Closes FAMIS85524

No new issues, LVEA5 is still not connected. The optics lab continues to have dust excursions likely caused by the wind conditions, the PSL anteroom and laser room also see these but at a lesser magnitude.

Closes FAMIS 85574, last checked in alog91931
Laser Status:
    NPRO output power is 1.853W
    AMP1 output power is 70.55W
    AMP2 output power is 139.2W
    NPRO watchdog is GREEN
    AMP1 watchdog is GREEN
    AMP2 watchdog is GREEN
    PDWD watchdog is GREEN

PMC:
    It has been locked 1 days, 0 hr 4 minutes
    Reflected power = 28.55W
    Transmitted power = 105.5W
    PowerSum = 134.1W

FSS:
    It has been locked for 0 days 2 hr and 22 min
    TPD[V] = 0.3879V

ISS:
    The diffracted power is around 3.4%
    Last saturation event was 0 days 20 hours and 15 minutes ago

Possible Issues:
    PMC reflected power is high
    FSS TPD is low, its at its lowest in over 2 months

S. Koehlenbeck, B. Lantz [posted by J. Kissel]

We're looking at the results posted by Jeff in LHO:91990, and are suspicious of the new ISI-DIFF channels. Here, Sina compares various available versions of the HAM2 table motion, 

    (1) H1:ISI-HAM2_BLND_CPSX_IN1_DQ      capacitive position sensor, pre-blend
    
    (2) H1:ISI-HAM2_CAL_CART_X_OUT_DQ     GS13s, pre-blend, but calibrated already into displacement units 
  
    (3) H1:ISI-DIFF_H2_BLND_SS_X_DQ       blended CPS + GS13s, re-constructed in seiproc for the input to the DIFF channel

    (4) H1:ISI-HAM2_ISO_X_IN1_DQ          blended CPS + GS13s, in loop in the HAM2 feedback. Contains loop suppression

    (5) H1:ISI-HAM2_ISO_X_OUT             feedback control signal

    (6) H1:ISI-DIFF_H23_SS_X_OUT_DQ       differential HAM3 - HAM2, using the HAM2 blended CPS+GS13 reconstructed in seiproc (3).

The message -- where we use the pre-blended sum of (1) and (2), it should look identical to (4) the reconstructed HAM2 super sensor, but it does not.
Or, the GREEN trace is a factor of ~2x larger that RED below 0.2 Hz, and BLUE above 0.2 Hz.

The discussion and investigation continues...

The HV at EndX was switched back on yesterday afternoon, I ran the OPLEV charge measurement for ETMX first thing this morning. The GRD state of ETMX was changed from ALIGNED to MISALIGNED in the last ~2 minutes of my measurement for some reason, I had unmanaged it from ALIGN_IFO. It was during the last LR measurement, LR Yaw has the largest error bars so that might have played into that. There was also a ground motion increase from a 5.7 earthquake near Tonga from the 2nd measurement till the 4th but my coherences were all >0.9 and the errors looked ok.

15:16 - 15:50 UTC EQ mode

The charge has decreased towards zero on 3/4 quadrants in both P and Y, UL being the odd one out mostly in Yaw. All quadrants/dofs are now under +/- 50 V.

TITLE: 09/23 Day Shift: 1430-2330 UTC (0730-1630 PST), all times posted in UTC
STATE of H1: Corrective Maintenance
OUTGOING OPERATOR: None
CURRENT ENVIRONMENT:
    SEI_ENV state: CALM
    Wind: 2mph Gusts, 0mph 3min avg
    Primary useism: 0.02 μm/s
    Secondary useism: 0.17 μm/s 
QUICK SUMMARY:

• JAC and IMC were left in down overnight
• LVEA6 dust alarm
• GVs are still shut
• CDS shows 10 chans disconnected, DTS channels

[Elenna, Louis, Keita]

Today we continued working on the transition of DRMI to the 3f signals. We have not gotten there yet. What follows is a rough list of events. 

* After maintenance I measured the OLG of MICH, PRCL, and SRCL in DRMI (ISC_DRMI:PREP_DRMI_ASC). 

    - PRCL UGF was at 50Hz. 

    - MICH UGF is at about 7.2Hz. We don't understand the OLG TF feature at 30Hz+. We suspect that this is due to cross-coupling with other dofs. The MICH gain during the measurement is 3. There was discussion in the control room regarding the drop in MICH gain by a factor of 3 in 92004 (which helped the mode hopping at the time). It's not clear how/why this gain adjustment worked since it looks like the gain would have dropped the UGF through 0deg phase and should have gone unstable(?). i.e. Elenna & I would have expected the drop in gain to not have worked if this OLG TF is representative of MICH during Keita's adjustments on Monday night.

    - SRCL UGF is at 35Hz. 

* DRMI LSC is cross-coupled: At Keita's suggestion, I ran the OLG templates with the MICH, PRCL, and SRCL inputs to gauge the cross-coupling from each excitation to the other two LSC dofs. These are attached as the <_inj>. png files (MICH exc, SRCL exc, PRCL exc). Judging from the coherence alone (top right subplot), there is a substantial degree of cross-coupling at the moment in DRMI 1f.  For instance, it PRCL has more coherence than MICH during the MICH excitation above 10Hz.

* The 3f transition is only partially working right now. PRCL transition works well consistently. MICH is not yet working (it fails immediately). We decided to work on SRCL before coming back to MICH. 

* For the SRCL 3f transition, we measured the 3f input matrix gains today and got -3.7 for REFLAIR_B_RF135I and +2.7 for REFLAIR_B_RF27I. We put these gains into the 3f input matrix for YARM and measured YARM (3f) /SRCL_IN (1f) at 80Hz and showed that we pretty much get unity, suggesting good agreement between the 1f and 3f signals. So we're pretty sure that the input matrix gains are correct (assuming no dominant frequency-dependent contribution that we aren't seeing at 80Hz, chosen because notches already exist for this frequency in the relevant feedback loops). However, when we load the (ramping) input matrix values to transition to 3f it fails every time. 

* We decided to inject PRM, SRM, and BS lines to populate a full 3x3 sensing matrix and invert it to construct proper diagonalized input signals. As Elenna was injecting a PRM line Keita noticed that it was poorly phased in REFLAIR RF45. We paused to get that phased back up. Not sure why it wasn't phased properly. There was discussion about just having done that recently. We changed REFLAIR_A_RF45 by 20 degrees (from -171 to -151). Following that we changed the PRCL gain by 3dB, SRCL by 6dB, and had to change the SRCL RF9 input matrix element from -1.7 to -1.2 to account for how much PRCL was making it into RF9 due to the phase change.

* After this we started seeing bizarre features in the OLG tfs in both 1f and 3f (MICH OLG, PRCL OLG, SRCL OLG). During the SRCL excitation we pulled up the REFLAIR_B_RF135I (45 3f) signal (gold) and see a 15 Hz instability that we really don't understand. It's our conclusion for the evening that we can't transition to 3f while we don't understand the broadband nature of this signal. 

* We didn't finish collecting the full 3x3 sensing matrix measurements. We should probably restart and complete those measurements so that we can try diagonalizing the input matrix in both 1f and 3f.

I also want to mention that we lost lock several times today due to JAC suddenly unlocking throughout the day. 

* 22:55:56 UTC while Elenna was tuning up the alignment

* 23:45 UTC while we were debuggin the 3f transition

* again at 00:09 UTC 

* and again at 00:59 UTC

While would usually be able to acquire DRMI relatively quickly after JAC came back, the JAC-induced lock losses did make the process a bit more painful than it otherwise would have been.

Jennie W, Jeff K, Keita K,

Summary: Scattering nosie from IFO couples into QPD A, QPDB segment four has larger dark noise b y factor of ~40 compared to other segments.

After we broke the ground loops on the TIA chassis inputs last week I redid the QPD dark noise measurements.

First I measured the average value of each quadrant input on both QPDs using diaggui to take a triggered time measurement withe the shutter open.

Then I closed the shutter and set the QPD_{A,B}_SEG{1,2,3,4}_OFFSET values to the average value for all four QPD A segments (15050 counts) and all four QPD B segments (16750 counts).

Then I measured the dark noise using the template in /ligo/home/jennifer.wright/git/2026/SPI/20260922_SPI_dark_noise_ASD.xml

The first measurement looked like it had some glitches on QPD A so Jeff got me to check the time series. At his suggestion we checked for coherence with ASC_AS_C (anti-symmetric port of H1) and it seems to be correlated. The AS port was flashing through fringes hence the fringing seen on the time series.

Zooming in this becomes more obvious.

I unlocked and mis-aligned the IMC and unlocked the JAC to stop scattered light through HAM 2 and 3 while I retook the measurement.

The QPDA dark noise now looks better but QPD B segment four is still significantly noisier than the other quadrants.

Looking at the time series this noise is obvious also.

Keita and I then checked the raw signal inputs before the anti-whitening filter on the QPD segments and these still show this noisier segment four. NB: this measurement was done with the IFO back to locking so scatter is again visible in the QPD A spectrum. The noise is flat, which suggests that the whitening stages in the TIA are not engaged so its not a whitening gain problem.

We then did a test with the SPI unshuttered and the dark offsets back to nominal. QPD B segment 4 now looks not that different to the others, which suggests that the four segments do not have wildly different electronic gains.

Try swapping chassis for TIA or disconnectiong input and measuring output ASD for TIA.

Next steps: 

- Measure TIA output spectra from each quadrant on QPD B with input unplugged.

- Test QPD outputs without TIA in loop by measuring their voltage through a resistor and comparing all four quadrants.

Summary: guardian change messed up servo controller, will trial changes this weekend, have now backed out problematic part.

I changed the lines in the JAC temperature servo add in the PZT fb signal to the JAC temperature servo error point during maintenance.

I thought that I had it setup so the heater control error point gets changed as the JAC length changes, unfortunately I had a mistake in the code so this offset was only being added to the temperature servo once when the servo was switched on.

After updating it, this caused overshoot in the JAC temperature which kept unlocking it.

I have taken out these lines (line 46 in JAC_HEATER.py) so now the servo just tracks the set temperature of the heater.

I will leave this to settle overnight.

As part of our efforts to keep the JAC servo locked we had put the power output on the JAC heater to 0, I have turned this back to its nominal at 3W, and the set temperature back to its nominal at 25.4 degrees C.

I will also do another test at the weekend where I put the set temp up further to 30 degrees. The PMC has a set temperature of 32 degrees. While this is in air and so benefots from air cooling, a larger headroom in set temperature would make our control loop faster at cooling.

TITLE: 09/23 Eve Shift, all times posted in UTC
STATE of H1: Corrective Maintenance
INCOMING OPERATOR: None
SHIFT SUMMARY: Commissioners continued making measurements with DRMI locked, but an unstable JAC heating servo causing the JAC to unlock occasionally made this challenging. There will be another log from them posted soon with details, but DRMI is locking fairly easily with good alignment. Leaving ISC_LOCK in 'DOWN' with the IMC locked. 
LOG:

I reset the LIGO-SPI phase a minute ago.

WP 13643

The ESD HV supplies and Ring Heater Chassis are now powered on. The LV ESD Driver chassis was also powered on.

Today Caroline C. and I took PS4 down to EX to follow the directions on DCC Doc T1500062 for the End station measurement.  
This was the First ES measurement since the EndX station was Vented, Thankfully I had recently done an EX measurement last month!

Note for PEM crew: While setting up for our measurement,  the leg (#2) for a tripod holding an Accerlerometer/microphone slipped and fell at ~9:22 am -ish Local time. Tagging PEM.

Checking the Beam spots before we started, I was happy to see that we still have both beams, And the beams are well aligned!
While I was adjusting the beam block in the TX module we noticed that when I was checking for light behind the beam dump the WS sphere responded to the beam card's placement behind the beam block. I think what was going on is similar to what we saw in the lab where the diffuse light coming out of the sphere's apature is interacting with objects upstream of the apature and reflecting back. I then decided to move the beam blocks to before the steering mirrors.

Oh I was checking for the I limit LED to turn on, It never did, which is a good sign. I beleive this is the current limit LED and happens when there are power fluctuations.

After the measurement I check the Beam spots again. Looks good.

Command that were ran to make analysis happen:
@cdsws25: python3 generate_measurement_data.py --WS PS4 --date 2026-08-24
Reading in config file from python file in scripts
../../../Common/O4PSparams.yaml
PS4 rho, kappa, u_rel on 2026-08-24 corrected to ES temperature 300.1 K :
-4.698238515939288 -0.0002694340454223 0.00075040881877916
Copying the scripts into tD directory...
Connected to h1daqnds1
martel run
reading data at start_time:  1474131650
reading data at start_time:  1474132080
reading data at start_time:  1474132460
reading data at start_time:  1474133220
reading data at start_time:  1474133630
reading data at start_time:  1474134000
reading data at start_time:  1474134200
reading data at start_time:  1474134850
reading data at start_time:  1474135230
Ratios: -0.4613044966821107 -0.4660884801303913
writing nds2 data to files
finishing writing
Background Values:
bg1 =        9.463727; Background of TX when WS is at TX
bg2 =        5.116111; Background of WS when WS is at TX
bg3 =        9.483908; Background of TX when WS is at RX
bg4 =        5.220218; Background of WS when WS is at RX
bg5 =        9.517908; Background of TX
bg6 =        0.309874; Background of RX

The uncertainty reported below are Relative Standard Deviation in percent 

Intermediate Ratios
RatioWS_TX_it      = -0.461304;
RatioWS_TX_ot      = -0.466088;
RatioWS_TX_ir      = -0.455459;
RatioWS_TX_or      = -0.460916;
RatioWS_TX_it_unc  = 0.073428;
RatioWS_TX_ot_unc  = 0.073806;
RatioWS_TX_ir_unc  = 0.072766;
RatioWS_TX_or_unc  = 0.078002;
Optical Efficiency
OE_Inner_beam                      = 0.987351;
OE_Outer_beam                      = 0.988996;
Weighted_Optical_Efficiency        = 0.988174;

OE_Inner_beam_unc                  = 0.047979;
OE_Outer_beam_unc                  = 0.050724;
Weighted_Optical_Efficiency_unc    = 0.069821;

Martel Voltage fit:
Gradient      = 1636.905374;
Intercept     = 0.141593;

 Power Imbalance = 0.989736;

Endstation Power sensors to WS ratios::
Ratio_WS_TX                        = -1.078292;
Ratio_WS_RX                        = -1.391839;

Ratio_WS_TX_unc                    = 0.044772;
Ratio_WS_RX_unc                    = 0.038846;

=============================================================
============= Values for Force Coefficients =================
=============================================================

Key Pcal Values :
GS           =      -5.135100; Gold Standard Value in (V/W)             
WS           =      -4.698239; Working Standard Value             

costheta     =      0.988362; Angle of incidence
c            =      299792458.000000; Speed of Light
             
End Station Values : 
TXWS         =        -1.078292; Tx to WS Rel responsivity (V/V)
sigma_TXWS   =        0.000483; Uncertainity of Tx to WS Rel responsivity (V/V)
RXWS         =        -1.391839; Rx to WS Rel responsivity (V/V)
sigma_RXWS   =        0.000541; Uncertainity of Rx to WS Rel responsivity (V/V)

e            =        0.988174; Optical Efficiency                                           (compare from from last month!------->:  0.988725; Optical Efficiency)
sigma_e      =        0.000690; Uncertainity in Optical Efficiency              (compare from from last month!------->:  0.000661; Uncertainity in Optical Efficiency)

Martel Voltage fit : 
Martel_gradient         =        1636.905374; Martel to output channel (C/V)
Martel_intercept   =        0.141593; Intercept of fit of     Martel to output (C/V)

Power Loss Apportion : 
beta          =        0.998895; Ratio between input and output (Beta)                      
E_T          =        0.993520; TX Optical efficiency 
sigma_E_T          =        0.000347; Uncertainity in TX Optical efficiency 
E_R          =        0.994619; RX Optical Efficiency                                                  (compare from from last month!------->: 0.994896; RX Optical Efficiency)
sigma_E_R          =        0.000347; Uncertainity in RX Optical efficiency              (compare from from last month!------->:  0.000332; Uncertainity in RX Optical efficiency) 

Force Coefficients : 
FC_TxPD          =        7.899630e-13; TxPD Force Coefficient                      (compare from from last month!------->:   7.900632e-13; TxPD Force Coefficient) 
FC_RxPD          =        6.193277e-13; RxPD Force Coefficient                      (compare from from last month!------->:   6.191631e-13; RxPD Force Coefficient)
sigma_FC_TxPD          =        3.755608e-24; TxPD Force Coefficient           (compare from from last month!------->:  3.624112e-24; TxPD Force Coefficient)
sigma_FC_RxPD          =        2.797039e-24; RxPD Force Coefficient           (compare from from last month!------->:  2.753947e-24; RxPD Force Coefficient)
data written to ../../measurements/LHO_EndX/tD20260922/ and can be found at the gitlab pcal repo

I added a little context for those that may be wondering if there was an decrease in Optical efficiancy, uncertainty, Force, or Displacement due to the EX venting. The numbers in bold are from last month's alog 91681 to show that things have not seen much change at all. We did not have a repeat of LLO's EX vent experience! YAY!
For see how these measurements compare with all of the measurements for the past few years click here!  

WP 13641
WP 13642

In preparation for the installation of the Newtonian Noise Array, a power cable was installed from the LY Vacuum rack to BSC8.

Removed 7 BNC cables routed from the Biergarten to SUS-R3. Cables last used two years ago and causing tripping hazard by HAM4 /SUS-R4.

F. Clara, R. Schofield

I ran the OPLEV charge measurements this morning. I failed to notice that the HV was off for ETMX, the QUAD_BIO medm was showing me it that it was on so I took a few bad looking measurements. On ETMY the QUAD_BIO medm was not updating when I tried to toggle the HV off and on.

For ETMY, the sign the of the charge looks to have flipped. I found a set of measurements from 09/01 that I can't find any reference in the alog of, I processed them and they looked good (good coherence, small errors...). The charge flip occured before Sept 1st but after July 31st, sometime in August. I trended the bias offset and saw it was changed from -4.9 not engaged (SWSTAT 37889) to -8.9 and engaged (SWSTAT 39937) alog91729 on August 28th. ETMYs' charge is trending towards zero on all quadrants and DOFs, it is just above +/-50V on half of the quadrants/dofs.

TITLE: 09/22 Day Shift: 1430-2330 UTC (0730-1630 PST), all times posted in UTC
STATE of H1: Corrective Maintenance
INCOMING OPERATOR: Ryan S
SHIFT SUMMARY: Maintenance day wrapped up without much of a fuss. EX ans CS gate valves are still closed making this afternoon's locking unusual. I just finished a modified initial alignment described below.

• Once maintenance concluded I ran a very modified initial alignment:
  • PRX locked and touched up PRM by hand
  • MICH dark, touching up the BS to reduce the camera spot and AS_A as best I could. This proves hard once you get close because the beam seems to bounce around and the remnants of the spot on the camera can be tough to say which is better or worse.
  • SR2 align ran great.
  • SRY wouldn't lock until I increased AS_A flashes by adjusting SRM. Then I increased AS_A with SRM and a touch of SR2.

LOG:

FAMIS 63917

There have been three incursions into the enclosure over the past week; two last week for the EOM swap and one this morning to check some beam alignments. Overall things are still running smoothly and things have leveled out after the incursions.

Tom requested some time with the damping OFF for the BBSS

I did this in two segments. First segment is in the Sum Feedback configuration, and the second segment is in the Constant Current configuration. Since these times were taken during maintenance, the seismic configuration at the time was with seismic correction OFF.

BBSS DAMP OFF Times
- Sensor Correction OFF
- SEI in FULLY_ISOLATED

Sum Feedback ON
Damp OFF : 2026/09/22 17:52:00 - 18:27:00 UTC [1474134738 - 1474136838]

Sum Feedback OFF
Damp OFF : 2026/09/22 18:33:30 - 19:01:00 UTC [1474137198 - 1474138878]

After these were done, I turned BBSS M1 and M3->M2 damping back on and flipped the current switches on the satamp back to the Sum Feedback configuration.

J. Kissel

Sina has posted some of the first SPI L results in LHO:91794 and subsequent comments in LHO:91861. They conclude, via passive ASD measurement and minimal unit conversion, that "the visual agreement is remarkably good."

Here I post some retrospective results from the driven transfer function set I took on 2026-09-03 (LHO:91798) to get a more quantitative comparison.
Using all channel conversions described in LHO:91809, which are, in summary "just" calibrating the front-end channels into the SI order of magnitude units (i.e. diplacement channels from [nm] to [m], and inertial sensor channels "inertial sensor response asymptoting to 1 [nm/s] at high-frequency" to [m]), I compare the ASDs and transfer functions during the reference time and HAM2 injection times, 
    Reference Time  2026-09-03 17:09:49 UTC 
    HAM2 excitation 2026-09-03 18:34:14 UTC - 18:58:09 UTC

Note -- while I had thought the CRS as blended into the HAM3 sensor array during this time, Jim confirms that it was NOT in play in the HAM3 RY loop (LHO:91866).
Also -- there were questions why "I didn't just use the same excitation that Jim did for the optical lever signals;" the real answer is that I hadn't had the chance to talk to him, couldn't find it easily on my own, and assumed it was some matlab infrastructure that I wouldn't know how to use. I now have talked to him, and he's pointed me to LHO:91754, which points to LHO:91607, which points to the actual path to the file in LHO:91179. But, even if I did find that text file to drive awggui with, it has a low-frequency-focused tilt de-coupling color too it, which is different from what I ended up concocting in DTT. C'est la vie, I think both sets of TFs will be interesting. Certainly this one was.

Attachment 1
Building up an understanding of the front-end-computed HAM3-HAM2 super sensor signal, H1:ISI-DIFF_H23_SS_X_OUT_DQ.

This ASD collection compares the CPS and GS13s of HAM2 and HAM3 against the differential super sensor during the HAM2 excitation (only). Since HAM3 was NOT being driven, we can treat this like the "reference" performance for the HAM2 ISI -- because the HAM2 and HAM3 ISI typically perform similarly in the longitudinal, or ISI and IFO X direction (when the CRS is not engaged into the HAM3 blend). 

- Compare BLUE, DARK GREEN, and HOT PINK traces. We see that the drive on causes displacement on HAM2 is factors of 2x to 50x above the reference level
- Compare THIN DARK PURPLE against CYAN and BRIGHT GREEN traces. We see that the blended input to the super sensor for HAM3 has -- for some reason -- a lot more motion than the "raw" blended CPS and GS13s input. 
- COMPARE BLUE, DARK GREEN, HOT PINK, and BLACK traces. Where the CPS and GS13s are not noise limited (i.e. where're signals are used in the blend to form the super sensor sum), All of the HAM2 and the differential HAM3-HAM2 signal agree, showing the excitation on HAM2.

Conclusion: the front-end computed measure of the differential motion between HAM3 - HAM2 using the onboard CPS and GS13s is functional, comes with a calibration that makes sense, and is measuring the right thing.

Attachment 2
Building up more trust in the HAM3-HAM2 super sensor signal, H1:ISI-DIFF_H23_SS_X_OUT_DQ as a faithful signal for comparison with the SPI L signal H1:SPI-H23_DIFFDISP_MAIN_OUT_DQ.

This ASD collection compares the CPS- and GS13-computed differential X motion (BLACK) and SPI L measured differential X motion (RED) during both the reference quiescient time (DASHED traces) and during the HAM2 excitation (SOLID traces). The excitation is also shown (H1:ISI-HAM2-ISO_X_EXC, calibrated into displacement units [m]).

- During the reference time (DASHED), the SPI L and the on-board sensors only agree above 5 [Hz]. *very interesting* We know the low-frequency-end -- below ~2 [Hz] -- is dominated by the SPI seed laser's frequency noise -- which is dominated by the IMC's displacement. Remember, at the time of measurement, only the IMC is locked (but now with the JAC locked between the PSL and IMC). It looks like -- at least during this measurement -- that's larger or different or incoherent with the HAM3-HAM2 motion. So... maybe this is all suspension noise (or ISI tilt)? Needs more study / noise budgeting.

- During the excitation time (SOLID), the SPI L and the on-board sensors agree across a much broader frequency-band, only disagreeing between 1.5 and 10 [Hz]. *very interesting*. *great* that the excitation i.e. this amount of differential motion *makes* the SPI L and on-board sensors agree for the most part. I have even less of a guess at an explanation for the frequency region where they're not, tho.

Conclusion: Under large differential displacement, the SPI L agrees with the on-board sensors over a very broad range of frequencies, from 0.005 - 2 [Hz] and 10 - 60 [Hz] Lots still to investigate, tho.

Attachment 3
Linear transfer function between the HAM3-HAM2 super sensor signal, H1:ISI-DIFF_H23_SS_X_OUT_DQ and the SPI L signal H1:SPI-H23_DIFFDISP_MAIN_OUT_DQ, as well as the length/frequency control channel for the input mode cleaner (H1:IMC-F_OUT_DQ. 

I show the driven transfer function magnitude for these signals on a log-log plot. Coherence shown separately below.

- Where the SPI noise didn't match the ISI-DIFF noise between ~2 - 10 [Hz], the TF is incoherent (coherence shown separately below), so ignore that.
- At other frequencies, where the ASD "visually agree" the transfer function is NOT exactly 1.0 -- see more discussion of the values of the TF magnitude in the semilogx version of the plot below. *very interesting* 
- I don't understand the magnitude of the IMC-F transfer function at all below 1 [Hz]. The next plot shows it's coherent... *very interesting* or *I'm missing something obvious*

The IMC-F channel has the following calibration into [m]:
    Gain: 1.1683e-06
    Poles: 0
    Zeros: (none)
I don't remember how I calculated this, or where I got it from. To be (re)investigated... but I would have guessed -- since IMC-F_OUT_DQ is already calibrated into [kHz], that it *should* be something like a factor of (2 * L_IMC * lambda / c) = 1.1724e-13 [m/Hz] or 1.1724e-13 [m/kHz] with no poles at 0 [Hz], from df / f0 = dL / L_rt math, but that doesn't seem to be it at all. I probably just need to go back to the code used to produce plots in the SPI final design doc ... just haven't had time.

Also -- side note -- looked into the IMC_X calibration infrastructure that uses the length drive to MC2 to calibrate the control signal into displacement units and that doesn't work.

Attachment 4

Coherence between SPI L and the ISI-DIFF channel and the IMC-F channel for the two TFs shown above.
I also show the coherence between the SPI L channel and the individual ISI CPS and GS13s to understand from where the coherence comes (expecting more from HAM2 since this is during the HAM2 drive.)
I also show the coherence between the ISI-DIFF channel and the IMC just to see how that's different.

Conclusion: Lots to see here, but I haven't really digested it or tried to make sense of it.

Attachment 5
Same transfer function as in Attachment 3, just shown in semi-log x so we can read off what the magnitude of the TF is at coherent frequencies.

- The TF is indeed almost a flat 1.0 [m/m] above 10 Hz; but not quite. *very interesting*
- Between 0.1 and 1 [Hz], where the SPI and ISI-DIFF are *definitely* coherent, the TF magnitude is *not* 1.0, not is it flat. It's got bumps and wiggles between 1.0 and 0.7. Best first guess it that this has something to do with gain peaking in the blend filters. *very interesting*

Conclusion: this TF is going to be very interesting, and we won't be able to "just" blend the SPI "right in" with a simple filter. And, I need to try to get more coherence below 0.1 [Hz].

Very interesting!