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  17336   Mon Dec 5 16:24:45 2022 AnchalUpdateASCIMC WFS servo diagnosis

Also reply to: 40m/17255


I ran the toggleWFSoffsets.py script to generate a step response of the WFS loops in operation. Attachment 1 shows the diaggui measured time response following the parameters mentioned in 40m/17255. There are few things to quickly note from this measurement without doing detailed analysis:

  • WFS2_PIT is heavily cross-coupled with WFS1_PIT and MC2_TRANS_PIT. This was also the inference from the previous post based on loop shape for WFS2_PIT loop. This needs to be fixed.
  • Weirdly enough, it seems that WFS2_PIT is also cross coupled with MC2_TRANS_YAW.
  • MC2_TRANS_PIT is not coupled to WFS1_PIT or WFS2_PIT. This was the major issue in last measurement in 40m/17255.
  • WFS1_PIT is coupled to MC2_TRANS_PIT by about half, but is not cross-coupled to WFS2_PIT.
  • For YAW, the DOFs are mostly disentangled except for a cross coupling of WFS1_YAW to MC2_TRANS_YAW by about 60%.

To get out the UGF of the loops from the step responses, I need to read this into python and apply the same filters and analyze time constants. I still have to do this part, but I thought I'll put out the result before spending more time on this.


GPSTIME: 1354314478

 

  17337   Mon Dec 5 20:02:06 2022 AnchalUpdateASCIMC WFS heads electronic feasibility test for using for Arm ASC

I took transfer function measurement of WFS2 SEG4 photodiode between 1 MHz to 100 MHz in a linear sweep.


Measurement details:

  • The reincarnated Jenne laser head was used for this test. The laser diode is 950 nm though, which should just mean a different responsivity of the photodiode while we are mainly interested in relative response of the WFS heads at 11 MHz and 55 MHz with respect to 29.5 MHz.
  • See attachment 2 for how the laser was placed on AP table.
  • The beam was injected in between beam splitter for MC reflection camera and beam splitter for beam dump.
  • The input was aligned such that all the light of the laser was falling on Segment 4 of WFS2.
  • Using moku, I took RF transfer function from 1 MHz to 100 MHz, 512 points, linearly spaced, with excitation amplitude of 1 V and 100,000 cycles of averaging.
  • Measurement data and settings are stored here.

Results:

Relative to 29.5 MHz, teh photodiode response is:

  • At 11 MHz: -20.4 dB
  • At 55 MHz: -36.9 dB
  • At 71.28 MHz: -5.9 dB

I'm throwing in an extra number at the end as I found a peak at this frequency as well. This means to use these WFS heads for arm ASC, we need to have 10 times more light for 11 MHz and roughly 100 times more light for 55 MHz. According to Gautam's thesis Table A.1 and this elog post, the modulation depth for 11 MHz is 0.193 and for 55 MHz is 0.243 in comparison to 0.1 for 29.5 MHz., so the sideband TEM00 light available for beating against carrier TEM01/TEM10 is roughly twice as much for single arm ASC. That would mean we would have 5 times less error signal for 11 MHz and 40 times less error signal for 55 MHz. These are rough calculations ofcourse.

 

  17342   Tue Dec 6 16:52:26 2022 AnchalUpdateASCIMC WFS heads electronic feasibility test for using for Arm ASC

I tested teh WFS demod board for possibility of demodulating 11 MHz or 55 MHz signal with it. It definitely has some bandpass filter inside as the response is very bad for 11 MHz and 55 MHz. See attached the ASD curves for the excitations seens on I and Q inputs of WFS1 Segment 2 when it was demodulated with a clock of different frequencies but same amplitude of 783.5 mVpp (this was measured output of 29.5 MHz signal from RF distribution board). See attachments 2-4 for mokulab settings. Note for 29.5 MHz case, I added an additional 10 dB attenuator to output 1.

The measurement required me to change signal power level to see a signal of atleast 10 SNR. If we take signal level of 29.5 MHz as reference, following are the responses at other frequencies:

  • At 11 MHz:
    • I: -92 dB
    • Q: -97 dB
  • At 55 MHz:
    • I: -75 dB
    • Q: -72 dB

Note that I and Q outputs are unbalanced as well for the two different demodulation frequencies.

This means that if we want to use the WFS demodulation boards as is, we'll need to amplify the photodiode signal by the above amounts to get same level of outputs. I stil need to see the DCC document of these board and if the LO is also bandpassed. In which case, we can probably amplify the LO to improve the demodulation at 11 and 55 MHz. THe beatnote time series for the measured data did not show an obvious sinusoidal oscillation, so I chose to not show a plot with just noise here.

 

  17344   Tue Dec 6 17:40:13 2022 KojiUpdateASCIMC WFS heads electronic feasibility test for using for Arm ASC

We have spare WFS demods in a plastic box along the Y arm. So you don't need to modify the IMC demod boards, which we want to keep in the current state.

  17348   Thu Dec 8 20:40:14 2022 AnchalUpdateASCWFS demodulation board modification attempt

Based on the previous two elog posts, Koji and I decided that we should use 11 MHz signal for arm cavity ASC and modify a spare WFS demod board to work at 11 MHz. This board LIGO-D980233, uses a PLL to lock the to LO input and generate I and Q ECL clock signals from it. For this purpose, it uses POS-XX minicircuits VCO. For IMC WFS boards the model number is POS-75 and with the board design, it can work for 18.75 MHz to 37.5 MHz modulation frequencies.

To make it work for 11 MHz, we have to swap this with POS-25 but that is not available for purchase anywhere. So Koji and I decided to use Moku:GO as a VCO and make connections to the pin holes on the board. Today, I modified a spare WFS board to make this possible. I added a right angle SMA connector to take in VCO output signal and a BNC connector to send out tuning signal. See attached photos for the details of this hack.

Then I went to 1X2 and tried on this modified board on a Euro crate empty slot. I used Moku:GO in a multi-instrument mode in which first instrument was a Waveform generator set to modulate from external input 1 at 6 MHz/V. The output RF level was checked on an oscilloscope and increased until I got about 9.5 dBm power at the output. The second instrument was just an spectrum analyzer to see if the test output from ICLK looks ok. I fed LO from a spare output port on RF distribution box for 11 MHz signal. I made sure to attenuate this signal to get 2 dBm LO signal which is the case for the WFS demod board LO input as well. 

This test however failed. I could not see any signal from ICLK or QCLK output. I then tried to use the same slot as the demod board for WFS1 is used and I still did not see any output on ICLK or QCLK. I split the VCO tuning signal coming from the board to see it on an oscilloscope and it was mostly noise of ~1 mV level. I then tried to check ICLK and QCLK on oscilloscope and saw that they had a huge offset of -1.7 V. I suspect some ground mismatch issue between Moku:GO and the demod board.

I decided to call it a day here.

I reset everything back to how it was on the rack and turned on IMC WFS again. It is working as usual keeping lock steady for atleast last 20 min that I have seen it.


 

  17349   Fri Dec 9 05:04:45 2022 ranaSummaryASCMC WFS sensing matrix measurement

I made a script to toggle the offsets in the MC SUS so that we can see the resulting error signals in the MC WFS / MC-TRANS_QPD.

I ran it just before 5 AM local time Friday morning.

It goes in order and applies a 50 count offset to the pitch filter banks. During this test the input to the IMC WFS servos is set to zero, so that the integrators hold the mirror position in the aligned state.

I will analyze this 3x3 measurement and post the resulting sensing matrix soon. It would be good if someone can post here the actuation calibration in radians, so that we can have a physical calibration of the sensing matrix in counts/radian.

  17350   Fri Dec 9 10:08:54 2022 RadhikaUpdateASCYEND green alignment chronicles

Today I set out to align and lock the YEND green laser, and observe the expected PDH error signal and PZT control signal. 

- I took note of PDH servo knobs:

    - gain knob: 10.0
    - LO phase knob: 2.86
    - boost: on
    - inversion: -

- Disconnected PDH servo PZT output to break loop

- Scanned pitch and yaw of steering mirrors 1 and 2 [Attachment 1] and achieved transmission ~1.2.

- Re-engaged the loop and with TEM00 locked, and did fine adjustment of steering mirrors to maximize transmission to 1.4.

- At this point I broke the loop again to look at the PDH error signal and piezo control signal in an oscilloscope. The error signal had high frequency noise, so the SR560 was used to low pass it before sending it to the scope.

- Once I reconnected the loop and locked to TEM00, I noticed lots of noise in green transmission. Paco took spectra of GTRY and found it was line noise at multiples of 60 Hz. I checked if any BNC shields at the servo box were touching. I shifted the LO frequency from 213.12 kHz to 213.15 kHz, so that the modulation/demodulation was not an integer multiple of 60 Hz. However, these steps didn't get rid of the line noise. To be further investigated.

Next I plan to revisit the XEND AUX loop and try to reach higher lock stability. 

  17354   Fri Dec 9 18:32:11 2022 KojiSummaryASCMC WFS sensing matrix measurement

[Rana, Koji]

The IMC WFS pitch Output Matrix was recalculated based on a DC Sensing Matrix measurement.

The IMC and the WFS heads were realigned and the WFS offsets were reset. The WFS servo is running stably for ~1.5hrs now.


Using Rana's test with the optic offsets, the sensitivity of the sensors against the misalignment of each optic was measured. First of all, we accessed the recorded 900s data on Dec 9 2022 12:48:00 UTC (Attached 1). This DTT XML file is stored in /users/koji/221209/221209_IMC_WFS_PIT.xml

You can see the attachment that the foton style smoothing filter was used to reduce high freq noise above 0.1Hz.

Then the averaged values were read from "Cursor" tab (Attachment 2). This gave us this following sensing matrix.

Null to {WFS1P, WFS2P, MCTransP}
-36.7 +/- 90
401   +/- 200
-19.4 +/- 5
MC1 to {WFS1P, WFS2P, MCTransP}
2870 +/- 150
 910 +/- 150
1240 +/- 7
MC2 to {WFS1P, WFS2P, MCTransP}
  3950 +/- 200
-21700 +/- 490
  1210 +/- 13
MC3 to {WFS1P, WFS2P, MCTransP}
 -988 +/- 100
-7870 +/- 350
 1010 +/- 4
The inverse of this matrix is
           To MC1    MC2    MC3
From WFS1    1.2    1.0    -2.7
From WFS2    0.5   -0.4    -0.1
From MCT     5.0   -2.2     6.1

This is transposed for the MEDM output matrix. So the actual output matrix tried was

From WFS1  WFS2   MCT
     1.2    0.5   5.0   to MC1
     1.0   -0.4  -2.2   to MC2
    -2.7   -0.1   6.2   to MC3

We then individually tested the servo stability and the response to the input offset.
This matrix seemed indeed well diagnalized w.r.t the sensors. We injected the error signal offset in the MCTrans Pitch servo. This didn't reduce the IMC Trans indicating that the WFS1/2 were still as it was while the spot position was displaced. (very nice!)

The new matrix made all the pitch loops stable with negative gains (-0.1, -0.2, -0.5) together with the input gain slider of x1.0. The servo also worked together with the presence of the Yaw loops. Good.

The WFS1 gain was a bit too low. So we wanted to give 50% boost.
We decided to multiply the matrix elements by -0.3, increasing the servo GAIN fields by  -1/0.3. The resulting servo gain settings and the output matrix screen look like Attachment 3.


Then the IMC was aligned so that the reflection is minimized while the MC2 trans goes onto the center of the QPD.

Then the WFS offset script has been run with low and stable IMC Reflection DC (Attachment 4)

RXA Update 220109: I find the text based matrix hard to understand, so I am attaching the matrix I use to simulate this. Its the same as 'Sensing Matrix' that Koji has, but this one is scaled by an overall gain to account for the 200 counts actuation we put into the suspension actuators, and a minus sign as described above. Also its written in the usual way we represent vectors and matrices.
  17355   Fri Dec 9 21:54:40 2022 RadhikaUpdateASCMoku digital filter for low-frequency resonances (ALS/calibration)

[Radhika, Paco]

I modeled a digital filter for adding a resonance at a desired frequency (Q~100), with a complex-conjugate pole pair and 2 real zeros (2nd order system). Paco suggested I start with a 575 Hz resonance. I loaded the digital filter onto the Moku using the Moku python API (script at labutils/moku/mokuGoPro/mokuDigitalFilter.py). I tested the filter by feeding the Moku a 2 Vpp signal around 575 Hz and looking for some noticeable gain - however the signal passed though unchanged. There might be an additional Moku command for enabling the filter - I'll look into this.

TODO:

- Debug deployment of digital filter to Moku:Go
- Test on preset low-pass filter, before custom filter
- Once successful, add multiple resonances helpful for calibration
- Deploy filters in xarm AUX-PDH loop
  17356   Fri Dec 9 23:44:14 2022 ranaSummaryASCMC WFS sensing matrix measurement

with the new output matrix, we repeated the diagonalization script that Anchal ran previously. In the attached plot you can see that as we successively apply offsets to the WFS1, WFS2, and MC_TRANS Pitch loops, there is the offset in the loop we offset, but there is no appreciable step seen in the other loops.

Maybe we could do better, but this is the best DC diagonalization I have ever seen in this system. So we should just keep it for now.

At some point, we should run this procedure for YAW as well, but not urgent.

 

  17363   Fri Dec 16 21:55:54 2022 AnchalUpdateASCWFS demodulation board modification attempt 2 - sort of working

[Koji, Anchal]

short version: We checked signals at different points in the circuit to make sense of why it was not working. We found out that teh comparator chip AD96687BR was not working as expected and was not converting the analog signal from our VCO or LO inputs to ECL. We tested 2 other spare board with same behavior. We decided to try replacing the comparator chip with a new one, and indeed that was the issue. The new chip was working as expected and we are able to get PLL lock on the board with Moku:Lab as the VCO. However, there are some issues that need to be ironed out. The PLL does not catch lock right away and we could not figure our a systematic way of reaching to a locked state. That smells fishy to me as in my experience, when PLLs work, they work very robustly. More analysis with data and figures will follow. For now, we have some hope that this can work.

There is always the option of not closing PLL loop and injected twice the demodulation frequency at the VCO port that we have access two. For this, I'll need to create a SHG unit for 11 MHz with 21.4 MHz BLP. I'll look into this solution as well.

  17365   Sat Dec 17 16:56:19 2022 AnchalUpdateASCWFS demodulation board modification - further study

I played with the PLL bit more today to understand the issue. From what I understand, the following is the summary:

Moku as VCO in WFS demod board PLL:

  • Moku input in VCO mode is actually limited to ~ +/-21 V contrary to what it says on the app (10 Vpp)
  • Whenever the VCO tuning signal goes beyond this range, Moku just ignores the input and sends a pure sine wave at the carrier frequency.
  • I think because of this rail point behavior, the PLL goes off to a bad mode where the VCO tuning signal from demod board rails to +15 or -15V, and thus Moku does nothing to correct for it.
  • I found a deterministic way of catching lock with Moku VCO:
    • With whatever carrier frequency, set the VCO slope to at least 1 MHz/V (10 MHz/V is better).
    • The VCO tuning signal most probably would rail to +15V or -15V.
    • Reduce +/- 15V supply, this moves the railing voltage with it.
    • When the voltage rails reach +/2 V, the PLL catches the lock.
    • Now slowly ramp back the power supply back to +/- 15V.
  • This way I was able to repeatedly catch the lock (see attachment 1), but of course, this can't be done when our board is mounted in the Eurocrat.
  • So I thought if I attenuate the VCO tuning signal by 20 dB and pass it through an SR560, I can control the VCO tuning signal amplitude. This approach however did not work. It was always required to reduce the +/- 15V supply to the board to catch the lock.
  • This makes me think that the phase detector chip AD9901 needs to be turned off initially or supplied with low voltage rails. I'm not sure why.
  • With this, I think we should scrap this idea of using Moku as VCO, it will be just too unreliable.
  • So we need to move to the possibility of feeding 22 MHz signals to the WFS demod board where VCO output goes.

Basically, we make our own PLL outside the board to generate 2 times LO frequency or we create 2 times LO frequency by second harmonic generation.

Moku:Pro as a frequency multiplier

This white paper from liquid instruments describes how Moku:Pro can be used as a frequency multiplier in the phasemeter app now. This functionality however has not been extended to Moku:Lab, so in 40m, we can not do this right now. If we get access to Moku:Pro, following will be required:

  • Send 11 MHz LO signal to Moku:Pro input 1 with phasemeter app on.
  • Select frequency multiplier option of 2 at the output 1. Set voltage to 2 Vpp and feed this signal to VCO RF out port on the modified demod board.
  • Leave VCO tuning port unconnected.
  • This way we would replace the internal PLL with Moku digital PLL. Moku's PLL can be run upto 10 kHz bandwidth and would be very robust for such use.

Second harmonic generation using mixer and bandpass filter

  • Split the 14 dBm 11 Mhz output from frequency generation box (I simulated this with benchtop function generator) using a splitter.
  • Send both outputs to ZP-3+ mixer (level 7).
  • Filter the output with SBP-21.4 band pass filter. Koji has measured this filter in 2013. See elog 40m/9010.
  • Amplify the output twice, first with ZFL-500HLN+ (20dB amplification), then with ZFL-1HADX (11 dB).
  • This setup provides enought output amplitude for the comparator chip AD96687 to generate clean ECL signal at 22 MHz without slipping. With only 20dB amplification, I could see the phase slip by 180 degrees enough times that the oscilloscope shows both outputs overlapped.
  • Attachment 2 shows the ICLK and QCLK signals generated by the board with this setup.

Next steps:

  • I'll modify one more board for sending in LO like this.
  • I'll test the demodulation performance of the board with LO input from the second harmonic generation.
  • Setup the optical path for AS WFS.
  17368   Tue Dec 20 23:32:58 2022 ranaUpdateASCWFS demodulation board modification - further study

That's great - I think this solution will be best. Having the PLLs actually gives us some problems - the square wave action in these demod boards because of the ECL drives pollutes the air with all the harmonics.

In the future, it would be best to get rid of these boards and just use the new aLIGO boards with a direct LO feed.

Quote:

I played with the PLL bit more today to understand the issue. From what I understand, the following is the summary:

 

Second harmonic generation using mixer and bandpass filter

  17391   Tue Jan 10 20:24:29 2023 AnchalUpdateASCWFS demodulation board 111B - Working as expected

I've completed the modifications on two WFS demod boards. This required replacing all 8 mixer ICs on each board. I also tuned each channel to get less than 2 mV offset on all of them.

I was able to complete testing the board SNo. 111B today. The results are attached. The test was done by feeding the board 22 MHz LO generated by frequency doubling. A signal at 11 MHz was generated using Moku:Lab at 1mVpp and then further attenuated by 10 dB to make a fair comparison with the previous testing of the IMC WFS board at 29.5 MHz. This board has the same response as the IMC WFS board at 29.5 MHz. I tested all four channels in the second plot.

I'll complete the testing of the second board SNo 112 B and then move on to setting up the optical path for AS WFS.

  17393   Wed Jan 11 17:05:55 2023 AnchalUpdateASCWFS demodulation board 112B - Working as expected

The other modified board 112B has been fixed and tested now. See the results attached. The issue was in some malfunctioning OP284 which have been replaced by AD8672.

  17406   Thu Jan 19 20:35:54 2023 AnchalUpdateASCInstalled 2 flipper mirrors for handingl MC reflection beam to camera

Today I installed two flipper mirrors M3 and M4 (see attached photo) to create alternate route for MC reflection camera beam. Both these mirrors are Y1-1037-45S. In nominal operation where IMC is using the WFS, we will keep M3 upright and M4 flipped down. When using WFS for AS, M3 will be flipper down and M4 will be upright to save the camera from the high intensity MC reflection beam.

Note that everytime M3 is flipper and put back upright, the alignment into WFS would need to be tuned as the flipper apparatus does not come back to same alignment everytime. I centered the beams on the WFS heads today and zeroed RF offsets usingC1IOO_WFS_MASTER>!Actions>Correct WFS RF Offsets script. After this, the IMC WFS loops are working as expected atleast for last 15 minutes that I have monitored them. Hopefully, this will remain consistent.


Upcoming work:

  • Change the steering mirror that steers the beam to black hole to be a flipper mirror too as AS beam strength (measured when MICH was locked to bright port) is 0.3 mW and IMC WFS heads combined power is 0.5 mW in nominal operation, so we can not afford to dump any AS beam light.
  • Put flipper mirror M1 and fixed mirror M2 mentioned in 40m/17320 for steering AS beam to IMC WFS heads.
  17407   Fri Jan 20 20:13:20 2023 AnchalUpdateASCInstalled 2 flipper mirrors for handingl MC reflection beam to camera

After discussions with Yuta, I figured that a better optical layout is possible which does not interfere with the existing IMC WFS path at all. So I reset the IMC WFS path today (and zeroed RF offsets again) and changed the MC reflection camera and MC reflection beam dump (black hole) position to create space for a flipper mirror that will pop up in the IMC WFS path and steer in the AS beam. New proposed path is shown in the photo in cyan. Red is MC reflection beam, yellow is IFO reflection beam and orange is teh AS beam that we will pick up using flipper mirror M1. Note that I found an intense 6.4 mW ghost beam coming out of the interferometer in between IFO refl and MC refl beams. This beam is shown in pink which I have dumped now. This beam was earlier not dumped. We will need to investigate more on the source of this beam and correct it in the next vent.

  17408   Sat Jan 21 15:32:40 2023 AnchalUpdateASCAS WFS path nominally set

I've completed the beam redirection path for AS beam to WFS heads in a nominal way. By that I mean that all mirrors (M1, M2, M3, and M4) are now in their final positions and we will need to install one or two lenses to collimate the beam to match the mode that the WFS path is expecting as it has it's on the focusing lens before the photodiodes. For this last part, I think the fasted way would be to profile the beam and calculate the correct lens and position rather than trial and error as the beam intensity is very low for estimating the beam size by eye.

IMC WFS state: Flip M1 and M2 down.

AS WFS state: Flip M1 and M2 up.

  17412   Mon Jan 23 20:50:58 2023 AnchalUpdateASCAS WFS path beam profiled

I measured the expected beam profile by WFS photodiodes by measuring the beam when mode cleaner was unlocked from the point where beam is picked for WFS. See attachment 1 for beam details. z=0 is the point in the path where AS beam will merge.

For measuring the beam profile of AS beam, I had to focus it using a lens. I picked up a 360.6 mm ROC lens and placed it at z=-67 inch point. Then I profiled the beam at some comfortable section of the path and fitted it. with reverse z-axis. Using this method, I can place the lens back and obtain the original beam back. Attachment 2 shows this fitting process and identification of the original beam profiles. I plotted the AS beam profiles again in attachment 3 and saved them for seeding mode matching effort later. Note that we don't want to be super accurate here, so I did not do any error analysis, just wanted to finish this fast. Also pardon me for the bad quality plots, I did not want to learn Matlab plotting to make it beautiful.

Note: There is significant astigmatism in both IMC reflection beam and AS beam. This could be due to beam going through far off-center on lens. Something to keep in mind, again this measurement is not ideal in terms of precision but this large an astigmatism could not be due to measurement error.


Next:

  • Identify correct len(s) and their positions
  • Align the AS beam to WFS heads
  • Test the full signal chain.
  17416   Tue Jan 24 21:04:59 2023 AnchalUpdateASCAS WFS path beam profiled

I completed the mode matching calculation today and found good solution with 360.6 mm ROC PLCX lens at -1.2 m from z=0 point. I placed the lens there today and aligned all mirrors to get centered beam on both WFS PDs when the flipper mirrors are flipper up. This alignment would probably require tweaking everying we flip the mirrors as the flipper mirrors do not come back to same position usually.

I mounted the modified WFS boards 111B and 112B next to the whitening filter boards of existing WFS. Now to switch over, onewould need to transfer the 8 RF lemo cables and the 2 IDE ribbon cables.

I'm working on rtcds model to read AS WFS data and handle it separately. I'll keep a WPICS binaruy switch to switch between IMC WFS or AS WFS. I need to figure out some build issues on this work still.

 

  17425   Thu Jan 26 15:56:30 2023 AnchalUpdateASC1X1 -5V sorenson tripped

[Yuta, Anchal]

Quote:

I mounted the modified WFS boards 111B and 112B next to the whitening filter boards of existing WFS.

The mounting of two additional WFS demodulation boards drew too much current on -5V rail which tripped the sorenson on 1X1. This was undetected until today. Because of this, the existing WFS boards were not working either. After investicgation to beam paths and PD to board signal chain, we found out this issue. We raised the current limit on -5V supply and it came back to 5V. This brought back functioning of the exisitng WFS boards as well. We increased the current limit slightly on +5V supply too as these boards take a lot of current on +/5 V rails. But we should do this more properly by knowing what current limit the supply is set to. We'll do this part in near future after reading the manuals/wiki.
IMC WFS loops are now working.

  17444   Fri Feb 3 12:50:47 2023 AnchalUpdateASCAS WFS model changes and phase calibration

Model and medm changes

After incrementally doing the model changes, I found out that the model was failing to build because of creation of a subsystem. If I just kept all divertor blocks out in the main model instead of in a single subsystem, the compilation works. Maybe the reason is because RCG can only take subsystems at base level which have top_names attribute. But I did nto test this, I just went with what works.

In summary, I added a new subsystem in c1ioo model called AWS (stands for Antisymmetric Wavefront Sensors). This subsystem and IOO subsystem receive teh WFS RF demodulated signals based on a single binary switch named C1:IOO-SEL_WFS_IMC_OR_AS. Value 0 connects the subsystem IOO to the inputs and value 1 connects AWS to the inputs. There is a switch on the left edge in the WFS screens now to select between the two.

Inside the AWS, the WFS I/Q phase rotation is done and then it goes into one of the two subsystems called AWS-XARM or AWS-YARM for using the AS for either XARM or YARM. THis is based on a single binary switch called C1:AWS-SEL_ARM_X_OR_Y. Value 0 selects output to XARM and value 1 selects output to YARM. There is a switch near top left of  C1AWS_XARM_WFS_MASTER.adl and C1AWS_YARM_WFS_MASTER.adl screens. I copied these screens from C1IOO_WFS_MASTER.adl, so they have same structure. See attachment 1. Any edits should be made to /opt/rtcds/caltech/c1/medm/c1ioo/master/C1AWS_XARM_WFS_MASTER.adl and simply run python opt/rtcds/caltech/c1/medm/c1ioo/master/createYARMWFSscreensFromX.py to create teh YARM screen from it.

Along with this, models c1scy and c1scx were edited also to take in IPC directly from c1ioo instead of going through RFM. We should phase out use of RFM eventually and directly connect all IPC connections with the ends.

First tests

[Anchal, Yuta]

After the model is up and running, we flipped the WFS path to use AS beam. I switched the 8 RF outputs of the WFS from IMC WFS boads to AS WFS boards and switched the IDC connectors to WFS. Attachment 2 shows teh photo in this flipped state. Then we misaligned both ITMX and ETMX. First simple test was to check if we see the YARM PDH error signal when YARM was flashing. And indeed we saw that on all 16 channels. So next we locked YARM and injected 311 Hz line with 300 counts amplitude at ETMY. We looked for this peak in the Q channels of WFS outputs and adjusted all phases to 0.1 degrees to minimize Q signal to the noise floor. For WFS2 case, teh SNR is bit higher due to more power than WFS1 and their phase angle might be adjusted to even better degree but we did not got for it.

Then I used C1AWS_XARM_WFS_MASTER.adl>!Actions>Correct WFS RF offsets button to remove offsets in all the RF demodulated signals. I have set this button to use /opt/rtcds/caltech/c1/Git/40m/scripts/RFPD/resetOffsets.py script.

At this point, we are ready to see if we have WFS sensitivity but I need to work on other projects today and Yuta and Paco took over interferometer for 60 Hz noise hunting.

 

 

  17448   Sat Feb 4 14:55:25 2023 AnchalUpdateASCDC sensing matrix for AS WFS for YARM

Filter and scripts setup

I copied IOO_WFS1_I filter bank to AWS_WFS1/2_I/Q filter banks to copy the dewhitening and 60comb filters. Then I turned them on.

Similarly, I copied IOO_WFS1_PIT filter bank to AWS_YARM/XARM_WFS1/2_PIT/YAW filter banks. I created a generalised script to handle all WFS on/off.hold/onfromhold operations here. I also generalized toggleWFSoffsets script to be used for measuring DC sensing matrix.

DC sensing matrix measurement

This measurement folllowed the method used by Koji in 40m/17354. The measurement is pushed here. Ntoe that when using this method, while the test finishd in ~1000 seconds, it takes dtt >20 min to retrieve the timeseries data from DQ channels. Thisis weird because cdsutils.getdata does not have this lag. If anyone knows why this is the case, it would be helpful in making this method faster.

  • Locked YARM and misaligned ITMX and ETMX
  • Centered the AS beam on WFS using DC value.
  • Ran ASS on YARM to get to best aligned cavity state.
  • Unlocked YARM and ran C1AWS_YARM_WFS_MASTER>!Actions>Correct WFS RF offsets to zero teh offsets.
  • Locked YARM again and waited for >120 seconds.
  • Ran python /opt/rtcds/caltech/c1/Git/40m/scripts/AWStoggleWFSoffsets.py AWS BOTH -a YARM -t 120
    • Measurement start time: 04/02/2023 22:37:00 UTC
  • The offset values required for step response test above were determined by trying out values and making sure that transmission does not go down by more than 15%.
  • I had to leave by 3:30 pm, so I couldn't complete the analysis of measured data.I'll post data here soon.

 


Additions Sun Feb 5 18:06:54 2023:

Data analysis

I got the step response data using cdsutils.getdata and measured the sensing matrix and took and inverse with error propagation. Attachment 1 page 1 shows the raw data measured. Then the data was segmented based on step response time data and a linear fit is used to get linear trend of each channel in null configuration. This is used to remove bias later while measuring the step heights in each sensor. Page 2 shows this data. Page 3 shows final detrended and normalized step response data that was used to measure the sensing matrix. It came out to be:

                                                             YARM WFS DC Sensing Matrix

        ITMY PIT         ETMY PIT         ITMY YAW         ETMY YAW
   1.94 +/- 0.02    0.83 +/- 0.07   -0.15 +/- 0.04      1.3 +/- 0.1  to WFS1 PIT
   5.62 +/- 0.05      8.8 +/- 0.2     -0.2 +/- 0.1      2.5 +/- 0.2  to WFS2 PIT
  -0.43 +/- 0.03   -1.13 +/- 0.07    1.51 +/- 0.04     -0.9 +/- 0.2  to WFS1 YAW
  -1.42 +/- 0.05     -7.1 +/- 0.2      3.3 +/- 0.1    -19.5 +/- 0.4  to WFS2 YAW

Taking it's inverse with uncertainties supported matrix inverse function gave following output matrix to be used:

                                                         YARM WFS Estimated Output Matrix
        WFS1 PIT         WFS2 PIT         WFS1 YAW         WFS2 YAW
   0.628+/-0.022   -0.031+/-0.007   -0.027+/-0.020    0.039+/-0.004  to ITMY PIT
  -0.431+/-0.020    0.146+/-0.007   -0.002+/-0.018 -0.0099+/-0.0030  to ETMY PIT
  -0.086+/-0.031    0.078+/-0.010    0.728+/-0.029   -0.029+/-0.008  to ITMY YAW
   0.097+/-0.009 -0.0377+/-0.0030    0.126+/-0.008 -0.0555+/-0.0020  to ETMY YAW
  13157   Tue Aug 1 19:23:06 2017 ranaUpdateALSX - arm alignment

Rana, Naomi

We dither locked the X arm and then aligned the green beam to it using the PZTs. Everything looks ready for us to do a mode scan tomorrow.

We got buildup for Red and Green, but saw no beat in the control room. Quick glance at the PSL seems OK, but needs more investigation. We did not try moving around the X-NPRO temperature.

Tomorrow: get the beat, scan the PhaseTracker, and get data using pyNDS.

  13177   Wed Aug 9 12:35:47 2017 gautamUpdateALSFiber ALS

Last week, we were talking about reviving the Fiber ALS box. Right now, it's not in great shape. Some changes to be made:

  1. Supply power to the PDs (Menlo FPD310) via a power regulator board. The datasheet says the current consumption per PD is 250 mA. So we need 500mA. We have the D1000217 power regulator board available in the lab. It uses the LM2941 and LM2991 power regulator ICs, both of which are rated for 1A output current, so this seems suitable for our purposes. Thoughts?
  2. Install power decoupling capacitors on the PDs.
  3. Clean up the fiber arrangement inside the box.
  4. Install better switches, plus LED indicators.
  5. Cover the box.
  6. Install it in a better way on the PSL table. Thoughts? e.g. can we mount the unit in some electronics rack and route the fibers to the rack? Perhaps the PSL IR and one of the arm fibers are long enough, but the other arm might be tricky.

Previous elog thread about work done on this box: elog11650

  13180   Wed Aug 9 19:21:18 2017 gautamUpdateALSALS recovery

Summary:

Between frequent MC1 excursions, I worked on ALS recovery today. Attachment #1 shows the out-of-loop ALS noise as of today evening (taken with arms locked to IR) - I have yet to check loop shapes of the ALS servos, looks like there is some tuning to be done.

On the PSL table:

  • First, I locked the arms to IR, ran the dither alignment servos to maximize transmission.
  • I used the IR beat PDs to make sure a beat existed, at approximately.
  • Then I used a scope to monitor the green beat, and tweaked steering mirror alignment until the beat amplitude was maximized. I was able to improve the X arm beat amplitude, which Koji and Naomi had tweaked last week, by ~factor of 2, and Y arm by ~factor of 10.
  • I used the DC outputs of the BBPDs to center the beam onto the PD.
  • Currently, the beat notes have amplitudes of ~-40dBm on the scopes in the control room (there are various couplers/amplifiers in the path so I am not sure what beatnote amplitude this translates to at the BBPD output). I have yet to do a thorough power budget, but I have in my mind that they used to be ~-30dBm. To be investigated.
  • Removed the fiber beat PD 1U chassis unit from the PSL table for further work. The fibers have been capped and remain on the PSL table. Cleaned the NW corner of the PSL table up a bit.

To do:

  • Optimization of the input pointing of the green beam for X (with PZTs) and Y (manual) arms.
  • ALS PDH servo loop measurement. Attachment #1 suggests some loop gain adjustment is required for both arms (although the hump centered around ~70Hz seem to be coming from the IR lock).
  • Power budgeting on the PSL table to compare to previous such efforts.

Note: Some of the ALS scripts are suffering from the recent inablilty of cdsutils to pull up testpoints (e.g. the script that is used to set the UGFs of the phase tracker servo). The workaround is to use DTT to open the test points first (just grab 0.1s time series for all channels of interest). Then the cdsutils scripts can read the required channels (but you have to keep the DTT open).

  13204   Mon Aug 14 16:24:09 2017 gautamUpdateALSFiber ALS

Today, I borrowed the fiber microscope from Johannes and took a look at the fibers coupled to the PDs. The PD labelled "BEAT PD AUX Y" has an end that seems scratched (Attachments #1 and #2). The scratch seems to be on (or at least very close to) the core. The other PD (Attachments #3 and #4) doesn't look very clean either, but at least the area near the core seems undamaged. The two attachments for each PD corresponds to the two available lighting settings on the fiber microscope.

I have not attempted to clean them yet, though I have also borrowed the cleaning supplies to facilitate this from Johannes. I also plan to inspect the ends of all other fiber connections before re-installing them.

Quote:

Last week, we were talking about reviving the Fiber ALS box. Right now, it's not in great shape. Some changes to be made:

  1. Supply power to the PDs (Menlo FPD310) via a power regulator board. The datasheet says the current consumption per PD is 250 mA. So we need 500mA. We have the D1000217 power regulator board available in the lab. It uses the LM2941 and LM2991 power regulator ICs, both of which are rated for 1A output current, so this seems suitable for our purposes. Thoughts?
  2. Install power decoupling capacitors on the PDs.
  3. Clean up the fiber arrangement inside the box.
  4. Install better switches, plus LED indicators.
  5. Cover the box.
  6. Install it in a better way on the PSL table. Thoughts? e.g. can we mount the unit in some electronics rack and route the fibers to the rack? Perhaps the PSL IR and one of the arm fibers are long enough, but the other arm might be tricky.

Previous elog thread about work done on this box: elog11650

 

  13222   Wed Aug 16 20:24:23 2017 gautamUpdateALSFiber ALS

Today, with Johannes' help, I cleaned the fiber tips of the photodiodes. The effect of the cleaning was dramatic - see Attachments #1-4, which are X Beat PD, axial illumination, X Beat PD, oblique illumination, Y beat PD, axial illumination, Y beat PD, oblique illumination. They look much cleaner now, and the feature that looked like a scratch has vanished.

The cleaning procedure followed was:

  • Blow clean air over the fiber tip
  • First, we tried cleaning with the Q-tip like tool, but the results weren't great. The way to use it is to dip the tip in the cleaning solvent for a few seconds, hold the tip to the fiber taking into account the angled cut, and apply 10 gentle quarter turns.
  • Next, we tried cleaning with the wipes. We peeled out an approximately 5" section of the wipe, and laid it out on the table. We then applied cleaning solvent liberally on the central area where we were sure we hadn't touched the wipe. Then you just drag the fiber tip along the soaked part of the wipe. If you get the angle exactly right, the fiber glides smoothly along the surface, but if you are a little misaligned, you get a scratchy sensation. 
  • Blow dry and inspect.

I will repeat this procedure for all fiber connections once I start putting the box back together - I'm almost done with the new box, just waiting on some hardware to arrive.

 

Quote:

Today, I borrowed the fiber microscope from Johannes and took a look at the fibers coupled to the PDs. The PD labelled "BEAT PD AUX Y" has an end that seems scratched (Attachments #1 and #2). The scratch seems to be on (or at least very close to) the core. The other PD (Attachments #3 and #4) doesn't look very clean either, but at least the area near the core seems undamaged. The two attachments for each PD corresponds to the two available lighting settings on the fiber microscope.

I have not attempted to clean them yet, though I have also borrowed the cleaning supplies to facilitate this from Johannes. I also plan to inspect the ends of all other fiber connections before re-installing them.

 

  13229   Fri Aug 18 23:59:53 2017 gautamUpdateALSX Arm ALS lock

[ericq, gautam]

  • I was just getting the IFO aligned, and single arm lock going, when EricQ came in and asked if we could get some ALS data.
  • ALS beats seemed fine, in particular the X-Arm. The broad hump around ~70Hz that was present in my previous ALS update was nowhere to be seen - reasons unknown.
  • Copied over /opt/rtcds/caltech/c1/scripts/YARM/Lock_ALS_YARM.py to /opt/rtcds/caltech/c1/scripts/XARM/Lock_ALS_XARM.py. Could be useful when we want to do arm cavity scans.
  • Made appropriate changes to allow ALS locking of Xarm - the testpoint inaccessibility makes things a little annoying but for tonight we just used DQ channels in place (or slow channels when DQ chans were not available)
  • Calibration of X arm error signal seemed off - so we fixed it by driving a line in ETMX and matching up the peaks in the ALS error signal and POX11. We then updated the gain of the filter in the CINV filter bank accordingly.
  • Got some decent data - X arm stayed locked on ALS for >60mins, during which time the Y arm stayed locked on POY11, and the Y green also reained locked yes. There was no evidence of the X arm 00 mode randomly dropping out of lock tonight.
  • EQ will update with a sick comparison plot - today we looked at the ALS noise from the perspective of the Green Locking Izumi et. al. paper.
  • Y arm ALS noise didn't look so hot tonight - to be investigated...

Leaving LSC mode OFF for now while CDS is still under investigation


Not really related to this work: We saw that the safe.snap file for c1oaf seems to have gotten overwritten at some point. I restored the EPICS values from a known good time, and over-wrote the safe.snap file.

  13230   Sat Aug 19 01:35:08 2017 ericqUpdateALSX Arm ALS lock

My motivation tonight was to get an up-to-date spectrum of a calibrated measurement of the out-of-loop displacement of an arm locked on ALS (using the PDH signal as the out-of-loop sensor) to compare the performance of ALS control noise with the Izumi et al green locking paper. 

I was able to fish out the PSD from the paper from the 40m svn, but the comparison as plotted looks kind of fishy. I don't see why the noise from 10-60Hz should be so different/worse. We updated the POX counts to meters conversion by looking at the Hz-calibrated ALSX signal and a ~800Hz line injected on ETMX.

  13237   Mon Aug 21 23:38:55 2017 gautamUpdateALSALS out-of-loop noise

I worked a little bit on the Y arm ALS today. 

  • Started by locking the Y arm to IR with POY, and then ran the dither alignment script to maximize Y arm transmission.
  • Green TRY DC monitor was around 0.16, whereas I have seen ~0.45 when we were doing DRFPMI locking.
  • So I went to the Y end table and tweaked the steering mirrors a little. I was able to get GTRY to ~0.42. I think this can be tweaked a little further but I decided to push on for tonight.
  • The beat amplitude on the network analyzer in the control room is comparable to the X arm beat now.
  • Adjusted the gain of the phase tracker servos, cleared phase history.
  • Looking at the ALS beat noise with the arms locked to IR and the slow ALS temperature control loops ON (see Attachment #1), the current measurements line up quite well with the reference traces.

I am now going to measure the OLTFs of both green PDH loops to check that the overall loop gain is okay, and also check the measurement against EricQ's LISO model of the (modified) AUX green PDH servos. Results to follow.


Some weeks ago, I had moved some of the Green steering optics on the PSL table around, in order to flip some mirror mounts and try and get angles of incidence closer to ~45deg on some of the steering mirrors. As a result of this work, I can see some light on the GTRY CCD when the X green shutter is open. It is unclear if there is also some scattered light on the RFPDs. I will post pictures + a more detailed investigation of the situation on the PSL table later, there are multiple stray green beams on the PSL table which should probably be dumped.


As I was writing this elog, I saw the X green lock drop abruptly. During this time, the X arm stayed locked to the IR, and the Y arm beat on the control room network analyzer did not jump (at least not by an amount visible to the eye). Toggling the X end shutter a few times, the green TEM00 lock was re-acquired, but the beatnote has moved on the control room analyzer by ~40MHz. On Friday evening however, the X green lock held for >1 hour. Need to keep an eye on this.

  13238   Tue Aug 22 02:19:11 2017 gautamUpdateALSALS OLTFs

Attachment #1 shows the results of my measurements tonight (SR785 data in Attachment #2). Both loops have a UGF of ~10kHz, with ~55 degrees of phase margin.

Excitation was injected via SR560 at the PDH error point, amplitude was 35mV. According to the LED indicators on these boxes, the low frequency boost stages were ON. Gain knob of the X end PDH box was at 6.5, that of the Y end PDH box was at 4.9. I need to check the schematics to interpret these numbers. GV Edit: According to this elog, these numbers mean that the overall gain of the X end PDH box is approx. 25dB, while that of the Y end PDH box is approx. 15dB. I believe the Y end Lightwave NPRO has an actuator discriminant ~5MHz/V, while the X end Innolight is more like 1MHz/V.

Not sure what to make of the X PDH loop measurement being so much noisier than the Y end, I need to think about this.

More detailed analysis to follow.

Quote:

 

I am now going to measure the OLTFs of both green PDH loops to check that the overall loop gain is okay, and also check the measurement against EricQ's LISO model of the (modified) AUX green PDH servos. Results to follow.

 

  13244   Tue Aug 22 23:27:14 2017 ranaUpdateALSALS OLTFs

Didn't someone look at what the OLG req. should be for these servos at some point? I wonder if we can make a parallel digital path that we switch on after green lock. Then we could make this a simple 1/f box and just add in the digital path (take analog control signal into ADC, filter, and then sum into the control point further down the path to the laser) for the low frequency boost.

  13246   Wed Aug 23 17:22:36 2017 gautamUpdateALSFiber ALS - reinstalled

I completed the revamp of the box, and re-installed the box on the PSL table today. I think it would be ideal to install this on one of the electronic racks, perhaps 1X2 would be best. We would have to re-route the fibers from the PSL table to 1X2, but I think they have sufficient length, and this way, the whole arrangement is much cleaner.

Did a quick check to make sure I could see beat notes for both arms. I will now attempt to measure the ALS noise with this revamped box, to see if the improved power supply and grounding arrangement, as well as fiber cleaning, has had any effect.

Photos + power budget + plan of action for using this box to characterize the green PDH locking to follow. 

For quick reference: here is the AM/PM measurement done when we re-installed the repaired Innolight NPRO on the new X endtable.

  13254   Fri Aug 25 15:54:14 2017 gautamUpdateALSFiber ALS noise measurement

[Kira, gautam]

Attachment #1 - Photo of the revamped beat setup. The top panel has to be installed. New features include:

  • Regulated power supply via D1000217.
  • Single power switch for both PDs.
  • Power indicator LED.
  • Chassis ground isolated from all other electronic grounds. For this purpose, I installed all the elctronics on a metal plate which is only connected to the chassis via nylon screws. The TO220 package power regulator ICs have been mounted with the TO220 mounting kits that provide a thin piece of plastic that electrically insulates its ground from the chassis ground.
  • PD outputs routed through 20dB coupler on front panel for diagnostic purposes.
  • Fiber routing has been cleaned up a little. I installed a winding fixture I got from Johannes, but perhaps we can install another one of these on top of the existing one to neaten up the fiber layout further.
  • 90-10 light splitter (meant for diagnostic purposes) has been removed because of space constraints. 

Attachment #2 - Power budget inside the box. Some of these FC/APC connectors seem to not offer good coupling between the two fibers. Specifically, the one on the front panel meant to accept the PSL light input fiber seems particularly bad. Right now, the PSL light is entering the box through one of the front panel connectors marked "PSL + X out". I've also indicated the beat amplitude measured with an RF analyzer. Need to do the math now to confirm if these match the expected amplitudes based on the power levels measured.

Attachment #3 - We repeated the measurement detailed here. The X arm (locked to IR) was used for this test. The "X" delay line electronics were connected to the X green beat PD, while the "Y" delay line electronics were connected to the X IR beat PD. I divided the phase tracker Hz calibration factor by 2 to get IR Hz for the Y arm channels. IR beat was at ~38MHz, green beat was at ~76MHz. The broadband excess noise seen in the previous test is no longer present. Indeed, below ~20Hz, the IR beat seems less noisy. So seems like the cleaning / electronics revamp did some good. 

Further characterization needs to be done, but the results of this test are encouraging. If we are able to get this kind of out of loop ALS noise with the IR beat, perhaps we can avoid having to frequently fine-tune the green beat alignment on the PSL table. It would also be ideal to mount this whole 1U setup in an electronics rack instead of leaving it on the PSL table.

Quote:

Photos + power budget + plan of action for using this box to characterize the green PDH locking to follow. 

GV Edit: I've added better photos to the 40m Google Photos page. I've also started a wiki page for this box / the proposed IR ALS  system. For the moment, all that is there is the datasheet to the Fiber Couplers used, I will populate this more as I further characterize the setup.

  13255   Fri Aug 25 17:11:07 2017 ranaUpdateALSFiber ALS noise measurement

Is it better to mount the box in the PSL under the existing shelf, or in a nearby PSL rack?

Quote:

 

Further characterization needs to be done, but the results of this test are encouraging. If we are able to get this kind of out of loop ALS noise with the IR beat, perhaps we can avoid having to frequently fine-tune the green beat alignment on the PSL table. It would also be ideal to mount this whole 1U setup in an electronics rack instead of leaving it on the PSL table

 

  13257   Sun Aug 27 11:57:31 2017 ranaUpdateALSFiber ALS noise measurement

It seems like the main contribution to the RMS comes from the high frequency bump. When using the ALS loop to lock the arm to the beat, only the stuff below ~100 Hz will matter. Interesting to see what that noise budget will show. Perhaps the discrepancy between inloop and out of loop will go down.

  13266   Tue Aug 29 02:08:39 2017 gautamUpdateALSFiber ALS noise measurement

I was having a chat with EricQ about this today, just noting some points from our discussion down here so that I remember to look into this tomorrow.

  • I believe that currently, the channels C1:ALS-BEATX_FINE_PHASE_OUT_HZ_DQ and the Y arm analog read out the frequency of the green beat, in Hz.
  • In the comparison I plotted, I WRONGLY divided the spectrum of the IR beat by 2, instead of multiplying in by 2, which is what should actually be done for an apples-to-apples comparison.
  • The deeper question is, what should this channel actually readout?
  • Looking at my codes from past arm scans etc, I see that I am dividing the downloaded data by 2 in order to convert the X-axis of these scans to "IR Hz". But this should really be all we care about.
  • So I think I will have to re-do the cts-to-Hz calibration in the ALS models. It should be possible to do ~10FSR scans with the IR beat, and then we can use the sideband resonances (presumably the sideband frequencies are known with better precision than the arm length, and hence the FSR) to calibrate the phase tracker.
  • I don't think this changes the fact that the Fiber ALS situation has been improved - but I will have to repeat the measurement to be sure. The improvement may not be as stellar as I tried to sell in my previous elog sad.

    Other thoughts: 

  • Can we make use of the Jetstor raid array for some kind of consolidated 40m CDS backup system? Once we've gotten everything of interest out of it...

  13288   Fri Sep 1 19:15:40 2017 gautamUpdateALSFiber ALS noise measurement

Summary:

I did some work today to see if I could use the IR beat for ALS control. Initial tests were encouraging.

I will now embark on the noise budgeting.

Details:

  • For this test, I used the X arm
  • I hooked up the X-arm + PSL IR beat to the X-arm DFD channel, and used the Y-arm DFD channels to simultaneously monitor the X-arm green beat.
  • I then transitioned to ALS control and used POX as an out-of-loop sensor for the ALS noise.
  • Attachment #1 shows a comparison of the measurements. In red is the IR beat, while the green traces are from the test EricQ and I did a couple of nights ago using the green beat.
  • I also wanted to do some arm cavity scans with the arm under ALS control with the IR beat - but was unsucessful. The motivation was to fix the ALS model counts->Hz calibration factors.
  • I did however manage to do a 10 FSR scan using the green beatnote - however, towards the end of this scan, the green beat frequency (read off the control room analyzer) was ~140MHz, which I believe is outside (or at least on the edge) of the bandwidth of the Green BBPDs. The fiber coupled IR beat photodiodes have a much larger (1GHz) spec'd bandwidth.

I am leaving the green beat electronics on the PSL table in the switched state for further testing...

 

  13325   Thu Sep 21 01:32:00 2017 gautamUpdateALSAUX X Innolight AM measurement running

[rana,gautam]

We set up a measurement of the AUX X laser AM today. Some notes:

  • PDA 55 that was installed as a power monitor for the AUX X laser has been moved into the main green beam path - it is just upstream of the green shutter for this measurement.
  • AUX X laser power into the doubling crystal was adjusted by rotating HWP upstream of IR Faraday (original angle was 100, now it is 120), until the DC level of the PDA 55 output was ~2.5V on a scope (high impedance).
  • BNC-T was installed at the PZT input of the Innolight - one arm of the T is terminated to ground via 50 ohms. The purpose of this is to always have the output of the power splitter from the network analyzer RF source drive a 50 ohm load.
  • The output of the Green PDH servo to the Innolight PZT was disconnected downstream of the summing Pomona box - it is now connected to one output of a power splitter (borrowed from SR function generator used to drive the PZT) connected to the RF source output of the AG4395.
  • Other output of power splitter connected to input R of AG4395.
  • PDA55 output has been disconnected from CH5 of the AA board. It is connected to input A of the AG4395 via DC block.

Attachment #1 shows a preliminary scan from tonight - we looked at the region 10kHz-10MHz, with an IF bandwidth of 100Hz, 16 averages, and 801 log-spaced frequencies. The idea was to get an idea of where some promising notches in the AM lie, and do more fine-bandwidth scans around those points. Data + code used to generate this plot in Attachment #2.

Rana points out that some of the AM could also be coming from beam jitter - so to put this hypothesis to test, we will put a lens to focus the spot more tightly onto the PD, repeat the measurement, and see if we get different results.

There were a whole bunch of little illegal things Rana spotted on the EX table which he will make a separate post about.

I am running 40 more scans with the same params for some statistics - should be done by the morning.

Quote:

I borrowed the HP impedance test kit from Rich Abbott today. The purpose is to profile the impedance of the NPRO PZTs, as part of the AUX PDH servo investigations. It is presently at the X-end. I will do the test in the coming days.
 


Update 12:00 21 Sep: Attachment #3 shows schematically the arrangement we use for the AM measurement. A similar sketch for the proposed PM measurement strategy to follow. After lunch, Steve and I will lay out a longish BNC cable from the LSC rack to the IOO rack, from where there is already a long cable running to the X end. This is to facilitate the PM measurement.

Update 18:30 21 Sep: Attachment #4 was generated using Craig's nice plotting utility. The TF magnitude plot was converted to RIN/V by dividing by the DC voltage of the PDA 55 of ~2.3V (assumption is that there isn't significant difference between the DC gain and RF transimpedance gain of the PDA 55 in the measurement band) The right-hand columns are generated by calculating the deviation of individual measurements from the mean value. We're working on improving this utility and aesthetics - specifically use these statistics to compute coherence, this is a work in progress. Git repo details to follow.

There are only 23 measurements (I was aiming for 40) because of some network connectivity issue due to which the script stalled - this is also something to look into. But this sample already suggests that these measurement parameters give consistent results on repeated measurements above 100kHz.

TO CHECK: PDA 55 is in 0dB gain setting, at which it has a BW of 10MHz (claimed in datasheet).


Some math about relation between coherence \gamma_{xy}(f) and standard deviation of transfer function measurements:

\mathrm{SNR}(f) = \sqrt{\frac{\gamma_{xy}^{2}(f)}{1-\gamma_{xy}^{2}(f)}}

\sigma_{xy}^{2} = \frac{1-\gamma_{xy}^{2}(f)}{2N\gamma_{xy}^{2}(f)}|H(f)|^2  --- relation to variance in TF magnitude. We estimate the variance using the usual variance estimator, and can then back out the coherence using this relation.

\sigma_{\theta_{xy}} = \mathrm{tan}^{-1}\left [ \sqrt{\frac{1-\gamma_{xy}^{2}(f)}{2N\gamma_{xy}^{2}(f)}} \right ] --- relation to variance in TF phase. Should give a coherence profile that is consistent with that obtained using the preceeding equation.

It remains to code all of this up into Craig's plotting utility.

  13326   Thu Sep 21 01:55:16 2017 ranaUpdateALSX End table of Shame

Image #1: No - we do not use magnetic mounts for beam dumps. Use a real clamp. It has to be rigid. "its not going anywhere" is a nonsense statement; this is about vibration amplitude of nanometers.

Image #2: No - we do not use sticky tape to put black glass beam dumps in place ever, anywhere. Rigid dumps only.

Image #3: Please do not ruin our nice black glass with double sticky tape. We want to keep the surfaces clean. This one and a few of the other Mickey Mouse black glass dumps on this table were dirty with fingerprints and so very useless.

Image #4: This one was worst of all: a piece of black glass was sticky taped to the wall. Shameful.

Please do not do any work on this table without elogging. Please never again do any of these type of beam dumping - they are all illegal. Better to not dump beams than to do this kind of thing.

All dumps have to be rigidly mounted. There is no finger contacting black glass or razor dumps - if you do, you might as well throw it in the garbage.

  13327   Thu Sep 21 15:23:04 2017 gautamOmnistructureALSLong cable from LSC->IOO

[steve,gautam]

We laid out a 45m long BNC cable from the LSC rack to the IOO rack via overhead cable trays. There is ~5m excess length on either side, which have been coiled up and cable-tied for now. The ends are labelled "TO LSC RACK" and "TO IOO RACK" on the appropriate ends. This is to facilitate hooking up the output of the DFD for making a PM measurement of the AUX X laser. There is already a long cable that runs from the IOO rack to the X end.

  13333   Tue Sep 26 19:10:13 2017 gautamUpdateALSFiber ALS setup neatened

[steve, gautam]

The Fiber ALS box has been installed on the existing shelf on the PSL table. We had to re-arrange some existing cabling to make this possible, but the end result seems okay (to me). The box lid was also re-installed.

Some stuff that still needs to be fixed:

  1. Power supply to ZHL amplifiers - it is coming from a table-top DC supply currently, we should hook these up to the Sorensens.
  2. We should probably extend the corrugated fiber protection tubing for the three fibers all the way up to the shelf. 

Beat spectrum post changes to follow.

Quote:

Is it better to mount the box in the PSL under the existing shelf, or in a nearby PSL rack?

Quote:

 

Further characterization needs to be done, but the results of this test are encouraging. If we are able to get this kind of out of loop ALS noise with the IR beat, perhaps we can avoid having to frequently fine-tune the green beat alignment on the PSL table. It would also be ideal to mount this whole 1U setup in an electronics rack instead of leaving it on the PSL table

 

 

  13335   Wed Sep 27 00:20:19 2017 gautamUpdateALSMore AM sweeps

Attachment #1: Result of AM sweeps with EX laser crystal at nominal operating temperature ~ 31.75 C.

Attachment #2: Tarball of data for Attachment #1.

Attachment #3: Result of AM sweeps with EX laser crystal at higher operating temperature ~ 40.95 C.

Attachment #4: Tarball of data for Attachment #2.


Remarks:

  • Confirmed that PDA 55 is in the "0dB" setting - the actual dial is unmarked, and has 5 states. I guessed that the left-most one is 0dB, and checked that if I twiddled the dial by one state to the right, the DC level on the scope increased by 10dB as advertized. Didn't check all the states.
  • DC level is ~2.3V on a high-impedance scope. So it will be ~1.15V to a 50ohm load, which is what the DC block is. The inverse of this value is used to calibrate the vertical axis of the TF measurement to RIN/V.
  • Input R (split RF source signal) attenuation: 20dB. Input A (PDA55 output) attenuation: 0dB.
  • Main problem is still network hangups when trying to do many sweeps.
  • Seems to persist even when I connect the GPIB box to one of the network switches - so don't think we can blame the WiFi.
  • Need to explore possibility of speedup - takes >2hours to run ~50scans!

To-do:

  • Overlay median and uncertainty plots for the two temp. settings. There is a visible diference in both the locations and depths/heights of various notches/peaks in the AM profile.
  • Repeat test with a fast focusing lens to focus the beam more tightly on the PD active area to confirm that the measured AM is indeed due to the PZT drive and not from beam-jitter (presently, spot diameter is ~0.5x active area diameter, to eye).
  • Get the PM data.
  • Depending on what the PM data looks like, do a more fine-grained scan around some promising AM notches / PM peaks.
  13337   Wed Sep 27 23:44:45 2017 gautamUpdateALSProposed PM measurement setup

Attachment #1 is a sketch of the proposed setup to measure the PM response of the EX NPRO. Previously, this measurement was done via PLL. In this approach, we will need to calibrate the DFD output into units of phase, in order to calibrate the transfer function measurement into rad/V. The idea is to repeat the same measurement technique used for the AM - take ~50 1 average measurements with the AG4395, and look at the statistics. 

Some more notes:

  • Delay line box is passive, just contains a length of cable.
  • IQ Demodulation is done using an aLIGO 1U chassis unit, with the actual demod board electronics being D0902745
  • The RF beatnote amplitude out of the IR beat PD is ~ -8dBm.
  • The ZHL-3A amplifiers have gain of 24dB, so the amplified beat should be ~16dBm
  • At the LSC rack, the amplified beat is split into two - one path goes to the LO input of D0902745 (so at most 13dBm), the other goes through the delay line.
  • On the demod board, the LO signal is amplified with a AP1053, rated at 10dB gain, max output of 26dBm, so the signal levels should be fine for us, even though the schematic says the nominal LO level is 10dBm - moreover, I've ignored cable losses, insertion losses etc so we should be well within spec.
  • The mixer is PE4140. The datasheet quotes LO levels of 17dBm for all the "nominal" tests, we should be within a couple of dBm of this number.
  • There is no maximum value specified for the RF input signal level to the mixer on the datasheet, but I expect it to be <10dBm.
  • We should park the beatnote around 30MHz as this should be well within the operational ranges for the various components in the signal chain.
  13346   Fri Sep 29 11:16:52 2017 SteveUpdateALSY End table corrected

The first Faraday isolater rejected beam path from the NPRO is fixed.

 

  13366   Fri Oct 6 17:08:09 2017 SteveUpdateALSX End table beam traps corrected

There are no more double sided tape on this table.

 

  13502   Thu Jan 4 12:46:27 2018 gautamUpdateALSFiber ALS assay

Attachment #1 is the updated diagram of the Fiber ALS setup. I've indicated part numbers, power levels (optical and electrical). For the light power levels, numbers in green are for the AUX lasers, numbers in red are for the PSL.

I confirmed that the output of the power splitter is going to the "RF input" and the output of the delay line is going to the "LO input" of the demodulator box. Shouldn't this be the other way around? Unless the labels are misleading and the actual signal routing inside the 1U chassis is correctly done :/

  • Mode-matching into the fibers is rather abysmal everywhere.
  • In this diagram, only the power levels measured at the lasers and inputs of the fiber couplers are from today's measurements. I just reproduced numbers for inside the beat mouth from elog13254.
  • Inside the beat mouth, the PD output actually goes through a 20dB coupler which is included in this diagram for brevity. Both the direct and coupled outputs are available at the front panel of the beat mouth. The latter is meant for diagnostic purposes. The number of -8dBm of beat @30MHz is quoted using the direct output, and not the coupled output.

Still facing some CDS troubles, will start ALS recovery once I address them.

Attachment #2 is the svg file of Attachment #1, which we can update as we improve things. I'll put it on the DCC 40m tree eventually.

  13519   Tue Jan 9 21:38:00 2018 gautamUpdateALSALS recovery
  • Aligned IFO to IR.
    • Ran dither alignment to maximize arm transmission.
    • Centered Oplev reflections onto their respective QPDs for ITMs, ETMs and BS, as DC alignment reference. Also updated all the DC alignment save/restore files with current alignment. 
  • Undid the first 5 bullets of elog13325. The AUX laser power monitor PD remains to be re-installed and re-integrated with the DAQ.
    • I stupidly did not refer to my previous elog of the changes made to the X end table, and so spent ages trying to convince Johannes that the X end green alignment had shifted, and turned out that the green locking wasn't going because of the 50ohm terminator added to the X end NPRO PZT input. I am sorry for the hours wasted sad
    • GTRY and GTRX at levels I am used to seeing (i.e. ~0.25 and ~0.5) now. I tweaked input pointing of green and also movable MM lenses at both ends to try and maximize this. 
    • Input green power into X arm after re-adjusting previously rotated HWP to ~100 degrees on the dial is ~2.2mW. Seems consistent with what I reported here.
    • Adjusted both GTR cameras on the PSL table to have the spots roughly centered on the monitors.
    • Will update shortly with measured OLTFs for both end PDH loops.
    • X end PDH seems to have UGF ~9kHz, Y end has ~4.5kHz. Phase margin ~60 degrees in both cases. Data + plotting code attached. During the measurement, GTRY ~0.22, GTRX~0.45.

Next, I will work on commissioning the BEAT MOUTH for ALS beat generation. 

Note: In the ~40mins that I've been typing out these elogs, the IR lock has been stable for both the X and Y arms. But the X green has dropped lock twice, and the Y green has been fluctuating rather more, but has mangaged to stay locked. I think the low frequency Y-arm GTRY fluctuations are correlated with the arm cavity alignment drifting around. But the frequent X arm green lock dropouts - not sure what's up with that. Need to look at IR arm control signals and ALS signals at lock drop times to see if there is some info there.

  13531   Thu Jan 11 14:22:40 2018 gautamUpdateALSFiber ALS assay

I did a cursory check of the ALS signal chain in preparation for commissioning the IR ALS system. The main elements of this system are shown in my diagram in the previous elog in this thread.

Questions I have:

  1. Does anyone know what exactly is inside the "Delay Line" box? I can't find a diagram anywhere.
    • Jessica's SURF report would suggest that there are just 2 50m cables in there.
    • There are two power splitters taped to the top of this box.
    • It is unclear to me if there are any active components in the box.
    • It is unclear to me if there is any thermal/acoustic insulation in there.
    • For completeness, I'd like to temporarily pull the box out of the LSC rack, open it up, take photos, and make a diagram unless there are any objections.
  2. If you believe the front panel labeling, then currently, the "LO" input of the mixer is being driven by the part of the ALS beat signal that goes through the delay line. The direct (i.e. non delayed) output of the power splitter goes to the "RF" input of the mixer. The mixer used, according to the DCC diagram, is a PE4140. Datasheet suggests the LO power can range from -7dBm to +20dBm. For a -8dBm beat from the IR beat PDs, with +24dB gain from the ZHL3A but -3dB from the power splitter, and assuming 9dB loss in the cable (I don't know what the actual loss is, but according to a Frank Seifert elog, the optimal loss is 8.7dB and I assume our delay line is close to optimal), this means that we have ~4dBm at the "LO" input of the demod board. The schematic says the nominal level the circuit expects is 10dBm. If we use the non-delayed output of the power splitter, we would have, for a -8dBm beat, (-8+24-3)dBm ~13dBm, plus probably some cabling loss along the way which would be closer to 10dBm. So should we use the non-delayed version for the LO signal? Is there any reason why the current wiring is done in this way?

 

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