An update on calibration of the BS actuator : A fitting has been done.
- status update on LSC activity :
The measurement of the LSC sensing matrix has begun. But no useful results yet.
The measurement script (#4850) ran pretty well after I did some modifications to adopt the script to the latest LSC model.
However the SNR weren't so great particularly in REFL33 in the PRMI configuration.
So I will tune the amplitude of excitations and integration times tomorrow.
Currently the excitation is at 238.1 Hz, where no disturbing structures are found in the spectra.
The lock of DRMI wasn't stable enough to measure the sensing matrix. Failed.
PRMI and SRMI were okay and in fact they could stay locked robustly for a long time.
I added a new option in the C1IFO_CONFIGURE screen so that one can choose Signal-Recycled Michelson in carrier resonant condition.
Additionally the orthogonalization of the I-Q signals on REFL55 should be done because it hasn't been done.
Anyway, things are working now:
Good job ! Thank you so much
To make things faster, I think we can just make a LOCKIN which has 3 inputs: it would have one oscillator, but 6 mixers. Should be simple to make.
I think the idea of having multiple inputs in a LOCKIN module is also good for the LSC sensing matrix measurement.
Because right now I am measuring the responses of multiple sensors one by one while exciting a particular DOF by one oscillator.
Moreover in the LSC case the number of sensors, which we have to measure, is enormous (e.g. REFL11I/Q, REFL33I/Q, REFL55I/Q, ... POY11I/Q,...) and indeed it has been a long-time measurement.
I made some attempts to measure the sensing matrix of the central part.
I could measure the matrix in the PRMI configuration but wasn't able to measure the matrix in the DRMI configuration.
=> I will report the result of the PRMI sensing matrix tomorrow.
The main reason why I couldn't lock DRMI was that the suspensions were touchy and especially the SRM suspension wasn't good.
Some impacts due to the feedback during the lock acquisition completely kicks SRM away.
The watchdogs' RMS monitor on SRM easily rang up to more than 10 counts once the acquisition started.This is quite bad.
Also the stability of the PRMI lock was strongly depending on the gains of the PRM oplevs.
I guess I have to revisit the vertex suspensions more carefully (i.e. f2a coupling, actuator output matrix, damping gains, input matrices, oplev filters)
otherwise any LSC works in the vertex will be totally in vain.
[Suresh / Koji / Rana / Kiwamu]
Last night we had a discussion about what we do for the RFAM issue. Here is the plan.
1. Build and install an RFAM monitor (a.k.a StochMon ) with a combination of a power splitter, band-pass-filters and Wenzel RMS detectors.
=> Some ordering has started (#5682). The Wenzel RMS detectors are already in hands.
2. Install a temperature sensor on the EOM. And if possible install it with a new EOM resonant box.
=> make a wheatstone bridge circuit, whose voltage is modulated with a local oscillator at 100 Hz or so.
3. Install a broadband RFPD to monitor the RFAMs and connect it to the StochMon network.
=> Koji's broadband PD or a commercial RFPD (e.g. Newfocus 1811 or similar)
4. Measure the response of the amount of the RFAM versus the temperature of the EO crystal.
=> to see whether if stabilizing the temperature stabilizes the RFAM or not.
5. Measure the long-term behavior of the RFAM.
=> to estimate the worst amount of the RFAM and the time scale of its variation
6. Decide which physical quantity we will stabilize, the temperature or the amount of the RFAM.
7. Implement a digital servo to stabilize the RFAMs by feeding signals back to a heater
=> we need to install a heater on the EOM.
8. In parallel to those actions, figure out how much offsets each LSC error signal will have due to the current amount of the RFAMs.
=> Optickle simulations.
9. Set some criteria on the allowed amount of the RFAMs
=> With some given offsets in the LSC error signal, we investigate what kind of (bad) effects we will have.
The following optics were kicked:
Wed Oct 19 04:22:53 PDT 2011
I made some efforts to fix the situation of SRM but it is still bad.
The POS motion wasn't well damped. Something is wrong either (maybe both) sensing part or actuation part.
I am going to check the sensing matrix with the new free swinging spectra (#5690)
When I was trying to lock SRMI I found that the fringes observed at the AS camera didn't show spatial higher order modes, which is good.
So I thought the SRM suspension became quiet, but it actually wasn't. Because the RMS monitor of the SRM OSEMs already went to about 30 counts.
At the same time the opelev error signals were well suppressed. It means some DOFs which were insensitive to the oplev were ringing up, namely POS and SIDE.
According to the LSC error signal and the ASDC signal, I believe that the POS was going wild (although I didn't check the OSEM spectra).
+ Readjusted the f2a filters (see the attachment).
+ Tried to eliminate a coupling between the POS and SIDE drives by tweaking the output matrix.
=> In order to eliminate the coupling from the POS drive to SIDE sensor, I had to put a comparable factor into an element.
So it might be possible that the POS sensor was showing the SIDE signal and vice versa.
In order to check it I left SRM free swinging (#5690).
The SRM oplevs were found to be oscillating because of a small phase margin.
I reduced the gains to the half of them. The peak which Steve found today maybe due to this oscillation.
The SRM bounce peak 18.33 Hz. Suresh helped me to retune filter through Foton, but we failed to remove it.
Kiwamu removed the 18.3 Hz ocsillation by turning down the oplev servo gain.
Status update on dichroic mirror:
I got the specification sheet of an aLIGO 2" dichroic mirror from Lisa.
This is the one from ATF. It has low loss, a high R for 1064 nm and high T for 532 nm. So it matches our needs.
Based on this sheet we may reset some of the parameters in the specification (e.g. incident angle and etc.,) and will get a quote from ATF.
We will buy 3 of them, including 1 spare. First I need to review the specification.
The SRM input matrix has been readjusted.
However still there is the unwanted coupling from the POS drive to SIDE signal and from the SIDE drive to POS signal.
Some of the sub-suspension screens need labels to describe what those row and column are.
The mechanical shutter on the Y end is now fully functional.
The mechanical shutter on the Y end is now fully functional.
It is newly named to 'C1AUX_GREEN_Y_Shutter' in the EPICS world.
It uses the same binary output channel which had been served for the POY shutter.
To change the EPICS name I edited a db file called ShutterInterLock.db, which resides in /cvs/cds/caltech/target/c1aux.
After editing the file I rebooted the c1aux machine, by telnet and the reboot command in order to make the change effective.
Also I added this new shutter on the ALS overview screen (see the attachment below)
The ETMY shutter can be remotely switched from medm screen POY of mechanical shutters.
The new cable from ETMY controller goes to east vertex EV-ISCT where it is connected to POY shutter hook up BNC cable.
[Koji / Kiwamu]
We tried finding a possible clipping in the vertex part.
We couldn't find an obvious location of a clipping but found that the recycling gain depended on the horizontal translation of the input beam.
We need more quantitative examination and should be able to find a sweet spot, where the recycling gain is maximized.
(what we did)
+ locked the carrier-resonant PRMI.
+ with IR viewers we looked at the inside of ITMX, ITMY and BS chambers to find an obvious clipping.
=> found two suspicious bright places and both were in the ITMY chamber.
(1) POY pick off mirror : looked like a small portion of a beam was horizontally clipped by the mirror mount but not 100% sure whether if it is the main beam or a stray beam.
(2) The top of an OSEM cable connectors tower : although this is in the way of the SRC path and nothing to do with PRC.
+ Made a hypothesis that the POY mirror is clipping the main beam.
+ To reject/prove the hypothesis we shifted the translation of the incident beam horizontally such that more beam hits on the suspicious mirror
+ Realigned and relocked PRMI.
=> Indeed the recycling gain went down from 6 to 0.8 or so. This number roughly corresponds to a loss of about 50%.
However the MICH fringe still showed a very nice contrast (i.e. the dark fringe was still very dark).
Therefore our conclusion is that the POY mirror is most likely innocent.
The RF distribution box has been modified so that it generates two more 55 MHz LO signals.
After the modification I put the box back in place.
Then I checked the MICH and YARM locking quickly as a working test of the distribution box and it is working fine so far.
I will update the diagram of the RF distribution box (#4342) tomorrow.
Since we newly installed POP55 (#5743) an LO signal was needed for the demodulation.
However the RF distribution box didn't have any extra LO outputs.
Therefore we had to make a modification on the RF distribution box so that we can have a 55MHz LO signal for POP55.
Eventually I made two more 55MHz outputs including one spare.
The box actually had two extra output SMAs which had been just feed-thru connectors on the front panel without any signals going through.
In the box the modules consist of two categories; the 11MHz system and 55MHz system. I modified only a part of the 55MHz system.
The modification was done in this way:
* split two branches of 55MHz into four branches by installing two new power splitters (ZMSC-2-1).
* made and installed some SMA cables whose length were adjusted to be nicely fit in the box.
* readjustment of the RF levels to 0-2 dBm at the outputs by replacing some attenuators.
* checked the signals if all of them were happily coming out or not.
Also I found that the POX11 and POY11 demod boards were connected to the whitening filters in a wrong way.
The I and Q signals were in a wrong order. So I corrected them so that the upper inputs in the whitening filter is always the I signal.
(RF levels on 55MHz LO outputs)
Since the demod board requires a certain level of the RF signal as as LO, the LO signals have to be 0-2 dBm.
Here are the RF level in each 55MHz output after the adjustment of the level.
AS55 = 0.76 dBm
REFL55 = 0.76 dBm
POP55 = 0.79 dBm
spare = 0.83 dBm
Those numbers were measured by an oscilloscope and the oscilloscope was configured to measure the rms with the input impedance matched to 50Ohm.
In the measurement I used the actual input seed 55MHz signal from the RF generation box to drive the distribution box.
The diagram of the RF distribution box has been updated according to the modification ( #5744).
Both pdf and graffle files are available on the 40m svn : https://nodus.ligo.caltech.edu:30889/svn/trunk/suresh/40m_RF_upgrade/
Here shows the latest version of the diagram.
The amount of offsets in the LSC signals due to the RFAMs have been estimated by an Optickle simulation.
The next step is to think about what kind of effects we get from the RFAMs and estimate how much they will degrade the performance.
(Results : Offsets in LSC error signals)
For clarity, I also note the definition of PM/AM ratio as well as how the first order upper sideband looks like.
I found that the sum of the ITMX oplev signals had gone down to zero yesterday.
I checked the ITMX table and found two iris on the He-Ne laser path were blocking the beam on their apertures.
I guess this is because we were working around there for installation of POP/POX and may have touched some of the oplev optics.
Then I fully opened the apertures of those two iris and the sum went back to nominal of 600 counts.
The POX beam had been 80% clipped at a black glass beam dump of the POX11 RFPD.
I steered the first mirror in the POX path to fix the clipping. Then the beam was realigned onto the RFPD.
However the beam is still very close to the black glass, because the incident angle to the second mirror is not 45 deg .
We need to refine the arrangement of the POX11 optics a bit more so that the beam will never be clipped at the black glass.
The POP optics also need to be rearranged to accommodate one more RFPD.
Additionally Rana, Suresh and I discussed the possible solutions of POP22/110 and decided to install a usual PD (PDA10A or similar) instead of a custom-made.
So a plan for the POP detectors will be something like this:
+ design an optical layout.
+ buy a 2 inch lens whose focul length is long enough (#5743)
+ buy a 2 inch lens whose focul length is long enough (
+ rearrange the optics and install POP22/110
+ lay down a long SMA cable which sends the RF signal from POP22/110 to the LSC rack.
+ install a power splitter just before the demod board so that the signal is split into the 22MHz demoad board and 110MHz demod board.
=> make sure we have a right splitter for it.
+ install a band pass filter after the power splitter in each path.
=> A 22MHz band pass filter is already in hand. Do we have 110MHz band pass filter somewhere in the lab ?
The picture here shows the latest configuration on the ITMX table.
RF photo diodes POP55 and POX11 are installed. The beams are aligned to the photo diodes.
Here is an actual time series of the I and Q signals in dataviewer. The I signal outputs just junk while the Q showed a nice sine curve.
Status update on the LSC activity:
I have shifted the alignment of the MC suspensions such that the PZT won't rail.
Since I didn't care of the spot positions on the MC mirrors, currently they are terribly off from the centers.
After the shift, I realigned the Stochmon PD again.
The attachments below shows the alignment of MC and PZTs before shifting the just for a record
Quote from #5754
I horizontally swept the translation of the incident beam in order to investigate a possible clipping in Power-recycled Michelson (PRMI).
The recycling gain of PRMI depended on the beam pointing but it did't improve the recycling gain.
I guess the amount of the entire shift I introduced was about +/- the beam diameter = +/- 5 mm or so.
Within the range of about +/- 5mm in the horizontal beam translation I didn't find any obvious sign of a clipping.
Here shows the measured recycling gain and the power reflectivity of PRMI as a function of the beam pointing.
It turns out that nodus doesn't know how to NDS2, so I can't run diagAllSUS as a cron job on nodus. To further complicate things, no other machines can run the elog utility, so I am going to have to do something shifty...
Actually in the last 40m meeting we discussed the SUS diagnosis and decided not to post the results on the elog.
Alternatively we will have a summary web page which will contain all the information (sensitivity, UGF monitors, etc.,) and will be updated everyday like GEO.
This will be a place where we should post the SUS results every week.
So we don't need to worry about the cron-elog job, and for running the scripts you can simply use one of the lab machines as a cron host.
Once you get the scripts running on a machine as a cron job, it will be the point where we should quit developing the SUS diagonalizer and pass it to the web summary people.
[Steve / Kiwamu]
They were traced and labeled. One goes to 1X2 and the other to AS-ISCT. They are Andrew Heliax 1/4" od. made by CommScone, model number FSJ1-50A
It turned out that the signal was too small with PDA10A to detect the 22 and 110 MHz RF sidebands.
The DC output coming out from it was about half mV or so (corresponding to few uW in laser power) when the PRCL was locked to the carrier.
This is because PDA10A is a silicon detector which is more sensitive to visible light than IR.
The reason we chose PDA10A was that it has relatively a large diode size of 1 mm in diameter.
However according to the data sheet the responsibility at 1064 nm is about 0.05 A/W which is sad.
I will replace it by PDA10CF, which is made from InGaAs and supposed to have 10 times bigger responsibility.
Though the diode size will be half mm in diameter, which may require another strong lens in front of it.
The POP22/110 RFPD has been replaced by PDA10CF. As a result the 22 and 110 MHz signals became detectable.
However the signal level maybe too low according to a quick look with an RF spectrum analyzer.
The level at 22 and 110 MHz were both approximately -70 dBm although these values were measured when the central part was freely swinging.
Perhaps we need to amplify the signals depending on the actual SNR.
Also I have updated the optical tables' wiki page :
I pulled out the POX11 demod board and found the power splitter on the board hadn't been modified yet.
I am going to replace the splitter which had been made with a hand-wounded coil because it can work only at a specific tailored frequency.
The modification on the POX11 demod board has been successfully done.
I followed the procedure which had been posted in a past entry (#4554).
The home-made splitter was replaced by PSCQ-2-51W, which has a relatively wide band of 5 - 50 MHz.
The usual orthogonality adjustment will be done in the daytime.
The attached snapshot was taken when an sinusoidal RF signal with a slight frequency offset from LO was injected to the RF input.
It is clear that the I and Q output show healthy signals (i.e. almost the same amplitude and 90 deg phase difference.)
[Offsets in MC]
I have introduce an offset in MC2 PIT because the PZT1 again started railing.
Right now the PZT1 EPICS value is within the range happily.
Please keep this MC eigen axis as a nominal configuration.
I have modified the IFO configure scripts such that XARM and YARM are locked with POX11 and POY11 respectively.
A big advantage in use of POX and POY is that we don't need to misalign ITMs when we align each arm.
Those scripts are now available from the C1IFO_CONFIGURE screen as usual.
Did somebody delete all the scripts in /opt/rtcds/caltech/c1/scripts/ASS ?
I think you also should check the PZT's capacitance of the 700mW LightWave because 2.36 nF is the one for the 1W Innolight laser.
To combat this, I propose we simply change the resistor in the modulation path from 1M to 10k. This leaves the feedback path TF unchanged, and changes the mod path into a sort of bandpass filter for the modulation frequency. The fact that the phase is near zero at fmod means we don't have to come up with some way to phase shift the signal for demodulation.
A nice plot !
Can you put another y-axis on the right hand side of the same plot in terms of the cavity displacements ?
And can you also measure a more important spectrum, namely the suppressed error signal ?
Quote from #5837
I measured the power spectrum of channel C1:GCY_SLOW_SERVO1_IN1, which is the PZT driving voltage.
EDIT by KI:
The definition of the recycling gain is wrong here.
See the latest entry (#5875)
Here is a summary about the Power Recycled Michelson (PRMI).
It seems the mode matching is also one of the greatest contributor on the low recycling gain.
+ Loss = 5.3% (or effective reflectivity of 93.28% in Michleson) => Under coupling !!
+ Mode matching efficiency = 47.4 % => Really bad !!
With these values we end up with a recycling gain of 7 and a normalized REFLDC of 0.5 as observed (#5773).
Also according the incident beam scan measurement (#5773) the loss is NOT a local effect like a clipping, it is more like uniformly distributed thing.
As for the mode matching, the number indicates that approximately the half of the incident light is coming back to the REFL port without interacting with PRMI.
This is bad because the non-mode-matched light, which is just a junk light, is entering into the photo detectors unnecessarily.
In the worst scenario, those junk light may create a funny signal, for example a signal sensitive to the alignment of PRM.
The method to estimate the loss and the MM (Mode-Matching efficiency) is essentially the same as before (#5541).
One difference from the previous estimation is that the I used more realistic parameters on the transmissivity of ITMs and PRM :
PRM : T = 5.637 % (see the 40m wiki)
ITM : T = 1.384 % (see the 40m wiki)
In addition to the basic calculations I also made plots which are handy for figuring out where we are.
Quantities we can measure are the reflected light from PRMI and the recycling gain using the REFL PD and the POY PD respectively.
So I wanted to see how the loss and MM can be estimated from the measured REFL DC and recycling gain.
The plots below are the ones.
The first figure shows a contour map of the loss as a function of the measured REFL DC and recycling gain.
The white area is a place where no proper solutions can be found (for example MM can get to more than 100 or loss becomes negative).
The star mark in the plot corresponds to the place where we are now. Obviously the loss is about 5%.
If we somehow decrease the amount of the loss the star mark will mostly go up in the plot.
The second figure shows a contour map of the MM as a function of the measured REFL DC and recycling gain.
The X and Y axis are exactly the same as that of the first plot. Again the star mark represents the place where we are.
We are currently at MM=47%
Here are some solutions to bring the recycling gain higher.
We don't work on these things immediately since it requires opening of the chambers again and it will take some times.
But we should think about those options and prepare some stuff for a coming vent.
+ Refinement of the position of the mode matching telescopes. => The Recycling gain can go up to 15.
=> Assuming the loss in the cavity doesn't change, the star mark in the first plot will go to the left hand side along the "0.05" black solid line.
=> However PRMI will be still under coupled.
=> Needs an estimation about which way we move the telescopes.
+ Locate the place of the dominant loss source and reduce it somehow.
=> The recycling gain will be more than 18 if the loss reduces by a factor of more than 5.
=> Needs a clever way to find it otherwise we have to do it in the classical way (i.e. white light and trying to find dirty surfaces)
Goal of this week : ALS on the Y arm
Minimum success : Detection of the green beatnote between the freq-doubled PSL and the Y arm transmitted light
Indeed it is strange. I took a quick look at it.
In order to recover the same condition (e.g. the same amount of the reflected DC light and the same temperature readout),
it needed to have +8.9V in the slow input from the DAC through EPICS.
Obviously applying an offset in the slow input to maintain the same condition is not good.
It needs another solution to maintain the sweet frequency where the frequency of the PSL and the Y end laser is close in a range of 200 MHz.
Plugging in the thermal feedback BNC cable to the laser reduced the DC voltage of the green PDH photo diode from 3.12 V to 1.5V off resonance.
[Katrin / Kiwamu]
The beat-note between the PSL green laser and the Y end green laser was successfully detected.
The detection was done by the new broad-band RFPD.
The next step will be an extraction of the frequency fluctuation signal using the delay-line-mixer frequency discriminator.
(What we did)
+ Connected a BNC cable which goes from the c1iscey's DAC to the laser slow input
=> this enables a remote control of the laser frequency via the temeperature actuation
+ Realigned the beam pointing of the Y end green laser
+ Installed all the necessary optics on the PSL table
=> currently the PSL green light is adjusted to completely S-polarization
+ readjusted the mode matching telescopes
=> the Y green beam becomes the one with a long Rayleigh range
+ Health check on the broad-band RFPD to see if it is working
+ Installed the BB-RFPD with a +/-15V power supply
+ Fine alignment of the beam combining path
+ Fine tuning of the Y end laser temperature
=> T_PSL = 31.72 deg when the slow FSS feedback is zero.
=> Based on Bryan's measurement (see #elog) the Y end laser temperature was adjusted to 34.0 deg by applying an offset to the slow input.
+ Found the beat note at 100 MHz or so.
=> optimizing the alignment of the beam combining path by maximizing the peak height of the beat-note.
=> maximum peak height observed with an RF spectrum analyzer was about -36 dBm.
The recycling gain is determined by the optical configuration and the optical loss in the cavity.
How much is the actual recycling gain? And how does it affect the signal extraction?
As Koji pointed out I made a wrong definition on the recycling gain of PRMI (Power-Recycled Michelson Interferomter).
Reflectivity of PRMI (measured by REFLDC):
Power build up (measured by POY DC) :
Mode Matching (MM) efficiency :
Loss in the PRMI cavity :
(Results of Measurement and Estimation)
Estimated recycling gain = 15
Estimated MM efficiency = 47.4%
Estimated Loss = 5.3%
Measured power build Up = 7
Measured reflectivity of PRMI = 0.5
Goal of this week : Noise budgeting on the Y arm ALS
Minimum success : bring the Y arm to the resonance by using ALS NOISE BUDGETING!!!
=> as a preparation the incident beam pointing needs to be fixed by steering the MC suspensions.
Goal of this week : ALS on the Y arm (DONE)
Leaving a note on the ALS feedback before I forget:
The MC2 suspension needs to have an input for the ALS feedback in the realtime model like ETMs.
[Tomotada / Kiwamu]
The open loop transfer function of the Y end PDH loop was remeasured : the UGF was found to be at 17 kHz.
The phase margin at the UGF was about 27 deg.
While the measurement we noticed that the modulation onto the laser PZT was too big
and it was creating a big AM on the reflected light with an amplitude of a few mV.
So we put a 20 dB attenuator to decrease the modulations and the reflected light became much quitter.
Also the servo shape formed by Newfocus LB1005 looks too simple : we should have a more sophisticated servo filter (i.e. PDH box!!).
Locking activity last night :
The free run beat-note in 532 nm has been measured.
However I couldn't close the ALS loop somehow.
Every time I tried closing the loop it broke the Y end PDH lock in a couple of minutes.
(Things to be done)
1. Optimization of the Y end PDH servo loop
2. Refinement of the broadband RFPD setup
Dataviewer is not able to access to fb somehow.
I restarted daqd on fb but it didn't help.
Also the status screen is showing a blank white form in all the realtime model. Something bad is happening.
Some updates on the Y end green PDH lock
(Measurement of the Y arm fluctuation)
(Temporary servo setup)
I found that the temperature controller of the PSL doubling oven had been disabled.
The Y arm green PDH servo is working fine with a sufficient amount of suppression.
And the servo configuration looks like this :
(the Error signal)
I took a spectrum of the error signal when the laser was locked to the Y arm and found that it meets the requirement.
The noise budget on the Y arm ALS has begun.
Right now the fluctuation of the green beat-note seems mostly covered by unknown noise which is relatively white.
(Though I feel I made a wrong calibration ... I have to check it again)
[Suresh / Kiwamu]
The power switch button of the RF generation box is not properly working
For tonight we are leaving it as it is but it needs to be fixed at some point.
The temporary solution we decided is to leave it ON so that we can survive tonight.
The box was back in place. The MC is find and 11 MHz and 55 MHz seem okay.
Please be aware of it.
This is a picture showing the rear view of the RF generation box. The red arrow is pointing the blue LED switch button.
Jenne gave me a spare LED power switch .
I will replace the broken one on Monday.
By the way here is a picture album of the RF generation box which I took last night.