I (with help from Q)
Two quadratures working in harmony.
We locked PRMI in carrier. Measured power recycling gain was ~25.
Here's some plot of PRC intra-cavity powers and MICH,PRCL error signals. As you can see from POPDC, cavity buildup was about 400, which means power recycling gain was ~25. Power recyling gain is fluctuating up to ~45 during lock. We need some gain normalization or something.
Here's 30 sec movie of AS, POP, REFL when acquiring PRMI carrier lock. Although there's oscillation when acquiring lock, beam spot motion is less and stable compared with the past(before flipping PR2).
== PRMI carrier ==
MICH: AS55_Q_ERR, AS55_PHASE_R = -12 deg, MICH_GAIN = -0.1, feedback to ITMX(-1),ITMY(+1)
PRCL: REFL55_I_ERR, REFL55_PHASE_R = 70 deg, PRCL_GAIN = 5, feedback to PRM
- Better filters and gains for stable lock
- Kakeru method to measure g-factor (see elog around #1434)
- OSA to measure g-factor
- There is more room to improve the differential ITM alignment to make the dark port more dark, then you will gain more PRG
- The AS spot is definitely clipped.
I don't think the loss of 25 ppm is outrageous. Its just surprisingly good. The SIS model predicted numbers more like 1 ppm / mirror taking into account just the phase map and not the coating defects.
However, we should take into account the lossed in the DRMI to be more accurate: AR coating reflectivities, scatter loss on those surfaces, as well as possible clipping around BS or some other optics.
The Demod board with S. No. 022 (being used earlier as REFL11) has been modified. It now has SCLF-65 as its input LP filter on the PD input line and a PQW-2-90 power splitter. The unit functioning okay (I and Q signals are 90 deg apart.
The loss of Q output was traced to a possible loose solder joint and we now have both the I and Q signals after resoldering all components in the vicinity of U7 (Ref Schematic of D990511)
There is a strong oscillation around 350Hz present on I and Q signals of both REFL55_Demod and POY55_Demod. Don't know the source.
We have run out of power splitters to continue with the Demod board modification. We do not currently have an AS11_Demod board. All the others are in place and ready for the I<->Q phase angle measurement.
In summary we now have the following Demod boards in place:
[ REFL11, POY11, REFL55, AS55, POY55, POY22, POY110]_Demod
The ~350 Hz noted in the elog below was traced to an RF modulation of the 11 MHz sideband. This modulation was set up in the Marconi which is currently supplying the 11 MHz local oscillator signal to the RF source. lt was used during the MC length study completed last week by Valera and Ryan. The frequency measured was 322 Hz.
As we do not require this any longer, I have switched off this modulation.
Last Saturday the POY55 RFPD (see this entry) was installed on the ITMY optical bench for the trial of the DRMI locking.
Since the amount of the light coming into the diode is tiny, the DC monitor showed ~ 3 mV even when the PRC was locked to the carrier.
In order to amplify the tiny RF signal from the photo diode a ZHL amplifier was installed next to the RFPD. The RF amp is sitting on delrin posts for insulation from the table.
The DC Transimpedance of POP55 was increased from 50 Ohm to 10010 Ohm. There is the offset of 46mV. This should be cancelled in the CDS.
The full characterization of POY11 is found in the PDF.
Resonance at 11.03MHz
Q of 7.6, transimpedance 1.98kOhm
shotnoise intercept current = 0.17mA (i.e. current noise of 7pA/rtHz)
Notch at 21.99MHz
Q of 56.2, transimpedance 35.51 Ohm
Notch at 55.20MHz
Q of 48.5, transimpedance 37.5 Ohm
- First ran burtgooey as last time.
- Installed pyepics on base environment of donatella
- Clicked on ON in the drop down of "! More Scripts" below "! Scripts XARM" in C1ASS.adl
- Clicked on "Freeze Outputs" in the same menu after some time.
- Noticed that the sensing and output matrix of ASS on XARM and YARM look very different. The reason probably is because the YARM outputs have 4 TT1/2 P/Y dof instead of BS P/Y on the XARM. What are these TT1/2?
(Probably, unrelated but MC Unlocked and kept on trying to lock for about 10 minutes attaining the lock eventually.)
- From scripts/XARM we ran lockXarm.py from outside any conda environment using python command.
- Weirdly, we see that YARM is locked??? But XARM is not. Maybe this script is old.
- C1:LSC-TRY-OUTPUT went to around 0.75 (units unknown) while C1:LSC-TRX-OUTPUT is fluctuating around 0 only.
POY11 Spectrum measurement when YARM is locked:
- Created our own template as we couldn't find an existing one in users/Templates.
- Template file and data in Attachment 2.
- It is interesting to see most of the noise is in I quadrature with most noise in 10 to 100 Hz.
- Given the ARM is supposed to be much calmer than MC, this noise should be mostly due to the mode cleaner noise.
- We are not sure what units C1:LSC-POY11_I_ERR_DQ have, so Y scale is shown with out units.
Trying to lock Green YEND laser to YARM:
- We opened the Green Y shutter.
- We ensured that when temperature slider og green Y is moved up, the beatnote goes up.
- ARM was POY locked from previous step.
- Ran script scripts/YARM/Lock_ALS_YARM.py from outside any conda environment using python command.
- This locked green laser but unlocked the YARM POY.
Things moving around:
- Last step must have made all the suspension controls unstable.
- We see PRM and SRM QPDs moving a lot.
- Then we did burt restore to /opt/rtcds/caltech/c1/burt/autoburt/today/08:19/*.snap to go back to the state before we started changing things today.
[Paco left for vaccine appointment]
- However the unstable state didn't change from restore. I see a lot of movement in ITMX/Y. PRM and BS also now. Movement in WFS1 and MC2T as well.
- I closed PSL shutter as well to hopefully disengage any loops that are still running unstably.
- But at this point, it seems that the optics are just oscillating and need time to come back to rest. Hopefully we din't cause too much harm today :(.
My guess on what happened:
POY11 PD was installed last night. The lock of the Y arm was confirmed with the POY11I signal.
- The DC transimpedance was modified to be 1010V/A as the incident power is tiny.
- The demodulation phase of the roughly adjusted (148deg) to have PDH signal at the I-phase.
The comparison with AS55I signal exhibits that POY11I have ~150 times weaker signal with 45dB whitening.
(In total 25000 times weaker.)
On the way to make POY11 functioning, there were many fixes at the LSC rack...
- The PD interface cards (power supply for the RFPDs) were checked:
So far the two card at the right hand side were checked.
Desipite the previous entry reported the issues on those boards, they did not show any problem yesterday.
One hypothetical possibility is the enabling switches that is controlled from the old slow epics targets.
- POY55 was removed
This 55MHz PD is supposed to be installed at POP.
The PD, an RF cable, an RF amp, the power supply of the RF amp were removed.
- POY11 was installed
The PD was placed where the 55MHz was placed.
The beam was aligned on the diode using the IR viewer and the digital multimeter.
The power supply cable and the RF cable for POY on the ITMY table were used.
There were an ND filter on the POY beam path. It was removed.
- On the LSC rack
The PD RF was connected to the patch panel at the top of the rack.
There were loose connectors on the patch panel. Some connectors were tightened on the panel.
I found that POY11 and POX11 had I&Q signal reversely connected to the whitening board.
==> These were fixed but require the orthogonality test again for those channels.
The I phase output of the AS11 demod board had a broken connector.
The onboard SMA has got disintegrated because of too much twist on the connector.
The board was once removed from the rack and the connector was fixed using a heat gun and soldering.
The DC signals were checked. POYDC was not correctly connected. POYDC were correctly connected to the POYDC channel.
c1lsc was found with the RFM frozen.
The c1lsc machine was soft-rebooted after stopping all of the RT processes.
Once the RT processes came back, they were all burtrestored.
- PDH locking
Restored Y-arm. Locked it with AS55Q.
Ran ASS alignment for Y-arm.
100cnt 150Hz sinusoidal signal is applied to ETMY
Measured the PSD of AS55Q, POY11I, and POY11Q.
Adjusted the demod phase so that the excitation could be minimized in POY11Q.
New channels, POP55 and POY11 are connected to the rack and now available on the data system.
POX11 I is not working. I didn't investigate what was wrong. Please make sure when you come to need POX11.
The orthogonalities of POY11 and POP55 were measured and already adjusted. The results are below:
ABS = 0.973633
PHASE = 92.086483 [deg]
ezcawrite C1:LSC-POY11_Q_GAIN 1.027081 && ezcawrite C1:LSC-POY11_PHASE_D 92.086483
ABS = 1.02680579
PHASE = 88.5246 [deg]
ezcawrite C1:LSC-POP55_Q_GAIN 0.973894 && ezcawrite C1:LSC-POP55_PHASE_D 88.524609
I've finished tuning POY11 and it is now sitting on top of the analyzer waiting for Koji to test its noise.
Keiko, Paul, Kiwamu
We found that POP beam is clipped by the steering mirrors inside the tank. POY beam is also likely to be clipped inside. Also the hight of POY beam is too high (about 5 cm higher than the normal paths) at the first lens. These imply the input pointing is bad.
I looked at the CAD layout and it seems like we will clearly be clipping POY if we move SRM by 7.5cm. Since POY is not visible at low power, we cannot be sure about the clipping.
I was bad and forgot to elog this yesterday (bad grad student!), but I setup a laser pointer to show us where the POY beam is.
To do this, I removed the tiny mirror that sends the beam to the POY RF PD (so we do not have POY to lock the Yarm right now. I think Q has successfully been using AS). The laser pointer goes through 2 temporary steering mirrors, then passes through the place that the tiny mirror usually sits, and then travels along the POY path into the vacuum system. The idea here is that we should be able to adjust the laser pointer and the temp steering mirrors, and not touch any of the actual POY mirrors, but still get the green beam to go all the way to ITMY. Yesterday I confirmed that the laser pointer was hitting the in-vac POY pickoff mirror, and today Q and Manasa are doing final adjustment to get the beam all the way to the ITM.
[Koji and Kevin]
I measured the shot noise of POY and fit the data to determine the RF transimpedance at 11 MHz and the dark current. The transimpedance is (3.860 +- 0.006) kΩ. I realize that there are not many data points past the dark current but I did not want to take any further data because the light bulb was getting pretty bright. If this is a problem, I can try to redo the measurement using a lens to try to focus more of the light from the bulb onto the photodiode.
I also measured the spectrum and recorded a time series of the RF signal with the light to the photodiode blocked. These measurements do not show any large oscillations like the ones found for POX.
The plots of the measurements are on the wiki at http://lhocds.ligo-wa.caltech.edu:8000/40m/Electronics/POY.
I wonder why POY11 has the dark noise level of 90nV/rtHz that is 5 times larger than that of POX (18nV/rtHz)
even though the Q are the same (~15) and the transimpedance is better (3.9k instead of 2k).
What cause this high noise level?
What is the expected dark noise level?
The previous measurement for the shot noise of POY had the dark noise at ~100 nV/rtHz. I redid the measurement and got 26 nV/rtHz for the dark noise. I think that when I made the previous measurement, the spectrum analyzer had automatically added some attenuation to the input that I failed to remove. This added attenuation raised the noise floor of the measurement making the dark noise of POY appear larger than it is.
The updated measurement can be found on the wiki at http://lhocds.ligo-wa.caltech.edu:8000/40m/Electronics/POY.
Sitting down to work on the IFO, I couldn't lock the Yarm. I looked at the error signal as well as the transmission on Dataviewer, as usual, and saw that the POY error signal was almost non-existant.
Since there was work on the POY table today (Steve removed the oplev test setup, elog 10489 and Q centered the SRM oplev after doing SRMI alignment, no elog yet), I went out to have a look at the table.
There was nothing occluding the POY beam, which I traced back to the edge of the table. The beam looked nice and round, so I decided that wasn't it. I jiggled the PD cables, and lo and behold, the POY RF out cable almost came off in my hand it was so loose. My suspicion is that whomever was the last to put the POY RF out back didn't tighten the cable and then the work today jiggled the cable loose. I tightened the cable, and by the time I was back to the control room the arm was locked and Koji was already running the alignment scripts.
[Rana and Kevin]
I measured the optical transfer function of POY and fit the data using LISO. The fit can be found at http://lhocds.ligo-wa.caltech.edu:8000/40m/Electronics/POY. POY was missing the RF cage and back cover so I took those parts from AS55 in order to make these measurements.
POY does not have the unwanted oscillations at 225 MHz that POX has. Attachment 1 shows the transfer functions of POX and POY.
To measure the transfer functions, I used a 50/50 beam splitter to send half the light from an AM laser to POY and half the light to a New Focus 1611 reference photodiode. The transfer function for POY was measured as the transfer function of the signal from POY divided by the signal from the 1611. When I was measuring the transfer function for POX, I failed to ensure that the photodiodes were operating linearly. Before making the measurements for POY, I varied the RF power modulating the AM laser and recorded the magnitude of the transfer function at the 11 MHz peak. Attachment 2 shows these values. The measurements for POY were made in the linear region at an RF power of -10 dBm. The measurements for POX were made at 0 dBm and were most likely not in the linear region for POX.
The performance plots for POX_11 in the wiki are horrendous and the schematic is missing.
I opened up the box and found all kinds of horrors. There were multiple tunable parts and a flurry of excess nonsense.
The top 2 worst offenders:
1) The main tunable inductor was busted. I removed it and found that the coil was open. Too much indelicate soldering in its vicinity had melted the wire. Someone had put extra inductors and capacitors around it to make it seem as if the PD was working fine, but the noise performance was off by a factor of ~100.
2) The MAX4107 had a 1.4k series resistor. This make the output go through a 1450/50 voltage division which is not nice for the SNR. I removed it.
I then struggled for awhile to get a sensible response. It turned out that the TEST IN input was not giving me a sensible TF. Jenne and I fired the Jenne laser at it and found that the 11 MHz main resonance is there. In the morning I'll finish this off and post more results. I think its going to end up being fine.
I used the Jenne AM laser to tune up the PD (used to be POX_11 but now is called REFL_11). In addition to the notch at 22 MHz, I have also put in a LC notch at 5*f = 55.3 MHz. The transfer function below shows the RF OUT of the PD v. the drive to the laser. I didn't divide out by the 1811 because its not on the EE bench.
I used 50 mA to drive the laser diode. The light is split 50/50 between the DUT (Device Under Test) and the New Focus 1611 (1 GHz BW) diode used as the reference.
This measurement is the TF of DUT/(New Focus). The resonances are there, but clearly there's an issue with instability around 200 MHz. The setup is still powered up, so please be careful around the RFPD testing table (don't stomp around yank the cables out of the power supplies).
I looked at the RF Photodiode wiki that Alberto has started - most of the TF features are replicated there. Todo:
* Update the 'schematic' with a real schematic instead of the cartoon.
* Change the circuit to remove the resistor in the RF path.
* Add compensation to avoid the 200 MHz instability.
* Make sure to include opamp current noise in the noise model (it is the dominant noise source but has been left out in the noise estimation plot).
* Make the output into a true 50 Ohms.
I have unplugged POXDC and POYDC from their whitening inputs. They have labels on them which whitening channel they belong to (POY=5, POX=6) on the DCPD whitening board.
TT3_LR's DAC output is Tee-ed, going to the POYDC input and also to an SR560 near the Marconi.
TT4_LR's DAC output is Tee-ed, going to the POXDC input and also to the CM board's ExcB input.
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.
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.)
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.
I pulled out the POX11 demod board and found the power splitter on the board hadn't been modified yet.
RF photo diodes POP55 and POX11 are installed. The beams are aligned to the photo diodes.
I used 0.7 A/W for the response and 50V/A for POP55 according to elog page #4576.
To install the third RF photo diode we need to order a plano-convex lens with a focal length of 750 or
maybe even better 1000
There is an imbalance between the POX and POY detector outputs reported in the CDS system. Possibilities are (i) the POX PD has a uncoated glass window whereas POY does not or (ii) there is some problem in the elctronics.
So increasingly, it looks like the electronics are the source of the problem.
Doing POX-POY noise measurement as a poor man's FPMI for diagnostic purposes. (Notebook in /opt/rtcds/caltech/c1/Git/40m/measurements/LSC/POX-POY/Noise_Budget.ipynb)
The arms were locked individually using POX11 and POY11. The optical gain was estimated to be by looking at the PDH signal of each arm: the slope was computed by taking the negative peak to positive peak counts and assuming that the arm length change between those peaks is lambda/(2*Finesse), where lambda = 1um and the arm finesse is taken to be 450.
Xarm peak-to-peak counts is ~ 850 while Yarm's is ~ 1100. This gives optical gains of 3.8e11 cts/m and 4.95e11 cts/m respectively.
Next, ETMX actuation TF is measured (attachments 1,2) by exciting C1:LSC-ETMX/Y_EXC and measuring at C1:LSC-X/YARM_IN1_DQ and calibrating with the optical gain.
Using these calibrations I plot the POX-POY (attachment 3) and POX+POY (attachment 4) total noise measurements using two methods:
1. Plotting the calibrated IN and OUT channels of XARM-YARM (blue and orange). Those two curves should cross at the UGF (200Hz in this case).
2. Plotting the calibrated XARM-YARM IN channels times 1-OLTF (black).
The UGF bump can be clearly seen above the true noise in those plots.
However, POX+POY OUT channel looks too high for some reason making the crossing frequency between IN and OUT channels to be ~ 300Hz. Not sure what was going on with this.
Next, I will budget this noise with the individual noise contributions.
Unaltered PR2 images, with IR card, without card, and steering mirror:
Unaltered POX and POY images:
The POX images only needed a major brightness reduction and increased contrast to view:
The POY images needed their intensity histograms shifted slightly right and made left-tailed:
After my investigations this afternoon (with help from Sendhil and Shivaraj), I do not find any problems with the POX whitening switching.
Earlier this afternoon / evening I was misleading myself into thinking that either the switching component (ADG333ABR) was broken, or that the whitening op amps (LT1124CS8) were broken on the POX I&Q and POY I&Q channels. I had not realized until Jamie mentioned the possibility, that some of the DC gain stages were on for POX and POY. POX and POY (I&Q for both) all had +36dB of gain, so when I was injecting my 60Hz sine wave into those channels, the whitening opamps were already saturated, which is why it didn't look like I was getting any gain. When I set them all to 0dB (which is what AS11 and REFL11, the other 2 PDs using that whitening board, were set to), all 8 channels behaved the same.
The shaped whitening (which is either bypassed or not, depending on the condition of the software "unwhite" switch) is 2 filters in series, each with a zero at 15Hz, and a pole at 150Hz, with DC gain of 0dB. For a 60Hz sine wave, this gives a factor of ~4 from each stage. After setting all of the whitening gains to 0dB, I was able to see on all 8 channels of the board an input sine wave, a larger (by 4-ish) sine wave, and then a larger (by 4ish again) sine. When I looked at the output of the switch of all 8 channels, the signal was either the same as the input amplitude, or the same as after the 2nd whitening stage, depending on the "unwhite" filters.
Before looking at actual signals, Sendhil and I also had checked to see that indeed, the board was receiving the digital signal input to the switch chip, requesting switching based on the state of the "unwhite" filters.
I looked through the elogs, and the only "symptoms" I find are from an IFO check-up session that Koji, Den and I had back in May, where we declared in the elog that POX whitening may or may not be switching. See elog 6595. We didn't mention what the actual symptoms we saw were, so unless Koji or Den remember something that I don't, I cannot confirm that we are no longer seeing those symptoms. However, based on the number of "?" after "POX whitening not toggling the analog whitening", I don't think that we were totally sure that something was wrong in the first place.
Anyhow, the whitening board in the LSC rack labeled "WF1", serving AS11, REFL11, POX11 and POY11 has had a thorough checkup, and I give it a clean bill of health.
At the time you, den and I worked together, we could not lock the X-arm on TEM00 with the FM1s of the POX11 on.
We could lock the arm only on the higher order mode but he gain was low. Once we turned off the FM1s, we immediately
locked the cavity on TEM00.
Don't you have the direct measurement of the TF with FM1 on and off?
Here are the transfer functions that we took back in 2011 (see elog 4915 and replies) for POX:
The table of all whitening filter zpk values is on the wiki: https://wiki-40m.ligo.caltech.edu/Electronics/WhiteningFilters
I'm trying to lock / align the Xarm, and POX 11 I looks funny sometimes.
I attach 2 screenshots so you can see what I mean. I'm leaving them uncropped so that you can see the only thing that has changed is the LSC enable / disable button.
PRM, SRM, ITMY, ETMY all misaligned. BS, ITMX, ETMX aligned so that most of the time I can't lock better than 04, bad in yaw, but very occasionally I'll get lucky and catch a 00. When the LSC enable switch is ON (2nd attachment), the POX signal (green trace in dataviewer in both attachments) looks almost square-ish, and definitely funny. It doesn't seem to correspond directly to flashing in the cavity (red trace in dataviewer in both attachments). However when I disable the LSC, POX goes back to looking normal - 1st attachment. Right around -5 seconds in the 1st attachment, I disabled the LSC.
I don't really know what this means.
The alignment was way off. We moved the PZT, the BS, and the x arm to get it to lock. Along the way we noticed that giving the ETM and POS offsets makes it tilt a lot. The DC coil balancing is no good at all.
After locking, we tuned up the X arm filters in the LSC and activated the filter module triggers. I would attach a screenshot of the trigger screen, but sadly it has no snapshot button on it.
WE changed the integrator into a double integrator with a complex zero pair. We also replaced the 1:50 boost with a 2nd order complex pole:zero pair. And added a 18 Hz RG. These were all set by looking at the error point spectra and minimizing the RMS. Hopefully, this kind of work will all be obsolete once we get the optimal feedback code. For now, the arm is very stable - we're leaving it locked overnight since the filter triggering seems to work well.
The loop kept oscillating, so we turned the xarm gain down from the 0.3 that we found it at down to 0.045. We measured the loop gain using our old xarm loopgain DTT template (which is in the Templates directory, not in /users/IAmAnAmateur/secret/secret/bozo/). It shows that we are missing ~20 deg of phase at the peak of the phase bubble compared to the old days. We guess that its because of the downsample/upsample digital AA filters which we now have in addition to the 7kHz hardware AA/AI which we still have from the pre-upgrade times). We (Jamie) have to think about how to rationalize this: we cannot survive with double AA/AI.
Another big hindrance in the lock acquisition is that the whitening filters were on. Because the WG is set to 45 dB, the ADCs are getting saturated when the flashes are large. We should have the whitening filters switch after acquiring lock.
Also, why are all the camera views of the ITMs and ETMs different? Steve, please go back and make them all the same (angles, aperture, lenses, etc.). Without them being the same, we cannot compare them.
I have found the video capture scripts in Yuta's personal directory. This is illegal, of course. All useful scripts (even when in development) go into the shared scripts directory. As a punishment, I have added some nasty typos to a couple of his other scripts and then backdated the timestamps so that he cannot find it easily.
Also, I fixed the "mcup" script. After the ringdown people inserted the pickoff for MC2 trans, no one adjusted the thresholds in the MC autolocker. I've fixed mcup to trigger at 7000 cts. This should be changed back if the pickoff is removed someday. MC WFS now coming on.
Continuting the IFO recovery - I am unable to recover similar levels of TRX RIN as I had before. Attachment #1 shows that the TRX RIN is ~4x higher in RMS than TRY RIN (the latter is commensurate with what we had previously). The excess is dominated by some low frequency (~1 Hz) fluctuations. The coherence structure is confusing - why is TRY RIN coherent with IMC transmission at ~2 Hz but not TRX? But anyways, doesn't look like its intensity fluctuations on the incident light (unsurprisingly, since the TRY RIN was okay). I thought it may be because of insufficient low-frequency loop gain - but the loop shape is the same for TRX and TRY. I confirmed that the loop UGF is similar now (red trace in Attachment #2) as it was ~1 month ago (black trace in Attachment #2). Seismometers don't suggest excess motion at 1 Hz. I don't think the modulation depth at 11 MHz is to blame either. As I showed earlier, the spectrum of the error point is comparable now as it was previously.
What am I missing?
There is no visible PDH error signal on the POX11 channels. As a result, I am unable to lock the XARM length to the laser frequency. See Attachment #1 - the Y arm length is locked to the PSL frequency, and control is disabled for the XARM servo.
Now that several of the c1iscaux functionality tests have been completed, I wanted to push ahead with some locking. However, I was foiled at this early stage, for reasons as yet unknown. One possibility is that the
Nice work. That was a lot of effort, but having done it so nicely will definitely pay off, since it is now much harder to break the fibers.
2 small issues: In your attachment 3, I see a coil of fiber just outside the POX table. I thought Koji had asked that all spare coiled-up length of fiber always be at the splitter side. Also, in securing the plastic tubing as it comes down near the PSL table, you have zip-tied the tubing to the PSL table. Since that is a space that we need to access to align the Xgreen beatnote stuff, please disconnect that zip tie, and secure the tubing on the north side somewhere, underneath the AP table, rather than the PSL table (when you look closer, you may notice that no cables in that bundle are attached to the PSL side at the bottom, for this same reason).
We decided we needed a DC channel to sense the gain in the PRC, so we set to align POY55. It took a while because the beam was very weak, and it comes in upwards, so we used a couple of mirrors to bring to a reasonable flat level, and put it on the PD. Then we went to read the DC out and we got 1.3V stationary! Nonsense. We also realized there is no LO for this PD, or any other 55MHz PD, aside from REFL55. Oh well, we only wanted the DC for now. POY55 is aligned (decently).
Koji told me to try swapping the power cable, so I unplugged it at the rack and plugged it in another power card. And it worked! I then moved the DC out (back of rack) to follow the front, and it turns out POY55 diode is read on the POXDC channel. I plugged and unplugged it in disbelief, but it is what it is. At least we have a readout on the power level in PRC.
I attach a picture of the power cards for the LSC RFPDs, with the 3 I found to be bad, and showing current config. I had to move REFL11 and POY55 from their assigned spot.
The two on the lower left are bad in the sense that they put an offset on the PD and make the DC readout be 1.3V for no reason (when working, for example, POY55 read 60mV). The one on the lower right I had trouble with some time ago, it made the PD not read any voltage at all (when working it would read at least 100mV). Beyond that I have not investigated what is up, since I could find working plugins.
Manasa and Jan were having trouble locking the Yarm, and asked me to take a look at it. After a good long time of trying to figure out what was going on, it finally occurred to me that I did not turn the DC gain on POX and POY back to the nominal 36dB. As soon as I did that, both arms acquired lock. Ooops.
Now that the IMC is remaining locked for extended periods of time, the next problem to attack is the ASS dither alignment system. For a start, I decided to try and get the POX and POY locking working again, as we have not fully recovered the interferometer alignment after the most recent pumpdown. I spent a couple of hours tweaking the alignment of the arm cavity mirrors, BS, and TTs to try and recover the maximum possible TRX and TRY - however, my best efforts only yielded TRX~0.8, TRY~0.75. Moreover, the beam axis is such that the spot is significantly off in YAW on both ETMs, as evidenced by the camera views (also true but less obvious on the ITMs). However, trying to bring the beam back to the center of the optics yields TRY and TRX values lower than the above reported maxima. The EX green beam is currently unavailable to verify the arm cavity alignment because of my hijacking the EX NPROs PZT control for PLL investigations, but with the Y arm, I'm able to lock a TEM00 mode. Probably just needs more careful systematic alignment, but I'm not pursuing this tonight.
After a more systematic alignment effort, I was able to get the spots better centered on the optics (judged by eye from the analog camera views). TRY ~0.7, TRX~1.15. The X-arm dither alignment system seems to work out-of-the-box with the existing settings, I was able to run it and maximize the X-arm transmission.
Other work: I also cleaned up the area around MC2 a litte - laptop from on top of the vacuum chamber was removed and a rogue ethernet cable was also removed. The resulted in some misalignment of the IMC, which I corrected by manual alignment. Now the IMC is locked again with nominal transmission levels.
On the PSL table, I re-routed the RF output from the BeatMouth to the regular IR-ALS electronics chain (it was hijacked for PLL investigations). At EX, I disconnected the cable running from the LB1005 to the EX NPRO laser PZT (again was being used for PLL locking), and re-connected the output from the Green uPDH box to allow for some ALS tests to be done. I could then lock the EX green beam to the X-arm, and achieved GTRY ~ 0.35 using the ASX system. More to follow on ALS tests later today.
We checked POX and POY RF signal chains for sanity check since Xarm cannot be locked in IR stably as opposed to Yarm.
POX beam seems to be healthy. This issue doesn't prevent us from closing the vacuum tank.
- RF PD has SPB-10.7+ and ZFL-500NL+ attached to the RF output.
- At the demodulation electronics rack, SMA connectors are used everywhere.
- With Yarm flashing at ~1, RF output has ~24 mVpp right after RF PD, ~580mVpp after SPB-10.7+ and ZFL-500NL+, and ~150mVpp at right before the demodulation box.
- There is roughly a factor of 3 loss in the cabling from POY RF PD to the demodulation rack.
- Laser power at POY RF PD was measured to be 16 uW
- RF PD doesn't have amplifiers attached.
- At the demodulation electronics rack, N connector is used.
- With Xarm flashing at ~1, RF output has ~30 mVpp right after RF PD, and ~20mVpp at right before the demodulation box.
- Losses in the cabling from POX RF PD to the demodulation rack is small compared with that for POY.
- Laser power at POX RF PD was measured to be 16 uW
- POX and POY RF PDs are receiving almost the same mount of power
- POY has larger error signal than POX because of RF amplifier, but the cable loss is high
- There might be something in the electronics, but we can close the vacuum tanks
I redid the optical POX transfer functions and updated the wiki at http://lhocds.ligo-wa.caltech.edu:8000/40m/Electronics/POX.
I measured each transfer function several times to calculate uncertainties for each measured point. There is one large transfer function from 1 MHz to 500 MHz showing a resonance peak at 11 MHz and notches at 22 MHz and 55 MHz. I also made more detailed measurements around each of these resonance peaks. These measurements were fit to a resonance curve to determine the resonant frequency, transimpedance at resonance, and Q for each peak. These measurements agree with the shot noise measurement for the transimpedance at 11 MHz taken earlier considering that this measurement was made at 11 MHz instead of at the resonant frequency of 11.14 MHz.
I measured these transfer functions with the Agilent 4395a using the netgpib.py script last week. I realized that when using this script to save multiple copies of the same measurement after setting up the instrument, the first and second measurements are saved but all measurements saved after are identical to the second measurement until the instrument is physically reset. This happens because the analyzer switches the trigger from continuous to hold after making a measurement using this script. Kiwamu said that the script can be modified to return the trigger to continuous after saving the data so that multiple measurements can be saved without being at the analyzer physically. I did not want to waste more time figuring out how to modify the script to do this so I used one of the netbooks and sat at the analyzer manually returning the trigger to continuous after each measurement.
TF looks fine except for the large peak at around 200MHz which has been reported by Rana. The time series and the spectrum without the light are pathetic...
I still prefer to see the fit by LISO as the pole/zero fitting of LISO as the fit result is more physically understandable.
Anyone can ask me about the instruction how to use LISO
I guess Idc of 24mA would be just a mistake. It looks like ~0.2mA from the plot that sounds normal for the transimpedance of 2kOhm.
Question: What is the HWHM of the reesonance when you have f0 and Q.
The value of I_dc was a mistake. The value should be 240 µA.
The widths of the resonance peaks are listed below the fits to each peak on the wiki.
We fit the entire POX optical transfer function from 1 MHz to 500 MHz in LISO. The fit is on the wiki at http://lhocds.ligo-wa.caltech.edu:8000/40m/Electronics/POX. Using LISO's root fitting mode, we found that the transfer function has five poles and four zeros.
I will work on making plots of the residuals. This is difficult because by default, LISO does not calculate the fitting function at the frequencies of the data points themselves and I haven't figured out how to force it to do this yet.
I confirmed that there is light incident on the POX photodiode. So the problem must lie downstream in the demod / whitening / AA electronics. With the PRM aligned (i.e. PRFPMI config with all DoFs uncontrolled), I could see the flashing beam on an IR card. I could also see the spikes in DC power incident on the photodiode using the "DC Monitor" port on the photodiode head and an oscilloscope.
Update 245 pm: I confirmed that I could see a 11 MHz sine wave by connecting the POX11 RFPD output cable at the 1Y2 end to an oscilloscope. The amplitude of this signal was also changing, corresponding to the cavity fringing in and out of resonance. I couldn't, however, see any signal on the RFPDmon port, or the I/Q demodulated output ports. So as of now, the culprit seems to be something on the Demod board. Further investigations underway...
Update 315pm: I did the following checks:
Look for the POX beam with an IR viewer.