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 Cryo Lab eLog, Page 3 of 61 Not logged in
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2975   Thu Aug 18 15:27:09 2022 aaronLab InfrastructureLab Workparticle counts, uncovering experiments.

Great, thanks Chris for resetting the DAQ!

Here's one more trend plot for completion... the y-axis is log(counts), though I can't seem to change the axis label in ndscope.

Attachment 1: 220818_particleCounts.png
2974   Wed Aug 17 17:39:05 2022 ChrisLab InfrastructureLab Workparticle counts, uncovering experiments.

The timeline so far as I’m aware:

• Around 5pm yesterday, the cymac was restarted to restore the DAQ.
• The Rocket Lake machine has been in the rack since last Friday. It’s a short-term loan to us from LDAS for testing purposes. Nothing was happening with it last night around 11pm.
2973   Wed Aug 17 10:43:05 2022 aaronLab InfrastructureLab Workparticle counts, uncovering experiments.

Not sure what happened between yesterday and today, but dataviewer is now reporting particle counts data that vary with time, including trends. The data only start at around 5pm on Tuesday, so don't capture the time when the work was being done.

The particle counter recorded a large spike in dust around 11 pm last night -- not sure what that would be associated with, since the lab was empty. When was the hard drive bay "Rocket Lake" installed into Aux rack? If it was last night, it's plausible the fans would have directed dust towards the particle counter.

The last spike in dust is from my mopping with a pre-wetted cloth this morning. Here were my uncovering steps:

1. Uncover cryo cantilevers experiment, and throw away its cover in the hallways. A large amount of dust had accumulated on top of the plastic.
2. mop the floors
3. wipe down large horizontal surfaces like desks, tops of spectrum analyzers
4. Unwrap the PSOMA table, folding up the plastic from bottom to top so the plastic above the enclosure is covered before being moved
5. Turn on the PSOMA table HEPA FFU, set to high
Attachment 1: Screenshot_from_2022-08-17_10-57-02.png
2972   Tue Aug 16 08:55:24 2022 aaronLab InfrastructureLab Workparticle count debug

So what's going on with this leap second error?

I found some entries from the 40m with suggested steps on fixing the annual 0x4000 error for realtime models. Looking in the referenced file, I see some lines commented out that look like Anchal's reference elog, followed by a call to some ligo function that might (or might not) take care of the leap second offset issue.

# pHardware->gpsOffset += #######;
pHardware->gpsOffset = ligo_get_gps_driver_offset( );

Since I'm unfamiliar with the functions, I'm letting Chris know so I don't break anything.

2971   Tue Aug 16 07:06:10 2022 aaronLab InfrastructureLab Workmoving cryo lab light fixture

This morning, JC and I finished covering the cryo cavs table and cantilever Qs workbench. Moving the light fixture was completed by the afternoon. Photos and video from today are available on the cryo lab google drive.

### Particle counts

I tried grabbing the recent particle count trends... but am getting an error when plotting trends with dataviewer (nds). Opening the same channels in ndscope gives the error

Leap second data is expired.

There are no problems with length of frames as checked by /frames/trend/minute_raw/find_bogus_lengths. The counter is still connected directly to cominaux as earlier this year.

The raw data are plausible but inconsistent with the reading from the particle counter display panel (in particular, the recorded counts for 0.7 um and 0.5 um seem to be swapped). The table below is manually recorded from the particle counter. The counter is updating every other minute, and I confirmed the particle count on the front panel does change with each measurement... so its odd that the data recorded by cominaux is constant in time (attachment 1, data over previous two days. x-axis is in GPS units).

 Time count @ 0.3 um (CF) count @ 0.5 um (CF) count @ 0.7 um (CF) count @ 1.0 um (CF) count @ 2.0 um (CF) count @ 5.0 um (CF) Rel Hum % Temp (F) Note Tue Aug 16 07:14:46 2022 63,790 3,630 690 280 140 70 37 82 start of day Tue Aug 16 08:(20):21 2022 57,300 4,630 1,350 720 490 200 39 80 after covering remaining tables Tue Aug 16 08:43:47 2022 53,210 4,140 1,090 610 320 90 39 81 starting to expose light fixtures Tue Aug 16 09:20:43 2022 43,720 3,090 720 430 250 80 38 81 before drilling Tue Aug 16 09:42:50 2022 51,410 8,740 4,610 3,530 2,130 570 37 81 after drilling with vacuum Tue Aug 16 10:02:34 2022 94,600 30,780 18,590 13,950 9,000 2,770 37 81 after drilling w/o vacuum Tue Aug 16 10:05:33 2022 80,960 17,410 9,580 6,860 3,990 900 37 81 after drilling fourth hole w/ vacuum Tue Aug 16 10:58:40 2022 48,910 2,770 490 170 100 60 37 80 before moving light Tue Aug 16 11:12:33 2022 52,630 6,510 3,400 2,510 1,800 810 38 80 after moving light Tue Aug 16 14:45:47 2022 52,970 3,450 1,160 680 420 170 38 80 end of job

Derek arrived to start working on the lights around 8:20 am. After removing the light bulbs and covers down to the fixture, he measured the location of the new holes and started drilling around 9:20 am. He drilled two holes where the North end of the fixture attaches to the ceiling beam, using a vacuum attachment that collects most dust during the drilling and then vacuumed the area with a shop vac. In the center of the fixture, the enclosure prevented the vacuum-endowed drill from being used, so he put a drop cloth directly under the drilling area to catch falling debris while drilling a single hole. He drilled one more hole (using the vacuum attachment) for the far South end of the fixture.

Tue Aug 16 10:12:42 2022  We're taking a 30 min break for another facilities worker to join Derek to move the fixture itself.

Tue Aug 16 10:59:09 2022  Back in the lab, setting up to move the fixture itself.

Tue Aug 16 11:15:47 2022 Fixture moved, mandatory lunch break and will finish installing the light bulbs in the early afternoon.

Tue Aug 16 14:45:26 2022 Job completed.

Attachment 1: Screenshot_from_2022-08-16_07-24-11.png
2970   Mon Aug 15 15:05:25 2022 aaronLab InfrastructureLab Workmoving cryo lab light fixture

[aaron, jc, derek]

Derek from facilities came to help JC and me cover our tables and optics cabinets in preparation for moving the cryo lab light fixture tomorrow morning (7 am). We used plastic wrap to cover:

• PSOMA table
• cryo cavs table
• silicon cabinet (NW corner of the lab)
• optics cabinet (S wall of the lab, next to the sink)

Tomorrow morning we will finish wrapping

• cantilever Qs experiment
• roof of the cryo cavs table

Photos of the wrapped equipment attached.

PS: Chub also came by and re-mounted our laser safety goggles. Thanks Chub!

Attachment 1: 20779F72-32CC-4F1B-8E31-1D984D27204E.jpeg
Attachment 2: 16F84836-C7EB-4003-B83C-E16A01170B2F.jpeg
Attachment 3: BEB56AB5-AE9D-453A-B61F-398BB3687F93.jpeg
Attachment 4: 8413A03F-A842-4D34-B7B3-B37621E6F584.jpeg
Attachment 5: B61E0E56-7F04-4513-81C5-517C6A707C9D.jpeg
2969   Thu Aug 11 16:44:10 2022 OjoSummary Q Factor Code

As suggested by Rana I added 2 extra parameters to the fit for the ringdowns and created a data sample to test it. The d parameter which dictates the vertical shift has to be really small or the fit goes extremely off and doesn't work. With the data sample used the sum of square error is about 0.6 where closer to 0 indicates the better fit. Later I'll see how it works with real data but Matlab has been running real slow.

Attachment 1: ojqs2.png
2968   Thu Aug 11 12:54:42 2022 rana, aaronDailyProgressPSOMAcavity locking again after RF scrubbing

[rana, aaron]

To debug the cavity locking we looked at the RF chain (RFPD to demod) and made several changes. Cavity is now locking again!

1. Inserted PBC cube upstream of the focusing lens for the RFPD (old model New Focus 1811).
2. There was already a 1/2 wave plate installed upstream of the cube's mount, so this allows us to continuously adjust the power.
3. We confirmed that this 1811 is the old model with Zrf = 40 kOhms, and Zdc = 1 kOhm. We labeled this 1811 as such.
4. The 1811 was saturating on both the DC and RF ports (see attached movie).
5. Aaron lowered the modulation depth by 10x. From 500 mVpp to 50 mVpp. Check to make sure the Moku has a 50 Ohm output and that the EOM has a 50 Ohm input.
6. Rotated the waveplate to turn the DC level down to 500 mV. Previously @ 2 Vdc.
7. So the RF signal is now ~40x smaller, and the RF output (directly into a 100 MHz scope (should use a faster scope for looking at 33 MHz RF, because...harmonics)), is now, ~1 Vrms into 50 Ohms.
8. The ixBLue phase modulator has a mod coeff of 3.5 V / pi radians, or ~ 1 V/rad. A modulation depth of ~0.1 is reasonable, so now we're in a good place.
9. We also replaced the flaky BNC cable with a new SMA LMR cable to go directly from the PD output to the Moku input.
10. Aaron replaced (and labelled) the other permanent or semi-permanent cables in the PDH loop with new SMA LMR cables -- no more lossy pink SMA cables!
11. The REFL DC signal is up to 350 mV with the cavity unlocked, and 296 mV with the cavity blocked. The cavity flashes have ~50% dips in REFL DC

To do:

• verify Moku PLL and PDH functions with fast scope and 785 SA -- are there glitches at high frequency? how's the noise of the PLL? How do Moku's input stage attenuators work?
• There are four modes for operating the Moku laser lock box, all of which have tradeoffs. Personally, I think option (5) below has the right balance of Moku convenience and analog reliability.
1. Use the Moku's internal oscillator to demodulate REFL. This is nice because we can easily change the demod phase, but if we want to use the same LO and RF modulation we must send Moku's aux oscillator (which is "phase-locked to LO", though I don't know what the PLL parameters or performance are) to one of the Moku's outputs. This also means we can't use the slow path of the Moku laser lock box as a temperature controller, and instead need to use a separate PID instrument in multi-instrument mode.
2. Demodulate with an external signal. Requires setting the demod phase with cables outside of the Moku, and uses one additional Moku input to deliver the LO. Has the benefit of using a (presumably) cleaner LO and mod sine wave, no PLL, and lets us use the slow controller path of Moku's laser lock module freeing up one instrument slot in multi-instrument mode. Personally, I like that tradeoff.
3. Demodulate with a sine wave generated by Moku and phase locked to an external modulation by PLL. Relative to case (2), this is nice because we can digitally change the demod phase. The downside is our LO has extra noise from the PLL.
4. No demodulation. In this case, we would use an analog mixer before the Moku. The benefit is we are only sending IF to the Moku's BNC inputs, but it's a bit awkward because there's no way to shunt Moku's lowpass filter in the laser lock module.
5. Forget the laser lock box module, and instead use an analog mixer and lowpass filter then send the IF to Moku's PID controller. This is the closest analogue to how we were using the LB servo. But, since the PID controller module has a 2x2 control matrix, each output of which is sent to two cascaded PID filters, we could handle both fast and slow control with a single PID controller. We could use two such PID controller modules to control both laser frequencies, and still have two inputs and two instrument slots available for spectrum analyzer, phasemeter, function generator (for sweeping), etc.
• I also note that the sampling rate of Moku's lowpass filter in the laser lock box instrument is only 78.125 MHz, compared to our 33.59 MHz modulation... hm, what's happening at the 2f harmonic?
• more sticky mats (JC)
• order RF couplers
• hang SMA cables
•
2967   Fri Aug 5 15:12:34 2022 OjoSummaryGeneralQ Factor Calcalculation

Altered the Q Factor code by starting the 0 point at the beginning of the sine wave. First it calculates the period using peak finder and gets the mean difference between the peaks in the sample, once the frequency is calculated this can be used for the fit approximation. The Q factor is around 2000 in these data samples. The code needs some improvement since the start point can be wrong for a bad data sample. When the oscilloscope and QPD is first turned on the oscillation data was distorted but after a while went back to normal. The vacuum chamber has gone down to 10^-3 torr though not sure why.

Attachment 1: ojqs1.png
2966   Tue Aug 2 16:32:51 2022 Ojo Summary

Adjusted the optical lever with Chris so that the laser was centered on the QPD. The oscillations are now double sided so the data collection is improved. It may be easier to do alignment with the lights off. The Q Calculation needs some work to ensure accuracy.

2965   Fri Jul 29 16:57:42 2022 OjoSummaryGeneralQ factor collection of cantilever in vacuum chamber

Took 10 sets of data for the cantilever ringdowns. The updated code to calculate the Q fits the data to an exponentially decaying sine wave which makes it much more accurate.

Q Factors calculated: 424, 5800, 894, 912, 6000, 2200, 2600, 10000, 1900, 2082. The current method still needs more improvement to be accurate. The force with which you drive the cantilever to oscillate affects the ringdown so its hard to calculate a consistent Q when the data is inconsistent. You also have to manually adjust the bounds because the ringdown start time changes with each set, so automating that step out would improve the code as well. The next steps are refining the ringdown technique or exploring other options and estimating the Q limits from thermoelastic and gas damping losses.

Attachment 1: Screenshot_from_2022-07-29_17-24-32.png
2964   Wed Jul 27 16:13:27 2022 Ojo SummaryGeneralVacuum Chamber Setup

Me and Aaron attached the tubes and vacuum pump and activated it. There could be a leak limiting the vacuum suction to look at later. It's essential to let the turbine completely stop before the pressure is changed. The ndscope shows the pressure data in the figure below.

Attachment 1: x1pr.png
2963   Tue Jul 26 17:34:26 2022 aaronDailyProgressLab Workcharacterizing pdh loop - beat setup

[aaron, shruti]

We adjusted the PDH servo controller but couldn't get a stable lock with the boost in place. After removing the boost filter, we got a more or less stable lock but couldn't turn on the temperature loop. We continued to be puzzled by why our servo must have such a high gain after our cavity finesse increased...

Eventually we noticed two things:

• the polarization had again drifted. We adjusted the input HWP to send S polarization to the cavity
• 12 mVpp would imply 0.005 rad phase deviations according to the spec sheet of our EOM. We want more like 0.3 rad phase deviations (not sure we've understood phase modulation amplitude to modulation depth correctly, we should measure the resulting sideband amplitudes on a spectrum analyzer). Anyway, we increased the modulation amplitude to 500 mVpp (still well within the acceptable range for our EOM) and the PDH error signal looks much cleaner (100s mV range compared to 10s mV range)

[aaron]

later, I added back the boost filter since in principle increasing we'd just increased our PDH responsivity.

I noticed that changing the PDH LO phase also changes the DC level of the PDH error signal (even with the beam blocked inside the cavity). This offset could be due to the EOM applying some amplitude modulation at the RF frequency. If so, the offset would be minimized when the LO is exactly out of phase with the signal at the mixer. Indeed, when I adjust the LO phase to minimize the offset, then unblock the cavity, I do not get a clean PDH signal; rotating the LO phase 90 degrees recovers a clean PDH signal but also introduces a 25 mV or more offset.

I adjusted the 'setpoint' after the lowpass filter to null the DC offset.

The offset level drifts by O(mV) on 100 s timescales. Note that before increasing the modulation dept, the offset was only up to about 5 mV.

Attachments help explain the discussion of offsets above.

1.
2962   Tue Jul 26 17:26:08 2022 OjoSummaryGeneralQ Data

Switched out the oscilloscope and made the optical lever more stable. Using the ethernet port directly from the oscilloscope to get data instead of from the nds board.

2961   Mon Jul 25 14:19:23 2022 aaronDailyProgressLab Workcharacterizing pdh loop - beat setup

I found some suitable settings for the Moku lock box, but the loop is only marginally stable and needs some tuning. Will try to measure a transfer function to point in the right direction.

2960   Thu Jul 21 17:16:58 2022 OjoSummaryGeneralCryo Chamber set up

Discussed with Aaron using a Spectrum Analyzer to see the noise the nds2 board is picking up but the signal wasn't strong enough. Will use the oscilloscope directly to get the ringdowns. Ordering an adapter for the cryostat to do the pump down.

2959   Thu Jul 21 12:11:53 2022 aaronDailyProgressLab Workcharacterizing pdh loop

The reason the analog boost wasn't working most recently is... the solder broke. I'm remaking our Pomona filter and closing the lid this time so I can get the appropriate pole-zero pair on Moku without translating foton-to-moku data structures.

I removed the old R1/R2/C1 from the Pomona box, stuffed it with new resistors and caps with the same values, and relabeled and closed the lid. Then, I measured the attached transfer function (50 Ohm moku output to 1 MOhm moku input across the Pomona boost filter). I see qualitative agreement with the analytic model from Shruti above, and since we didn't fine tune filter parameters it's good enough (vertical reference lines in the figures attached are at the same frequencies as above, I haven't fitted the data to a pole-zero model).

The data for attachment 1 will be in git lfs at cryo_lab/data/TFs/*20220721*PomonaBoost*

Attachment 1: E4A5BF46-EF67-42F1-B729-BFBE515B3B60.png
2958   Wed Jul 20 16:11:55 2022 aaronDailyProgressLab Workcharacterizing pdh loop - beat setup

I removed the PBS between MC1 and REFL PD to avoid the unnecessary output polarization tuning.

I also tried adding a PBS between the first and second input steering mirrors to reject P polarization up (towards the ceiling). However, I couldn't get the cavity flashing again, so removed the input PBS and went back to improving lock acquisition.

After adjusting the focusing lens into REFL PD (1.8 mW out of 2.5 mW reported by REFL DC mon), I could obtain stable locks with the LB servo. I then switched over to locking with the Moku laser lock application, since we want to implement digital filtering (and zero PDH offsets).

I managed to get a stable lock with the Moku laser lock box after much messing with filters, but to add a resonant pole-zero boost requires uploading custom filter coefficients to the filter module. I'll try that tomorrow.

2957   Fri Jul 15 17:37:04 2022 ranaNotesControl Systemhelp! I'm worried about stability in the Lyapunov sense

I sense that there are issues with loop stability in these designs. Generally, Bode plots are not trusted was of determining loop stability. I usually use things like impulse response and step response to characterize stability. Its also possible to use Nyquist plots.

Take a look in Astrom and Murray. Also, I've left a new controls textbook on your desk the coffee table - I haven't read it yet, but its supposed to be useful.

2956   Fri Jul 15 14:13:20 2022 aaronNotesControl Systemcontrols model status update

I'm modeling the PSOMA control system for the configuration with a Mach-Zehnder to cancel pump noise, but only one cavity (so the MZ is unbalanced). Here's an update on the current state of the model, and some plots. I'm adjusting some parts of the model (especially sensor response calibration and control filter design) to match reality, and will highlight some features that still don't make sense to me.

## Description of loops and model

1. Lock pump frequency to cavity frequency by sensing PDH signal at symmetric output port RF PD
2. Lock signal frequency to pump frequency by sensing beat note between pump sideband and DC signal
3. Lock Mach Zehnder length to a dark fringe by introducing a macroscopic offset to the MZ arm length and measuring the sideband at the antisymmetric output port
4. Lock the homodyne angle by zeroing the BHD difference channel
5. lock the pump and signal relative phase by feeding back the BHD sum channel?

A while ago, I made a qlance-Finesse version of our PSOMA 'theoretical' model. I've built a control system around this model using the qlance controls toolkit. The relevant files on the PSOMA repo are:

• optomechanical + controls model: PSOMA/experiment/csPSOMA.py
• parameters file: PSOMA/experiment/parcsPSOMA.py
• plotting notebook: PSOMA/experiment/Controls.ipynb

## Results

I'll let most of the plots live in the notebook, but will highlight a few in attachments. Much credit to Kevin Kuns for creating an extremely user friendly 'quantum optomechanics loop and noise calculation' engine. The code to generate these plots is almost directly copied from his FPMI control system example, which I just updated with my own topology and labels.

1. Control filters
2. Open loop transfer functions
3. Closed loop transfer functions
4. Cross coupling between signal frequency and the other degrees of freedom
5. calibration of the pump frequency control loop (transfer function from pump frequency to the error point)
6. Sensing noises referred to the signal frequency
7. Residual pump and signal laser frequency noise (due to sensing noises)
8. Overview of the controls system

(the attachments are examples of the plots when I hadn't implemented loop (5) to lock the pump and signal relative phase, but the updated figures are available in Control.ipynb on github)

## Questions and complaints

• The loop controlling the pump frequency (1) has a pole in the OLTF at the mechanical frequency of the light suspended optic. I guess this is an optical spring effect... but I was a bit surprised because we haven't measured the resulting 1/f^4 OLTF (for a pure I controller) in the lab. Is the pole more prominent due to some effect of the Mach Zehnder? For now, I've placed the PI corner of the pump frequency servo controller at 40 Hz to compensate the mechanical resonance.
• I haven't taken particular care to calibrate or shape the signal frequency, MZ length, or homodyne angle loops
• The colors and line types of the plots aren't carefully chosen. Also, should add units to some of the transfer function plots (like the calibrations, which have nontrivial dimension)
• Need to implement loop (5) to stabilize pump and signal relative phase. I'm looking into what's been done for the waveguide squeezer or our other labs with this problem.
• The mirrors have no actuation transfer function (it's the identity by default, so uniformly 1 m / V response to the control signal)
• All degrees of freedom are controlled by only one sensor, but one could imagine a combination of sensors providing more optical control
• The pump-signal relative phase (5) is controlled by feeding back to a steering mirror, but in the lab we would probably instead feed back to EOM or the DC offset of the pump-signal PLL
Attachment 1: control_filters.pdf
Attachment 2: OLTF.pdf
Attachment 3: CLTF.pdf
Attachment 4: couplings_fsig.pdf
Attachment 5: cal_fpump.pdf
Attachment 6: noise_fsig.pdf
Attachment 7: residual_frequency.pdf
Attachment 8: conceptual_configs_RingMZ.pdf
2955   Wed Jul 13 17:55:06 2022 aaronSummaryGeneralOptical Lever and QPD

Nice. You also re-mounted most of the optics using proper screws-and-washers technique. Note that the shadow laser was a back reflection from one of the vacuum chamber's windows, and adding the extra mirror let us move the QPD farther from the chamber so the ghost beams could be separated from the main beam.

Could you please post your measurement data and fit each time? It's useful to see what's going on in detail.

We noticed that the laser power is at least 10x less in this new setup (mostly due to using a less powerful laser), which means the electronics noise floor is a bit higher relative to the maximum excitable cantilever amplitude. Also noted that it is possible to saturate the optical lever, that is excite the cantilever enough that the beam moves completely to one side of the other of the QPD. We need to make sure to fit the ringdown only for data that are neither saturating the optical lever nor dominated by electronics noise. We could increase the laser power and add lenses to the optical lever to improve our sensitivity and dynamic range.

 Quote: Added an extra mirror to eliminate the shadow laser that was reflected onto the QPD. Cantilever broke (Put cantilever on clamp before it goes in the vaccuum chamber); trying to pick it up if it falls is difficult and causes it to break. The Q factor of the first cantilever was around 600. The 2nd is about 500.

2954   Wed Jul 13 17:00:19 2022 Ojo AkinwaleSummaryGeneralOptical Lever and QPD

Added an extra mirror to eliminate the shadow laser that was reflected onto the QPD. Cantilever broke (Put cantilever on clamp before it goes in the vaccuum chamber); trying to pick it up if it falls is difficult and causes it to break. The Q factor of the first cantilever was around 600. The 2nd is about 500.

2953   Wed Jul 13 10:23:14 2022 aaronSummaryGeneralOptical Lever Setup

I found one port of the vacuum chamber opened without foil covering. Reminder to always close all vacuum ports when not actively working on the chamber. If left open, dust will settle and spoil your vacuum, optics, and Qs. You'll waste a week or more cleaning everything off.

I covered the port with HV aluminum foil.

2952   Wed Jul 13 10:21:48 2022 aaronDailyProgressLab Workcharacterizing pdh loop - beat setup

Since I haven't been with Shruti in the lab, I'm doing a sanity check for myself that might repeat some of Shruti's checks.

• The power out of the S EOM is 5 mW, but after the 90-10 BS only 2.5 mW. This is much more excess loss than we would expect from this beamsplitter, so we should clean the fiber tips and look for our missing power.
• According to the 1611 1811 manual, the DC bias monitor gain is 10 V/mA (which for 1550nm light implies 10 V/mW). Despite ~2.4 mW reflected from the cavity, I was only seeing ~215 mV on the DC bias monitor (implying 21.5 uW incident power). That could be our factor of 100!
• I removed the reflective ND=0.6 filter from the lens in front of REFL PD, and immediately saw 58 uW on the REFL PD.
• I also adjusted the ND filter between MC1 and REFL PD to maximize REFL DC signal. I now see 150 uW on REFL PD.
• The REFL DC monitor has dips up to 30% of its maximum level (from 1.5 V to 1.0 V)
• At this point, I'm able to locked easily and stably (10s of s can touch the table) to a higher order (vertical) mode
• I'm still a bit suspicious about the polarization into the cavity. I know Shruti recently changed the input polarization to recover resonant flashing after making some changes to the fiber path, but since the launching fiber is polarization maintaining it's surprising to me that up stream modifications would change the free space polarization substantially.
• I placed a PBS in between the first two steering mirrors, and indeed find that most of light is transmitted (P polarized) with only about 119 uW reflected (S polarized).
• I adjust the half waveplate from 201 degrees to 250 degrees, where the reflected power is maximized (2.31 mW reflected)
• I then remove the PBS from the beam path... I still see resonances but they are much narrower. See attachments 1 (P laser) and 2 (S laser). Whereas before the cavity was essentially always moving through a broad resonance (such that even sweeping the laser current at 1 kHz, it was challenging to observe a PDH error signal), now the cavity is occassionally moving through a narrow resonance.
• Because the cavity is so much easier to lock in the low-finesse state with P-polarized light, I'm cleaning up the mode matching a bit with the input waveplate set to 201 degrees; I adjusted the output waveplate to maximize the DC power on REFL. I adjusted the input alignment until I reliably lock on the 00 mode, and maximize the TRANS mon signal relative to REFL mon signal.
• Even after improving mode matching, the power incident on the TRANS PD is less than 1 uW when locked
• After switching back to S polarization (rotated both HWP by 45 degrees), I can still see flashing but can't get the cavity locked...

Note that the Pomona box filter was not connected during all of the above; I tried adding the Pomona boost to help lock with S polarization, but still wasn't able to do so.

[after lunch]

• I measured the transmissivity of MC1 using both S and P polarization.
• S polarized: 1300 ppm (based on 2.5 mW incident on MC1, 3.2 uW is transmitted after subtracting ~85 nW visible with the beam blocked)
• P polarized: 22% (based on 2.5 mW incident on MC1, 550 uW is transmitted)
• This transmissivity is higher than I expected, and indeed even the S polarization transmission is higher than I thought we had measured... but I'll take it.
• I tuned the laser to S polarization by monitoring the power transmission through MC1 and rotating the input HWP until the transmitted power is minimized; is this cleaner than using a PBS?
• Then, I spent some time tuning the temperature to find flashes and adjusting the gain... not much luck here.
• Finally, with the lock 'on' and gain knob at 8.55, I fiddled the LB servo's input offset until, lo, the laser locks to a bright 00 mode. The lock is stable for minutes, and I can tap the table without losing lock (google drive link).

To summarize, I improved the lock stability by the following key steps:

1. Increased incident power on the REFL PD by removing an unnecessary (until we inject high power TeraXion laser) ND filter
2. Increased incident power on the REFL PD by rotating output HWP to maximize laser power reaching the REFL PD
3. Increased cavity finesse by rotating the laser to S polarization, specifically by minimizing the transmission through MC1
4. Adjusted the PDH servo's input offset so the loop is stabilized to the true resonant condition

I tweaked the mode matching a bit with the cavity locked (S polarization). Here are some parameters of the new system:

• Mode matching efficiency about 7% (REFL mon is 1.28 V unlocked, 1.2 V locked)
• TRANS PD sees 0.35 uW when locked (compared to 18 uW in front of the transmission camera, implying the pickoff BS is something like 98-2 or 99-1)
• Wed Jul 13 16:46:01 2022 adjusted input offset until mean PDH error signal under +- 100 uV
• Wed Jul 13 17:18:34 2022 offset is now over 2 mV
• Wed Jul 13 17:37:20 2022 offset now -4 mV
• tweaked the mode matching for a couple hours by adjusting the input steering mirrors to increase TRANS_MON/REFL_MON, then adjusting the output steering mirror to center the beam on REFL PD. Still only about 12% efficiency (based on min(REFL)/max(REFL) when tapping the table to move the cantilever with the loop off)
• looks like the polarization might also be drifting? The transmission through MC1 can be reduced by adjusting the input polarization, despite already minimizing this transmission earlier in the day.

Attachment 1: P_pol.jpg
Attachment 2: S_pol.jpg
2951   Tue Jul 12 11:00:00 2022 ranaSummaryGeneralQ Factor Code

From the waveform, it looks like the mode is ringing down at first, but then rings up. Why is that?

 Quote: The Q code has 2 Q values. First the oscillation data finds the maximum amplitude then cuts the data to a few seconds after that. The first q calculation part uses Matlab's built in exponential fit to calculate the time constant. The 2nd finds the x value of the time data where the amplitude is the max amplitude/e which gives you the time constant manually. The 2 Q values are relatively close. The python script should get the data from the ports run the matlab code to calculate the Q then add the Q value and time stamp to a file.

2950   Tue Jul 12 10:46:42 2022 aaronSummaryGeneralQ Factor Code

Cool, thanks for the code and plot! If I understand correctly (for my own sanity check), the code does the following

1. Use a Hilbert transform to estimate the instantaneous amplitude of the dominant sine wave during the measurement window (that's the envelope you've plotted).
2. Fit the function $a e^{bx}$ to the envelope, and extract the time constant of the exponential decay as $\tau = 1/b$
3. Compute a Q estimate using your fitted time constant by assuming the mode frequency is 120 Hz
4. Assuming the maximum observed signal on the QPD is the initial mode amplitude, divide by 'e' to get the mode amplitude after one decay time elapses. Then, shift the data series down by the desired mode amplitude and find the times where the shifted data are close to zero (within some tolerance). Finally, compute the Q by multiplying the resulting decay times by your mode frequency.
• You sort of lucked out here, I don't think this procedure will always work. I tried to reproduce it with some generated data, and ended up with no candidate decay times. It would usually work for high Q samples, but depends on you observing the top of some oscillation just as the mode amplitude reaches 1/e of the initial amplitude. I think the fitting method is the way to go.

For the next iteration, here are some suggestions

• It looks like the ringdown doesn't really start until about t=0.5s. For a single exponential decay, the slode of the amplitude envelope is typically steepest at the beginning of the decay, but the log(amplitude) slope is constant. Likewise, as Rana suggests it's suprising that the mode amplitude appears to ring up again after 2.5s. You should restrict your fit to just the data undergoing a clean exponential decay. And, come up with some reasoning as to why the ringdown doesn't start at t=0s or rings up after apparently decaying to the level of background.
• Instead of the generic matlab fitting functions, fit the product of an exponential decay and a sine wave. This will let you jointly estimate the mode frequency and Q.
• Plot your fitted exponential decay curve to give a visual check that the fit is reasonable. Better yet, plot the best fit curve and a shaded region representing the uncertainty on your fit.
• You might also plot the exponential decay you expect to observe if the Q is limited by gas damping (for the in-air measurement) or thermoelastic loss (for the in-vacuum measurement).
• Add this code to the Qryo git repo so you can version control your progress (and easily share the code with collaborators)
• Export the plot to a pdf so you have a nicely formatted reference version that's convenient to add to your report or elog later
• Please also use git-lfs to share your raw data on the github. Git-lfs lets you store large data files on github without wasting space by version controlling a bunch of binaries. This lets others run your code and reproduce your plots.
• git lfs track filename.dat
git commit -m "adding data files to git lfs"
git push

2948   Mon Jul 11 16:53:04 2022 OjoSummaryGeneralQ Factor Code

The Q code has 2 Q values. First the oscillation data finds the maximum amplitude then cuts the data to a few seconds after that. The first q calculation part uses Matlab's built in exponential fit to calculate the time constant. The 2nd finds the x value of the time data where the amplitude is the max amplitude/e which gives you the time constant manually. The 2 Q values are relatively close. The python script should get the data from the ports run the matlab code to calculate the Q then add the Q value and time stamp to a file.

Attachment 1: ojqss.png
2947   Mon Jul 11 16:03:01 2022 PeterUpdateOpticsMode Matching Update
Attachment 1: ModeMatchingPaper_RoughDraft2.pdf
2946   Mon Jul 11 12:09:51 2022 shrutiDailyProgressLab Workcharacterizing pdh loop - beat setup

- Updated the Moku firmware. Have not tried using the phasetracker yet, but the settings in the phasetracker app say the bandwidth is now 1 MHz for the digital PLL and max acquisition rate is 152 kHz.

- I saw that the beat between the two lasers was actually not set up currently. I also set it up differently from before, with the EOM before the beat BS on the south laser path so the RF mod depth can be measured. I made the followinig changes:

• South laser-> FI -> EOM -> 90-10 BS -> (10% sent to 50-50 beat BS, 90% sent to the free space coupler/cavity).
• North laser-> FI -> 50-50 beat BS -> (50-50 mixed signal (with South laser)) 90-10 BS -> 10% output sent to Newfocus 1611 fiber coupled

DC level at 1611: -240 mV

Beat (from AC out): -45 dBm peak on spectum analyzer, rougly the 33 MHz sidebands on this spectrum appear with levels ~ -56 dBm. Roughly translates to modulation depth amplitude of 0.3. I will measure this again with the delay line / phase meter.

- I had to change the polarization angle with the first half-wave plate in order to once again see resonances after making the above changes in the fiber setup. Power at the free space coupler is now a little less than 3 mW.

2945   Fri Jul 8 15:50:53 2022 OjoSummaryGeneralOptical Lever Setup

Changed the clamp of the cantilever since the laser was pointing to high to reach the QPD. Hooked up the oscilloscope to do the ring-down measurements but could not get a signal from the QPD.

2944   Thu Jul 7 17:35:05 2022 OjoSummaryGeneralCantilevber Optical lever setup

I added a mirror to better aim the laser at the cantilever and attempted to get the right angles to get the maximum signal on the QPD. I didn't hook up the oscilloscope this time but it looks like the laser was able to reach the photodiode.

Attachment 1: ojs1.jpg
2943   Thu Jul 7 12:21:23 2022 shrutiDailyProgressLab Workcharacterizing pdh loop

(Updated 11 -Jul-22)

1. (Coming soon: setting up beat measurement)

2. (I have not yet been able to get a stable lock for long enough to measure this).  But in the free state 88 microW on the power meter corresponded to 98 mV DC at the 1811 output, but we would expect ~800 mV. I tried moving around the alignment quite a bit but could not make it higher. Earlier we actually had > 300 microW incident on the diode to show ~ 300 mW we were seeing -- I decreased the level because this is over the 100 microW of max prescribed power.

3. While unlocked, the dips seem 40% lower than the maximum. Comparing to the locked it is difficult to estimate mode-matching percentage because there seems to be a DC shift in the current/power provided by the LB1005.

4. AC-coupled 1811: 40V /mA AC, 10 V/mA DC

 Quote: How to increase gain for this loop? What we want is an overall gain increase wihtout any shaping. What is the RF modulation depth? it should be ~0.2-0.4 radians. This should be measured, not inferred from the data sheets. What is the power level on the reflected PD, when the cavity is locked? What is the mode matching fraction? What is the AC transimpedance of the RFPD? We are missing a factor of ~100x in the gain here, so most likely there is something broken. The RF phase most likely can give us a factor of a few if we're way off. It would be good to see the modeled servo loop Bode plot on this plot (modeled using knowledge of all the pieces, rather than a fit).

2942   Thu Jul 7 11:32:25 2022 PeterNotesLab WorkMeasuring cavity parameters

I just spent about an hour taking measurements of all the distances of the optical components in the PSOMA cavity. ie, the distance from the laser to lens1, distance from lens1 to SM1, SM1t to WP, and so on. I was just using a ruler.  Overall, I got some fairly accurate measurements. Kind of hard to measure with the setup since I didn't want to actually get close and touch anything, and I succeeded since nothing was touched. This data will be useful for me in creating a working model of the cavity in FINESSE.

Shruti and I then decided to try and measure the beam profile. However, the computer died on us before we could get it working. Even before then, we were experiencing some problems in actually collecting that data. The computer was reading the beam, but it wasn't giving us any output. We'll try again after lunch most likely.

Until then I'm going to get this code of the cavity parameters working. Now that I have the distances, I can create a model of the mode matching tolerances of this cavity with hopefully some accurate data.

2941   Wed Jul 6 17:23:08 2022 Ojo AkinwaleSummaryGeneralOptical Lever and vacuum chamber setup

Me and Aaron put the vacuum chamber and helium laser on a breadboard to prepare the optical setup for the cantilever measurements. The cantilever will have the clamp's base replaced for stability. The plan is for a mirror to reflect the laser onto the cantilever and then to the quadrant photodiode.

2940   Thu Jun 30 19:33:16 2022 ranaDailyProgressLab Workcharacterizing pdh loop

How to increase gain for this loop? What we want is an overall gain increase wihtout any shaping.

1. What is the RF modulation depth? it should be ~0.2-0.4 radians. This should be measured, not inferred from the data sheets.
2. What is the power level on the reflected PD, when the cavity is locked?
3. What is the mode matching fraction?
4. What is the AC transimpedance of the RFPD?

We are missing a factor of ~100x in the gain here, so most likely there is something broken. The RF phase most likely can give us a factor of a few if we're way off.

It would be good to see the modeled servo loop Bode plot on this plot (modeled using knowledge of all the pieces, rather than a fit).

2939   Thu Jun 30 10:35:55 2022 shrutiDailyProgressLab Workcharacterizing pdh loop

[aaron, shruti]

• Estimating that the cavity pole is around 100 kHz, I played with the PI corner and locked the cavity with the corner at 100 kHz in hope that that would increase our UGF. The transmitted beam always looked very dim on the monitor in this configuration so we switched back to a pure integrator
• We're also adjusting the cable lengths to optimize the PDH signal
• Added a lambda/2 filter to make the beam into the cavity s-polarized. Added the lambda/2 followed by a PBS, rotated the polarization to maximize the power of reflected light, then removed the PBS.
2938   Tue Jun 28 14:38:23 2022 shrutiDailyProgressLab Workcharacterizing pdh loop

I tried measuring some open loop transfer functions while keeping the cavity locked without slow control.

## Attachment 1

The red line is the measured open loop TF dividing the PDH/LB error mon after injecting a small signal at the -B port of the LB1005 controller. There seems to be a kink in the measured curve at ~ 1 kHz so we would have to repeat this measurement.

The gain being used is nearly at the limit of what the LB1005 can provide but the UGF is only a few kHz. Adding the pomona filter with design in Attachment 2 required us to increase the servo gain by ~18 dB to recover the UGF we had earlier. But seems like we could only increase it by ~ 6 dB with the knob.

How can we increase the gain further?

While chatting with Aaron, we realized since new cables were added, the PDH demod phase might not be optimized and could be the cause of the lower open loop gain.

### Attachment 2: the updated pomona filter for 1 kOhm output impedance

• The blue curves in Attachment 2 shows Vout/Vin for the circuit in Attachment 3
• The vertical dashed lines in the the magnitude (of Attachment 2) are the zero and pole one would expect for high impedance output as calculated by pole=1 / (2*pi*R1*C1) and zero=1/(2*pi*R2*C1)
Attachment 1: LoopTFs_wpomona_knob9_20220628.pdf
Attachment 2: 20220628_FilterTF.pdf
Attachment 3: IMG_F1C22B0747F7-1.jpeg
2937   Mon Jun 27 18:25:29 2022 ranaNoise HuntingNoise Budgetimproving cavity mode matching
1. In the DTT, you can edit the "Legend" field so that the traces have useful names that describe the measurement.
2. I believe you should also be able to print the plot as PDF (which is what we want for all ELOG graphics)
3. It seems like the error signal you're measuring is limited by some ADC noise or other electronics readout noise, and is not the true error signal. I recommend using an SR 560, AC coupled, low-noise, G = 100, 10 kHz LP, to Tee off the error signal readout and go into another DAQ channel. Then you get the full error signal in the DC coupled path, and then the high gain one when you're in lock. With a less noisy error signal we may be able to see differences in the error signal for Boost / No Boost.
Draft   Mon Jun 27 17:53:24 2022 Ojo GeneralMeasuring Q factor of silicon cantilevers

Used exponential fits in matlab to measure the quality factor of the cantilever from the optical lever setup of last week. The Q factor was around 800. Will look at contributing losses from the clamp and gas damping in the future and look at optically contacting silicon to reduce losses.

2935   Mon Jun 27 15:44:53 2022 aaronDailyProgressLab Workimproving cavity mode matching

[shruti, aaron, ojo, peter]

• We found the schematic of the LIGO current driver and saw that the input impedance for the current modulation path is 1 kOhm.
• WIth the cavity locked, the power meter was measuring only 10s of nW where our CCD camera should monitor the transmitted light. The TRANS PD would have predicted several uW instead. We adjusted the transmission pickoff BS so its reflection was sending the full beam towards the camera, and moved the camera around until we could see the transmitted beam. Peter scanned the temperature while sweeping the current modulation at 1 Hz, eventually locking to a bright 00 mode.
• We monitored the ratio of transmitted to reflected light while adjusting the input alignment to improve the modematching
• Shruti modified the Pomona box to be impedance matched to the custom driver, and moved the pole to ~50 Hz and the zero to ~400 Hz. We measured the transfer function of the Pomona box.
• We used nds to measure the power spectrum of the PDH control and error signals, as well as the RMS power. In attachment 2, the reference traces are with no Pomona box boost and the measurement traces are with the boost. We noticed a few peaks below 100 Hz in the "non-boosted" PDH error signal were absent in the error signal with boost.

Attachment 2 is the transfer function of the updated Pomona box and was measured with 1 kOhm in parallel with the output (assuming the current driver has a 1 kOhm input impedance which was what it seemed from the dcc data sheet)

Attachment 1: 220627_boosted.png
Attachment 2: MokuFrequencyResponseAnalyzerData_20220627_174435_Screenshot.png
2934   Fri Jun 24 14:13:57 2022 PeterDailyProgressPSOMA

[peter, aaron]

• Peter showed aaron the behavior of PDH error signal on the moku, and we decided to try locking with the LB servo box instead since it was stable before
• Aaron set up pdh lock using LB1005 servo.
• Aaron spent about 5-10 mins adjusting input offset. Set it to 5.01V.
• Peter and Aaron tried unlocking and relocking several times with different gains.
• Tried connecting Shruti's filter to A+ port. Found that it hindered us from acquiring lock. When we disconnected it we were able to acquire lock.
• Once locked, we found that the transmitted light had small oscillations. Aaron suspects it has to do with cantilever oscillating. When the PDH error signal offset is not quite correct, the servo will hold the laser frequency slightly off resonance. Off of resonance, residual frequency fluctuations (such as the ~40 Hz oscillation at the cantilever resonance) appear to first order in the transmitted signal. We adjusted the LB box input offset to minimize the size of the 40 Hz transmission fluctuations.
• Peter spent a bit more time trying to acquire temperature lock, yet unsuccessful. Also spent time adjusting gain and input offset. Was able to maintain lock at higher gain and slightly differeing offsets.
2933   Wed Jun 22 15:47:29 2022 JCElectronicsGeneralMini-Circuits Frequency Counter

The RF Frequenct Counter from Mini-Circuits is a counter with a very wide range, 1 - 6000 MHz. The module has a REF-IN (BNC) port, RF-IN (SMA) port, and a USB Port. The device receives its input frequency from the SMA port and uses the BNC Port as a refernce, or guide. After I installed the software for the device and grabbed some data, it seemed the program only repeats what is said on the screen of the frequency counter. The advantage is that you are able to grab the data and save it for a specified time interval. As for the accuracy, this device has about a 100 Hz uncertainty. As frequency increase, the uncertainty rises aswell. For calibrating the device, the manual states calibration is not necessary. Although, after a bit more digging, there is a calibration service number.

2932   Wed Jun 22 14:00:14 2022 Peter, OjoNoise HuntingPSOMADetermining noise sources from cantilever

The objective today was to determine the frequency spectrum of noise in the cantilever.

We started by creating a mount for the cantilever and making space on the east side of the table for beam alignment. We then created a setup that had the laser hitting the cantilever first, which was then directed into a mirror, and then reflected into the QPD and then into the dump. The mirror was used as a way of giving us degrees of freedom to center the beam on the QPD.

The oscilloscope wiring had already been done by Chris before the lab had started, and Ojo centered the beam on the QPD to give us minimal pitch and yaw readings.

Once the laser was on and running, Chris then used Simulink to script the ADC input into channels giving us pitch and yaw in. He then showed us how to use Linux commands in the terminal:

• matlab/simulink to edit the system's block diagram
• rtcds to activate the system (running on cymac1)
• ndscope to plot time series
• diaggui to produce a power spectrum as a function of frequency.

We saw that there was a resonant frequency near $\sim$120Hz (but not a power line harmonic), primarily in the pitch spectrum. This leads us to believe that it's the cantilever producing this noise, since the fundamental mode of the cantilever mostly produces displacement and pitch motion of the surface, with little yaw motion.

We were able to get a much better understanding of how experimentalists probe for unknown noises and uncertainties in their setup, and we now have a better way of utilizing this thought process for future problems in our SURF projects.

[attach spectrum plot]

2931   Thu Jun 16 14:28:32 2022 Peter, OjoLab InfrastructureLab WorkLab set up for clamp testing

Today we moved some of the mirrors and lenses on the back end of the table where the 630nm laser is. We wanted to prepare a space to be able to test the optical lever. We learned a bit about what the setup of a model cavity looks like within the lab. We were also introduced to some of the PDH locking and control systems.

it was said that we couldn't determine if the PSOMA cavity was locked to the 00 mode, or to a higher-order mode, so Shruti, Dr. Chris, Ojo, and Peter did a small bit of preparation to test the optical lever and see how it's aligned.

Next time, we plan on creating clamps of one of the cantilevers and setting up the photodiodes.

Draft   Thu Jun 16 11:04:13 2022 shrutiDailyProgressLab Workalignment

Attachment 1 shows 4 composite posts that I placed around the cantilever for some minimal protection.

After aligning to see some resonances in the transmission and reflection, I turned off the teraxion laser and switched the fibers to send the light after South Rio laser->Faraday->EOM chain to the fiber launch to begin locking. Attachment 2 shows the reflected light (blue) and transmitted light (yellow) before I optimized the mode-matching further.

For attempting the locking, I am now just using the Laser Lock Box on the Moku:Pro. The error signal looks weird even after checking with multiple phase offsets. Not sure what's happening. (Attachment 3)

Attachment 1: fortress.pdf
Attachment 2: Screen_Shot_2022-06-16_at_11.10.56.png
2929   Wed Jun 8 11:09:21 2022 ChrisLab InfrastructureLaserTeraxion software installed and connected on new HP laptop

See attached screenshot for the status. To connect, it was necessary to switch the serial port to COM3 in the connection settings dialog.

Attachment 1: Screenshot_(1).png
2928   Tue Jun 7 10:14:42 2022 shrutiDailyProgressLab Worknew cantilever clamped

I have de-bonded the mirror from the other cantilever also following this procedure re-using this setup. It took about 10 minutes or so to de-bond.

I saw that there were two cantilevers (possibly selected earlier by Aaron) left in the 'clean' part of our enclosure that looked good to bond the mirrors to.

• I cleaned both sides using drag wiping with 100% 2-propanol, especially the outline of the window where the optic would be placed
• I also used drag wiping on both the HR and AR surfaces of both mirrors.

[Rana, Shruti]

Then, with cryo varnish borrowed from QIL, we followed this procedure and bonded the AR surface of the mirror to the cantilever.

After roughly 3-4 hrs, the mirrors seemed to have bonded to the cantilever. I checked this by picking up the cantilever by holding the mirror edges with ceramic tipped tweezers. I clamped one of them and placed it roughly where it should be in the setup and stored the other one in a wafer case.

Images can be found here.

Rana: photos from my phone and somewhat processed here in the ligo.wbridge Google Photos account. I'm also attaching one showing that the second mirror we bonded is most likely cracked, rather than scratched as I previously thought. It still might be fine for in air testing.

Attachment 1: PXL_20220607_183717642.jpg
2927   Thu Jun 2 09:59:16 2022 aaronDailyProgressLab Workalignment

I took microscope photos of the mirror surface (attachment 1, 2)

I'm de-bonding the mirror following the procedure used previously. (attachment 3)

Attachment 1: Photo_on_6-2-22_at_09.54_#2.jpg
Attachment 2: Photo_on_6-2-22_at_09.55.jpg
Attachment 3: IMG_2953.jpg
2926   Wed Jun 1 16:02:42 2022 aaronDailyProgressLab Workalignment

Spent 4 hours aligning today (mostly just chasing my tail) before breaking another cantilever.

2925   Thu May 26 15:12:46 2022 shrutiPhotosstuff happenscsi cryo lab: fingerprint and fibers

When I tried to take pictures of the HR surface of the mirror on the broken cantilever using the USB microscope, I noticed a fingerprint and some fibers.

Initially I thought of drag wiping the surface to get a better image of the actual surface but with the fibers I am not sure how (or if?) to proceed.

Also, there appears to be something like a scratch in the center.

After taking these pictures, I placed the broken cantilever and optic in the enclosure with some lens tissue.

I cleaned the optic and took more pictures. All images (before, after) and a video while drag-wiping are on the ligo.wbridge google drive.

Attachment 1 and 2 are representative before and after pictures respectively.

Attachment 1: HR1.jpg
Attachment 2: HRa1.jpg
ELOG V3.1.3-