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ID Date Author Type Category Subjectup
  10955   Thu Jan 29 10:14:21 2015 manasaUpdateGeneralX end space issues

It is certain that we have space issues at the X end that has been preventing us from sticking in a lens to couple light into the fiber. 

The only way out is to install a platform on the table where we can mount the lens. I have attached the a photo of how things look like at the X end (attachment 1) and also a drawing of the platform that which can hold the lens (attachment 2). Additional support to the raised platform will be added depending on how much space we can clear up on the table by moving the clamping forks of the doubler.
Steve and I have been able to gather parts that can be put together into something similar to what is shown in the drawing. 

Proposed modifications to the X end table:

1. The side panels of the table enclosure will come out while putting in the new platform.

2. The clamping forks for the doubling crystal will be moved.

Let me know of any concerns about the proposed solution. 

Attachment 1: photo.png
photo.png
Attachment 2: drawing.png
drawing.png
  12056   Wed Mar 30 17:38:52 2016 gautamUpdateendtable upgradeX end table proposed layout

Attachment 1: This is a photo of the current X end table optical layout with the beampaths of the various sub-systems overlaid. For the labels, see Attachment #2.

Attachment 2: This is a summary of all the optical components that are currently being used. I've noted some things we may want to change when we effect the swap. The important ones are:

  • Switch out all 1" and 2" optic mounts which are not of the Polaris type to the Polaris type. I have checked that we have sufficient numbers of these in hand.
  • Adjust the collimating lens of the fiber collimating telescope to get a better mode
  • Many of the labels are probably outdated, now would be a good time to update them
  • For the mode-matching of the AUX IR into the doubling crystal, a la mode suggests a better (i.e. less sensitive to lens position) solution is effected with L2 as a 100mm fl lens rather than 88.3mm. I did not change this during the laser swap in order to minimize the number of components changed. Since we are doing a wholesale change now, it may not be a bad idea to swap this out as well. I have checked that we have a suitable AR1064 coated lens.
  • Some optics probably need to be cleaned...
  • PZT mirror 2 has a new mount ready that is the "correct" height so we don't have to keep using makeshift stacked posts.
  • The plan as it stands is to use the green coloured mount for the IR faraday (IO-5-1064-HP).

Have I missed anything important?

Attachment #3: I've made a CAD drawing of the proposed new layout and have overlaid the beampath in an amateur way because I couldn't figure OptoCad out - I figure this will suffice for now. I have adopted elements from the current Y-end layout, but have used Anders' mode-matching solution (same lenses, same positions of optics) to make sure we have good Guoy phase separation between the two PZT steering mirrors. Some notes:

  • I've tried to palce the optics for the AUX IR into the doubler and subsequent steering of green into the arm cavity as per the mode matching solution. These should be pretty accurate, and the layout suggests we have some room to maneuver 
  • The Green REFL beampath is exaggerated but I think we have enough room to place Y16 appropriately and steer the reflected beam into the PDA36A
  • We need two more 1" 1064nm coated mirrors for the initial steering into the doubling oven, I have checked we have these in hand.
  • The IR pickoff into the fiber coupler may change somewhat once we change the mode and redo the mode-matching calculations. But again, I think we have sufficient room to implement a workable solution.
  • After accounting for the fact that the new endtable will be a little closer to the vacuum chamber, Y12 in the proposed layout will be ~10cm further away from ETMX than it is currently. But as discussed at the meeting today, the Rayleigh range of the green beam should be large enough here such that this shouldn't be a significant change.

Steve says the table is ready - so if we are happy with this layout, we can move forward...

Attachment 1: ETMX_3x2.JPG
ETMX_3x2.JPG
Attachment 2: layout_details_20160328.pdf
layout_details_20160328.pdf
Attachment 3: ETMX_proposed_layout.pdf
ETMX_proposed_layout.pdf
  10457   Fri Sep 5 04:07:44 2014 ericqUpdateGreen LockingX end uPDH Box Replaced

Just a quick note, plots and data will come tomorrow:

I grabbed an unused uPDH board from the ATF (thanks Zach!), and re-stuffed almost the entire thing to match Jenne's latest schematic for the y end box. I also threw some 22uF caps on the regulators, as Koji did with the previous box, to eliminate some oscillations up in the high 10s of kHz. I replaced the tragedy of a box that I created on Wednesday with this new box. The arm locks pretty stably with the boost on, 30 degrees of phase margin with 10kHz UGF, and locks pretty darn reliably. 

Now we should now have two nicely boosted PDH loops. I'll do a noise/loop breakdown again in the upcoming days. 

  12073   Wed Apr 13 00:56:07 2016 gautamUpdateendtable upgradeX endtable repopulation

Over the last couple of days, I've been working on restoring the optical layout on the X-endtable. Some notes about the status as of today:

Lightwave NPRO output power

The output power from the lightwave NPRO is about 210mW (as measured with the calorimeter). This is significantly lower than the value of ~300mW reported in this elog. It may be that the laser crystal temperature has changed compared to that measurement, but the "ADJ" parameter is at 0, both today and in that measurement. The laser has also been on for more than a day now, that should be sufficient time for the crystal to equilibriate to its final operating state? Is such a large change in output power possible just because of a change in laser crystal temperature? Or did the laser really lose ~1/3rd of its output power over the last two months?

Alignment into IR Faraday, and changes to the planned layout

I've set up the layout until steering the beam through the IR faraday. The input power into the IR Faraday is ~210mW. The output power is ~186mW, after optimizing the angle of the HWP. These numbers seem consistent with what I had reported in this elog (although this was for the Innolight NPRO). The alignment looks reasonably good to the eye as well.

I've made one change to the planned layout (latest version here). Y1 is now a 2" 99% reflective for S polarization beam splitter, instead of a 1" HR mirror. I made this change because we want some light from the NPRO to be transmitted through this optic to couple into the fiber eventually, for the IR beat. I measured the transmitted power to be ~1.5mW, which is around what we were coupling into the fiber before, and should suffice now. The Lightwave NPRO datasheet (page 4) suggests that the polarization of the output of the laser is S, and the measured power before and after this optic suggests that it is working as advertised. This means that HWP 1 also has to be moved downstream (to rotate the polarization so as to maximize transmission through the IR faraday). Space constraints meant that I could not mount HWP 1 on the baseplate+3/4" OD post assembly which is what we want where possible on the new table, so for this optic, I used a 1" OD post and a fork. There may be a couple of other optics in the final layout where space constraints dictate we compromise in this way.

I've also installed beam dumps for the rejected light from the Faraday. For now, these are the old beam dumps. They looked reasonably intact. I believe we have a bunch of new beam dumps on hand as well, so these can be swapped out if deemed necessary.

Cleaning of optics

All the optics are being cleaned using first contact before being installed on the table. 

As I found out the hard way, it is not a good idea to clean small optics like half-wave plates while in their mounts. The first contact tends to bond to the frame while drying, and doesn't come off cleanly. Koji helped me clean the offending pieces (he used tweezers to manually remove the residual first contact, and then some acetone to clean up any remaining residue). Subsequently, he re-cleaned these optics, again using first contact, but this time being careful not to extend all the way out to the edge of the optic. The idea is to cover as much area as possible with first contact, while staying clear of the edge. This approach worked reasonably well.


The next major step is to achieve optimal alignment into the doubler. I've placed the doubler on the table in it's approximate final position, I wanted to make sure the enclosure support wasn't in the way (it isn't). The cable from the oven won't run all the way to the Thorlabs temperature controller in it's usual place, we need to either extend the cable, or figure out a new place where we can keep the temperature controller.

  12074   Wed Apr 13 11:00:28 2016 SteveUpdateendtable upgradeX endtable repopulation

ETMX optical table is grounded to ETMX chamber through 1 Mohms

The doubling oven temp controller is installed to reach its cable.

 

  10981   Thu Feb 5 15:21:25 2015 manasaUpdateGeneralX endtable work

[EricG, Manasa]

We were at the X end today trying to couple AUX X light into the fiber. 

The proposed plan still did not give a good beampath. The last steering mirror before the fiber coupler was sticking out of the table enclosure. I tried a few other options and the maximum coupling that I could get was ~10%

I am working on plan C now; which would be to use fixed mount mirrors and steer the beam to the space created by Koji near the IR trans path and use a set of lenses instead of a single lens. I will elog more details after some modematching calculations.

We moved one of the clamps for the doubling crystal to make space. Also, the NPRO current was reduced during this work.

I reset things to how they were before I touched the table. I ensured that the green power was still the same (~3mW) after the doubler and that it could lock to the arm in TEM00.

  10978   Wed Feb 4 21:09:43 2015 manasaUpdateGeneralX endtable work scheduled tomorrow

The X end fiber setup will be put together tomorrow morning. Let me know if there are any concerns.

Quote:

It is certain that we have space issues at the X end that has been preventing us from sticking in a lens to couple light into the fiber. 

The only way out is to install a platform on the table where we can mount the lens. I have attached the a photo of how things look like at the X end (attachment 1) and also a drawing of the platform that which can hold the lens (attachment 2). Additional support to the raised platform will be added depending on how much space we can clear up on the table by moving the clamping forks of the doubler.
Steve and I have been able to gather parts that can be put together into something similar to what is shown in the drawing. 

Proposed modifications to the X end table:

1. The side panels of the table enclosure will come out while putting in the new platform.

2. The clamping forks for the doubling crystal will be moved.

Let me know of any concerns about the proposed solution. 

 

  5133   Sun Aug 7 14:01:58 2011 kiwamuUpdateGreen LockingX green beam re-aligned

[Jenne / Kiwamu]

 The X green beam has been realigned to compensate the effect of the ETMX repositioning.

After the alignment we became able to lock the 00 mode with the X green beam.

 

For the alignment:

  spot position on the ETMX mirror = within ~ 1 cm. This number is strictly constrained by a homemade aluminum iris that Jamie put last Friday.

  spot position on the ITMX mirror = unknown, but looks pretty good on the CCD camera.

  spot position on the PSL table = ~ 1 mm downward from what it used to be. The horizontal alignment is perfect.

Conclusions :

  The X green beam again became a reference of the beam axis.

  The ETMX suspension tower is in a good place.

Quote from #5127

Kiwamu will work on the green alignment over the weekend.  Assuming everything works out, we'll try the same procedure on ETMY on Monday.

 

  5135   Sun Aug 7 18:41:12 2011 JenneUpdateGreen LockingX green beam re-aligned

Quote:

The ETMY suspension tower is in a good place.

Quote from #5127

Kiwamu will work on the green alignment over the weekend.  Assuming everything works out, we'll try the same procedure on ETMY on Monday.

 

 You meant ETMX, right?  ETMY still hasn't been touched.

KI : sorry, I meant ETMX. I fixed the entry.

  6342   Wed Feb 29 20:27:00 2012 JenneUpdateGreen LockingX green beat - found it!

Found it!

The actual temperature of the Xend laser is 0.02 C higher than anticipated based on the formula in elog 3759.  Both the PSL and the Xend laser are at their nominal diode currents (2.100 A for the PSL, 2.003 A for Xend), so the curves should be used as they are.  The PSL temp (when the slow servo offset is ~0) is 31.71 C.  Using curve 2 from elog3759, the Xend laser should be 37.78, which I found was +10 counts on the Xgreen slow servo offset. 

Right now the Xend laser is at 37.80 C, and the beat is around 30 MHz.  This is +80 counts on the Xgreen slow servo.  +60 counts gave me ~80 MHz.  When (a few minutes ago) the MC unlocked and relocked, it came back to a slightly different place, so the temp of the Xend laser had to go up a few 10's of counts to get the same beat freq.  Right now the PSL slow servo offset is 0.076 V. 

The HP8591E is set with ResBW=100kHz, Ref Level= -39dBm (so I'm not attenuating my input signal!).  The largest peak I see for the beatnote is -66dBm.  The nose floor around the peak is -83dBm.  Trace (trace button!) A is set to MaxHoldA, and Trace B is set to ClearWriteB, so B is giving me the actual current spectrum, while A is remembering the peak value measured, so it's easier to see if I went past the peak, and just didn't see it on the analyzer. 

Also, I went back and realigned the beams earlier, to ensure that there was good overlap both near the BS which combines the PSLgreen and Xgreen beams, and at the PD.  The overlap I had been looking at was okay, but not stellar.  Now it's way better, which made the peak easier to see.  Also, also, the waveplate after the doubling oven on the PSL table is still rotated so that I get max power on the Xgreen side of things, and not much at all on the Ygreen side.  I'll need to rebalance the powers, probably after we make sure we are seeing the beatnote with the BeatBox.

Next Steps:

Lay a cable from the BBPD to the BeatBox in 1X2, make the BeatBox do its thing.

Use the dichroic locking to do a sweep of the Xarm.

  8666   Mon Jun 3 21:09:55 2013 ManasaUpdateGreen LockingX green beatnote through beatbox

I connected the X green beat PD output back to the beatbox, did the usual PSL alignment for green and searched for the beat note from the RFmon of the beatbox.

Yuta had used a power splitter which took Xbeat-RFmon and Ybeat-RFmon and used the SUM port to monitor the beat signals. I have removed this splitter and just used the X beat RFmon.

I found the beat note with:

Beat@58.7MHz : Amplitude -30dBm
C1:ALS-TRX_OUT16 = 3000 counts
C1:PSL-FSS_SLOWDC = 0.2250
PSL temperature = 31.52 degC
X- green temperature = 39.34 degC (OFFSET = 5140)

Next
Beatbox calibration

IMG_0608.JPG

  10000   Wed May 28 17:51:48 2014 manasaUpdateLSCX green broadband PD NOT working

Quote:

Grr.  I am very frustrated.  After lunch I redid alignment for both X and Y green systems (Yarm both at the end and on the PSL table, Xarm just on the PSL table).  After that realignment work, I cannot find a beatnote for the Xarm!!! 

At this point, I still hadn't touched anything on the X path (except the PZT input steering mirrors, remotely from the control room).  The beatnote was about the same size as it was on Friday, around -27dBm.  I went onto the PSL table and did the same alignment procedure that I had just done for the Yarm:  Remove the green trans PD and the accompanying lens so that I get far-field spots on the wall, and then steer the PSL green and the X green spots until they are nicely overlapped at both the camera (near-field) and on the wall.  I looked at the DC output of the beat PD, and centered the beam on the diode.  I put back the thorlabs DC transmission PD and the lens, and centered the beam on that.  However, after this work, I cannot find a beatnote for the X arm!  I still see the nice big Ygreen beatnote, and I have the PSL and Xend temperatures where they usually are (  abs(FSS Slow) < 0.1, and X end Slow around 10,090. )  I scanned -10,000 counts, and +5,000 counts from there, and still don't find a beatnote!

I went back inside, and I don't see an RF signal coming into the beatbox from the Xarm.  It's not the cable's fault though, since I then hooked the RF output of the beat PD to a 'scope, and still didn't see any beatnote.  The DC path of the PD is definitely seeing things, because when I switch the 'scope over to the DC output of the Xbeat PD, and I block/unblock the beam, I see the voltage step up and down as expected. 

I have not pulled out the Xgreen broadband PD, but unless someone else has a good idea of what to check, that might be one of the next things to do. 

Ideas of things I could try:

* Put the X broadband PD on the Y beatnote path to see if I see the same Y beatnote (use the port where the Y green trans PD is, since it has the coaligned beams, and a lens).

* Open the PD and see if anything on the RF path is fried.

* Move the Y PD over to the X path, to see if it sees the beatnote.

* ????

I made my attempts trying to figure out what was wrong.

Checking if we are at the right X end laser temperature: 
I aligned the arms and found the Y beatnote.I blocked the light falling on the X beat PD so that the RF analyser was only looking at the output from the Y beat PD. AT the RF analyser, I found the strong Y-PSL beatnote, the X-Y beat note and a weak  X-PSL beatnote. This confirmed that we have the X end laser at the right temperature to be able to detect the beatnote. Unblocking the light on the X beat PD did not bring in any additional peaks. 

Checking the RF cabling from the X beat PD to the beat box:
I swapped the RF cables such that the signal from the Y beat PD output was going to the X input on the beatbox. I could still see the beatnote on the RF analyser. This confirmed that there aren't any broken RF cables along the X path.

Checking X green PSL alignment:
I replaced the X beat PD with the Y beat PD to check if the alignment of X&PSL green are alright. I could find the X beat note this way without any alignment tweaking.

I suspect we probably have some RF component burnt in the X beat PD. Do we have any spares lying around? There is a Koji's box with a PD having the same serial number.

IFO status report for anyone who is looking to do some locking tonight : 
The Y beat PD is back along the Y path and I have confirmed the presence of Y-PSL beat note after replacing the PD.
The X beat PD has been removed and now rests on the electronics bench for checking. 

While aligning the arms today, I noticed that enabling LSC would cause misalignment of the ETMY suspension. I haven't tried to find out what has been causing this. Could be something similar to what was noticed with the ETMX suspension a couple of weeks ago elog9969 

  10001   Wed May 28 19:15:38 2014 KojiUpdateLSCX green broadband PD NOT working

If the PD is the suspect, just pull it from the table and bring it to the PD testing setup.

The transimpedance of the PD should be ~2000 Ohm for both of the RF and DC outputs.

The test setup gives you the systematic opportunity for examination of the signal line.
Check the signal level with the active probe.

Once the broken component is found replace it. You are supposed to have the replacement
components on the blue tower.

  9996   Tue May 27 21:48:31 2014 JenneUpdateLSCX green broadband PD not working???!?

Grr.  I am very frustrated.  After lunch I redid alignment for both X and Y green systems (Yarm both at the end and on the PSL table, Xarm just on the PSL table).  After that realignment work, I cannot find a beatnote for the Xarm!!! 

The Ybeat, after aligment, was up to -5.5 dBm when the beat was at 11 MHz. Last week it was something like -20 dBm, so alignment makes a big difference.  After doing IR alignment I had noticed that the green transmitted through the Yarm didn't look very bright on the camera, and the power was around 0.2, so I went to the Yend and gently touched the green input steering mirrors, and got the Ygreen trans PD back to more than 0.9 with the PSL green shutter closed.  Awesome.  Then I touched up the Ygreen PSL alignment, and then saw that the beatnote was nice and large.  Hooray.  I measured the out of loop noise, and it was even better than the best we saw last week:  (greenish was best last week for Yarm, teal blue is new Ygreen):

ALS_outofloop_27May2013_2.pdf

At this point, I still hadn't touched anything on the X path (except the PZT input steering mirrors, remotely from the control room).  The beatnote was about the same size as it was on Friday, around -27dBm.  I went onto the PSL table and did the same alignment procedure that I had just done for the Yarm:  Remove the green trans PD and the accompanying lens so that I get far-field spots on the wall, and then steer the PSL green and the X green spots until they are nicely overlapped at both the camera (near-field) and on the wall.  I looked at the DC output of the beat PD, and centered the beam on the diode.  I put back the thorlabs DC transmission PD and the lens, and centered the beam on that.  However, after this work, I cannot find a beatnote for the X arm!  I still see the nice big Ygreen beatnote, and I have the PSL and Xend temperatures where they usually are (  abs(FSS Slow) < 0.1, and X end Slow around 10,090. )  I scanned -10,000 counts, and +5,000 counts from there, and still don't find a beatnote!

I went back inside, and I don't see an RF signal coming into the beatbox from the Xarm.  It's not the cable's fault though, since I then hooked the RF output of the beat PD to a 'scope, and still didn't see any beatnote.  The DC path of the PD is definitely seeing things, because when I switch the 'scope over to the DC output of the Xbeat PD, and I block/unblock the beam, I see the voltage step up and down as expected. 

I have not pulled out the Xgreen broadband PD, but unless someone else has a good idea of what to check, that might be one of the next things to do. 

Ideas of things I could try:

* Put the X broadband PD on the Y beatnote path to see if I see the same Y beatnote (use the port where the Y green trans PD is, since it has the coaligned beams, and a lens).

* Open the PD and see if anything on the RF path is fried.

* Move the Y PD over to the X path, to see if it sees the beatnote.

* ????

  11473   Fri Jul 31 10:36:22 2015 SteveUpdatePEMX seismo station short cable removed

 

Quote:

Atm1,  New short-50" long cable was installed at ETMY end ( Y-station ) between Guralp-B ( MIT ) and granite base.

Interface box input 2 was left connected to cable 1 and input 1 to cable 2. This plot shows no change.

 

Atm2, Than I swapped the two long cables at the interface box

                                                                                                   Now the signal seems to be ok <2 Hz,

                                                                                                                                                       >2 Hz some problem exist.

      Channel Name Location Seismometer 40m long cable

Interfacebox input

 

 50" short cable

C1:PEM-RMS_GUR2X_.... ETMX Guralp -A  2   2                             Jenne's friend                
C1:PEM-RMS_GUR1X_.... ETMY  Guralp-B  1   1  Koji

I will look for more bad soldering tomorrow. How many cables did she make?

 

 

We have to redo this cable also

Attachment 1: IMG_0009.JPG
IMG_0009.JPG
  11475   Sat Aug 1 20:46:29 2015 KojiUpdatePEMX seismo station short cable removed

OMG

  9496   Thu Dec 19 19:45:12 2013 ericqUpdateGreen LockingX-Arm Green PDH Loop Stuff
With the fixed servo box, I remeasured the OLTF, the servo, and the low pass filter between the mixer output and servo input. Dividing the OLTF by the servo and LPF transfer functions should just leave the the [laser PZT->cavity->PD] transfer function, which should have the shape of the cavity pole plus any delay in the loop, up until the PZT is no longer linear / the measurement has bad SNR.

I'm missing a few pieces of the loop. While I know the PD gain in V/W, I don't know how much power is in the sideband, which affects the slope of the PDH error function. Also, I've found old ELOG posts mentioning either 1 or 5MHz/V being the NPRO PZT response, but am not sure how to determine what it actually is. These are essentially just scalars though, so finding the reason for low phase margin doesn't depend on them.

Here are the TFs I've measured ("residual" refers to OLTF/(servo*LPF)):



The teal "residual" TF presumably owes its shape to the cavity pole + the time delay around the loop. Messing around with the data, the shape fits very well to a real pole at 27kHz and a ~3usec delay. I have no real way to back that up as the unique truth behind it, however. Is there a good way to measure the delay? Without assuming any delay, the shape is best fit by a real pole at 26kHz and some funky complex zeros.

Another thing to look at is the CLG implied by the measurement of the OLTF, given by 1/(1-G). I plotted this quantity for the measured loop, and also for G/2 and 3G/2 to get an idea for how it changes as you turn the servo gain knob. I measured with the knob at 4.0. There seems to be quite a bit of gain peaking!



Also, I drew up a simple block diagram sort of thing to show how everything is connecting down at the green electronics rack at the end of the X arm (while totally glossing over the optical elements involved). This hopefully helps anyone who wants to inspect/take apart/massacre the setup.

  7171   Tue Aug 14 04:53:45 2012 YoichiSummaryLSCX-Arm noise spectrum

Yoichi, Rana

Here is the noise spectrum of the X-arm error signal along with the TRX DC power fluctuations.

The spectra were taken while the whitening filters for POX11 were OFF.

EDIT (Integrity Fairy): Shall we assume these units are "Intergalactic translational qubits/sqrt(Hz)"?

Attachment 1: xarm-spectrum.png
xarm-spectrum.png
  8983   Wed Aug 7 23:40:49 2013 gautamUpdateCDSX-End Green ASS - A first update

 I have done some preliminary testing of the X-End Green ASS Servo. I will write a more detailed elog about this soon, but I thought I'd note down the important stuff here.


Yesterday, while we were venting, I aligned the X-arm to the green using the sliders on IFOalign, maximizing the transmission. Then I retook a power spectrum so as to determine the LO frequencies. Jenne pointed out that LO frequencies should not be integers (it usually suffices to append a .098725 or something to the frequency) so I made the necessary changes.

I did a first run of the servo yesterday, and more runs today. Notable points:

  1. I was able to lock to 00 from a 08 or 09 mode using the PZT sliders
  2. The green transmission having locked to 00 was ~0.2. I then ran the servo and got it up to ~0.4 and then 0.6 (see time series plot attached). The servo was able to recover this level of transmission after misaligning the steering mirrors using the PZT sliders.
  3. This was not the optimal transmission level as when Koji moved ETMX a little, the transmission improved.
  4. The actuators are degenerate. Most of the time, only two of the four servos are doing anything significant. This is probably because of the fact that the two steering mirrors are so close to each other, that moving one or the other produces virtually the same effect. I do however have some cool videos of mode-hopping :)
  5. The range of actuation of the PZTs is probably not enough to maximize the green transmission from an arbitrary state because of point 4 (i.e. we need to move one mirror in some direction a lot, and move the other a lot to compensate for the change, and the overall gain in input pointing/alignment is marginal). It may be that things will be slightly better at the Y-end. It would also be interesting to see if there is any improvement in the servo performance by dithering the cavity mirrors as opposed to the PZT mirrors.
  6. To this end, I tried modifying the c1asx model to incorporate an option to dither the cavity mirrors. The plan was to make a second set of LOs in the model that output to ITMX and ETMX suspensions. However, for some reason, when I recompiled the model and restarted it, c1iscex crashed. Parity has now been restored. Note that in order to accommodate the new LOs, I had to make changes to C1SUS, C1RFM and C1SCX as well. I have since removed all my additions, saved, built and installed these models, but have not restarted them (with the exception of C1SCX which restarted when I manually restarted c1iscex). 
  7. The plan tomorrow is to try incorporating cavity dither into the model again. This time, I'll try grabbing the LO-related signals from c1ass directly, as I am not clear why my approach did not work.

More details to follow.

time-series.pdf

  8993   Sat Aug 10 05:53:51 2013 gautamUpdateCDSX-End Green ASS - Roundup

Over the last three days, I've had the interferometer to test and optimize the ASX Servo. Based on what I have seen, I think the conclusion is that with the current parameters, the servo does its job provided the input pointing set up at the endtable with the coarse adjustment knobs is reasonably good. Once the cavity is aligned and IR transmission maximized using ASS, I have been able to get the green transmission up to 0.8 which is close to the best we had pre-vent. I have not been elogging regularly over the last few days, so this one is going to be a longish one.


Major changes made:

  1. The SIMULINK model has been modified to accommodate an option to dither the cavity mirrors and not the PZT mirrors. Details are as follows:
    • I have sent the LO signals (CLK,SIN and COS) from the ASS model to the ASX model via the RFM model. Appropriate changes were made to all these three models, and recompiling and restarting the models was done without issue. The SIN and COS signals are used to demodulate green transmission at the dither frequencies. ***The CLK signal is not required to be sent between models as it is not being used by ASX (I turn the dither ON using the channels already set up for ASS). I realised this a little late, and at present the ASS and RFM models are compiled such that the CLK signal is also sent from ASS to RFM. This can be removed, thus freeing up 4 unnecessary inter-process communication channels. Also, I am not too sure if this is relevant, but the maximum computation time of both the RFM and ASX models seem to have gone up after I added these inter-process communication links.***
    • The rest of this part of the servo is a replica of the part where PZT mirrors are dithered. At present the servo output is the sum of its two branches (PZT mirror dither branch and cavity mirror dither branch) which works fine under the assumption that at any one time, only one arm will run. Ideally, the summing block should be replaced by a switch. However, when I tried (in an earlier attempt to include the cavity dither) to do this and restart the model, c1iscex crashed, and so I decided against using the switch block for this trial.
    • The control signal generated using green transmission demodulated at the ETM dither frequencies are used to actuate on M1 while the ITM ones are used to actuate on M2. Of course, by setting the appropriate off-diagonal elements in the output matrix, this can be modified as desired.
  2. The main MEDM screen has been updated to reflect the new additions to the SIMULINK model. Screenshot is attached. The picture isn't entirely accurate as the monitor channels in the upper row actually show the servo output + slider output. This needs to be changed in the model, and a new set of monitors need to be added to the MEDM screen. In the end, we require four sets of monitor-points in the model: PZT dither servo output, cavity dither servo output, sum of these with any offset from the PZT sliders, and the sum of the latter with the dither signal (this is what eventually goes to the PZT mirrors while the dither is on).
  3. I added scripts to the MEDM screen that turn the PZT mirror dither servo on and off. Note that when you want to run a new script on an MEDM screen using medmrun, you need to change the permissions of the file by going to the path where your script is located and running chmod 755 <name of script>. Manasa has updated the same on the wiki.

 Details of tests runs:

For the most part, I have been trying to optimize the PZT mirror dither servo. To this end, I did the following:

  • Went to the X-end and fixed the input pointing which was not optimal. Manasa first aligned the arm and ran ASS to maximize the IR transmission. I then used the coarse adjustment knobs on the mirror mounts to get the green transmission up to ~0.6.
  • I then set the following parameters in the servo (these are all in the script, path to which is /opt/rtcds/caltech/c1/scripts/ASX):
    1. LO frequencies of 10, 19, 34 and 39 Hz respectively for M1 PIT, M1 YAW, M2 PIT and M2 YAW.
    2. LO amplitudes of 75 for all the four degrees of freedom (determined by using PZT calibration to see what amplitude would couple 10% of power into the first higher-order-mode assuming a perfectly aligned beam to start with.
    3. LIA BP filters centered at the above frequencies with 2Hz passband on either side.
    4. LIA LP filters with corner frequency 0.5 Hz.
    5. LIA Signal filter bank gain set to 100 for all degrees of freedom.
    6. LIA Demod I phase filter bank gain set to 5 for all degrees of freedom.
    7. Control filter gains to 1 for all degrees of freedom (control filters are all integrators).
    8. Demod phase set to 0 for all degrees of freedom. I did not really try to optimize this but the servo seems to be doing reasonably well even with this setting.
    9. Overall servo gain to 1 (the servo worked well when I increased this to 5 as well, but became unstable when I increased it further).
  • I ran the servo. Observations were as follows:
    • Having fixed the input pointing to get green transmission up to ~0.6, the servo was able to improve it to ~0.8, which is the best we had after hours spent at the X-end prior to the vent.
    • Given a good input pointing, we can use the PZT mirrors to lock to 00 mode from some misaligned state using either the sliders, or by leaving the servo on, and helping it out at the points where it gets 'stuck' in some higher mode using either the sliders or by toggling the shutter.
    • In order to recover green transmission of ~0.8, it was often necessary to first run ASS to optimize the IR transmission. Otherwise, green-transmission saturates at ~0.6 or 0.4 depending on the misalignment of the arm cavity mirrors. The servo was unable to change the input pointing enough to deal with overly misaligned cavity mirrors. 
    • The servo is sometimes capable of bringing about mode-hopping from a higher order mode to a lower one, though this is not always the case as the PDH lock is sometimes too strong, in which case I toggled the shutter after which the servo kicked in.
    • I tested the servo under as many different conditions as I could. For instance, having left the green shutter open overnight, I saw that the transmission had fallen from 0.8 (which was what we saw on Thursday night) to ~0.4 on Friday morning. Running the servo got the transmission up to 0.6. I then asked Manasa to run ASS, (while leaving the ASX servo on), after which point the green transmission went up to 0.8. Sometimes, the servo locks to a 'bad' 00 mdoe, where the transmission saturates at ~0.2, but toggling the shutter fixes this most of the time.

Attempt to measure transfer function:

One of the things that came up during my presentation was how fast the loop was capable of responding. I was able to get a quantitative idea of this by playing around with the overall servo gain. Initially, it took ~30 seconds for the servo to get the transmission up to its peak value, with a servo gain of 1. When I ramped this up to 5, the response was much faster, with the peak transmission being reached in ~5seconds. 

 

I wanted to get a more quantitative picture, and hence tried to measure the transfer function by first injecting an excitation into the 'SIG' filter-bank in the demodulation stage. However, coherence between the IN1 and IN2 signals was very poor for all the amplitude configurations I tried. At Jenne's suggestion, I tried injecting the excitation at the control-filters stage, but found no improvement. Perhaps the amplitude envelope was wrong or the measurement technique has to be rethought. 


 Misc remarks:

  1. M1 is the first steering mirror and M2 is the second one (right before the beam enters the arm cavity).
  2. Though I have added the cavity dither feature to the model, I was not able to optimize this servo. Some calculations need to be done to get an estimate of the output matrix, after which the filter gains etc can be optimized.
  3. Today, I cleaned up my temporary setup at the SP table to calibrate the PZTs. Most of the hardware for the Y-end is now in the tupperware box. The QPD and laser have been restored to the optical bench next to MC2 where I found them. The second KEPCO HV supply which I had set up has now been installed at 1Y4 in anticipation of the PZT mirrors at the Y-endtables. It is currently powered OFF.
  4. Performance plots to follow as I have not pulled the data out yet.
  5. I had bought a cake from chandler today in an effort to clear my meal plan, but in the rush in the afternoon, completely forgot about it. It is in the fridge, and is strawberry tart, hope it tastes good.

 


 New MEDM screen:

New_ASX_MEDM_MAIN.pdf 

  8995   Mon Aug 12 12:57:59 2013 JenneUpdateCDSX-End Green ASS - Roundup

Quote:
  1. The SIMULINK model has been modified to accommodate an option to dither the cavity mirrors and not the PZT mirrors. Details are as follows:
    • I have sent the LO signals (CLK,SIN and COS) from the ASS model to the ASX model via the RFM model. Appropriate changes were made to all these three models, and recompiling and restarting the models was done without issue. The SIN and COS signals are used to demodulate green transmission at the dither frequencies. ***The CLK signal is not required to be sent between models as it is not being used by ASX (I turn the dither ON using the channels already set up for ASS). I realised this a little late, and at present the ASS and RFM models are compiled such that the CLK signal is also sent from ASS to RFM. This can be removed, thus freeing up 4 unnecessary inter-process communication channels. Also, I am not too sure if this is relevant, but the maximum computation time of both the RFM and ASX models seem to have gone up after I added these inter-process communication links.***

    •  

 Getting rid of the LO transmission will certainly help / be good.  After adding these channels, the RFM model is regularly hitting 62usec (out of a max acceptable of 60).

I'm not really sure why the ASS was involved in this.  I feel like it might have been simpler to just do everything in the ASX model, to keep things cleaner.  Also, the IPC blocks for this stuff (in both ASS and ASX) are not on the top level of the model.  I had thought that this was expressly forbidden (although I'm not sure why).  I'm emailing Jamie, to see if he remembers what, if anything, is breakable if the IPC blocks are down a level.

  8996   Mon Aug 12 13:30:33 2013 JamieUpdateCDSX-End Green ASS - Roundup

Quote:

I'm not really sure why the ASS was involved in this.  I feel like it might have been simpler to just do everything in the ASX model, to keep things cleaner.  Also, the IPC blocks for this stuff (in both ASS and ASX) are not on the top level of the model.  I had thought that this was expressly forbidden (although I'm not sure why).  I'm emailing Jamie, to see if he remembers what, if anything, is breakable if the IPC blocks are down a level.

I'm not sure if it's forbidden by the RCG, but you should definitely NOT do it.  All IO, whether it be between ADC/DACs or IPCs, should always be at the model top level.  That's what keeps things portable, and makes it easier to keep track of where are signals are going/coming from.

  9044   Wed Aug 21 00:18:03 2013 MasayukiSummaryGreen LockingX-arm PDH OLTF measurement

[Manasa Masayuki]
Today we measured the openloop transfer function of the PDH green lock of the x-arm.

Edit //manasa// The excitation was given from SR785 source. SR560 was used as the summing node at the PDH servo box output where the loop was broken to measure the OLTF. The SR785 was used to measure the frequency response (CH2/CH1; CH1 A SR560 output and CH2 A PDH servo output) in sweptsine mode.

We measured with two different servo gain. We started with the servo gain of 3 and at that gain the UGF was 1.5 kHz and the phase margin was 50 degree. After that we increase the servo gain to 5.5 and at that gain the UGF was 6.2 kHz and the phase margin was 55 degree. In all the measurement we use the source amplitude of 1.0 mV for all frequencies (from 100 Hz to 100 kHz). We could not increase the gain and also the source amplitude any more because the green was kicked out of lock.

Next work list
1. In the earlier measurements we found the UGF of the PDH green lock of the x-arm as 10 kHz and the phase margin as 45 degree, so we will investigate what has changed from these measurements.elog 4490

2. We will measure the power spectrum of the error signal and the feedback signal.

3. We will calibrate the above signals to compare with ALS out of loop noise.

netgpib was taking forever to transfer data. So the measurements are just photos of the display.

attachment1 - servo gain 3

IMG_1226.JPG

attachment2 - servo gain 5.5

IMG_1228.JPG

  9047   Wed Aug 21 19:37:25 2013 MasayukiSummaryGreen LockingX-arm PDH OLTF measurement

[Manasa, Masyauki]

Today we measured OLTF of PDH green lock of x-arm again. In the previous measurement the excitation signal was injected at the PDH servo box output(elog 9044), but in this measurement we changed the injection point to the RFPD mixer output (just before the servo input).

We measured the OLTF with the servo gain of 6.5 and source amplitude of 5 mV for all frequency band. The measured UGF was 11 kHz and the phase margin was 48 degree.

Next that measurement, we tried to measure the power spectrum density of the error signal and feedback signal. But the alignment was not so good, so we aligned the green light injection point. Tomorrow we will continue the alignment and will measure the PSD.

attatchment1 - OLTF of PDH green lock with servo gain of 6.5

OLTF_PDH_Glock_6_5_2.png

  4490   Tue Apr 5 21:20:11 2011 KojiSummaryGreen LockingX-arm cavity locked with LB1005 servo box

Last Thursday, I tested Newport Servo Controller LB1005 with the X_arm green PDH servo.

The setup and the settings I could lock the arm is depicted in the attached figure.
To lock the cavity, follow the steps below

1) Toggle the switch to the "lower" position. This disengages the servo and reset the integrator.

2) Toggle the switch to the "middle" position. The zero freq is set to the "PI corner" freq. At the low freq the gain is limited
at the value of "LF Gain Limit". This gives us a single pole at the low freq.

3) Once the lock is acquired, toggle the switch to the "upper" position. This moves the pole freq to DC, resulting in the complete integration of the signal at the low frequency.

I measured the openloop transfer function (attachment 2). The amp is quite fast and exhibits almost no phase delay upto 100kHz.
The UGF was 10kHz with the phase mergin of ~45deg. I had to tune the input offset carefully to stay at the center of the resonance.

Attachment 1: servo.png
servo.png
Attachment 2: OLTF.pdf
OLTF.pdf
  717   Tue Jul 22 22:11:58 2008 YoichiUpdateLSCX-arm g factor measurement
Alberto, Yoichi

We measured the g factor of the X-arm by slightly shifting the 166MHz sideband frequency:

We first locked the X-arm to TEM00 mode. Then misaligned the ETMX in yaw a little bit until the transmitted power is a half of the normal value.
In this way, we can expect that TEM01 mode will be resonated in the arm if a sideband with a suitable frequency is introduced.
To add such a sideband, we used the 166MHz EOM. According to John's calculation (ELog entry 690), the TEM01 mode of the 166MHz upper sideband is only about 100kHz away from the resonance. So by changing the 166MHz modulation frequency, we should be able to see the 166MHz upper sideband resonating in the X-arm.
We used the 166MHz PD at the AS to find the resonance.
When we modulated the 166MHz RF frequency by +/- 100kHz, we could see spikes in the AS166_I signal.
Then we fine tuned the RF frequency slowly by hand to find the exact resonant frequency. At that time, the X-arm PDH servo was oscillating at ~480Hz.
So the resonance was determined by maximizing this signal in the AS166_I.
The 166MHz signal was originally at 165.977195 MHz. I found the resonance around 165.985MHz. It is surprisingly close to the original modulation frequency (only 7.3kHz away). This number yields the g factor of 0.626 and the transverse mode interval of 0.285*FSR. I used the arm length of 38.5750m in this calculation. Because of the 480Hz oscillation, it was difficult to precisely determine the resonant frequency. We will try this again tomorrow after mitigating the oscillation.
Although the resonance of the 166MHz upper sideband is located at a lower frequency in John's prediction, we found a resonance at a higher frequency.
This can be interpreted as the discrepancy between the actual g-factor and the designed g-factor.

To confirm what we saw was really an arm cavity resonance, we will try to do the same thing with the arm cavities all mis-aligned.
(We expect no signal in this configuration.)

Appendix: the expected signal from AS166 port when the 166MHz upper sideband passes by a resonance of the arm cavity.
Since the carrier is resonating in the cavity and kept there by the PDH feedback using 33MHz sideband, its phase is virtually fixed at the AS166 port. The lower sideband's phase also does not change much because it is off resonance. The upper sideband get a large phase change when approaching to the resonance. This effectively rotates the modulation angle of the 166MHz sidebands, which was orthogonal to the carrier when off resonance (i.e. phase modulation), to create 166MHz amplitude modulation. Because the sideband axis is rotated, the signal should appear both in I and Q phases.
  7224   Sat Aug 18 03:55:12 2012 YoichiSummaryLSCX-arm locking again

Tonight, I worked on the X-arm locking again. I did not have any significant progress, but observed several issues and will give some suggestions for future work here.

What I did tonight was basically re-alignment of the X-arm (because Rana touched the PZT mirrors for the Y-arm alignment, the X-arm alignment was screwed up). Then I measured the open loop gain. Of course it was almost identical to the one posted in this entry. It reminded myself of how small the phase bubble is. This means we have to finely adjust the gain to set the UGF at the right frequency, i.e. 100Hz. So I decided to do the signal normalization using the TRX power. Using the MC path method described here,  the appropriate normalization coefficient was determined to be 1.6, when the XARM gain is set to 0.05. Using burtgooey, I updated the burt snapshot used by the X-arm restore script.

Now I observed the following things:

When the normalization is used, the lock itself is stable, but the lock acquisition takes loner (i.e. fails more often).

I don't know the exact reason, but here is my guess: Usually, the error signal is divided by the square root of the transmitted power to widen the linear range of the PDH error signal. However, what I'm doing here is dividing the error signal with the power itself, not the sqrt. This might distort the error signal in a not-friendly-for-lock way ? I don't know.

I checked the c1lsc FE code. There seems to be the sqrt(TRX) and sqrt(TRY) signals computed in the code. However, these are not used for the normalization. 

Now, there are two requirements. When dragging the mirrors into the resonance, we want to normalize the error signal with sqrt(TRX). When the mirrors reach the resonance, the gain of the loop must be normalized by TRX. How do we smoothly connect those two states ? Someone should spend some time on this. Maybe I will work on this in Japan.  

We really need a time delay in the filter trigger

The automatic filter trigger is awesome. However, the [0^2:5^2] filter, which is an integrator, takes time to switch on and off. Every time the cavity passes by a resonance, this filter gets turned on and off slowly, giving some large transients. This transient combined with the bad coil balance of ETMX sometimes made the optical lever of ETMX crazy. This can be avoided by turning on this filter a few seconds after the power reaches the threshold. As Rana suggested, we should be able to put an arbitrary time delay to the filter trigger.

Someone should balance the coils

The coil balance of ETMX is bad and causing the above mentioned problem. I tweaked the coil balance by injecting a sinusoidal signal (10Hz) into ETMX pos and trying to minimizing the spectral peak in the optical lever signals. Of course, this is a cheesy work. Someone should put more serious effort on this.

A civilized interferometer should have an auto-alignment capability

After my alignment work, the X-arm power got to about 0.7. (This is probably because the MC transmission power has been low for the past 5 hours or so (attachment 1)).

In anyway, after the cavity locked to the TEM00 mode, the alignment has to be automatically improved by dithering. It is anachronism to sit down and click on the MEDM screen until the power gets big enough.

 

 

Attachment 1: MC_Trans.png
MC_Trans.png
  11978   Fri Feb 5 15:02:13 2016 gautamUpdateGreen LockingX-end NE cable

[Steve, gautam]

Steve thinks that the X-end Innolight does not come with the noise-eater option (it is an add-on and not a standard feature, and the purchase order for the PSL Innolight explicitly mentions that it comes with the NE option, but the X-end Innolight has no such remarks), which would explain why there is no difference with the noise eater ON/OFF. During earlier investigations however, I had found that there was a cable labelled "Noise-Eater" connected to one of the Modulation Inputs on the rear of the Innolight controller. Today, we traced this down. The modulation input on the rear says "Current Laser Diode 0.1A/V". To this input, a Tee is connected, one end of which is terminated with a 50ohm terminator. The other end of the Tee is connected to a BNC cable labelled "Nosie-Eater", which we traced all the way to the PSL table, where it is just hanging (also labelled "X end green noise eater"), unterminated, at the southeast corner of the PSL table. It is unlikely that this is of any consequence given the indicated coefficient of 0.1A/V, but could this somehow be introducing some junk into the laser diode current which is then showing up as intensity fluctuations in the output? Unfortunately, during the PLL measurements, I did not think to disconnect this BNC and take a spectrum. It would also seem that the noise-eater feedback to the laser diode current is implemented internally, and not via this external modulation input jack (the PSL, which I believe has the noise-eater enabled, has nothing connected to this rear input)...

 

  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
P1070634.JPG
  9584   Tue Jan 28 23:32:12 2014 KojiUpdateGeneralX/Y arm locked with the IR beam

[Koji EricQ]

The both arms have been locked with IR and aligned by ASS.

The IFO was left with ITMX/Y, ETMX/Y, BS, and PRM aligned, and the PSL shutter closed.


YARM
SIGNAL PATH:
POY11I(+45dB)->YARM(G=+1.0)->ETMY
NORM: TRYx10
TRIG: TRY 0.01up/0.005down
FM TRIG: FM2/3/6/7/8/9 0.01up/0.05down, 0.5 sec delay

XARM
SIGNAL PATH:
POX11I(+45dB)->XARM(G=+4.0)->ETMX
NORM: TRXx10
TRIG: TRX 0.01up/0.005down
FM TRIG: FM2/3/6/7/8/9 0.01up/0.05down, 0.5 sec delay


For decent locks, it was necessary that the offset of the error signals are trimmed at the input filters
even after running LSCoffset.py script.

Once the cavities were aligned for the IR, we could see the green beams are also flashing.
The Y arm was actually locked with the green with a TEM00 mode

Attachment 1: good_alignment.png
good_alignment.png
  10492   Wed Sep 10 22:17:29 2014 KojiSummaryLSCX/Y green beat mode overlap measurement

[Koji Manasa]

We made quantitative inspection of the X/Y green beat setup on the PSL table.

DC output of the BBPD for each arm was measured by blockiing the beams at either or both side of the recombination BS.

The power over lap for the X arm beat note setup was 7.8% and is now 53%.
There is 3dB of headroom for the improvement of the mode overlap.

The power over lap for the Y arm beat note setup was 1.2% and is now 35%.
There is 4dB of headroom for the improvement of the mode overlap.

The RF analyzer monitor for the beat power is about 10dB lower than expected. Can we explain this only by the cable loss?
If not it there something causing the big attenuation?


             XARM   YARM
o BBPD DC output (mV)

 V_DARK:   -  3.3  + 1.9
 V_PSL:    +  4.3  +22.5
 V_ARM:    +187.0  + 8.4


o BBPD DC photocurrent (uA)

I_DC = V_DC / R_DC ... R_DC: DC transimpedance (2kOhm)

 I_PSL:       3.8   10.3
 I_ARM:      95.0    3.3


o Expected beat note amplitude
I_beat_full = I1 + I2 + 2 sqrt(e I1 I2) cos(w t) ... e: mode overwrap (in power)

I_beat_RF = 2 sqrt(e I1 I2)

V_RF = 2 R sqrt(e I1 I2) ... R: RF transimpedance (2kOhm)

P_RF = V_RF^2/2/50 [Watt]
     = 10 log10(V_RF^2/2/50*1000) [dBm]

     = 10 log10(e I1 I2) + 82.0412 [dBm]
     = 10 log10(e) +10 log10(I1 I2) + 82.0412 [dBm]


for e=1, the expected RF power at the PDs [dBm]
 P_RF:      -12.4  -22.6


o Measured beat note power (before the alignment)     
 P_RF:      -23.5  -41.7  [dBm] (38.3MHz and 34.4MHz) 
    e:        7.8    1.2  [%]                         
o Measured beat note power (after the alignment)      
 P_RF:      -15.2  -27.1  [dBm] (26.6MHz and 26.8MHz) 
    e:       53     35    [%]                         

Measured beat note power at the RF analyzer in the control room
 P_CR:      -25    -20    [dBm]
Expected    -17    - 9    [dBm]

Expected Power:
Pin + External Amp Gain (0dB for X, 20dB for Y)
    - Isolation trans (1dB)
    + GAV81 amp (10dB)
    - Coupler (10.5dB)


  11368   Mon Jun 22 12:57:09 2015 ericqSummaryLSCX/Y green beat mode overlap measurement redone

I took measurements at the green beat setup on the PSL table, and found that our power / mode overlap situation is still consistent with what Koji and Manasa measured last September [ELOG 10492]. I also measured the powers at the BBPDs with the Ophir power meter.

Both mode overlaps are around 50%, which is fine. 

The beatnote amplitudes at the BBPD outputs at a frequency of about 50MHz are -20.0 and -27.5 dBm for the X and Y beats, respectively. This is consistent with the measured optical power levels and a PD response of ~0.25 A/W at 532nm. The main reason for the disparity is that there is much more X green light than Y green light on the table (factor of ~20), and the greater amount of green PSL light on the Y BBPD (factor of ~3) does not quite make up for it. 

One way to punch up the Y beat a little might be to adjust the pickoff optics. Of 25uW of Y arm transmitted green light incident on the polarizing beamsplitter that seperates the X and Y beams, only 13uW makes it to the Y BBPD, but this would only win us a couple dBms at most. 

In any case, with the beat setup as it exists, it looks like we should design the next beatbox iteration to accept RF inputs of around -20 to -30 dBm. 


In the style of the referenced ELOG, here are today's numbers. 

            XARM   YARM 
o BBPD DC output (mV)
 V_DARK:   +  1.0  + 2.2
 V_PSL:    +  7.1  +21.3
 V_ARM:    +165.0  + 8.2


o BBPD DC photocurrent (uA)
I_DC = V_DC / R_DC ... R_DC: DC transimpedance (2kOhm)

 I_PSL:       3.6   10.7
 I_ARM:      82.5    4.1


o Expected beat note amplitude
I_beat_full = I1 + I2 + 2 sqrt(e I1 I2) cos(w t) ... e: mode overwrap (in power)

I_beat_RF = 2 sqrt(e I1 I2)

V_RF = 2 R sqrt(e I1 I2) ... R: RF transimpedance (2kOhm)

P_RF = V_RF^2/2/50 [Watt]
     = 10 log10(V_RF^2/2/50*1000) [dBm]

     = 10 log10(e I1 I2) + 82.0412 [dBm]
     = 10 log10(e) +10 log10(I1 I2) + 82.0412 [dBm]

for e=1, the expected RF power at the PDs [dBm]
 P_RF:      -13.2  -21.5


o Measured beat note power (no alignment done)     
 P_RF:      -20.0  -27.5  [dBm] (53.0MHz and 46.5MHz) 
    e:       45.7   50.1  [%]                         

 

  11370   Mon Jun 22 14:53:37 2015 ranaSummaryLSCX/Y green beat mode overlap measurement redone
  • Why is there a factor of 20 power difference? Some of it is the IR laser power difference, but I thought that was just a factor of 4 in green.
  • Why is the mode overlap only 50% and not more like 75%?
  • IF we have enough PSL green power, we could do the Y-beat with a 80/20 instead of a 50/50 and get better SNR.
  • The FFD-100 response is more like 0.33 A/W at 532 nm, not 0.25 A/W.

In any case, this signal difference is not big, so we should not need a different amplifier chain for the two signals. The 20 dB of amplification in the BeatBox was a fine way, but not great in circuit layout.

The BBPD has an input referred current noise of 10 pA/rHz and a transimpedance of 2 kOhm, so an output voltage noise of 20 nV/rHz (into 50 Ohms). This would be matched by an Amp with NF = 26 dB, which is way worse than anything we could bur from mini-circuits, so we should definitely NOT use anything like the low-noise, low output power amps used currently (e.g. ZFL-1000LN....never, ever use these for anything). We should use a single ZHL-3A-S (G = 25 dB, NF < 6 dB, Max Out = 30 dBm) for each channel (and nothing else) before driving the cables over to the LSC rack into the aLIGO demod board. I just ordered two of these now.

  12587   Fri Oct 28 15:46:29 2016 gautamSummaryLSCX/Y green beat mode overlap measurement redone

I've been meaning to do this analysis ever since putting in the new laser at the X-end, and finally got down to getting all the required measurements. Here is a summary of my results, in the style of the preceeding elogs in this thread. I dither aligned the arms and maximized the green transmission DC levels, and also the alignment on the PSL table to maximize the beat note amplitude (both near and far field alignment was done), before taking these measurements. I measured the beat amplitude in a few ways, and have reported all of them below...

             XARM   YARM 
o BBPD DC output (mV), all measured with Fluke DMM
 V_DARK:     +1.0    +3.0
 V_PSL:      +8.0    +14.0
 V_ARM:      +175.0  +11.0


o BBPD DC photocurrent (uA)
I_DC = V_DC / R_DC ... R_DC: DC transimpedance (2kOhm)

 I_PSL:       3.5    5.5
 I_ARM:      87.0    4.0


o Expected beat note amplitude
I_beat_full = I1 + I2 + 2 sqrt(e I1 I2) cos(w t) ... e: mode overlap (in power)

I_beat_RF = 2 sqrt(e I1 I2)

V_RF = 2 R sqrt(e I1 I2) ... R: RF transimpedance (2kOhm)

P_RF = V_RF^2/2/50 [Watt]
     = 10 log10(V_RF^2/2/50*1000) [dBm]

     = 10 log10(e I1 I2) + 82.0412 [dBm]
     = 10 log10(e) +10 log10(I1 I2) + 82.0412 [dBm]

for e=1, the expected RF power at the PDs [dBm]
 P_RF:      -13.1  -24.5


o Measured beat note power (measured with oscilloscope, 50 ohm input impedance)      
 P_RF:      -17.8dBm (81.4mVpp)  -29.8dBm (20.5mVpp)   (38.3MHz and 34.4MHz)  
    e:        34                    30  [%]                          
o Measured beat note power (measured with Agilent RF spectrum analyzer)       
 P_RF:      -19.2  -33.5  [dBm] (33.2MHz and 40.9MHz)  
    e:       25     13    [%]                          

I also measured the various green powers with the Ophir power meter: 

o Green light power (uW) [measured just before PD, does not consider reflection off the PD]
 P_PSL:       16.3    27.2
 P_ARM:       380     19.1

Measured beat note power at the RF analyzer in the control room
 P_CR:      -36    -40.5    [dBm] (at the time of measurement with oscilloscope)
Expected    -17    - 9    [dBm] (TO BE UPDATED)

Expected Power: (TO BE UPDATED)
Pin + External Amp Gain (25dB for X, Y from ZHL-3A-S)
    - Isolation trans (1dB)
    + GAV81 amp (10dB)
    - Coupler (10.5dB)


The expected numbers for the control room analyzer in red have to be updated. 

The main difference seems to be that the PSL power on the Y broadband PD has gone down by about 50% from what it used to be. In either measurement, it looks like the mode matching is only 25-30%, which is pretty abysmal. I will investigate the situation further - I have been wanting to fiddle around with the PSL green path in any case so as to facilitate having an IR beat even when the PSL green shutter is closed, I will try and optimize the mode matching as well... I should point out that at this point, the poor mode-matching on the PSL table isn't limiting the ALS noise performance as we are able to lock reliably...

  12531   Tue Oct 4 22:18:24 2016 JohannesUpdateGeneralX/YARM loss measurement

[gautam, johannes]

We let the PSL shutter closed overnight and observed the POXDC, POYDC and ASDC offsets. While POY has small fluctuations compared to the signal level, POX is worse off, and the drifts we observed live in the DC reading are in the same ballpark as the offset fluctuations. The POXDC level also unexpectedly increased suddenly without the PSL shutter being opened, which we can't explain. The data we took using POXDC cannot be trusted.

Even the ASDC occasionally shows some fluctuations, which is concerning because the change in value rivals the difference between locked and misaligned state. It turns out that the green shutters were left open, but that should not really affect the detectors in question.

We obtained loss numbers by measuring the arm reflections on the ASDC port instead. LSCoffsets was run before the data-taking run. For each arm we misaligned the respective other ITM to the point that moving it no longer had an impact on the ASDC reading. By taking a few quick data points we conclude the following numbers:

XARM: 247 ppm +/- 12 ppm
YARM: 285 ppm +/- 13 ppm

This is not in good agreement with the POYDC value. The script is currently running for the YARM for better statistics, which will take a couple hours.

ITMX is misaligned for the purpose of this measurement, with the original values saved.

GV edit 5Oct2016: Forgot to mention here that Johannes marked the spot positions on the ITMs and ETMs (as viewed on the QUAD in the control room) with a sharpie to reflect the current "well aligned" state.

Attachment 1: anomalousData.png
anomalousData.png
  8554   Wed May 8 22:36:42 2013 KojiUpdateASSXARM ASS (YARM ASS - faster and more precise convergence)

Same ASS setup for the X arm has been done.

Now Arm ASS can run simultaneously.

I reverted the number of the lockin banks from 6 to 8 for future implementation of A2L for the ITMX by coil balancing.
Since A2L for the ITMX is just barely visible for now, I am going to leave the coil balance untouched.

Attachment 1: XARM_ASS.png
XARM_ASS.png
  16732   Thu Mar 17 16:50:53 2022 PacoUpdateBHDXARM AUX alignment

[Ian, Paco]

We opened the ITMX chamber and

  • Inspected PR2 and LO1 and didn't see anything suspicious.
  • Took the EQ stops off ITMX in preparation for alignment

Alignment:

  • Ian started at the ETMX station, slightly tweaking the M1 M2 XAUX mirrors by hand and Paco on the ITMX chamber looking at the beam. The beam was visibly making it to the ITMX optic and reflecting back though at a negative pitch angle. No small motion on the M1-M2 knobs caused visible correction on this.
  • We decided to try adding an alignment offset to ITMX, and quickly saturated to 25000 (on the SUS screen) but fell short of fully correcting this PIT offset.
  • We scanned further the M1 M2 input alignment, and briefly lost the first reflection.
    • We recovered the first reflection, but the beam spot is now incident near the LL OSEM position.
  • We kept scanning M1 - M2 with Ian on the ITMX chamber this time, providing feedback through facetime.
  • Leaning on the ITMX chamber table, we noticed the magnitude of PIT correction left to be done and verified that M1-M2 two axis alignment + ITMX offsets should be enough for it.

We stopped our effort here, the XAUX beam spot is near the lower half of the ITMX face. Tomorrow, we will resume, but we will use airpods and a clean go-pro for real-time audiovisual feedback. Furthermore, ITMX OSEMs should be rebalanced as they haven't been touched after the table was balanced for PR2 and LO1.

  16735   Fri Mar 18 17:15:19 2022 PacoUpdateBHDXARM AUX alignment cont.

[Paco, Ian]

First, we re-balanced the ITMX OSEMs so that they would damp at around half-a-shadow.


Then, we set up a clean camera inside ITMX chamber looking at the ITMX optic. Then, using the live feed we aligned the AUX beam from the ETMX station using M1 and M2. The camera was great to help us align the beam properly close to the ITMX center. It wasn't very long until we could see a green beam on the IR card, but we didn't really see any flashing, so this may just be the bare transmission away from XARM resonance (Attachment #1).

Ian checked the reflection from ITMX using the IR card with holes, and he pretty much only saw one beam spot, so we turned to look for a beam scattering on the vacuum tube but didn't really see anything. This could mean that we were hitting the ETMX again, or missing slightly, or missing completely. We tried scanning the ITMX pitch and yaw using the bias (alignment) sliders, and with the illuminators off, try seeing some scattered green beam on the ETMX. We can't really see anything yet, but we will keep trying. If there are any tips on our method, it would be great to know them.

Attachment 1: Screen_Shot_2022-03-18_at_4.09.38_PM.png
Screen_Shot_2022-03-18_at_4.09.38_PM.png
  16739   Mon Mar 21 18:00:05 2022 Ian MacMillanUpdateBHDXARM AUX alignment cont.

[Ian, Paco]

Continuing with the previous alignment that we stoped on friday, we re set up my heavily cleaned iPhone on FaceTime. The Phone alowed us to see the laser on the ITMX and center it on that optic.

  • We increased the trigger level for the watchdog on the optics.
  • Green beam was centered on th ITMX.
  • aligned the green laser: prompt reflection off of the ETMX to maximize the signal on the reflection PD
  • Went back to ITMX chamber, looked for the beam in the tube to see if the laser was hitting the beam tube off of the ITMX. From there we comunicated how to adjust the beam to move the beam towards the ETMX.
  • On the ETMX the reflection PD signal was measured and the ITMX was adjusted using CDS until ripples/"flashes" were seen in the reflection PD channel (C1:ALS-X_REFL_DC_OUT_DQ).
  • Once we saw flashing we tried to minimize the reflection pd signal using only ITMX alignment slider so that all the light was being held in the cavity.
  • Once we had this going the PDH lock engaged the higher order mode that we were seeing.
  • We removed the phone setup and closed up the ITMX chamber.
  • From here we moved to the control room and continude to adjust the ITMX and ETMX to see if we could lock to a lower order mode.
    • This proved unsuccessful so we will resume by trying to replicate the ASS action manually (with M1 - M2 PZT sliders and the REFL PD)
Attachment 1: PXL_20220322_015247138.jpg
PXL_20220322_015247138.jpg
  16399   Wed Oct 13 15:36:38 2021 HangUpdateCalibrationXARM OLTF

We did a few quick XARM oltf measurements. We excited C1:LSC-ETMX_EXC with a broadband white noise upto 4 kHz. The timestamps for the measurements are: 1318199043 (start) - 1318199427 (end).

We will process the measurement to compute the cavity pole and analog filter poles & zeros later.

Attachment 1: Screenshot_2021-10-13_15-32-16.png
Screenshot_2021-10-13_15-32-16.png
  16363   Tue Sep 28 16:31:52 2021 PacoSummaryCalibrationXARM OLTF (calibration) at 55.511 Hz

[anchal, paco]

Here is a demonstration of the methods leading to the single (X)arm calibration with its budget uncertainty. The steps towards this measurement are the following:

  1. We put a single line excitation through the C1:SUS-ETMX_LSC_EXC at 55.511 Hz, amp = 1 counts, gain = 300 (ramptime=10 s).
  2. With the arm locked, we grab a long timeseries of the C1:LSC-XARM_IN1_DQ (error point) and C1:SUS-ETMX_LSC_OUT_DQ (control point) channels.
  3. We assume the single arm loop to have the four blocks shown in Attachment #1, A (actuator + sus), plant (mainly the cavity pole), D (detection + electronics), and K (digital control).
    1. At this point, Anchal made a model of the single arm loop including the appropriate filter coefficients and other parameters. See Attachments #2-3 for the split and total model TFs.
    2. Our line would actually probe a TF from point b (error point) to point d (control point). We multiplied our measurement with open loop TF from b to d from model to get complete OLTF.
    3. Our initial estimate from documents and elog made overall loop shape correct but it was off by an overall gain factor. This could be due to wrong assumption on RFPD transimpedance or analog gains of AA or whitening filters. We have corrected for this factor in the RFPD transimpedance, but this needs to be checked (if we really care).
  4. We demodulate decimated timeseries (final sampling rate ~ 2.048 kHz) and I & Q for both the b and d signals. From this and our model for K, we estimate the OLTF. Attachment #4 shows timeseries for magnitude and phase.
  5. Finally, we compute the ASD for the OLTF magnitude. We plot it in Attachment #5 together with the ASD of the XARM transmission (C1:LSC-TRX_OUT_DQ) times the OLTF to estimate the optical gain noise ASD (this last step was a quick attempt at budgeting the calibration noise).
    1. For each ASD we used N = 24 averages, from which we estimate rms (statistical) uncertainties which are depicted by error bands (\pm \sigma) around the lines.

** Note: We ran the same procedure using dtt (diaggui) to validate our estimates at every point, as well as check our SNR in b and d before taking the ~3.5 hours of data.

Attachment 1: OLTF_Calibration_Scheme.jpg
OLTF_Calibration_Scheme.jpg
Attachment 2: XARM_POX_Lock_Model_TF.pdf
XARM_POX_Lock_Model_TF.pdf
Attachment 3: XARM_OLTF_Total_Model.pdf
XARM_OLTF_Total_Model.pdf
Attachment 4: XARM_OLTF_55p511_Hz_timeseries.pdf
XARM_OLTF_55p511_Hz_timeseries.pdf
Attachment 5: Gmag_55p511_Hz_ASD.pdf
Gmag_55p511_Hz_ASD.pdf
  16369   Thu Sep 30 18:04:31 2021 PacoSummaryCalibrationXARM OLTF (calibration) with three lines

[anchal, paco]

We repeated the same procedure as before, but with 3 different lines at 55.511, 154.11, and 1071.11 Hz. We overlay the OLTF magnitudes and phases with our latest model (which we have updated with Koji's help) and include the rms uncertainties as errorbars in Attachment #1.

We also plot the noise ASDs of calibrated OLTF magnitudes at the line frequencies in Attachment #2. These curves are created by calculating power spectral density of timeseries of OLTF values at the line frequencies generated by demodulated XARM_IN and ETMX_LSC_OUT signals. We have overlayed the TRX noise spectrum here as an attempt to see if we can budget the noise measured in values of G to the fluctuation in optical gain due to changing power in the arms. We multiplied the the transmission ASD with the value of OLTF at those frequencies as the transfger function from normalized optical gain to the total transfer function value.

It is weird that the fluctuations in transmission power at 1 mHz always crosses the total noise in the OLTF value in all calibration lines. This could be an artificat of our data analysis though.

Even if the contribution of the fluctuating power is correct, there is remaining excess noise in the OLTF to be budgeted.

Attachment 1: XARM_OLTF_Model_and_Meas.pdf
XARM_OLTF_Model_and_Meas.pdf XARM_OLTF_Model_and_Meas.pdf
Attachment 2: Gmag_ASD_nb_withTRX.pdf
Gmag_ASD_nb_withTRX.pdf Gmag_ASD_nb_withTRX.pdf Gmag_ASD_nb_withTRX.pdf
  7170   Tue Aug 14 04:37:06 2012 YoichiSummaryLSCXARM Open Loop Gain

Yoichi, Rana

Here is the open loop gain of the XARM loop.

The reference is from the pre-upgrade era. We get the extra phase delay because we have two anti-aliasing filters. One is the hardware filter at about 7kHz for 16kHz sampling. This filter should have been replaced to the one for 64kHz sampling but it has not yet happened. The second one is the software anti-aliasing filter applied when down sampling from 64kHz to 16kHz. So we have double AA filters, which are the culprits for the extra phase delay.

We should either replace the hardware AA filter to the 64kHz one (preferred way), or change the software AA filter to a less aggressive one (easier temporary fix).

Attachment 1: xarm-opltf.png
xarm-opltf.png
  16303   Mon Aug 30 17:49:43 2021 PacoSummaryLSCXARM POX OLTF

Used diaggui to get OLTF in preparation for optimal system identification / calibration. The excitation was injected at the control point of the XARM loop C1:LSC-XARM_EXC. Attachment 1 shows the TF (red scatter) taken from 35 Hz to 2.3 kHz with 201 points. The swept sine excitation had an envelope amplitude of 50 counts at 35 Hz, 0.2 counts at 100 Hz, and 0.2 at 200 Hz. In purple continous line, the model for the OLTF using all the digital control filters as well as a simple 1 degree of freedom plant (single pole at 0.99 Hz) is overlaid. Note the disagreement of the OLTF "model" at higher frequencies which we may be able to improve upon using vector fitting.

Attachment 2 shows the coherence (part of this initial measurement was to identify an appropriately large frequency range where the coherence is good before we script it).

Attachment 1: XARM_POX_OLTF.pdf
XARM_POX_OLTF.pdf
Attachment 2: XARM_POX_Coh.pdf
XARM_POX_Coh.pdf
  16304   Tue Aug 31 14:55:24 2021 ranaSummaryLSCXARM POX OLTF

this model doesn't seem to include the analog AA, analog AI, digital AA, digital AI, or data transfer delays in the system. I think if you include those you will get more accuracy at high frequencies. Probably Anchal has those included in his DARM loop model?

 

  16351   Tue Sep 21 11:09:34 2021 AnchalSummaryCDSXARM YARM UGF Servo and Oscillators added

I've updated the c1LSC simulink model to add the so-called UGF servos in the XARM and YARM single arm loops as well. These were earlier present in DARM, CARM, MICH and PRCL loops only. The UGF servo themselves serves a larger purpose but we won't be using that. What we have access to now is to add an oscillator in the single arm and get realtime demodulated signal before and after the addition of the oscillator. This would allow us to get the open loop transfer function and its uncertaintiy at particular frequencies (set by the oscillator) and would allow us to create a noise budget on the calibration error of these transfer functions.

 

The new model has been committed locally in the 40m/RTCDSmodels git repo. I do not have rights to push to the remote in git.ligo. The model builds, installs and starts correctly.

  16354   Wed Sep 22 12:40:04 2021 AnchalSummaryCDSXARM YARM UGF Servo and Oscillators shifted to OAF

To reduce burden on c1lsc, I've shifted the added UGF block to to c1oaf model. c1lsc had to be modified to allow addition of an oscillator in the XARm and YARM control loops and take out test points before and after the addition to c1oaf through shared memory IPC to do realtime demodulation in c1oaf model.

The new models built and installed successfully and I've been able to recover both single arm locks after restarting the computers.

 

  16830   Wed May 4 15:08:59 2022 TegaUpdateBHDXARM alignment to get flashing

[Yuta, Tega]

We aligned the BS, ITMY, and ETMY PIT and YAW to get the flashing on X-arm whilst also keeping the flashing of Y-arm. From attachment 1, it is clear that POXDC photodiode is not receiveing any light, so our next task is to work on POX alignment.

 

Quote:
  • Align X-arm cavity and regain flashing.
  • Fix the Oplev path for ITMX.
  • Tune POX11 phase angle to get an error signal with which we can lock the cavity.
  • Finish AS beam path setup.

 

Attachment 1: IFO_XY_ARMS_Flashing.png
IFO_XY_ARMS_Flashing.png
  16352   Tue Sep 21 11:13:01 2021 PacoSummaryCalibrationXARM calibration noise

Here are some plots from analyzing the C1:LSC-XARM calibration. The experiment is done with the XARM (POX) locked, a single line is injected at C1:LSC-XARM_EXC at f0 with some amplitude determined empirically using diaggui and awggui tools. For the analysis detailed in this post, f0 = 19 Hz, amp = 1 count, and gain = 300 (anything larger in amplitude would break the lock, and anything lower in frequency would not show up because of loop supression). Clearly, from Attachment #3 below, the calibration line can be detected with SNR > 1.

We read the test point right after the excitation C1:LSC-XARM_IN2 which, in a simplified loop will carry the excitation suppressed by 1 - OLTF, the open loop transfer function. The line is on for 5 minutes, and then we read for another 5 minutes but with the excitation off to have a reference. Both the calibration and reference signal time series are shown in Attachment #1 (decimated by 8). The corresponding ASDs are shown in Attachment #2. Then, we demodulate at 19 Hz and a 30 Hz, 4th-order butterworth LPF, and get an I and Q timeseries (shown in Attachment #3). Even though they look similar, the Q is centered about 0.2 counts, while the I is centered about 0.0. From this time series, we can of course show the noise ASDs in Attachment #3.


The ASD uncertainty bands in the last plot are statistical estimates and depend on the number of segments used in estimating the PSD. A thing to note is that the noise features surrounding the signal ASD around f0 are translated into the ASD in the demodulated signals, but now around dc. I guess from Attachment #3 there is no difference in the noise spectra around the calibration line with and without the excitation. This is what I would have expected from a linear system. If there was a systematic contribution, I would expect it to show at very low frequencies.

Attachment 1: XARM_signal_asd.pdf
XARM_signal_asd.pdf
Attachment 2: XARM_demod_timeseries.pdf
XARM_demod_timeseries.pdf
Attachment 3: XARM_demod_asds.pdf
XARM_demod_asds.pdf
Attachment 4: XARM_cal_0921_timeseries.pdf
XARM_cal_0921_timeseries.pdf
  16353   Wed Sep 22 11:43:04 2021 ranaSummaryCalibrationXARM calibration noise

I would expect to see some lower frequency effects. i.e. we should look at the timeseries of the demod with the excitation on and off.

I would guess tat the exc on should show us the variations in the optical gain below 3 Hz, whereas the exc off would not show it.

Maybe you should do some low pass filtering on the time series you have to see the ~DC effects? Also, reconsider your AA filter design: how do you quantitatively choose the cutoff frequency and stopband depth?

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