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ID Date Author Typeup Category Subject
  49   Mon Dec 31 03:11:45 2012 KojiOpticsCharacterizationFurther more RoC measurement

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

New results

C6: RoC: 2.57321 +/− 4.2e-05m

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

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

C9: RoC: 2.57051 +/− 6.7e-05m

Previous results

C1: RoC: 2.57845 +/− 4.2e−05m

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

C3: RoC: 2.57130 +/− 6.3e−05m   

C4: RoC: 2.58176 +/− 6.8e−05m

C5: RoC 2.57369 +/− 9.1e−05m

Attachment 1: Cav_scan_response_zoom_20121125_C6_9.pdf
Cav_scan_response_zoom_20121125_C6_9.pdf Cav_scan_response_zoom_20121125_C6_9.pdf Cav_scan_response_zoom_20121125_C6_9.pdf Cav_scan_response_zoom_20121125_C6_9.pdf
  50   Wed Jan 2 07:35:55 2013 KojiOpticsCharacterizationThickness of a curved mirror

Measured the thickness of a curved mirror:

Took three points separated by 120 degree.

S/N: C2, (0.2478, 0.2477, 0.2477) in inch => (6.294, 6.292, 6.292) in mm

  51   Wed Jan 2 07:45:39 2013 KojiOpticsCharacterizationFirst Contact test

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


- Construct a cavity with A1 and C2

- Measure the transmission and FWHM (of TEM10 mode)

- Apply First Contact on both mirrors

- Measure the values again


Transmission:

2.66 +/- 0.01 V -> 2.83  +/- 0.01 V

==> 6.3% +/- 0.5 % increase

FWHM of TEM10:

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

==> 5.1% +/- 2.7% decrease

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

Attachment 1: Cav_scan_response_zoom_20121125_C2_before.pdf
Cav_scan_response_zoom_20121125_C2_before.pdf
Attachment 2: Cav_scan_response_zoom_20121125_C2_after.pdf
Cav_scan_response_zoom_20121125_C2_after.pdf
  53   Thu Jan 10 18:37:50 2013 KojiOpticsCharacterizationWedging of the PZTs

Yesterday I measured the thickness of the PZTs in order to get an idea how much the PZTs are wedged.

For each PZT, the thickness at six points along the ring was measured with a micrometer gauge.
The orientation of the PZT was recognized by the wire direction and a black marking to indicate the polarity.

A least square fitting of these six points determines the most likely PZT plane.
Note that the measured numbers are assumed to be the thickness at the inner rim of the ring
as the micrometer can only measure the maximum thickness of a region and the inner rim has the largest effect on the wedge angle.
The inner diameter of the ring is 9mm.



The measurements show all PZTs have thickness variation of 3um maximum.

The estimated wedge angles are distributed from 8 to 26 arcsec. The directions of the wedges seem to be random
(i.e. not associated with the wires)



As wedging of 30 arcsec causes at most ~0.3mm spot shift of the cavity (easy to remember),
the wedging of the PZTs is not critical by itself. Also, this number can be reduced by choosing the PZT orientations
based on the estimated wedge directions --- as long as we can believe the measurements.



Next step is to locate the minima of each curved mirror. Do you have any idea how to measure them?

Attachment 1: PZT_wedging.pdf
PZT_wedging.pdf
  54   Wed Jan 16 14:10:50 2013 KojiOpticsCharacterizationAutocollimator tests of optics perpendicularity/parallelism

The items:

- Autocollimator (AC) borrowed from Mike Smith (Nippon Kogaku model 305, phi=2.76", 67.8mm)

- Retroreflector (corner cube)

- Two V grooves borrowed from the 40m

Procedure:

- Autocollimator calibration

o Install the AC on a optical table

o Locate the corner cube in front of the AC.

o Adjust the focus of the AC so that the reflected reticle pattern can be seen.

o If the retroreflection and the AC are perfect, the reference reticle pattern will match with the reflected reticle pattern.

o Measure the deviation of the reflected reticle from the center.

o Rotate the retroreflector by 90 deg. Measure the deviation again.

o Repeat the process until total four coordinates are obtained.

o Analysis of the data separates two types of the error:
   The average of these four coordinates gives the systematic error of the AC itself.
   The vector from the center of the circle corresponds to the error of the retroreflector.

- Wedge angle measurement

 

To be continued

  55   Fri Jan 18 13:25:17 2013 KojiOpticsConfigurationAutocollimator calibration

An autocollimator (AC) should show (0,0) if a retroreflector is placed in front of the AC.
However, the AC may have an offset. Also the retroreflector may not reflect the beam back with an exact parallelism.

To calibrate these two errors, the autocollimator is calibrated. The retroreflector was rotated by 0, 90, 180, 270 deg
while the reticle position are monitored. The images of the autocollimator were taken by my digital camera looking at the eyepiece of the AC.

Note that 1 div of the AC image corresponds to 1arcmin.

Basically the rotation of the retroreflector changed the vertical and horizontal positions of the reticle pattern by 0.6mdeg and 0.1mdeg
(2 and 0.4 arcsec). Therefore the parallelism of the retrorefrector is determined to be less than an arcsec. This is negligibly good for our purpose.

The offset changes by ~1div in a slanted direction if the knob of the AC, whose function is unknown, is touched.
So the knob should be locked, and the offset should be recorded before we start the actual work every time.

Attachment 1: autocollimator_calibration.pdf
autocollimator_calibration.pdf autocollimator_calibration.pdf autocollimator_calibration.pdf autocollimator_calibration.pdf
  56   Sat Jan 19 20:47:41 2013 KojiOpticsCharacterizationWedge measurement with the autocollimator

The wedge angle of the prism "A1" was measured with the autocollimator (AC).

The range of the AC is 40 arcmin. This means that the mirror tilt of 40arcmin can be measured with this AC.
This is just barely enough to detect the front side reflection and the back side reflection.

The measured wedge angle of the A1 prism was 0.478 deg.

Ideally a null measurement should be done with a rotation stage.

Attachment 1: autocollimator_wedge_measurement.pdf
autocollimator_wedge_measurement.pdf
  59   Mon Feb 4 00:39:08 2013 KojiOpticsCharacterizationWedge measurement with the autocollimator and the rotation stage

Method:

  • Mount the tombstone prism on the prism mount. The mount is fixed on the rotation stage.
  • Locate the prism in front of the autocollimator.
  • Find the retroreflected reticle in the view. Adjust the focus if necessary.
  • Confirm that the rotation of the stage does not change the height of the reticle in the view. 

    If it does, rotate the AC around its axis to realize it.
    This is to match the horizontal reticle to the rotation plane.
  • Use the rotation stage and the alignment knobs to find the reticle at the center of the AC.
Make sure the reticle corresponds to the front surface.
  • Record the micrometer reading.
  • Rotate the micrometer of the rotation stage until the retroreflected reticle for the back surface.
  • There maybe the vertical shift of the reticle due to the vertical wedging. Record the vertical shi
  • Record the micrometer reading. Take a difference from the previous value.
     

Measurement:

  • A1: α = 0.68 deg, β = 0 arcmin (0 div)
  • A2: α = 0.80 deg, β = -6 arcmin (3 div down)
  • A3: α = 0.635 deg, β = -1.6 arcmin (0.8 div down)
  • A4: α = 0.650 deg, β = 0 arcmin (0div)
  • A5: α = 0.655 deg, β = +2.4 arcmin (1.2 div up)

Analysis:

  • \theta_H = ArcSin[Sin(α) / n]
  • \theta_V = ArcSin[Sin(β) / n]/2
     
  • A1: \theta_H = 0.465 deg, \theta_V = 0.000 deg
  • A2: \theta_H = 0.547 deg, \theta_V = -0.034 deg
  • A3: \theta_H = 0.434 deg, \theta_V = -0.009 deg
  • A4: \theta_H = 0.445 deg, \theta_V = 0.000 deg
  • A5: \theta_H = 0.448 deg, \theta_V = 0.014 deg

 

Attachment 1: autocollimator_wedge_measurement.pdf
autocollimator_wedge_measurement.pdf
  60   Wed Feb 6 02:34:10 2013 KojiOpticsCharacterizationWedge measurement with the autocollimator and the rotation stage

Measurement:

  • A6:   α = 0.665 deg, β = +3.0 arcmin (1.5 div up)
  • A7:   α = 0.635 deg, β =   0.0 arcmin (0.0 div up)
  • A8:   α = 0.623 deg, β = - 0.4 arcmin (-0.2 div up)
  • A9:   α = 0.670 deg, β = +2.4 arcmin (1.2 div up)
  • A10: α = 0.605 deg, β = +0.4 arcmin (0.2 div up)
  • A11: α = 0.640 deg, β = +0.8 arcmin (0.4 div up)
  • A12: α = 0.625 deg, β = - 0.6 arcmin (-0.3 div up)
  • A13: α = 0.630 deg, β = +2.2 arcmin (1.1 div up)
  • A14: α = 0.678 deg, β =   0.0 arcmin (0.0 div up)
  • B1:   α = 0.665 deg, β = +0.6 arcmin (0.3 div up)
  • B2:   α = 0.615 deg, β = +0.2 arcmin (0.1 div up)
  • B3:   α = 0.620 deg, β = +0.9 arcmin (0.45 div up)
  • B4:   α = 0.595 deg, β = +2.4 arcmin (1.2 div up)
  • B5:   α = 0.635 deg, β = - 1.8 arcmin (-0.9 div up)
  • B6:   α = 0.640 deg, β = +1.6 arcmin (0.8 div up)
  • B7:   α = 0.655 deg, β = +2.5 arcmin (1.25 div up)
  • B8:   α = 0.630 deg, β = +2.8 arcmin (1.4 div up)
  • B9:   α = 0.620 deg, β = - 4.0 arcmin (-2.0 div up)
  • B10: α = 0.620 deg, β = +1.2 arcmin (0.6 div up)
  • B11: α = 0.675 deg, β = +3.5 arcmin (1.75 div up)
  • B12: α = 0.640 deg, β = +0.2 arcmin (0.1 div up)

Analysis:

  • \theta_H = ArcSin[Sin(α) * n]
  • \theta_V = ArcSin[Sin(β) / n]/2
     
  • A6:   \theta_H = 0.490 deg, \theta_V =  0.017 deg
  • A7:   \theta_H = 0.534 deg, \theta_V =  0.000 deg
  • A8:   \theta_H = 0.551 deg, \theta_V = -0.0023 deg
  • A9:   \theta_H = 0.482 deg, \theta_V =  0.014 deg
  • A10: \theta_H = 0.577 deg, \theta_V =  0.0023 deg
  • A11: \theta_H = 0.526 deg, \theta_V =  0.0046 deg
  • A12: \theta_H = 0.548 deg, \theta_V = -0.0034 deg
  • A13: \theta_H = 0.541 deg, \theta_V =  0.013 deg
  • A14: \theta_H = 0.471 deg, \theta_V =  0.000 deg
  • B1:   \theta_H = 0.490 deg, \theta_V =  0.0034 deg
  • B2:   \theta_H = 0.563 deg, \theta_V =  0.0011 deg
  • B3:   \theta_H = 0.556 deg, \theta_V =  0.0051 deg
  • B4:   \theta_H = 0.592 deg, \theta_V =  0.014 deg
  • B5:   \theta_H = 0.534 deg, \theta_V = -0.010 deg
  • B6:   \theta_H = 0.526 deg, \theta_V =  0.0091 deg
  • B7:   \theta_H = 0.504 deg, \theta_V =  0.014 deg
  • B8:   \theta_H = 0.541 deg, \theta_V =  0.016 deg
  • B9:   \theta_H = 0.556 deg, \theta_V = -0.023 deg
  • B10: \theta_H = 0.556 deg, \theta_V =  0.0068 deg
  • B11: \theta_H = 0.475 deg, \theta_V =  0.020 deg
  • B12: \theta_H = 0.526 deg, \theta_V =  0.0011 deg

Quote:

Measurement:

  • A1: α = 0.68 deg, β = 0 arcmin (0 div)
  • A2: α = 0.80 deg, β = -6 arcmin (3 div down)
  • A3: α = 0.635 deg, β = -1.6 arcmin (0.8 div down)
  • A4: α = 0.650 deg, β = 0 arcmin (0div)
  • A5: α = 0.655 deg, β = +2.4 arcmin (1.2 div up)

Analysis:

  • \theta_H = ArcSin[Sin(α)*n]
  • \theta_V = ArcSin[Sin(β) / n]/2
     
  • A1: \theta_H = 0.465 deg, \theta_V = 0.000 deg
  • A2: \theta_H = 0.547 deg, \theta_V = -0.034 deg
  • A3: \theta_H = 0.434 deg, \theta_V = -0.009 deg
  • A4: \theta_H = 0.445 deg, \theta_V = 0.000 deg
  • A5: \theta_H = 0.448 deg, \theta_V = 0.014 deg

 

  62   Thu Feb 7 23:01:45 2013 KojiOpticsCharacterizationUV epoxy gluing test

 [Jeff, Yuta, Koji]

Gluing test with UV-cure epoxy Optocast 3553-LV-UTF-HM

- This glue was bought in the end of October (~3.5 months ago).

- The glue was taken out from the freezer at 1:20pm.
- Al sheet was laid on the optical table. We made a boat with Al foil and pour the glue in it (@1:57pm)
- We brought two kinds of Cu wires from the 40m. The thicker one has the diameter of 1.62mm.
The thinner one has the diameter of 0.62mm. We decided to use thinner one being cut into 50mm in length.

- The OMC glass prisms have the footprint of 10mmx20mm = 200mm^2. We tested several combinations
of the substrates. Pairs of mirrors with 1/2" mm in dia. (127mm) and a pair of mirrors with 20mm in dia. (314mm).

- Firstly, a pair of 1/2" mirrors made of SF2 glass was used. A small dub on a thinner Cu wire was deposited on a mirror.
  We illuminated the glue for ~10sec. When the surfaces of the pair was matched, the glue did not spread on the entire
  surface. The glue was entirely spread once the pressure is applied by a finger. Glue was cured at 2:15pm. 12.873mm
  thickness after the gluing.

Some remark:
1. We should be careful not to shine the glue pot by the UV illuminator.
2. The gluing surface should be drag wiped to remove dusts on the surface.

- Secondly, we moved onto 20mm mirror pair taken from the remnant of the previous gluing test by the eLIGO people.
This time about 1.5 times more glue was applied.

- The third trial is to insert small piece of alminum foil to form a wedge. The thickness of the foil is 0.041mm.
The glue was applied to the pair of SF2 mirror (1/2" in dia.). A small dub (~1mm in dia) of the glue was applied.
The glue filled the wedge without any bubble although the glue tried to slide out the foil piece from the wedge.
So the handling was a bit difficult. After the gluing we measured the thickness of the wedge by a micrometer gauge.
The skinny side was 12.837mm, and the thicker side was 12.885mm. This is to be compared with the total thickness
12.823mm before the gluing. The wedge angle is 3.8mrad (0.22deg). The glue dub was applied at 2:43, and the UV
illumination was applied at 2:46.

- At the end we glued a pair of fused silica mirrors. The total thickness before the gluing was 12.658 mm.
The glue was applied at 2:59pm. The thickness after the gluing is 12.663 mm.
This indicates the glue thickess is 5um.

  63   Thu Feb 21 18:44:18 2013 KojiOpticsConfigurationPerpendicularity test

Perpendicularity test of the mounting prisms:

The perpendicularity of the prism pieces were measured with an autocollimator.

Two orthogonally jointed surfaces forms a part of a corner cube.
The deviation of the reflected image from retroreflection is the quantity measured by the device.

When the image is retroreflected, only one horizontal line is observed in the view.
If there is any deviation from the retroreflection, this horizontal line splits into two
as the upper and lower halves have the angled wavefront by 4x\theta. (see attached figure)

The actual reading of the autocollimator is half of the wavefront angle (as it assumes the optical lever).
Therefore the reading of the AC times 30 gives us the deviation from 90deg in the unit of arcsec.

SN / measured / spec

SN10: 12.0 arcsec (29 arcsec)

SN11: 6.6 arcsec (16 arcsec)

SN16: 5.7 arcsec (5 arcsec)

SN20: -17.7 arcsec (5 arcsec)

SN21: - 71.3 arcsec (15 arcsec)

 

Attachment 1: perpendicularity_test.pdf
perpendicularity_test.pdf perpendicularity_test.pdf
Attachment 2: P2203206.JPG
P2203206.JPG
  64   Wed Feb 27 18:18:48 2013 KojiOpticsConfigurationMore perpendicularity test

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

21  -1.7      -51.     15
01  -0.5      -15.     52
02  -2.5      -75.     48
06  -1.0      -30.     15
    good
07   1.7       51.     59
12  -2.2      -66.     40
13  -0.3      - 9.     12
    good
14  -2.8      -84.     27
15  -2.5      -75.     50
17   0.7       21.     48
22   2.9       87.    
63

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

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

  65   Fri Mar 1 23:06:15 2013 KojiOpticsConfigurationMore perpendicularity test final

Perpendicularity of the "E" mirror was measured.


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

21  -1.7      -51.     15
01  -0.5      -15.     52
02  -2.5      -75.     48
06  -1.0      -30.     15
    good
07   1.7       51.     59
12  -2.2      -66.     40
13  -0.3      - 9.     12
    good
14  -2.8      -84.     27
15  -2.5      -75.     50
17   0.7       21.     48
22   2.9       87.    
63

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

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

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

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

  66   Fri Mar 1 23:52:18 2013 KojiOpticsCharacterizationWedge measurement with the autocollimator and the rotation stage

Measurement:

  • E1:   α = 0.672 deg, β = +0.0 arcmin (0 div up)
  • E2:   α = 0.631 deg, β = - 0.3 arcmin (-0.15 div down)
  • E3:   α = 0.642 deg, β = +0.0 arcmin (0 div up)
  • E4:   α = 0.659 deg, β = +1.4 arcmin (0.7 div up)
  • E5:   α = 0.695 deg, β = +0.5 arcmin (0.5 div up)
  • E6:   α = 0.665 deg, β = - 0.4 arcmin (-0.2 div down)
  • E7:   α = 0.652 deg, β = +1.0 arcmin (0.5 div up)
  • E8:   α = 0.675 deg, β = +2.0 arcmin (1.0 div up)
  • E9:   α = 0.645 deg, β = - 2.4 arcmin (-1.2 div down)
  • E10: α = 0.640 deg, β = +2.2 arcmin (1.1 div up)
  • E11: α = 0.638 deg, β = +1.6 arcmin (0.8 div up)
  • E12: α = 0.660 deg, β = +1.6 arcmin (0.8 div up)
  • E13: α = 0.638 deg, β = +0.8 arcmin (0.4 div up)
  • E14: α = 0.655 deg, β = +0.4 arcmin (0.2 div up)
  • E15: α = 0.640 deg, β = +1.4 arcmin (0.7 div up)
  • E16: α = 0.655 deg, β = +0.6 arcmin (0.3 div up)
  • E17: α = 0.650 deg, β = +0.8 arcmin (0.4 div up)
  • E18: α = 0.640 deg, β = +2.4 arcmin (1.2 div up)

Analysis:

  • \theta_H = ArcSin[Sin(α) / n]
  • \theta_V = ArcSin[Sin(β) / n]/2
     
  • E1:   \theta_H = 0.460 deg, \theta_V =   0.000 deg
  • E2:   \theta_H = 0.432 deg, \theta_V =  -0.0034 deg
  • E3:   \theta_H = 0.439 deg, \theta_V =   0.000 deg
  • E4:   \theta_H = 0.451 deg, \theta_V =  0.016 deg
  • E5:   \theta_H = 0.475 deg, \theta_V =  0.011 deg
  • E6:   \theta_H = 0.455 deg, \theta_V =  -0.0046 deg
  • E7:   \theta_H = 0.446 deg, \theta_V =  0.011 deg
  • E8:   \theta_H = 0.462 deg, \theta_V =  0.023 deg
  • E9:   \theta_H = 0.441 deg, \theta_V =  -0.027 deg
  • E10:   \theta_H = 0.438 deg, \theta_V = 0.025 deg
  • E11:   \theta_H = 0.436 deg, \theta_V = 0.018 deg
  • E12:   \theta_H = 0.451 deg, \theta_V = 0.018 deg
  • E13:   \theta_H = 0.436 deg, \theta_V = 0.0091 deg
  • E14:   \theta_H = 0.448 deg, \theta_V = 0.0046 deg
  • E15:   \theta_H = 0.438 deg, \theta_V = 0.016 deg
  • E16:   \theta_H = 0.448 deg, \theta_V = 0.0068 deg
  • E17:   \theta_H = 0.444 deg, \theta_V = 0.0091 deg
  • E18:   \theta_H = 0.438 deg, \theta_V = 0.027 deg
  67   Tue Mar 5 19:37:00 2013 ZachOpticsCharacterizationeLIGO OMC visibility vs. power measurement details

EDIT (ZK): Koji points out that (1 - Ti) should really be the non-resonant reflectivity of the aligned cavity, which is much closer to 1. However, it should *actually* be the non-resonant reflectivity of the entire OMC assembly, including the steering mirror (see bottom of post). The steering mirror has T ~ 0.3%, so the true results are somewhere between my numbers and those with (1 - Ti) -> 1. In practice, though, these effects are swamped by the other errors.

More information about the power-dependent visibility measurement:

As a blanket statement, this measurement was done by exact analogy to those made by Sam and Sheon during S6 (c.f. LHO iLog 11/7/2011 and technical note T1100562), since it was supposed to be a verification that this effect still remains. There are absolutely better ways to do (i.e., ways that should give lower measurement error), and these should be investigated for our characterization. Obviously, I volunteer.

All measurements were made by reading the output voltages produced by photodetectors at the REFL and TRANS ports. The REFL PD is a BBPD (DC output), and the TRANS is a PDA255. Both these PDs were calibrated using a Thorlabs power meter (Controller: PM100D; Head: S12XC series photodiode-based---not sure if X = 0,2... Si or Ge) at the lowest and highest power settings, and these results agreed to the few-percent level. This can be a major source of error.

The power was adjusted using the HWP/PBS combination towards the beginning of the experiment. For reference, an early layout of the test setup can be seen in LLO:5978 (though, as mentioned above, the REFL and TRANS PDs have been replaced since then---see LLO:5994). This may or may not be a "clean" way to change the power, but the analysis should take the effect of junk light into account.

eOMC_visibility_3_4_13.png

Below is an explanation of the three traces in the plot. First:

  • TRANS: TRANS signal calibrated to W
  • REFL_UL: REFL signal while cavity is unlocked, calibrated to W
  • REFL_L: REFL signal while cavity is locked, calibrated to W
  • Psb: Sideband power (relative to carrier)
  • Ti: Input mirror transmission (in power)

Now, the traces

  1. Raw transmission: This measurement is simple. It is just the raw throughput of the cavity, corrected for the power in the sidebands which should not get through. I had the "AM_REF" PD, which could serve as an input power monitor, but I thought it was better to just use REFL_UL as the input power monitor and not introduce the error of another PD. This means I must also correct for the reduction in the apparent input power as measured at the REFL PD due to the finite transmission of the input coupler. This was not reported by Sam and Sheon, but can be directly inferred from their data.
    • trans_raw = TRANS ./ ( REFL_UL * (1 - Psb) * (1 - Ti) )
    • Equivalently, trans_raw = (transmitted power) ./ (input power in carrier mode)
  2. Coupling: This is how much of the power incident on the cavity gets coupled into the cavity (whether it ends up in transmission or at a loss port). Sheon plots something like (1 - coupling) in his reply to the above-linked iLog post on 11/8/2011.
    • coupling = ( REFL_UL * (1 - Ti) - REFL_L ) ./ ( REFL_UL * (1 - Psb) * (1 - Ti) )
    • Equivalently, coupling = [ (total input power) - (total reflected power on resonance) ] ./ (input power in carrier mode)
  3. Visibility: How much of the light that is coupled into the cavity is emerging from the transmitted port? This is what Sam and Sheon call "throughput" or "transmission" and is what is reported in the majority of their plots.
    • visibility = TRANS ./ ( REFL_UL * (1 - Ti) - REFL_L )
    • Equivalently, visibility = (transmitted power) ./ [ (total input power) - (total reflected power on resonance) ]
    • Also equivalently, visibility = trans_raw ./ coupling

The error bars in the measurement were dominated, roughly equally, by 1) systematic error from calibration of the PDs with the power meter, and 2) error from noise in the REFL_L measurement (since the absolute AC noise level in TRANS and REFL_L is the same, and TRANS >> REFL_L, the SNR of the latter is worse).

(1) can be helped by making ALL measurements with a single device. I recommend using something precise and portable like the power meter to make measurements at all the necessary ports. For REFL_L/UL, we can place a beam splitter before the REFL PD, and---after calibrating for the T of this splitter very well using the same power meter---both states can be measured at this port.

(2) can probably be helped by taking longer averaging, though at some point we run into the stability of the power setting itself. Something like 30-60s should be enough to remove the effects of the REFL_L noise, which is concentrated in the few-Hz region in the LLO setup.

One more thing I forgot was the finite transmission of the steering mirror at the OMC input (the transmission of this mirror goes to the QPDs). This will add a fixed error of 0.3%, and I will take it into account in the future.

  68   Wed Mar 6 23:24:58 2013 ZachOpticsCharacterizationeLIGO OMC visibility vs. power measurement details

I found that, in fact, I had lowered the modulation depth since when I measured it to be 0.45 rads --> Psb = 0.1.

Here is the sweep measurement:

TEK00005.PNG TEK00007.PNG

This is Psb = 0.06 --> gamma = 0.35 rads.

This changes the "raw transmission" and "coupling", but not the inferred visibility:

eOMC_visibility_3_4_13.png

I also measured the cavity AMTF at three powers today: 0.5 mW, 10 mW, and 45 mW input.

eOMC_AMTF_vs_power_3_6_13.png

They look about the same. If anything, the cavity pole seems slightly lower with the higher power, which is counterintuitive. The expected shift is very small (~10%), since the decay rate is still totally dominated by the mirror transmissions even for the supposed high-loss state (Sam and Sheon estimated the roundtrip loss at high power to be ~1400 ppm, while the combined coupling mirrors' T is 1.6%). I have not been able to fit the cavity poles consistently to within this kind of error.

  74   Wed Mar 20 09:38:02 2013 ZachOpticsCharacterization[LLO] OMC test bench modified

 For various reasons, I had to switch NPROs (from the LightWave 126 to the Innolight Prometheus).

I installed the laser, realigned the polarization and modulation optics, and then began launching the beam into the fiber, though I have not coupled any light yet.

A diagram is below. Since I do not yet have the AOM, I have shown that future path with a dotted line. Since we will not need to make AMTFs and have a subcarrier at the same time, I have chosen to overload the function of the PBS using the HWP after the AEOM. We will operate in one of two modes:

  1. AMTF mode: The AOM path is used as a beam dump for the amplitude modulation setup. A razor dump should physically be placed somewhere in the AOM path.
  2. Subcarrier mode: The AEOM is turned off and the HWP after it is used to adjust the carrier/subcarrier power ratio. I chose a 70T / 30R beamsplitter for the recombining, since we want to be able to provide ~100 mW with the carrier for transmission testing, and we don't need a particularly strong subcarrier beam for probing.

new_setup_traced.jpg

One thing that concerns me slightly: the Prometheus is a dual-output (1064nm/532nm) laser, with separate ports for each. I have blocked and locked out the green path physically, but there is some residual green light visible in the IR output. Since we are planning to do the OMC transmission testing with a Si-based Thorlabs power meter---which is more sensitive to green than IR---I am somewhat worried about the ensuing systematics. I *think* we can minimize the effect by detuning the doubling crystal temperature, but this remains to be verified.

 EDIT (ZK): Valera says there should be a dichroic beam splitter in the lab that I can borrow. This should be enough to selectively suppress the green.

  76   Sat Mar 23 02:41:00 2013 KojiOpticsGeneralBlack glass beam dumps for the first OMC

Received black glass beam dumps from MIT

- gluing by EP30-2 looks pretty fine. Enough sturdy.

- some gap visible between the glass => incident angle should be considered so that the first beam does not exit from the gap

- Dusts are visible on the glass surface. Some have a lot, the other have less. But every piece still needs to be wiped.

Attachment 1: P3223314.JPG
P3223314.JPG
Attachment 2: P3223319.jpg
P3223319.jpg
Attachment 3: P3223320.jpg
P3223320.jpg
  77   Sat Mar 23 13:34:14 2013 KojiOpticsGeneralPZT assembly prototype glued

Prototype PZT assembly

Motivation:

Before we glue the PZT assembly, we need to build a prototype. This is to confirm the heat cure process
does not cause any cracking of the PZT or glass components. The CTE of the PZT is 2~3ppm
(depends on the direction) while the one for Fused Silica is 0.55ppm.

Materials:

- A fused silica substrate, 1/2" in dia. Supplied from Garilynn. I defined the chamfered side as the front side.

- PZT: Noliac NAC2124, serial #24, this is a spare PZT as this has the worst length to angle coupling.

- Mounting Prism: D1102069 SN22. This has the worst perpendicularity among the prisms.

- Fixtures:

D1300185 aLIGO OMC CURVED MIRROR BONDING FIXTURE ASSY
D1300186 aLIGO OMC CURVED MIRROR BONDING FIXTURE FRONT
D1300187 aLIGO OMC CURVED MIRROR BONDING FIXTURE BACK
D1300188 aLIGO OMC CURVED MIRROR BONDING FIXTURE RING

P3223322.jpg

Procedure:

- Wipe all of the components with the isopropanol.

- Attach the back piece of the fixture on the Al wrapped bracket.
(The current 4-40 screws for the middle piece are too long and stick out from the back side of the back piece.
Therefore a 1/16" shim for a 1/2" rod is inserted between the bracket and the back piece)

- Brought a glue package to the lab (10:40PM)

- Loosely attach the middle piece to the back piece with four 4-40 screws.

- Insert the mounting prism in the fixture. Insert the PZT in the fixture too.

- Insert a dummy substrate in the fixture.

- Attach the front piece with spring loaded screws.

- Align the PZT and the optic in the fixture. (Basically apply downward force to them)

- Test the rigidity of the assembly (11:30PM)

- Remove the PZT and the mirror. Apply UV epoxy.
(A single dub was applied for each PZT surface of the PZT but this was too much.)

- Make sure the PZT and the optic are aligned by applying the downward force.

- Illuminate UV light from the front.

- Illuminate UV light from the back. (11:50PM)

Procedural issues:

- Long 4-40 screws (described above)
(Circumvented)

- As the PZT is not constrained with the middle piece, it tends to move vertically and rotationally
because of the wire tension. (This is not a mistake but the design so that the PZT is constrained by the optic.)
Therefore after applying glue on the PZT, the motion of the PZT spreads the glue on the back surface of
the curved mirror.

(Solution to be tried) Our solution is to glue the PZT and the mounting prism first with a dummy optics (made of SF2).
The wires should be tacked somewhere on the mount 

- The amount of glue on the PZT was too much. I gave one dub of glue for each side.
As a result, excess glue leaks out along the ring.

- The front plate has a chamfered hole but this tends to slip and move the mirror vertically.
Later I used the flat side of the plate to hole the mirror.
(Circumvented) It seems that this hold the mirror in a better way as the plate can't rock

- Spring load for the front plate was too strong. This was because the natural length of the spring was too long.
(Circumvented) The spring was cut at the length of the 4-40 screw. Then attaching the screws became completely fine.

P3223323.jpg


Result:

P3233336.jpg P3233348.jpg

Slide show:

  81   Mon Mar 25 19:31:16 2013 KojiOpticsGeneralOMC Top-side gluing

[Koji Jeff Zach]

AAA

P3253372.jpg

BBB

P3253353.jpg

CCC

P3253394.jpg

DDD

P3253400.jpg

  86   Thu Mar 28 03:37:07 2013 ZachOpticsConfigurationTest setup input optics progress

[Lisa, Zach]

Last night (Tuesday), I finished setting up and aligning most of the input optics for the OMC characterization setup. See the diagram below, but the setup consists of:

  • Faraday isolator/polarization definition
  • HWP+PBS for power splitting into two paths:
    • EOM path
      • Resonant EOM for PDH sideband generation
      • Broadband EOM for frequency scanning
    • AOM path
      • Double-passed ~200-MHz Isomet AOM for subcarrier generation. NOTE: in this case, I have chosen the m = -1 diffraction order due to the space constraints on the table.
  • Recombination of paths on a 50/50 beam splitter---half of the power is lost through the unused port into a black glass dump
  • Coupler for launching dual-field beam into a fiber (to OMC)

OMC_test_setup_IO.jpg 2013-03-27_05.48.20.jpg

Today, we placed some lenses into the setup, in two places:

  1. In the roundabout section of the AOM path that leads to the recombination, to re-match the AOM-path beam to that of the EOM path
  2. After the recombination beam splitter, to match the combined beam mode into the fiber

We (Koji, Lisa, and myself) had significant trouble getting more than ~0.1% coupling through the fiber, and after a while we decided to go to the 40m to get the red-light fiber illuminator to help with the alignment.

Using the illuminator, we realigned the input to the coupler and eventually got much better---but still bad---coupling of ~1.2% (0.12 mW out / 10 mW in). Due to the multi-mode nature of the illuminator beam, the output cannot be used to judge the collimation of the IR beam; it can only be used to verify the alignment of the beam.

With 0.12 mW emerging from the other end of the fiber, we could see the output quite clearly on a card (see photo below). This can tell us about the required input mode. From the looks of it, our beam is actually focused too strongly. We should probably replace the 75mm lens again with a slightly longer one.

Lisa and I concurred that it felt like we had converged to the optimum alignment and polarization, which would mean that the lack of coupling is all from mode mismatch. Since the input mode is well collimated, it seems unlikely that we could be off enough to only get ~1% coupling. One possibility is that the collimator is not well attached to the fiber itself. Since the Rayleigh range within it is very small, any looseness here can be critical.

2013-03-28_02.29.36.jpg

I think there are several people around here who have worked pretty extensively with fibers. So, I propose that we ask them to take a look at what we have done and see if we're doing something totally wrong. There is no reason to reinvent the wheel.

  87   Fri Mar 29 08:55:00 2013 ZachOpticsConfigurationBeam launched into fiber

Quote:

Lisa and I concurred that it felt like we had converged to the optimum alignment and polarization, which would mean that the lack of coupling is all from mode mismatch. Since the input mode is well collimated, it seems unlikely that we could be off enough to only get ~1% coupling. One possibility is that the collimator is not well attached to the fiber itself. Since the Rayleigh range within it is very small, any looseness here can be critical.

My hypothesis about the input-side collimator turned out to be correct.

I removed the fiber from the collimator and mount at the input side, and then injected the illuminator beam from this side. Since we already saw a nice (but dim) IR beam emerging from the output side the other night, it followed that that collimator was correctly attached. With the illuminator injected from the input side, I also saw a nice, collimated red beam emerging from the output. So, the input collimator was not properly attached during our previous attempts, leading to the abysmal coupling.

The problem is that the mount does not allow you to remove and reattach the fiber while the collimator is already attached, and the dimensions make it hard to fit your fingers in to tighten the fiber to the collimator once the collimator is in the mount. I disassembled the mount and found a way to attach/reattach the fiber that preserves the tight collimator contact. I will upload a how-to shortly.

With this fix, I was able to align the input beam and get decent coupling:

EOM path: ~70%

AOM path: ~50%

  88   Mon Apr 1 03:13:41 2013 KojiOpticsGeneralFailure of PZT-glass joints

[Koji, Jeff, Zach, Lisa]

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

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

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

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

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

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

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

 

  89   Mon Apr 1 03:23:48 2013 KojiOpticsGeneralUV power calibration

[Koji Lisa Jeff Zach]

Eric G bought a UV power meter from American Ultraviolet.

Our UV illuminator was calibrated by this power meter.

The first blast (i.e. cold start): 3.9W/cm^2

After many blasting: 8.3W/cm^2

The spec is 20W/cm^2

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

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

Motivation:

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

Measurement technique:

When a curved mirror is completely axisymmetric (in terms of the mirror shape), any rotation of the mirror does not induce change on the axis of the refected beam.
If the curvature minimum is deviated from the center of the mirror, the reflected beam suffer precession. As we want to precisely rotate the mirror, we use the gluing
fixture for the PZT assembly. In this method, the back surface of the curved mirror is pushed on the mounting prism, and the lateral position of the mirror is precisely
defined by the fixture. As you rotate the mirror in clockwise viewing from the front, the spot moves in counter clockwise on the CCD.
curved_mirror_precession1.png

 

 

Setup and procedure:

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

curved_mirror_precession2.png

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

curved_mirror_precession3.png

Measurement result:

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

Analysis:

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

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

R: Radius of curvature of the mirror

theta_R: angle of incidence/reflection

curved_mirror_precession4.png

 

 

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

Therefore,

d = r R / (2 L)

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

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

curved_mirror_minimum_position.png

Attachment 5: curved_mirror_precession.pdf
curved_mirror_precession.pdf
  93   Wed Apr 3 18:42:45 2013 KojiOpticsGeneralEP30-2 gluing test

EP30-2 gluing test

  94   Thu Apr 4 00:35:42 2013 ZachOpticsConfigurationMMT installed on breadboard, periscope built

[Koji, Zach]

We installed the MMT that matches the fiber output to the OMC on a 6"x12" breadboard. We did this so that we can switch from the "fauxMC" (OMC mirrors arranged with standard mounts for practice locking) to the real OMC without having to rebuild the MMT.

The solution that Koji found was:

z = 0: front face of the fiber output coupler mount

z = 4.8 cm: f = 35mm lens

z = 21.6 cm: f = 125mm lens

This should place the waist at z ~ 0.8 m. Koji has the exact solution, so I will let him post that.

The lenses are on ±0.5" single-axis OptoSigma stages borrowed from the TCS lab. Unfortunately, the spacing between the two lenses is very close to a half-integer number of inches, so I had to fix one of them using dog clamps instead of the screw holes to preserve the full range.

Koji also built the periscope (which raises the beam height by +1.5") using a vertical breadboard and some secret Japanese mounts. Part of it can be seen in the upper left corner of the photo below---sorry for not getting a shot of it by itself.

2013-04-03_23.43.00.jpg

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

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

http://nodus.ligo.caltech.edu:8080/OMC_Lab/105

  96   Thu Apr 4 01:43:06 2013 KojiOpticsCharacterizationMirror T measurement

[Zach, Koji]

The measurement setup for the transmission measurement has been made at the output of the fiber.

- First, we looked at the fiber output with a PBS. It wasn't P-pol so we rotated the ourput coupler.
  What we found was that it wasn't actually linearly polarized.
  So the input coupler was rotated to correct it. This terribly misaligned the input coupling.
  After some iteration of rotating and aligning the input/output couplers, we obtained reasonable
  extiction ratio like 10mW vs 100uW (100:1) with 11mW incidence. (Where is the rest 0.9mW!?)

- The P-pol (transmission) out of PBS goes into the mirror. Here we tested mirror A1.
  The mirror is mounted on the prism mount supported by a rotational stage for precise angle adjustment
  We limited the input power down to 5mW so that we can remove the attenuator on the power meter.
  The reading of the power meter was fluctuating, indeed depending on MY position.
  So we decided to turn off the lighting of the room. This made the reading very stable.

  The offset of the power meter was -0.58uW

  The transmitted power for the normal incidence was 39.7uW with the incident 4.84mW.
  [39.7-(-0.58)] / [4.84*1000-(-0.58)] *10^6 = 8320 ppm

  The transmitted power for the 4deg incidence was 38.0uW with the incident 4.87mW.
  [38.0-(-0.58)] / [4.87*1000-(-0.58)] *10^6 = 7980 ppm

 cf. The specification is 7931ppm

 

  97   Thu Apr 4 23:44:52 2013 KojiOpticsConfigurationBeam launched into fiber

We had to move our flipper mirror to share the beam between Peter's setup and ours as our flipper is at the place where the ISS PD array base is supposed to be!
There was no place to insert the flipper in the setup. We (Peter and Koji) decided to move the laser back for ~2".

This entirely changed the alignment of the setup. The fiber coupler was my reference of the alignment.
Once the beam is aligned, I check the coupling to the fiber. It was 50%.

I tweaked the lens and eventually the coupling is improved to 83%. (24.7mW incident, 20.4mW obtained.)

Then, I started to check the AOM path. I noticed that the 1st (or -1st) order beam is very weak.
The deflection efficiency is ~0.1%. Something is wrong.
I checked the driver. The driver's coupler output (1:10) show the amplitude ~1V. (good)
I check the main output by reducing the offset. When the coupler output is 100mV, the main output was 1V. (good)
So is the AOM itself broken???

  99   Fri Apr 5 18:18:36 2013 ZachOpticsConfigurationAOM probably broken

Quote:

Then, I started to check the AOM path. I noticed that the 1st (or -1st) order beam is very weak.
The deflection efficiency is ~0.1%. Something is wrong.
I checked the driver. The driver's coupler output (1:10) show the amplitude ~1V. (good)
I check the main output by reducing the offset. When the coupler output is 100mV, the main output was 1V. (good)
So is the AOM itself broken???

As Koji noticed that the AOM efficiency was very low, I figured I would try looking at it with a fresh set of eyes. The end result is that I have to agree that the AOM appears to be broken.

First, I measured the input impedance of the AOM using the AG4395A with the impedance test kit (after calibrating). The plot is below. The spec sheet says the center frequency is 200 MHz, at which Zin should be ~50 ohms. It crosses 50 ohms somewhere near 235 MHz, which may be reasonable given that the LC circuit can be tuned by hand. However, it does surprise me that the impedance varies so much over the specified RF range of ±50 MHz. Maybe this is an indication that something is bad.

Isomet_1250C_zin_4_5_13.png

I removed the cover of the modulator (which I think Koji did, as well) and all the connections looked as I imagine they should---i.e., there was nothing obviously broken, physically.

I then tried my hand at realigning the AOM from scratch by removing and replacing it. I was not able to get better than 0.15%, which is roughly what Koji got.

So, perhaps our best course of action is to decide what we expect the Zin spectrum to look like, and whether that agrees with the above measurement.

  100   Mon Apr 8 11:11:37 2013 KojiOpticsCharacterizationMore Mirror T measurement

More Ts of the mirrors were measured.

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

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

 

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

 

  101   Mon Apr 8 11:29:08 2013 KojiOpticsCharacterizationMirror/PZT Characterization links
  103   Mon Apr 8 20:56:52 2013 KojiOpticsConfigurationPZT & Curverd Mirror arrangement

Assembly #1:

Mounting Prism #16
PZT #26
Mirror C6

Assembly #2:

Mounting Prism #20
PZT #23
Mirror C5

Attachment 1: PZT_assembly.pdf
PZT_assembly.pdf PZT_assembly.pdf
  104   Mon Apr 8 21:11:14 2013 KojiOpticsGeneralPZT assembly gluing

[Jeff, Zach, Koji]

PZT assembly gluing

Glue gun -> to be returned to MIT
Fixtures x2
Al bases, spacers
spare screws
mirrors / prisms / PZTs
IPA bottle
clean tools x2
first contact kit
gloves (7.5)

  105   Mon Apr 8 23:42:33 2013 KojiOpticsConfigurationFake OMC roughly aligned

Mode matching:

 

Attachment 1: beam_profile.pdf
beam_profile.pdf
Attachment 2: mode_matching.pdf
mode_matching.pdf
  106   Tue Apr 9 13:56:09 2013 KojiOpticsGeneralPZT assembly post gluing / pre baking pictures

 

 

  107   Wed Apr 10 00:40:30 2013 ZachOpticsConfigurationfauxMC locked

[Koji, Zach]

Tonight, we locked the "fauxMC". We obtained a visibility of >99%.

Koji had aligned it roughly last night, but we wanted to have a couple steering mirrors in the path for this practice cavity (the periscope mirrors will serve this function in the real setup), so we marked the alignment with irises and installed two extra mirrors.

After obtaining flashes with the WinCam placed at the output coupler, we removed the WinCam and put a CCD camera at one of the curved mirror transmissions and used this to get a strong TEM00 flash. Then, we installed the REFL PD/CCD, swept the laser PZT and optimized the alignment by minimizing the REFL dips. Finally, we connected the RF electronics and locked the cavity with the LB box. We used whatever cables we had around to trim the RF phase, and then Koji made some nice SMA cables at the 40m.

One thing we noticed was that we don't have enough actuation range to keep the cavity locked for very long---even with the HV amp (100V). We are going to offload to the NPRO temperature using an SR560 or pomona box circuit. We may also make an enclosure for the cavity to protect it from the HEPA blasting.

Tomorrow, after we do the above things, we will practice measuring the transmission, length (FSR) and mode spectrum of the cavity before moving on to the real McCoy.

fauxMC_labeled.jpg

  109   Fri Apr 12 09:25:31 2013 KojiOpticsCharacterizationAlignment of the OMC (without glue)

[Zach Koji]

The first attempt not to touch the curved mirrors did not work. (Not surprising)
The eigenmode is not found on the mirror surface.

We decided to touch the micrometers and immediately found the resonance.
Then the cavity alignment was optimized by the input steering mirrors.

We got the cavity length L and f_TMS/f_FSR (say gamma, = gouy phase / (2 pi) ) as
    L=1.1347 m        (1.132m nominal)
    gamma_V = 0.219176    (0.21879 nominal)
    gamma_H = 0.219418    (0.21939 nominal)


This was already sufficiently good:
- the 9th modes of the carrier is away from the resonance 10-11 times
  of the line width (LW)
- the 13th modes of the lower f2 sideband are 9-10 LW away
But
- the 19th modes of the upper f2 sideband are 1-3 LW away
  This seems to be the most dangerous ones.
and
- The beam spots on the curved mirrors are too marginal

So we decided to shorten the cavity round-trip 2.7mm (= 0.675mm for each micrometer)
and also use the curved mirrors to move the eigenmode toward the center of the curved mirrors.

After the movement the new cavity length was 1.13209 m.
The spot positions on the curved mirrors are ~1mm too close to the outside of the cavity.
So we shortened the outer micrometers by 8um (0.8 div).
This made the spot positions perfect. We took the photos of the spots with a IR sensor card.

The measured cavity geometry is (no data electrically recorded)
    L=1.13207 m        (1.132m nominal, FSR 264.8175MHz)
    gamma_V = 0.218547    (0.21879 nominal, 57.8750MHz)
    gamma_H = 0.219066    (0.21939 nominal, 58.0125MHz)

- the 9th modes of the carrier is 11-13 LW away
- the 13th modes of the lower f2 sideband are 5-8 LW away
- the 19th modes of the upper f2 sideband are 4-8 LW away

The raw transmission is 94.4%. If we subtract the sidebands and
the junk light contribution, the estimated transmission is 97.6%.

Note:
Even if a mirror is touched (i.e. misaligned), we can recover the good alignment by pushing the mirror
onto the fixture. The fixture works pretty well!
 

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

[Jeff, Zach, Lisa, Koji]

Gluing of the cavity mirrors went very well!!!

Preparation

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

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

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

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

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

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

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

BS1/FM1/FM2 gluing

- Aligned the cavity

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

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

- Spot positions (II)
  Looked OK.

CM2 gluing

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

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

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

CM1 gluing

- Glued CM1.

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

- Spot positions (final confirmation)
  Looked OK. 

Final measurement

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

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

Final values for the micrometers

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

0.90         0.78
\------------/
0.90         0.89

 

Attachment 1: Cav_scan_response_130412_Pitch.pdf
Cav_scan_response_130412_Pitch.pdf
Attachment 2: Cav_scan_response_130412_Yaw.pdf
Cav_scan_response_130412_Yaw.pdf
  111   Tue Apr 16 00:40:45 2013 KojiOpticsGeneralPD/QPD path gluing ~ preparation

[Jeff Koji]

- Placed the optics on the PD/QPD path

- Checked the alignment of the beam on the dummy PD/QPD mounts

- There is a bit of (~0.5mm) shift of the spot position from the center. Mainly downward. This is well within a ball park of the PD mounts.

- The PD/QPD path gluing will take place tomorrow.


- Went to the 40m and received the DCPDs from Bob's lab.

- Took six ISC QPDs for the sake of the OMCs.

- They are now in the OMC lab. 


- Measured the B mirror / E mirror R&Ts.

- Found anomalously high loss (3%) for the B mirrors (BSs)

- Went through the all mirrors. Some mirrors (3 or 4) seemed less lossy (<~1%). They will be used for the DCPD BS.

  112   Tue Apr 16 08:12:14 2013 KojiOpticsCharacterizationFurther More Mirror T measurement

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

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

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

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

 

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

L1 OMC

Cavity Mirrors

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

DCPD path

BS3 (BS for DCPDs): B5 B7

QPD path

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

OMC_breadboard_mirror_config.png

  114   Tue Apr 16 23:26:51 2013 KojiOpticsCharacterizationFurther More Mirror T measurement

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

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

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

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

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

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

 

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

  115   Wed Apr 17 07:30:04 2013 KojiOpticsGeneralQPD path glued

Yesterday, all of the glass components for the QPD path were glued.

- Check the alignment of the beam with the cavity.

- Placed the prisms

- Placed the QPD mount for the gluing test. An alignment disk instead of a diode was placed on the mount.

- Checked the spot positions at the QPDs. A CCD camera with a lens was used to find the spot.
  The spots were ~0.5mm lower on the QPD1, and ~1mm lower on the QPD2.

- Glued the first steering mirror while the spot position was continuously monitored.

- Glued the BS in the QPD path while the spot position was monitored.

- FInally a glass bracket was glued.

- The spot on QPD2 was too low to absorb by the QPD shim.

- Once the steering mirror was clamped by a cantilever spring (to prevent slipping), the spot moved up a bit.
  (Or, we should say, the cantilever misaligned the optics a bit in pitch in a preferrable direction.)

- The other steering mirror is clamped by a cantilever spring (to prevent slipping), the spot moved up a bit.
  Or, we should say, the cantilever misaligned the optics a bit in pitch in a preferrable direction.)

- The last steering mirrors was also glued in a same way. As a result the spot is 0.5mm below the center of the alignment disk.

- Once the PD mounting brackets were glued, we can't place the QPD mount on it as the PEEK bar can't be inserted without moving the gluing template.

- The QPD mount with out the glass bracket was used to check the alignment of the beam dumps.
  As the beam dumps have a wide aperture and the yaw alignment of the QPD is big, we could accommodate the beams in the dumps easily.

- The dumps were glued.

  120   Mon May 6 19:31:51 2013 KojiOpticsCharacterizationSpot position measurement on the diode mounts

Measurement Order: DCPD2->DCPD1->QPD1->QPD2

DCPD1: 1.50mm+0.085mm => Beam 0.027mm too low

DCPD2: 1.75mm+0.085mm => Beam 0.051mm too high (...less confident)

QPD1:   1.25mm+0.085mm => Beam 0.077mm too low

QPD2:   1.25mm+0.085mm => Beam 0.134mm too low
          or 1.00mm+0.085mm => Beam 0.116mm too high

Attachment 1: DCPD1.png
DCPD1.png
Attachment 2: DCPD2.png
DCPD2.png
Attachment 3: QPD1.png
QPD1.png
Attachment 4: QPD2.png
QPD2.png
  121   Wed May 8 15:08:57 2013 KojiOpticsCharacterizationSpot position measurement on the diode mounts

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
 

Attachment 1: DCPD1.png
DCPD1.png
Attachment 2: DCPD2.png
DCPD2.png
Attachment 3: QPD1.png
QPD1.png
Attachment 4: QPD2.png
QPD2.png
  132   Thu May 30 15:00:28 2013 KojiOpticsGeneralQPD alignment

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 /

  133   Fri May 31 05:46:54 2013 KojiOpticsGeneralQPD alignment

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.

QPD1.JPG QPD2.JPG

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

Attachment 3: QPD_calib.nb.zip
  134   Fri May 31 14:07:54 2013 KojiOpticsCharacterizationTransverse Mode Spacing measurement afte the baking

Measurement for pitch

Free Spectral Range (FSR): 264.9703 +/− 0.0007 MHz
Cavity roundtrip length: 1.131419 +/− 0.000003 m
Transverse mode spacing (TMS): 57.9396 +/− 0.0002 MHz
TMS/FSR: 0.218664 +/− 0.000001
 
Assuming the line width of the cavity 1/400 of the FSR...
- the 9th modes of the carrier is 12.8 line width (LW) away from the carrier resonance
- the 13th modes of the lower f2 sideband are 5.7 LW away
- the 19th modes of the upper f2 sideband are -6.8 LW away

Measurement for yaw

Free Spectral Range (FSR): 264.9696 +/− 0.0004 MHz
Cavity roundtrip length: 1.131422 +/− 0.000002 m
Transverse mode spacing (TMS): 58.0479 +/− 0.0002 MHz
TMS/FSR: 0.219074 +/− 0.000001
 
- the 9th modes of the carrier is 11.3 line width (LW) away from the carrier resonance
- the 13th modes of the lower f2 sideband are 7.8 LW away
- the 19th modes of the upper f2 sideband are -3.7 LW away

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

Attachment 1: Cav_scan_response_130530_Pitch.pdf
Cav_scan_response_130530_Pitch.pdf
Attachment 2: Cav_scan_response_130530_Yaw.pdf
Cav_scan_response_130530_Yaw.pdf
ELOG V3.1.3-