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ID Date Author Type Category Subject
16132   Wed May 12 10:53:20 2021 Anchal, PacoUpdateLSCPSL-IMC PDH Loop and XARM PDH Loop diagram

Attached is the control loop diagram when main laser is locked to IMC and a single arm (XARM) is locked to the transmitted light from IMC.

 Quote: I'll post a clean loop diagram soon to make this loopology clearer.

Attachment 1: IMC_SingleArm.pdf
16228   Tue Jun 29 17:42:06 2021 Anchal, Paco, GautamSummaryLSCMICH locking tutorial with Gautam

Today we went through LSC locking mechanics with Gautam and as a "Hello World" example, worked on locking michelson cavity.

### MICH settings changed:

• Gautam at some point added 9 dB attenuation filters in MICH filter module in LSC to match the 9 dB pre-amplifier before digitization.
• This required changing teh trigger thresholds, C1:LSC-MICH_TRIG_THRESH_ON and C1:LSC-MICH_TRIG_THRESH_OFF.
• We looked at C1:LSC-AS55_Q_ERR_DQ and C1:LSC-ASDC_OUT_DQ on ndscope.
• The zero crossings in AS55_Q correspond to ASDC going to zero. We found the threshold values of ASDC by finding the linear region in zero crossing of AS55_Q.
• We changed the thresold values to UP: -0.3mW and DOWN -0.05mW. The thresholds were also changed in C1LSC_FM_TRIG.
• We also set FM2,3,6 and 8 to be triggered on threshold.

We characterized the loop OLTF, found the UGF to be 90 Hz and measured the noise at error and control points.

gautam: one aim of this work was to demonstrate that the "Lock Michelson (dark)" script call from the IFOconfigure screen worked - it did, reliably, after the setting changes mentioned above.

16232   Wed Jun 30 18:44:11 2021 AnchalSummaryLSCTried fixing ETMY QPD

I worked in Yend station, trying to get the ETMY QPD to work properly. When I started, only one (quadrant #3) of the 4 quadrants were seeing any lights. By just changing the beam splitter that reflects some light off to the QPD, I was able to get some amount of light in quadrant #2. However, no amount of steering would show any light in any other quadrants.

The only reason I could think of is that the incoming beam gets partially clipped as it seems to be hitting the beam splitter near the top edge. So for this to work properly, a mirror upstream needs to be adjusted which would change the alignment of TRX photodiode. Without the light on TRX photodiode, there is no lock and there is no light. So one can't steer this beam without lossing lock.

I tried one trick, in which, I changed the YARM lock trigger to POY DC signal. I got it to work to get the lock going even when TRY was covered by a beam finder card. However, this lock was still bit finicky and would loose lock very frequently. It didn't seem worth it to potentially break the YARM locking system for ETMY QPD before running this by anyone and this late in evening. So I reset everything to how it was (except the beam splitter that reflects light to EMTY QPD. That now has equal ligth falling on quadrant #2 and #3.

The settings I temporarily changed were:

• C1:LSC-TRIG_MTRX_7_10 changed from 0 to -1 (uses POY DC as trigger)
• C1:LSC-TRIG_MTRX_7_13 changed from 1 to 0 (stops using TRY DC as trigger)
• C1:LSC-YARM_TRIG_THRESH_ON changed from 0.3 to -22
• C1:LSC-YARM_TRIG_THRESH_OFF changed from 0.1 to -23.6
• C1:LSC-YARM_FM_TRIG_THRESH_ON changed from 0.5 to -22
• C1:LSC-YARM_FM_TRIG_THRESH_OFF changed from 0.1 to -23.6

All these were reverted back to there previous values manually at the end.

16233   Thu Jul 1 10:34:51 2021 Paco, AnchalSummaryLSCETMY QPD fixed

Paco worked on alignign the beam splitter to get light on the ETMY QPD and was successful in centering it without any other changes in the settings.

16237   Fri Jul 2 12:42:56 2021 Anchal, Paco, GautamSummaryLSCsnap file changed for MICH

We corrected the MICH locking snap file C1configure_MI.req and saved an updated C1configure_MI.snap. Now the 'Restore MICH' script in IFO_CONFIGURE>!MICH>Restore MICH works. The corrections included adding the correct rows of PD_DOF matrices to be at the right settings (use AS55 as error signal). The MICH_A_GAIN and MICH_B_GAIN needed to be saved as well.

We also were able to get to PRMI SB resonance. PRM was misalgined earlier from optimal position and after some manual aligning, we were able to get it to lock just by hitting IFO_CONFIGURE>!PRMI>Restore PRMI SB (3f).

16241   Thu Jul 8 11:20:38 2021 Anchal, Paco, GautamSummaryLSCPRFPMI locking attempts

Last night Gautam walked us through the algorithm used to lock PRFPMI. We tried it several times with the PSL HEPA filter off between 10:00 pm July 7th to 1:00 am July 8th. None of our attempts were successful. In between, we tried to do the locking with old IMC settings as well, but it did not change the result for us. In most attempts, the arms would start to resonate with PRMI with about 200 times the power than without power recycling while the arms are still controlled by ALS beatnote. The handover of lock controls "CARM+DARM locked to ALS beatnote" to "Main laser + IMC locked to the CARM+DARM" would always fail. More specifically, we were seeing that as soon as we hand over the DC control of CARM from ALS beatnote to IR by feeding back to MC2, the lock would inevitably fail before the rest of the high-frequency control can be transferred over.

Nonetheless, Paco and I got a good demo of how to do PRFPMI locking if the need appears. With more practice and attempts, we should be able to achieve the lock at some point in the future. The issues in handover could be due to any of the following:

• Although it seems like ALS beatnote fed control of arms keep them within the CARM IR linewidth as we see the IR resonating, there still could be some excess noise that needs to be dealt with.
• Gautam conjectures, that the presence of high power in the arms connects the ITMs and the ETMs with an optical spring changing the transfer function of the pendula. This in turn changes the phase margin and possibly makes the CARM loop in IR PRFPMI unstable.
• We should also investigate the loop transfer functions near the handover point for the ALS beatnote loop and the IR CARM loop and calculate the crossover frequency and gain/phase margins there.

More insights or suggestions are welcome.

Note; An earthquake came around lunch time and tripped all watchdogs. Most suspensions were recovered without issues, but ITMX appeared to be stuck. We tried the shaking procedure, but after this we couldn't restore the XARM lock. From alignment, we tried optimizing the TRX but we only got up to ~0.5 and ASS wouldn't work as usual. In the end the issue was that we had forgotten to enable the LL coil output so after we did this, we managed to recover the XARM.

16247   Wed Jul 14 20:42:04 2021 gautamUpdateLSCLocking

[paco, gautam]

we decided to give the PRFPMI lock a go early-ish. Summary of findings today eve:

1. Arms under ALS control display normal noise and loop UGFs.
2. PRMI took longer than usual to lock (when arms are held off resonance) - could be elevated sesimic, but warrants measuring PRMI loop TFs to rule out any funkiness. MICH loop also displayed some saturation on acquisition, but after the boosts and other filters were turned on, the lock seemed robust and the in-loop noise was at the usual levels.
3. We are gonna do the high bandwidth single arm locking experiments during daytime to rule out any issues with the CM board.

The ALS--> IR CARM handoff is the problematic step. In the past, getting over this hump has just required some systematic loop TF measurements / gain slider readjustments. We will do this in the next few days. I don't think the ALS noise is any higher than it used to be, and I could do the direct handoff as recently as March, so probably something minor has changed.

16248   Thu Jul 15 14:25:48 2021 PacoUpdateLSCCM board

[gautam, paco]

We tested the CM board by implementing the high bandwidth IR lock (single arm). In preparation for this test we temporarily connected the POY11_Q_MON output to the CM board IN1 input and checked the YARM POY transfer function by running the AA_YARM_TEMPLATE under users/Templates/LSC/LSC_loops/YARM_POY/. We made sure the YARM dither optimized TRY so as to maximize the optical gain stage. Then we proceeded as follows:

• From the LSC --> CM Servo screen, we controlled the REFL 1 Gain (dB) slider (nominal +25) and MC Servo IN2 Gain (dB) slider (nominal -32 dB) to transfer the low bandwidth (digital) control to the high bandwidth (analog) control of the YARM.
• During this game, we monitored the C1:LSC-POY11_I_ERR_DQ & C1:LSC-CM_SLOW_OUT_DQ error signal channels for saturation, oscillations, or stability.
• Once a set of gains was successful in maintaining a stable lock, we measured the OLTF using SR 785 to track the UGF as we mix the two paths.
• Once the gains have increased, a boost and super-boost stages may be enabled as well.

Ultimately, our ability to progressively increase the control bandwidth of the YARM is a proxy that the CM board is working properly. Attachment 1 shows the OLTF progression as we increased the loop's UGF. Note how as we approached the maximum measured UGF of ~ 22 kHz, our phase margin decreased signifying poor stability.

At the end of this measurement, at about ~ 15:45 I restored the CM board IN1 input and disconnected the POY11_Q_MON

gautam: the conclusion here is that the CM board seems to work as advertised, and it's not solely responsible for not being able to achieve the IR handoff.

Attachment 1: high_BW_TFs.pdf
16251   Mon Jul 19 22:16:08 2021 pacoUpdateLSCPRFPMI locking

[gautam, paco]

Gautam managed to lock PRFPMI a little before ~ 22:00 local time. The ALS to RF handoff logic was found to be repeatable, which enabled us to lock a total of 4 times this evening. Under this nominal state, we can work on PRFPMI to narrow down less known issues and carry out systematic optimization. The second time we achieved lock, we ran sensing lines before entering the ASC stage (which we knew would destroy the lock), and offline analysis of the sensing matrix is pending (gpstime = 1310792709 + 5 min).

Things to note:

(a) there is an unexpected offset suggesting that the ALS and RF disagreed on what the lock setpoint should be, and it is still unclear where the offset is coming from.

(b) the first time the lock was reached, the ASC up stage destroyed it, suggesting these loops need some care (we were able to engage the ASC loops at low gains (0.2 instead of 1) but as soon as we enabled some integrators this consistently destroyed the lock

(c) gautam had (burt) restored to the settings from back in March when the PRFPMI was last locked, suggesting there was a small but somehow significant difference in the IFO that helped today relative to last week

Take home message--> The mere fact that we were able to lock PRFPMI rules out the considerably more serious problems with the signal chain electronics or processing. This should also be a good starting point for further debugging and optimization.

gautam: the circulating power, when the ASC was tweaked, hit 400 (normalized to single arm locked with a misaligned PRM) suggesting a recycling gain of 22.5, and an average arm loss of ~30ppm round trip (assuming 2% loss in the PRC).

16261   Tue Jul 27 23:04:37 2021 AnchalUpdateLSC40 meter party

[ian, anchal, paco]

After our second attempt of locking PRFPMI tonight, we tried to resotre XARM and YARM locks to IR by clicking on IFO_CONFIGURE>Restore XARM (POX) and IFO_CONFIGURE>Restore YARM (POY) but the arms did not lock. The green lasers were locked to the arms at maximum power, so the relative alignments of each cavity was ok. We were also able to lock PRMI using IFO_CONFIGURE>Restore PRMI carrier.

This was very weird to us. We were pretty sure that the aligment is correct, so we decided to cehck the POX POY signal chain. There was essentially no signal coming at POX11 and there was a -100 offset on it. We could see some PDH signal on POY11 but not enough to catch the locks.

We tried running IFO_CONFIGURE>LSC OFFSETS to cancel out any dark current DC offsets. The changes made by the script are shown in attachment 1.

We went to check the tables and found no light visible on beam finder cards on POX11 or POY11. We found that ITMX was stuck on one of the coils. We unstuck it using the shaking method. The OPLEVs on ITMX after this could not be switched on as the OPLEV servo were railing to limits. But when we ran Restore XARM (POX) again, they started working fine. Something is done by this script that we are not aware of.

We're stopping here. We still can not lock any of the single arms.

Wed Jul 28 11:19:00 2021 Update:

[gautam, paco]

Gautam found that the restoring of POX/POY failed to restore the whitening filter gains in POX11 / POY11. These are meant to be restored to 30 dB and 18 dB for POX11 and POY11 respectively but were set to 0 dB in detriment of any POX/POY triggering/locking. The reason these are lowered is to avoid saturating the speakers during lock acquisition. Yesterday, burt-restore didn't work because we restored the c1lscepics.snap but said gains are actually in c1lscaux.snap. After manually restoring the POX11 and POY11 whitening filter gains, gautam ran the LSCOffsets script. The XARM and YARM were able to quickly lock after we restored these settings.

The root of our issue may be that we didn't run the CARM & DARM watch script (which can be accessed from the ALS/Watch Scripts in medm). Gautam added a line on the Transition_IR_ALS.py script to run the watch script instead.

Attachment 1: Screenshot_2021-07-27_22-19-58.png
16264   Wed Jul 28 17:10:24 2021 AnchalUpdateLSCSchnupp asymmetry

[Anchal, Paco]

I redid the measurement of Schnupp asymmetry today and found it to be 3.8 cm $\pm$ 0.9 cm.

### Method

• One of the arms is misalgined both at ITM and ETM.
• The other arm is locked and aligned using ASS.
• The SRCL oscillator's output is changed to the ETM of the chosen arm.
• The AS55_Q channel in demodulation of SRCL oscillator is configured (phase corrected) so that all signal comes in C1:CAL-SENSMAT_SRCL_AS55_Q_DEMOD_I_OUT.
• The rotation angle of AS55 RFPD is scanned and the C1:CAL-SENSMAT_SRCL_AS55_Q_DEMOD_I_OUT is averaged over 10s after waiting for 5s to let the transients pass.
• This data is used to find the zero crossing of AS55_Q signal when light is coming from one particular arm only.
• The same is repeated for the other arm.
• The difference in the zero crossing phase angles is twice the phase accumulated by a 55 MHz signal in travelling the length difference between the arm cavities i.e. the Schnupp Asymmetry.

I measured a phase difference of 5 $\pm$1 degrees between the two paths.

The uncertainty in this measurement is much more than gautam's 15956 measurement. I'm not sure yet why, but would look into it.

 Quote: I used the Valera technique to measure the Schnupp asymmetry to be $\approx 3.5 \, \mathrm{cm}$, see Attachment #1. The data points are points, and the zero crossing is estimated using a linear fit. I repeated the measurement 3 times for each arm to see if I get consistent results - seems like I do. Subtle effects like possible differential detuning of each arm cavity (since the measurement is done one arm at a time) are not included in the error analysis, but I think it's not controversial to say that our Schnupp asymmetry has not changed by a huge amount from past measurements. Jamie set a pretty high bar with his plot which I've tried to live up to.

Attachment 1: Lsch.pdf
16275   Wed Aug 11 11:35:36 2021 PacoUpdateLSCPRMI MICH orthogonality plan

[yehonathan, paco]

Yesterday we discussed a bit about working on the PRMI sensing matrix.

In particular we will start with the "issue" of non-orthogonality in the MICH actuated by BS + PRM. Yesterday afternoon we played a little with the oscillators and ran sensing lines in MICH and PRCL (gains of 50 and 5 respectively) in the times spanning [1312671582 -> 1312672300], [1312673242 -> 1312677350] for PRMI carrier and [1312673832 -> 1312674104] for PRMI sideband. Today we realize that we could have enabled the notchSensMat filter, which is a notch filter exactly at the oscillator's frequency, in FM10 and run a lower gain to get a similar SNR. We anyways want to investigate this in more depth, so here is our tentative plan of action which implies redoing these measurements:

Task: investigate orthogonality (or lack thereof) in the MICH when actuated by BS & PRM
1) Run sensing MICH and PRCL oscillators with PRMI Carrier locked (remember to turn NotchSensMat filter on).
2) Analyze data and establish the reference sensing matrix.
3) Write a script that performs steps 2 and 3 in a robust and safe way.
4) Scan the C1:LSC-LOCKIN_OUTMTRX, MICH to BS and PRM elements around their nominal values.
5) Scan the MICH and PRCL RFPD rotation angles around their nominal values.

We also talked about the possibility that the sensing matrix is strongly frequnecy dependant such that measuring it at 311Hz doesn't give us accurate estimation of it. Is it worthwhile to try and measure it at lower frequencies using an appropriate notch filter?

Wed Aug 11 15:28:32 2021 Updated plan after group meeting

- The problem may be in the actuators since the orthogonality seems fine when actuating on the ITMX/ITMY, so we should instead focus on measuring the actuator transfer functions using OpLevs for example (same high freq. excitation so no OSEM will work > 10 Hz).

16303   Mon Aug 30 17:49:43 2021 PacoSummaryLSCXARM POX OLTF

Used diaggui to get OLTF in preparation for optimal system identification / calibration. The excitation was injected at the control point of the XARM loop C1:LSC-XARM_EXC. Attachment 1 shows the TF (red scatter) taken from 35 Hz to 2.3 kHz with 201 points. The swept sine excitation had an envelope amplitude of 50 counts at 35 Hz, 0.2 counts at 100 Hz, and 0.2 at 200 Hz. In purple continous line, the model for the OLTF using all the digital control filters as well as a simple 1 degree of freedom plant (single pole at 0.99 Hz) is overlaid. Note the disagreement of the OLTF "model" at higher frequencies which we may be able to improve upon using vector fitting.

Attachment 2 shows the coherence (part of this initial measurement was to identify an appropriately large frequency range where the coherence is good before we script it).

Attachment 1: XARM_POX_OLTF.pdf
Attachment 2: XARM_POX_Coh.pdf
16304   Tue Aug 31 14:55:24 2021 ranaSummaryLSCXARM POX OLTF

this model doesn't seem to include the analog AA, analog AI, digital AA, digital AI, or data transfer delays in the system. I think if you include those you will get more accuracy at high frequencies. Probably Anchal has those included in his DARM loop model?

16320   Mon Sep 13 09:15:15 2021 PacoUpdateLSCMC unlocked?

Came in at ~ 9 PT this morning to find the IFO "down". The IMC had lost its lock ~ 6 hours before, so at about 03:00 AM. Nothing seemed like the obvious cause; there was no record of increased seismic activity, all suspensions were damped and no watchdog had tripped, and the pressure trends similar to those in recent pressure incidents show nominal behavior (Attachment #1). What happened?

Anyways I simply tried reopening the PSL shutter, and the IMC caught its lock almost immediately. I then locked the arms and everything seems fine for now .

Attachment 1: VAC_2021-09-13_09-32-45.png
16322   Mon Sep 13 15:14:36 2021 AnchalUpdateLSCXend Green laser injection mirrors M1 and M2 not responsive

I was showing some green laser locking to Tega, I noticed that changing the PZT sliders of M1/M2 angular position on Xend had no effect on locked TEM01 or TEM00 mode. This is odd as changing these sliders should increase or decrease the mode-matching of these modes. I suspect that the controls are not working correctly and the PZTs are either not powered up or not connected. We'll investigate this in near future as per priority.

16368   Thu Sep 30 14:13:18 2021 AnchalUpdateLSCHV supply to Xend Green laser injection mirrors M1 and M2 PZT restored

Late elog, original date Sep 15th

We found that the power switch of HV supply that powers the PZT drivers for M1 and M2 on Xend green laser injection alignment was tripped off. We could not find any log of someone doing it, it is a physical switch. Our only explanation is that this supply might have a solenoid mechansm to shut off during power glitches and it probably did so on Aug 23 (see 40m/16287). We were able to align the green laser using PZT again, however, the maximum power at green transmission from X arm cavity is now about half of what it used to be before the glitch. Maybe the seed laser on the X end died a little.

16888   Fri Jun 3 15:22:51 2022 yutaUpdateLSCBoth arms locked with POY/POX, IR beam centered on TMs with ASS

[JC, Paco, Yuta]

We locked both Y and X arms with POY11 and POX11.
RFM fix (40m/16887) enabled us to use triggering using C1:LSC-TRY/X_OUT.
IR beam is now centered on TMs using ASS (for Yarm, ASS loops cannot be closed fully, so did it manually).

What we did:
- Aligned both arms so that the beams are roughly centered at TMs using cameras.
- Yarm lock was easy, but Xarm lock required gain tuning. Somehow, Xarm required x3 higher gain as follows, although the amplitude of POX11_I_ERR seems to be almost the same as POY11_I_ERR. I suspect it is something to do with power normalization matrix (TRX flashing is almost a double of TRY flashing).

C1:LSC-YARM_GAIN = 0.01
C1:LSC-XARM_GAIN = 0.03

- Run ASS for Yarm. ASS loops cannot be closed fully using default feedback parameters. I guess this is because ITMY ULCOIL is not working (40m/16873). ASS demodulated signals were manually zero-ed by manually aligning ETMY, ITMY and PR3 (and some TT1 and TT2), except for demodulated signals related to ITMY. Beam on ITMY was centered just by using our eyes.
- Run ASS for Xarm. It seemed to work well.
- After this, TRX and TRY were as follows and beam positions on TMs were as attached.

C1:LSC-TRX_OUT ~0.95
C1:LSC-TRY_OUT ~ 0.58

(TRX is somehow lower than what we had yesterday... 40m/16886; TRX and TRY photodiode alignment was checked, but seems to be OK.)

- Centered TMs and BS oplevs.

Next:
- POX and POY demodulation phases are not fully optimized. Needs re-tuning.
- Tweak GRX and GRY injection (restore GRY PZTs?)
- Install ETMXT camera (if it is easy)
- MICH locking
- RTS model for BHD needs to be updated

Attachment 1: IRBeamsOnTMs.JPG
Attachment 2: Screenshot_2022-06-03_15-03-51.png
16889   Fri Jun 3 17:42:50 2022 yutaUpdateLSCMICH locks with AS55_Q

AS path at AP table as re-aligned and confirmed that MICH can be locked with AS55 Q.

What we did:
- Aligned AS55 and AS110 paths at AP table. AS55 was not receiving enough light. AS110 was not receiving light at all.
- Changed AS55 I and Q whitening gain from 3dB to 42dB.
- Zero-ed the RF offsets manually. C1:LSC-AS55_Q_IN1 is having too large offset. When PSL shutter was closed, it reads 13950! Needs investigation.
- Locked MICH with PRM mis-aligned with configurations attached.

Other Issues:
- C1:IOO-MC_TRANS_SUM is now stuck at 14009. MC auto locker doesn't work correctly. FIX ME!

Attachment 1: Screenshot_2022-06-03_17-41-55.png
16890   Sun Jun 5 19:46:40 2022 PacoUpdateLSCFixed IMC Trans sum issue

[Paco]

Fixed the issue below:

 Quote: Other Issues:  - C1:IOO-MC_TRANS_SUM is now stuck at 14009. MC auto locker doesn't work correctly. FIX ME!

by noting that the C1:IOO-MC_TRANS_SUMFILT_OUT was being held to 14009 counts for some reason. Disabling hold quickly let the IMC autolocker act back.

WFS were also turned ON, and there were a couple other control outputs being held on that loop... Strange!

16892   Mon Jun 6 13:35:11 2022 PacoUpdateLSCFirst calibrated spectra of MICH at AS55 Q

[Paco, Yuta]

On the topic of high AS55_Q RFPD offset, it seems it stems from a small residual offset on top of the 42 dB whitening filter gain (previously 3 dB). We verified this by looking in the past using dtt and seeing an offset of ~ 100 counts, which are consistent with the hotfix. We reverted the whitening filter gain to +24 dB, in order to accomodate the 10% power difference from AS2. We decided to move forward, and try locking MICH using AS55_Q_ERR. The IQ mixing angle was changed to -167 deg from -122 deg to minimize the signal in AS55_I_ERR. We have also added comb60 filters for AS55. The LSC_MICH filter gain was adjusted to -6 (used to be -13 in the configuration script) to get a MICH_OLTF UGF of 90 Hz (which is the previously measured value as of 2021 July), see Attachment #1 for the MICH OLTF estimate.

We then calibrate MICH using the fringe amplitude, so that  $4 \pi I_{0} / \lambda = 1.299 \times 10^9 {\rm cts / m}$, where $I_{0}$ is the amplitude of the error point (C1:LSC-AS55_Q_ERR_DQ) in our case ~ 110 +- 2 counts. The calibrated error point spectral density is shown in Attachment #2. Calibration is done into meters in terms of difference between BS to ITMX length and BS to ITMY length.

Attachment 1: Screenshot_2022-06-06_17-30-16_MICHOLTF.png
Attachment 2: Calibrated_MICH_ERR.pdf
16929   Fri Jun 17 16:22:21 2022 yutaUpdateLSCActuator calibration of BS. ITMX, ITMY, updated MICH displacement spectra from c1cal

Following what we have done in 2013 (40m/8242), actuator calibration was done using MICH.

AS55_Q in MICH : 9.74e8 counts/m
BS   : 26.08e-9 /f^2 m/counts
ITMX : 5.29e-9 /f^2 m/counts
ITMY : 4.74e-9 /f^2 m/counts

Optical gain is 25% lower than the measurement in June 6 (40m/16892), probably because our estimate was too rough then and also we now have ~15% lower IMC transmission.
Actuator gains are 2-30% higher than the measurement in 2013.

MICH error signal calibration:
C1:LSC-AS55_Q_ERR was calibrated by taking data with C1:LSC-ASDC_OUT, when Michelson was aligned and free swinging (Attachment #1).
AS55_Q and ASDC were X-Y plotted and fitted with ellipse to get an amplitude of AS55_Q to be 82.51 counts (Attachment #2).
4*pi*A/lambda gives you 9.74e8 counts/m, where meters are in terms of difference between BS to ITMX length and BS to ITMY length.
Jupyter notebook: https://git.ligo.org/40m/scripts/-/blob/main/CAL/MICH/MICHOpticalGainCalibration.ipynb

Openloop transfer function for actuator calibration:
C1:LSC-MICH_GAIN was lowered to -1 (instead of -6), and some of filters are turned off to make the MICH UGF to be ~10.
Also, ellip("LowPass",4,1,40,50) was added to C1:LSC-MICH_A filter bank to cut the feedback above 50 Hz, so that the loop does not suppress the measurement.
The configuration is in Attachment #3.

Actuator calibration of BS, ITMX, ITMY:
With this MICH OLG, transfer functions from C1:LSC-BS,ITMX,ITMY_EXC to C1:LSC-AS55_Q_ERR were measured.
AS55_Q was calibrated to meters using the calibration factor above, and fitted the transfer function with 1/f^2 in 70-150 Hz range to get the actuator efficiency mentioned above (Attachement #4).
Thus, meters in this calibration is in terms of ITM POS motion (not in BS POS motion).
Jupyter notebook: https://git.ligo.org/40m/scripts/-/blob/main/CAL/MICH/MICHActuatorCalibration.ipynb

MICH displacement noise:
Measured values were added to c1cal model as follows.
C1:CAL-MICH_CINV FM2: 1/9.74e8 = 1.03e-9
C1:CAL-MICH_A FM2: 2.608e-8 (it was 2.07e-8 from 2013!)
C1:CAL-MICH_A_GAIN = 0.5 to take into account of C1:LSC-OUTPUT_MTRX_8_2=0.5 in the LSC output matrix for BS
Spectrum of C1:CAL-MICH_W_OUT (now calibrated in nm) with configuration in Attachment #5 was taken.
Attachement #6 is the result. I also took the spectrum with PSL shutter off to measure the sensing noise. The sensing noise limits our sensitivity above ~40 Hz at 5e-11 m/rtHz.

Attachment 1: MICHOpticalGainCalibrationFig1.png
Attachment 2: MICHOpticalGainCalibrationFig2.png
Attachment 3: Screenshot_2022-06-17_14-23-04_MICHOLTF_ActuatorCalibration.png
Attachment 4: MICHActuatorCalibration.png
Attachment 5: Screenshot_2022-06-17_15-54-41_MICHCalibrationFilters.png
Attachment 6: Screenshot_2022-06-17_15-53-41_MICHDisplacement.png
16940   Wed Jun 22 18:55:31 2022 yutaUpdateLSCDaily alignment work; POY trouble solved

[Koji, Yuta]

I found that Yarm cannot be locked today. Both POY11 and POYDC were not there when Yarm was aligned, and ITMY needed to be highly misaligned to get POYDC.
POY beam also could not be found at ITMY table.
Koji suggested to use AS55 instead to lock Yarm. We did it (AS55_I_ERR, C1:LSC-YARM_GAIN=-0.002) and manually ASS-ed to get Yarm aligned (ASS with AS55 somehow didn't work).
After that, we checked ITMY table and found that POY beam was clipped at an iris which was closed!
I opened it and now Yarm locks with POY11 again. ASS works.
PMC was also aligned.

C1:PSL-PMC_PMCTRANSPD ~0.74
C1:IOO-MC_TRANS_SUM ~14000
C1:LSC-TRY_OUT ~0.7
C1:LSC-TRX_OUT ~0.8

Attachment 1: Screenshot_2022-06-22_17-17-42_XYaligned.png
Attachment 2: Screenshot_2022-06-22_18-58-26_Transmission.png
16941   Wed Jun 22 19:41:13 2022 KojiUpdateLSCDaily alignment work; POY trouble solved

Before the final measurement of the DC values for the transmissions, I aligned the PMC. This made the PMC trans increased from 0.67 to 0.74.

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
16968   Fri Jul 1 08:50:48 2022 yutaSummaryLSCFPMI with REFL/AS55 trial

[Anchal, Paco, Yuta]

We tried to lock FPMI with REFL55 and AS55 this week, but no success yet.
FPMI locks with POX11, POY11 and ASDC for MICH stably, but handing over to 55's couldn't be done yet.

What we did:
- REFL55: Increased the whitening gain to 24dB. Demodulation phase tuned to minimize MICH signal in I when both arms are locked with POX and POY. REFL55 is noisier than AS55. Demodulation phase and amplitude of the signal seem to drift a lot also. Might need investigation.
- AS55: Demodulation phase tuned to minimize MICH signal in I when both arms are locked with POX and POY. Whitening gain is 24dB.
- Script for demodulation phase tuning lives in https://git.ligo.org/40m/scripts/-/blob/main/RFPD/getPhaseAngle.py
- Locking MICH with REFL55 Q: Kicks BS much and not so stable probably because of noisy REFL55. Offtet also needs to be adjusted to lock MICH to dark fringe.
- BS coil balancing: When MICH is "locked" with REFL55 Q, TRX drops rapidly and AS fringe gets worse, indicating BS coil balancing is not good. We balanced the coils by dithering POS with different coil output matrix gains to minimize oplev PIT and YAW output manually using LOCKINs.
- Locking MICH with ASDC: Works nicely. Offset is set to -0.1 in MICH filter and reduced to -0.03 after lock acquisition.
- ETMX/ETMY actuation balancing: We found that feedback signal to ETMX and ETMY at LSC output is unbalanced when locking with POX and POY. We dithered MC2 at 71 Hz, and checked feedback signals when Xarm/Yarm are locked to find out actuation efficiency imbalance. A gain of 2.9874 is put into C1:LSC-ETMX filter to balance ETMX/ETMY. I think we need to check this factor carefully again.
- TRX and TRY: We normalized TRX and TRY to give 1 when arms are aligned. Before doing this, we also checked the alignment of TRX and TRY DC PDs (also reduced green scattering for TRY). Together with ETMX/ETMY balancing, this helped making filter gains the same for POX and POY lock to be 0.02 (See, also 40m/16888).
- Single arm with REFL55/AS55: We checked that single arm locking with both REFL55_I and AS55_Q works. Single arm locking feeding back to MC2 also worked.
- Handing over to REFL55/AS55: After locking Xarm and Yarm using POX to ETMX and POY to ETMY, MICH is locked with ASDC to BS. Handing over to REFL55_I for CARM using ETMX+ETMY and AS55_Q for DARM using -ETMX+ETMY was not successful. Changing an actuator for CARM to MC2 also didn't work. There might be an unstable point when turning off XARM/YARM filter modules and switching on DARM/CARM filter modules with a ramp time. We also need to re-investigate correct gains and signs for DARM and CARM. (Right now, gains are 0.02 for POX and POY, -0.02 for DARM with AS55_Q (-ETMX+ETMY), -0.02 for CARM with REFL55_I with MC2 are the best we found so far)

Next:
- Measure ETMX and ETMY actuation efficiencies with Xarm/Yarm to balance the output matrix for DARM.
- Measure optical gains of POX11, POY11, AS55 and REFL55 when FPMI is locked with POX/POY/ASDC to find out correct filter gains for them.
- Make sure to measure OLTFs when doing above to correct for loop gains.
- Lock CARM with POY11 to MC2, DARM with POX11 to ETMX. Use input matrix to hand over instead of changing filter modules from XARM/YARM to DARM/CARM.
- Try using ALS to lock FPMI.

16977   Thu Jul 7 18:18:19 2022 yutaUpdateLSCActuator calibration of ETMX and ETMX

(This is a complete restore of elog 40m/16970 from July 5, 2022 at 14:34)

ETMX and ETMY actuators were calibrated using single arm lock by taking the actuation efficiency ratio between ITMs. Below is the result.

ETMX :  2.65e-9 /f^2 m/counts (0.5007 times ITMX)
ETMY : 10.91e-9 /f^2 m/counts (2.3017 times ITMY)

Motivation:
- ETMX and ETMY actuators seemed to be unbalanced when locking DARM (see 40m/16968)

What we did:
- Reverted to C1:LSC-ETMX_GAIN = 1
- XARM was locked using POX11_I_ERR (42dB whitening gain, 132.95 deg for demod phase) with ETMX and C1:LSC-XARM_GAIN=0.06
- YARM was locked using POY11_I_ERR (18dB whitening gain, -66.00 deg for demod phase) with ETMX and C1:LSC-YARM_GAIN=0.02
- OLTFs for each was measured to be Attachment #1; UGF was ~180 Hz for XARM, ~200 Hz for YARM.
- Measured TF from C1:LSC-(E|I)TM(X|Y)_EXC to C1:LSC-(X|Y)ARM_IN1 (see Attachment #2)
- Took the ratio between ITM actuation and ETM actuation to calculate ETM actuation. For ITM actuation, we used the value measured using MICH (see 40m/16929). The average of the ratio in the frequency range 70-150 Hz was used.

Files:
- Measurement files live in https://git.ligo.org/40m/measurements/-/tree/main/LSC/XARM and YARM
- Script for calculation lives at https://git.ligo.org/40m/scripts/-/blob/main/CAL/ARM/ETMActuatorCalibration.ipynb

Discussion:
- ETMX actuation is 4.12 times less compared with ETMY. This is more or less consistent with what we measured in 40m/16968, but we didn't do loop-correction at that time.
- We should check if this imbalance is as expected or not.

Summary of actuation calibration so far:
BS   : 26.08e-9 /f^2 m/counts (see 40m/16929)
ITMX :  5.29e-9 /f^2 m/counts (see 40m/16929)
ITMY :  4.74e-9 /f^2 m/counts (see 40m/16929)
ETMX :  2.65e-9 /f^2 m/counts (0.5007 times ITMX) ETMY : 10.91e-9 /f^2 m/counts (2.3017 times ITMY)

Attachment 1: Screenshot_2022-07-05_14-52-01_OLTF.png
Attachment 2: Screenshot_2022-07-05_14-54-03_TF.png
Attachment 3: Screenshot_2022-07-05_14-56-41_Ratio.png
16978   Thu Jul 7 18:22:12 2022 yutaUpdateLSCActuator calibration of MC2 using Yarm

(This is also a restore of elog 40m/16971 from Jul 5, 2022 at 17:36)

MC2 actuator calibration was also done using Yarm in the same way as we did in 40m/16970 (now 40m/16977).
The result is the following;
MC2 : -14.17e-9 /f^2 m/counts in arm length (-2.9905 times ITMY) MC2 :   5.06e-9 /f^2 m/counts in IMC length MC2 :  1.06e+05 /f^2 Hz/counts in IR laser frequency

What we did:
- Measured TF from C1:LSC-MC2_EXC to C1:LSC-YARM_IN1 during YARM lock using ETMY (see Attachment #1). Note that the sign of MC2 actuation and ITMY actuation is flipped.
- Took the ratio between ITM actuation and MC2 actuation to calculate MC2 actuation. For ITM actuation, we used the value measured using MICH (see 40m/16929). The average of the ratio in the frequency range 70-150 Hz was used (see Attachment #2).
- The actuation efficiency in meters in arm length was converted into meters in IMC length by multiplying it by IMCLength/ArmLength, where IMCLength=13.5 m is half of IMC round-trip length, ArmLength=37.79 m is the arm length.
- The actuation efficiency in meters in arm length was converted into Hz in IR laser frequency by multiplying it by LaserFreq/ArmLength, where LaserFreq=1064 nm / c is the laser frequency.

Files:
- Measurement files live in https://git.ligo.org/40m/measurements/-/tree/main/LSC/YARM
- Script for calculation lives at https://git.ligo.org/40m/scripts/-/blob/main/CAL/ARM/ETMActuatorCalibration.ipynb

Summary of actuation calibration so far:
BS   : 26.08e-9 /f^2 m/counts (see 40m/16929)
ITMX :  5.29e-9 /f^2 m/counts (see
40m/16929)
ITMY :  4.74e-9 /f^2 m/counts (see
40m/16929)
ETMX :  2.65e-9 /f^2 m/counts (0.5007 times ITMX) ETMY : 10.91e-9 /f^2 m/counts (2.3017 times ITMY)
MC2 : -14.17e-9 /f^2 m/counts in arm length (-2.9905 times ITMY) MC2 :   5.06e-9 /f^2 m/counts in IMC length

NOTE ADDED by YM on July 7, 2022

To account for the gain imbalance in ETMX, ETMY, MC2, LSC violin filter gains were set to: C1:LSC-ETMX_GAIN = 4.12 C1:LSC-MC2_GAIN = -0.77 This is a temporary solution to make ETMX and MC2 actuation efficiencies from LSC in terms of arm length to be the same as ETMY 10.91e-9 /f^2 m/counts.

I think it is better to make C1:LSC-ETMX_GAIN = 1, and put 4.12 in C1:SUS-ETMX_TO_COIL gains. We need to adjust local damping gains and XARM ASS afterwards. As for MC2, it is better to put -0.77 in LSC output matrix, since this balancing depends on LSC topology.

Attachment 1: TF.png
Attachment 2: MC2.png
16981   Fri Jul 8 16:18:35 2022 ranaUpdateLSCActuator calibration of MC2 using Yarm

although I know that Yuta knows this, I will just put this here to be clear: the NNN/f^2 calibration is only accurate abouve the pendulum POS eiegenfrequency, so when we estimate the DC part (in diaggui, for example), we have to assume that we have a pendulum with f = 1 Hz and Q ~5, to get the value of DC gain to put into the diaggui Gain field in the calibration tab.

17002   Thu Jul 14 00:10:08 2022 yutaSummaryLSCFPMI with REFL/AS55 trial continued

[Paco, Koji, Yuta]

We managed to lock MICH using REFL55_Q by setting the demodulation phases and offsets right.
The following is the current FPMI locking configuration we achieved so far.

DARM: POX11_I / gain 0.007 / 0.5*ETMX-0.5*ETMY (or 1*ETMX) / UGF of ~100 Hz
CARM: POY11_I / gain 0.018 / 1*MC2 / UGF of ~200 Hz
MICH: REFL55_Q / gain -10 / 0.5*BS / UGF of ~30 Hz

Transitioning DARM error signal from POX11_I to 0.5*POX11_I+0.5*POY11_I was possible with FM4 filter off in DARM filter bank, but not to AS55_Q yet.

REFL55 and AS55 demodulation phase tuning:
- We found that both AS55 and REFL55 are contaminated by large non-MICH signal, by making a ASDC vs RF plot (see 40m/16929).
- After both arms are locked with POX and POY, MICH was locked with AS55_Q. ASDC was minimized by putting an offset to MICH filter.
- With this, REFL55 offsets were zeroed and demodulation phase was tuned to minimize REFL55_Q.
- Locked MICH with REFL55_Q, and did the same thing for AS55_Q.
- Resulting ASDC vs RF plots were attached. REFL55_Q now looks great, but REFL55_I and AS55 are noisy (due to signals from the arms?).

Jupyter notebook: https://git.ligo.org/40m/scripts/-/blob/main/CAL/MICH/MICHOpticalGainCalibration.ipynb

Sensing matrix:
- With FPMI locked using POX/POY, DARM and CARM lines were injected at around 300 Hz to measure the sensing gains. For line injection, C1:CAL-SENSMAT was used, but for the demodulation we used a script. The following is the result.

 Sensors              DARM (ETMX)         CARM (MC2)         C1:LSC-AS55_I_ERR    3.10e+00 (-34.1143 deg)    1.09e+01 (-14.907 deg)     C1:LSC-AS55_Q_ERR    9.96e-01 (-33.9848 deg)    3.30e+00 (-27.9468 deg)     C1:LSC-REFL55_I_ERR    6.75e+00 (-33.7723 deg)    2.92e+01 (-34.0958 deg)     C1:LSC-REFL55_Q_ERR    7.07e-01 (-33.4296 deg)    3.08e+00 (-33.4437 deg)     C1:LSC-POX11_I_ERR    3.97e+00 (-33.9164 deg)    1.51e+01 (-30.7586 deg)     C1:LSC-POY11_I_ERR    6.25e-02 (-20.3946 deg)    3.59e+00 (38.4207 deg)

Jupyter notebook: https://git.ligo.org/40m/scripts/-/blob/main/CAL/SensingMatrix/MeasureSensMat.ipynb

- By taking the ratios of POX11_I and AS55_Q for DARM, POY11_I and REFL55_I for CARM, we tried to find the correct gains for REFL55 and AS55 for DARM and CARM. x3.96 more gain for AS55_Q than POX11_I and x0.123 less gain for REFL55_I than POY11_I.

Next:
- Try locking the arms with no triggering, and then try locking FPMI with REFL/AS without triggering. No FM4 for this, since FM4 kills gain margin.
- Lock single arm with AS55_Q and make a noise budget. Make sure to misalign ITMX(Y) completely when locking Y(X)arm.
- Lock single arm with REFL55_I and make a noise budget.
- Repeat Xarm noise budget with Yarm locked with POY11_I and MC2 (40m/16975).
- Check IMC to reduce frequency noise (40m/17001)

Attachment 1: AS55_I.png
Attachment 2: AS55_Q.png
Attachment 3: REFL55_I.png
Attachment 4: REFL55_Q.png
17007   Fri Jul 15 19:13:22 2022 PacoSummaryLSCFPMI with REFL/AS55 demod phase adjust

[Yuta, Paco]

• We first zero the offsets in ASDC, AS55, REFL55, POX11, and POY11 when PSL shutter is closed.
• After this, we checked the offsets with only ITMX aligned. Some of RFPDs had ~2 counts of offsets, which indicate some RFAM of sidebands, but we decided not to tune Marconi frequencies since the offsets were small enough.
• We went over the demod phases for AS55, REFL55, POX11, and POY11.
• For POX11/POY11 first we just minimized the Q in each locked XARM/YARM individually. The newfound values were
• C1:LSC-POX11_PHASE_R = 106.991
• C1:LSC-POY11_PHASE_R = -12.820
• Then we misaligned the XARM by getting rid of the MICH fringe in the ASDC port with ITMX yaw offset, and locked YARM using AS55_Q and REFL55_I and found the demod phase that minimized the AS55_I and REFL55_Q. The newfound values were
• C1:LSC-AS55_PHASE_R = -65.9586
• C1:LSC-REFL55_PHASE_R = -78.6254
• Repeating the above, but now misaligning YARM with ITMY yaw offset, locking XARM with AS55_Q and REFL55_I, we found the demod phases that minimized AS55_1 and REFL55_Q. The newfound values were
• C1:LSC-AS55_PHASE_R = -61.4361
• C1:LSC-REFL55_PHASE_R = -71.0434
• The above demod phases difference, Schnupp asymmetry between X and Y were measured. We repeated the measurement three times to derive the error.
• Optimal demod phase difference between X arm and Y arm for both AS55 and REFL55 were measured to be -4.5 +/- 0.1 deg, which means that lx-ly = 3.39 +/- 0.05 cm (Marconi frequency: 11.066195 MHz).
• We measured the gain difference between AS55_Q and POX11/POY11 = -0.5
• We measured the gain difference between REFL55_I and POX11/POY11 = -2.5

After this, we locked DARM, CARM and MICH using POX11_I, POY11_I and AS55 error signals respectively, and actuating on ETMX, MC2, and BS with NO TRIGGERS (but FM triggers were on for boosts as usual). Under this condition, FM5 is used for lock acquisition, and FM1, FM2, FM3, FM6 are turned on with FM triggers. No FM4 was on. We also noticed:

• CARM FM6 "BounceRoll" is slightly different than "YARM" FM6 "Bounce". The absent roll resonant gain actually makes it easier to control the CARM, we just had to use YARM filter for locking it.
• When CARM is controlled, we often just kick the ETMX to bring it near resonance, since the frequency noise drops and we otherwise have to wait long.
17008   Fri Jul 15 22:36:04 2022 ranaSummaryLSCFPMI with REFL/AS55 demod phase adjust

Very nice!

DARM feedback should go to ETMY - ETMX, not just a single mirror: Differential ARM.

For it to work with 1 mirror the UGF of the CARM loop must be much larger than DARM UGF. But in our case, both have a UGF of ~150 Hz.

In principle, you could run the CARM loop with higher gain by using the CM servo board, but maybe that can wait until the X,Y -> CARM, DARM handoff.

17012   Mon Jul 18 16:39:07 2022 PacoSummaryLSCFPMI locking procedure using REFL55 and AS55

[Yuta, Paco]

In summary, we locked FPMI using REFL55_I, REFL55_Q, and AS55_Q. The key to success was to mix POX11_I and POY11_I in the right way to emulate CARM/DARM, and to find out the correct demodulation phase for AS55.

Procedure

1. Close PSL shutter and zero offsets in AS55, REFL55, POX11, POY11, and ASDC
• For ASDC run python3 resetOffsets.py -c C1:LSC-ASDC_IN1, otherwise use the zer offsets on I and Q inputs from the RFPD medm screen.
2. Lock XARM/YARM using POX/POY to tune demodulation phase.
• Today, the demode phase in POX11 changed to 104.801, and POY11 to -11.256 deg.
3. XARM and YARM are used in the following configuration
• INMAT
• 0.5 * POX11_I - 0.5 * POY --> XARM
• 0.5 * POX + 0.5*POY --> YARM
• REFL55_Q --> MICH (** this should be turned on after POX11/POY11)
• LSC Filter gains
• XARM = 0.012
• YARM = 0.012
• MICH = +40 (note the sign flip from last time)
• OUTMAT
• XARM --> 0.5 * ETMX - 0.5 * ETMY
• YARM --> MC2
• MICH --> BS
• UGFs (sanity check)
• XARM (DARM) ~ 100 Hz
• YARM (CARM) ~ 200 Hz
• MICH (MICH) ~ 40 Hz
4. Run MICHOpticalGainCalibration.ipynb to see if ASDC vs REFL55_Q looks nice (ellipse in the XY plot), and find any residual offset in REFL55_Q.
• If the plot doesn't look nice in this regard, the IFO needs to be aligned.
5. Sensing matrix for CARM/DARM and MICH.
• With the DARM, CARM and MICH lines on, verify the demod error signals look ok both in mag and phase.
• For example, we found that CARM error signals were correctly represented by either 0.5 * POX11_I + 0.5 * POY11_I or 0.5 * REFL55_I.
• Similarly, we found that DARM error signal was correctly represented by either 0.5 * POX11_I - 0.5 * POY11_I or 2.5 * AS55_Q.
• To find this, we minimized CARM content in AS55_Q, as well as CARM content in REFL55_Q.
6. We acquired the lock by re-configuring the error point as below:
• INMAT
• 0.5*REFL55_I --> YARM (CARM)
• 2.5 * AS55_Q --> XARM (DARM)
• During the hand-off trials, we repeatedly ran the sensing matrix and UGF measurements while stopping at various intermediate mixed error points to check how the error signal calibrations changed if at all.
• Attachment #1 shows the DARM OLTF using POX/POY (blue), only with CARM handoff (green), and after DARM handoff (red)
• Attachment #2 shows the CARM OLTF using POX/POY (blue), only with CARM handoff (green), and after DARM handoff (red)
• Attachment #3 shows the MICH OLTF using POX/POY (blue), only with CARM handoff (green), and after DARM handoff (red)
• The sensing matrix after handoff is below:
Sensing Matrix with the following demodulation phases
{'AS55': 192.8, 'REFL55': 95.63177865911078, 'POX11': 104.80089727128349, 'POY11': -11.256509422276006}
Sensors          	           DARM     	           CARM     	            MICH
C1:LSC-AS55_I_ERR_DQ	5.09e-02 (89.6761 deg)	2.03e-01 (-114.513 deg)	1.28e-04 (-28.9254 deg)
C1:LSC-AS55_Q_ERR_DQ	4.78e-02 (88.7876 deg)	3.61e-03 (-68.7198 deg)	8.34e-05 (-39.193 deg)
C1:LSC-REFL55_I_ERR_DQ	5.18e-02 (-92.2555 deg)	1.20e+00 (65.2507 deg)	1.15e-04 (-102.027 deg)
C1:LSC-REFL55_Q_ERR_DQ	1.81e-04 (59.0854 deg)	1.09e-02 (-114.716 deg)	1.77e-05 (-23.6485 deg)
C1:LSC-POX11_I_ERR_DQ	8.51e-02 (91.2844 deg)	4.77e-01 (67.1709 deg)	7.97e-05 (-72.5252 deg)
C1:LSC-POX11_Q_ERR_DQ	2.63e-04 (114.584 deg)	1.32e-03 (-113.505 deg)	2.10e-06 (118.146 deg)
C1:LSC-POY11_I_ERR_DQ	1.58e-01 (-88.9295 deg)	6.16e-01 (67.6098 deg)	8.71e-05 (172.73 deg)
C1:LSC-POY11_Q_ERR_DQ	2.89e-04 (-89.1114 deg)	1.09e-03 (70.2784 deg)	3.77e-07 (110.206 deg)


Lock gpstimes:

1. [1342220242, 1342220260]
2. [1342220420, 1342220890]
3. [1342221426, 1342221574]
4. [1342222753, 1342223230]

### Sensitivity estimate (NANB)

Using diaggui, we look at the AS55_Q error point and the DARM control point (C1:LSC-XARM_OUT). We roughly calibrate the error point using the sensing matrix element and actuation gain at the DARM oscillator freq 4.78e-2 / (10.91e-9 / 307.880^2). The control point is calibrated with a 0.95 Hz SUS pole. Attachment #4 shows the sensitivity estimate.

Attachment 1: DARM_07_18_2022_FMPI.pdf
Attachment 2: CARM_07_18_2022_FPMI.pdf
Attachment 3: MICH_07_18_2022_FPMI.pdf
Attachment 4: fpmi_darm_nb_2022_07.pdf
17014   Mon Jul 18 17:07:12 2022 yutaUpdateLSCx4.12 added to ETMX coil outputs to balance with ETMY

To balance the actuation on ETMX and ETMY, x4.12 was aded to C1:SUS-ETMX_(UL|UR|LR|LL|SD)COIL FM1. OSEM damping filter gains, oplev loop gains, and alignment offsets were divided by this factor.
C1:LSC-ETMX_GAIN is now 1.

To do:
- Balance ETM and ITM. It should make ASS more sensible.
- Re-commission Xarm ASS and Yarm ASS.

17016   Mon Jul 18 21:41:42 2022 AnchalSummaryLSCFPMI locking procedure using REFL55 and AS55

Now that you have found a working configuration, I suggest we update CARM and DARM filter banks so that they are used in locking those degrees of freedom instead of repurposing XARM/YARM banks. It would be bit easier to understand and leaves room for future changes for one configuration while keeping single arm lock configurations untouched.

17069   Tue Aug 9 19:54:31 2022 yutaSummaryLSCFPMI locking tonight

[Tega, Anchal, Yuta]

We resored FPMI locking settings. Below is the summary of locking configurations tonight.
To ease the lock acquisition, the step to feedback POX11_I to ETMX and POY11_I to MC2 before POX and POY mixing was necessary tonight.

CARM (YARM):
- 0.5 * POX11_I + 0.5 * POY11_I handed to 0.5 * REFL55_I
- YARM filter module, FM4,5 for acquisition, FM1,2,3,6,8 triggered, C1:LSC-YARM_GAIN = 0.012
- Actuation on -0.77 * MC2
- UGF ~ 250 Hz

DARM (XARM):
- 0.5 * POX11_I - 0.5 * POY11_I handed to 4.6 * AS55_Q (it was 2.5 in 40m/17012)
- XARM filter module, FM5 for acquisition (no FM4), FM1,2,3,6,8 triggered, C1:LSC-XARM_GAIN = 0.015
- Actuation on 0.5 * ETMX - 0.5 * ETMY
- UGF ~ 120 Hz

MICH:
- 1 * REFL55_Q (turned on after XARM and YARM acquisition)
- MICH filter module, FM4,5,8 for acquisition, FM2,3 triggered, C1:LSC-MICH_GAIN = +40
- Actuation on 0.5 * BS
- UGF ~ 100 Hz

Measured sensing matrix:
Sensing Matrix with the following demodulation phases
{'AS55': 200.41785156862835, 'REFL55': 93.7514468401475, 'POX11': 105.08325063571438, 'POY11': -11.343909976281823} Sensors              DARM                    CARM                   MICH C1:LSC-AS55_I_ERR_DQ 5.27e-02 (-154.105 deg) 2.83e-01 (132.395 deg) 1.17e-04 (-40.1051 deg) C1:LSC-AS55_Q_ERR_DQ 3.99e-02 (-151.048 deg) 1.42e-02 (125.504 deg) 1.41e-04 (-2.42846 deg) C1:LSC-REFL55_I_ERR_DQ 5.59e-02 (77.6871 deg) 1.15e+00 (-44.589 deg) 3.55e-04 (69.2585 deg) C1:LSC-REFL55_Q_ERR_DQ 1.84e-03 (16.3186 deg) 3.35e-03 (125.67 deg) 4.59e-05 (4.18718 deg) C1:LSC-POX11_I_ERR_DQ 1.54e-01 (-157.852 deg) 6.07e-01 (-42.1078 deg) 5.55e-05 (73.3963 deg) C1:LSC-POX11_Q_ERR_DQ 6.83e-05 (-148.591 deg) 6.37e-04 (121.983 deg) 1.35e-06 (43.7201 deg) C1:LSC-POY11_I_ERR_DQ 1.85e-01 (36.1624 deg) 5.73e-01 (-43.1776 deg) 2.12e-04 (82.16 deg) C1:LSC-POY11_Q_ERR_DQ 2.16e-05 (130.937 deg) 6.38e-05 (-173.194 deg) 1.40e-06 (47.5416 deg) 

FPMI locked periods:
- 1344129143 - 1344129520
- 1344131106 - 1344131305
- 1344133503 - 1344134020

Next:
- Restore CM servo for CARM

17089   Thu Aug 18 14:49:35 2022 YehonathanSummaryLSCFPMI Sensitivity

{Yuta, Yehonathan}

We wrote a notebook found on Git/40m/measurements/LSC/FPMI/NoiseBudget/FPMISensitivity.ipynb for calculating the MICH, DARM (currently XARM), CARM (currently YARM) sensitivities in the FPMI lock which can be run daily.

The IN and OUT channels of each DOFs are measured at a certain GPS time and calibrated using the optical gains and actuation calibration measured in the previous post.

Attachment shows the results.

It seems like the UGFs for MICH and DARM (currently XARM) match the ones that were estimated previously (100Hz for MICH, 120Hz for DARM) except for CARM for which the UGF was estimated to be 250Hz and here seems to be > 1kHz.

Indeed one can also see that the picks in the CARM plot don't match that well. Calculation shows that at 250Hz OUT channel is 6 times more than the IN channel. Calibrations for CARM should be checked.

MICH sensitivity using REFL55 at high frequencies is not much better than what was measured with AS55.

DARM sensitivity at 10Hz is a factor of a few better than the single arm lock sensitivity.

Now it is time to do the budgeting.

Attachment 1: Sensitivity_Plot_1344133503.pdf
17091   Thu Aug 18 18:10:49 2022 KojiSummaryLSCFPMI Sensitivity

The overlapping plot of the calibrated error and control signals gives you an approximately good estimation of the freerun fluctuation, particularly when the open-loop gain G is much larger or much smaller than the unity.
However, when the G is close to the unity, they are both affected by "servo bump" and both signals do not represent the freerun fluctuation around that frequency.

To avoid this, the open-loop gain needs to be measured every time when the noise budget is calculated. In the beginning, it is necessary to measure the open-loop gain over a large frequency range so that you can refine your model. Once you gain sufficient confidence about the shape of the open-loop gain, you can just use measurement at a frequency and just adjust the gain variation (most of the cases it comes from the optical gain).

I am saying this because I once had a significant issue of (project-wide) incorrect sensitivity estimation by omitting this process.

17122   Wed Aug 31 11:39:48 2022 YehonathanUpdateLSCUpdated XARM noise budget

For educational purposes we update the XARM noise budget and add the POX11 calibrated dark noise contribution (attachment).

Attachment 1: Screenshot_2022-08-31_11-38-46.png
17137   Thu Sep 8 16:03:25 2022 YehonathanUpdateLSCRealignment, arm locking, gains adjustments

{Anchal, Yehonathan}

We came this morning and the IMC was misaligned. The IMC was realigned and locked. This of course changed the input beam and sent us down to a long alignment journey.

We first use TTs to find beam on BHD DCPD/Camera since it is only single bounce on all optics.

Then, PR2/3 were used to find POP beam while keeping the BHD beam.

Unfortunately, that was not enough. TTs and PRs have some degeneracy which caused us to lose the REFL beam.

Realizing this we went to AS table to find the REFL beam. We found a ghost beam that decieved us for a while. Realizing it was a ghost beam, we moved TT2 in pitch, while keeping the POP DCPD high with PRs, until we saw a new beam on the viewing card.

We kept aligning TT1/2, PR2/3 to maximize the REFL DCPD while keeping the POP DCPD high. We tried to look at the REFL camera but soon realized that the REFL beam is too weak for the camera to see.

At that point we already had some flashing in the arms (we centered the OpLevs in the beginning).

Arms were aligned and locked. We had some issue with the X-ARM not catching lock. We increased the gain and it locked almost immediately. To fix the arms gains correctly we took OLTFs (Attachment) and adjusted the XARM gain to 0.027 to make the UGF at 200Hz.

Both arms locked with 200 Hz UGF from:

From GPS: 1346713049
To GPS: 1346713300

From GPS: 1346713380
To GPS: 1346714166

HEPA turned off:
From GPS: 1346714298
To GPS: 1346714716

17141   Thu Sep 15 16:19:33 2022 YehonathanUpdateLSCPOX-POY noise budget

Doing POX-POY noise measurement as a poor man's FPMI for diagnostic purposes. (Notebook in /opt/rtcds/caltech/c1/Git/40m/measurements/LSC/POX-POY/Noise_Budget.ipynb)

The arms were locked individually using POX11 and POY11. The optical gain was estimated to be by looking at the PDH signal of each arm: the slope was computed by taking the negative peak to positive peak counts and assuming that the arm length change between those peaks is lambda/(2*Finesse), where lambda = 1um and the arm finesse is taken to be 450.

Xarm peak-to-peak counts is ~ 850 while Yarm's is ~ 1100. This gives optical gains of 3.8e11 cts/m and 4.95e11 cts/m respectively.

Next, ETMX actuation TF is measured (attachments 1,2) by exciting C1:LSC-ETMX/Y_EXC and measuring at C1:LSC-X/YARM_IN1_DQ and calibrating with the optical gain.

Using these calibrations I plot the POX-POY (attachment 3) and POX+POY (attachment 4) total noise measurements using two methods:

1. Plotting the calibrated IN and OUT channels of XARM-YARM (blue and orange). Those two curves should cross at the UGF (200Hz in this case).

2. Plotting the calibrated XARM-YARM IN channels times 1-OLTF (black).

The UGF bump can be clearly seen above the true noise in those plots.

However, POX+POY OUT channel looks too high for some reason making the crossing frequency between IN and OUT channels to be ~ 300Hz. Not sure what was going on with this.

Next, I will budget this noise with the individual noise contributions.

Attachment 1: XARM_Actuation_Plot.pdf
Attachment 2: YARM_Actuation_Plot.pdf
Attachment 3: Sensitivity_Plot_1347315385.pdf
17135   Thu Sep 8 11:54:37 2022 JCConfigurationLab OrganizationLab Organization

The arms in the 40m laboratory have now been sectioned off. Each arm has been divided up into 15 sections. Along the Y arm, the section are labelled "Section Y1 - Section Y15". For the X arm, they are labelled "Section X1- Section X15". Anything changed or moved will now be updated into the elog with their appropriate section.

Below is an example of Section X6.

Attachment 1: 1A7026BC-82A9-49E9-BA22-1A700DFEC5D2.jpeg
Attachment 2: 2A904809-82F0-40C0-B907-B48C3A0E789E.jpeg
Attachment 3: CB4B8591-B769-454D-9A16-EE9176004099.jpeg
17136   Thu Sep 8 12:01:02 2022 JCConfigurationLab OrganizationLab Organization

The floor cable cover has been changed out for a new one. This is in Section X11.

Attachment 2: FF5F2CE8-85E8-4B6F-8F8A-9045D978F670.jpeg
8331   Fri Mar 22 01:28:56 2013 ManasaUpdateLasersBeam profile of NPRO from ATF

The NPRO from ATF has been installed on the POY table.

I have been making measurements to characterize the beam profile of this laser. I am using an AR coated laser window as a beam sampler at 45deg and the razor blade technique to measure the beam size along z. Details of the procedure along with analysis and results from this will follow.

231   Thu Jan 10 00:12:01 2008 tobinSummaryLockingDR
[John, Tobin, Rana]

1. We found SUS_BS_SENSOR_UL to have a ratty signal and low DC value. Twiddling the cables at the BS satellite amplifier and vacuum feedthrough brought the signal back (to 0.667V), but it is still spiky, spiking up to a couple times per second. Rana suggested that these spikes might be scattered YAG laser light (as hypothesized in August). The spikes go away when we misalign the PRM or either ITM, and when we unlock the mode cleaner, lending credance to this theory. SUS_BS_SENSOR_UR also spikes, but much less frequently. We turned off C1:SUS-BS_ULSEN_SW2 and continued.

2. After dither alignment the oplev beams were centred and we were able to lock DRM plus either arm reliably (however locking in this state broke ./drstep_bang at the first Going DD''). We ran scripts/DRFPMI/bang/nospring/drdown_bang and were subsequently able to lock DRFPMI (i.e., full IFO) a couple times.

3. To do: Debug ./drstep_bang with just the DRM (no arms).
313   Tue Feb 12 16:39:52 2008 robUpdateLockingreport

Did some locking work on DRFPMI on sunday and (with John) on monday nights. So far progress has not been terribly encouraging.

Problems include the DD_handoffs not working and the CARM->MCL handoff not working so well. To get around the DD signals trouble, I decided for now to just ignore 67% of the DD signals. We should be able to run with PRC & MICH on single demod signals, and SRC on a DD signal. This seems to work well in a DRMI state, and it also works well in a DRMI+2ARMs state.

The CARM->MCL handoff actually works, but it doesn't take kindly to the AO path and it doesn't work very stably. I guess this was always the most fragile part of the whole locking procedure, and it's fragility is really coming to light now. Investigation continues.
362   Thu Mar 6 00:17:37 2008 robUpdateLockingDD handoff working
Got the DD (double demod) handoff scripts working tonight, with just the DRMI. So, now acquisition with the single demod signals is working well, and handoffs to all double demod signals using the input matrix ramping worked several times with the scripts. Up next will be more work with the DRM+ARMs.
366   Mon Mar 10 02:05:08 2008 robUpdateLockingDRMI+2ARMs working better

Some encouraging progress on the locking front tonight. After the work on the DRM loops last week and a review of the settings for initial lock acquisition (loop gains, tickle amplitude, filter states, so on), the DRMI+2ARMS locking is working pretty well. That's to say, it takes from 5-15 minutes generally for the IFO to lock in the offset CARM state, with the arm powers at 0.5. It's then possible to raise the arm powers slightly, and handing off control of CARM to MCL works at low power, but engaging the AO path (using PO_DC as an error signal) is not working so well. Taking swept sines indicates that the PO_DC should be a good error signal. The next good thing to try might be just using PO_DC as an error signal for the length path, without using the AO path at all, to see if it's something in the hardware.
442   Thu Apr 24 14:10:26 2008 robUpdateLockinglocking work
Rob, Johnnie

We made some progress on locking last night (Wed night), namely that we were able to handoff (briefly) the CARM-MCL path the REFL-DC error signal. We tried this because we suspect that the reason the PO-DC is not a good CARM error signal is because at low powers, the dc light level in the recycling cavity is dominated by the +f2 RF sideband. Thus, REFL-DC should work a bit better at low powers, which it did. It wasn't super stable, though, so this will require a bit of work to make the transition reliable & stable. The next things to work on include setting the AO path gain properly and possibly going to higher arm powers before handing off (thus increasing the discriminant).

Another thing we found is that the alignment scripts are not working in an ideal fashion. Running the alignment scripts for the two arms (XARM & YARM) leaves the Michelson badly misaligned, making it impossible to get good DRM alignment. This will have to be fixed.
531   Thu Jun 12 01:51:23 2008 robUpdateLockingreport
rob, john

We've been working (nights) on getting the IFO locked this week. There's been fairly steady incremental progress each night, and tonight we managed to control CARM(MCL) using PO-DC, with the CARM(AO) path also on PO-DC. In the past, reaching this state has usually meant we're home free, as we could just crank the gain on the common mode servo and merrily reduce the CARM offset. Tonight, however, this state has been very twitchy, and efforts to ramp up the gain have been unsuccessful.

I've attached a diagram which I hope makes clear where we are in the stages of lock acquisition.
Attachment 1: lock_control_sequence.png
ELOG V3.1.3-