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.
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.
I took transfer function measurement of DFD AM coupling using noise excitation.
Noise is injected using C1:BAC-SPARE_CH14_EXC using awggui which is filtered by a foton filter to simulate the real beatnote RF amplitude noise measured by taking quadrature sum of C1:ALS-BEATY_FINE_I_OUT and C1:ALS-BEATY_FINE_Q_OUT. See attachment 1.
The DAC output is connected to MP1 at CH1. MP1 is set to run in waveform generation mode with following settings:
The AWGUI is set to excite C1:BAC-SPARE_CH14_EXC using settings mentioned in attachment 2.
With this setup, the RF amplitude noise is simulated with MP1 and DAC excitation.
With AWGGUI running as mentioned above, I simply used diaggui in spectrum mode for channels C1:BAC-SPARE_CH14_EXC and C1:ALS-BEATY_FINE_PHASE_OUT_HZ. The second channel is already calibrated into Hz, and the first channel is in counts. To convert it into voltage of amplitude fluctuation, I first converted DAC excitation to voltage by assuming 16 bit DAC with +/- 10 V range, this gives conversion constant of 10/2**15 V/cts. Then since MP1 is doing 100%/V AM modulation, for 500 mVpp RF level, this means 0.25 V/V AM modulation. Multiplying these two together gives, 7.6294e-5 V/cts. I put this number in teh diaggui calibration for C1:ALS-BEATY_FINE_PHASE_OUT_HZ.
This created the transfer function measurement attached in attachment 3.
The measurement resulted in roughly 2kHz/V AM to frequency coupling in DFD + phase tracker setup. The previous measurement with coherent sinusoidal excitation was exactly a factor of 1000 less than this, so I believe I might have made some error in calibrating or there could be an error in the previous elog. Please check my calculations. But a solid thing to note is the coherence measured below 1Hz. I'll do more sophisticated analysis on weekdays.
I also think that coherence was low because of low excitation. We should redo this test with more noise power to get good coherence in all frequency band to have good idea of what would happen to ebatnote RF amplitude noise at all frequencies.
Mon Jan 23 11:47:23 2023 Adding Attachment 4:
I realised that with the noise excitation setup set to mimic real beatnote amplitude noise with very low frequency noise as it is seeded with Moku:Pro, the measured frequency noise by the DFD+Phase Tracker setup at C1:ALS-BEATY_FINE_PHASE_OUT_HZ is an indicator of how much RF amplitude noise of beatnote contribute to the frequency noise measured by DFD+Phase tracker. Attachment 4 is the spectrum measured during this measurement.
Here's the beam path of BH44.
Both the TF measurement and the noise measurements are useful, but the nosie measurement is much more meaningful. Since we expect the main coupling to be incoherent, what we really want is a noise budget style measurement:
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.
[Paco, Yehonathan, Yuta]
Since we have installed BH44, we are seeing side lobes of 60 Hz + harmonics in AS55, REFL55, BH55, BH44, preventing us from locking FPMI BHD (40m/17405).
BH55 RF amp removed:
- We have noticed that the side lobes are there in BH55 (but not in BH44) when LO-ITMX single bounce is fringing (ETMs and ITMY mis-aligned).
- Changing whitening gains and turning on/off whitening/unwhitening filters didn't help.
- When LO-ITMX single bounce is locked with BH55, the side lobe in BH55 reduces.
- Dithering LO1 at 11 Hz created 180 +/- 11 Hz signal, which confirms that this side lobes are from the up conversion of optic motion.
- We thought it could be from RF saturation, so we have put a 55-67 MHz bandbass filter (SBP-60+) in between BH55 RFPD and RF amp (ZFL-1000LN+; 40m/17195). Didn't help.
- We then removed the RF amp. This largely reduced the side lobes (but still some at 180 Hz). We could lock LO-ITMX single bounce without the RF amp, so we decided to remove it for now.
Side lobes only when one of the arms is locked:
- When ETMs are mis-aligned, MICH fringing and BHD fringing, there are 60 Hz + harmonics, but the side lobes are not there.
- But with Xarm is locked (ETMY, ITMY mis-aligned) or Yarm is locked (ETMX, ITMX mis-aligned), the side lobes appear in AS55, REFL55, BH55, BH44.
- Changing whitening gains and turning on/off whitening/unwhitening filters didn't help.
- As the error signals are normalized by TRX and TRY, we turned on/off the power normalization, but didn't help.
- Switching 60 Hz comb in BS, ITMX, ITMY, ETMX, ETMY suspension damping didn't help.
- When ETMs are mis-alined, POX11 had relatively large 60 Hz + harmonics, but almost none in POY11 (unlike other RFPDs; see Attchment #1).
- However, when ETMY is aligned and Yarm is loked with POY11, the side lobe grows in POY11.
- Changing the feedback point from ETMY to ITMY or MC2 didn't help.
- We have unplugged the IQ demod board for BH44 from the eurorack (without removing the cables) and removed the fuse for the power supply of the RF amp for 44 MHz generation (40m/17401), but these also didn't help.
- We have also tried locking Yarm with REFL55(= ~2 x POY11), BH55(= ~10 x POY11), ALSY(= ~2000 x POY11), but the side lobes were always there.
- Disconnect cables in BH44 to open possible ground loops made during BH44 installation (especially 44 MHz generation part??).
- Check if the noise was there before BH44 installation using past data.
Just to show how bad 60 Hz noise is, I compared FPMI displacement noise with pre-BH44 era (measured on Jan 13, 40m/17400).
Blue curve in Attachment #1 is the sensitivity with FPMI locked with RF in pre-BH44 era, and pink curves are that measured today (C1:CAL channels are currently unavailable due to 0x2000 appeared after running restatAllModels.sh).
60 Hz + harmonics pedestals are apparent today, but was not there on Jan 13. Today, DARM could be handed over to AS55_Q from POX11-POY11, but CARM could not be handed over to REFL55_I from POX11+POY11 (this was possible last night).
Attachment #2 shows FPMI error signals when electronic FPMI is locked. Too much 60 Hz, especially in REFL55_I_ERR and AS55_I_ERR (note that REFL55_Q is used for MICH lock, but AS55_Q is not in-loop yet when this screenshot was taken.)
- Fix c1cal 0x2000 issue
- Fix REFL55 loose RF output
- Disconnect cables in BH44 to open possible ground loops made during BH44 installation (especially 44 MHz generation part??).
1) do a comparison with the whtiening before the ADC on/off. This will tell us if it is pickup before the whtiening filter or not.
2) If there are ground loops made by 44 MHz setup, we want to draw a simple diagram which includes which sides are grounded and which have transformers. How about make a drawing to bring to the group meeting tomorrow? IN the lab we have these coaxial BALUNs for making a 1:1 transformer coupling.
3) Another source of 60 Hz is the unintentional demodulation of spikes made by the Sorensen switching supplies: they produce spikes all the way up to 100 MHz, so if they land near 44 MHz, you may get some 60 Hz on the demodulation. You should be able to see this with a dipole antenna or a hoop antenna.
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.
1) Turning the whitening filter before the ADC on/off didn't changed the relative height of 60 Hz peak compared with the noise floor. When the whitening filter was turned on, increase of the dark noise measured at C1:LSC-****_(I|Q)_IN1 was roughly consistent by eye with the whitening filter transfer function (gain of 1 at DC, ~15 Hz zero x2, ~150 Hz pole x2), which suggests the 60 Hz pickup is before the whitening filter.
2) Attached is the electronics diagram around BH44 and BH55.
We came this morning and noticed the FSS_FAST channel was moving very rapidly. Short inspection showed that MC3 watchdog got tripped. After reenabling the watchdog the issue was fixed and the MC is stable again.
There is a spike in the seismometers 8 hours ago and it was probably due to the 4.2 magnitude earthquake that happened in Malibu beach around that time.
Following was done to investigate 60 Hz noise issue, but no significant change in the FPMI noise observed.
- Even before BH44 installation, we have been experiencing flaky REFL55 RF output. When some work was done at AP table or something, sometimes the amplitude of REFL55_I and REFL55_Q goes very low, and/or offset changes. This was usually fixed by touching the RF output of REFL55.
- So, we took out REFL55 and opened the back lid to inspect. RF output seemed rigid and the SMA connector was properly grounded to the box; didn't find any issue (Attachment #1).
- REFL55 was put back to its original position, and the cables were also put back.
BH44 Kapton tape:
- I realized that other RFPDs have Kapton tape in between the RFPD golden box and the black mount, but not for BH44 we recently installed.
- I have checked that the golden box of BH44 and the optical table is not grounded when RF output and the DB15 cable was disconnected, but is gounded when they are connected, just like BH55.
- Anyway I removed BH44 and put a Kapton tape (Attachment #2), just in case, and BH44 was put back to its original position, and the cables were also put back.
FPMI noise spectra after the work:
- Attachment #3,4,5 are noise spectra of FPMI BHD sensors when FPMI is RF locked with AS55_Q, REFL55_I, and REFL55_Q, and LO_PHASE is locked with BH55 with the following configurations.
- Attachment #3: whitening/unwhitening filters for AS55, REFL55, POX11, POY11, BH55, BH44 turned on (nominal configuration after lock acquisition)
- Attachment #4: whitening/unwhitening filters for AS55, REFL55, POX11, POY11, BH55, BH44 turned off. No significant change except for expected whitening filter transfer function.
- Attachment #5: whitening/unwhitening filters for AS55, REFL55, POX11, POY11, BH55, BH44 turned on, 30 dB resonant gain at 60 Hz, Q=10 in CARM loop. Significant 60 Hz reduction everywhere. This was not observed when resonant gain at 60 Hz was put in DARM loop (only 60 Hz at AS55_Q was reduced). 60 Hz noise mainly coming from something in CARM loop?
Don't forget to:
- Put a beam dump for BH44
I returned the half-wave plates on the XEND table back to their original angles, and restored the loop configuration with the PDH servo box. I returned the PD gain to 40 dB (original setting), and set the servo gain knob to 6. This was the region of highest loop stability, with the lock holding for a few seconds (as before). The control signal on the scope did not look intuitive - the peaks of the control signal corresponded with zero crossings of the error signal.
Paco encouraged me to retake transfer function measurements of the PDH servo box. The main takeaway is the PDH servo (boost on) has the expected frequency response at a gain setting of 3 or under, up to 100 mVpp of input. Attachment 1 shows the frequency response at a servo gain of 2, for varying input amplitudes.
The rest of the bode plots correspond to servo gain of 4, 6, 8, and 10 (boost on). The saturation LED would turn on above a gain value of ~3.25, so these results can't be analyzed or interpreted. But it does seem like a steep, low-frequency jump is a signature of the saturated servo. This jump doesn't appear with 10 mVpp input, at least at or above 1 Hz.
Kapton tape is a good insulator, so its a good block for 60 Hz. But it is mostly useless for RF since the capacitance between the mount and the table is
C = epsilon * A / d
For Kapton the dielectric constant is 3.5, the PD mount area is 10 cm x 10 cm, and the film thickness is ~50 um. So C ~ 5 nF.
Z ~ 1 / (2 * pi * 44 MHz) / C
~ 0.5 Ohms
Thus far, the software needed for the Magewell video encoder has been successfully installed on Donatella. OBS studio has also been installed and works correctly. OBS will be the video recording software that can be interfaced via command line once the SDI video encoder starts working. (https://github.com/muesli/obs-cli)
So far, the camera can not be connected to the Magewell encoder. The encoder continues to have a pulsing error light that indicates "no signal" or "signal not locked". I have begun testing on a secondary camera, directly connected to the Magewell encoder with similar errors. This may be able to be resolved once more information about the camera and its specifications/resolution is uncovered. At this time I have not found any details on the LCL-902K by Watec that was given to me by Koji. I will begin looking into the model used in the 40 meter next.
[Paco, Anchal, Yuta]
Isolating BH44 setup from the rest didn't help reducing the 60 Hz noise.
Frequency noise from IMC also seems unchanged before and after BH44 installation.
- To see if BH44 setup installed is causing the 60 Hz issue, we compared the spectra of FPMI sensors with BH44 setup and with BH44 setup disconnected.
- In the latter configuration, BH44 setup was isolated from the rest by disconnecting the SMA cables and the RFPD power cable, as shown in Attachment #1.
- There was no significant difference in the spectra with BH44 and with BH44 isolated.
We have even put the old AS156 IQ demodulator board we have pulled out to insert BH44 IQ demodulator board back, but didn't change.
- We have also disconnected the 22 MHz generation setup around 40m Frequency Generation Unit at 1X2 for switchable IMC/AS WFS, but it also didn't help.
- Attachment #2 is the orignal spectra with both arms locked with POX and POY, feeding back to respective ETMs (MICH is not locked), and Attachment #3 is those with BH44 setup isolated, AS156 IQ demod back, and 1X2 22MHz generation isolated. Both look basically the same.
- BH44 setup was reverted after the comparison.
IMC frequency noise:
- As adding a resonant gain at 60 Hz helped reducing the 60 Hz noise (40m/17419), the noise might be from frequency noise. It also explains why it is not present in MICH when ETMs are mis-aligned, and only present when one of the arms is involved (40m/17413).
- To see if the frequeny noise at 60 Hz increased after BH44 installation, I compared the spectrum of C1:IOO-MC_F_DQ on January 11 (same Wednesday) with that measured today at almost the same time.
- Attachment #4 is the result. 60 Hz noise and its harmonics seems almost the same in MC_F. It is rather noisy today in other frequencies, but not at 60 Hz.
- Read the book.
Connect any video signal supported by the adapter. Use Windows / Mac or any other OS. If it keeps complaining, contact Magwell support.
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.
PMC aligned (Attachment #1).
Over the past month, PMC transmission is actually slowly growing from 0.68 to 0.70 (Attachment #2), since it suddenly dropped from 0.72 on Dec 27 (40m/17390).
I implemented the BLRMS on WFS1/2_I_PIT/YAW outputs and using there value, a HEPA state can be defined. I've currently set it up to use average of 10-30 Hz noise on WFS signals low passed at 0.3 Hz. For ON threshold of 100 and OFF threshold of 50, it is working for my limited testing time. To read HEPA state, one can do caget C1:IOO_HEPA_STATE. I've turned OFF HEPA for tonight's shimmer test. This is bare bones quick attempt, people can make the screen more beautiful and add more complexity if required in future.
EP30-2 Epoxy bonding of V beam dumps for LSC PDs.
- Supplied 1"x0.5" glass pieces from the stock in the OMC lab.
- The black glass pieces were cleaned by IPA / Aceton / Aceton+Cotton Qtip scrub / First Contact
- 3 beam dumps are built. They require ~24 hrs to get cured.
=> Handed to Yuta on Jan 27, 2023
this is very exciting! Its the beginning of the task of reducing vast amounts of PEM data into human-useful (bite sized) info. Imagine if we had 60 Hz BLRMS on various channels - we would know exactly when ground loops were happening or disappearing.
So far different measurements are consistent with the hypothesis that the 60 Hz noise is from PSL frequency noise (40m/17423).
We have done several measurements in REFL55 and POX/POY to show this hypothesis, and all are consistent with the frequency noise hypothesis.
However, 60 Hz noise in the IMC error point seems too small to explain the 60 Hz noise in DARM.
[Koji, Paco, Yuta]
REFL55 attenuation experiment:
- To check if the 60 Hz is in the light or not, we have compared the spectrum of REFL55_I_IN1 with different ND fiters in front of REFL55 RF PD.
- Attachment #1 shows the result. Spectrum was taken when both arms are locked indivitually using POX and POY, feeding back to ETMs, MICH freely swinging. Red curve is nominal, blue is with OD0.5, and green is with OD1.
- Attenuation in 60 Hz noise and side lobes are consistent with OD filter attenuation, which suggets that the noise is from the light.
- Note that having side lobes is natural, as MICH is fringing (sorry for confusing plot). However, if the side lobes come from the RF saturation, we expect side lobes to decrease more than OD filter attenuation, but this was not the case.
Phase measurements between POX and POY:
- When both arms are locked indivitually using POX and POY, feeding back to ETMs, transfer function from POX to POY had gain of ~1 and the phase of -10 deg (Attachment #2).
- With PSL shutter is closed, transfer function from POX to POY had gain of ~0.1 and the phase of -100 deg, with lower coherence (Attachment #3).
- These also support that 60 Hz noise in POX and POY when the arms are locked are from common origin, such as frequency noise.
[Michael, Paco, Yuta]
IMC error point measurement:
- Attachment #4 shows the IMC Servo Board configuration we used for the all three measurements below.
For this measurement we took TP1A (from MC Servo board) and buffered it with a battery powered SR560 (DC coupled, low noise, gain x1) before connecting it to the single ended A1 channel on a SR785. The noise level was set to -42 dBVpk, and three different noise spectra were acquired:
The estimated (in loop) line noise (60 Hz) levels are 70 uV/rtHz, which using the calibration 13 kHz/Vrms (from 40m/14691) amounts to 0.9 Hz/rtHz of (supressed) frequency noise at IMC Error point.
This number (0.9 Hz/rtHz) in terms of displacement corresponds to 1.28e-15 m/rtHz. The measured DARM noise (2e-10 m/rtHz @ 60 Hz from 40m/17414) is not accounted for by this amount.
- Check the IMC error signal calibration
- Measure the calibrated out-of-loop frequency noise using various signals (POX, POY, REFL55, AS55 with single arm, ALSBEAT, PMC_CTRL)
Timeline (as far as written in the elog):
- Dec 20: FPMI BHD locked using BH55 (40m/17367).
- Dec 21: FPMI RF locked, but not BHD, DARM noise 1e-11 m/rtHz @ 60 Hz (40m/17369).
- Jan 10-11: AS WFS boards testing at 1X2 (40m/17391, 40m/17393).
- Jan 11: FPMI BHD locked using BH55, DARM noise 2e-11 m/rtHz @ 60 Hz (40m/17392).
- Jan 13 2pm: FPMI BHD locked using BH55, DARM noise 2e-11 m/rtHz @ 60 Hz (40m/17399).
- After measuring the sensing matrix etc., LO_PHASE locking became unstable and FPMI BHD could not be recovered (I thought something similar to Dec 21 is happening).
- Jan 13 6pm: FPMI BHD locked using BH55 recovered. DARM noise 2e-11 m/rtHz @ 60 Hz. Discovered that the 60 Hz noise is higher when LO_PHASE locking is unstable (40m/17400).
- Jan 17: BH44 hardware/software installed. Found IQ demod board needs tuning (40m/17401).
- Jan 18: Tuned IQ demod board for BH44 installed (40m/17402).
- Jan 19: BH44 RF PD placed and connected to IQ demod board. FPMI RF locked, LO_PHASE locked with BH44, but found 60 Hz noise everywhere (40m/17405).
- Jan 24: FPMI RF locked (with CARM locked with POX11+POY11 instead of REFL55_I). DARM noise 2e-10 m/rtHz @ 60 Hz (40m/17414).
- Jan 24: AS WFS boards mounted in 1X2 (40m/17416).
- Jan 25: Isolating BH44 setup didn't help (40m/17423).
- Jan 26: Fixed tripping of -5V supply in 1X1 (40m/17425).
- Jan 27: IMC error point measurements at 1X2 (this elog).
One of these V beam dumps was installed for BH44 RF PD.
The rest is now stored in the box in the shelf along Yarm, together with RF PD mounts.
PMC hit a drop around mid-day on Saturday and has been going down since. As of now,
C1:PSL-PMC_PMCTRANSPD - 0.664
I will go in and adjust now.
I tried restarting all models this afternoon to see if the DC error 0x2000 on c1cal model cleared (currently no frame data is being written from c1cal). By running ./restartAllModels.sh on the scripts/cds/ folder, and then BURT restoring, but unfortunately this didn't work. I also tried restarting DAQD without success. Finally, I guess since the error has been related to channel inconsistencies in the model's .INI file (what where when?) I tried rtcds build c1cal and rtcds install c1cal and then another full restart. No success.
The 0x2000 error happens when the rtcds model can not acquire the requested number of channels at their data rates. Basically, there is a maximum total data acquisition that one model can do (which is unknown to me). To fix this, I removed 2048 Hz acquiring of C1:CAL-SENSMAT_<DOF>_<RFPD>_<I/Q>_DEMOD_SIG_IN1. This would not allow us to do software demodulation of calibration lines ourselves. but C1:CAL-SENSMAT_<DOF>_<RFPD>_<I/Q>_DEMOD_<I/Q>_IN1 are still acquired at 2048 Hz to do our own low pass filtering in software and C1:CAL-SENSMAT_<DOF>_<RFPD>_<I/Q>_DEMOD_<I/Q>_OUT are acquired at 256 Hz.
This removal worked, and restarting DAQD worked and now c1cal does not have any DC errors. Current total data acquisition C1:DAQ-FEC_50_TOTAL is 2521 which is less than our other heavy models like c1lsc, c1sus etc. So c1cal can probably acquire more in future, but care is required while adding new channels. This issue happened because we added BH44 to the calibration model.
Today I setup Moku:Pro MP1 with phasemeter app to replace DFD + Phase tracker.
Moku Input output settings:
The phasemeter is set to autotrack the frequency with PLL bandwidth fo 1 MHz. The output of the phasemeter (frequency offset) is sent out through the output channels at 1mV/Hz rate. These are digitized at c1lsc ADC and are available as an alternative to phase tracker output channel. One can switch between the two ways of measurement by using C1:ALS-SEL_PHASE_SOURCE channel. See attachment 1 and 2 for the two mode options. For this, I modified c1lsc model today
I used marconi to send 45 MHz RF output as -2 dBm level with internal FM modulation of peak 200 Hz at 211 Hz. This was used to calibrate the Moku Phasemeter outputs to set channels
C1:ALS-BEATX_MOKU_PHASE_OUTPUT_HZ and C1:ALS-BEATY_MOKU_PHASE_OUTPUT_HZ in units of Hz. This method is not very reliable as I do not know if marconi actually sent 200 Hz peak. The calculations from ADC conversion and moku slope of 1mV/Hz give similar numbers though. However, if we want to be accurate in our calibration project, more detailed calibration of these channels is required with a better technique. For now, I assumed that this value is good atleast to a 1% level.
I followed the exact same setup as in 40m/17409 to create a RF signal using MP1 waveform generator which is AM modulated by awggui noise excitation to create similar AM noise as measured for BEATY RF output. The measurement can then take AM coupling transfer function measurements. Attachment 3 are the results of this measurement. In comparison to DFD + Phase tracker system, the transfer function is 2 orders of magnitude less. Even if my calibration of AM modulation is wrong, same calibration is sued for both transfer functions, so the difference measured is real. We are mostly measuring noise in this measurement as the coherence is also very low for all of the frequency range. See the 4th plot to see the inferred measurement noise of Moku phasemeter setup. Attachment 4 shows this data in comparison to data taken in 40m/17409 with DFD + Phase Tracker setup. Moku Phasemter setup provides roughly factor of 4 less noise in our calibration line frequency band.
Attachments 1 and 2 are two separate lock durations, with x-axes spanning 1 second each. The trace of interest (error signal out of mixer) is Channel 1. Channel 2 contains the control signal outputted by the PDH servo box.
The error signal is contained in a slow-moving envelope at ~4.5 Hz, zoomed in with time cursors in Attachments 3 and 4.
Zooming in further, the error signal has a fast component at ~150 Hz (Attachments 5, 6).
Before taking these traces, I captured the green REFL signal and open-loop PDH error signal shapes (Attachment 7). This error signal linear range spans ~500 mVpp. From looking at this signal it seems like the closed loop contains excess noise.
From considering the above traces and loop calculations I can start to infer the closed loop shape and/or UGF, and what direction we need to move in to recover good locking.
I wondered if Moku could have lied about its noise measurement since the RF source was the same Moku device. To avoid this bias, today I repeated this measurement with sendinf RF from Marconi. Marconi settings were:
The Marconi was fed noise from DAC output to match the measured BEATY RF amplitude like the previous posts: Attachment 1 shows AWGGUI settings required and attachment 2 shows the measured RF amplitude noise with the simulated source.
This source was then fed one by one to DFD + Phase tracker system (attachment 3) and then Moku Phasemeter setup (attachment 4). The phasemeter settigns were same as the previous post. Attachment 5 shows the two transfer functions of AM to frequency coupling on the same plot for comparison. Attachment 6 shows the comparison of frequency noise floor between the two methods on the same plot. In this measurement, I rechecked by DAC actuation calibration by measuring it directly. For Marconi AM modulation slope, I took into account the fact that the slope is in %/Vrms. I got it crosschecked with Paco this time. I think the calibration is correct. Moku phasemeter is indeed better by atleast 20 times in the frequency region of interest. The nosie floor is a factor of 3 less. I think this measurement clears Moku phasemter as the choice of frequency discriminator for calibration project. Any comments/opinions are welcome.
I reconnected the green REFL monitor channel and acquired its spectra when the laser was (mostly) locked. During the collection window, TEM00 would catch lock for a few seconds, drop, and catch again. As of today this is the longest the lock will hold. I'm uploading a screenshot for now but will replace with a proper .pdf spectra image.
There is a peak ~558 Hz and at its second harmonic. Additionally there is a less sharp peak at 760 Hz.
Chub mentioned to Paco and I that the Nitrogen seemed to be losing pressure quicker than usual. After looking over the previous 4 months on Dataviewer, the pressure has a pretty consistent slope. I have ran into the issue of the neck of the N2 tank slighty leaking, so this may have been the issue. For now, there does not seem to be any significant or obvious problem.
During my time shadowing Anchal, we discussed the need for digital control systems on the suspension systems for the 40 meter optics. The controls and diagnostics system (CDS) allows us to develop our own feedback controls and filters for the suspension systems by taking in analog signals from the shadow sensors. The feedback control system developed in the CDS then utilizes the OSEM actuators to dampen harmonic motion and noise on the suspension lines. While improving these feedback loops is an ongoing challenge, it is a problem that is likely non-linear, meaning the system must be understood on a much higher level to make further improvements. This brings us to the new addition of a wavefront sensor in the 40m lab, which will allow for constant monitoring of the active wavefront in the interferometer. The wavefront will soon be used for gathering training data for a neural net that will help further analyze the non-linear effects within the suspension and damping system. What Anchal was working on today was an update within a CDS model for clioo to allow for the integration of the wavefront sensor such that he may use a switch to change between connections in the mode cleaner and the arm cavity. The CDS models may be edited and updated using Matlab/Simulink to arrange blocks and code in a robust and visual manner. The final system designed in Simulink can then be saved and compiled using the real-time code generator (RCG), which cross-compiles the Simulink file into C code that can be read by the CDS system to assign inputs, outputs, and various logic or algorithms for filtering.
Today while aligning optics at the xend, my knee engaged the AUX laser interlock. I spent some time trying to disable the interlock, and I'm putting the solution here for mainly my reference: pull on the red interlock button. This shorts the two pins on the back of the Mephisto controller.