

- The positive side is marked by a knot on the wire.

FC painting

- The new FC bottle was brought from Downs, thanks to Margot.

 

  175   Mon Nov 4 19:43:56 2013 KojiGeneralGeneralH1OMC Packed

H1OMC PZT connector was replaced with the correct one. This was the final step for H1OMC.

Jeff and I packed the OMC and put it in the perikan case. It will be shipped tomorrow.

The other tools are also packed in the other box. Here is the list of the items

- Spare PD/QPDs (2 cages)
- Test PD/QPD cables
- Torque driver / bits
- Low noise transimpedance amp
- Kapton sheets
- First Contact kit
- 1/4-20 Screws for the balance weights
- OMC-Structure cables
- Preamp adapter plate
- Screws for the cable mounts
- Clean tools
  (scissors, tweezers, forceps, Diagonal pliers, long nose prier)
- Spare Peek cable ties
  176   Thu Nov 21 00:05:35 2013 KojiGeneralGeneralH1OMC electronics arrangement

Checked the PZT arrangement: Mighty Mouse Pin1&2 -> PZT2 (DCPD side), Mighty Mouse Pin3&4 -> PZT1 (QPD side)

DCPD response:
Illuminate DCPD1 (T) -> DCPD B responded in MEDM
Illuminate DCPD2 (R) -> DCPD A responded in MEDM

QPD response:
Illuminate QPD1 -> QPD A responded in MEDM
Illuminate QPD2 -> QPD B responded in MEDM

--------

DCPD1 (T) is marked as "A". This PD is SN"0288"

DCPD2 (R) is marked as "B". This PD is SN"0721"

Corresponding iLOG for the performance

Attachment 1: H1OMC_cable_arrangement.pdf
H1OMC_cable_arrangement.pdf
  177   Tue Dec 10 16:41:51 2013 KojiGeneralGeneralTo Buy

Masks / Wipes => done

  178   Tue Feb 18 18:58:38 2014 KojiGeneralGeneralLHO H1 OMC installation photos

LHO OMC installation photos

  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
misalignment.pdf
  180   Mon Mar 3 02:46:21 2014 KojiGeneralCharacterizationSpot positions scanned

Spot positions on CM1 and CM2 scanned according to the recipes provided by the previous entry.

The best result obtained was:

Transmission from FM2: 32.7mW
Incident on BS1: 34.4mW

Reflection (Unlocked): 5.99V
Reflection (Locked): 104mV
Reflection (Dark): -7.5mV

to accomodate the spot on BS1 it had to be about a mm moved from the template.

This gives us:
- Portion of the TEM00 carrier: R = 1-(104+7.5)/(5990+7.5) = 0.981
- Raw transmission: 32.7/34.4 = 0.950
- TEM00 transmission 0.950/R = 0.969
- Excluding the transmission of BS1: 0.969/0.9926 = 0.976
  => loss per mirror ~40ppm

 

  181   Tue Mar 25 17:10:10 2014 KojiOpticsCharacterizationOMC spot position estimation

Spot positions were inferred from the photos

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

STORY:

- 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???

Analysis:

- 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.

Solution:

- 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.

Attempt:

- 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

Result:

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!

Next:

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

 

  183   Mon May 12 22:43:02 2014 KojiOpticsCharacterizationMeasured FSR/TSM of the OMC cavity

Data analysis of the FSR/TSM measruement last week.

1. FSR was measured with "the golden arches" technique.

FSR = 263.0686 MHz +/- 900Hz

Lcav = 1.1396 m --> 7.6 mm too long! (nominal 1.132m)

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

TMS/FSR = 0.219366 (V) / 0.220230 (H) (Predicted value with the current cavity length 0.2196/0.2202 very close!)

We want to make this to be ~0.219 (~3% less)

With the current parameters, the 19th-order lower sideband make the coincident resonance.

Attachment 1: Cav_scan_response_Pitch.pdf
Cav_scan_response_Pitch.pdf
Attachment 2: Cav_scan_response_Yaw.pdf
Cav_scan_response_Yaw.pdf
  184   Wed May 14 02:15:15 2014 KojiOpticsCharacterizationFSR/TSM adjustment of the OMC cavity

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.

Attachment 1: Cav_scan_response_140503_Pitch.pdf
Cav_scan_response_140503_Pitch.pdf
Attachment 2: Cav_scan_response_140503_Yaw.pdf
Cav_scan_response_140503_Yaw.pdf
  185   Fri May 16 00:13:36 2014 KojiOpticsCharacterizationCavity mirror gluing part 1

BS1/FM1/FM2 for I1OMC were glued.

FM1 had to be intentionally rotated.
FM1 had to be intentionally shifted to avoid scattering spot.

Pin: 36.3 / Ptrans: 33.7 = Raw transmission 92.8%
Vunlock = 6.30 / Vlock = 0.120

Mode matching (estim) 0.98
Loss per mirror 84ppm
Cavity transmission 0.947

ummm

Tomorrow:
- Transmission needs to be optimized
- Apply 50V to a PZT
- Cavity FSR/HOM should be optimized
- gluing

Put a cover
Return power meter / DC supply

  186   Sat May 17 07:40:14 2014 KojiOpticsCharacterizationI1OMC cavity mirrors glued

I1OMC cavity mirrors were glued.

FSR = 264.82MHz => Lcav = 1.132m (nominal 1.132m)

TMS/FSR for Vpzt1=Vpzt2=0: 0.2185 (V) and 0.2196 (H) (nominal 0.219)

 

aLIGO OMC: Power Budget 2014/5/16

<<<Measured Values>>>
Input Power: 35.7 [mW]
Transmitted Power through FM2: 33.5 [mW]
Transmitted Power through CM1: 0.188 [mW]
Transmitted Power through CM2: 0.192 [mW]
Reflection PD DC output (Unlocked): 6.2 [V]
Reflection PD DC output (Locked): 0.096 [V]
Reflection PD DC output (Dark Offset): -0.00745 [V]
Assumed cavity finesse : 400.

<<<Results>>>
Input Power: 35.7 [mW]
Uncoupled light Power (Junk light + sidebands): 0.575698 [mW]
Input TEM00 Carrier Power: 35.1243 [mW]  (Ratio: 0.983874)
Cavity reflectivity (in power): 548.319 ppm
Cavity transmission (in power): 0.953756
Loss per mirror: 70.1183 ppm
FM1 power transmission: 7640.17 ppm
FM2 power transmission: 7640.17 ppm
CM1 power transmission: 43.2093 ppm
CM2 power transmission: 44.1337 ppm

 

Attachment 1: Cav_scan_response_140516_Pitch.pdf
Cav_scan_response_140516_Pitch.pdf
Attachment 2: Cav_scan_response_140516_Yaw.pdf
Cav_scan_response_140516_Yaw.pdf
  187   Thu Jun 19 23:16:50 2014 KojiOpticsGeneralAll of the prisms have been glued

- All of the PRISM mirrors have been glued

- 4 out of 5 beam dumps have been glued


TODO

EP30-2 gluing of the INVAR blocks for the PDs

PDs/QPDs need to be slightly lower -> order more shims

Remove the templates

Glue the last beam dump

Vibration test?

Bring the OMC to the bake lab

Vacuum baking

Bring it back to the OMC lab

Cabling / Wiring

Optical tests

Backscattering test

Packing / Shipping

P6196525.JPG

  188   Fri Jun 20 18:59:12 2014 KojiOpticsGeneralAll of the invar blocks have been glued

All of the INVAR blocks have been glued.

I found thinner shims in the stock.

On Monday, the template will be removed.

EP30-2 7g mixed with 0.35g of 75-90um sphere


TODO

EP30-2 gluing of the INVAR blocks for the PDs

PDs/QPDs need to be slightly lower -> order more shims

Remove the templates

Glue the last beam dump

Vibration test?

Bring the OMC to the bake lab

Vacuum baking

Bring it back to the OMC lab

Cabling / Wiring

Optical tests

Backscattering test

Packing / Shipping

  189   Mon Jun 23 21:54:16 2014 KojiOpticsGeneralAll of the gluing completed

The bottom-side templates were removed.

The last beam dump was removed

TODO

ICS entry

Bring the OMC to the bake lab

Vacuum baking

Bring it back to the OMC lab

Cabling / Wiring

VIbratin test

Optical tests

Backscattering test

Packing / Shipping

 

  190   Tue Jun 24 18:43:15 2014 KojiGeneralGeneralICS entries for the OMC baking/assembly

For baking:

  • Assembly Name aLIGO Output Mode Cleaner
    Assembly Number D1201439
     
  • Part Name: Breadboard transport fixture
    Part # / Drawing #: D1201515
     

TO BE ADDED TO THE ASSEMBLY after the bake: [DONE]
803-003-07M6-4PN-598A-0-Bulk-H42Q001
D1201274-V1-00-S009: OMC DCPD Housing        (remove part)
D1201274-V1-00-S010: OMC DCPD Housing        (remove part)
D1201275-V1-00-0006: OMC DCPD FACE PLATE        (remove part)
D1201275-V1-00-0007: OMC DCPD FACE PLATE        (remove part)
D1201280-V1-00-0006: OMC QPD HOUSING        (remove part)
D1201280-V1-00-0007: OMC QPD HOUSING        (remove part)
D1201281-V1-00-0006: OMC QPD FACE PLATE        (remove part)
D1201281-V1-00-0007: OMC QPD FACE PLATE        (remove part)
D1300052-V1-00-0003: aLIGO OMC BRACKET, CABLE CONNECTOR        (remove part)
D1300057-v2-00-0021: aLIGO CABLE PEG        (remove part)
D1300057-v2-00-0022: aLIGO CABLE PEG        (remove part)
D1300057-v2-00-0023: aLIGO CABLE PEG        (remove part)
D1300057-v2-00-0024: aLIGO CABLE PEG        (remove part)
D1300057-v2-00-0025: aLIGO CABLE PEG        (remove part)
D1300057-v2-00-0026: aLIGO CABLE PEG        (remove part)
D1300057-v2-00-0027: aLIGO CABLE PEG        (remove part)
D1300057-v2-00-0028: aLIGO CABLE PEG        (remove part)
D1300057-v2-00-0029: aLIGO CABLE PEG        (remove part)
D1300057-v2-00-0030: aLIGO CABLE PEG        (remove part)
D1300060-V1-00-0005: aLIGO OMC BRACKET, MASS MOUNTING        (remove part)
D1300060-V1-00-0006: aLIGO OMC BRACKET, MASS MOUNTING        (remove part)


====================================
More entries to be added (Found in the LHO OMC entry) [DONE]
D1300371-V2-00-S1301806: ISC DCPD Cable for OMC-Breadboard Bracket to DCPD #1
D1300372-V2-00-S1301807: ISC DCPD Cable for OMC-Breadboard Bracket to DCPD #2
D1300373-V3-00-S1301810: ISC QPD Cable for OMC-Structure to Breadboard Bracket
D1300374-V2-00-S1301813: ISC QPD Cable for OMC-Breadboard Bracket to QPD #1

  191   Fri Jun 27 12:29:50 2014 KojiGeneralGeneralOMC baking

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

P6266536.jpg

  192   Fri Jun 27 18:51:33 2014 KojiGeneralGeneralSupply

PTOUCH TAPE (12mm white) x 2

9V batteries

  193   Wed Jul 2 16:41:43 2014 KojiGeneralGeneralOMC baking

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

  194   Wed Jul 2 18:58:42 2014 KojiGeneralGeneralBeam dump delamination

While the OMC breadboard was being inspected, it was found that two out of five black-glass beam dumps showed sign of delamination.
(attached photos).

The base of the each beam dump is a fused silica disk (25mm dia.). The black glass pieces are bonded to the disk. The bond is EP30-2
epoxy without glass beads for bond lining. The disk is bonded on the fused silica bread board with Optocast UV low-viscous epoxy.
The delamination is about 70% of the bonded area. They don't seem to fall off immediately. But the glass pieces are not completely secure.
(i.e. finger touch can change the newton ring fringes) So there might be some risk of falling off during transportation.

The engineering team and I are exploring the way to secure them in-situ, including the method to apply UV epoxy with capillary action.

Attachment 1: beamdump_delamination.png
beamdump_delamination.png
  195   Thu Jul 3 17:45:18 2014 KojiGeneralGeneralBeam dump delamination

Here is the resolution.

I'll apply fillets of EP30-2 along the edges of the black glass (See figure).
In order to allow the air escape from the gap, the inside of the V will not be painted.
In any case, I don't have a good access to the interior of the V.

Dennis assured that the outgassing level will be ok even if the EP30-2 is cured at the room temp if the mixture is good.
But just in case, we should run an RGA scan (after 50degC for 24hour vac bake).
I prefer to do this RGA scan right after all of the test and cabling and right before the shipment.
Dennis is checking if we can even waive the RGA scan owing to the small volume of the glue.

beamdump_delamination_solution.png

  196   Sun Jul 6 02:45:56 2014 KojiOpticsGeneralFSR Measurement

3rd OMC FSR / Finesse measurement

RF AM was injected by detuning a HWP.

Attachment 1: finesse_measurements_log.pdf
finesse_measurements_log.pdf
  197   Sun Jul 6 02:46:20 2014 KojiOpticsCharacterizationOMC power budget

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


  198   Sun Jul 6 03:56:40 2014 KojiOpticsCharacterizationHOM measurement with PZT vol swept

Cavity FSR/TMS measurement (2014/7/5) with PZT voltages swept from 0V to 200V (50V step)

Attachment 1: Cav_scan_response_PZT1.pdf
Cav_scan_response_PZT1.pdf Cav_scan_response_PZT1.pdf Cav_scan_response_PZT1.pdf Cav_scan_response_PZT1.pdf Cav_scan_response_PZT1.pdf Cav_scan_response_PZT1.pdf Cav_scan_response_PZT1.pdf Cav_scan_response_PZT1.pdf
Attachment 2: Cav_scan_response_PZT2.pdf
Cav_scan_response_PZT2.pdf Cav_scan_response_PZT2.pdf Cav_scan_response_PZT2.pdf Cav_scan_response_PZT2.pdf Cav_scan_response_PZT2.pdf Cav_scan_response_PZT2.pdf Cav_scan_response_PZT2.pdf Cav_scan_response_PZT2.pdf
Attachment 3: OMC_HOM_140705.pdf
OMC_HOM_140705.pdf
  199   Sun Jul 6 08:31:14 2014 KojiOpticsCharacterizationHOM measurement with PZT vol swept

3rd OMC, HOM diagram at PZT1=0V and PZT2=50V.

First coincidence with the carrier is the 32nd-order carrier mode. Very good.

Attachment 1: HOM_plot.pdf
HOM_plot.pdf
  200   Mon Jul 7 01:36:03 2014 KojiGeneralGeneralTo 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

Backscattering test

Cabling / Wiring

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

Vibration test

Baking

First Contact

Packing / Shipping

  201   Tue Jul 8 04:08:06 2014 KojiGeneralGeneralExpoxy reapplication for beam dumps

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.

ELOG V3.1.3-