FAMIS 27831, last checked in alog88548

No water was added, filters looked good, and Dixie cup was dry. Updated T2200289 spreadsheet.

M. Todd, G. Vajente, L. Dartez

Thursday 12/18

1. We compared the beam profile that we fit to the modeled beam in that region, as well as what both of these beams look like at the ITM. We were initially very confused so we went back and more carefully placed the optics, taking care of the of and between the lenses in the telescope.
2. It seemed that the astigmatism was much worse than anticipated so we thought about tilting one of the lenses and seeing if we could compensate for the astigmatism. This gave us pretty confusing results, and especially because the fit to the first dataset was yielding non-physical values. For reference, the fit is done by fitting a quadratic to the beam radius squared as a function of z (i.e. w² = a+bz+cz²).
3. After deliberating in the control room, and returning to corroborate the fintrace model with jammt, we came to the conclusion that the telescope model is sensible; however, the measurement that we were taking is not descriptive enough of the beam to understand how the active telescope performs.
4. We finally decided to go in and take out the pick off to get as close of beam profile measurements to the waist of the beam after L2. We then shifted L2 5cm back toward the laser which was closer to the nominal position in the modeled layout. Here are the two plots of those beam profiles with their fits (I used a quadratic allowing M2 to vary, Gabriele has plots of minimized error of a Gaussian beam). L2 5cm further from M1 than the model. L2 close to model nominal position.

M. Todd, G. Vajente, L. Dartez

Wednesday 12/17

1. Additional optics mounted
   1. ZnSe 2” lens
   2. 2” silver and gold flipper mirrors (not installed)
   3. Additional beam dump for reflection of Polarizer2
2. We had the PD chassis milled out further to take an offset out that prevented the board from sitting flush.
3. We noticed that the coating had been burned on the first beam sampler we got from EdmundOptics. Emailed vendor to ask if this is common, because the power density is not at all expected to have produced this.
4. We also took beam profiles with a rail installed to get a fit of the beam evolution between M2 and M3. I made a fit of the data, assuming that M2 was perfect (I was having trouble with the nonlinear fit without M2=1, will revisit).

To do tomorrow:

1. Try and compare the lens solution to the fitted q we have from measurements.
2. Try and set up the coaligned visible laser

M. Todd, G. Vajente, L. Dartez

Tuesday 12/16

1. This morning we got the power monitor working with the old ICS computer that seemed to have the software on it already. We were not able to get the QPD software working because it requires Windows10 or newer; of course, this is only temporary because the other signals will be routed into the bekhoff eventually.
2. We got the package that arrived today with the beam profiler, and pins for the PDs. We took out the socket from one of the PD boards, but decided to have the chassis machined which should allow the sockets to fit in the chassis correctly.
3. We began, and made significant progress, on the alignment process for the optics. We got the beam mostly aligned well through all the optics, including lenses, to the output of the optics table. A few caveats
   1. We added a dogleg to the initial laser path so that the cables going to the feedthrough panel would not interfere with the laser .
   2. The first leg of the beam path along the long edge nearest to the rotation stage does not have enough room and will need to be readjusted.
   3. We will want to put the profiler in near the exit to see if the telescope is functioning as designed.
   4. The ZnSe lens needs to be mounted as well as the flipper. We still need to test the flipper.

FAMIS 27830 TCS Chiller top off

12/16/2025    Tony    30.7    100    30.8    10.2    125    10.4    Top of ball reading

M. Todd, G. Vajente, L. Dartez

Monday 12/15

1. We went through a checklist of things that still needed to be mounted, and decided to change the layout of laser position a bit to include a dogleg so that the laser connector had more room, free from the cable connectors near the feedthrough panel
2. Redesigned the feedthrough panels, now the same design can be used for all 4 tables (2 at each site) – and got a quote to be ordered
3. Connected and tested the laser interlock 
4. Mounted and installed laser (SN 0918) & cooler, confirmed that it draws current & delivers a reasonable amount of power as read out on the powermeter
5. Assembled pedestals for the lenses & various optics using assorted spacers to ensure center of all optics is at 4” height
6. Started a cart for additional components that we’ll need since we’re dipping into table 2 parts due to the adjustments we’re making to the layout

To Do:

1. Finish mounting the mirrors in the flipper mount (supposed to be a double mirror)
2. Mount the ZnSe QPD 2” lens.
3. Implement the dogleg
4. Align the optics
5. Profile the laser where the translation stage is now or where the beam is supposed to be going.
6. Integrate the power meter into a laptop with a usb?

M. Todd, S. Dwyer, J. Driggers

Summary

We turned on inverse ring heater filters to speed up the heating for those (using nominal values for the settings). Because of the weekend mayhem with the earthquakes we did not get a SUPER long HWS transient measuring the full response, but we could get a pretty good estimate of the ring heater effect on the substrate thermal lens without any other heating in the measurement. This is good to compare to modeled values that we have.

I also turned on SR3 heater on Sunday to get estimates of the coupling of SR3 heating to the defocus of SR3. To do this, Jenne helped me untrip a lot of the SU watchdogs for the relevant optics to the HWS. About 3 hours after the SR3 was turned on the watchdogs must have tripped again and misaligned the optics. But fortunately we got the cooldown data for this as well and it's all pretty consistent. These measurement suggest a 4.7 uD/W coupling for SR3 heating, which is very similar to modeled coupling from Gouy phase measurements at different SR3 heater powers.

Overall, while these measurements provide more pieces to the puzzle, they make previous analyses a bit more confusing, requiring some more thought (as usual).

Attached are monthly TCS trends for HWS & CO2 lasers.  (FAMIS link)

Closes FAMIS27829, last checked in alog88104.

For TCSX I added 100mL to bring it from 30.3 to 30.4.

For TCSY I added 80mL to bring it from 10.3 to 10.4.

The dixie cup was empty.

In prep for the upcoming CDS upgrades and vent Ryan, Jennie, and I went through the safe SDFs and accepted any values we thought needed it. We accepted all of the sus alignment sliders and checked on things like th IMC PZTs. The HWS had the center cross positions different, accepted. The ZM5 SAMS servo limit was also accepted.

We did our best combing through other subsystems and checking on both monitored and unmonitored channels, and they looked good to our eyes by either being automation controlled or reverted in SDF revert.

Editing: TJ found my mistake, I should say ezca['TCS-ITMX_CO2_LASERPOWER_COMMAND'] = 2 to go to the requested power, not 1.  1 is search for home.  Thank you TJ.

Lasty night I added some lines to Kevin's script that I hoped would make the CO2 powers step down from 1.7W to 0.9W at midnight.  

M. Todd, S. Dwyer

I've been polishing up the analysis of models estimating the various couplings of TCS powers to substrate and surface defocus in the test masses. This can be used to test the validity of the HWS estimate of the absorption in the ITMs. For reference, assuming the HWS are correct in their calibration of what the substrate defocus is in the test masses [ITMY = 63.5uD, ITMX = 54.5uD], and that my model is right for the coupling of substrate defocus from absorbed Watts of arm power [250 uD/W], then we have rougly 254mW of absorbed power in ITMY and 218mW of absorbed power in ITMX. Naively this seems too much, but I wanted to see if this could be consistent with measurements of the arm cavity Gouy phase.

Surface Defocus from Ring Heaters -- Models and Measurements

From both models and measurements, we have a much better idea now of how the ring heaters couple into test mass surface defocus. Fitting the HOM spacing in the YARM as a function of different ETMY ring heater powers, we obtain an estimate of the coupling factor of ETM ring heater power to surface defocus [1.53 +/- 0.2 uD/W]. The SQZ dataset which was taken at 2W, can be used to estimate the ring heater coupling as well because the HOM spacing of the YARM is purely the combination of the completely cold RoC (from galaxy) from the test masses plus the defocus from the ETMY ring heater (assuming negligible defocus from absorbed arm power) . The YARM cavity g-factor in the 2W state with ETMY ring heater on (2.93W) is calculated to be 0.8345. The cold cavity g-factor (without ring heaters or absorbed power) is calculated to be 0.8235. This yields a coupling factor (again, assuming negligible defocus from absorbed arm power) of ETM ring heater to surface defocus of 1.77 uD/W , which is almost within the bounds of the estimate above. These are both consistent, however, with modeled coupling factor [2.0 uD/W] with some imperfect efficiency of the ring heater heating. We can do the same analysis for the XARM with the caveat that we must assume a known ratio of the coupling factors of ring heater to surface defocus of the ITM and the ETM (we did not have to do this for the YARM because ITMY has no ring heater power). Assuming the coupling factors have a ratio beta = 1.73 (ITM_coupling/ETM_coupling)  and that the XARM cavity g-factor measured in the 2W state is 0.8373 then the inferred coupling factor for the ETMX ring heater to surface defocus is 1.80uD/W. This is consistent with the inference for ETMY. These values are consistent enough with each other that we can use them in the next inference, I believe.

Surface Defocus from Absorbed Arm Power to Infer the Circulating Power in the Arms

Since now we have a good understanding of the ring heater's contribution to the surface defocus and cavity g-factor shift, we can infer the absorbed arm power's contribution using the cavity g-factor measured at 60W. The measured cavity g-factors, calculated from the HOM spacings, were 0.8173 for the XARM and 0.8228 for the YARM. Assuming all the absorptions reporteed by galaxy are correct we can use the measured cavity g-factor shift along with modeled coupling factors of absorbed arm power to defocus to infer the arm power (JAAPE = Just Another Arm Power Estimate). The absorptions for the ITMs are 0.5 ppm, ETMY is 0.21ppm and ETMX is 0.20ppm. If we assume the coupling factors for ring heater surface defocus from the SQZ dataset and the modeled coupling factors of absorbed power to surface defocus, we get an arm power estimate of 283kW in the YARM and 481kW in the XARM. These indicate that the true absorptions in the test masses are most likely different from the galaxy numbers, as these arm powers are not consistent with the arm gain inference of the arm power, especially for the XARM.

Surface Defocus from Absorbed Arm Power to check the HWS Estimate of Absorbed Arm Power

We can repeat the above analysis, but instead assume nothing about the absorptions, and instead use the HWS estimates of the absorbed power in each input test mass. Then we can infer what the absorbed powers are in the end test masses to have measured the cavity g-factor as calculated from the HOM spacing. For ITMX, the HWS estimate an absorbed power of 218mW, and for ITMY the HWS estimates 254mW of absorbed power. To have measured a cavity g-factor in the XARM as mentioned above, with the HWS estimate of ITMX absorbed power, the absorbed power in ETMX would have to be 121mW. For the YARM measurement, using the HWS estimate of the ITMY absorbed power, the ETMY absorbed power would need to be -54.5mW. This indicates the HWS may be wrong, especially the ITMY HWS, as it is physically impossible to have measured the cavity g-factor that we did and simulataneously have that much absorbed power in ITMY (assuming the coupling factors from my model are correct).

Summary

Using two different methods, I've come a round-about-way to say that it is unlikely our absorptions are exactly as reported in galaxy, but that the HWS may not be giving us any better estimate (of the absorbed power). I am currently trying to calibrate the HWS using independent measurements, but more work is needed on that. Despite the ITMX HWS SLED just recently being replaced (we thought it was miscalibrated because it was dying), the defocus reported by the two HWS for CO2 heating differs by almost a factor of 2!

I am not well versed in HWS code and I'm not totally sure how these values of defocus are calculated from the deflection of each partitioned beam but these errors may be mis-identification of the position of the centroid.

This is a table of parameters describing the various coupling factors from the modeling. 

This is a summary table using the above modeled parameters

Conclusion: we have much more confidence in our models of various coupling factors thanks to measurements of the ring heaters effect on surface defocus, however we do not have a very good estimate of the absorbed powers or absorptions.

Closes FAMIS#27828, last checked 87799

TCSX Chiller read 30.5, TCSY read 10.5, so I did not add any water. Filters and water flow looks good, and there is no water in the Dixie Leak Detector™

Attached are monthly TCS trends for CO2 and HWS lasers.  (FAMIS link)

NOTE:  The change for ITMx HWS is due to its SLED being swapped on Oct 7 (alog 87353).

The IR sensor for CO2Y was intermittently going into fault. I resat the connector on the sat box and it seems to be okay now.

Today during maintenance the CO2Y laser tripped off 3 times. The first one we figured was due to cable pulling activity in the area, the second was a bit more of a mystery, and the third made us think there was definitely something wrong. Ryan C restarted the first two at the control box, needing to power cycle it at least once each time. The third time I went out there and noticed the IR fault light going on and off. I touched the cable that goes to the IR sensor itself and the lights on the IR satellite box went red. Simply placing my finger on the cable near the connector on the box was enough to bring it into fault. I checked the connector there and it had some play in it, so I tried to seat it a bit better and then it seemed to not be as sensitive to me touching it. I turned the key off and on again and it was good to go.

Because this last trip happened while we were powering up to 25W, there was about 20 minutes or so when CO2X was on at its nominal annular power, but CO2Y was off (~2107-2131UTC). Perhaps this is an interesting bit of time for someone to look at?

We ended up losing lock when powering up to 60W. Perhaps I should have waited longer after CO2Y was back to let it "catch up" to ITMX's thermal state.

FAMIS27827

No water was added, but the filters all looked good. There was no water in the Dixie Leak Detector. Updated the T2200289 sheet.

M. Todd, S. Dwyer

As derived in previous alogs, we are able to relate the HOM spacing observed in each arm to the surface defocus of the test masses -- which is a combination of self-heating and ring heater power (ignoring CO2 affects on the ITM RoC). From the fits we've made of the HOM spacing / surface defocus change as a function of ring heater power we can get a value for the ring heater to surface defocus coupling factor.

Theoretically from this we should be able to solve for the self heating contribution in the test masses as well -- allowing us to constrain things like the coupling of absorbed power to surface defocus at the ITMs if we assume to know the arm power and absorption values (from HWS).

Upper Limits

If we assume no absorption in ETMs (obviously not physical), and we assume the HWS values for the ITM absorptions are correct, then with a HOM spacing measurement from each arm we can get an upper limit of the coupling factor of self-heating to surface defocus for each ITM (they shouldn't be different but this is a good exercise).

Assuming alpha is the absorption coefficient, i subscript is for the ITM, and x/y is which arm. P_y,i_rh is the itmy ring-heater. G-factors are the product of ITM and ETM g-factors. Then from the formula in section 1.2 of the notes file : Gy = Gyc - B*L*gyic*(Pyerh+Pyirh) - L*(Ai*alpha_yi*Pyarm*gyec + beta*Ai*alpha_e*Pyarm*gyic), we can solve for Ai which is the coupling factor of self-heating to surface defocus.

Middling Values

If we assume quoted absorption in ETMs (measured by LIGO, on galaxy), and we assume the HWS values for the ITM absorptions are correct, then with a HOM spacing measurement from each arm we can get a more realistic value of the coupling factor of self-heating to surface defocus for each ITM (they shouldn't be different but this is a good exercise).

Assuming alpha is the absorption coefficient, i subscript is for the ITM, and x/y is which arm. P_y,i_rh is the itmy ring-heater. G-factors are the product of ITM and ETM g-factors. Then from the formula in the notes file : Gy = Gyc - B*L*gyic*(Pyerh+Pyirh) - L*(Ai*alpha_yi*Pyarm*gyec + beta*Ai*alpha_e*Pyarm*gyic), we can solve for Ai which is the coupling factor of self-heating to surface defocus.

Summary

Both of these values indicate there is certainly an overestimation of the self-heating impact on surface defocus.

For reference, the current TCS-SIM values for this coupling factor are Ai_y = Ai_x = -36.5 uD/W.   More examination is required into this.

Links to previous alogs:

1. Estimating HOM spacing shift from self-heating alone:  https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=84172