Remeasured the spot positions:

DCPD1: 1.50mm+0.085mm => Beam 0.084mm too high

DCPD2: 1.50mm+0.085mm => Beam 0.023mm too high

QPD1:   1.25mm+0.085mm => Beam 0.001mm too low

QPD2:   1.25mm+0.085mm => Beam 0.155mm too low
 

The QPD alignment was adjusted using the aligned beam to the cavity and the 4ch transimpedance amplifier.

As I have a test cable for the QPD, I attached a DB9 connector on it so that I can use the QPD transimpedance
amplifier to read the photocurrent. The transimpedance of the circuit is 1kV/A.
As this board (D1001974) does not have X/Y/SUM output, I quickly made the summing circuit on a universal
board I took from Japan a while ago.

The spot on the QPD1 (shorter arm side) seems too low by ~0.64mm. It seems that the QPD is linearly responding
to the input misalignment, so there is no optical or electrical problem.

As I wonder how much I can improve the situation by replacing the diodes, I swapped the diodes between QPD1 and QPD2.
Now QPD1 and QPD2 have the diode #43 and #38, respectively. It improved the situation a llitle (about 60um).
But the beam is still 0.58mm too low. 95% of the power is on the upper two elements.
Of course this is at the edge of the linear range.
I confirmed we still can observe the cavity is fringing even with the beam is aligned on this QPD. So this may be
sufficient for the initial alignment.

The QPD2 was in a better situation. The spot is about 100um too low but this is still well with in the linear range.

The incident powers on the diodes were also measured. The estimated responsivities and Q.E.s are listed below.
The reflection from the diode is adjusted to hit the beam dump properly.

Here are the raw numbers

QPD#            QPD1       QPD2
Diode#          #43        #38
-------------------------------------
Power Incident  118.8 uW   115.7uW
Sum Out          78.8 mV   84.6 mV
Vertical Out     69.1 mV   11.9 mV
Horizontal Out    9.8 mV   -1.6 mV
SEG1             -1.90 mV -17.8 mV
SEG2             -2.18 mV -17.5 mV
SEG3            -32.0 mV  -25.3 mV
SEG4            -42.0 mV  -23.8 mV
-------------------------------------
Responsivity[A/W] 0.66      0.73
Q.E.              0.77      0.85
-------------------------------------

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

Peter F suggested to check the bottom surface of the PD housings if there is any protrusion/interference/whatever.
And that was true! It was found that the front side of QPD1 (Left) was lifted by a machining burr.
It seems that this burr consistently exists as the other one also have it (see QPD2 picture (right)) although it is not too terrible compared to the one in QPD1.

Once these burrs were removed, the spots were found on the right position of each diode.
From the measurement of the power on each segment, the positions of the spots were estimated. (listed in the table)
They indicate that the spots are within 0.1mm from the center. This is good enough.

The quantum efficiency was measured from the incident power and the sum output. It seems that there are
some difference between the diodes. The numbers are consistent with the measurement the other day.

QPD#              QPD1       QPD2
Diode#            #43        #38
-------------------------------------
Power Incident     84.7 uW   86.2 uW
Sum Out            56   mV   61   mV
Vertical Out       -6.8 mV   10   mV
Horizontal Out      4.2 mV    8.8 mV
SEG1              -17   mV  -15   mV
SEG2              -14.5 mV  -11   mV
SEG3              -11   mV  -15   mV
SEG4              -13   mV  -20   mV
-------------------------------------
Spot position X   +25   um  +46   um  (positive = more power on SEG1 and SEG4)
Spot position Y   -42   um  +46   um  (positive = more power on SEG3 and SEG4)
-------------------------------------
Responsivity[A/W] 0.66      0.71
Q.E.              0.77      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

Measurement for pitch

The followings are the previous values before the bake
[from this entry]

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

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

- 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

This is the analysis of the cavity finesse data taken on  Apr/13/2013 (before baking), May/30/2013 (after baking), and Jun/02/2013 (after cleaning).
If we believe this result, baking contaminated the cavity, and the first contact removed it. That agrees with the power measurement of the transmitted light.

OMC(002)

Cavity Mirrors

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

DCPD path

BS3 (BS for DCPDs): B10

QPD path

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

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)

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

[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.

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)

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.

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.

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

LHO OMC power budget

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

 shim 1.5mm 001/002

Spot positions were inferred from the photos

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

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.

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.

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

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

- 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

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

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

3rd OMC FSR / Finesse measurement

RF AM was injected by detuning a HWP.

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

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

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

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

QPD#              QPD1       QPD2
Housing#          #006       #007
Diode#            #50        #51
Shim              1.25mm 03  1.25mm 02   (1.25mm = D1201467-10)
-------------------------------------
Power Incident    123.1-13.0 uW  124.5-8.0 uW
Sum Out            77.0 mV   82.5 mV
Vertical Out      -24.0 mV  - 8.8 mV
Horizontal Out      4.2 mV    9.0 mV
SEG1              -11.6 mV  -16.0 mV
SEG2              -12.6 mV  -18.0 mV
SEG3              -25.2 mV  -24.4 mV
SEG4              -21.4 mV  -21.4 mV
-------------------------------------
Spot position X   -21   um  -19   um  (positive = more power on SEG1 and SEG4)
Spot position Y   +102  um  +47   um  (positive = more power on SEG3 and SEG4)
-------------------------------------
Responsivity[A/W] 0.70      0.71
Q.E.              0.82      0.83
-------------------------------------

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

DCPD#             DCPD1      DCPD2
Housing#          #009       #010
Diode#            #07        #10
Shim              1.00mm 01  1.00mm 02   (1.00mm = D1201467-09)
-------------------------------------
Power Incident     11.1 mW   10.6 mW
Vout                7.65 V    7.33 V
Responsivity[A/W]   0.69      0.69
Q.E.                0.80      0.81
-------------------------------------
photo              2nd        1st

PD alignment confirmation

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.

L1 OMC Cavity power budget

H1 OMC Cavity power budget

3IFO OMC Cavity power budget

Motivation: Characterize the loss of the Calcite Brewster PBS.

Setup: (Attachment 1)

- The beam polarization is rotated by an HWP
- The first PBS filters out most of the S pol
- The second PBS further filters the S and also confirms how good the polarization is.

- The resulting beam is modulated by a chopper disk. The chopping freq can be 20~1kHz.

- The 50:50 BS splits the P-pol beam into two. One beam goes to the reference PD. The other beam goes to the measurement PD.

- Compare the transfer functions between RefPD and MeasPD at the chopping frequency with and without the DUT inserted to the measurement pass.

- The PBS shift the beam significantly. The beam can't keep the alignment on the Meas PD when the crystal is removed.
  Therefore the "On" and "Off" states are swicthed by moving the PBS and the steering mirror at the same time.
  The positions and angles of the mounts are defined by the bases on the table. The bases are adjusted to have the same spot position for these states as much as possible.

Device Under Test:

Brewster polarizer https://dcc.ligo.org/LIGO-T1300346

The prisms are aligned as shown in Attachment 2

Between the prisms, a kapton sheet (2MIL thickness) is inserted to keep the thin air gap between them.

Result:

Set1: (~max power without hard saturation)
PD1(REF) 10dB Gain (4.75kV/A) 6.39V
PD2(PBS) 10dB Gain (4.75kV/A) Thru 4.77V, PBS 4.75
Chopping frequency 234Hz, FFT 1.6kHz span AVG 20 (1s*20 = 20s)

Thru 0.748307, PBS 0.745476 => 3783 +/- 5 ppm loss
Thru 0.748227, PBS 0.745552 => 3575 +/- 5 ppm
Thru 0.748461, PBS 0.745557 => 3879 +/- 5 ppm
Thru 0.748401, PBS 0.745552 => 3806 +/- 5 ppm
Thru 0.748671, PBS 0.745557 => 4159 +/- 5 ppm
=> Loss 3841 +/- 2 ppm

Set2: (half power)
PD1(REF) 10dB Gain (4.75kV/A) 3.20V
PD2(PBS) 10dB Gain (4.75kV/A) Thru 2.38V, PBS 2.37
Chopping frequency 234Hz, FFT 1.6kHz span AVG 20 (1s*20 = 20s)

Thru 0.747618, PBS 0.744704 => 3898 +/- 5 ppm loss
Thru 0.747591, PBS 0.744690 => 3880 +/- 5 ppm
Thru 0.747875, PBS 0.744685 => 4265 +/- 5 ppm
Thru 0.747524, PBS 0.744655 => 3838 +/- 5 ppm
Thru 0.747745, PBS 0.744591 => 4218 +/- 5 ppm
=> Loss 4020 +/- 2 ppm

Set3: (1/4 power)
PD1(REF) 10dB Gain (4.75kV/A) 1.34V
PD2(PBS) 10dB Gain (4.75kV/A) Thru 1.00V, PBS 0.999
Chopping frequency 234Hz, FFT 1.6kHz span AVG 20 (1s*20 = 20s)

Thru 0.745140, PBS 0.741949 => 4282 +/- 5ppm loss
Thru 0.745227, PBS 0.741938 => 4413 +/- 5ppm
Thru 0.745584, PBS 0.741983 => 4830 +/- 5ppm
Thru 0.745504, PBS 0.741933 => 4790 +/- 5ppm
Thru 0.745497, PBS 0.741920 => 4798 +/- 5ppm
Thru 0.745405, PBS 0.741895 => 4709 +/- 5ppm
=> Loss 4637 +/- 2ppm

Possible improvement:

- Further smaller power
- Use the smaller gain as much as possible
- Compare the number for the same measurmeent with the gain changed

- Use a ND Filter instead of HWP/PBS power adjustment to reduce incident S pol
- Use a double pass configuration to correct the beam shift by the PBS

To be measured

- Angular dependence
- aLIGO Thin Film Polarizer
- HWP
- Glasgow PBS

Calcite Brewster PBS Continued

The transmission loss of the Calcite brewster PBS (eLIGO squeezer OFI) was measured with different conditions.
The measured loss was 3600+/-200ppm. (i.e. 900+/-50 ppm per surface)
The measurement error was limited by the systematic error, probably due to the dependence of the PD response on the spot position.

I wonder if it is better to attenuate the beam by a ND filter instead of HWP+PBS.

o First PBS power adjustment -> full power transmission, OD1.0 ATTN Full Power
   PDA20CS Gain 10dB
   Thru 0.746711, PBS 0.744155 => Loss L = 3423 +/- 5ppm

o Same as above, PDA20CS Gain 0dB (smaller amplitude = slew rate less effective?)
   Thru 0.748721, PBS 0.746220 => L = 3340 +/- 5ppm

o Same as above but OD1.4 ATTN
   Thru 0.744853, PBS 0.742111 => L = 3681 +/- 5ppm

o More alignment, more statistics
(PDA20CS 0dB gain =  0.6A/W, 1.51kV/A)
PD(REF, 0dB) 0.426V = 0.47W
PD(MEAS, 0dB) Thru 0.320V, PBS 0.318V = 0.35W, L = 6000+/-3000ppm

Chopping 234Hz, TF 1.6kHz AVG10
Thru 0.745152, PBS 0.742474 => 3594 +/- 5 ppm
Thru 0.745141, PBS 0.742467 => 3589 +/- 5ppm
Thru 0.745150, PBS 0.742459 => 3611 +/- 5ppm
Thru 0.745120, PBS 0.742452 => 3581 +/- 5ppm
Thru 0.745153, PBS 0.742438 => 3644 +/- 5ppm
=> 3604ppm +/-25ppm

o More power

Attenuation OD 1.0
PD(REF, 0dB) 0.875V = 0.97W
PD(MEAS, 0dB) Thru 0.651V, PBS 0.649V = 0.72W, L = 3100+/-1600ppm

Chopping 234Hz, TF 1.6kHz AVG10
Thru 0.746689, PBS 0.743789 => 3884 +/- 5ppm
Thru 0.746660, PBS 0.743724 => 3932 +/- 5ppm
Thru 0.746689, PBS 0.743786 => 3888 +/- 5ppm
Thru 0.746663, PBS 0.743780 => 3861 +/- 5ppm
Thru 0.746684, PBS 0.743783 => 3885 +/- 5ppm
=> 3890ppm +/- 26ppm

o Much less power

Attenuation OD 2.4
PD(REF, 0dB) 67.1mV = 74.0mW
PD(MEAS, 0dB) Thru 53.7V, PBS 53.5V = 59mW, L = 3700+/-1900ppm

Thru 0.745142, PBS 0.742430 => 3640 +/- 5ppm
Thru 0.745011, PBS 0.742557 => 3294 +/- 5ppm
Thru 0.744992, PBS 0.742537 => 3295 +/- 5ppm
Thru 0.745052, PBS 0.742602 => 3288 +/- 5ppm
Thru 0.745089, PBS 0.742602 => 3338 +/- 5ppm
=> 3371ppm +/- 151ppm

o Much less power, but different gain

Attenuation OD 2.4
PD(REF, 20dB) 662mV = 73.1mW
PD(MEAS, 20dB) Thru 501V, PBS 500V = 55.3mW, L = 2000+/-2000ppm

Thru 0.744343, PBS 0.741753 => 3480 +/- 5ppm
Thru 0.744304, PBS 0.741739 => 3446 +/- 5ppm
Thru 0.744358, PBS 0.741713 => 3553 +/- 5ppm
Thru 0.744341, PBS 0.741719 => 3523 +/- 5ppm
Thru 0.744339, PBS 0.741666 => 3591 +/- 5ppm
=> 3519ppm +/- 58ppm

Using the last 4 measurements, mean loss is 3596, and the std is 218. => Loss = 3600+/-200ppm

Brewster calcite PBS (eLIGO Squeezer OFI)

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

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

Wave plate (eLIGO Squeezer OFI?)

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

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

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

Thin Film Polarlizer (aLIGO TFP)

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

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

Glasgow PBS

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

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

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

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

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.

On friday, I removed a glass cover of a G30655 with a PD can cutter.

When a beam shoots a Perkin Elmer/Excelitas PD, we usually observe three reflections.
We always wonder what these are.

When the glass window is illuminated by a beam, I could see two reflections. So they are the front and rear reflection from the glass windows.

Direct comparison of the PD responsibities

We can expect 5% increase of the QE with the new PD.

P-pol 10deg incident

Power meter Ophir RM9C (Systematic error +/-5%)
Vbias = 6V

C30665GH (#07)
Incident: 7.12mW
Reflection: 0.413mW (=> R=5.8%)
PD output: 5.690+/-0.006V
=> Responsibity 0.799+/-0.001 A/W
=> QE = 0.931+/-0.001

HQE PD (A1-23)
Incident: 7.15mW
Reflection: 0.020+/-0.1mW (=> R=0.28%)
PD output: 6.017+/-0.007V
=> Responsibity 0.842+/-0.001 A/W
=> QE = 0.981+/-0.001

Note that there is a 5% systematic error with the power meter.

Calibration of the transimpedance

Use KEITHLEY 2450 as a calibrated current source. Model 2450 has the current source accuracy of 0.020%+1.5uA at 10mA range. For 6mA current output, the error is 3uA (0.05%).

The output of the current amp at 10³ Ohm setting was 6.0023V when -6.000mA current was applied. i.e R_trans = 1000.4 +/- 0.5 Ohm. This is a negligible level.

QE of the diodes (As of 07/30/2016)

Refer E1800372

1. Calum and GariLynn checking the CM1 defect from the front side.
2. Same as above
3. Close up of the defect
4. Using dino-lite microscope to get a close up view of the defect from the front surface.
5. Same as 4
6. Finished for the day and setting up a safefy clamp
7. Finally a tefron cover was attached.

Initial inspection results by Calum, et al.
https://dcc.ligo.org/LIGO-E1600268

D1102211 OMC Diode Mount Glass Block (11pcs) have been given to Calum@Downs

- About 1.5 month ago, an 700mW LWE NPRO has been brought to OMC Lab.

- The SOP can be found here.

- The base was made for the beam elevation of 3" height. Four 1" pedestals were attached to rise the beam elevation to 4".

- The output from the laser is ~740mW

- After the faraday and the BB EOM, the output is ~660mW

- After the usual struggle, the beam was coupled to the SM fiber. The output is 540mW. The coupling efficiency is >80%.

- Will proceed to the OMC cavity alignment.

FIber Input Mount 132deg
Fiber output mount 275deg
-> 525mW P: 517mW S: 8mW extinction ratio: 0.016