40m QIL Cryo_Lab CTN SUS_Lab TCS_Lab OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop
  OMC elog, Page 3 of 7  Not logged in ELOG logo
Entry  Tue Mar 28 21:04:27 2017, Koji, Electronics, Characterization, PDH amp 6x

Attachment 1: PDH amp RF part (before the preamp was installed)

Attachment 2: RF-AF transmission

Attachment 3: Attachment 3: LO dependence

Attachment 4: RF amp gain (saturation)

Attachment 5: Input/output noise level

Attachment 6: Attachment 6: Preamp/DCPD out buffer AF circuit

    Reply  Sat Jul 29 18:44:38 2017, rana, Electronics, Characterization, PDH amp 

attachment 6: DCPD preamp looks like the opamp is wired for positive feedback?

       Reply  Sat Jul 29 21:42:51 2017, Koji, Electronics, Characterization, PDH amp 

The polarities indicated in the right circuits were opposite, obviously.

Entry  Wed Jul 5 16:59:44 2017, Koji, General, General, The OMC #002 was packed DSC_0360.JPG

[Stephen Koji]

The OMC #002 was packed for the transportation to Downs.

===> And transported to Downs 227 on Jul 6th.

Entry  Sat Jul 1 21:33:18 2017, Koji, General, General, Some purchase notes 

- Forgot to close the cylinder valve...

v HEPA prefilter (20"x20"x1" MERV 7)

- Replace the filter for the air conditioning

v Texwipe TX715 SWAB http://www.texwipe.com/store/p-817-tx715.aspx

v Gloves ~3 bags
VWR GLOVE ACCTCH NR-LTX SZ7.0 PK25 79999-304 x3
VWR GLOVE ACCTCH NR-LTX SZ7.5 PK25 79999-306 x1

v Vectra IPA soaked cloths

v Sticky mats


  • GLOVE ACCTCH NR-LTX SZ7 PK25 / 79999-304 / PK4
  • GLOVE ACCTCH NR-LTX SZ7.5 PK25 / 79999-306 / PK1
  • WIPER 100% IPA 23X23CM PK50. / TWTX8410 / PK2
  • SWAB CLEANTIPS ALPHA PK100. / TW-TX715 / PK1
  • MAT CLEAN ROOM 18X36IN BLUE / 89021-748 / CS1 (Qty4)
  • FILTER PLET AIR MERV8 20X20X1 / 78002-422 / EA4 / Direct from Supplier

ORDERED AUG 9, 2017

Entry  Sat Jul 1 15:29:57 2017, Koji, Optics, General, Black glass cleaning / Final bonding for the emergency repair for OMC #002 DSC_0347.jpgDSC_0348.jpgDSC_0350.jpgDSC_0352.jpgDSC_0354.jpg

[Alena, Koji]

Report of the work on June 30.

1. Cleaning of the black glass beam dumps

As reported in the previous entry, the beam dumps on the OMC breadboard exhibited accumulation of dusts or contaminants on the black glass surfaces. We worried about transfer of the dusts over a period or of the contaminant during baking. It was already known that the contaminants are persistent and not easy to remove only by drag wiping with IPA. So Alena brought a set fo tools to try. Here is the procedure described.

- Inventory (Attachment 1): A small glass beaker, TX715 Alpha® Sampling Swab, plastic brushes, syringes with pure IPA, inspection flash light, Vectra IPA soaked wipes

- Apply clean IPA on a brush. Some IPA should be removed by the IPA soaked wipe so as not to splash IPA everywhere. Rub a glass surface with the brush while the surface is inspected by the flash light. The strokes migrate the contaminants to the direction of wiping. So the brush should be moved outward. This does some cleaning, but it is not enough to remove smudges on the surface. Occasionally clean the brush with IPA poured in the small beaker.

- Apply clean IPA on a swab. Rub the surface with the swab outward. This removes most of the visible smudges.

We decided not to apply FirstContact on the beam dumps at this occasion. In any case, we need to apply FC on all the optical surfaces after the baking. We judged that the current cleanliness level of the beam dump does not affect the over all contamination of the OMC considering the FC application after the baking.

2. Gluing of the reinforcement Al bars on the delaminated Invar mounting brackets
One of the mounting bracket (=invar shim) on the top side (= suspension I/F side) showed the sign of delamination (Attachment 3). This invar is the one at the beam entrance side (Attachment 2).

EP30-2 was mixed as usual: 6g of EP30-2 was mixed with 0.3g glass sphere. The glue was tested with a cooking oven and the result was perfect. The glue was applied to two Al bars and the bars were attached on the long sides of the invar shim with the beveled corner down (to avoid stepping on the existing original epoxy) (Attachments 4, 5). The photo quality by my phone was not great. I will take better photos with a better camera next week.


Glue condition was checked on Monday Jul 3rd. It was all good. New photos were taken. OMC #002 Repair - Gluing of reinforcement AL bars

Entry  Fri Jun 23 10:55:07 2017, Koji, Optics, General, Dust layer on black glass beam dumps? black_glass_dust.JPG

I wondered why the black glass beam dumps looked not as shiny as before. It was in fact a layer of dusts (or contaminants) accumulated on the surface.
The top part of the internal surface of the black glass was touched by a piece of lens tissue with IPA. The outer surface was already cleaned. IPA did not work well i.e. Required multiple times of wiping. I tried FirstContact on one of the outer surface and it efficiently worked. So I think the internal surfaces need to be cleaned with FC.

Entry  Fri Jun 23 01:58:11 2017, Koji, Optics, General, OMC #002 Repair - CM1 gluing 6x

[Alena, Koji]

Jun 21: Alena and Koji worked on gluing of the CM1 mirror on the OMC breadboard #002. This is an irregular procedure. Usually, the PZT mirror subassembly is prepared before the mounting prism is glued on the breadboard. In this occasion, however, a PZT and a mirror are bonded on an existing prism because only the damaged mirror and still functional PZT were debonded from the mouting prism.

For this purpose, the mirror and the PZT were fixed on the mounting prism with the modified fixture set (D1600338). The original PZT was reused, and the new mirror #8 was used. The alignment of the mirror was checked OK using the cavity beam before any glue was applied. The arrow of the CM mirror is facing up.

We mixed 8g EP30-2 (it was almost like 3~4 pushes) and 0.4g glass sphere bond lining. Along with EP30-2 procedure, the bond was mixed in an Al pot and tested with 200degF (~93degC) preheated the oven for 15min. The cured bond showed perfect dryness and crispness. The bond was painted on the PZT and the PZT was placed on the fixture. Then more bond was painted on the other side of the PZT. The mirror was placed in the fixture. The spring-loaded front plate was fixed, and the breadboard was left for a day. (Attachment 1~3)

Jun 22: The fixture was removed without causing any visible delamination or void. The attachment 4~6 show how wet the joint is (before baking). There were some excess of EP30-2, which bonded the fixture and the mounting prism as usual. The fixture was detached by prying the front piece against the rear piece with a thin allen key. Some of the excess bond on the mounting prism was removed by scratching.

The alignment of the cavity was checked with the cavity beam and it is still fine.

More photos can be found here: Link to Google Photos Album "OMC #002 Repair - CM1 gluing"

Entry  Fri May 26 21:53:20 2017, Koji, General, Configuration, Trans RF PD setup 

Recent work

- DC output of the trans RF PD was connected to the BNC patch panel. => Now CH4 of the scope is monitoring this signal

- The RF sweep signal from the network analyzer is connected to the power combiner for the EOM drive via the SMA patch panel.

- The trans RF PD was aligned first to the leakage beam. It turned out that this signal is too weak. Then the PD was aligned to one of the main OMC transmission. For this purpose, the OMC DCPD (T) was removed from the OMC breadboard.

- It seems that there is a significant amount of RF AM from the EOM. I suspect it is associated with the residual S-pol and birefringence of the steering mirrors (45deg HR). But the HWP at the output of the Faraday is fixed on the Faraday body with a screw and cumbersome for fine adjustment. A PBS and an HWP are added right before the EOM. This made the fiber coupler slightly misaligned. I suppose this new setup still has S&P on the fiber too. Thus, readjustment of the fiber rotations at the input is necessary.

Next step

- Input power to the fiber should be determined before the EOM. Otherwise, touching the HWP before the EOM causes too much power change at the optics of the OMC side.

- Precise adjustment of the RFAM is still necessary.

- The OMC curved mirror should be held by the new fixture.

- Check the beam spots

- Measure cavity parameters. (transmission/FSR/HOM/etc)

==> Then the curved mirror and the PZT will be glued on the prism

    Reply  Tue Jun 6 00:49:48 2017, Koji, General, Configuration, Trans RF PD setup 

Last week, I further worked on the RF system to install 20dB coupler on the agilent unit and setup the R channel. This allowed me to make the FSR/TMS measurement of the OMC.

And today several optical improvement has been done.

- The input/output fiber couplers were adjusted to have the maximum transmission through the PBS right before the OMC.
- The HWP on the output side of the faraday was adjusted to have ~40mW input to the OMC.

Then, the OMC curved mirror is now held by the new in-situ gluing fixture instead of the conventional fixture attached upside down.
The OMC was ocked again and the input alignment was adjutsed. The fixture is blocking the QPD path, so it's not possible to confirm the proper alignment of the cavity (w.r.t. the QPD paths).

The precise positions of the spots could not be confirmed as the battery of the IR viewer was empty. Quick check of the spots by the card tells that the spot on the CM2 (PD side) is slightly too close to FM2 (output coupler). I wonder if this could be solved by rotating the curved mirror.

Otherwise everything look good. Let's try to glue the curved mirror tomorrow.

Note: Spot on CM2 is too close to the edge of the hole on the mounting prism. The meausrementof CM1 is telling that the curverture center is located 2.7mm upper side of the center of the mirror if the HR side arrow is up (and it is the case). If we move the arrow to the QPD path side (90deg CW viewed from the face side), this corresponds to ~1.1mrad CCW tilt in Yaw (viewed from the top of the prism). According to the matrix calculation (T1500060) this will induce ~1.5mm shift of the beam. This should be tried before gluing.

       Reply  Tue Jun 6 22:00:36 2017, Koji, General, Configuration, Trans RF PD setup 

- Replaced the PZT with the one used from the beginning. This must be PZT #21. After the replacement, the spot positions look very good. I even went up. So I decided this is the configuration to proceed to the gluing. The CM1 mirror has the HR arrow at the top.

- The input beam was realigned w.r.t. the OMC.

- Tried to use the IR viewer with the new rechargable battery brought from the 40m. But the view still didn't work. The possibility is a) the viewer is broken b) the battery is empty.

- Tried to use the stainless clean regulartor for the UHP N2. The outlet has a short tube with a different diameter. The O.D. of the old tube is 6.3mm, while the new one is 9.5mm. If I insert the thinner tube in the new tube, it approximately fits. But I don't believe this is the way...

Entry  Tue May 16 19:05:18 2017, Koji, Optics, Configuration, OMC SN002 fix - temporary optics 

Working on the SN002 OMC fix. Checked the inventory. I think I am using C8 mirror as the new temporary CM1 and PZT24 as the new temporary CM2.

Entry  Thu Jan 19 20:57:53 2017, Koji, Supply, General, Purchase 

Ordered:

Office Depot
v AA battery Qty. 24
v 9V battery Qty. 4
v Floor cable cover (6ft)

Thorlabs
v HV PZT Driver
v Lenses

    Reply  Thu Feb 16 17:23:12 2017, Koji, Supply, General, Purchase 

 

Entry  Wed Dec 7 21:18:35 2016, Koji, General, General, OMC placed on the table / the beam roughly aligned DSC_0082.jpgDSC_0084.jpg

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

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

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

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

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

    Reply  Thu Dec 8 21:17:09 2016, Koji, General, General, OMC placed on the table / the beam roughly aligned 

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

Some notes:

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

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

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

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

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

- The optical table needs cleaning.

Entry  Mon Nov 21 21:19:20 2016, Koji, Optics, General, LWE NPRO Laser / Input Optics / Fiber Coupling 

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

- The SOP can be found here.

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

- The output from the laser is ~740mW

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

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

- Will proceed to the OMC cavity alignment.

    Reply  Wed Dec 7 19:18:10 2016, Koji, Optics, General, LWE NPRO Laser / Input Optics / Fiber Coupling 

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

Entry  Fri Sep 9 19:43:32 2016, Koji, Optics, General, D1102211 OMC Diode Mount Glass Block went to Downs 

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

Entry  Tue Aug 23 23:36:54 2016, Koji, Optics, Characterization, Inspection of the damaged CM1 (prev H1OMC) 7x

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

    Reply  Thu Aug 25 02:17:09 2016, Koji, Optics, Characterization, Inspection of the damaged CM1 (prev H1OMC) 

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

Entry  Mon Aug 22 12:58:16 2016, Koji, General, General, UV bond samples -> Garilynn 

- FS base + Mounting Prism

- FS or SF2 1/2" piece + FS or SF2 1/2" piece

- FS? plate + FS or SF2 1/2" piece + FS or SF2 1/2" piece + FS? plate

Entry  Mon Aug 15 10:09:10 2016, Koji, General, General, Prev H1 OMC shipped to CIT 

Previous H1 OMC shipped from LHO to CIT

https://ics-redux.ligo-la.caltech.edu/JIRA/browse/Shipment-8196

Entry  Fri Aug 12 14:58:17 2016, Koji, General, Configuration, H1 OMC DCPD replacement  

Preparation of 3rd OMC for the use in H1

New DCPD(T) = B1-01
DCPD(T) = DCPDA: extracted and accomodated in CAGE-A SLOT1

New DCPD(R) = B1-16
DCPD(R) = DCPDB: extracted and accomodated in CAGE-A SLOT2

Entry  Fri Jul 22 22:24:05 2016, Koji, General, General, HQEPD inventory 

As of Jul 22, 2016
As of Aug 11, 2016

As of Aug 16, 2016


A1-23 in Cage G https://ics-redux.ligo-la.caltech.edu/JIRA/browse/IHGQEX3000-0-00-A1-23
-> Shipped to LLO https://ics-redux.ligo-la.caltech.edu/JIRA/browse/Shipment-8181
-> Now in https://ics-redux.ligo-la.caltech.edu/JIRA/browse/ASSY-D1201439-1
= Replaced C30665 eLIGO PD (SN 01 in Cage G now) ICS: C30665GH-0-00-0001
-> Removed PD@LLO, Waiting for the shipment to CIT

A1-25 in Cage G https://ics-redux.ligo-la.caltech.edu/JIRA/browse/IHGQEX3000-0-00-A1-25
-> Shipped to LLO https://ics-redux.ligo-la.caltech.edu/JIRA/browse/Shipment-8181
-> Now in https://ics-redux.ligo-la.caltech.edu/JIRA/browse/ASSY-D1201439-1
= Replaced C30665 eLIGO PD (SN 02 in Cage G now) ICS: C30665GH-0-00-0002
-> Removed@LLO, Waiting for the shipment to CIT


B1-01 in Cage A https://ics-redux.ligo-la.caltech.edu/JIRA/browse/IHGQEX3000-0-00-B1-01
-> Shipped to LHO https://ics-redux.ligo-la.caltech.edu/JIRA/browse/Shipment-8182
-> Now in https://ics-redux.ligo-la.caltech.edu/JIRA/browse/ASSY-D1201439-3_2
= replaced C30665 eLIGO PD (SN 11 in Cage A now) ICS: C30665GH-0-00-0011
-> Removed PD@LHO
-> Shipped from LHO to CIT https://ics-redux.ligo-la.caltech.edu/JIRA/browse/Shipment-8187

B1-16 in Cage A https://ics-redux.ligo-la.caltech.edu/JIRA/browse/IHGQEX3000-0-00-B1-16
-> Shipped to LHO https://ics-redux.ligo-la.caltech.edu/JIRA/browse/Shipment-8182
-> Now in https://ics-redux.ligo-la.caltech.edu/JIRA/browse/ASSY-D1201439-3_2
= replaced C30665 eLIGO PD (SN 12 in Cage A now) ICS: C30665GH-0-00-0012
-> Removed PD@LHO
-> Shipped from LHO to CIT https://ics-redux.ligo-la.caltech.edu/JIRA/browse/Shipment-8187


C1-05 in Cage F https://ics-redux.ligo-la.caltech.edu/JIRA/browse/IHGQEX3000-0-00-C1-05
-> @CIT contamination test cavity

C1-07 in Cage F https://ics-redux.ligo-la.caltech.edu/JIRA/browse/IHGQEX3000-0-00-C1-07
-> @CIT contamination test cavity


C1-17 in Cage E https://ics-redux.ligo-la.caltech.edu/JIRA/browse/IHGQEX3000-0-00-C1-17
-> Shipped to LHO https://ics-redux.ligo-la.caltech.edu/JIRA/browse/Shipment-8182
-> Left @LHO as a spare

C1-21 in Cage E https://ics-redux.ligo-la.caltech.edu/JIRA/browse/IHGQEX3000-0-00-C1-21
-> Shipped to LHO https://ics-redux.ligo-la.caltech.edu/JIRA/browse/Shipment-8182
-> Left @LHO as a spare


D1-08 in Cage E https://ics-redux.ligo-la.caltech.edu/JIRA/browse/IHGQEX3000-0-00-D1-08
-> Shipped to LHO https://ics-redux.ligo-la.caltech.edu/JIRA/browse/Shipment-8182
-> Moved to Cage A3
-> Shipped from LHO to CIT https://ics-redux.ligo-la.caltech.edu/JIRA/browse/Shipment-8186
-> Arrived at CIT (Aug 16)

D1-10 in Cage E https://ics-redux.ligo-la.caltech.edu/JIRA/browse/IHGQEX3000-0-00-D1-10
-> Shipped to LHO https://ics-redux.ligo-la.caltech.edu/JIRA/browse/Shipment-8182
-> Moved to Cage A4
-> Shipped from LHO to CIT https://ics-redux.ligo-la.caltech.edu/JIRA/browse/Shipment-8186
-> Arrived at CIT (Aug 16)

Entry  Fri Jun 10 17:12:57 2016, Koji, General, Configuration, L1 OMC DCPD replacement 

New DCPD(T) = A1-23
DCPD(T) = DCPDB: extracted and accomodated in CAGE-G SLOT1

New DCPD(R) = A1-25
DCPD(R) = DCPDA: extracted and accomodated in CAGE-G SLOT2

Entry  Sat Mar 26 17:39:50 2016, Koji, Electronics, Characterization, HQEPD dark noise PD_dark_current.pdf

Dark noise measurement for 6 HQEPDs and 1 C30665. All of these showed sufficiently low dark current noise levels compared with the noise level of the DCPD preamp. The measurement was limited by the input noise (ADC) noise of the FFT analyzer as the line noises were too big.

The measurement has been done with the transimpedance of 1e7. The bandwidth of the measurement was 50kHz.

    Reply  Sat Mar 26 18:22:24 2016, Koji, Electronics, Characterization, Baking / Contamination tests of the PDs 

For the production of the aLIGO PDs, the following transfer of the PDs were carried out
A1-23 Cage A1 -> G1
A1-25 Cage A2 -> G2

The cage A will be baked at 75degC to see if this improves AMU=64 emission.

At the same time, we will put C1-05 (F1) and C1-07 (F2) into the contamination test cavity.

       Reply  Tue Apr 5 18:22:40 2016, Koji, Electronics, Characterization, Baking / Contamination tests of the PDs QE_after_air_bake.pdf

Possible reduction of the QE was observed after air-bake at 75degC.


Yesterday I received Cage G from Bob for intermediate test of the PD performance after air bake but before vacuum bake.
This cage was prepared to be the production pair.

According to the ICS, https://ics-redux.ligo-la.caltech.edu/JIRA/browse/Bake-8047
the PDs were air baked at 75degC for 48 hours.

I took the PDs to my lab to check if there is any issue in terms of the performance.
- Dark current: No change observed
- Dark noise: No noise increase observed
- QE: Probably reduced by ~0.5%.

Here I attached the result of the QE measurement. I have measured the QEs of the baked ones (A1-23 and A1-25) and the reference. Since the reference PD has not been baked, this gives us the measure of the systematic effect. The reference showed the reduction of ~0.1%. Assuming this reduction came from the systematic effect of the measurement system, I observed at least 0.5% QE reduction (A1-23). Note that the previous measurement of 99.8% for A1-25 was too high and dubious. But both A1-23 and A1-25 showed ~0.4% lower QEs.

So I believe the air-baking process reduced the QE.

Another evidence was that now I could clearly see the beam spots on these air-baked-PDs with an IR viewer when the PDs were illuminated with a 1064nm beam. Usually it is difficult to see the spot on the PD. The spot on the reference PD was still dark. So this difference was very obvious. I was afraid that something has been deposited on the surface of the photosensitive element. The surface of the diodes looked still very clean when they were checked with a green LED flash light.

          Reply  Tue Apr 5 21:20:15 2016, Koji, Electronics, Characterization, More dark noise measurement PD_dark_current.pdf

All survived PDs have been measured.

Entry  Tue Apr 5 18:14:55 2016, Koji, General, Loan / Lending, QPD Lending Crackle 

Xiaoyue

QPD head
X-Z stage
Mounting brackets
DB15 cable
QPD matrix circuit
+/-18V power supply cable

Entry  Sat Mar 26 01:49:48 2016, Koji, Optics, Characterization, HQEPD QE QE1.pngQE2.png

Calibration of the transimpedance

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

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

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

Refer E1800372

Entry  Sun Mar 13 22:02:09 2016, Koji, Optics, Characterization, HQEPD QE measurement (direct comaprison) 

Direct comparison of the PD responsibities

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


P-pol 10deg incident

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

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

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

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

Entry  Sat Feb 20 19:11:22 2016, Koji, Electronics, Characterization, Dark current measurement of the HQE PD and other PDs P2197992.jpgPD_dark_current.pdfPD_dark_current_others.pdf

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)

    Reply  Sun Mar 13 21:22:27 2016, Koji, Electronics, Characterization, Dark current measurement of the HQE PD and other PDs 

Transfered for RGA scan

B4 (C1-05) -> F1
C1 (C1-07) -> F2

 

Entry  Sun Mar 6 02:13:28 2016, Koji, Optics, Characterization, PD glass reflections P3048124.JPGP3048125.JPG

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

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

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

Entry  Thu Feb 18 21:08:32 2016, Koji, General, Loan / Lending, (all returned) Antonio loan 

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

Entry  Tue Dec 29 12:15:46 2015, Koji, General, General, Glasgow polarizer passed to Kate 

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

Entry  Fri Dec 18 15:33:24 2015, Koji, General, Loan / Lending, Loan 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

Entry  Tue Dec 15 13:42:37 2015, Koji, Optics, Characterization, Dimensions / packaging of HQE PDs PC147842.jpgPC147846.jpgPC147848.jpgHQEPD_dimension.pdf

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.

Entry  Tue Dec 15 13:39:13 2015, Koji, Electronics, Characterization, Phase noise measurement of aLIGO EOM drivers phase_noise.pdfphase_noise_9MHz.pdf

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.

Entry  Tue Dec 15 13:38:34 2015, Koji, Electronics, Characterization, EOM Driver linearity check Output_linearity.pdfCtrl_Bias.pdf

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???

Entry  Tue Sep 8 11:18:10 2015, Koji, Optics, Characterization, PBS Transmission measurement setup.JPGCaF2Prism.jpgCaF2Prism2.JPG

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

    Reply  Wed Sep 9 01:58:34 2015, Koji, Optics, Characterization, PBS 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

       Reply  Thu Sep 10 04:03:42 2015, Koji, Optics, Characterization, More polarizer optics measurement (Summary) eLIGO_PBS.pdfHWP.pdfTFP.pdfGlasgow_PBS.pdf

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

 

          Reply  Wed Sep 23 17:49:50 2015, Koji, Optics, Characterization, More polarizer optics measurement (Summary) Glasgow_PBS_spotsize.pdf

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

Entry  Mon Aug 10 02:11:47 2015, Koji, Electronics, AM Stabilized EOM Driver, RF AM Measurement Unit E1500151 IMG_20150803_223403975.jpgIMG_20150803_221210816_HDR.jpgIMG_20150803_223420267.jpg

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

 

    Reply  Mon Aug 10 11:39:40 2015, Koji, Electronics, AM Stabilized EOM Driver, RF 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

       Reply  Mon Aug 10 11:57:17 2015, Koji, Electronics, AM Stabilized EOM Driver, RF AM Measurement Unit E1500151 screen_shot.png

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

          Reply  Mon Aug 10 12:09:49 2015, Koji, Electronics, AM Stabilized EOM Driver, RF AM Measurement Unit E1500151 IMG_20150809_215628585_HDR.jpg

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.

             Reply  Fri Aug 28 01:08:14 2015, Koji, Electronics, AM Stabilized EOM Driver, RF AM Measurement Unit E1500151 ~ Calibration RFAM_detector_calib.pdfRFAM_detector_calib_spectra.pdf

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.

 

                Reply  Fri Aug 28 02:14:53 2015, Koji, Electronics, AM Stabilized EOM Driver, RF AM Measurement Unit E1500151 ~ 37MHz OCXO AM measurement OCXO_AM_noise.pdf

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.

 

                   Reply  Tue Sep 8 10:55:31 2015, Koji, Electronics, AM Stabilized EOM Driver, RF AM Measurement Unit E1500151 ~ 37MHz OCXO AM measurement 

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

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

Entry  Sun Sep 6 16:50:51 2015, Koji, Electronics, General, Unit test of the EOM/AOM Driver S1500118 P9037810.JPGRF_AM_spectra.pdf

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.

Entry  Thu Aug 20 01:35:01 2015, Koji, Electronics, General, OMC DCPD in-vacuum electronics chain test OMC_DCPD_Chain.pdfOMC_DCPD_Transimpedance.pdf

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.

 

    Reply  Wed Aug 26 11:31:33 2015, Koji, Electronics, General, OMC DCPD in-vacuum electronics chain test OMC_DCPD_OutputNoise.pdf

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.

Entry  Wed Jul 15 22:23:17 2015, Koji, Electronics, AM Stabilized EOM Driver, E1400445 first look IMG_20150714_195534852.jpgIMG_20150714_195227746_HDR.jpg

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

    Reply  Sat Jul 18 11:37:21 2015, Koji, Electronics, AM Stabilized EOM Driver, D0900848 power board ~ oscillation issue solved 6x

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.

       Reply  Wed Jul 22 09:43:01 2015, Koji, Electronics, AM Stabilized EOM Driver, Power 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)

 

          Reply  Wed Jul 22 10:15:14 2015, Koji, Electronics, AM Stabilized EOM Driver, RF 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

 

 

 

             Reply  Sat Jul 25 17:24:11 2015, Koji, Electronics, AM Stabilized EOM Driver, RF test of the EOM/AOM Driver S1500117 7x

(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.

 

                Reply  Tue Jul 28 18:36:50 2015, Koji, Electronics, AM Stabilized EOM Driver, RF test of the EOM/AOM Driver S1500117 IMG_20150727_214536773_HDR.jpgEOM_Driver_DAQ_TF_test.pdfEOM_Driver_Mon_PSD.pdf

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.
 

Entry  Wed Feb 18 21:51:23 2015, Koji, General, General, Notes 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.

Entry  Sat Jan 17 11:40:04 2015, Koji, General, General, 3rd 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

Entry  Mon Jul 21 01:02:43 2014, Koji, Mechanics, Characterization, Some structual mode analysis 6x

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

    Reply  Tue Sep 9 20:59:19 2014, Koji, Mechanics, Characterization, Structural mode analysis for the PZT mirror 6x

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

Entry  Wed Aug 27 23:13:13 2014, Koji, Optics, Characterization, Collection of the power budgetting info 

L1 OMC Cavity power budget

H1 OMC Cavity power budget

3IFO OMC Cavity power budget

Entry  Tue Aug 5 13:03:25 2014, Koji, General, General, Missing 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

Entry  Mon Aug 4 18:59:50 2014, Koji, General, General, A memorandom 

On breadboarfd cabling for 3IFO OMC

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

Entry  Sun Jul 20 17:20:39 2014, Koji, General, General, The 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.

 

Entry  Thu Jul 17 02:19:20 2014, Koji, Mechanics, Characterization, I1OMC vibration test 6x

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

    Reply  Sun Jul 20 17:19:50 2014, Koji, Mechanics, Characterization, I1OMC vibration test ~ 2nd round 9x

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

Entry  Sun Jul 13 17:46:28 2014, Koji, Optics, Characterization, OMC backscatter measurement OMC_backscatter.pdf

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?

    Reply  Tue Jul 15 03:00:42 2014, Koji, Optics, Characterization, OMC 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.

 

       Reply  Tue Jul 15 03:34:16 2014, Koji, Optics, Characterization, OMC backscatter measurement OMC_backscatter.pdfOMC_backscatter.png

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.

Entry  Fri Jul 11 00:06:33 2014, Koji, Optics, Characterization, I1OMC 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

Entry  Thu Jul 10 23:22:28 2014, Koji, Optics, Characterization, I1OMC 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

Entry  Mon Jul 7 01:36:03 2014, Koji, General, General, To Do 

Optical tests

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

Backscattering test

Cabling / Wiring

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

Vibration test

Baking

First Contact

Packing / Shipping

    Reply  Thu Jul 10 08:34:57 2014, Koji, General, General, To Do 

Optical tests

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

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

Entry  Thu Jul 10 01:39:38 2014, Koji, Electronics, General, PZT wire P7096669.JPG

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.

Entry  Tue Jul 8 18:54:54 2014, Koji, Mechanics, Characterization, PZT characterization PZT_Scan.pdfI1OMC_PZT_Response.pdf

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.

Entry  Wed Jul 2 18:58:42 2014, Koji, General, General, Beam dump delamination beamdump_delamination.png

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

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

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

    Reply  Thu Jul 3 17:45:18 2014, Koji, General, General, Beam dump delamination beamdump_delamination_solution.png

Here is the resolution.

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

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

beamdump_delamination_solution.png

       Reply  Tue Jul 8 04:08:06 2014, Koji, General, General, Expoxy reapplication for beam dumps 

Firstly, the excess epoxy was removed using a cleaned razor balde

Secondly, EP30-2 epoxy was applied at the exterior edges of the beam dump.
Interior of the V were glued at two points. This is to keep the gap away from being trapped

Here is the result of the gluing. Some epoxy was sucked into the gap by capillary action.
I believe, most of the rigidity is proivded by the bonds at the edges.

ELOG V3.1.3-