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ID Date Author Type Category Subject
11216   Mon Apr 13 19:34:02 2015 ericqUpdateIOOModulation Frequency Tuned to IMC Length

I've been fiddling with the mode cleaner and green beat box today, to try and get an absolute frequency calibration for MC2 motion. The AC measurements have all turned out weird, I get fractional power laws instead of the 1/f^2 that we expect from the MC2 pendulum. At DC, I get a rough number of 15 green kHz per MC2 count, but this translates to ~7e-10 m/count which is in contrast to the 6e-9 m/count from 2009. I will meditate on this a bit.

In any case, while working at the IOO rack, I tuned the 11MHz modulation frequency, as was done in ELOGs 9324 and 10314, by minimizing one of the beats of the 11MHz and 29.5MHz sidebands.

The new modulation frequency / current IMC FSR is 11.066209 +- 1 Hz, which is a only a few ppm change from the tuning from last July.

This implies a IMC round trip length of 27.090800m +- 2um.

Attached is a plot showing the beat of 55-29.5 going down as I changed the marconi frequency.

Attachment 1: fMod_tuning.pdf
8264   Sat Mar 9 19:29:27 2013 KojiUpdatePSLModulation depth

Last night I measured the modulation depth of the MC incident beam.

Method:

The beam is taken from one of the  PO beam at the wedge plate before the IMC.
After removing the knife edge to dump this beam, the beam is sent to the west side
of the PSL table and put into the OSA cavity.
[The beam dump was returned after the measurement.]

I had some confusion and after all I use the OSA labeled as AS OSA rather than the one on the PSL table.
[The AS OSA was returned to the AP table.]

The transmission was detected by PDA255 and filtered by ITHACO 1201 preamp with G=10, no HPF, 30kHz LPF.
It was confirmed that the peak amplitudes are not reduced by the LPF filter. The resulting time series
was recorded by an oscilloscope.

Three measurements have been taken. The 11MHz peaks are offset by the carrier peak. They appropriately
removed. The ratio of the sideband and carrier peaks is converted to the modulation depth using the following formula.

P_sb / P_ca = [J1(m)/J0(m)]^2

Measurement

The modulation depth for the 11MHz: 0.190 +/- 0.003

The modulation depth for the 55MHz: 0.2564 +/- 0.0003

The three scans showed very similar numbers. That's why the statistical error is such small.
I don't think the systematic error is not such good.

This number is much different form the previous meaurement by Mirko.

http://nodus.ligo.caltech.edu:8080/40m/5519 m=0.14 (11MHz) & 0.17 (55MHz)
but the measured voltages and the modulatio depths are inconsistent.

http://nodus.ligo.caltech.edu:8080/40m/5462 m=0.17 (11MHz) & 0.19 (55MHz)

Probably the modulation depths should be checked by the IMC again.
However, it is certain that the 55MHz modulation exists, and even larger than the 11MHz one.

The next is to confirm that the modulation frequency is matched with the IMC FSR.
It is to make sure that the modulation is transmitted to the main IFO without attenuation.

Attachment 1: mod_depth.pdf
15715   Mon Dec 7 22:54:30 2020 gautamUpdateLSCModulation depth measurement

Summary:

I measured the modulation depth at 11 MHz andf 55 MHz using an optical beat + PLL setup. Both numbers are ~0.2 rad, which is consistent with previous numbers. More careful analysis forthcoming, but I think this supports my claim that the optical gain for the PDH locking loops should not have decreased.

Details:

• For this measurement, I closed the PSL shutter between ~4pm and ~9pm local time.
• The photodiode used was the NF1611, which I assumed has a flat response in the 1-200 MHz band, and so did not apply any correction/calibration.
Attachment 1: modDepth.pdf
15769   Sat Jan 16 18:59:44 2021 gautamUpdateLSCModulation depth measurement

I decided to analyze the data I took in December more carefully to see if there are any clues about the weird LSC sensing.

Attachment #1 shows the measurement setup.

• The PSL shutter was closed. All feedback to both lasers was disconnected during the measurement. I also disabled the input switch to the FSS Box - so the two laser beams being interfered shouldn't have any modulations on them other than the free running NPRO noise and the main IFO modulations.
• Everything is done in fiber as I had the beams already coupled into collimators and this avoided having to optimize any mode matching on the beat photodiode.
• The pickoff of the PSL is from the collimator placed after the triply resonant EOM that was installed for the air BHD experiment.
• The other beam is the EX laser beam, arriving at the PSL table via the 40m long fiber from the end (this is the usual beam used for ALS).
• I didn't characterize precisely the PLL loop shape. But basically, I wasn't able to increase the SR560 gain any more without breaking the PLL lock. Past experience suggests that the UGF is ~20 kHz, and I was able to get several averages on the AG4395 without the lock being disturbed.

Attachment #2 shows the measured spectrum with the PSL and EX laser frequency offset locked via PLL.

• The various peaks are identified.
• There are several peaks which I cannot explain - any hypothesis for what these might be? Some kind of Sorensen pollution? They aren't any multiples of any of the standard RF sources. They are also rather prominent (and stationary during the measurement time, which I think rules out the cause being some leakage light from the EY beam, which I had also left connected to the BeatMouth during the measurement).
• In the previous such characterization done by Koji, such spurious extra peaks aren't seen.
• Also, I can't really explain why some multiples of the main modulation are missing (could also be that my peak finding missed the tiny peaks)?
• The measuremet setup is very similar to what he had - important differences are
• Much of the optical path was fiber coupled.
• Beat photodiode is NF1611, which is higher BW than the PDA10CF.
• The second laser source was the Innolight EX NPRO as opposed to the Lightwave that was used.
• The RF source has been modified, so relative phasing between 11 MHz and 55 MHz is different.

Fitting the measured sideband powers (up to n=7, taking the average of the measured upper and lower sideband powers to compute a least squares fit if both are measured, else just that of the one sideband measured) agains those expected from a model, I get the following best fit parameters:

\begin{align*} \Gamma_1 &= 0.193 \pm 0.004 \\ \Gamma_2 &= 0.246 \pm 0.008 \\ \phi &= 75.5^{\circ +17.5^{\circ}}_{\, -40.3^{\circ}} \end{align*}

To be explicit, the residual at each datapoint was calculated as

$\Delta = \bigg| \frac{\rm{model}-\rm{measurement}}{\rm{model}}\bigg|^2$.

The numbers compare favourably with what Koji reported I think - the modulation depths are slightly increased, consistent with the RF power out of the RF box being slightly increased after I removed various attenuators etc. Note the large uncertainty on the relative phase between the two modulations - I think this is because there are relatively few sidebands (one example is n=3) which has a functional dependence that informs on phi - most of the others do not directly give us any information about this parameter (since we are just measuring powers, not the actual phase of the electric field).

Attachment #3 shows a plot of the measured modulation profile, along with the expected heights plugging the best fit parameters into the model. The size of the datapoint markers is illustrative only - the dependence on the model parameters is complicated and the full covariance would need to be taken into account to put error bars on those markers, which I didn't do.

Attachment #4 shows a time domain measurement of the relative phasing between the 11 MHz and 55 MHz signals at the EOM drive outputs on the RF source box. I fit a model there and get a value for the relative phase that is totally inconsistent from what I get with this fit.

Attachment 1: PLL.pdf
Attachment 2: modDepth.pdf
Attachment 3: modProfile.pdf
Attachment 4: EOMpath_postMod.pdf
13642   Tue Feb 20 13:59:30 2018 KojiUpdateGeneralModulation depth measurement for an aLIGO EOM

Last night I worked at the PSL table for the modulation depth measurement for an aLIGO EOM. Let me know if the IFO behavior is unusual.

What I did was:

• Cranked up the HEPA speed to 100
• Placed an aLIGO EOM in the AUX beat path (south side of the PSL laser). (It is still on the PSL table as of Feb 20, 2018)
• Closed the PSL shutter
• Turned off the main Marconi forr 11MHz. The freq and output power of this marconi have not been touched.
• Turned off the freq generation unit

• Worked on my measurement with the spectrum and network analyzers + aux marconi.

• Turned down the HEPA speed to 30
• Turned on the freq generation unit
• Turned on the main Marconi
• Opened the PSL shutter => IMC locked
13652   Thu Feb 22 17:19:47 2018 KojiUpdateGeneralModulation depth measurement for an aLIGO EOM

aLIGO EOM test: Setup

• The modulation signal was supplied from an aux Marconi.
• Between the Marconi and the EOM, a 20dB coupler (ZFDC-20-5) was inserted. There the Marconi was connected to the output port, while the EOM was to the input port. This way, we can observe how much of the RF power is reflected back to Marconi.
• The beat setup (40m ELOG 13567) was used for the measurement. The EOM was placed in the beam path of the beat setup in the PSL side.
• To eliminate the modulation sidebands of 11MHz and 55MHz, the 40m Marconi and the freq generator were turned off (in this order).
• The nominal amplitude of the carrier beat note was -15dBm ~ -16dBm.
• The cable from the source to the EOM was ~3m. And the loss of this cable was ~0.4dB.

Measurement

• The EOM had three input ports.
1. 9MHz input - In reality, there was no matching circuit.
2. Center port - matched at 24.1MHz and 118.3MHz. 24.1MHz port has no amplification (just matching), and 118.3MHz is resonant.
3. 45.5MHz port - resonantly matched at 45.5MHz
• The Marconi output power was set to be +13dBm. For the 45MHz measurement, 20dB attenuator is inserted right next to the Marconi so that the VSWR seen from the Marconi was improbed. (Marconi did not like the full reflection of unmatched circuit and shutdown due to the protection function.)
• The amplitude ratios between the sidebands and the carrier were multiplied by a factor of 2, to obtain the modulaiton depths. ( BesselJ(1,m)/BesselJ(0,m) ~ m/2 )

• The result is found in Attachment 2.
• The center port showed the modulation response of 0.7mrad/V and 15mrad/V for 24.1MHz and 118.3MHz, respectively. This suggests that the amplification factor for 118.3MHz is ~x21.
• The VSWR of the center port is below 1.5 at the target frequencies. That's as tuned in Downs and has not been changed by the crystal replace.
• The 45MHz port has the modulation response of 0.034mrad/V. This later tuned out that the amplification of ~x19. The circuit is well matched at the resonant frequency.

• The linearity was checked with the 45MHz port (Attachment 3). The input power (idrectly connected to the EOM without 20dB attn) was varied between -17dBm to +13dBm. There was no sign of non linearity.

• The modulation response at 24MHz was compared at various input ports. (Attachment 4)
• The input signal was amplified tobe 23dBm by ZHL-3A for better sideband visibility. The actual amplifier output was ~30dBm, and a 6dB ATTN was used to improve the VSWR to protect the amplifier.
• The 9MHz port showed 3.6mrad/V and 1.8mrad/V with the port unterminated and terminated, respectively. This factor of two difference is as expected.
This 1.8mrad/V is roughly x2.6 higher compared to the one of the matched 24/118MHz port. This is close number to the ratio of the plate sizes (14mm/5mm = 2.8).
• With the current condition, the 9MHz (unterminated), 9MHz (terminated), 24/118MHz, and 45MHz ports requires 22dBm, 27dBm, 36dBm, and 21dBm to realize the current modulation depth of 0.014 at 24MHz.
• Comparing this matched 9MHz performance, the amplification of the 45MHz port at 45MHz was determined to be ~x19.

• Considering these results, the modulation response of the center port at 24MHz seems too low. We don't want to supply 36dBm for the 0.014rad modulation (nominal number for H1).
Here are some thoughts:
• Use the 45MHz or 9MHz port for 24MHz modulation. Probably the unit is unmatched but, we can come up with the idea to improve the VSWR at 24MHz somehow?
• Redistribute the plate length to have better modulation at 24MHz. Can we achieve sufficient modulation capability with the frequency of the long and short ports swapped? We hope that we don't need to start over the matching of the 24/118MHz again because the capacitances of the ports are almost the same.
Attachment 1: IMG_3436.JPG
Attachment 2: modulation_depth.pdf
Attachment 3: modulation_linearity.pdf
Attachment 4: modulation_24MHz.pdf
13725   Mon Apr 2 15:14:21 2018 KojiUpdateGeneralModulation depth measurement for an aLIGO EOM

The new matching circuit was tested.

Results:

f_nominal  f_actual  response    required mod.  drivng power
9.1       9.1        55         0.22      =>   22
118.3     118.2        16         0.01      =>    6

45.5      45.4        45         0.28      =>   25
24.1       N/A         2.1       0.014     =>   27

- 9.1MHz and 118.3MHz: They are just fine.

- 24.1MHz: Definitely better (>x3) than the previous trial to combine 118MHz & 24MHz.
We got about the same modulation with the 50Ohm terminated bare crystal (for the port1).
So, this is sort of the best we can do for the 24.1MHz with the current approach.
The driving power of 27dBm is required at 24.1MHz

- The driving power of 27dBm is required at 24.1MHz
- The maximum driving power with the AM stabilized driver is 23dBm, nominally to say.
- I wonder how we can reduce resistance (and capacitance) of the 45MHz further...?
- I also wonder if the IFO can be locked with reduced modulation (0.28 rad->0.2 rad)
- Can the driver max power be boosted a bit? (i.e. adding an attenuator in the RF power detection path)

Attachment 1: modulation_depth.pdf
Attachment 2: impedance_eom.pdf
13819   Sat May 5 22:32:07 2018 KojiUpdatePSLModulation depth measurement for the 3IFO aLIGO EOM

The 3IFO EOM was formerly tuned as the H2 EOM, so the resonant frequencies are different from the nominal aLIGO ones.

PORT1: 8.628MHz / 101 +/- 6 mrad_pk/V_pk
PORT2: 24.082MHz / 41.2 +/- 0.7 mrad_pk/V_pk
PORT3: 43.332MHz / 62.2 +/- 4 mrad_pk/V_pk

9MHz modulation is about x2.4 better than the one installed at LHO.
24MHz modulation is about x14 better. (This is OK as the new 24MHz is not configured to be resonant.)
45MHz modulation is about x1.4 better.

13818   Sat May 5 20:30:21 2018 KojiUpdatePSLModulation depth measurement for the 3IFO aLIGO EOM and aftermath

Caution: Because of this work and my negligence, the RF output of the main Marconi for the IFO modulation is probably off. The amplifier (freq gen. box) was turned on. Therefore, we need to turn the Marconi on for the IFO locking.

I worked on my EOM m easurement using the beat setup. As there was the aux injection electronics, I performed my measurement having tried not to disturb the aux setup. The aux Marconi, the splitted PD output, and an open channel of the oscilloscope were used for my purpose. I have brought the RF spectrum analyzer from the control room. I think I have restored all the electronics back as before. I have re-aligned the beat setup after the EOM removed. Note that the aux NPRO, which had been on, was turned off to save the remaining life of the laser diode.

13842   Tue May 15 10:42:14 2018 KojiUpdatePSLModulation depth measurement for the 3IFO aLIGO EOM and aftermath

The marconi RF output was turned on and thus the RF generator condition was restored to the nominal state on Friday 11th.

13593   Wed Jan 31 16:29:42 2018 gautamUpdateALSModulation depths

I used the Beat Mouth to make a quick measurement of the PMC and EX modulation depths. They are, respectively, 60mrad and 90mrad. See Attachments #1 and #2 for spectra from the beat photodiode outputs, monitored using the Agilent analyzer, 16 averages, IF bandwidth set to resolve peaks offset from the main beat frequency peak by 33.5MHz for the PMC and by ~230kHz for the EX green PDH.

For this work, I had to re-align the IFO so as to lock the arms to IR. c1susaux was unresponsive and had to be power-cycled. As mentioned in the earlier elog, to avoid saturating the Fiber Coupled beat PDs, I placed a ND=0.5 filter in the fiber collimator path, such that the coupled power was ~1mW, which is well inside the safe regime.

For the EX modulation depth, I could have gotten multiple estimates of the modulation depth using the higher order products that are visible in the spectrum, but I didn't.

Attachment 1: PMCmodDepth.pdf
Attachment 2: XPDH.pdf
16952   Mon Jun 27 18:54:27 2022 yutaUpdateLSCModulation depths measurement using Yarm cavity scan

[Yehonathan, Yuta]
EDITED by YM on 22:11 June 27, 2022 to correct for a factor of two in the modulation index

Since we have measured optical gain in MICH to be an order of magnitude less compared with Yehonathan's FINESSE model (40m/16923), we measured the power at AS55 RF PD, and measured the modulation depths using Yarm cavity scan.
We found that 50/50 beam splitter which splits AS55 path into RF PD and RF QPD was not included in the FINESSE model. Measured modulation index were as follows:

TEM00 peak height: 0.6226 +/- 0.0237
RF11 peak height: 0.0067 +/- 0.0007
RF55 peak height: 0.0081 +/- 0.0014
RF11 modulation index: 0.208 +/- 0.012
RF55 modulation index: 0.229 +/- 0.020
RF11 modulation index: 0.104 +/- 0.006
RF55 modulation index: 0.114 +/- 0.010

Here, modulation depth m is defined in E=E_0*exp(i*(w*t+m*sin(w_m*t))), and m m/2 equals to square of the intensity ratio between sidebands and TEM00.

Power measurement at AS55 RF PD:
- ITMY and ITMX single bounce reflection was measured to be 50-60 uW at the front of AS55 RFPD.
- In the FINESSE model, it was expected to be ~110 uW with 0.8 W input to PRM (0.8 W * 5%(PRM) * 50%(BS) * 50%(BS) * 10%(SRM) * 10%(AS2) gives 100 uW)
- In AP table, AS55 beam was split into two paths with 50/50 beam splitter, one for AS55 RF PD and one for AS WFS and AS110. This will be included in the FINESSE model.

Modulation depth measurement using Yarm cavity scan:
- Aligned Yarm using ASS, and unlocked Yarm to get the 2sec scan data of C1:LSC-TRY_OUT_DQ, C1:LSC-POY11_I_ERR_DQ, C1:LSC-AS55_I_ERR_DQ.
- TRY data was used to get TEM00 peak heights
- POY11/AS55 data was used to find RF11/RF55 sideband peaks, and height was measured at TRY (see attached).
- If we define m to be E=E_0*exp(i*(w*t+m*sin(w_m*t))), the amplitude of TEM00 I_00 is proportional to J_0(m) and the amplitude of upper/lower sideband I_f1 is proportional to J_1(m), where J_n(m) is the bessel function of the first kind.
- m can be calculated using 2*sqrt(I_f1 / I_00).
- Results were shown above. Error is calculated from the standard deviation of multiple measurements with multiple peaks,
- The code for doing this lives in https://git.ligo.org/40m/measurements/-/blob/main/LSC/YARM/modulationIndex.ipynb

Discussion:
- Power at AS55 account for the factor of 2, In the FINESSE model, modulation index of 0.3 was used (could be m=0.3/2 or m=0.3; needs check). These combined can explain a factor of 3 at least (or 6).
- Gautam's measurement in Jan 2021 (40m/15769) gives almost double modulation index, but I'm not sure what is the definition Gautam used. It agrees with Gautam's measurement in Jan 2021.

Attachment 1: YarmModIndex.png
10314   Thu Jul 31 23:43:00 2014 KojiUpdateIOOModulation frequency adjustment

The main IFO modulation frequency was adjusted to match with the FSR of the IMC.

The new frequency is 11.066128 MHz. This corresponds to the IMC round-trip length of 27.0910 m

This has been done by looking at the peak at 25.845MHz (5* fmod - 29.5MHz) in the MC REFL PD mon.

16190   Mon Jun 7 15:37:01 2021 Anchal, Paco, YehonathanSummaryCamerasMon 7 in Control Room Died

We found Mon7 in control room dead today afternoon. It's front power on green light is not lighting up. All other monitors are working as normal.

This monitor was used for looking at IMC camera analog feed. It is one of the most important monitors for us, so we should replace it with a different monitor.

Yehonathan and Paco disconnected the monitor and brought it down. We put it under the back table if anyone wants to fix it. Paco has ordered a BNC to VGA/HDMI converter to put in any normal monitor up there. It will happen this Wednesday. Meanwhile, I have changed the MON4 assignment from POP to Quad2 to be used for IMC.

16204   Wed Jun 16 13:20:19 2021 Anchal, PacoSummaryCamerasMon 7 in Control Room Replaced

We replaced the Mon 7 with an LCD monitor from back bench. It is fed the analog signal from BNC converted into VGS with a converter box that Paco bought. We can replace this monitor with another monitor if it is required on the back bench. For now, we definitely need a monitor to show IMC camera's up there.

Attachment 1: IMG_20210616_083810.jpg
2456   Mon Dec 28 10:29:31 2009 JenneUpdateComputersMonday Morning Bootfest

Nothing like a good ol' Bootfest to get back into the swing of things after vacation....

It was a regular bootfest, keying crates and running everyone's startup.cmd .  There wasn't any RFM funny business which we had been dealing with a lot earlier in December (maybe Kiwamu took care of that part of things last night).

After finishing the bootfest, I tried to re-enable the watchdogs.  I noticed that the optics weren't damping at all (not that any of them were swinging crazily, they just weren't damped like regular).  This was traced to the OSEM sensor inputs and outputs being disabled on all of the suspensions' screens.  I suspect that no burt-restoring happened after c1dcuepics was powercycled yesterday.

All of the optics are now happy as clams.

5239   Mon Aug 15 14:10:56 2011 JenneUpdateSUSMonday SUS update

The moral of the story here is that none of the suspensions are overwhelmingly awesome, but most of them will be fine if we leave them as-is.

 SUS DoF Plot Input Matrix "BADness" (1==good) ITMX       pit     yaw     pos     side    butt UL    0.438   1.019   1.050  -0.059   0.717  UR    0.828  -0.981   1.128  -0.215  -0.956  LR   -1.172  -1.201   0.950  -0.275   1.241  LL   -1.562   0.799   0.872  -0.120  -1.087  SD   -0.579  -0.847   2.539   1.000  -0.170   4.68597 ITMY       pit     yaw     pos     side    butt UL    1.157   0.185   1.188  -0.109   0.922  UR    0.020  -1.815   0.745  -0.051  -0.970  LR   -1.980  -0.090   0.812  -0.024   1.158  LL   -0.843   1.910   1.255  -0.082  -0.949  SD   -0.958   1.080   1.859   1.000   0.325   4.82756 ETMX       pit     yaw     pos     side    butt UL    0.338   0.476   1.609   0.316   1.046   UR    0.274  -1.524   1.796  -0.069  -1.180   LR   -1.726  -1.565   0.391  -0.100   0.938   LL   -1.662   0.435   0.204   0.286  -0.836   SD    0.996  -2.629  -0.999   1.000  -0.111  4.32072 ETMY       pit     yaw     pos     side    butt UL    1.123   0.456   1.812   0.231   0.936  UR   -0.198  -1.489   0.492  -0.096  -1.098  LR   -2.000   0.055   0.188  -0.052   0.764  LL   -0.679   2.000   1.508   0.275  -1.201  SD    0.180  -0.591   3.355   1.000   0.200   10.643 BS        pit     yaw     pos     side    butt UL    1.575   0.697   0.230   0.294   1.045  UR    0.163  -1.303   1.829  -0.133  -0.958  LR   -1.837  -0.308   1.770  -0.171   0.944  LL   -0.425   1.692   0.171   0.257  -1.053  SD    0.769   0.345  -3.380   1.000   0.058  6.111 PRM        pit     yaw     pos     side    butt UL    0.597   1.553   2.000  -0.469   1.229   UR    1.304  -0.447   0.383  -0.043  -0.734   LR   -0.696  -1.048  -0.277   0.109   0.687   LL   -1.403   0.952   1.340  -0.317  -1.350   SD    0.518  -1.125  -1.161   1.000   0.394   8.43363 SRM       pit     yaw     pos     side    butt UL    0.831   1.039   1.153  -0.140   1.065  UR    1.071  -0.961   1.104  -0.057  -1.061  LR   -0.929  -0.946   0.847  -0.035   0.837  LL   -1.169   1.054   0.896  -0.118  -1.037  SD    0.193  -0.033   1.797   1.000   0.045  4.17396

230   Wed Jan 9 20:36:42 2008 GoUpdateTreasureMoney in lab
Go's Desk.
Attachment 1: DSC_0370.JPG
3263   Thu Jul 22 01:02:08 2010 ranaUpdateTreasureMonsters, LNVR, and Phase noise

On Picasa

3265   Thu Jul 22 07:19:56 2010 AlbertoUpdateTreasureMonsters, LNVR, and Phase noise

 Quote: On Picasa

"They (shellfish) shall be an abomination to you; you shall not eat their flesh, but you shall regard their carcasses as an abomination." (Leviticus 11:11)

15507   Thu Aug 6 00:34:38 2020 YehonathanUpdateBHDMonte Carlo Simulations

I've pushed an MCMC simulation to the A+ BHD repo (filename MCMC_TFs.ipynb). The idea is to show how random offsets around ideal IFO change the noise couplings of different DOFs to readout.

At each step of the simulation:

1. Random offsets for the different DOFs are generated from a normal distribution. The RMSs are taken from experimental data and some guesses and can be changed later. The laser frequency is tuned to match the CARM offset.

These are the current RMS detunings I use:

 DOF RMS Taken from DARM 10fm PHYSICAL REVIEW D 93, 112004 (2016), Table 2 CARM 1fm PHYSICAL REVIEW D 93, 112004 (2016), Table 2 MICH 3pm PHYSICAL REVIEW D 93, 112004 (2016), Table 2 PRCL 1pm PHYSICAL REVIEW D 93, 112004 (2016), Table 2 SRCL 10pm PHYSICAL REVIEW D 93, 112004 (2016), Table 2 OMCL 0.1pm Guess OMC Breadboard angle 1\mu rad Guess Differential arm loss 15ppm Guess BHD BS imbalance 10% Guess OMC finesse imbalance 5ppm Guess

2. A transfer function is computed for the noisy DOFs.

3. Projected noise is calculated.

These are the noise level for the DOFs:

 DOF Noise Taken from MICH 2e-16 m PHYSICAL REVIEW D 93, 112004 (2016), Fig 9 PRCL 0.5e-17 m PHYSICAL REVIEW D 93, 112004 (2016), Fig 9 SRCL 5e-16 PHYSICAL REVIEW D 93, 112004 (2016), Fig 9 OMCL 2.5e-17*(100/f)^(1/2) LIGO-G1800149 OMC Breadboard angle 1nrad Guess RIN 2e-9 Optics Letters Vol. 34, Issue 19, pp. 2912-2914 (2009)

The attachments show the projected noise levels for the noisy DOFs. Each curve is a different instance of random offsets. The ideal case - "zero offsets" is also shown.

OMC Comm and OMC diff refer to the common and differential length change of the OMCs.

Attachment 1: MICH_Aplus_MCMC.pdf
Attachment 2: PRCL_Aplus_MCMC.pdf
Attachment 3: SRCL_Aplus_MCMC.pdf
Attachment 4: OMC_Comm_Aplus_MCMC.pdf
Attachment 5: OMC_Diff_Aplus_MCMC.pdf
Attachment 6: OMC_Angle_Yaw_Aplus_MCMC.pdf
Attachment 7: OMC_Angle_Pitch_Aplus_MCMC.pdf
Attachment 8: L0_RIN_Aplus_MCMC.pdf
15509   Fri Aug 7 11:23:47 2020 ranaUpdateBHDMonte Carlo Simulations

that's great. I think we would like to figure out how to present this so that its clear what the distribution of TFs is. Maybe we can plot the most likely curve as well as a shaded region indicating the 5% and 95% values?

 Quote: I've pushed an MCMC simulation to the A+ BHD repo (filename MCMC_TFs.ipynb). The idea is to show how random offsets around ideal IFO change the noise couplings of different DOFs to readout.

and then we add the loops

15512   Mon Aug 10 07:13:00 2020 YehonathanUpdateBHDMonte Carlo Simulations

I fixed some stuff in the MCMC simulation:

1. Results are now plotted as shades from minimum to maximum. I tried making the shade the STD around a mean but it doesn't look good on a log scale when the STD is bigger than the mean.

2. Added comparison with aLigo. The OMCL diff and comm motions in A+ are both compared to the single OMCL DOF of aLigo.

3. I fixed a serious error in the code that produced incorrect results.

4. Imbalances in the IFO such as differential arm loss are generated randomly at the beginning and stay fixed for the rest of the simulation instead of being treated as an offset.

5. The simulation now runs with maxtem=2. That is, TEM modes up to 2nd order are considered.

The results are attached.

Attachment 1: MICH_AplusMCMC.pdf
Attachment 2: PRCL_AplusMCMC.pdf
Attachment 3: SRCL_AplusMCMC.pdf
Attachment 4: OMC_Comm_AplusMCMC.pdf
Attachment 5: OMC_Diff_AplusMCMC.pdf
Attachment 6: OMC_Angle_Yaw_AplusMCMC.pdf
Attachment 7: OMC_Angle_Pitch_AplusMCMC.pdf
Attachment 8: L0_RIN_AplusMCMC.pdf
15539   Tue Aug 25 05:51:29 2020 YehonathanUpdateBHDMonte Carlo Simulations

I re-plotted the MCMC results as semi-transparent lines so that probable lines stick out.

This also reveals what is behind the extreme sparsity in the aLIGO simulation results (In the previous post).

There seem to be some bi-stability/phase transition/whatever in the aLIGO simulation. The aLIGO transfer functions are very sensitive to one or more of the DOFs. Not sure which yet.

Attachment 1: MICH_AplusMCMC.pdf
Attachment 2: PRCL_AplusMCMC.pdf
Attachment 3: SRCL_AplusMCMC(1).pdf
Attachment 4: OMC_Diff_AplusMCMC.pdf
Attachment 5: OMC_Comm_AplusMCMC.pdf
Attachment 6: OMC_Angle_Yaw_AplusMCMC.pdf
Attachment 7: OMC_Angle_Pitch_AplusMCMC.pdf
Attachment 8: Main_Laser_RIN_AplusMCMC.pdf
15569   Mon Sep 14 07:50:01 2020 YehonathanUpdateBHDMonte Carlo Simulations

Turns out what was causing the instability in the aLIGO plots were the lock commands which I forgot to remove before running the simulation. Removing these also made the simulation much faster.

Other than that I improved other stuff in the simulations:

• The LO phase in the aPlus simulation is now optimized for the lowest noise at 100Hz.
• Added RF PDs diagnostics (see attachments 8 for aPlus and 9 for aLIGO). The thresholds (red dashed lines in attachments 8,9) for cutting marginal simulations are set such that roughly 30% of the simulations are discarded.
• Removed DHARD because it jacks up the RF PD readings in aPlus for some reason.
• Fixed the sign of laser frequency shift in response to CARM offset.

Still need to do:

• Incorporate Jon’s noise curves.
• Add phase noise for LO beam.
• Include feedback loops using Pytickle.

Feel free to add to the todo list.

Attachment 1: MICH_AplusMCMC.pdf
Attachment 2: PRCL_AplusMCMC.pdf
Attachment 3: SRCL_AplusMCMC(1).pdf
Attachment 4: OMC_Comm_AplusMCMC.pdf
Attachment 5: OMC_Diff_AplusMCMC.pdf
Attachment 6: OMC_Angle_Yaw_AplusMCMC.pdf
Attachment 7: OMC_Angle_Pitch_AplusMCMC.pdf
Attachment 8: Main_Laser_RIN_AplusMCMC.pdf
Attachment 9: aPlus_RF_Diagnostics.pdf
Attachment 10: aLIGO_RF_Diagnostics.pdf
15631   Fri Oct 16 09:16:37 2020 YehonathanUpdateBHDMonte Carlo Simulations

Pushed another update to MCMC simulation. This includes:

• Added new imbalances: ITM transmission, ITM & ETM RoCs.
• Added new static offsets: DHARD, DSOFT, CHARD, CSOFT. All pitch. The RMS is calculated from the data Jon fetched with /input_noises/input_noises.ipynb.
• SRCL noise ASD and RMS are now taken from data in /input_noises.
• RF PD diagnostics were redone: Instead of post-discarding marginal simulations, simulations are now discarded when one or more of the RF PDs demodulated signal does not cross zero when the associated DOFs are scanned by 1um in the offset state.

The DOFs<->RFPD associations I use are:

 DARM AS_f2_I CARM REFL_f1_I MICH POP_f2_Q PRCL POP_f1_I SRCL REFL_f2_I

However, one thing that bothers me is that for some reason ~ 15 out of 160 aLigo simulations are discarded while none for A+. It can also be seen that the A+ simulations are more spread-out which might be related.

The new simulation results are attached.

Attachment 1: MICH_AplusMCMC.pdf
Attachment 2: PRCL_AplusMCMC.pdf
Attachment 3: SRCL_AplusMCMC.pdf
Attachment 4: OMC_Comm_AplusMCMC.pdf
Attachment 5: OMC_Diff_AplusMCMC.pdf
Attachment 6: OMC_Angle_Yaw_AplusMCMC.pdf
Attachment 7: OMC_Angle_Pitch_AplusMCMC.pdf
Attachment 8: Main_Laser_RIN_AplusMCMC.pdf
15637   Thu Oct 22 11:48:08 2020 YehonathanUpdateBHDMonte Carlo Simulations

I found this H1 alog  entry by Izumi confirming that the calibrated channels CAL-CS_* need the same dewhitening filter.

This encouraged me to download the PRCL and MICH data and using Jon's example notebook. I incorporated these noise spectra into the MCMC simulation. The most recent results are attached.

I am still missing:

• Laser frequency noise
• Laser RIN
• Estimation of the LO phase noise
• Estimation of the BHD breadboard angular noise

Also, now the MCMC repeats a simulation if it doesn't pass the RF PDs test so the number of valid simulations stays the same. I'm still not sure about why the A+ simulations are much more robust to these tests than aLigo simulations.

Attachment 1: MICH_AplusMCMC.pdf
Attachment 2: PRCL_AplusMCMC.pdf
Attachment 3: SRCL_AplusMCMC.pdf
Attachment 4: OMC_Comm_AplusMCMC.pdf
Attachment 5: OMC_Diff_AplusMCMC.pdf
Attachment 6: OMC_Angle_Yaw_AplusMCMC.pdf
Attachment 7: OMC_Angle_Pitch_AplusMCMC.pdf
Attachment 8: Main_Laser_RIN_AplusMCMC.pdf
15727   Thu Dec 10 14:48:00 2020 YehonathanUpdateBHDMonte Carlo Simulations

I have rebuilt the MCMC simulation in an OOP fashion and incorporated Lance/Pytickle functionality into it. The usage of the MCMC now is much less messy, hopefully.

I made an example that calculates the closed-loop noise-coupling from SRCL sensing and displacement to DARM in A+. I used the control filters that Kevin defined in his controls example.

The resulting noise budget is in attachment 1. The code is in the 40m/bhd git.

I also investigated why aLIGO simulations behave so different than the A+ simulation (See few previous elogs in this thread). That is why aLIGO results are much less variable, and the simulations in aLIGO barely pass the validity checks, while A+ simulations almost always pass.

The way I check for the validity of a kat model is by scanning all the DOFs and checking that the corresponding sensing RFPDs demodulated signals cross zero. Attachment 2 shows these scanning for 3 such RFPDS for 3 cases:

A+ model with maxtem = 2

ALigo model with maxtem = 2

ALigo model with maxtem = 'off'

It seems like the scanning curves for A+ and ALigo with no HOMs are well behaved and look like normal PDH signals, while the ALigo with maxtem = 2 curves look funky. I believe that the aLIGO+HOMS curves indicate that the IFO is not really in a good locking point. All the IFO lockings were done by using the locking methods straight out of the PyKat package.

Attachment 1: MCMCLance_NoiseBudget_Example.pdf
Attachment 2: IFO_Check.pdf
15732   Fri Dec 11 09:28:52 2020 ranaUpdateBHDMonte Carlo loop coupling Simulations

Cool. Can you give us Bode plots of the open loop gain for each of the 5 length control loops?

 Quote: I have rebuilt the MCMC simulation in an OOP fashion and incorporated Lance/Pytickle functionality into it. The usage of the MCMC now is much less messy, hopefully.

15734   Mon Dec 14 11:09:28 2020 YehonathanUpdateBHDMonte Carlo loop coupling Simulations

I spent a few hours monkeying around with the control filters. They are totally made up and also it's my first time trying to design control filters.

The OLTFs of the different length controls are shown in attachment 1.

The open-loop couplings of the DOFS to DARM are shown in attachment 2.

Note that in Lance/Pytickle the convention is that CLTFs are 1/(1 - G). Where G is the OLTF.

 Quote: Cool. Can you give us Bode plots of the open loop gain for each of the 5 length control loops?

Attachment 1: MCMC_LANCE_OLTFs.pdf
Attachment 2: MCMC_LANCE_OLCoupling2DARM.pdf
15758   Mon Jan 11 16:11:51 2021 YehonathanUpdateBHDMonte Carlo loop coupling Simulations

I dived into the alog to make the OLTFs in the MC_controls example more realistic. I was mainly inspired by these entries:

https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=18742

https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=20466

and Evan's and Dennis's Theses.

Attachment 1 shows the new OLTFs. I tried to make them go like 1/f around the UGF and fall as quickly as possible at higher frequencies. I didn't do more advanced stability checks.

I also noticed that imbalances and detunings in the MC simulation can change the plants significantly. Especially DARM, CARM, and sometimes PRCL. I added the option to fix some OLTFs throughout the simulation. At every iteration, the simulation computes the required control filter to fix the selected OLTFs such that it will match the OLTFs in the undetuned and balanced IFO.

Attachment 1: MC_LANCE_OLTFs.pdf
15759   Mon Jan 11 19:10:10 2021 ranaUpdateBHDMonte Carlo loop coupling Simulations
• looking better, but the CARM plot still looks weird.
• you should plot from 0.01 - 10,000 Hz
• All of the loops should have true integrators below 1 Hz.
• I don't think these loops are stable; the Bode plot is not a good way to check stability for LTI systems since you can be fooled by phase wrapping.
14213   Sun Sep 23 20:15:35 2018 KojiSummaryOMCMontecarlo simulation of the phase difference between P and S pols for a modeled HR mirror

The number of soldered resistors seems to be less than that on the schematics. They are related to duotone, so check if it's OK upon use.

Attachment 1: P_20210415_183139_1.jpg
14849   Sat Aug 17 16:49:23 2019 gautamUpdateCDSMore 1Y3 work

Work done today:

1. All ribbon cable connections to the backplane of the 1Y2 Eurocrates were removed. The cables themselves were cleared for more space to work with.
2. 20x 15ft DB37 Cables were run between 1Y2 and 1Y3 via overhead cable tray.
3. Backplane interface boards were installed for 1Y2 Eurocrate boards.
4. Connections were made between the Acromag chassis and the eurocrate electronics modules.

Testing of functionality:

1. Fast BIO switching was verified to work for the following photodiodes:
• AS55, AS110, REFL11, REFL33, REFL55, REFL165, POX11, POY11, POP22, POP110.
• No light was incident on the PDs.
• Test was done by increasing the whitening gain to +45 dB, and then looking at the ASD of the electronics noise between 50 Hz and 500 Hz with the whitening enabled/disabled. We expect x10 difference between the two states. This was seen.
2. "DetMon" channels were verified to work - see Attachment #1
• Y-axis units is volts
• Test was done by toggling the output of the 11 MHz Marconi, and looking for a change.
• As seen in the attachment, all 5 monitor channels show a change.
• This needs to be calibrated into some sensible units - I don't know why the different modulation frequencies have such different readbacks from supposedly identical Demod Board monitor points.
• Not sure if the ~10 V reported by the REFL165 monitor point is real or saturated.
• These channels are installed to signal/help debug the infamous ERA-5 decay problem, but maybe already some are decayed?
3. QPD interface channels were verified to work - see Attachment #2
• Test was done by shining a green laser pointer on QPD quadrants.

Much testing remains to be done, but I defer further testing till Monday - the main functionality to be verified in the short run is the whitening gain stepping. The strain-relief of cables and general cleanup will be undertaken by Chub. Current state of affairs is in Attachment #3, leaves much to be desired in terms of cleanliness.

I will also setup the autoburt for the new machine on Monday. We will also need to add some channels to C0EDCU.ini if we want to trend them over some years (e.g. RF signal powers for monitoring ERA-5 health).

* c1lsc FE was rebooted using the usual script, and everything seems to be healthy in CDS-land again, see Attachment #4.

 Quote: Next steps:  We did not get around to running the DB37 cables between the Acromag chassis and the 1Y2 Eurocrates today - this operation itself took the whole day as we also needed to lay out some support struts etc on the rack to support the Sorensens and the Acromag chassis. Once the Acromags are connected to the Eurocrates, we have to run in-situ tests to make sure the appropriate functionality has been restored. We must have bumped something in the c1lsc expansion chassis - the CDS FE overview screen is reporting some errors (see Attachment #3). I will fix this. General tidiness, strain-relief etc.
Attachment 1: Screen_Shot_2019-08-17_at_3.00.57_PM.png
Attachment 2: Screen_Shot_2019-08-17_at_3.12.23_PM.png
Attachment 3: IMG_7804.JPG
Attachment 4: Screenshot_from_2019-08-17_17-04-47.png
10729   Fri Nov 21 02:22:25 2014 ericqUpdateLSCMore ALS PRFPMI exploration

Similar to what Jenne did the other night, I kept the PRFPMI arm DoFs locked on ALS, in hopes to check out the RF error signals.

I was able to stably sit at nominally zero offset in both CARM and DARM, tens of minutes at a time, and the PRMI could reacquire without a fuss. Arm powers would rest between 10 and 20, intermittently exhibiting the "buzzing" behavior that Jenne mentioned when passing through resonance. 100pm CARM offset means arm powers of around 10, so since our ALS RMS is on this order, this seems ok. I saw TRX get as high as 212 counts, which is just about the same that I've simulated as the maximum power in our IFO.

To get this stable, I turned off all boosts on MICH and PRCL except PRCL FM6, and added matrix elements of 0.25 for TRX and TRY in the trigger line for the PRMI DoFs. The logic for this is that if the arm powers are higher than 1, power recycling is happening, so we want to keep things above the trigger down value of 0.5, even if POP22 momentarily drops.

I also played around a bit with DARM offsets. We know from experience that the ALS IR resonance finding is not super precise, and thus zero in the CARM FM is not zero CARM offset when on ALS. The same obviously holds for DARM, so I moved the DARM offset around, and could see the relative strengths of flashes change between the arms as expected.

I've written down some GPS times that I'm going to go back and look at, to try to back out some information about our error signals.

Lastly, there may be something undesirable happening with the TRX QPD; during some buzzing, the signal would fluctuate into negative values and did not resemble the TRY signal as it nominally would. Perhaps the whitening filters are acting up...

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.
Attachment 1: TFAG4395A_26-09-2017_202344_FourSquare.pdf
Attachment 2: lowTemp.tgz
Attachment 3: TFAG4395A_26-09-2017_231630_FourSquare.pdf
Attachment 4: highTemp.tgz
16548   Thu Jan 6 14:08:14 2022 KojiUpdateCDSMore BHD SUS screens added to sitemap

More BHD SUS screens added to sitemap (Attachment 1)

Attachment 1: Screenshot_2022-01-06_14-06-15.png
14136   Mon Aug 6 00:26:21 2018 gautamUpdateCDSMore CDS woes

I spent most of today fighting various CDS errors.

• I rebooted c1lsc around 3pm, my goal was to try and do some vertex locking and figure out what the implications were of having only ~30% power we used to have at the AS port.
• Shortly afterwards (~4pm), c1lsc crashed.
• Using the reboot script, I was able to bring everything back up. But the DC lights on c1sus models were all red, and a 0x4000 error was being reported.
• This error is indicative of some timing issue, but all the usual tricks (reboot vertex FEs in various order, restart the mx_streams etc) didn't clear this error.
• I checked the Tempus GPS unit, that didn't report any obvious problems (i.e. front display was showing the correct UTC time).
• Finally, I decided to shut down all watchdogs, soft reboot all the FEs, soft reboot FB, power cycle all expansion chassis.
• This seems to have done the trick - I'm leaving c1oaf disabled for now.
• The remaining red indicators are due to c1dnn and c1oaf being disabled.

Let's see how stable this configuration is. Onto some locking now...

Attachment 1: CDSoverview.png
14139   Mon Aug 6 14:38:38 2018 gautamUpdateCDSMore CDS woes

Stability was short-lived it seems. When I came in this morning, all models on c1lsc were dead already, and now c1sus is also dead (Attachment #1). Moreover, MC1 shadow sensors failed for a brief period again this afternoon (Attachment #2). I'm going to wait for some CDS experts to take a look at this since any fix I effect seems to be short-lived. For the MC1 shadow sensors, I wonder if the Trillium box (and associated Sorensen) failure somehow damaged the MC1 shadow sensor/coil driver electronics.

 Quote: Let's see how stable this configuration is. Onto some locking now...
Attachment 1: CDScrash.png
Attachment 2: MC1failures.png
14140   Mon Aug 6 19:49:09 2018 gautamUpdateCDSMore CDS woes

I've left the c1lsc frontend shutdown for now, to see if c1sus and c1ioo can survive without any problems overnight. In parallel, we are going to try and debug the MC1 OSEM Sensor problem - the idea will be to disable the bias voltage to the OSEM LEDs, and see if the readback channels still go below zero, this would be a clear indication that the problem is in the readback transimpedance stage and not the LED. Per the schematic, this can be done by simply disconnecting the two D-sub connectors going to the vacuum flange (this is the configuration in which we usually use the sat box tester kit for example). Attachment #1 shows the current setup at the PD readout board end. The dark DC count (i.e. with the OSEM LEDs off) is ~150 cts, while the nominal level is ~1000 cts, so perhaps this is already indicative of something being broken but let's observe overnight.

Attachment 1: IMG_7106.JPG
14142   Tue Aug 7 11:30:46 2018 gautamUpdateCDSMore CDS woes

Overnight, all models on c1sus and c1ioo seem to have had no stability issues, supporting the hypothesis that timing issues stem from c1lsc. Moreover, the MC1 shadow sensor readouts showed no negative values over a ~12hour period. I think we should just observe this for another day, in any case I don't think there is any urgent IFO related activity scheduled.

14143   Tue Aug 7 22:28:23 2018 gautamUpdateCDSMore CDS woes

I am starting the c1x04 model (IOP) on c1lsc to see how it behaves overnight.

Well, there was apparently an immediate reaction - all the models on c1sus and c1ioo reported an ADC timeout and crashed. I'm going to reboot them and still have c1x04 IOP running, to see what happens.

[97544.431561] c1pem: ADC TIMEOUT 3 8703 63 8767 [97544.431574] c1mcs: ADC TIMEOUT 1 8703 63 8767 [97544.431576] c1sus: ADC TIMEOUT 1 8703 63 8767 [97544.454746] c1rfm: ADC TIMEOUT 0 9033 9 8841
 Quote: Overnight, all models on c1sus and c1ioo seem to have had no stability issues, supporting the hypothesis that timing issues stem from c1lsc. Moreover, the MC1 shadow sensor readouts showed no negative values over a ~12hour period. I think we should just observe this for another day, in any case I don't think there is any urgent IFO related activity scheduled.
9778   Wed Apr 2 20:13:04 2014 JenneUpdatePEMMore Chile EQs

2 more earthquakes in Chile:  a M6.4 and a M7.8.

We got them about 15 minutes ago (according to the BLRMS on the wall), but when I go tin, the MC was already locked, and engaging the LSC immediately got me PRMI lock (since that's the alignment state that the IFO was left in).

17103   Wed Aug 24 16:37:52 2022 CiciUpdateGeneralMore DFD/AUX PZT resonance measurements

Some more measurements of the PZT resonances (now zoomed in!) I'm adjusting parameters on our model to try and fit to it by hand a bit, definitely still needs improvements but not bad for a 2-pole 2-zero fit for now. I don't have a way to get coherence data from the moku yet but I've got a variety of measurements and will hopefully use the standard deviation to try and find a good error prediction...

Attachment 1: AUX_PZT_Actuator_narrow_fit.pdf
14298   Fri Nov 16 00:47:43 2018 gautamUpdateLSCMore DRMI characterization

Summary:

• More DRMI characterization was done.
• I was working on trying to improve the stability of the DRMI locks as this is necessary for any serious characterization.
• Today I revived the PRC angular feedforward - this was a gamechanger, the DRMI locks were much more stable. It's probably worth spending some time improving the POP LSC/ASC sensing optics/electronics looking towards the full IFO locking.
• Quantitatively, the angular fluctuations as witnessed by the POP QPD is lowered by ~2x with the FF on compared to off [Attachment #1, references are with FF off, live traces are with FF on].
• The first DRMI lock I got is already running 15 mins, looking stable.
• Update: Out of the ~1 hour i've tried DRMI locking tonight, >50 mins locked!
• I think the filters can be retrained and this performance improved, something to work on while we are vented.
• Ran sensing lines, measured loop TFs, analysis tomorrow, but I think the phasing of the 1f PDs is now okay.
• MICH in AS55 Q, demod phase = -92deg, +6dB wht gain.
• PRCL in REFL11 I, demod phase = +18 deg, +18dB wht gain.
• SRCL in REFL55 I, demod phase = -175 deg, +18dB wht gain.
• Also repeated the line in SRCL-->witness in MICH test.
• At least 10 minutes of data available, but I'm still collecting since the lock is holding.
• This time I drove the line at ~124 Hz with awggui, since this is more a regime where we are sensing noise dominated.

Prep for this work:

• Reboots of c1psl, c1iool0, c1susaux.
• Removed AS port PD loss measurement PD.
• Initial alignment procedure as usual: single arms --> PRMI locked on carrier --> DRMI

I was trying to get some pics of the optics as a zeroth-level reference for the pre-vent loss with the single arms locked, but since our SL7 upgrade, the sensoray won't work anymore . I'll try fixing this during the daytime.

Attachment 1: PRCff.pdf
Attachment 2: DRMI_withPRCff.png
13359   Thu Oct 5 02:14:51 2017 gautamUpdateLSCMore DRMI coupling measurements - setup

In the end I decided to access the available spare DAC channels via the C1ASS model - for this purpose, I added a namespace block "TEST" in the C1ASS simulink model, which is a SISO block. Inside is just a single CDS filter module. My idea is to use the EXC of this filter module to inject excitations for measuring various couplings. Rather than have a simple testpoint, we also have the option of adding in some filter shapes in the filter module which could possibly allow a more direct read-off of some coupling TF. Recompiling the model went smooth - there was a crash earlier in the day which required me to hard-reboot c1lsc (and also restart all models on c1sus and c1ioo but no reboots necessary for those machines).

Note that to get the newly added channels to show up in the channel lists in DTT/AWGGUI etc, you need to ssh into fb1 and restart the daqd processes via sudo systemctl restart daqd_*. If I remember right, it used to be enough to do telnet fb 8088 followed by shutdown. This is no longer sufficient.

It took me a while to get the DRMI locking going again. The model restarts earlier in the evening had changed a bunch of EPICS channel settings (and out config scripts don't catch all of these settings). In particular, I forgot to re-enable the x3 digital gain for the ITMs, BS and SRM (necessitated by removing an analog x3 gain on the de-whitening boards). I was hesitant to spend time re-adjusting all damping / oplev loop gains because if we change the series resistor on the coil driver board, we will have to do this again. I also didn't want this arbitrary FM to be enabled in the SDF safe.snap. But maybe it's worth doing it anyways - if nothing it'll be good practise.

Once I hunted down all the setting diffs and tweaked alignment, the DRMI locks were pretty robust.

I had hoped to make some of these TF measurements tonight. But I realized I needed to look up a bunch of stuff in manuals/datasheets, and think about these measurements a little. I wasn't sure if the DW/AI board could drive a signal over 40m of BNC cabling so I added an SR560 (DC coupled, gain=1, low noise mode, 50ohm output used) to buffer the output. The Marconi's external modulation input is high impedance (100k) but for the AOM driver we want 50ohm. For the Marconi, the external input accepts 1Vrms max, while for the AOM driver, we want to drive a signal between 0V and 1V at most.

The general measurement setup is schematically shown in Fig 1. Questions to address:

• What happens if we apply a negative voltage to the input of the AOM driver? What is the damage threshold? Do we have to worry about SR560 offset level?
• Is there a way to dynamically adjust the offset in DTT such that we can have different amplitude signals at different frequencies (usually done by specifying an envelope in DTT) but still satisfy the requirement that the entire signal lie between 0-1V?
• For the Laser Intensity noise -> MICH coupling TF measurement, I guess we can use the AOM to inject an excitation, and measure the ratio of the response in MC_TRANS and in MICH_IN1. Then we multiply the in-loop MC_TRANS spectrum by the magnitude of this TF to get the Laser Intensity Noise contribution to MICH.
• The Laser Frequency Noise coupling should be negligible in MICH - but the measurement principle should be the same. Drive the AO input of the Mode Cleaner Servo board from the DAC, look at ratio of response in MICH_IN1 and MC_F. Multiply the DRMI in-lock MC_F spectrum by this TF.
• The oscillator noise seems more tricky to me (also Finesse modeling suggests this may be the most significant of the 3 couplings described in this elog, though I may just be computing the coupling in Finesse wrongly)
• I don't understand all the External Modulation options specified in the manual.
• DC? AC? FM? PM? AM? Need to figure out what is the right settings to use.
• I'm not sure how independent the various modulations will be - i.e. if I select PM, how much AM is induced as a result of me driving the EXT MOD input?
• What is the right level of excitation drive? I tried this a bunch of times tonight - set the PM range to 0.1rad (for the full scale 1Vrms sine wave input), but with an excitation of just a few counts, already saw non-lineaer coupling in MICH_IN1 which probably means I'm driving this too hard.
• This measurement needs a bit more algebra. We have an estimate of the Marconi phase noise from Rana (is this the right one to use?). But the "Transfer Function" we'd measure is cts in MICH_IN1 in response to counts to Marconi via the signal chain in Attachment #1. So we'd need to know (and divide out) the AI/DW board TF, and the Marconi's TF, which the datasheet suggests has a lower 3dB frequency of 100Hz (assuming SR560 and cable can be treated as flat).
• A simpler test may be to just hook up the Marconi to the Rb standard, and the Rb to 1pps from GPS, and look for a change in the MICH noise.

Am I missing something?

Attachment 1: CB4709D0-3FA7-43E3-BC25-3CF4164E6C6A.jpeg
14838   Fri Aug 9 16:37:39 2019 gautamUpdateALSMore EY table work

Summary:

1. 220 uW / 600 uW (~36 % mode-matching) of IR light coupled into fiber at EY.
2. Re-connected the RF chain from the beat mouth output on the PSL table to the DFD setup at 1Y2.
3. A beat note was found between the PSL and EY beams using the BeatMouth.

Motivation:

We want to know that we can lock the interferometer with the ALS beat note being generated by beating IR pickoffs (rather than the vertex green transmission). The hope is also to make the ALS system good enough that we can transition the CARM offset directly to 0 after the DRMI is locked with arms held off resonance.

Details:

Attachment #1: Shows the layout. The realized MM is ~36 %. c.f. the 85% predicted by a la mode. It is difficult to optimize much more given the tight layout, and the fact that these fast lenses require the beam to be well centered on them. They are reasonably well aligned, but I don't want to futz around with the pointing into the doubling crystal. Consequently, I don't have much control over the pointing.

Attachment #2: Shows pictures of the fiber tips at both ends before/after cleaning. The tips are now much cleaner.

The BeatMouth NF1611 DC monitor reports ~580 mV with only the EY light incident on it. This corresponds to ~60 uW of light making it to the photodiode, which is only 25% of what we send in. This is commensurate with the BS loss + mating sleeve losses.

To find the beat between PSL and EY beams, I had to change the temperature control MEDM slider for the EY laser to -8355 cts (it was 225 cts). Need to check where this lies in the mode-hop scan by actually looking at the X-tal temperature on the front panel of the EY NPRO controller - we want to be at ~39.3 C on the EY X-tal, given the PSL X-tal temp of ~30.61 C. Just checked it, front panel reports 39.2C, so I think we're good.

Next steps:

• Fix the IMC suspension
• Measure the ALS noise for the Y arm
• Determine if improvements need to be made to the IR beat setup (e.g. more power? better MM? etc etc).

EY enclosure was closed up and ETMY Oplev was re-enabled after my work. Some cleanup/stray beam dumping remains to be done, I will enlist Chub's help on Monday.

Attachment 1: IMG_7791.JPG
Attachment 2: fiberCleaning.pdf
863   Wed Aug 20 17:02:01 2008 SharonUpdate More FIR to IIR
I tested another method for converting from FIR to IIR other than the 2 mentioned in post 841.
I got this one from Yoichi, called poles fitting, you can read about it more if you want at: http://www.rssd.esa.int/SP/LISAPATHFINDER/docs/Data_Analysis/DA_Six/Heinzel.pdf.

Seems it's not doing much good for us though.

I am attaching a PDF file with the plots, which have N=50,100,600,1000, respectivaly.
Attachment 1: polefit1.pdf
13765   Thu Apr 19 00:03:51 2018 gautamUpdateIOOMore IMC NBing

Summary:

As shown in the Attachments, it seems like IMC DAC and coil driver noise is the dominant noise source above 30Hz. If we assume the region around the bounce peak is real motion of the stack (to be confirmed with accelerometer data soon), this NB is starting to add up. Much checking to be done, and I'd also like to get a cleaner measurement of coil driver and DAC noise for all 3 optics, as there seems to be a factor of ~5 disagreement between the MC3 coil driver noise measurement and my previous foray into this subject. The measurement needs to be refined a little, but I think the conclusion holds.

Details:

1. I had a measurement of the MC3 coil driver noise from ~2weeks ago when I was last working on this that I had not yet added to the NB.
2. Today I added it. To convert from measured voltage noise to frequency noise, I assumed the usual 0.016N/A per coil number, which is probably a large source of systematic error.
3. I define the "nominal" IMC operating condition as MC1 and MC3 having the analog de-whitening filters switched on, but MC2 switched off.
4. So length noise should be dominated by coil driver noise on MC1 and MC3, and DAC noise on MC2.
5. The measurement I had was made with the input to the coil driver board terminated in 50ohms. Measurement was made in-situ. The measurement has a whole bunch of 60Hz harmonics (despite the Prologix box being powered by a linear power adapter, but perhaps there are other ground loops which are coupling into the measurement). So I'd like to get a cleaner measurement tmrw.
6. To confirm, Koji suggested some On/Off test by driving some broadband noise in the coils. I figured toggling the analog de-whitening, such that the DAC noise or coil driver electronics dominate is an equally good test.
7. Attachment #2 shows the effect in arm error and control signal spectra. Note that I engaged analog de-whitening on all 3 optics for the red curves in this plot. But even leaving MC2 de-whitening off, I could see the read curve was below the black reference trace, which was taken with de-whitening off on all 3 optics.

Remarks:

Since I sunk some time into it already, the motivation behind this work is just to try and make the IMC noise budget add up. It is not directly related to lowering the IR ALS noise, but if it is true that we are dominated by coil driver noise, we may want to consider modifying the MC coil driver electronics along with the ITM and ETMs.

Attachment 1: IMC_NB_20180409.pdf
Attachment 2: IMC_coils_20180418.pdf
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