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  OMC elog, Page 5 of 9  Not logged in ELOG logo
ID Dateup Author Type Category Subject
  202   Tue Jul 8 18:54:54 2014 KojiMechanicsCharacterizationPZT characterization

Each PZT was swept with 0-150V 11Hz triangular wave.
Time series data for 0.2sec was recorded for each PZT.

The swept voltage at the resonances were extracted and the fringe number was counted.
Some hysteresis is seen as usual.

The upward/downward slopes are fitted by a linear line.

The average displacement is 11.3nm/V for PZT1 and 12.7nm/V.

The PZT response was measured with a FFT analyzer. The DC calibration was adjusted by the above numbers.

  203   Thu Jul 10 01:39:38 2014 KojiElectronicsGeneralPZT wire

Rich came to the OMC lab. Pins for the mighty mouse connector were crimped on the 4 PZT wires.
We found the male 4pin mighty mouse connector in the C&B area.

The cable inventory was checked with ICS/DCC combo. It turned out that most of the on-board cables
are at LHO. We decided to send the OMC there and then the cables are installed at the site.

  204   Thu Jul 10 08:34:57 2014 KojiGeneralGeneralTo Do

Optical tests

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

Backscattering test

Cabling / Wiring

  • Attaching cable/mass platforms
  • PZT cabling
  • DCPD cabling (to be done at LHO)
  • QPD cabling (to be done at LHO)

Vibration test

Baking

First Contact

Packing / Shipping

  205   Thu Jul 10 23:22:28 2014 KojiOpticsCharacterizationI1OMC QPD

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

  206   Fri Jul 11 00:06:33 2014 KojiOpticsCharacterizationI1OMC PD

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

  207   Sun Jul 13 17:46:28 2014 KojiOpticsCharacterizationOMC backscatter measurement

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?

  208   Tue Jul 15 03:00:42 2014 KojiOpticsCharacterizationOMC backscatter measurement

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.

Quote:

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. Assuming his measurement is done with the single bounce beam from an ITM,
and assuming this plot is already normalized for RIN, we may need to multiply the number on the plot by factor of two or so. Then it's about factor of 5 lower RIN
than the expected RIN. And in terms of R, it is 25 times lower.

 

  209   Tue Jul 15 03:34:16 2014 KojiOpticsCharacterizationOMC backscatter measurement

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.

OMC_backscatter.png


Backscattering measurement

- Pin = 12.3 +/- 0.001 [mW]

- RBS = 0.549 +/- 0.005

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

- Pback = 3.9 +/- 0.05 [nW] (OMC unlocked)   ==> ROMC(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.

  210   Thu Jul 17 02:19:20 2014 KojiMechanicsCharacterizationI1OMC vibration test

Summary

- The breadboard has a resonance at 1.2kHz. The resonant freq may be chagned depending on the additional mass and the boundary condition.

- There is no forest of resonances at around 1kHz. A couple of resonances It mainly starts at 5kHz.

- The PZT mirrors (CM1/CM2) have the resonance at 10kHz as I saw in the past PZT test.


Motivation

- Zach's LLO OMC characterization revealed that the OMC length signals have forest of spikes at 400-500Hz and 1kHz regions.

- He tried to excite these peaks assuming they were coming from mechanical systems. It was hard to excite with the OMC PZT,
but actuating the OMCS slightly excited them. (This entry)

Because the OMC length control loop can't suppress these peaks due to their high frequency and high amplitude, they limit
the OMC residual RMS motion. This may cause the coupling of the OMC length noise into the intensity of the transmitted light.
We want to eventually suppress or eliminate these peaks.

By this vibration test we want to:

- confirm whether the peaks are coming from the OMC or not.
- identify what is causing the peaks if they are originated from the OMC
- correct experimental data for comparison with FEA

Method

- Place a NOLIAC PZT on the object to be excited.
- Look at the actuation signal for the OMC locking to find the excited peaks.

Results

Breadboard

- This configuration excited the modes between 800-1.2kHz most (red curve). As well as the others, the structures above 5kHz are also excited.

- The mode at 1.2kHz was suspected to be the bending mode of the breadboard. To confirm it, metal blocks (QPD housing and a 4" pedestal rod)
  were added on the breadboard to change the load. This actually moved (or damped) the mode (red curve).

- Note that the four corners of the breadboard were held with a PEEK pieces on the transport fixture.
  In addition, the installed OMC has additional counter balance mass on it.
  This means that the actual resonant frequency can be different from the one seen in this experiment. This should be confirmed with an FEA model.
  The breadboard should also exhibit higher Q on the OMCS due to its cleaner boundary condition. 

 

I1OMC_vibration_test_Breadboard.png

DCPD / QPD

- Vibration on the DCPDs and QPDs mainly excited the modes above 3kHz. The resonances between 3 to 5kHz are observed in addition to the ubiquitous peaks above 5kHz.
  So are these coming from the housing? This also can be confirmed with an FEA model.

- Some excitation of the breadboard mode at 1.2kHz is also seen.

 

I1OMC_vibration_test_DCPD.pngI1OMC_vibration_test_QPD.png

CM1/CM2 (PZT mirrors)

- It is very obvious that there is a resonance at 10kHz. This was also seen in the past PZT test. This can be concluded that the serial resonance of the PZT and the curved mirror.
- There is another unknown mode at around 5~6kHz.

- Some excitation of the breadboard mode at 1.2kHz is also seen.

I1OMC_vibration_test_CM.png

FM1/FM2 and Peripheral prism mirrors (BSs and SMs)

- They are all prism mirrors with the same bonding method.

- The excitation is concentrated above 5kHz. Small excitation of the breadboard mode at 1.2kHz is also seen. Some bump ~1.4kHz is also seen in some cases.

I1OMC_vibration_test_FM.png I1OMC_vibration_test_Prism.png

Beam dumps

- The excitation is quite similar to the case of the peripheral mirrors. Some bump at 1.3kHz.

I1OMC_vibration_test_BD.png


Other tapping test of the non-OMC object on the table

- Transport fixture: long side 700Hz, short side 3k. This 3K is often seen in the above PZT excitation

- Fiber coupler: 200Hz and 350Hz.

- The beam splitter for the back scattering test: 900Hz

  211   Sun Jul 20 17:19:50 2014 KojiMechanicsCharacterizationI1OMC vibration test ~ 2nd round

Improved vibration measurement of the OMC

Improvement

- Added some vibration isolation. Four 1/2" rubber legs were added between the OMC bread board and the transport fixture (via Al foils).
  In order to keep the beam height same, 1/2" pedestal legs were removed.

- The HEPA filter at the OMC side was stopped to reduce the excitation of the breadboard. It was confirmed that the particle level for 0.3um
  was still zero only with the other HEPA filter.


Method

- Same measurement method as the previous entry was used.

Results

Breadboard

- In this new setup, we could expect that the resonant frequency of the body modes were close to the free resonances, and thus the Q is higher.
  Noise is much more reduced and it is clear that the resonance seen 1.1kHz is definitely associated with the body mode of the breadboard (red curve).

  As a confirmation, some metal objects were placed on the breadboard as tried before. This indeed reduced the resonant frequency (blue curve).

I1OMC_vibration_test_Breadboard.pngI1OMC_vibration_test_Breadboard_HiRes.png

DCPD / QPD

- Vibration on the DCPDs and QPDs mainly excited the modes above 2~3kHz.
  In order to check if they are coming from the housing, we should run FEA models.

- Some excitation of the breadboard mode at 1.1kHz was also seen.

I1OMC_vibration_test_DCPD.pngI1OMC_vibration_test_QPD.png

CM1/CM2 (PZT mirrors)

- Baseically excitation was dominated by the PZT mode at 10kHz. Some spourious resonances are seen at 4~5kHz but I believe this is associated with the weight placed on the excitation PZT.

I1OMC_vibration_test_CM.png

FM1/FM2 and peripheral prism mirrors (BSs and SMs)

- The modes of the FMs are seen ~8k or 12kHz. I believe they are lowered by the weight for the measurement. In any case, the mode frequency is quite high compared to our frequency region of interest.

- As the prism resonance is quite high, the excitation is directly transmitted to the breadboard. Therefore the excitation of the non-cavity caused similar effect to the excitation on the breadboard.
  In fact what we can see from the plot is excitation of the 1.1kHz body mode and many high frequency resonances.

I1OMC_vibration_test_FM.pngI1OMC_vibration_test_Prism.png

Beam dumps

- This is also similar to the case of the peripheral mirrors.

I1OMC_vibration_test_BD.png

  212   Sun Jul 20 17:20:39 2014 KojiGeneralGeneralThe 3rd (LIO) OMC was shipped out to LHO

The 3rd (LIO) OMC was shipped out to LHO on Friday (Jul 18) Morning.

At LHO

- All of the on-breadboard cables should be attached and tied down.

- Peel First Contact paint and pack the OMC for storage.

 

  213   Mon Jul 21 01:02:43 2014 KojiMechanicsCharacterizationSome structual mode analysis

Prisms

Fundamental: 12.3kHz Secondary: 16.9kHz

PRISM_12_3kHz.png PRISM_16_9kHz.png

DCPDs

Fundamental: 2.9kHz Secondary: 4.1kHz

DCPD_2_9kHz.png DCPD_4_1kHz.png

QPDs

Fundamental: 5.6kHz Secondary: 8.2kHz

QPD_6_0kHz.png QPD_8_2kHz.png

  214   Thu Jul 31 15:07:53 2014 KojiGeneralGeneralItem lending

Tara: Laser Safety goggle -> Returned

Evan:
HP signal generator (990MHz) (prev. setting 32.7MHz / +3dBm)
Black glass beam dump

Dmass:

LB1005 Oct 24.

  215   Mon Aug 4 18:59:50 2014 KojiGeneralGeneralA memorandom

On breadboarfd cabling for 3IFO OMC

D1300371 - S1301806
D1300372 - S1301808
D1300374 - S1301813
D1300375 - S1301815

  216   Tue Aug 5 13:03:25 2014 KojiGeneralGeneralMissing cable components

DCPD Connector Face: Qty2 https://dcc.ligo.org/LIGO-D1201276
QPD Connector Face: Qty2 https://dcc.ligo.org/LIGO-D1201282

PD faster: 92210A07 Qty 4: MCMASTER #2-56 x .25 FHCS

Spare DCPD

  217   Wed Aug 27 23:13:13 2014 KojiOpticsCharacterizationCollection of the power budgetting info

L1 OMC Cavity power budget

H1 OMC Cavity power budget

3IFO OMC Cavity power budget

  218   Tue Sep 9 20:59:19 2014 KojiMechanicsCharacterizationStructural mode analysis for the PZT mirror

Structural analysis of the PZT mirror with COMSOL.

Inline figures: Eigenmodes which involves large motion of the tombstone. In deed 10kHz mode is not the resonance of the PZT-mirror joint, but the resonance of the tombstone.

Attached PDF: Simulated transfer function of the PZT actuation. In order to simulate the PZT motion, boundary loads on the two sides of the PZT were applied with opposite signs.
10kHz peak appears as the resonance of the tombstone dominates the mirror motion. At 12kHz, the PZT extension and the backaction of the tombstone cancells each other and
the net displacement of the mirror becomes zero.

PZT_10.0kHz.png PZT_14.6kHz.png PZT_18.0kHz.png

PZT_22.5kHz.png PZT_29.7kHz.png

  219   Sat Jan 17 11:40:04 2015 KojiGeneralGeneral3rd OMC completed

Jan 15, 2015 3rd OMC completed

The face caps of the DCPD/QPD cables were installed (Helicoils inserted)
PD7&10 swapped with PD11(for DCPD T) and PD12(DCPD R).
Firct Contact coating removed

Note on the 3rd OMC

Before the 3rdOMC is actually used,

- First Contact should be applied again for preventing contamination during the installation

- DCPD glass windows should be removed

  220   Fri Jan 30 19:31:08 2015 KojiGeneralGeneralItem lending

Gabriele:

PZT HV Amp

Evan:
HP signal generator (990MHz) (prev. setting 32.7MHz / +3dBm)Returned March 23, 2016
Black glass beam dump

Dmass:

LB1005 Oct 24. This unit is permanently gone to Cryo lab. Acquired a new unit. Aug, 2016.

Quote:

Tara: Laser Safety goggle -> Returned

Evan:
HP signal generator (990MHz) (prev. setting 32.7MHz / +3dBm)
Black glass beam dump

Dmass:

LB1005 Oct 24.

 

  221   Tue Feb 3 18:23:49 2015 KojiGeneralGeneralItem lending

- The laser was removed and shipped to LHO today.

- UV illuminator / fused silica fiber light guide / UV power meter / UV face shield (Qty 2) will be shipped to MIT.
They are CIT properties except for the illuminator.

Quote:

Gabriele:

PZT HV Amp

Evan:
HP signal generator (990MHz) (prev. setting 32.7MHz / +3dBm)
Black glass beam dump

Dmass:

LB1005 Oct 24.

Quote:

Tara: Laser Safety goggle -> Returned

Evan:
HP signal generator (990MHz) (prev. setting 32.7MHz / +3dBm)
Black glass beam dump

Dmass:

LB1005 Oct 24.

 

 

  222   Wed Feb 4 20:07:24 2015 KojiGeneralGeneralItem lending

Shipment to MIT (L. Barsotti, J. Miller)

1. UV Illuminator (LESCO Super Spot MK III)

2. UV Power meter (American Ultraviolet AIB1001) Caltech property C30140

3. UV protection face shield (VWR UVC-803) Qty.2 Caltech property C30141/C30142

4. UV Fiber Optic Light Guide (American Ultraviolet OLB1081) C30143

All returned: Aug 30, 2016

  223   Wed Feb 18 21:51:23 2015 KojiGeneralGeneralNotes on OMC Transportation Fixtures & Pelican

LLO has one empty OMC transportation fixture.

LHO has one empty OMC transportation fixture.

LHO has one OMC transportation fixture with 3IFO OMC in it.

LHO has the Pelican trunk for the OMC transportation. Last time it was in the lab next to the optics lab.

  224   Wed Jul 15 22:23:17 2015 KojiElectronicsAM Stabilized EOM DriverE1400445 first look

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


E1400445 first look

LIGO DCC E1400445

Attachment 1: Record of the original state

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

  225   Sat Jul 18 11:37:21 2015 KojiElectronicsAM Stabilized EOM DriverD0900848 power board ~ oscillation issue solved

Power Supply Board D0900848 was oscillating. Here is the procedure how the issue was fixed.

PCB schematic: LIGO DCC D0900848

0. Extracting the power board.

The top lid and the front panel were removed. Top two modules were removed from the inter-board connection.
Some of the SMA cables were necessary to be removed to allow me to access to the botttom power board.

1. D1~D4 protection diodes

Daniel asked me to remove D1, D2, D3, D4 as the power supply sequence is controlled by the relays.
This was done.

2. Power supply oscillation
Since the power supply systems are entagnled, the oscillation of the transister boosted amps had to be checked one by one.

2.1 VREFP (U5)

First of all, the buffering stage of the positive voltage reference (U5) was oscillating. Attachment 1 is the observed voltage at "VREFP" at D13.
The oscillation was at 580kHz with 400mVpp. This was solved by replacing C20 with 1.2nF. (0805 SMD Cap)

2.2 VREFN (U6)

Then the buffering stage of the negative voltage reference (U6) was checked. Attachment 2 is the observed voltage at "VREFN" at D16.
The oscillation was at 26MHz with 400mVpp. This seemed to have a different mechanism from the U5 oscillation. This oscillation frequency is
higher than the GBW of OP27. So there must be some spurious path to the transister stage. This amplifier stage is a bit unique.
The input is VREFP, but the positive supply is also VREFP. And the feedback path between R31 and C24 is very long. I was afraid that this oscillation
was caused by some combination of L and stray C by the long feedback path and the output to power VREFP coupling, although I could not reproduce
the oscillation on LTSpice. 

After some struggles, adding a 100pF cap between the output of U6 op27 (PIN6) and VREFP (PIN7) stopped the oscillation.
I think this changes the loop function and fullfills the stability condition. I confirmed by a LTSpice model that additional cap does not
screw up the original function of the stage at audio frequencies when everything is functioning as designed.

2.3 Positive supply systems (U10, U11, U12)

Even after fixing the oscillations of U5 and U6, I kept observing the oscllative component of ~600kHz at U10 (+21V), U11 (+15V), and U12 (+5V) stages.
Among them, U11 had the biggest oscillation of 400mVpp at the opamp out (Attachment 3). The other two had small oscillation like 20mVpp at the opamp outputs.
The solution was the same as 2.1. C50, C51, and C52 were replaced to 1.2nF. After the modification I still had the 600kHz component with 2mVpp.
I wanted to check other channels and come back to this.

2.3 Negative supply systems (U7, U8, U9)

Similarly the outputs of U7, U8, and U9 had the oscillation at 600kHz with 40~80mVpp. Once C35, C36, and C37 were replaced with 1.2nF,
I no longer could see any 600kHz anywhere, including U10~U12.

2.4 -24V system (U13)

Last modification was U13. It had a noise of 50mVpp due to piled-up random pulses (Attachment 4). I just tried to replace C63 with 1.2nF
and remove a soldering jumber of W1
. There still looks random glitches there. But it's no longer the round shaped pulses but a sharp gliches
and the amplitude is 20mV each (Attachment 5). In fact, later I noticed that Q9 is not stuffed and W2 is closed. This means that the +24V external supply is
directly connected to +24AMP. Therefore U13 has no effect to the 24V suppy system.

3. Restoring all connections / final check of the voltages

Restore the middle and top PCBs to the intra-PCB connector board. Attach the front panel. Restore the SMA connections.

The missing soldering of the SMA cable (reported in the previous entry) was soldered.

Once all the circuits are connected again, the power supply voltages were checked again. There was no sign of oscillation.

All the above modifications are depicted in Attachment 6.

  226   Tue Jul 21 20:20:12 2015 KojiGeneralGeneralItem lending

Kate (ATF)

- 4ch color oscilloscope (Tektronix)

- Chopper controller

- Chopper with a rotating disk

  227   Wed Jul 22 09:43:01 2015 KojiElectronicsAM Stabilized EOM DriverPower supply test of the EOM/AOM Driver

Serial Number of the unit: S1500117
Tester: Koji Arai
Test Date: Jul 22, 2015

1) Verify the proper current draw with the output switch off:

+24 Volt current: 0.08 A Nom.
-24 Volt current: 0.07 A Nom.
+18 Volt current: 0.29 A Nom.
-18 Volt current: 0.24 A Nom.

2) Verify the proper current draw with the output switch on:
+24 Volt current: 0.53 A Nom.
-24 Volt current: 0.07 A Nom.
+18 Volt current: 0.21 A Nom.
-18  Volt current: 0.26 A Nom.

3) Verify the internal supply voltages:

All look good.

TP13 -5.001V
TP12 -15.00
TP11 -21.05
TP10 -10.00
TP5  -18.19
TP6  -24.22
TP2  +24.15
TP3  +18.22
TP9  + 9.99
TP17 +24.15
TP14 +21.04
TP15 +15.00
TP16 + 4.998

4) Verify supply OK logic:
All look good. This required re-disassembling of the PCBs...

Check then pin 5 on U1 (connected to R11) and U4 (connected to R23):

U1 3.68V (=Logic high)
U4 3.68V (=Logic high)

5) Verify the relays for the power supply sequencing: OK

Turn off +/-24 V. Confirm Pin 5 of K1 and K2 are not energized to +/-18V. => OK
Turn on +/-24 V again. Confirm Pin 5 of K1 and K2 are now energized to +/-18V. => OK

6) Verify noise levels of the internal power supply voltages:

TP13 (- 5V) 13nV/rtHz@140Hz
TP12 (-15V) 22
nV/rtHz@140Hz
TP11 (-21V) 32
nV/rtHz@140Hz
TP10 (-10V) 16nV/rtHz@140Hz
TP9  (+10V)  9
nV/rtHz@140Hz
TP14 (+21V) 21nV/rtHz@140Hz
TP15 (+15V) 13nV/rtHz@140Hz
TP16 (+ 5V) 11nV/rtHz@140Hz

 

Note that the input noise of SR785 is 9~10nV/rtHz@140Hz with -50dBbpk input (AC)

 

  228   Wed Jul 22 10:15:14 2015 KojiElectronicsAM Stabilized EOM DriverRF test of the EOM/AOM Driver S1500117

7) Make sure the on/off RF button works,
=> OK

8) Make sure the power output doesn't oscillate,

Connect the RF output to an oscilloscope (50Ohm)
=> RF output: there is no obvious oscillation

Connect the TP1 connector to an oscilloscope
=> check the oscillation with an oscilloscope and SR785 => OK

Connect the CTRL connector to an oscilloscope
=> check the oscillation with an oscilloscope and SR785 => OK

9) EXC check
Connect a function generator to the exc port.
Set the FG output to 1kHz 2Vpk. Check the signal TP1
Turn off the exc switch -> no output
Turn on the exc switch -> nominally 200mVpk

=> OK

10) Openloop transfer function

Connect SR785 FG->EXC TP2->CHA TP1->CHB
EXC 300mV 100Hz-100kHz 200 line

Network Analyzer (AG4395A)
EXC 0dBm TP1->CHA TP2->CHB, measure A/B
801 line
CHA: 0dBatt CHB: 0dBatt
1kHz~2MHz
UGF 133kHz, phase -133.19deg = PM 47deg

11) Calibrate the output with the trimmer on the front panel

13dB setting -> 12.89dBm (maximum setting)

12) Check MON, BIAS and CTRL outputs,
CTRL:    2.95V
MON(L):    6.5mV
BIAS(L):    1.81V
MON(R):    10.7mV
BIAS(R):    1.85V

13) Output check
4+0dB    3.99dBm
6    5.89
8    7.87
10    9.87
12    11.88
14    13.89
16    15.89
18    17.92
20    19.94
22    21.95
24    24.00
26    26.06

4dB+
0.0    3.99
0.2    4.17
0.4    4.36
0.6    4.56
0.8    4.75
1.0    4.94
1.2    5.13
1.4    5.32
1.6    5.53
1.8    5.73
2.0    5.92
2.2    6.10

16dB+
0.0    15.82
0.2    16.11
0.4    16.31
0.6    16.51
0.8    16.72
1.0    16.92
1.2    17.12
1.4    17.32
1.6    17.53
1.8    17.72
2.0    17.92
2.2    18.13

26dB+
0.0    26.06
0.2    26.27
0.4    26.46
0.6    26.58
0.8    26.68
1.0    26.69
1.2    26.70
1.4    3.98
1.6    3.99
1.8    3.99
2.0    3.99
2.2    3.99

 

 

 

  229   Sat Jul 25 17:24:11 2015 KojiElectronicsAM Stabilized EOM DriverRF test of the EOM/AOM Driver S1500117

(Calibration for Attachment 5 corrected Aug 27, 2015)


Now the test procedure fo the unit is written in the document https://dcc.ligo.org/LIGO-T1500404

And the test result of the first unit (S1500117) has also been uploaded to DCC https://dcc.ligo.org/LIGO-S1500117

Here are some supplimental information with plots

Attachment 1: OLTF of the AM amplitude stabilization servo.

Attachment 2: CLTF/OLTF of the 2nd AM detector self bias adj servo

The secondary RF AM detector provides us the out-of-loop measurement. The secondary loop has an internal control loop to adjust the DC bias.
This loop supresses the RF AM error signal below the control bandwidth. This has been tested by injecting the random noise to the exc and taking
the transfer function between the primary RF AM detector error (MON1) and the secondary one (MON2).

Then the closed loop TF was converted to open loop TF to see where the UGF is. The UGF is 1Hz and the phase margin is 60deg.

Above 10Hz, the residual control gain is <3%. Therefore we practically don't need any compensation of MON2 output above 10Hz.

Attachment 3: Comparison between the power setting and the output power

Attachment 4: Raw power spectra of the monitor channels

Attachment 5: Calibrated in-loop and out-of-loop AM noise spectra

Attachment 6: TFs between BNC monitor ports and DAQ differential signals

BIAS2 and CTRL look just fine. BIAS2 has a gain of two due to the differential output. The TF for CTRL has a HPF shape, but in fact the DC gain is two.
This frequency response comesfro that the actual CTRLis taken after the final stage that has LPF feature while the CTRL DAQ was taken before this final stage.

MON1 and MON2 have some riddle. I could not justify why they have the gain of 10 instead of 20. I looked into the issue (next entry)

Attachment 7: TF between the signals for the CTRL monitor (main unit) and the CTRL monitor on the remote control test rig

The CTRL monitor for the test rig is taken from the CTRL SLOW signal. There fore there is a LPF feature together with the HPF feature described above.
This TF can be used as a reference.

 

  230   Tue Jul 28 18:36:50 2015 KojiElectronicsAM Stabilized EOM DriverRF test of the EOM/AOM Driver S1500117

Final Test Result of S1500117: https://dcc.ligo.org/LIGO-S1500117


After some staring the schematic and checking some TFs, I found that the DAQ channels for MON2 have a mistake in the circuit.
Differential driver U14 and U15 of D0900848 are intended to have the gain of +10 and -10 for the pos and neg outputs.
However, the positive output has the gain of +1.

Daniel suggested to shift R66 and R68 by one pad, replace with them by ~5.5K and add a small wire from the now "in air" pad to
the GND near pad 4.

The actual modification can be seen on Attachment 1. The resulting gain was +10.1 as the resisters of 5.49k were used.

The resulting transfer function is found in the Attachment 2. ow the nominal magnitude is ~x20.

You may wonder why the transfer function for MON1 is noisy and lower at low freq (f<1kHz). This is because the input noise of the FFT analizer
contributed to the BNC MON1 signal. High frequency part dominated the RMS of the signal and the FFT analyzer could not have proper range
for the floor noise. The actual voltage noise comparison between the BNC and DAQ signals for MON1 and MON2 can be found in Attachment 3.
 

  231   Mon Aug 10 02:11:47 2015 KojiElectronicsAM Stabilized EOM DriverRF AM Measurement Unit E1500151

This is an entry for the work on Aug 3rd.

LIGO DCC E1500151

Power supply check

- Removed the RF AM detector board and exposed the D0900848 power board. The board revision is Rev. A.

- The power supply voltage of +30.2V and -30.5V were connected as +/-31V supplies. These were the maximum I could produce with the bench power supply I had. +17.2V and -17.1V were supplied as +/-17V supplies.

- Voltage reference: The reference voltages were not +/-10V but +/-17V. The cause was tracked down to the voltage reference chip LT1021-10. It was found that the chip was mechanically destroyed (Attachment 1, the legs were cut by me) and unluckily producing +17V. The chip was removed from the board. Since I didn't have any spare LT1021-10, a 8pin DIP socket and an AD587 was used instead. Indeed AD587 has similar performance or even better in some aspects. This fixed the reference voltage.

- -5V supply: After the fix of the reference voltage, I still did not have correct the output voltage of -5V at TP12. It was found that the backpanel had some mechanical stress and caused a leg of the current boost transister cut and a peeling of the PCB pattern on the component lalyer (Attachment 2). I could find some spare of the transister at the 40m. The transister was replaced, and the pattern was fixed by a wire. This fixed the DC values of the power supply voltages. In fact, +/-24V pins had +/-23.7V. But this was as expected. (1+2.74k/2k)*10V = 23.7V .

- VREFP Oscillation: Similarly to the EOM/AOM driver power supply board (http://nodus.ligo.caltech.edu:8080/OMC_Lab/225), the buffer stage for the +10V has an oscillation at 762kHz with 400mVpp at VREFP. This was fixed by replacing C20 (100pF) with 1.2nF. The cap of 680pF was tried at first, but this was not enough to completely elliminate the oscilation.

- VREFN Oscillation: Then, similarly to the EOM/AOM driver power supply board (http://nodus.ligo.caltech.edu:8080/OMC_Lab/225), the amplifier and buffer stage for the -10V has an oscillation at 18MHz with 60mVpp at VREFN. This was fixed by soldering 100pF between pin6 and pin7 of U6.

- Voltage "OK" signal: Checked the voltage of pin5 of U1 and U4 (they are connected). Nominally the OK voltage had +2.78V. The OK voltage turned to "Low (~0V)" when:
The +31V were lowered below +27.5V.
The +31V were lowered below -25.2V.
The +17V were lowered below +15.2V.
The +17V were lowered below -15.4V.

- Current draw: The voltage and current supply on the bench top supplies are listed below

+30.2V 0.09A, -30.5V 0.08A, +17.2V 0.21A, -17.1V 0.10A

- Testpoint voltages:

TP12(-5V) -5.00V
TP11(-15) -14.99V
TP10(-24V) -23.69V
TP9(-10V) -9.99V
TP5(-17V) -17.15V
TP6(-31V) -30.69

TP2(+31V) +30.37V
TP3(+17V) +17.24V
TP8(+10V) +10.00V
TP16(+28V) +28.00V
TP13(+24V) +23.70V
TP14(+15V) +15.00V
TP15(+5V) +5.00V

 

  232   Mon Aug 10 11:39:40 2015 KojiElectronicsAM Stabilized EOM DriverRF AM Measurement Unit E1500151

Entry for Aug 6th, 2015

I faced with difficulties to operate the RF AM detectors.

I tried to operate the RF AM detector. In short I could not as I could not remove the saturation of the MON outputs, no matter how jiggle the power select rotary switches. The input power was 10~15dBm.

D0900761 Rev.A
https://dcc.ligo.org/LIGO-D0900761-v1

I've measured the bias voltage at TP1. Is the bias such high? And does it show this inversion of the slope at high dBm settings?

Setting Vbias
 [dBm]   [V]

   0    21.4
   2    21.0
   4    20.5
   6    19.8
   8    18.8
  10    17.7
  12    16.3
  14    14.2
  16    11.9
  18    10.6
  20    11.8
  22    15.0


The SURF report (https://dcc.ligo.org/LIGO-T1000574) shows monotonic dependence of Vbias from 0.6V to 10V (That is supposed to be the half of the voltage at TP1). 
I wonder I need to reprogram FPGA?

But if this is the issue, the second detector should still work as it has the internal loop to adjust the bias by itself.
TP3 (Page 1 of D0900761 Rev.A) was railed. But still MON2 was saturated.
I didn't see TP2 was also railed. It was ~1V (not sure any more about the polarity). But TP2 should also railed.

Needs further investigation

  233   Mon Aug 10 11:57:17 2015 KojiElectronicsAM Stabilized EOM DriverRF AM Measurement Unit E1500151

Spending some days to figure out how to program CPLD (Xilinx CoolRunner II XC2C384).

I learned that the JTAG cable which Daniel sent to me (Altium JTAG USB adapter) was not compatible with Xilinx ISE's iMPACT.

I need to use Altium to program the CPLD. However I'm stuck there. Altium recognizes the JTAG cable but does not see CPLD. (Attachment 1)

Upon the trials, I followed the instruction on awiki as Daniel suggested.
http://here https://awiki.ligo-wa.caltech.edu/aLIGO/TimingFpgaCode

Altium version is 15.1. Xilinx ISE Version is 14.7

  234   Mon Aug 10 12:09:49 2015 KojiElectronicsAM Stabilized EOM DriverRF AM Measurement Unit E1500151

Still suffering from a power supply issue!

I have been tracking the issues I'm having with the RF AM detector board.

I found that the -5V test point did not show -5V but ~+5V! It seemed that this pin was not connected to -5V but was passive.

I removed the RF AM detector board and exposed the power board again. Pin 11 of P3 interboard connector indeed was not connected to TP12 (-5V). What the hell?

As seen in the attached photo, the PCB pattern for the Pin 11 is missing at the label "!?" and not driven. I soldered a piece of wire there and now Pin11 is at -5V.


This fix actually changed several things. Now the bias setting by the rotary switches works.

Setting BIAS1
 [dBm]   [V]

   0    0.585
   2    0.720
   4    0.897
   6    1.12
   8    1.42
  10    1.79
  12    2.25
  14    2.84
  16    3.60
  18    4.56
  20    5.75
  22    7.37

This allows me to elliminate the saturation of MON1 of the first RF AM detector. I can go ahead to the next step for the first channel.

Now the bias feedback of the second detector is also behaving better. Now TP2 is railing.

Still MON2 is saturated. So, the behavior of the peak detectors needs to be reviewed.

  235   Thu Aug 20 01:35:01 2015 KojiElectronicsGeneralOMC DCPD in-vacuum electronics chain test

We wanted to know the  transimpedance of the OMC DCPD at high frequency (1M~10M).
For this purpose, the OMC DCPD chain was built at the 40m. The measurement setup is shown in Attachment 1.

- As the preamp box has the differential output (pin1 and pin6 of the last DB9), pomona clips were used to measure the transfer functions for the pos and neg outputs individually.

- In order to calibrate the measurements into transimpedances, New Focus 1611 is used. The output of this PD is AC coupled below 30kHz.
This cutoff was calibrated using another broadband PD (Thorlabs PDA255 ~50MHz).

Result: Attachment 2
- Up to 1MHz, the transimpedance matched well with the expected AF transfer function. At 1MHz the transimpedance is 400.

- Above 1MHz, sharp cut off at 3MHz was found. This is consistent with the openloop TF of LT1128.

 

  236   Wed Aug 26 11:31:33 2015 KojiElectronicsGeneralOMC DCPD in-vacuum electronics chain test

The noise levels of the output pins (pin1/pin6) are measured. Note that the measurement is done with SE. i.e. There was no common mode noise rejection.

  237   Fri Aug 28 01:08:14 2015 KojiElectronicsAM Stabilized EOM DriverRF AM Measurement Unit E1500151 ~ Calibration

Worked on the calibration of the RF AM Measurement Unit.

The calibration concept is as follows:

  • Generate AM modulated RF output
  • Measure sideband amplitude using a network anayzer (HP4395A). This gives us the SSB carrier-sideband ratio in dBc.
  • Measure the output of the RF AM measurement unit with the same RF signal
  • Determine the relationship between dBc(SSB) and the output Vrms.

The AM modulated signal is produced using DS345 function generator. This FG allows us to modulate
the output by giving an external modulation signal from the rear panel. In the calibration, a 1kHz signal with
the DC offset of 3V was given as the external modulation source. The output frequency and output power of
DS345 was set to be 30.2MHz (maximum of the unit) and 14.6dBm. This actually imposed the output
power of 10.346dBm. Here is the result with the modulation amplitude varied

                 RF Power measured             Monitor output
Modulation       with HP4395A (dBm)           Measure with SR785 (mVrms)
1kHz (mVpk)   Carrier    USB      LSB          MON1       MON2
   0.5        9.841    -72.621  -73.325          8.832      8.800
   1          9.99     -65.89   -65.975         17.59      17.52
   2          9.948    -60.056  -59.747         35.26      35.07
   3          9.90     -56.278  -56.33          53.04      52.9
   5          9.906    -51.798  -51.797         88.83      88.57
  10          9.892    -45.823  -45.831        177.6      177.1
  20          9.870    -39.814  -39.823        355.3      354.4
  30          9.8574   -36.294  -36.307        532.1      531.1
  50          9.8698   -31.86   -31.867        886.8      885.2
 100          9.8735   -25.843  -25.847       1772       1769
 150          9.8734   -22.316  -22.32        2656       2652
 200          9.8665   -19.819  -19.826       3542       3539
 300          9.8744   -16.295  -16.301       5313       5308

The SSB carrier sideband ratio is derived by SSB[dBc] = (USB[dBm]+LSB[dBm])/2 - Carrier[dBm]

This measurement suggests that 10^(dBc/20) and Vrms has a linear relationship. (Attachment 1)
The data points were fitted by the function y= a x.

=> 10^dBc(SSB)/20 = 108*Vrms (@10.346dBm input)


Now we want to confirm this calibration.

DS345 @30.2MHz was modulated with the DC offset + random noise. The resulting AM modulated RF was checked with the network analyzer and the RFAM detector
in order to compare the calibrated dBc/Hz curves.

A) SR785 was set to produce random noise
B) Brought 2nd DS345 just to produce the DC offset of -2.52V (Offset display -1.26V)
Those two are added (A-B) by an SR560 (DC coupling, G=+1, 50 Ohm out).
The output was fed to Ext AM in DS345(#1)

DS345(#1) was set to 30.2MHz 16dBm => The measured output power was 10.3dBm.

On the network analyzer the carrier power at 30.2MHz was 9.89dBm

Measurement 1) SR785     1.6kHz span 30mV random noise (observed flat AM noise)
Measurement 2) SR785   12.8kHz span 100mV random noise (observed flat AM noise)
Measurement 3) SR785 102.4kHz span 300mV random noise (observed cut off of the AM modulation due to the BW of DS345)

The comparison plot is attached as Attachment 2. Note that those three measurements are independent and are not supposed to match each other.
The network analyzer result and RFAM measurement unit output should agree if the calibration is correct. In fact they do agree well.

 

  238   Fri Aug 28 02:14:53 2015 KojiElectronicsAM Stabilized EOM DriverRF AM Measurement Unit E1500151 ~ 37MHz OCXO AM measurement

In order to check the noise level of the RFAM detector, the power and cross spectra for the same signal source
were simultaneously measured with the two RFAM detectors.


As a signal source, 37MHz OCXO using a wenzel oscillator was used. The output from the signal source
was equaly splitted by a power splitter and fed to the RFAM detector CHB(Mon1) and CHA(Mon2).

The error signal for CHB (Mon1) were monitored by an oscilloscope to find an appropriate bias value.
The bias for CHA are adjusted automatically by the slow bias servo.

The spectra were measured with two different power settings:

Low Power setting: The signal source with 6+5dB attenuation was used. This yielded 10.3dBm at the each unit input.
The calibration of the low power setting is dBc = 20*log10(Vrms/108). (See previous elog entry)

High Power setting: The signal source was used without any attenuation. This yielded 22.4dBm at the each unit input.
The calibration for the high power setting was measured upon the measurement.
SR785 was set to have 1kHz sinusoidal output with the amplitude of 10mVpk and the offset of 4.1V.
This modulation signal was fed to DS345 at 30.2MHz with 24.00dBm
The network analyzer measured the carrier and sideband power levels
30.2MHz 21.865dBm
USB    -37.047dBm
LSB    -37.080dBm  ==> -58.9285 dBc (= 0.0011313)

The RF signal was fed to the input and the signal amplitude at Mon1 and Mon2 were measured
MON1 => 505   mVrms => 446.392 Vrms/ratio
MON2 => 505.7 mVrms => 447.011 Vrms/ratio
dBc = 20*log10(Vrms/446.5).


Using the cross specrum (or coherence)of the two signals, we can infer the noise level of the detector.

Suppose there are two time-series x(t) and y(t) that contain the same signal s(t) and independent but same size of noise n(t) and m(t)

x(t) = n(t) + s(t)
y(t) = m(t) + s(t)

Since n, m, s are not correlated, PSDs of x and y are

Pxx = Pnn + Pss
Pyy = Pmm+Pss = Pnn+Pss

The coherence between x(t) and y(t) is defined by

Cxy = |Pxy|^2/Pxx/Pyy = |Pxy|^2/Pxx^2

In fact |Pxy| = Pss. Therefore

sqrt(Cxy) = Pss/Pxx

What we want to know is Pnn

Pnn = Pxx - Pss = Pxx[1 - sqrt(Cxy)]
=> Snn = sqrt(Pnn) = Sxx * sqrt[1 - sqrt(Cxy)]

This is slightly different from the case where you don't have the noise in one of the time series (e.g. feedforward cancellation or bruco)


Measurement results

 

Power spectra:
Mon1 and Mon2 for both input power levels exhibited the same PSD between 10Hz to 1kHz. This basically supports that the calibration for the 22dBm input (at least relative to the calibration for 10dBm input) was corrected. Abobe 1kHz and below 10Hz, some reduction of the noise by the increase of the input power was observed. From the coherence analysis, the floor level for the 10dBm input was -178, -175, -155dBc/Hz at 1kHz, 100Hz, and 10Hz, respectively. For the 22dBm input, they are improved down to -188, -182, and -167dBc/Hz at 1kHz, 100Hz, and 10Hz, respectively.

 

  239   Sun Sep 6 16:50:51 2015 KojiElectronicsGeneralUnit test of the EOM/AOM Driver S1500118

TEST Result: S1500118

Additional notes

- Checked the power supply. All voltages look quiet and stationary.

- Checked the internal RF cables too see if there is any missing shield soldering => Looked fine

- Noticed that the RFAM detector board has +/-21V for the +/-24V lines => It seems that this is nominal according to the schematic

- Noticed that the RFAM detector sensitivity were doubled fomr the other unit.
  => This is reated to the modification (E1500353) of  "Controller Board D0900761-B Change 1" (doubling the monitor output gain)

- Noticed that the transfer function of the CTRL signal on the BNC and the DAQ output.
  => This is reated to the modification (E1500353) of  "Servo Board D0900847-B Change 1"  (servo transfer function chage)
  => The measured transfer function did not agree with the prediction from the circuit constants in this document
  => From the observation of the servo board it was found that R69 was not 200Ohm but 66.5 Ohm (See attachment 1).
       This explained the measured transfer function. The actuator TF has: P 2.36, Z 120., K -1@DC (0.020@HF)

- Similarly, the TF between the CTRL port on the unit and the CTRL port on the test rig was also modified.

Noise level

Attachment 2

- The amplitude noise in dBc (SSB) was measured at the output of 27dBm. From the test sheet, the noise level with 13dBm output was also referred. From the coherence of the MON1 and MON2, the noise level was inferred. It suggests that the floor level is better than 180dBc/Hz. However, there is a 1/f like noise below 1k and is dominating the actual noise level of the RF output. Daniel suggested that we should check nonlinear downconversion from the high frequency noise due to the noise attenuator. This will be check with the coming units.

  240   Tue Sep 8 10:55:31 2015 KojiElectronicsAM Stabilized EOM DriverRF AM Measurement Unit E1500151 ~ 37MHz OCXO AM measurement

Test sheet: https://dcc.ligo.org/LIGO-E1400445

Test Result (S1500114): https://dcc.ligo.org/S1500114

  241   Tue Sep 8 11:18:10 2015 KojiOpticsCharacterizationPBS Transmission measurement

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

  242   Wed Sep 9 01:58:34 2015 KojiOpticsCharacterizationPBS Transmission measurement

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

  243   Thu Sep 10 04:03:42 2015 KojiOpticsCharacterizationMore polarizer optics measurement (Summary)

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

 

  244   Wed Sep 23 17:49:50 2015 KojiOpticsCharacterizationMore polarizer optics measurement (Summary)

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

  245   Tue Dec 15 13:38:34 2015 KojiElectronicsCharacterizationEOM Driver linearity check

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

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

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

Therefore this means that:

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

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

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

  246   Tue Dec 15 13:39:13 2015 KojiElectronicsCharacterizationPhase noise measurement of aLIGO EOM drivers

This measurement has been done on Dec 1st, 2015.


The phase noise added by the EOM driver was tested.

The test setup is depicted in the attached PDF. The phase of the RF detector was set so that the output is close to zero crossing as much as possible with the precision of 0.5ns using a switchable delay line box. The phase to voltage conversion was checked by changing the delayline by 1ns. This gave me somewhat larger conversion factor compared to the sine wave test using an independent signal generator. This was due to the saturation of the phase detector as the LO and RF both have similar high RF level for the frequency mixer used.

The measurement has done with 1) no EOM driver involved, 2) one EOM driver inserted in the RF path, and 3) EOM drivers inserted in both the LO and RF paths.

I could not understand why the measurement limit is so high. Also the case 2 seems too low comsidering the noise level for 1) and 3).

At least we could see clear increase of the noise between the case 1) and 3). Therefore, we can infer the phase noise added by the EOM driver from the measurements.

Note: The additional phase noise could be associated with the original amplitude noise of the oscillator and the amplitude-to-phase conversion by the variable attenuator. This means that the noise could be corellated between two EOM drivers. The true test could be done using a PLL with a quiet VCO. Unfortuantely I don't have a good oscillator sufficient for this measurement.

  247   Tue Dec 15 13:42:37 2015 KojiOpticsCharacterizationDimensions / packaging of HQE PDs

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.

  248   Fri Dec 18 15:33:24 2015 KojiGeneralLoan / LendingLoan from Rich

Loan Record: I borrowed a PD can opener from Rich => Antonio Returned Sep 9, 2016

Tungsten Carbide Engraver (permanently given to the OMC lab)

KEITHLEY SOURCE METER + Laptop

  249   Tue Dec 29 12:15:46 2015 KojiGeneralGeneralGlasgow polarizer passed to Kate

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

  250   Thu Feb 18 21:08:32 2016 KojiGeneralLoan / Lending(all returned) Antonio loan

Antonio borrowed: Rich's PD cutter (returned), Ohir power meter(returned), Thorlabs power meter head, Chopper

  251   Sat Feb 20 19:11:22 2016 KojiElectronicsCharacterizationDark current measurement of the HQE PD and other PDs

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

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

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

Slot \ Container A B C D E
1 A1-23 B1-22 C1-07 C1-11 C1-17
2 A1-25 B1-23 C1-08 C1-12 C1-21
3 B1-01 C1-03 C1-09 C1-14 D1-08
4 B1-16 C1-05 C1-10 C1-15 D1-10

- The measurement has been done with KEITHLEY sourcemeter SMU2450.

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

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

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

ELOG V3.1.3-