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ID Date Authorup Type Category Subject
  536   Tue Jun 17 22:00:53 2008 JohnHowToPSLProblems turning MZ servo on/off
We were unable to toggle the MZ servo on/off (Blank/Normal) from MEDM. Pushing on the Xycom board and cables changed the fault from constant to intermittent. At least one lock loss has been caused by a MZ glitch.
  557   Tue Jun 24 15:15:09 2008 JohnSummaryLSCLocking efforts
Rob, Rana, John

In the past week or so we've been working on reducing the CARM offset using a DC signal (SPOB DC).
We were able to get up to arm powers of around 30 (where a single arm cavity lock is a power of 1)
before instability set in and we would lose lock for, as yet, unknown reasons.

In recent nights locking efforts have taken a few backward steps.

Since last Thursday engaging the AO path has proved troublesome, i.e. engaging it would instantly
cause loss of lock. This seems to be related to problems with the mode cleaner servo. For the past
few nights it has been behaving strangely and could not be operated with the usual super boost stages.
Last night the situation was improved. MC boost stages could be used and the AO path engaged. The
cause of this problem and its spontaneous resolution are not understood.

Last night we were unable to switch CARM to SPOB DC. I've attached a spectrum of the MC2 length signal.
This path is being used for CARM and so gives an indication of the frequency noise after the mode
cleaner. At the moment the plot is calibrated in units of Rana's gut feeling. We already tested to see if
any of the excess noise was introduced by the WFS. No evidence was found. We'll try to make a useful
calibration soon and see if our problems are related to excess frequency noise.

Another realisation from last night was the effect of arm detuning on the analogue CARM path. When CARM is detuned
the coupled cavity pole removes an extra 90 degrees of phase. The digital path has the `moving zero' to compensate
for this. The analogue path has no such compensation and can therefore become unstable at moderate detunings.
We propose trying to reduce the CARM offset further before engaging the analogue path. This will give higher
gain and move the UGF to a region of increased phase margin.
Attachment 1: mcl080623.png
  562   Wed Jun 25 01:30:19 2008 JohnSummaryIOOFrequency noise after the MC
I made some (very) rough estimates of the contribution made to the noise after the mode cleaner by three sources.

Seismic noise - how much of the signal is due to the mode cleaner compenstaing for seismic disturbance of CARM.
Actuator noise - coil drivers and DAC noise.
MC_F - estimate of MC_F suppressed by the loop gain.
Attachment 1: MC2noise080623.png
  568   Wed Jun 25 13:56:56 2008 JohnSummaryLockingTuesday night locking
Rob, John

Worked to try and reduce the CARM offset using the dc arm transmissions before changing to SPOB DC. This proved somewhat unsuccessful, the offset couldn't be reduced to more than five (arms storing 5x more power than single arm cavity lock).
  573   Thu Jun 26 12:30:40 2008 JohnSummaryLockingCARM on REFL_DC

Try REFL_DC as the error signal for CARM rather than PO_DC.


The PO signal is dominated by sideband light when the arms are detuned so that any misalignment in the recycling cavity introduces spurious signals. Also, the transfer function from coupled cavity excitation to REFL signal is not so steep and hence REFL should give a little more phase. Finally, the slope of the REFL signal should make it easier to hand over to RF CARM.


The REFL signal showed no clear improvement over PO signals. We've gone back to PO.

During the night we also discovered that the LO for the MC loop is low.
  582   Fri Jun 27 14:36:39 2008 JohnSummaryLocking 
Rob, Yoichi, John

Some progress last night:

Switched back to SPOB_DC for CARM.

Shaped the MC LSC loop to reduce excess noise in the 20-30Hz band. Likely the most significant change.
Could this be due to fan noise from the laptop on the SPOB table?

Brought in the AO path earlier (at low gain).

Reduced offset to 6 and increased MC gain before handing off to SPOB. Ramped up AO and MC gain then switched off the
moving zero.

Looks like PD11 is the most promising candidate for RF CARM although the demod phase needs attention.
Attachment 1: gettingcloser.png
  586   Fri Jun 27 19:59:44 2008 JohnUpdateComputersc1iovme
C1susvme2 and C1iovme crashed which sent the optics swinging and tripped the watchdogs.

Koji and I were able to restore c1susvme2 without any trouble.

We have been unable to revive c1iovme. We have tried telneting in and running startup.cmd,
the process runs for a while then hangs with "DAQ init failed -- exiting".

Resetting the board doesn't help. I didn't try keying the whole crate.

All optics are back to normal with damping restored.
  588   Sat Jun 28 14:56:44 2008 JohnUpdateComputersini files
In short, I was editing the ini files yesterday evening, I didn't e-log it and after some investigation this afternoon it apears
that I am to blame for all the computer problems which followed.

I wanted to edit C0EDCU.ini and C1IOOF.ini to change C1: PSL-FSS_FAST to a fast channel as C1: PSL-FSS_FAST_F
was dead.

I opened these files and made backups. It appears this is where it all went awry. My backup for C1IOOF
is called C1IOO.ini.090627 i.e. missing the F.

Later c1susvme2 and c1iovme crashed. After failing to bring c1iovme back I wondered if my edits had
caused the problems so I restored the back up files. It appears that here I wrote over C1IOO with my backup of
C1IOOF (presumably because I had made a typo in the name).

To remedy the situation we could restore C1IOO from e.g. chans/archive/C1IOO_080618_160028.ini

No excuses for not e-logging this activity.
  589   Sat Jun 28 23:23:50 2008 JohnUpdateComputersRebooting
All of the computers are now showing green lights.

Remaining problems:

Alignment scripts are failing with "ERROR: LDS - NDS server error #13"
I think this is a server transmission error.

Dataviwer shows all channels as zero.
  591   Sun Jun 29 11:31:52 2008 JohnSummaryPSLISS
I reduced the gain of the ISS (C1: PSL-ISS_VGAGAIN) from 5dB to 2dB. Any higher and it constantly saturates.
  595   Sun Jun 29 19:53:26 2008 JohnSummaryPSLISS

I reduced the gain of the ISS (C1: PSL-ISS_VGAGAIN) from 5dB to 2dB. Any higher and it constantly saturates.

Seemed to go back to normal after the frame builder came back.
  596   Sun Jun 29 20:09:40 2008 JohnSummaryIOOmcup and mcdown indicators
I edited the mcup and mcdown scripts so that C1IFO_STATE shows when these scripts are running.

I also added indicators to the LockMC screen.
Attachment 1: mcscreen.png
Attachment 2: ifostate.png
  598   Mon Jun 30 01:49:06 2008 JohnUpdateIOOMC work
I'm in the process of aligning the mode cleaner/ input beam.

I turned off the WFS and cleared their histories, adjusted the input periscope and re-aligned the mode-cleaner accordingly.
I then unlocked the cavity and centred the beams on the WFS.

MC transmission is ~3.3 and the REFL beam looks a little better.

However, turning the WFS on now lowers the transmission. More thought tomorrow.

I'm leaving the MC locked with WFS off.
  601   Mon Jun 30 09:46:15 2008 JohnUpdateIOOMC WFS
MC WFS are on. They seem to do some good during the day.
  604   Mon Jun 30 15:08:52 2008 JohnSummaryPSLMZ alignment
I adjusted the alignmnet of the Mach-Zehnder's two North mirrors (downstream of the EOMs).

MZ REFL is reduced from 0.54 to 0.43. The largest improvement was due to pitch on the PZT mirror.
Attachment 1: mzalign.png
  613   Tue Jul 1 12:51:34 2008 JohnSummaryGeneralIFO alignment
Rana, Rob, Yoichi, John

The recent computer problems and MZ work had disturbed the alignment of the interferometer.

We adjusted the MC alignment back to nominal positions using old OSEM values. We then walked
the input beam to match the MC. Coupling into the interferometer has increased noticeably.
The rest of the IFO was then aligned to the new input beam.

Proceeding to full IFO locking we were able to engage the AO path and hand off CARM to SPOBDC.
Arm powers got up to 4.

If the new alignment proves successful we will centre all QPDs etc so we can easily return to
this state.
Attachment 1: align080701.png
  618   Tue Jul 1 21:45:48 2008 JohnUpdatePSLMach Zehnder script and screen
I've edited C1: PSL_MACH_ZEHNDER.adl and /cvs/cds/caltech/scripts/PSL/MZ/lockMZ
to reflect the changes described in entry #616.
  625   Wed Jul 2 17:19:03 2008 JohnSummaryComputersop440m - shutdown and restarted
After 160days op440m was getting a little slow.
  626   Wed Jul 2 18:30:01 2008 JohnUpdateIOOQPD alignment
I aligned the beams on the following QPDs

Attachment 1: IOO080702.png
Attachment 2: MC080702.png
  633   Thu Jul 3 16:57:23 2008 JohnSummaryGeneralFSS_RMTEMP
The FSS room temp alarm has been beeping a lot recently. I altered the FSS_RMTEMP alarm levels using the
same method as Rana.

The alarm is still souding so, at least by my calculations, it must be colder than usual.
Attachment 1: FSStime.png
Attachment 2: FSSalarm.png
  644   Tue Jul 8 00:14:28 2008 JohnSummaryComputersAlarm handler
Rob thought it would be nice to have some alarms on the cpu loads and FE syncs.
I added all these channels to the alarm handler config file and wrote a script
which would set their values (HIHI,HIGH etc).

Ezcawrite allowed me to set the alarm levels (and ezcaread would give the correct
value) but no matter what I set the value to the alarm wouldn't sound.

After experimenting with a few other channels it appears that the alarm handler will
not show alarms if the alarm levels are absent from the db file (even though ezca
gives a value).

I edited the following files so we can have alarms on the cpus.

In c1iscepics:

In c1losepics:

I saved backups in the appropriate folders.

Next time we have a bootfest please also do c1iscepics and c1losepics so these changes
will be implemented.
  648   Tue Jul 8 12:25:54 2008 JohnSummaryPSLISS gain set to 2dB
  651   Wed Jul 9 12:42:14 2008 JohnUpdateLockingHand off to RF CARM
Rob, Yoichi, John

Last night we were able to reduce the CARM offset to around 80. This was achieved by increasing the DARM gain and
switching to AS_I when AS_Q went bad. This is probably a temporary solution, we will probably switch to DC readout
for DARM as we bring the arms on resonance.

Having reduced the arm offset enough to get us into the linear region of the RF_CARM signal (POX_I) we worked on
analogue conditioning of this signal to allow us to hand over. Lock was maintained for over 20 minutes as we did
this work.

We were able to partially switch over both the frequency and length paths to this new signal before losing lock.
Attachment 1: LongLock080709.png
  653   Wed Jul 9 17:58:19 2008 JohnSummaryGeneralIlluminator alarms
This morning some time was wasted on alignment due to the illuminators.

I added the illuminators to the alarm handler. They will give a RED alarm whenever
they are turned on. You can find the alarms in 40M->Misc->Illuminators.

To do this I edited the Illuminators.db file and restarted c1aux by telneting and typing Ctl-X.
I then added the groups and channels to 40M.alhConfig.
  657   Thu Jul 10 23:27:57 2008 JohnMetaphysicsCamerasSecret handshakes
Rob and I have joined the ranks of the illuminati and exercised our power.

Osamu showed me the secret way to change the video labels for the quads and
so we fixed them. He made me swear not to divulge this art.

- Rana Adhikari
  664   Sun Jul 13 22:39:16 2008 JohnSummaryGeneralEdited medm screens
I've edited the FSS and PMC screens so that red boxes are shown around the appropriate slider if a gain or offset is not within the limits defined in C1PSL_SETTINGS_SET.adl

With the current setting of 0 V the FSS input offset is red. According to the settings screen the nominal value is 0.3 +/- 0.050. Are there any objections to editing the nominal value?

I changed the LockMC screen so that red boxes are not shown when the up/down scripts are not running; when they are active you should see a green box.
  665   Mon Jul 14 00:36:19 2008 JohnSummaryPSLSlow sweep of laser temp - PMC PZT response
John, Rana

Follow up to # 663

Top trace: C1: PSL-PMC_PZT

The only calibration I could find for the PMC PZT (LLO e-log Sep 3 2003 - 23 MHz/V) predicts 31V for an FSR. I did a rough calibration and got our FSR to be around 210 V. I assumed 713 MHz for an FSR and applied this calibration (~3.4 MHz/ V) to the PZT data.

In terms of volts per metre our PZT gives 2.54 nm/ V whereas the LLO PZT is 17.16 nm/ V.
Attachment 1: SlowTsweep.png
  667   Mon Jul 14 12:43:07 2008 JohnSummaryComputersRestarted fb40m, tpman and c1ass
  675   Tue Jul 15 12:44:08 2008 JohnSummaryLockingDRFPMI with DC readout
Rob, John

Last night, despite suspect alignment, we were again able to reduce the CARM offset to zero using
the RF signal.We were also able to transfer to dc readout taking calibrated spectra in both states.
DC readout shows a marked improvement over RF above ~1kHz but introduces some noise around 100Hz.
Broadband sensitivity appears to be more than ten times worse than previously. The calibration
being used remains to be confirmed.

Engaging the ETMY dewhitening caused lock to be lost. We'll check this today. The OMC alignment loops
may also need some attention.

We looked at REFL_166 as a candidate for CARM, at present POX still looks better.

The DARM filters were modified to reduce excess noise around 3Hz. Updating filter coefficients does
not cause loss of lock.
  684   Wed Jul 16 17:36:51 2008 JohnDAQPSLFSS input offset
I changed the nominal FSS input offset to 0 from 0.3. Tolerance remains unchanged at +/-0.05.
  690   Thu Jul 17 13:08:37 2008 JohnSummaryLSCHOM resonances in the arms
On Tuesday night we attempted to lock the full DRFPMI in the optical spring configuration with the +f2 sideband resonant in the SRC.
Despite having no problems locking on the +f2 in a DRM we couldn't lock the full IFO.

There was some discussion about whether a +f2 higher order mode resonance in the arms could cause this problem.

I calculated the positions of the first six higher order modes for the carrier and all sidebands (using Siegman p 762 (23) with a plus sign).
Plot attached. Colors indicate different frequency components, numbers are the mode index (m+n). Thick lines are fundamental modes of
the sidebands. Heights of HOM indicators have been scaled by 1/(m+n)^2.

It appears that the first order transverse mode of the +166 is indeed partially resonant. We might try to tweak the sideband frequencies a
little to see if this helps us. It would probably be prudent to measure the MC length first.

Numbers used:

L = 38.5750; %average of Alberto's recent measurements elog #556
Retm = 57.375;
f166 = 165.977195e6;
f33 = 33.195439e6;
Attachment 1: HOMresonances.png
  830   Tue Aug 12 21:38:19 2008 JohnUpdateLSCAccidental higher order mode resonances in the arms
Recently we had been having some trouble locking the full IFO in the spring configuration (SRC on +166).
It was thought that an accidental higher order mode resonance in the arms may have been causing problems.

I previously calculated the locations of the resonances using rough arm cavity parameters(Elog #690). Thanks to Koji
and Alberto I have been able to update this work with measured arm length and g factors for the y arm (Elog #801,#802).
I have also included the splitting of the modes caused by the astigmatic ETM. Code is attached.

I don't see any evidence of +166MHz resonances in the y arm.

In the attached plot different colours denote different frequencies +33, -33, +166, -166 & CR.
The numbers above each line are the mn of TEMmn.
Solid black line is the carrier resonance.
Attachment 1: HOMresonances.png
Attachment 2: HOMarms2.m
%Check for accidental resonances of HOM in the arms (maybe due to
%sidebands). At the moment there is only data for the y arm.

clear all
close all

%Stuff one might change often
modeorder = 0:5;          % Look for TEMmn modes where m,n run over modeorder
... 157 more lines ...
  858   Wed Aug 20 11:42:49 2008 JohnSummaryComputerspdftk
I've installed pdftk on all the control room machines.

  859   Wed Aug 20 11:50:10 2008 JohnSummaryComputersStripTools on op540m

To restart the striptools on op540m:

cd /cvs/cds/caltech/scripts/general/

  14111   Sat Jul 28 22:16:49 2018 John MartynUpdate Characterization of Transimpedance Amplifier

Kevin and I meaured the transfer function of the photodiode circuit using the Jenne laser and agilent in the 40m lab. The attached figures depict our measured transfer function over the modulation frequency ranges of 30kHz-30MHz and 1kHz-30MHz when the power of the laser was set to 69 and 95 μW. These plots indicate a clear roll off frequency around 300 kHz. In addition, the plots beginning at 1kHz display unstable behavior at frequencies below 30kHz. I am not sure why there is such a sharp change in the transfer function around 30kHz, but I suspect this to be due to an issue with the agilent or photodiode. 

Attachment 1: PD_TF1.pdf
Attachment 2: PD_TF2.pdf
Attachment 3: PD_and_TIA_Transfer_Function_Measurements.zip
  8757   Wed Jun 26 15:11:08 2013 John ZweizigUpdateSUSNDS2 Status


I've restarted the NDS2 process on Megatron so that we can use it for getting past data and eventually from outside the 40m.

1) from /home/controls/nds2 (which is not a good place for programs to run) I ran nds2-megatron/start-nds2

2) this is just a script that runs the binary from /usr/bin/ and then leaves a log file in ~/nds2/log/

3) I tested with DTT that I could access megatron:31200 and get data that way.

There is a script in usr/bin called nds2_nightly which seems to be the thing we should run by cron to get the channel list to get updated, but I' m not sure. Let's see if we can get an ELOG entry about how this works.

Then we want Jamie to allow some kind of tunneling so that the 40m data can be accessed from outside, etc.

 I have done the following:

  * installed the nds2-client in /ligo/apps/nds2-client

  * moved the nds2 configuration directories to /ligo/apps/nds2/nds2-megatron

  * set up a cron job to update the channel list every morning at 5 am. The cron line is:

     15 5 * * * /usr/bin/nds2_nightly /ligo/apps/nds2/channel-tracker /ligo/apps/nds2/nds2-megatron

    cron will send an email each time the channel list changes, at which point you will have to restart the server with:

     cd /ligo/apps/nds2/nds2-megatron
     pkill nds2

  * restarted nds2 with updated channel lists.

  8787   Fri Jun 28 17:33:33 2013 John ZweizigUpdateSUSNDS2 Status



I've restarted the NDS2 process on Megatron so that we can use it for getting past data and eventually from outside the 40m.

1) from /home/controls/nds2 (which is not a good place for programs to run) I ran nds2-megatron/start-nds2

2) this is just a script that runs the binary from /usr/bin/ and then leaves a log file in ~/nds2/log/

3) I tested with DTT that I could access megatron:31200 and get data that way.

There is a script in usr/bin called nds2_nightly which seems to be the thing we should run by cron to get the channel list to get updated, but I' m not sure. Let's see if we can get an ELOG entry about how this works.

Then we want Jamie to allow some kind of tunneling so that the 40m data can be accessed from outside, etc.

 I have done the following:

  * installed the nds2-client in /ligo/apps/nds2-client

  * moved the nds2 configuration directories to /ligo/apps/nds2/nds2-megatron

  * set up a cron job to update the channel list every morning at 5 am. The cron line is:

     15 5 * * * /usr/bin/nds2_nightly /ligo/apps/nds2/channel-tracker /ligo/apps/nds2/nds2-megatron

    cron will send an email each time the channel list changes, at which point you will have to restart the server with:

     cd /ligo/apps/nds2/nds2-megatron
     pkill nds2

  * restarted nds2 with updated channel lists.

 I have set the cron job up to restart the nds2 server automatically if the channel list changes. The only change is that the cron command was changes to /ligo/apps/nds2/nds2-megatron/test-restart.


  9216   Mon Oct 7 18:32:01 2013 John ZweizigSummaryComputer Scripts / Programsnds2 installed, restarted

The upgrade of megatron broke the nds2 service. I have fixed things by

  1) installing the latest version of framecpp (1.19.32) from the lsc debian repository (this was necessary because I couldn't link to the existing version)

  2) built nds2-server-0.5.11 and installed it in the system directories (/usr/bin)

  3) there were a few scripts/links/etc that didn't seem to be set up correctly and I fixed them to correspond with my preious message.

 nds2 is now running and the channel list should be updated regularly and the service restarted as appropriate.


  612   Tue Jul 1 12:08:38 2008 John, JoeConfigurationPSLPMC input PD
Joe and I switched cables so that the PMCR screen actually shows reflection not transmission.

The trans camera had a BNC connected to "video out" labelled PMC input PD. The video signal
going to the monitors does not come from "video out", it comes out the "DC in/sync" cable.
As far as we can see this diode doesn't exist. Where should the PMC input PD BNC cable be
  602   Mon Jun 30 13:48:47 2008 John, RobConfigurationPSLDon't put the bin in front of the air conditioning unit
We spotted that the laser power was dropping.

The air conditioning unit was blocked by the blue bin/trash can/cestino causing the laser head temp to increase by 2 degrees.

Let's be careful about this in the future.
Attachment 1: binremoval.png
  711   Tue Jul 22 03:03:22 2008 John, RobUpdatePSLFSS open loop transfer function
With the common gain slider maxed out the unity gain frequency is 58kHz.

The reference cavity refl diode appears to be okay. RF OUT/ TEST IN transfer function was normal.
There is a ~220mV offset in the RF out. We removed this using a coupler - no change. We also checked the
diode->FSS cable.

Tomorrow I'll take a closer look at the board.
  715   Tue Jul 22 13:16:09 2008 John, RobUpdatePSLFSS open loop transfer function

With the common gain slider maxed out the unity gain frequency is 58kHz.

The reference cavity refl diode appears to be okay. RF OUT/ TEST IN transfer function was normal.
There is a ~220mV offset in the RF out. We removed this using a coupler - no change. We also checked the
diode->FSS cable.

Tomorrow I'll take a closer look at the board.

Should note that the UGF of 58kHz was measured with the test cable (from RFPD to board), so the demod phase was presumably sub-optimal.
  13976   Sat Jun 16 20:57:59 2018 JonUpdateGeneralPRC modescan attempt

Here's a Finesse modeling of what we're expecting to observe with this test. It uses Gautam's base model of the 40m IFO with appropriate modifications for the needed configuration.

The idea is to lock the IFO in the SRMI configuration, with the phase-locked AUX beam injected from the AS port. The AUX beam is imprinted with AM sidebands and slightly misaligned relative to the SRC so as to transfer power into HOM1. The RF network analyzer provides the drive signal for the AOM, and its frequency is swept to coherently measure the transfer function [reflected AUX beam / drive]. The reflected AUX beam is sensed by the AS110 PDA10CF.

It is also possible to drive PM sidebands as Koji suggests, but the squeezer group has encouraged using AM for practical advantages. The SNR with AM is a bit higher (less power lost into harmonics at large modulation index), there is a broadband AOM already available aligned to the SQZ beam at LLO, and there is also concern that driving strong PM could interfere with the SQZ control loops.

Expected SRMI Response

Attachment #1 shows the expected response to swept-AM in SRMI. Resolving just the FSR and the first-order mode splitting is sufficient to extract the SRC Gouy phase.

Expected response in the SRMI configuration.

Expected DRMI Response

Since the 40m has not been opearted in SRMI since ~2016 (last done by Eric Q.), Gautam believes it may take some time to relock this configuration. However, the modeling indicates that we can likely obtain sufficient sensitivity in DRMI, which would allow us to proceed faster. Attachment #2 shows the expected response to swept-AM in DRMI. The PRC leakage signal turns out to be significantly smaller than the SRC reflection (a factor of ~30 in amplitude), so that the signal still retains its characteristic shape to a very good approximation. The tradeoff is a 10x reduction in SNR due to increased PSL shot noise reaching AS110.

Expected DRMI response. The main difference is a 10x increase in shot noise on AS110.

Based on this, we should proceed with DRMI scans instead of PRMI next week.


The PRC FSR is, of course, very close to twice of our f1 moudlation frequency (11MHz x 2 = 22MHz) .

I still don't understand what response the measurement is looking for. I understood the idea of using the subcarrier as a stablized carrier to the PRC with a certain freq offset from the main carrier. I suppose what was swept was the AOM modulation frequency (i.e. modulation frequency of the AM applied to the subcarrier). If that is the case, the subcarrier seemed fixed at an arbitorary frequency (i.e. 50MHz) away from the carrier. If one of the AM sidebands hits the PRC resonance (i.e. 22, 44, 66MHz away from the main carrier), you still have the other sideband reflected back to the AS. Then the RF signal at the AS is still dominated by this reflected sideband. I feel that the phase modulation is rather suitable for this purpose.

If you are talking about ~MHz AM modulation by the AOM and scanning the PLL frequency from 1MHz to 60MHz, the story is different. And this should involve demodulation of the AS signal at the AM modulation frequency. But I still don't understand why we don't use phase modulation, which gives us the PDH type signal at the reflection (i.e. AS) port...



Attachment 1: 40M_SRMI_AM_annotated.pdf
Attachment 2: 40M_DRMI_AM.pdf
  13987   Tue Jun 19 18:56:55 2018 JonUpdateGeneralAUX beam alignment issues

Not much progress today with the AUX cavity scans. I've determined there still are some alignment issues.

At the start of today a large AUX/PSL beat note was visible on the AS110 sensor, at a similar power as where we left off last night (-60 dBm). Proceeding from there, I attempted to reproduce Johannes' measurement of the cavity transmission resonances. I misaligned the X-arm, locked the Y-arm cavity, and scanned the AUX RF offset approximately 8 MHz in 2 kHz steps. This should have swept through two FSRs, but nothing was visible.

Further inspection revealed that none of the PSL light was making it back to through the AUX fiber to the PSL table. I take this to mean that the beam seen earlier on AS110 was the ITMY reflection, and that the AUX injection axis was no longer reaching ETMY. I also found that the AUX beam size just after the 90/10 beasmsplitter looks anomolously large. Maybe a lens was recently changed? In any case, the mode-matching looks like it is going to need to be readjusted.

  13994   Thu Jun 21 09:33:02 2018 JonUpdate AUX Mode Scans of YARM, PRC cavities

[Jon, Keerthana, Sandrina]

Yesterday we carried out preliminary proof-of-concept measurements using the new AS-port-injected AUX laser to resolve cavity mode resonances.

At the time we started, I found the beat note levels consistent with what Johannes had reported the night before post-realignment. Hence we did not change the AUX alignment.

Test 1: YARM Mode Scan

  • IFO locked in YARM configuration on carrier.
  • Confirmed the presence of a -80 dBm beat note on the temporary YEND broadband PD (i.e., at the cavity transmission).
  • Slowly canned the RF offset of the AUX laser from 50 MHz (nominal) to 60 MHz in 10 kHz steps.
  • Attachment 1 shows the measured scan in "max hold" mode. The bottom panel is the transmission spectrum and the top panel is the reflection, with the AUX/PSL carrier-carrier beat note visible to the far left. In addition to the FSR, it looks to me like the scan resolves at least two HOMs.

Test 2: PRC Mode Scan

  • IFO locked in PRMI configuration on carrier.
  • Moved the temporary 150 MHz PDA10CF from the YEND to an unused pickoff of the REFL33 beam (i.e., the PRC transmission of the AUX beam). There was an existing 50-50 beamsplitter just before REFL33 whose reflected beam was directed onto a beam dump. The PD is now placed in that location. The modification to the AS table is shown in Attachment 2.
  • We made a similar slow scan of the AUX RF offset over ~35 MHz in 10 kHz steps.
  • We resolve the 22 MHz FSR, but it is apparent that an incoherent "max-hold" analyzer measurement is inadequate. The problem is that in max-hold mode, because the 11 MHz-spaced PSL sidebands also beat with the AUX subcarrier, we measure a messy superposition of the PSLcarrier-AUXcarrier beat AND all of the PSLsideband-AUXcarrier beats. The next step is to use the AOM to make a coherent measurement at only the frequency of PSL/AUX carrier-carrier beat.

The SURFs have the data from last night's scans and will be separately posting plots of these measurements. We'll continue today with mode scans using AM sidebands rather than the AUX RF offset.

Attachment 1: YARM_AUX_RF-offset_scan.pdf
Attachment 2: temp_broadband_refl33.pdf
  14010   Sat Jun 23 13:08:41 2018 JonUpdateAUXFirst Coherent AUX Scan of PRC Using AM Sidebands

[Jon, Keerthana, Sandrine]

Thu.-Fri. we continued with PRC scans using the AUX laser, but now the "scanned" parameter is the frequency of AM sidebands, rather than the frequency of the AUX carrier itself. The switch to AM (or PM) allows us to coherently measure the cavity transfer as a function of modulation frequency.

In order to make a sentinel measurement, I installed a broadband PDA255 at an unused pickoff behind the first AUX steering mirror on the AS table. The sentinel PD measures the AM actually imprinted on the light going into the IFO, making our measurement independent of the AOM response. This technique removes not only the (non-flat) AOM transfer function, but also any non-linearities from, e.g., overdriving the AOM. The below photo shows the new PD (center) on the AS table.

With the sentinel PD installed, we proceeded as follows.

  • Locked IFO in PRMI on carrier.
  • Locked AUX PLL to PSL.
  • Tuned the frequency of the AUX laser (via the RF offset) to bring the carrier onto resonance with the PRC.
  • Swept the AOM modulation frequency 0-60 MHz while measuring the AUX reflection and injection signals.

The below photo shows the measured transfer function [AUX Reflection / AUX Injection]. The measurement coherence is high to ~55 MHz (the AOM bandwidth is 60 MHz). We clearly resolve two FSRs, visible as Lorentzian dips at which more AUX power couples into the cavity. The SURFs have these data and will be separately posting figures for the measurements.

With the basic system working, we attempted to produce HOMs, first by partially occluding the injected AUX beam with a razor blade, then by placing a thin two-prong fork in the beam path. We also experimented with using a razor blade on the output to partially occlude the reflection beam just before the sensor. We were able to observe an apparent secondary dip indicative of an HOM a few times, as shown below, but could not repeat this deterministically. Besides not having fine control over the occlusion of the beams, there is also large few-Hz angular noise shaking the AS beam position. I suspect from moment to moment the HOM content is varying considerably due to the movement of the AS beam relative to the occluding object. I'm now thinking about more systematic ways to approach this.


  14020   Tue Jun 26 17:20:33 2018 JonConfigurationCamerasLLO Python Camera Software is Working

Thanks to a discussion yesterday with Joe Betzweiser, I was able to identify and fix the remaining problem with the LLO GigE camera software. It is working now, currently only on rossa, but can be set up on all the machines. I've started a wiki page with documentation and usage instructions here:


This page is also linked from the main 40m wiki page under "Electronics."

This software has the ability to both stream live camera feeds and to record feeds as .avi files. It is described more on the wiki page.

  14033   Fri Jun 29 18:16:32 2018 JonConfigurationPSLChanges to AUX Optical Layout on PSL Table

In order to use the 0th-order deflection beam from the AOM for cavity mode scans, I've coaligned this beam to the existing mode-matching/launch optics set up for the 1st-order beam.

Instead of being dumped, the 0th-order beam is now steered by two 45-degree mirrors into the existing beam path. The second mirror is on a flip mount so that we can quickly switch between 0th-order/1st-order injections. None of the existing optics were touched, so the 1st-order beam alignment should still be undisturbed.

Currently the 0th-order beam is being injected into the IFO. After attenuating so as to not exceed 100 mW incident on the fiber, approximately 50 mW of power reaches the AS table. That coupling efficiency is similar to what we have with the 1st-order beam. With the Y-arm cavity locked and the AUX PLL locked at RF offset = 47.60 MHz (an Y-arm FSR), I observed a -50 dBm beat note at Y-end transmission.

Attachment 1: PSL_AUX_SETUP_CHANGE.pdf
  14035   Tue Jul 3 11:59:10 2018 JonUpdateAUXAUX Carrier Scan of Y-Arm Cavity

I made the first successful AUX laser scan of a 40m cavity last night.

Attachment #1 shows the measured Y-end transmission signal w.r.t. the Agilent drive signal, which was used to sweep the AUX carrier frequency. This is a distinct approach from before, where the carrier was locked at a fixed offset from the PSL carrier and the frequency of AM sidebands was swept instead. This AUX carrier-only technique appears to be advantageous.

This 6-15 MHz scan resolves three FSR peaks (TEM00 resonances) and at least six other higher-order modes. The raw data are also enclosed (attachment #2). I'll leave it as an excercise for the SURFs to compute the Y-arm cavity Gouy phase.

Attachment 1: yarm_carrier_trans.pdf
Attachment 2: AG4395A_02-07-2018_185504.txt
# AG4395A Measurement - Timestamp: Jul 02 2018 - 18:55:04
#---------- Measurement Parameters ------------
# Start Frequency (Hz): 6000000.0, 6000000.0
# Stop Frequency (Hz): 15000000.0, 15000000.0
# Frequency Points: 801, 801
# Measurement Format: LOGM, PHAS
# Measuremed Input: AR, AR
#---------- Analyzer Settings ----------
# Number of Averages: 16
# Auto Bandwidth: Off, Off
... 807 more lines ...
  14036   Wed Jul 4 19:11:49 2018 JonUpdateAUXMore Testing of AUX-Laser Mode Scanning

More progress on the AUX-laser cavity scans.

Changes to the Setup

  • For scans, the Agilent is now being used as a standalone source of the LO signal provided to the AUX PLL (instead of the Marconi), which sets the RF offset. We discovered that when the sweep is "held" in network analyzer mode, it does not turn off the RF drive signal, but rather continues outputting a constant signal at the hold frequency. This eliminates the need to use the more complicated double-deomdulation previously in use. The procedure is to start and immediately hold the sweep, then lock the PLL, then restart the sweep. The PLL is able to reliably remain locked for frequency steps of up to ~30 kHz. The SURFs are preparing schematics of both the double- and single-demodulation techniques.
  • Both the Marconi and Agilent are now phase-locked to the 10 MHz time reference provided by the rabidium clock. This did noticeably shift the measured resonance frequencies.
  • I raised the PI controller gain setting to 4.5, which seems to better suppress the extra noise being injected.
  • I've procured a set of surgical needles for occluding the beam to produce HOMs. However, I have not needed to use them so far, as the TEM00 purity of the AUX beam appears to already be low. The below scans show only the intrinisic mode content.

New Results

  • YARM scan at 70 uW injection power (Attachment #1). The previously reported YARM scan was measured with 9 mW of injected AUX power, 100x larger than the power available from the SQZ laser at the sites. This scan repeats the measurement with the AUX power attenuated to uW. It still resolves the FSR and at least three HOMs.
  • PRC scan (Attachment #2) at 9 mW injection power. It appears to resolve the FSR and at least three HOMs. Angular injection noise was found to cause large fluctuations in the measured signal power. This dominates the error bars shown below, but affects only the overall signal amplitude (not the peak frequency locations). The SQZ angular alignment loops should mitigate this issue at the sites.

Both data sets are attached.

Attachment 1: yarm_trans_70uW.pdf
Attachment 2: prc_trans_9mW.pdf
Attachment 3: yarm_carrier_trans_70uW.tar.gz
Attachment 4: prc_carrier_trans_9mW.tar.gz
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