40m QIL Cryo_Lab CTN SUS_Lab TCS_Lab OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop
  40m Log, Page 275 of 339  Not logged in ELOG logo
ID Date Author Type Categoryup Subject
  1931   Thu Aug 20 09:16:32 2009 steveHowToPhotosControl Room Workstation desks lowered to human height


There were no injuries...Now we need to get some new chairs.

 The control room desk tops heights on the east side were lowered by 127 mm


Attachment 1: P1040788.png
Attachment 2: P1040782.png
Attachment 3: P1040786.png
Attachment 4: P1040789.png
Attachment 5: P1040785.png
  1998   Thu Sep 24 19:35:20 2009 ranaHowToPhotos40m Google account

I've created a 40m Google account. Please post all the 40m related photos to this site. If you don't already have it, download Picasa to make this easier.

40m Installation Photos">

the password is in the usual password place.

  2242   Wed Nov 11 18:43:57 2009 rana, kojiHowToPhotosIlluminated Paintbrush Technique


1/4" exposure, standard room lights                                                                              3" exposure, slowly moving LED bar light from ~60 cm distance

Because of the light behind, the focus was attracted by the far objects...
Evenso the magnet ball looks better in the right picture.

The technique is as follows:
Use longer exposure time, move the LED bar illumination through the area like painting the light everywhere.
It is supposed to provide a picture with more uniform light and the diminished shadow.


  2465   Tue Dec 29 13:57:20 2009 Rana, Kiwamu, and HaixingUpdatePhotosPhotos of video switch box

Before we installed the video switch box, we also took some photos of it. We uploaded them onto the 40m Picasa.

Video Matrix

The first photo is the an entire view of the switch box. The following four photos are the details of the switch matrix.

 The slideshow below is a dump of the last several months of photos from the Olympus. The originals have been deleted.

  2956   Thu May 20 12:10:44 2010 kiwamuUpdatePhotosETMY end table

 I updated the photo of ETMY end table on the wiki.


Attachment 1: ETMY_s.png
  3093   Mon Jun 21 14:21:34 2010 Jenne, KiwamuUpdatePhotosInspection of Magnets for the TTs

Some pictures of "magnet inspection" from Picasa.

The coating of some magnets are chipped...

  3095   Mon Jun 21 20:11:21 2010 KojiUpdatePhotosInspection of Magnets for the TTs

Were these magnets chipped before the Ni plating?

RA: Yes, it looks like this is the case. We also smashed some of the magnets against a metal surface and saw that a black grime was left. We should hold the magnets with a clean teflon clamp to measure the Gauss. Then we have to wipe the magnets before installing. I share Jenne's concern about the press-fit damaging the plating and so we need to consider using using glue or the ole magnetic attachment method. We should not rely on the structural integrity of the magnets at all.

  3105   Wed Jun 23 12:52:35 2010 kiwamuUpdatePhotosBS chamber before cleaning up

  3421   Fri Aug 13 15:29:35 2010 AidanFrogsPhotosHere's the 40m team
Attachment 1: 40m_team.JPG
  3424   Mon Aug 16 13:33:06 2010 ZachFrogsPhotosHere's the 40m team

 One day I'll get to be part of the krew

  3682   Fri Oct 8 17:36:16 2010 steveFrogsPhotosvisiting undergrads

Prof Alan Weistein guided the 24 student through the 40m. His performance was rated as  an enthusiastic 9.5

Attachment 1: P1060916.JPG
Attachment 2: P1060921.JPG
Attachment 3: P1060922.JPG
Attachment 4: P1060915.JPG
  3683   Sun Oct 10 16:44:59 2010 KojiOmnistructurePhotosKepco Tube HV supply
Attachment 1: IMG_3637.jpg
Attachment 2: IMG_3640.jpg
  3987   Fri Nov 26 16:37:29 2010 kiwamuUpdatePhotospictures on PIcasa

 I uploaded some pictures taken in the last and this week. They are on the Picasa web albums.

 in vac work [Nov. 18 2010]

 in vac work [Nov 23 2010]

 CDS work [Nov 24 2010]


  4257   Mon Feb 7 19:21:32 2011 Beard PapaMetaphysicsPhotosThe Adventures of Dr Stochino and Beard Papa

  4430   Wed Mar 23 09:54:46 2011 steveOmnistructurePhotosLSC visitors

The 40m lab was visited by  ~ 30 LSC members  the end of last week.

Attachment 1: P1070467.JPG
Attachment 2: P1000414.jpg
  4447   Mon Mar 28 16:19:23 2011 steveFrogsPhotosvisithing 5th graders

Suresh is captivating his audience with gravity waves on last Friday, March 25

Attachment 1: P1070475.JPG
  4597   Mon May 2 13:43:05 2011 steveFrogsPhotosbirthday boys

.....Happy.... Birthday.... to.... Joseph... and... Jamie...Happy....Birthday..... to.... You............sing with us........Happy Birthday.....to you

Attachment 1: P1070622.JPG
  4615   Tue May 3 15:59:22 2011 steveFrogsPhotosX-mas comes early

The little red all terrain cargo wagon 40" x 18"  has just arrived on pneumatic wheels.

Model #29, 200 lbs max load at 26 PSI,  minimum age requirement 1.5 years

Attachment 1: P1070634.JPG
  4722   Sun May 15 19:55:15 2011 kiwamuUpdatePhotosETMY optical bench

Just for a record. This is the latest picture of the ETMY optical bench.

I will upload this picture on the wiki after the wiki gets up.


  4723   Sun May 15 21:27:51 2011 JenneUpdatePhotosETMY optical bench

I didn't notice it the other day when I was working on putting in the trans QPD, but do we need to switch the mirror mount for the first turning mirror of the IR trans beam, which the green transmits through to go into the cavity?  It seems like we've set ourselves up for potential clipping.


Just for a record. This is the latest picture of the ETMY optical bench.

I will upload this picture on the wiki after the wiki gets up.



  4724   Mon May 16 10:05:02 2011 kiwamuUpdatePhotosRe:ETMY optical bench

You are right. We should change or rotate the mirror mount.

Actually when Suresh and I were putting the mirror we rotated the mount  by 90 deg such that the fat side of the mount is at left had side.

It was because the fat side had been clipping the oplev beam when the fat side is at right.

At that moment we were blocking the green beam to only see the faint IR beam with a sensor card, so we haven't checked the green beam.

Anyway the mount is apparently not good for the green beam.

Quote from #4723

I didn't notice it the other day when I was working on putting in the trans QPD, but do we need to switch the mirror mount for the first turning mirror of the IR trans beam, which the green transmits through to go into the cavity?  It seems like we've set ourselves up for potential clipping.


  4814   Tue Jun 14 09:24:36 2011 steveConfigurationPhotosSUS binary IO chassis 2 and 3 moved from 1X5 to 1X4


While preping 1X4 for installation of c1lsc, we removed some old VME crates that were no longer in use.  This freed up lots of space in 1X4.  We then moved the SUS binary IO chassis 2 and 3, which plug into the 1X4 cross-connect, from 1X5 into the newly freed space in 1X4.  This makes the cable run from these modules to the cross connect much cleaner.

 Are we keeping these?

Attachment 1: P1070891.JPG
Attachment 2: P1070893.JPG
  4891   Mon Jun 27 16:57:06 2011 steveUpdatePhotosHaixing is back

He has moved the levitation stuff for his surf student to Jan's lab in W-Bridge.

Attachment 1: P1070914.JPG
  5329   Wed Aug 31 14:50:18 2011 kiwamuUpdatePhotospictures of OSEMs

The pictures that we took are now on the Picasa web site. Check it out.

Quote from #5280

Also, we took photos (to be posted on Picasa in a day or two) of all the main IFO magnet-in-OSEM centering, as best we could.  SRM, BS, PRM all caused trouble, due to their tight optical layouts.  We got what we could.

  5792   Wed Nov 2 22:02:39 2011 JenneUpdatePhotosNew screen snapshot script written!

After lots of trial and error, and a little inspiration from Koji, I have written a new script that will run when you select "update snapshot" in the yellow ! button on any MEDM screen. 

Right now, it's only live for the OAF_OVERVIEW screen.  View snapshot and view prev snapshot also work. 

Next on the list is to make a script that will create the yellow buttons for each screen, so I don't have to type millions of things in by hand.

The script lives in:  /cvs/cds/rtcds/caltech/c1/scripts/MEDMsnapshots, and it's called....wait for it....... "updatesnap".


  5793   Thu Nov 3 13:00:52 2011 JenneUpdatePhotosFormatting of MEDM screen names


After lots of trial and error, and a little inspiration from Koji, I have written a new script that will run when you select "update snapshot" in the yellow ! button on any MEDM screen. 

Right now, it's only live for the OAF_OVERVIEW screen.  View snapshot and view prev snapshot also work. 

Next on the list is to make a script that will create the yellow buttons for each screen, so I don't have to type millions of things in by hand.

The script lives in:  /cvs/cds/rtcds/caltech/c1/scripts/MEDMsnapshots, and it's called....wait for it....... "updatesnap".

 Currently the update snapshot script looks at the 3 letters after "C1" to determine what folder to put the snapshots in.  (It can also handle the case when there is no C1, ex. OAF_OVERVIEW.adl still goes to the c1oaf folder).  If the 3 letters after C1 are SYS, then it puts the snapshot into /opt/rtcds/caltech/c1/medm/c1sys/snap/MEDM_SCREEN_NAME.adl

Mostly this is totally okay, but a few subsystems seem to have incongruous names.  For example, there are screens called "C1ALS...." in the c1gcv folder.  Is it okay if these snapshots go into a /c1als/snap folder, or do I need to figure out how to put them in the exact same folder they currently exist in?  Or, perhaps, why aren't they just in a c1als folder to begin with? It seems like we just weren't careful when organizing these screens.

Another problem one is the C1_FE_STATUS.adl screen.  Can I create a c1gds folder, and rename that screen to C1GDS_FE_STATUS.adl?  Objections?


  6184   Tue Jan 10 09:17:23 2012 steveUpdatePhotosstrawman's visiters
Attachment 1: P1080491.JPG
Attachment 2: P1080492.JPG
  6904   Mon Jul 2 18:28:09 2012 JenneUpdatePhotosMany photos taken

Many photos were taken by many different people....most of the fuzzy ones are by yours truely (doing a reach-around to get to hard-to-reach places), so sorry about that.

I put all the photos from yesterday and today into 6 new albums on Picasa:  https://picasaweb.google.com/foteee

The album titles are generally descriptive, and I threw in a few comments where it seemed prudent.

Big note:  The tip tilt on the ITMX table does, in fact, have the arrow pointing in the correct direction.  Photo is in the TT album from today.

  13501   Wed Jan 3 18:00:46 2018 gautamUpdatePonderSqueezeplan of action

Notes of stuff we discussed @ today's meeting, and afterwards, towards measuring ponderomotive squeezing at the 40m.

  1. Displacement noise requirements
    • Kevin is going to see if we can measure any kind of squeezing on a short timescale by tuning various parameters.
    • Specifically, without requiring crazy ultra low current noise level for the coil driver noise.
  2. Investigate how much actuation range we need for lock acquisition and maintaining lock.
    • Specifically, for DARM.
    • We will measure this by having the arms controlled with ALS in the CARM/DARM basis.
    • Build up a noise budget for this, see how significant the laser noise contribution is.
  3. RC folding mirrors
    • In the present configuration, these are introducing ~2.5% RT loss in the RCs.
    • This affects PRG, and on the output side, measurable squeezing.
    • We want to see if we can relax the requirements on the RC folding mirrors such that we don't have to spend > 20 k$.
    • Specifically, consider spec'ing the folding mirror coatings to only have HR @1064 nm, and take what we get at 532 nm.
    • But still demand tolerances on RoC driven by mode-matching between the RCs and the arm cavities.
  4. ALS with Beat Mouth
    • Use the fiber coupled light from the ends to make the ALS signals.
    • Gautam will update diagram to show the signal chain from end-to-end (i.e. starting at AUX laser, ending at ADC input).
    • Make a noise budget for the same - preliminary analysis suggests a sensing noise floor of ~10 mHz/rtHz.


  • For the ALS-DARM budget the idea is that we can do lock acquisition better, so we don't need to care about the acquisition reqs. i.e. we just need to set the ETM coil driver current range based on the DARM in-lock values.
    • To get the coil driver noise to be low enough to detect squeezing we need to use a ~10-15 kOhm series resistor.
    • We assume that all DAC and coil driver input noises can be sufficiently filtered.
    • We are assuming that we don't change the magnet sizes or the number of coil windings in the OSEMs.
    • The noise in the ITMs doesn't matter because we don't use them for any locking activity, so we can easily set the coil driver series resistors to 15 kOhm.
    • We will do the bias for the ETMs and ITMs using some HV circuit (not the existing ones on the coil driver boards) and doing the summation after the main coil driver series resistor. This HV bias module needs to handle the ~ (2 V / 400 Ohm) = 5 mA which is now used. This would require (5 mA) x (15 kOhm) = 60+ V drivers.
  • IF we can get away with doing the ALS beat note with just red (still using GREEN light from the end laser to lock to the arms from the ends), we will not have any requirements for the 532 nm transmission of any optics in the DRMI area.
    • Get some quotes for the new PR/SR mirrors having tight RoC tolerance, high R for 1064, and no spec for 532.
    • Check that the 1-way fiber noise for 1064 nm is < 100 mHz/rHz in the 50-1000 Hz band. If its more, explore putting better acoustic foam around the fiber run.
    • Improve the mode-matching of the IR beam into the fibers at the ends. We want >80% to reduce the noise do to scattering; we don't really care about the amount of light available in the PSL - this is just to reduce the IR-ALS noise.
  13508   Sat Jan 6 05:18:12 2018 KevinUpdatePonderSqueezeDisplacement requirements for short-term squeezing

I have been looking into whether we can observe squeezing on a short timescale. The simulations I show here say that we can get 2 dBvac of squeezing at about 120 Hz using extreme signal recycling.

The parameters used here are

  • 100 ppm transmissivity on the folding mirrors giving a PRC gain of 40.
  • 10 kΩ series resistance for the ETMs; 15 kΩ series resistance for the ITMs.
  • 1 W incident on the back of PRM.
  • PD quantum efficiency 0.88.

The first attachment shows the displacement noise. The red curve labeled vacuum is the standard unsqueezed vacuum noise which we need to beat. The second attachment shows the same noise budget as a ratio of the noise sources to the vacuum noise.

This homodyne angle and SRC detuning give about the maximum amount of squeezing. However, there's quite a bit of flexibility and if there are other considerations, such as 100 Hz being too low, we should be able to optimize these angles (even with more pessimistic values of the above parameters) to see at least 0.2 dBvac around 400 Hz.

Attachment 1: displacement_noise.pdf
Attachment 2: noise_budget.pdf
  13509   Sat Jan 6 13:47:32 2018 ranaUpdatePonderSqueezeDisplacement requirements for short-term squeezing
  • ought to tune for 210 Hz (in-between powerlines) since 100 Hz is tough to work due to scattering, etc.
  • rename DAC - I think what this curve shows is really the coil driver noise. The DAC noise we can always filter out with the dewhitening board; i.e. once we have 1000x attenuation between the DAC and the coil driver input, DAC noise is not dominant.
  13511   Sat Jan 6 23:25:18 2018 KevinUpdatePonderSqueezeDisplacement requirements for short-term squeezing


  • ought to tune for 210 Hz (in-between powerlines) since 100 Hz is tough to work due to scattering, etc.

We can get 1.1 dBvac at 210 Hz.

The first two attachments are the noise budgets for these optimized angles. The third attachment shows squeezing as a function of homodyne angle and SRC detuning at 210 Hz. To stay below -1 dBvac, the homodyne angle must be kept between 88.5 and 89.7 degrees and the SRC detuning must be kept between -0.04 and 0.03 degrees. This corresponds to fixing the SRC length to within a range of 0.07/360 * 1064 nm = 200 pm.

Attachment 1: displacement_noise.pdf
Attachment 2: noise_budget.pdf
Attachment 3: angles.pdf
  13512   Sun Jan 7 03:22:24 2018 KojiUpdatePonderSqueezeDisplacement requirements for short-term squeezing

Interesting. My understanding is that this is close to signal recycling, rather than resonant sideband extraction. Is that correct?

For signal recycling, we need to change the resonant condition of the carrier in the SRC. Thus the macroscopic SRC length needs to be changed from ~5.4m to 9.5m, 6.8m, or 4.1m.
In the case of 6.8m, SRC legnth= PRC length. This means that we can use the PRM (T=5%) as the new SRM.

Does this T(SRM)=5% change the squeezing level?

  13513   Sun Jan 7 11:40:58 2018 KevinUpdatePonderSqueezeDisplacement requirements for short-term squeezing

Yes, this SRC detuning is very close to extreme signal recycling (0° in this convention), and the homodyne angle is close to the amplitude quadrature (90° in this convention).

For T(SRM) = 5% at the optimal angles (SRC detuning of -0.01° and homodyne angle of 89°), we can see 0.7 dBvac at 210 Hz.

  13514   Sun Jan 7 17:27:13 2018 gautamUpdatePonderSqueezeDisplacement requirements for short-term squeezing

Maybe you've accounted for this already in the Optickle simulations - but in Finesse (software), the "tuning" corresponds to the microscopic (i.e. at the nm level) position of the optics, whereas the macroscopic lengths, which determine which fields are resonant inside the various cavities, are set separately. So it is possible to change the microscopic tuning of the SRC, which need not necessarily mean that the correct resonance conditions are satisfied. If you are using the Finesse model of the 40m I gave you as a basis for your Optickle model, then the macroscopic length of the SRC in that was ~5.38m. In this configuration, the f2 (i.e. 55MHz sideband) field is resonant inside the SRC while the f1 and carrier fields are not.

If we decide to change the macroscopic length of the SRC, there may also be a small change to the requirements on the RoCs of the RC folding mirrors. Actually, come to think of it, the difference in macroscopic cavity lengths explains the slight differences in mode-matching efficiencies I was seeing between the arms and RCs I was seeing before.


Yes, this SRC detuning is very close to extreme signal recycling (0° in this convention), and the homodyne angle is close to the amplitude quadrature (90° in this convention).

For T(SRM) = 5% at the optimal angles (SRC detuning of -0.01° and homodyne angle of 89°), we can see 0.7 dBvac at 210 Hz.


  13515   Sun Jan 7 20:11:54 2018 KojiUpdatePonderSqueezeDisplacement requirements for short-term squeezing

In fact, that is my point. If we use signal recycling instead of resonant sideband extraction, the "tuning" of the SRC is opposite to the current setup. We need to change the macro length of the SRC to make 55MHz resonant with this tuning. And if we make the SRC macro length together with the PRC macro length for this reason, we need to thing again about the mode matching. Fortunately, we have the spare PRM (T=5%) which matches with this curvature. This was the motivation of my question. We may also choose to keep the current SRM because of its higher T and may want to evaluate the effect of expected mode mismatch.

  13808   Thu May 3 00:42:38 2018 KevinUpdatePonderSqueezeCoil driver contribution to squeezing noise budget

In light of the discussion at today's meeting, Guantanamo and I looked at how the series resistance for the test mass coil drivers limits the amount of squeezing we could detect.

The parameters used for the following calculations are:

  • 4.5 kΩ series resistance for the ETM's (this was 10 kΩ in the previous calculations, so these numbers are a bit worse); 15 kΩ for the ITM's
  • 100 ppm transmissivity on the folding mirrors giving a PRC gain of 40
  • PD quantum efficiency of 0.88

Since we need to operate very close to signal recycling, instead of the current signal extraction setup, we will need to change the macroscopic length of the SRC. This will change the mode matching requirements such that the current SRM does not have the correct radius of curvature. One solution is to use the spare PRM which has the correct radius of curvature but a transmissivity of 0.05 instead of 0.1. So using this spare PRM for the SRM and changing the length of the SRC to be the same as the PRC we can get

  • 0.63 dBvac of squeezing at 205 Hz for 1 W incident on the back of PRM
  • 1.12 dBvac of squeezing at 255 Hz for 5 W incident on the back of PRM

This lower transmissivity for the SRM also reduces the achievable squeezing from the current transmissivity of 0.1. For an SRM with a transmissivity of 0.15 (which is roughly the optimal) we can get

  • 1 dBvac of squeezing at 205 Hz for 1 W incident on the back of PRM
  • 1.7 dBvac of squeezing at 255 Hz for 5 W incident on the back of PRM

The minimum achievable squeezing moves up from around 205 Hz at 1 W to 255 Hz at 5 W because the extra power increases the radiation pressure at lower frequencies.

  13841   Mon May 14 18:58:32 2018 KevinUpdatePonderSqueezeSqueezing with no SRM

Note that for Signal Recycling, which is what Kevin tells us we need to do, there is a DARM pole at ~150 Hz.

To be quantitative, since we are looking at smaller squeezing levels and considering the possibility of using 5 W input power, it is possible to see a small amount of squeezing below vacuum with no SRM.

Attachment 1 shows the amount of squeezing below vacuum obtainable as a function of homodyne angle with no SRM and 5 W incident on the back of PRM. The optimum homodyne angle at 210 Hz is 89.2 deg which gives -0.38 dBvac of squeezing. Figure 2 is the displacement noise at this optimal homodyne angle and attachment 3 is the same noise budget shown as the ratio of the various noise sources to the unsqueezed vacuum.

The other parameters used for these calculations are:

  • 4.5 kΩ series resistance for the ETM coils; 15 kΩ for the ITM coils
  • 100 ppm transmissivity on the folding mirrors giving a PRC gain of 40
  • PD quantum efficiency of 0.88

So maybe it's worth considering going for less squeezing with no SRM if that makes it technically more feasible.

Attachment 1: homodyne_heatmap.pdf
Attachment 2: displacement_noise.pdf
Attachment 3: noise_budget.pdf
  14225   Tue Oct 2 23:57:16 2018 gautamUpdatePonderSqueezeSqueezing scenarios

[kevin, gautam]

We have been working on double checking the noise budget calculations. We wanted to evaluate the amount of squeezing for a few different scenarios that vary in cost and time. Here are the findings:

Squeezing scenarios

Sqz [dBvac] fmin [Hz] PPRM [W] PBS [W] TPRM [%] TSRM [%]
-0.41 215 0.8 40 5.637 9.903
-0.58 230 1.7 80 5.637 9.903
-1.05 250 1.7 150 1 17
-2.26 340 10 900 1 17

All calculations done with

  • 4.5kohm series resistance on ETMs, 15kohms on ITMs, 25kohm on slow path on all four TMs.
  • Detuning of SRC = -0.01 deg.
  • Homodyne angle = 89.5 deg.
  • Homodyne QE = 0.9. 
  • Arm losses is 20ppm RT.
  • LO beam assumed to be extracted from PR2 transmission, and is ~20ppm of circulating power in PRC.


  1. Existing setup, new RC folding mirrors for PRG of ~45.
  2. Existing setup, send Innolight (Edwin) for repair (= diode replacement?) and hope we get 1.7 W on back of PRM.
  3. Repair Innolight, new PRM and SRM, former for higher PRG, latter for higher DARM pole.
  4. Same as #3, but with 10 W input power on back of PRM (i.e. assuming we get a fiber amp).


  • The errors on the small dB numbers is large - 1% change in model parameters (e.g. arm losses, PRG, coil driver noise etc) can mean no observable squeezing. 
  • Actually, this entire discussion is moot unless we can get the RIN of the light incident on the PRM lower than the current level (estimated from MC2 transmission, filtered by CARM pole and ARM zero) by a factor of 60dB.
    • This is because even if we have 1mW contrast defect light leaking through the OMC, the beating of this field (in the amplitude quadrature) with the 20mW LO RIN (also almost entirely in the amplitude quad) yields significant noise contribution at 100 Hz (see Attachment #1).
    • Actually, we could have much more contrast defect leakage, as we have not accounted for asymmetries like arm loss imbalance.
    • So we need an ISS that has 60dB of gain at 100 Hz. 
    • The requirement on LO RIN is consistent with Eq 12 of this paper.
  • There is probably room to optimize SRC detuning and homodyne angle for each of these scenarios - for now, we just took the optimized combo for scenario #1 for evaluating all four scenarios.
  • OMC displacement noise seems to only be at the level of 1e-22 m/rtHz, assuming that the detuning for s-pol and p-pol is ~30 kHz if we were to lock at the middle of the two resonances
    • This assumes 0.02 deg difference in amplitude reflectivity b/w polarizations per optic, other parameters taken from aLIGO OMC design numbers.
    • We took OMC displacement noise from here.

Main unbudgeted noises:

  • Scattered light.
  • Angular control noise reinjection (not sure about the RP angular dynamics for the higher power yet).
  • Shot noise due to vacuum leaking from sym port (= DC contrast defect), but we expect this to not be significant at the level of the other noises in Atm #1.
  • Osc amp / phase.
  • AUX DoF cross coupling into DARM readout.
  • Laser frequency noise (although we should be immune to this because of our homodyne angle choice).

Threat matrix has been updated.

Attachment 1: PonderSqueeze_NB_LORIN.pdf
  15688   Tue Nov 24 16:51:29 2020 gautamUpdatePonderSqueezePonderomotive squeezing in aLIGO


On the call last week, I claimed that there isn't much hope of directly measuring Ponderomotive Squeezing in aLIGO without some significant configurational changes. Here, I attempt to quantify this statement a bit, and explicitly state what I mean by "significant configurational changes".

Optomechanical coupling:

The I/O relations will generally look something like:

\begin{bmatrix} b_1\\ b_2 \end{bmatrix} = \begin{bmatrix} C_{11} & C_{12}\\ C_{21} & C_{22} \end{bmatrix} \begin{bmatrix} a_{1}\\ a_2 \end{bmatrix} + \begin{bmatrix} D_1\\ D_2 \end{bmatrix} \frac{h}{h_{\mathrm{SQL}}}.

The. magnitudes of the matrix elements C_12 and C_21 (i.e. phase to amplitude and amplitude to phase coupling coefficients) will encode the strength of the Ponderomotive squeezing. 


For the inital study, let's assume DC readout (since there isn't a homodyne readout yet even in Advanced LIGO). This amounts to setting \zeta = \phi in the I/O relations, where the former angle is the "homodyne phase" and the latter is the "SRC detuning". For DC readout, the LO quadrature is fixed relative to the signal - for example, in the usual RSE operation, \zeta = \phi = \frac{\pi}{2}. So the quadrature we will read out will be purely b_1 (or nearly so, for small detunings around RSE operation). The displacement noises will couple in via the D_1 matrix element. Attachment #1 and Attachment #2 show the off-diagonal elements of the "C" matrix for detunings of the SRC near RSE and SR operation respectively. You can see that the optomechanical coupling decays pretty rapidly above ~40 Hz. 

SRC detuning:

In this particular case, there is no benefit to detuning the SRC, because we are assuming the homodyne angle is fixed, which is not an unreasonable assumption as the quadrature of the LO light is fixed relative to the signal in DC readout (not sure what the residual fluctuation in this quantity is). But presumably it is at the mrad level, so the pollution due to the orthogonal anti-squeezed quadrture can be ignored for a first pass I think. I also assume ~10 degrees of detuning is possible with the Finesse ~15 SRC, as the linewidth is ~12 degrees.

Noise budget:

To see how this would look in an actual measurement, I took the data from Lee's ponderomotive squeezing paper, as an estimate for the classical noises, and plotted the quantum noise models for a few representative SRC detunings near RSE operation - see Attachment #3. The curves labelled for various phis are the quantum noise models for those SRC detunings, assuming DC readout. I fudged the power into the IFO to make my modelled quantum noise curve at RSE line up with the high frequency part of the "Measured DARM" curve. To measure Ponderomotive Squeezing unambiguously, we need the quantum noise curve to "dip" as is seen around 40 Hz for an SRC tuning of 80 degrees, and that to be the dominant noise source. Evidently, this is not the case.

The case for balanced homodyne readout:

I haven't analyzed it in detail yet - but it may be possible that if we can access other quadratures, we might benefit from rotating away from the DARM quadrature - the strength of the optomechanical coupling would decrease, as demonstrated in Attachments #1 and #2, but the coupling of classical noise would be reduced as well, so we may be able to win overall. I'll briefly investigate whether a robust measurement can be made at the site once the BHD is implemented.

Attachment 1: QN_heatmap_RSE.pdf
Attachment 2: QN_heatmap_SR.pdf
Attachment 3: noiseBudget.pdf
  4503   Fri Apr 8 01:05:45 2011 SureshUpdateRF SystemRF Source Harmonics


 The measured power levels of the RF source harmonics are given below:



We are considering inclusion of bandpass filters centered on 11 and 55 MHz  to suppress the harmonics and meet the requirements specified in Alberto's thesis (page 88).


Attachment 1: RF_Source_Harmonics_Sheet1.pdf
RF_Source_Harmonics_Sheet1.pdf RF_Source_Harmonics_Sheet1.pdf RF_Source_Harmonics_Sheet1.pdf RF_Source_Harmonics_Sheet1.pdf
  4511   Mon Apr 11 19:09:59 2011 SureshUpdateRF SystemInstalled low pass filters in the demod boards


As part of the RF system upgrade some of the demod boards in the lab were modfied.  The filter U5 (see the circuit schematic) was replaced. These changes are tabulated below.


Filters installed in the demod boards
Serial number Old name of the card New name of the card Filter installed Remarks
107 POY33 REFL33 SCLF-33+ R14=50Ohm
118 AP133, ASDD133 REFL55 SCLF-65  
114 PO199 REFL165 SCLF-190 R14=50Ohm
120 PO133 POP110 SCLF-135  
123 SP133 POP55 SCLF-65+ AT1 removed, R14=50Ohm
122 SP199, REFLDD199 AS165 SCLF-190  
121 SP166, REFL16 POP11 SCLF-10.7  
116 AP199 199 MHz POP165 SCLF-190  
126 AS166 33.3 MHz POX11 SCLF-10.7  
119 POX 33.3 MHz POY11 SCLF-10.7  
021 24.5 MHz (LLO) REFL11 SCLF-10.7  
020 24.5 MHz SCLF-45 POP22 SCLF-21.4  
022 24.5 MHz SCLF-45 AS11 with amp SCLF-10.7  
029 24.5          SCLF-f5 AS55 with amp SCLF-65  


Next, I and Q phase has to be checked for orthogonality. And noise levels of the cards have to measured.




  4514   Mon Apr 11 23:35:02 2011 ranaUpdateRF SystemInstalled low pass filters in the demod boards

I am a little concerned about using these low pass filters so close to the band edge. Recall that there is no on-board preamp for the RF input to the mixer.

So, if the input impedance of the filters is not 50 Ohms, we will get some unwanted reflections and sensitivity to cable length.

I think its worth while to check the impedance or S-parameters of these things with the LO activated to find out if we need to remove them or not.

  4547   Wed Apr 20 21:53:01 2011 SureshConfigurationRF SystemRF system: Stray heliax cable

We found a stray unused heliax cable running from the LSC rack 1Y2 to a point between the cabinets 1X3 and 1X4. This cable will need to be redirected to the AS table in the new scheme.   It is labled C1LSC-PD5  The current situation has been updated as seen in the layout below


Attachment 1: rogue_cable_1.png
  4548   Wed Apr 20 22:29:07 2011 sureshUpdateRF SystemPlan for LSC rack

The suggested layout of the 1Y2 Rack is shown below.

To simplify the wiring, I have largely kept demod boards with the same same LO frequency close to each other. 

The Heliax cables land on the top and bottom of the of subracks.  These are currently flexible plastic sheets.  Steve has agreed to replace them with something more rigid.  It would be good to have eight N-type connectors on the top and eight  at the bottom.  As  demod boards occur in sets of eight per subrack.  So it would be convenient if the 11 and 55 Mhz Heliax cables land on the top and the rest at the bottom.  In the layout I have shown the current situation. 

The LO signals to the boards come from the RF Distribution box and this is kept in the middle so that cables to both the subracks can be kept short.

The outputs of the AA filter boards from both subracks  have to be connected to the SCSI Interface board with a twisted pair ribbon cable. 


  4551   Thu Apr 21 14:39:43 2011 steveUpdateRF Systemnew strain relieved N connectors at AP

New right angle PVC, 2 x 2 x  1/4" installed at the AP table to strain relief the 1/4" spiral corrugated RF coaxes.

Attachment 1: P1070562.JPG
Attachment 2: P1070564.JPG
  4557   Fri Apr 22 09:05:53 2011 SureshUpdateRF SystemRF Source Harmonics
As seen in the previous measurement the first harmonic of both the 11 MHz and 55 MHz outputs are about 30dB
higher than desired.  In an attempt to attenuate these and higher harmonics I introduced SBP-10.7 filters into
the 11MHz outputs and SLP-50 filters into the 55 MHz outputs.
Then I measured the height of the harmonics again and found that they were suppressed as expected.  Now harmonic
at 22 MHz is 58dB lower than the 11 MHz fundamental.  And the 110 MHz is lower by 55 dB compared to the 55 MHz
fundamental.  None of the higher harmonics are seen => they are below 70dB

SLP-50 has an insertion loss(IL) of 4.65 dB and Return Loss(RL) of 3dB.  It would be better to use SBP-60
(IL=1.4 dB and RL=23dB)

The filter on the 11 MHz lines is okay. The SBP-10.7 has IL=0.6 dB and RL=23 dB.
  4558   Fri Apr 22 09:25:43 2011 SureshUpdateRF SystemRF Source: Temperature sensor relocated

RF Amp operating temperature

Earlier measurement reported by Alberto in LIGO-T10004-61-v1 based on the LM34 temperature sensor were lower than that shown by placing a calibrated thermocouple sensor directly on the heat sink by about 5deg C. The difference probably arose because the LM34 was located on a separate free-hanging copper sheet attached to the RF Amp by a single screw, resulting in a gradient across the copper strip.   I tried to move the LM34 which was glued down, but broke the leads in the process.  I then replaced it with another one mounted much closer to the heat sink and held it down with a copper-strip clamp.  There is no glue involved and there is heatsink compound between the flat surface of the LM34 and the heatsink.  Picture attached. 

  The picture also shows the new filters which have been put in place to reduce the harmonics.  Note that the SBP-10.7 which was to go on the 11 MHz Demod output is located much farther upsteam due to space constraints.


  4559   Fri Apr 22 10:28:22 2011 ranaUpdateRF SystemRF Source Harmonics
You should be able to resolve the other harmonics by decreasing the IF BW or RBW on the analyzer. Even though
they're OK, its useful to have the final measurement of all of them in some kinds of physical units (like dBm, but
not dBm/Hz or dB or dBcubits).
  4578   Thu Apr 28 06:46:30 2011 SureshUpdateRF SystemRF Source installed

RF Source box has been mounted in the 1X2 rack. 



Heliax cables have been directly attached to the box and anchored on the side of the 1X2 rack.  Here is a list of Helix cables which have been connected so far.


Cables old name New name From -> To
1 133 MHz 11 Mhz Demod 1X2 to 1Y2 rack
2 199 MHz 55 MHz Demod 1X2 to 1Y2 rack
3 166 EOM 11 MHz EOM 1X2 to PSL table
4 33 EOM 55 MHz EOM 1X2 to PSL table
5 REFL 33 AS11 AS table to 1Y2


ELOG V3.1.3-