I did a yum-install of the latest ldg-client (to get onto the LIGO Clusters) on Rossa. 

I followed the instructions on the wiki page, and everything seemed to work nicely.

I think the new ldg client installs somewhere on the local computer, so if anyone wants cluster access on any other computer, they should follow the same directions.

David Nolting, chief LIGO Safety Officer and his lieutenants from LLO and LHO paid homage to the 40m lab this morning.

They give us a few recommendation: update safety documents, move optical table from the front of ETMX-rack and label-identify absorbent plastics on enclosure windows-doors.

We'll correct these short comings ASAP

I installed ligoDV in the /ligo/apps/ligoDV/

Now, by pointing the tool at the local NDS2 server (megatron:31200) you can access the recent local data (raw, trends, etc.)

by running /ligo/apps/ligoDV/ligodv from the command line.

40m crew and visitor Holger Muller from Berkeley.

Thanks to a discussion yesterday with Joe Betzweiser, I was able to identify and fix the remaining problem with the LLO GigE camera software. It is working now, currently only on rossa, but can be set up on all the machines. I've started a wiki page with documentation and usage instructions here:

https://wiki-40m.ligo.caltech.edu/Electronics/GigE_Cameras

This page is also linked from the main 40m wiki page under "Electronics."

This software has the ability to both stream live camera feeds and to record feeds as .avi files. It is described more on the wiki page.

To make this setup more permanent, I modified the c1lsc model to pipe the LO power monitor signals from the Demod chassis to unused channels ADC_0_25 (X channel LO) and ADC_0_26 (Y channel LO) in the c1lsc model. I also added a couple of CDS filter blocks inside the "ALS" namespace block in c1lsc so as to allow for calibration from counts to dBm. I didn't add any DQ channels for now as I think the slow EPICS records will be sufficient for diagnostics. It is kind of overkill to use the fast channels for DC voltage monitoring, but until we have acromag channels readily accessible at 1Y2, this will do.

Modified model compiled and installed successfully, though I have yet to restart it given that I'll likely have to do a major reboot of all vertex FEs

[Paco, Yehonathan, Yuta]

We measured power and counts at BHD DCPDs with LO beam only and ITM single bounce.
We found that LO beam power is ~7 times less than the expected.
We also confirmed that AS beam is clipped somewhere inside vacuum and have 20-50% less power compared with the expected.
LO/AS beams going to DCPD A and B also have power imbalance by 30-40%.

What we did:
 - Run LSCoffsets.py to zero the offsets. I modified the old script so that it can handle new BHD PDs. Also, a bug was fixed (it didn't take into account the gains in filer modules, so INMON is now used instead of OUT16 for calculating offsets).
https://git.ligo.org/40m/scripts/-/blob/main/RFPD/LSCoffsets.py
 - Measured powers and counts in BHD DCPDs at ITMY table with LO beam only and ITMX/ITMY single bounce.
 - During the measurement, we found that power into DCPD A and DCPD B are quite different. One of the reason was a lens and an iris right after the viewport for A path. We removed both of them. Also, only A path have a pickoff which picks off ~20% of light to BHD camera (called SRMF; 40m/16880).
 - We also found that LO beam shape is ugly. ITM single bounce beam from X and Y have similar clipping (see Attached photos). We tried to reduce clipping with various suspensions (LO1, LO2, AS1, AS4, SR2, SRM, BS, ITMX, PR2), but was not possible by moving only single suspension.

Result:
 - Result of counts and power measurements are as follows. Power was measured right in front of DCPD, and also right after the viewport to estimate the loss in the in-air paths. Note that LSC channels have gain of 1, but HPC channels have gain of -1.9 for DCPD_A and -1 for DCPD_B.

                       Blocked  LO       ITMX      ITMY    
C1:LSC-DCPD_A_OUT16    -0.01    -17.89    -91.62    -86.21    
C1:LSC-DCPD_B_OUT16    +0.06    -17.72   -131.83   -131.98    
C1:HPC-DCPD_A_OUT16    +0.07    +34.12   +174.63   +164.24    
C1:HPC-DCPD_B_OUT16    +0.13    +17.60   +131.31   +131.49    
Power at DCPD_A        19 uW    63 uW    278 uW    290 uW    
Power at DCPD_B        19 uW    65 uW    393 uW    404 uW    
Power at viewport A    -- uW    82 uW    350 uW    337 uW    
Power at viewport B    -- uW    64 uW    436 uW    431 uW

DCPD calibration:
 - From the measurements above, counts/W in IN1 can be calculated as follows. Offset of 19 uW is substracted from the measured power to take into account for background light.

C1:LSC-DCPD_A_IN1     -3.59e+05 counts/W
C1:LSC-DCPD_B_IN1     -3.61e+05 counts/W
C1:HPC-DCPD_A_IN1     -3.60e+05 counts/W
C1:HPC-DCPD_B_IN1     -3.57e+05 counts/W

Discussion:
 - DCPD calibration shows that DCPD to ADC itself is quite balanced within 1%. A factor of 1.8-1.9 seen was from unbalanced light between A path and B path (40m/17037).
 - Power expected for ITM single bounce to one of DCPDs is ~520 uW, but was 350-430 uW as measured right after the viewport. Power at A is significantly less than that for B. Note that power at AS55 was as expected (40m/16952). Also, clipping cannot be reduced by moving suspensions. These could mean that clipping is happening after AS2.

950 mW * 0.9 (IMC transmission?) * 5.637%(PRM) * 97.8%(PR2) * 50%(BS) * 98.6%(ITM) * 50%(BS) * 10%(SRM) * 90%(AS2) * 50%(BHDBS) = 520 uW

 - Power expected for LO beam to one of DCPDs is ~530 uW, but was 60-80 uW as measured right after the viewport. Power at A is significantly more than that for B, which is opposite for ITM single bounce. This could mean that something is happening at BHDBS? We are not sure why the power is so low. Are we seeing some ghost beam? For PR2 transmission, 22000 ppm was used for calculation, from 40m/16541.

950 mW * 0.9 (IMC transmission?) * 5.637%(PRM) * 2.2%(PR2) * 50%(BHDBS) = 530 uW

 - As far as we remember, beam shapes were not as bad when we closed out the chambers...

Next:
 - Check if measured power explains the visitivity of LO-ITM single bounce (40m/17020)
 - If not, what is the mode mismatch? Is it possible to explain the mode mismatch with deviations from designed mode-matching telescope?
 - Measure POP power to see if PR2 actually have T=2.2%
 - Play with LO1 and LO2 to invesitate LO beam shape and power
 - Check coherence between LO/AS power fluctuations with suspension motions
 - What is the expected counts/W for these DCPDs?
 - Balance the optical paths in ITMX table for A and B (same lenses, same mirrors)
 - Install better lens in front of camera

{Yuta, Yehonathan}

We went to the BS table to check the POP beam power. We first notice that the POP beam has a nice gaussan profile on the viewing card. We traced it the beam to the viewing port and measured the power there. Before measuring the power we misalign ITMY/ITMX to get rid of interferences. We measure the beam to be 205uW in both cases.

The expected power is

950 mW * 0.9 (IMC transmission?) * 5.637%(PRM) * 97.8%(PR2) * 50%(BS) * 98.6%(ITM) * 50%(BS)  * 2.2%(PR2) = 260uW

which is reasonably close to what we measure which confirms that PR2 transmission is around what we think it is.

This strengthen our suspicion that LO beam gets clipped somewhere.

We also improved the clipping on the POP camera by one of the beamsplitters along the beam path and the alignment to the POPDC PD (~100 cts before, ~ 1000 cts after).

[Yuta, Tega]

From our previous work (elog 17044) of shaking PR2 and seeing a signal in DCPD_A and the fact that LO beam power is far smaller than the expected nominal value, we decided to use TT1 and TT2 to realign the LO beam. This resulted in LO beam power going up by a factor of 6 and an improvement in the LO beam shape. We are still unable to find LO and AS alignment which realize BHD fringe with no clipping everywhere.

Deformed LO beam issue: Following the TT1 and TT2 alignments, used PR2 and PR3 to recover the transmission of the X and Y arms to 1. We also used LO1 and LO2 offsets to further reduce the beam deformation by eliminating the HOM concentric fringes that surounded the LO beam and to maximize the DCPD outputs. BHD optics in ITMY table was tweaked a lot to keep the LO beam centered on the BHD DCPDs and camera. The improved LO beam is still astigmatic in the yaw direction but at least now looks like a TEM00 mode. We also repositioned the DCPD_A path camera lens to remove the circular diffused fringes due to lens clipping. After the alignment, power was measured to be the following. It also reduced the coherence between DCPD outputs and suspension motions (see attached).

                       LO         ITMX
C1:HPC-DCPD_A_OUT16    +127.50    +96.24 (ITMX single bounce consistent to 40m/17040)
C1:HPC-DCPD_B_OUT16    +120.51    +141.52
Power at viewport A    504 uW (almost as expected 40m/17040)
Power at viewport B    385 uW

AP table AS beam clipping: We also noticed clipping in the AS beam in AP table which we removed by moving SR2 and AS1 in YAW and then used AS4 to keep the BHD AS beam centered in the BHD DCPDs.

BHD fringe: After overlaping the LO and AS beams, we saw diagonal fringes indicating beam tilt of LO wrt AS, so we tried to remove the AS beam tilt using AS1 and AS4 but failed to do so because the AS4 mirror seemed to completely distort the beam, so intead we decided to use SR2 and AS1 to remove the tilt between LO and AS beams, which realized BHD fringe. But the motion of SR2 and AS1 then moved the AS beam that it is no longer seen in AP table. The alignment to realize LO and AP AS beam without clipping, and that to realize BHD fringe are attached.

2PM: Arrived at the 40m. Started the work for the coupling of the RF modulated LO beam into a fiber. -> I left the lab at 10:30 PM.

The fiber coupling setup for the phase-modulated beam was made right next to the PSL injection path. (See attachment 1)

• For the alignment of the beam, the main PSL path, including the alignment of the 2" PO mirror, has not been touched.
• There are two PO beams with the optical power of 0.8mW (left) and 1.6mW (right). Both had been blocked but the right one was designed to be used for PSL POS and ANG. For the fiber coupling, the right beam was used.
• The alignment/mode-matching work has been done with a short (2m?) fiber patch cable from Thorlabs. The fiber is the same as the one used for LO delivery.
• I tried to have a mode-matching telescope in the LO path. I ended up having no lens for the best result. The resulting transmitted power is 1.21mW out of 1.64mW incident (~74%). These powers were measured with the Ophir power meter. (Note that Thorlabs' fiber power meter indicated 1.0mW transmission.)

Some notes

• After the PSL activity, the IMC locking was checked to see if I messed up the PSL alignment. It locks fine and looks fine.
  • The input shutter (left closed after Jon's vacuum work?) was opened.
  • The alignment was not optimal and had some pitch misalignment (e.g. TEM03).
  • After some MC SUS alignment, the automatic locking of TEM00 was recovered. Mainly MC3 pitch was moved (+0.17).
  • I've consulted with Gautam and he thinks this is with the level of regular drift. The AS beam was visible.
• The IMC and MI were moving so much, but this seemed just the usual Saturday night Millikan shake.
• During the activity, the PSL HEPA was turned up to 100 and it was reverted to 33 after the work.
• I have been wearing a mask and gloves throughout the work there.

The Rich demod box wants 10dBm for the local oscillator inputs, so I measured the values that we have coming out of the distribution box.  I'm using the "Spare 55MHz" and the "POP11" outputs, both of which had terminators so were not in use. 

The 55MHz had ~600mV peak, so between 5 and 6 dBm. 

The 11MHz had ~800mV peak, so about 8 dBm.

This is not enough dBm for either.  Going in search of RF amplifiers now...

I'm not sure I agree with your conversions, BUT:

The IQ boards use a PE4140, fancy MOSFET array as the mixer, and according to Peregrine (manufacturer), they can be operated with 0-20 dBm LO drive. I'm not recommending we drive them at 0 dBm, but perhaps the numbers you mentioned are OK.

Actually, the LO inputs to the IQ boards have AP1053 (Cougar) amps on them. These are 10 dB amps and so putting 10 dBm in puts us on the very maximum of the LO range at 20 dBm.

I think the distribution box levels are fine. 

 Yeah, I looked and saw that it's a semiconductor mixer, so it doesn't have to be as perfect. 

Everything is plugged in now to the new demod board.  More details soonly...

The I & Q outs are plugged into whitening filter #3, channels 5-8.  11MHz I = chan 5, 11MHz Q = chan 6, 55MHz I = chan 7, 55MHz Q = chan 8.  These channels are probably already recorded, but I haven't checked yet.  Hopefully I'll have time tonight after I pack for my trip.  But Zach, can you look into it tomorrow just to check??  Backup plan is to just go back to using the AS11 and POP55 boards and channels if the new board isn't doing what it's supposed to.

I disconnected the 3rd and 4th channels of the demod box since they were drawing unnecessary current, and making the box hot.  Now the box is just warmish.

In order to check the proper LO level, the IMC demod board was checked. As a short summary, -8dBm is the proper input for the IMC demod board. This was realized when the variable attenuator of the RF AM Stabilizer was set up be -7dB.

Initially, I tried to do the measurement using the extender board. But every board had the issue of +15V not working. After several extender boards were tried, I noticed that the current draw of the demod board burned the 15V line of the extender board.

Then I moved to the work bench. The signals were checked with the 10:1 probe. It's not properly the 50Ohm system, exactly to say.

I found that the LO signals at the mixers have huge distortion as it reaches the nominal 17dBm, and I wondered if ERA-5s were gone. Just in case I replaced the ERA-5s but didn't see any significant change. Then I thought it is due to the mixer itself. The mixer was removed and replaced with a 50Ohm SMD resister. Then the output of the last ERA-5 became sinusoidal, and the level was adjusted to be ~17dBm (4.52 Vpp) when the input power was measured to be -7.7dBm with the RF power meter. Once the mixer was reinstalled, it was confirmed that the waveform becase rectangular like, with the similar amplitude (4.42Vpp).

Now the module was returned to the rack. The RF level at the LO input was adjusted to be -8dBm by setting the attenuator level to be 7dBm.

Once the IMC is locked with this setting, the open loop transfer function was measured. The optical gain seemed almost unchanged compared with the recent nominal. The UGF and PM were measured to be 144kHz and 30deg.

Hmmm. Very non-standard demod. From the photo, looks like someone did some surgery with the attenuators (AT1, AT2, AT3) in the LO path. (might be me from a long time ago).

-8 dBm input to a circuit is a not a low noise situation. It would be best to remove the amplifiers in the I&Q paths and just have a single amplifier in the main path. Ideally we want the LO to never go below -3 dBm and certainly not below 0 dBm while outside of the board.

I doubt that all of the LSC demods were modified in this way - this one ought to get some sharpie or stickers to show its difference.

I didn't finish making the DCC entry for this module yet.

But the attenuators are
- AT1: 10dB. There is a sign that it was 3dB before ---  a 3dB chip was also attached on the boardnext to 10dB.
- AT2/3: Removed. They were replaced with 0Ohm resistors.

Currently the input is -8dBm. The input and output of the first ERA-5 are -17dBm and +7dBm, respectively.
Then the input and output of the second ERA-5 are -2dBm and 17dB, respectively.

In order to remove the second amplification stage, the first stage has to produce 26dBm. This is too much for either ERA-5 or any chips that fits on the foot print. If we use low gain but high output amp like GVA-81 (G=10dB, DF782 package), it is doable

Input 0dBm - [ATTN 3] - -3dBm - [ERA-5 G=20dB] - +16~+17dBm - [Circuits -9dB] - +7dBm - [Attn 0dB] - +7dBm - [GVA-81 G=10dB] - +17dBm

I think we should check the conditions of all the LSC demods.

Awwww. I found that the demod board has the power splitter (PSCJ-2-1) with one output unterminated.
This power splitter should be removed.

https://dcc.ligo.org/D1500443

Perhaps we can replace T1 with a mini-circuits hybrid 0-90 deg splitter and then remove the trim caps. (JSPQ-80, JYPQ-30, SCPQ-50)

I checked the RF levels at the LSC LO distribution box, with the agilent scope and a handful of couplers. This was all done with the Marconi at +13dBm. 

I only checked the channels that are currently in use, since the analyzer only measures 3 channels at a time, and rewiring involves walking back and forth to the IOO rack to make sure unpowered amps aren't driven, and I was getting hungry. 

For the most part, the LO levels coming into the LSC demod boards are all around +1.5dBm (i.e. I measured around -18.0dBm out of the ZFDC-20-5 coupler, which has a nominal 19.5dB coupling factor)

The inputs piped over from the IOO rack, labeled as "+6dBm" were found to be 4.7dBm and 2.9dBm for 11Mhz and 55MHz, respectively. 

The 2F signals were generally about 40dB lower, with two exceptions:

• REFL165's ~332MHz signal was around -18dBc
• POP22 had many more visible harmonics than any other LO signal
  • 11MHz: -32 dBc
  • 33MHz: -32 dBc
  • 44Mhz: -15dBc 

Here are the raw numbers I measured out of the couplers, all in dBm:

• 11MHz in: -14.8
• 55MHz in: -16.6
• POX11:    -18.7
• POY11:    -18.0
• REFL11:   -18.0
• REFL33:   -18.3
• POP110:   -17.9
• AS110:    -18.1
• POP22:    -19.9
• REFL165:  -18.5
• AS55:     -18.6
• POP55:    -18.8 (this port is used as the REFL55 LO)

T1000461 tells us that the nominal LO input is 2dBm although we don't know what's the LO level is at the mixers in the demod boards.

Locked the LO phase with a MICH offset=+91. The LO is midfringe (locked using the A-B zero crossing), so it's far from being "useful" for any readout but we can at least look at residual noise spectra.

I spent some time playing with the loop gains, filters, and overall lock acquisition, and established a quick TF template at Git/40m/measurements/BHD/HPC_LO_PHASE_TF.xml

So far, it seems that actuating on the LO phase through LO2 POS requires 1.9 times more strength (with the same "A-B" dc sensing). After closing the loop by FM4, and FM5, actuating on LO2 with a filter gain of 0.4 closes the loop robustly. Then, FM3 and FM6 can be enabled and the gain stepped up to 0.5 without problem. The measured UGF (Attachment #1) here was ~ 20 Hz. It can be increased to 55 Hz but then it quickly becomes unstable. I added FM1 (boost) to the HPC_LO_PHASE bank but didn't get to try it.

The noise spectra (Attachment #2) is still uncalibrated... but has been saved under Git/40m/measurements/BHD/HPC_residual_noise_spectra.xml

I tried some LO PHASE noise coupling measurements today. With MICH locked using AS55_Q, I control the LO phase using the single RF (BH55_Q) or double RF (BH44_Q) demodulation error signals. The calibrated error and control points for single RF sideband sensing are shown in Attachment #1. In either case feedback loop is closed using FM5, FM8 first with a gain of 1.5 and then a "boost" using FM4. The actuation point is LO1 POS and the UGF was measured to be ~ 35 Hz for both.

** While doing this measurement, I noticed our LO_PHASE dark noise is significantly contributing 180 Hz, 300 Hz and other high line harmonics into the control signal rms so that may be something to look into soon.

I first thought I could use the remaining sensor to measure the noise coupling (e.g. BH44 locks LO phase and BH55 senses injected noise or viceversa), but these two sensing schemes give two different LO phase sensitivities so I decided to just use the calibrated control signals.

-- Noise coupling for BH55_Q --

After locking the LO_PHASE I inject 2 Hz wide uniform noise into three different frequency bands *within the control bandwidth* through C1:SUS-LO2_LSC_EXC, C1:SUS-AS1_LSC_EXC, and C1:SUS-AS4_LSC_EXC. The injected noise settings are captured by Attachment #2 (the screenshot of the excitation settings in diaggui).

I read back the calibrated C1:HPC-LO_PHASE_OUT_DQ representing the true LO_PHASE noise within the control bandwidth and also calibrate the injected noise spectra with the help of the actuation coefficients in [elog40m:17274]. The result is summarized in Attachment #3.

The diaggui template and data for this measurement are saved under /opt/rtcds/caltech/c1/Git/40m/measurements/BHD/BH55Q_NoiseCoupling.xml

-- Noise coupling for BH44_Q -- 

I repeat the same procedure as above and the injected noise settings, and the result is summarized in Attachment #4. 

The diaggui template and data for this measurement are saved under /opt/rtcds/caltech/c1/Git/40m/measurements/BHD/BH44Q_NoiseCoupling.xml

- Discussion -

It seems that noise injected along the AS beam path (AS1-AS4 dither) couples more into the control point of the LO phase. I also seem to be off in terms of calibrating the noise excitation (even though I scaled using the suspension actuation from [elog40m:17274]. General feedback on the methods used for this measurement are welcome of course. 

- Next steps - 

    - Extend this to single RF + audio dither scheme and double audio dither schemes (although it's hard because the control bandwidth is pretty low already)
    - Investigate line noise in RFPD + demod chain (present on the dark noise). 
    - Investigate other more interesting noise couplings, e.g. angular degrees of freedom, RIN, laser freq noise, etc...
    - Repeat under more relevant IFO configurations (e.g. FPMI)

{Yuta, Yehonathan}

Today we lock LO phase using audio+RF method in two variants: AS1+RF and MICH(BS)+RF. We measure the TFs and find that AS1 variant has a UGF ~ 17Hz and MICH variant has a UGF ~ 32Hz.

Details

1. We lock MICH in the usual way using AS55. ITMs are aligned to make AS port dark. We use a single bounce and optimize mode-matching with LO beam by minimizing the BHDDC-A signal.

2. Using the new BHD Homodyne phase control MEDM screen we first try AS1. We put an elliptic filter with 80Hz corner frequency on the DEMOD1 filter bank. We find that the notch of that filter is at 281.768Hz and this is where we put the AS1 dither line.

AS1 is dithered with 20000 counts. We optimize the DEMOD1 demodulation angle by dithering LO1 at 27Hz and minimizing the Q quadrature in diaggui. We find that 45 degrees is the optimal demod angle. We lock the LO phase with a gain of ~ 45 and take the OLTF (attachment 1).

3. Next, we use MICH degree of freedom to lock LO phase. We dither BS with the same frequency as before with 4000 counts. Higher counts seem to put some offset on ASDC. As before we optimize the DEMOD1 demod angle and find it to be 115deg. We lock LO phase with a gain of 20 and take the OLTF (attachment 2).

[Yuta, Paco]

Today we locked LO phase with BH55 + Audio dithering

Configuration

We worked with MICH locked using AS55_Q with an offset = 50. Our BH55_Q_ERR is the same as in the previous elog (in this thread). We enabled audio dithering of AS1 to produce 280.54 Hz sidebands (exc gain = 15000). We used ELP80 (elliptic, 4th order lowpass with the second resonant notch at 280.54 Hz) at the BH55_Q_AS1_DEMOD_I output. This allowed us to generate an error signal to feedback into AS1 POS. Attachment #1 shows a screen capture of this configuration.

Lock

We close a loop with the above configuration to lock the LO phase using only filters FM5, FM8 and then optionally boost with FM2. The compromise we had to make because of our phase margin was to achieve UGF ~ 20 Hz (in contrast with ~ 70 Hz used in single bounce). Attachment #2 shows the measured OLTFs for LO_PHASE control using this scheme; the red was the final measured loop, while the blue was our initial reference before increasing the servo gain.

[Yuta, Paco]

Today we again locked the LO phase with BH55 + Audio dithering under a zero-offset MICH

Configuration

We worked with MICH locked using AS55_Q with an offset = 0. Our BH55_Q_ERR is the same as in the previous elog (in this thread).We reduced the MICH offset from 50 to 0 slowly and kept an eye on the BH55 error signals. We realized that at zero offset, most of the error signal was in BH55_I_ERR (why?) so we rotated it back to BH55_Q_ERR (146 deg --> 56 deg). We then looked at the audio demod angle, and optimized it to allocated the error signal in the I quadrature (-15 deg --> 40 deg).

Lock

We close a loop with the above configuration to lock the LO phase using only filters FM5, FM8 and then optionally boost with FM2. The measured UGF ~ 20 Hz similar to the configuration with an offset present; and it seems there is some residual noise at ~ 20 Hz (observed in the residual error signal time trace with ndscope).

Next tasks:

• Noise budget residual error in this configuration
• Investigate negative count offset in DCPDs
• Investigate why does the rotation angle change from single bounce to MICH?

[Paco, Yuta]

We are still struggling with locking LO phase in MICH or ITM single bounce with BH55 with audio dither.
Without audio dither, BH55 can be used to lock.

What works:
 - LO phase locking with ITMX single bounce, using BH55_Q
  - BH55_Q configuration: 45 dB whitening gain, with whitening filter on.
  - C1:LSC-BH55_PHASE_R=147.621 deg gives most signal in BH55_Q.
  - LO phase can be locked using BH55_Q, C1:HPC-LO_PHASE_GAIN=-0.5 (bright fringe for A, dark for B), feeding back to LO1 gives UGF of ~80Hz (funny structure in ~20 Hz region; see Attachment #1)

 - LO phase locking with ITMX single bounce, using BHDC_DIFF
  - BHDC B/A = 1.57 (gain balanced with C1:HPC-IN_MTRX)
  - LO phase can be locked using BHDC_DIFF, C1:HPC-LO_PHASE_GAIN=-0.4 (mid-fringe lock), feeding back to LO1 gives UGF of ~50 Hz (see Attachment #2).

 - LO phase locking with MICH locked with AS55_Q, using BH55_Q
  - AS55_Q configuration: 24 dB whitening gain, with whitening filter off
  - C1:LSC-AS55_PHASE_R=-150 deg gives most signal in AS55_Q
  - MICH can be locked using AS55_Q, C1:LSC-MICH_GAIN=-10, C1:LSC-MICH_OFFSET=30 (slightly off from AS dark fringe), feeding back to 0.5*BS gives UGF of ~100Hz (see Attachment #3)
  - LO phase can be locked using BH55_Q, C1:HPC-LO_PHASE_GAIN=-0.8 (bright fringe for A, dark for B), feeding back to LO1 gives UGF of ~45Hz (see Attachment #4)

 - LO phase locking with MICH locked with AS55_Q, using BHDC_DIFF
  - LO phase can be locked using BHDC_DIFF, C1:HPC-LO_PHASE_GAIN=1 (mid-fringe lock), feeding back to LO1. Not a very stable lock.

What does not work:
 - LO phase locking using BH55_Q demodulated at LO1 (or AS1) dither frequency, neither in ITMX sigle bounce or MICH locked with/without offset using AS55_Q
  - C1:HPC-AS1_POS_OSC_FREQ=142.7 Hz, C1:HPC-AS1_POS_OSC_CLKGAIN=3000, C1:HPC-BH55_Q_AS1_DEMOD_PHASE=-15 deg, BLP30 is used.
  - Attachment #5 shows error signals when LO phase is locked with BH55_Q. BHDC_DIFF and BH55_Q_AS1_DEMOD_I having some coherence is a good indication, but we cannot lock LO phase with BH55_Q_AS1_DEMOD_I yet.
  - Also, injection at 13.14 Hz with an amplitude of 300 for AS1 can be seen in both BH55_Q and BH55_Q_AS1_DEMOD_I (26 Hz peak for BHDC_DIFF, as it is quadratic, as expected), which means that BH55_Q_AS1_DEMOD_I is seeing something.

Next:
 - Check actuation TFs for LO1, LO2, AS1 too see if there are any funny structures at ~ 20 Hz.
 - LO phase locking might require at least ~50 Hz of UGF. Use higher audio dither frequency so that we can increase the control bandwidth.
 - Check analog filtering situation for BHDC_A and BHDC_B signals (they go minus when fringes are moving fast)

[Anchal, Paco]

We started the day by taking a spectrum of C1:HPC-LO_PHASE_IN1, the BHD error point, and confirming the absence of 268 Hz peaks believed to be violin modes on LO1. We then locked the LO phase by actuating on LO2, and AS1. We couldn't get a stable loop with AS4 this morning. In all of these trials, we looked to see if the noise increased at 268 Hz or its harmonics but luckily it didn't. We then decided to add the necessary output filters to avoid exciting these violin modes. The added filters are in the C1:SUS-LO1_LSC bank, slots FM1-3 and comprise bandstop filters at first, second and third harmonics observed previously (268, 536, and 1072 Hz); bode plots for the foton transfer functions are shown in Attachment #1. We made sure we weren't adding too much phase lag near the UGF (~ 1 degree @ 30 Hz).

We repeated the LO phase noise measurement by actuating on LO1, LO2 and AS1, and observe no noise peaks related to 268 Hz this time. The calibrated spectra are in Attachment #2. Now the spectra look very similar to one another, which is nice. The rms is still better when actuating with AS1.

[Paco]

After the above work ended, I tried enabling FM1-3 on the C1:HPC_LO_PHASE control filters. These filters boost the gain to suppress noise at low frequencies. I carefully enabled them when actuating on LO1, and managed to suppress the noise by another factor of 20 below the UGF of ~ 30 Hz. Attachment #3 shows the screenshot of the uncalibrated noise spectra for (1) unsupressed (black, dashed), (2) suppressed with FM4-5 (blue, solid), and (3) boosted FM1-5 suppression (red).

Next steps:

• Compare LO-ITMY and LO-ITMX single bounce noise spectra and MICH.
• Compare DC locking scheme versus BH55 once it's working.

I drafted a calibrated LO Phase noise budget using diaggui whose template is saved under /opt/rtcds/caltech/c1/Git/40m/measurements/BHD/LO_PHASE_cal_nb.xml which includes new estimates for laser frequency and intensity noises at the LO phase when MICH is locked (whether they couple through MICH or the LO path is to be determined with noise coupling measurements in the near future, but we expect them to couple through the LO phat mostly).

Attachment #1 shows the result.

Laser Frequency Noise

To calibrate the laser frequency noise contribution, I used the LO PHASE error point away from the control bandwidth (~ 20 Hz) and the calibrated C1:IOO-MC_F control point (in Hz) which should represent the laser frequency noise above 100 Hz. and dithered MC2 at frequencies around to 130, 215, and 325 Hz to match the LO phase error point with the MC_F signal. I was expecting to use a single 0 Hz pole + gain (to get the phase equivalent of the laser frequency noise) but in the end I managed to calibrate with a single gain of 3.6e-7 rad/Hz and no pole. Since the way the laser frequency noise couples into our BHD readout may be complicated (especially when using BH55 RF sensor) I didn't think much of this for now.

Laser Intensity Noise

For the intensity noise, I followed more or less a similar prescription as for laser frequency noise. This time, I used the AOM in the PSL table to actuate on the 0th order intensity going into the interferometer. Attachments #2-3 show the connection made to the RF driver where I added a 50 mVpp sine (at an offset of 0.1 V) excitation in the AM port to inject intensity noise calibration lines at 215 and 325 Hz and matched the LO_PHASE error point with the BHDC_SUM noise spectrum.

[Paco, Yuta]

MICH was locked with balanced homodyne readout with LO phase locked using BH55_Q and BH44_Q.
It turned out that BH44_Q gives better LO phase in MICH configuration (in FPMI, BH55_Q is better; see 40m/17506).
LO phase noise seems to contribute to MICH sensitivity in 30-200 Hz region in BH55 case, and 30-100 Hz in BH44 case (this was not the case in FPMI BHD, see 40m/17392).
The mechanism for this coupling needs investigation.

MICH BHD sensing matrix:
 - MICH BHD sensing matrix was measured when MICH is locked with AS55_Q and LO_PHASE is locked with BH55_Q or BH44_Q.
 - MICH UGF was at around 50 Hz, and LO_PHASE UGF was at around 10 Hz.
 - BHDC_DIFF had better sensitivity to MICH when LO_PHASE was locked with BH44_Q.
 - BH44 component was not measured well.

MICH sensing matrix with MICH locked with AS55_Q and LO_PHASE locked with BH55_Q

Sensing matrix with the following demodulation phases (counts/m)
{'AS55': 2.1, 'REFL55': 76.01784975834194, 'BH55': -63.16236453101908, 'BH44': -39.01036239539396}
Sensors       MICH @311.1 Hz           LO1 @315.17 Hz           
AS55_I       (+0.40+/-6.23)e+07 [0]    (-0.83+/-3.01)e+07 [0]    
AS55_Q       (+1.38+/-0.26)e+09 [0]    (+0.76+/-6.58)e+07 [0]   
BH55_I       (-3.22+/-0.37)e+09 [0]    (-0.81+/-8.42)e+07 [0]    
BH55_Q       (+4.03+/-0.52)e+09 [0]    (-4.01+/-1.05)e+08 [0]    
BH44_I       (-0.06+/-4.22)e+10 [0]    (+0.29+/-4.63)e+10 [0]    
BH44_Q       (-0.03+/-3.21)e+11 [0]    (+0.21+/-3.12)e+11 [0]    
BHDC_DIFF       (-1.07+/-0.39)e+09 [0]    (-3.35+/-7.47)e+07 [0]    
BHDC_SUM       (+2.07+/-0.57)e+08 [0]    (+0.32+/-1.65)e+07 [0]

MICH sensing matrix with MICH locked with AS55_Q and LO_PHASE locked with BH44_Q

Sensing matrix with the following demodulation phases (counts/m)
{'AS55': 2.1, 'REFL55': 76.01784975834194, 'BH55': -63.16236453101908, 'BH44': -39.01036239539396}
Sensors       MICH @311.1 Hz           LO1 @315.17 Hz           
AS55_I       (+0.22+/-5.36)e+07 [0]    (+0.91+/-3.10)e+07 [0]    
AS55_Q       (+1.43+/-0.08)e+09 [0]    (-0.78+/-7.45)e+07 [0]   
BH55_I       (+4.92+/-5.18)e+08 [0]    (-5.20+/-7.93)e+07 [0]    
BH55_Q       (-1.45+/-0.75)e+09 [0]    (+1.76+/-0.59)e+08 [0]    
BH44_I       (+0.01+/-1.14)e+11 [0]    (+0.02+/-1.08)e+11 [0]    
BH44_Q       (+0.03+/-1.95)e+11 [0]    (+0.07+/-1.98)e+11 [0]    
BHDC_DIFF       (+3.05+/-0.17)e+09 [0]    (+1.70+/-2.51)e+07 [0]    
BHDC_SUM       (-2.33+/-0.23)e+08 [0]    (+0.19+/-1.53)e+07 [0]

  - Jupyter notebook: /opt/rtcds/caltech/c1/Git/40m/scripts/CAL/SensingMatrix/ReadSensMat.ipynb

MICH BHD locking:
 - MICH lock with AS55_Q was handed over to BHD_DIFF using following ratio:
C1:LSC-PD_DOF_MTRX_3_4 = 1 (AS55_Q to MICH_A)
C1:LSC-PD_DOF_MTRX_4_34 = -1.34 (BHDC_DIFF to MICH_B, when BH55_Q is used)
C1:LSC-PD_DOF_MTRX_4_34 = 0.47 (BHDC_DIFF to MICH_B, when BH44_Q is used)

MICH BHD noise budget:
 - FM2 of C1:CAL-MICH_CINV was updated to 1/1.4e9 = 7.14e-10 to use measured optical gain.
 - Dark noise was measured at C1:CAL-MICH_W_OUT with PSL shutter closed, PD DOF matrix at various settings for various readout scheme.
 - Attachment #1 shows MICH sensitivity with MICH locked using AS55_Q (green), BHD_DIFF under BH55_Q (blue), BHD_DIFF under BH44_Q (red). BH44 case gives the least noise due to larger optical gain. However, there are excess noise at around 100 Hz, when MICH is locked with BHD_DIFF. The excess noise (bump at around 50 Hz) was similar to what we saw in LO phase noise estimate (40m/17511).
 - At low frequencies below ~30 Hz, the MICH sensitivity is probably limited by seismic noise, as it alignes with FPMI DARM sensitivity (orange curve; measured in 40m/17468).
 - Attachemnt #2 and #3 show estimate of LO phase noise contribution to MICH sensitivity in BH55 case and BH44 case. The coupling was estimated by measuring a transfer fuction from BH55_Q/BH44_Q to MICH_W_OUT. As there was significant coherence in 30-200 Hz region in BH55 case, and 30-100 Hz in BH44 case, transfer function value in that regions was used to estimate the coupling.
 - The coupling was estimated to be the following

 2e-10 m/count for BH55_Q to MICH_W_OUT (0.035 m/m using BH55_Q calibration factor to LO1 motion of 1.76e8 counts/m)
 2e-11 m/count for BH44_Q to MICH_W_OUT

 - Diaggui file: /opt/rtcds/caltech/c1/Git/40m/measurements/LSC/MICH/MICH_Sensitivity_Live.xml

Next:
  - Calibrate BH44_Q to LO1 motion
  - Measure transfer function from LO1 motion to BHD_DIFF under BH44 and BH55
  - Find out the cause of 50 Hz bump in LO phase noise
  - Compare LO phase noise coupling with simulations

[Anchal, Yuta]

We have measured LO phase noise in ITMX single bounce, simple MICH and FPMI configurations with LO phase locked with BH55 or BH44.
We found that BH55 and BH44 have almost exactly same noise in ITMX single bounce, but BH44 is noisier than BH55 in MICH and FPMI configurations.
In any case, LO phase can be locked within 0.1 rad RMS, so optical gain fluctuations in BHD_DIFF should be fine for BHD locking.

Method:
 - We have locked ITMX single bounce vs LO, AS beam under MICH locked with AS55_Q vs LO, and AS beam under FPMI locked with REFL55 & AS55 vs LO, using BH55_Q or BH44_Q
 - In each IFO configuration, we have minimized I phase to set RF demodulation phases for BH55 and BH44.
 - In each IFO configuration, optical gain of BH55_Q and BH44_Q was measured by elliptic fit of X-Y plot for BH55_Q vs BHDC_A or BH44_Q vs BH55_Q.
 - For each LO_PHASE lock, feedback gain was adjusted to set the UGF to around 50 Hz, and actuator used was LO1.
 - LO_PHASE_IN1 was calibrated using the measured optical gain, and LO_PHASE_OUT was calibrated using LO1 actuator gain of 26.34e-9 /f^2 m/counts measured in 40m/17285.
 - To convert meters in radians, 2*pi/lambda is used (which means dark fringe to dark fringe is pi).
 - Below summarizes the result of RF demodulation phases and optical gains (whitening gains were 45 dB for BH55 and 39 dB for BH44). RF demod phases aligns well with previous measurement, but optical gain for BH44 seems higher by an order of magnitude compared with 40m/17478 (whitening gain changed??). Optical gain for BH55_Q is consistent with previous measurement in 40m/17506 (note the demodulation phase change).

LO_PHASE lock in ITMX single bounce
        Demod phase  Optical gain     filter gain
BH55_Q  -99.8 deg    7.6e9 counts/m   -0.3
BH44_Q  -6.5 deg     1.3e10 counts/m  -0.15

LO_PHASE lock in MICH
        Demod phase  Optical gain     filter gain
BH55_Q  -67.7 deg    6.1e8 counts/m   -3.9
BH44_Q  -31.9 deg    8.5e8 counts/m   -3.1

LO_PHASE lock in FPMI
        Demod phase  Optical gain     filter gain
BH55_Q  35.7 deg     3.4e9 counts/m   -0.65
BH44_Q  -9.3 deg     4.3e10 4.3e9 counts/m  -0.84  (Typo fixed on Apr 18, 2023 by YM)

Result:
 - Attached are calibrated LO phase noise spectrum in different IFO configurations.
 - In ITMX single bounce, LO phase noise estimated using BH55 and BH44 are almost equivalent, and LO phase noise in-loop is ~0.04 rad RMS.
 - In MICH, LO phase noise estimated using BH44 is noisier than BH44 at around 20-60 Hz for some reason. LO phase noise in-loop is ~0.04 rad RMS for both cases.
 - In FPMI, LO phase noise estimated using BH44 is noisier than BH44 above ~20 Hz for some reason. LO phase noise in-loop is ~0.03 rad RMS for both cases. Dark noise is not limiting the measurement at least below 1 kHz.

Jupyter notebook: /opt/rtcds/caltech/c1/Git/40m/measurements/BHD/BH55_BH44_Comparison.ipynb

Next:
 - Lock MICH BHD with BH55 and BH44, and compare LO phase noise contributions to MICH sensitivity
 - Investigate why BH44 is noisier than BH55 in MICH and FPMI (offsets? contrast defect? mode-matching?)
 - Reduce 60 Hz + harmonics in BH55 and BH44

[Anchal, Yuta]

We have repeated LO phase noise measurement done in elog 40m/17511.
Method we took was the same, but this time, we used (1+G)*[C1:HPC-LO_PHASE_IN1]/[optical gain] to estimate the free-running noise, instead of using [C1:HPC-LO_PHASE_OUT] multiplied by LO1 actuator gain.
We confirmed that both method agrees down to ~ 10 Hz (at lower frequencies, OLTF measurement is not robust; we used interpolated measured OLTF (Attachment #1) for compensation).
Below is the summary of optical gains etc measured today.
Filter gains were adjusted to have UGF of 50 Hz for all.

LO_PHASE lock in ITMX single bounce
        Demod phase  Optical gain     filter gain
BH55_Q  -102.7 deg    6.9e9 counts/m  -0.34
BH44_Q  -5.7 deg     1.3e10 counts/m  -0.17

LO_PHASE lock in MICH
        Demod phase  Optical gain     filter gain
BH55_Q  -72.6 deg    8.7e8 counts/m   -4.4
BH44_Q  -27.6 deg    8.8e8 counts/m   -2.2

LO_PHASE lock in FPMI
        Demod phase  Optical gain     filter gain
BH55_Q  24.2 deg     3.7e9 counts/m   -0.67
BH44_Q  2 deg        5.3e8 counts/m   -4.4  (An order of magnitude smaller than elog 40m/17511)

The values are consistent with elog 40m/17511, except for BH44 in FPMI.
It took sometime to robustly rock LO_PHASE with BH44_Q in FPMI today.
After some alignment, offset tuning and demod phase tuning, it finally worked.
Demod phase of BH44 was tuned to have more DC signal when LO_PHASE was locked with BH55_Q, considering that BH55 and BH44 are orthogonal.
It actually created BH44_I having more amplitude (some noise?) than BH44_Q, but BH44_Q was more coherent to LO_PHASE fringe in BH55_Q.
It might be related to why we are not dark noise limited for BH44_Q, while BH55_Q is dark noise limited in FPMI, and why we cannot lock FPMI BHD with BH44.

[Paco, Koji]

We took lo phase noise spectra actuating on the for different optics-- LO1, LO2, AS1, and AS4. The servo was not changed during this time with a gain of 0.2, and we also took a noise spectrum without any light on the DCPDs. The plot is shown in Attachment #1, calibrated in rad/rtHz, and shown along with the rms values for the different suspension actuation points. The best one appears to be AS1 from this measurement, and all the optics seem to show the same 270 Hz (actually 268 Hz) resonant peak.

268 Hz noise investigation

Koji suspected the observed noise peak belongs to some servo oscillation, perhaps of mechanical origin so we first monitored the amplitude in an exponentially averaging spectrum. The noise didn't really seem to change too much, so we decided to try adding a bandstop filter around 268 Hz. After the filter was added in FM6, we turned it on and monitored the peak height as it began to fall slowly. We measured the half-decay time to be 264 seconds, which implies an oscillation with Q = 4.53 * f0 * tau ~ 3.2e5. This may or may not be mechanical, further investigation might be needed, but if it is mechanical it might explain why the peak persisted in Attachment #1 even when we change the actuation point; anyways we saw the peak drop ~ 20 dB after more than half an hour... After a while, we noticed the 536 Hz peak, its second harmonic, was persisting, even the third harmonic was visible.

So this may be LO1 violin mode & friends -

We should try and repeat this measurement after the oscillation has stopped, maybe looking at the spectra before we close the LO_PHASE control loop, then closing it carefully with our violin output filter on, and move on to other optics to see if they also show this noise.

Yuta and I had a discussion last week about the signal strength between the configurations. Here are some naive calculations.
=== Please check the result with a more precise simulation ===

Michelson: Homodyne (HD) phase signal @44MHz is obtained from the combination of LO11xAS55 and LO CAxAS44. SBs at AS rely on the Schnupp asymmetry, the signal is weaker than the one with a single bounce beam from an ITM.

PRMI Carrier resonant:
- Despite the non-resonant condition of the sidebands, the HD phase signal @44MHz is expected to be significantly stronger (~x300) compared with the MI due to the resonance of the carrier and the 44MHz sidebands (the 2nd-order SBs of 11 and 55) in the PRC. Thus, the LO CAxAS44 term dominates the signal.
- The MICH signal @55MHz is enhanced by the resonant carrier by a factor of ~5.5, in spite of the non-resonant 55MHz SBs.
- The MICH signal @BHD is enhanced by the resonant carrier by a factor of ~300. This is the comparable phase sensitivity to PRFPMI case.

PRMI Sideband resonant:
- Despite the non-resonant condition of the carrier, the HD phase signal @44MHz is expected to be even stronger (~x400) compared with the MI due to the resonance of the 11MHz and 55MHz sidebands in the PRC. Thus, the LO11xAS55 term dominates the signal.
- The level of the MICH signal @55MHz is expected to be comparable to the one with PRMI carrier resonant as the resonant condition for the CA and 55MHz SBs are interchanged.
- The MICH signal @BHD is expected to be negligibly small due to non-resonance of the carrier.

PRFPMI: Now the carrier and the 11 and 55MHz sidebands are resonant.
- The HD phase signal @44MHz is expected to be the same level as the SB resonant PRMI, and the LO11xAS55 term dominates the signal.
- The level of the MICH sensitivity @AS 55MHz shows x300 of the MICH signal of the MI and x50 of the MICH with PRMI.
- The MICH signal @BHD is going to be the same level as the one with PRMI Carrier resonant.
- The DARM signal shows up at the dark port signal enhanced by x300 from the MICH level due to the finesse of the arms.

Simple assumptions
1) PRM has a transmission of T_PRM = 0.05
2) PRG is limited by the transmission of PR2 (T_PR2=0.02 per bounce).
    If the IFO is lossless, PRG is 25 (i.e. theoretical maximum). In reality, the IFO loss is 2~3% -> PRG is ~15.
    The asymmetry of 30mm has a negligible effect.
3) For the anti-resonant fields, APRG is ~T_PRM/4 = 0.0125
4) Arm finesse is 450. Therefore the phase enhancement factor N is ~300.
5) Modulation depth is ~0.1. J0=1, J1=0.05, J2=0.00125
6) Sideband leakage by the asymmetry is ɑ=l_asym wm / c = 0.008 for 11MHz and 5ɑ for 55MHz.

Single Bounce

The numbers are power transmission to each port
   Carrier              11MHz                    55MHz
LO TPRM TPR2 = 1.0e-3   J1^2 TPRM TPR2 = 2.5e-6  J1^2 TPRM TPR2 = 2.5e-6
AS TPRM/4    = 1.3e-2   J1^2 TPRM/4    = 3.1e-5  J1^2 TPRM/4    = 3.1e-5

LO phase @44MHz: LO 11 x AS 55 = Sqrt(2.5e-6 * 3.1e-5) = 8.8e-6

Michelson

   Carrier               11MHz                     55MHz                      44MHz
LO TPRM TPR2 = 1.0e-3    J1^2 TPRM TPR2 = 2.5e-6   J1^2 TPRM TPR2   = 2.5e-6
AS TPRM ε^2  = 0.05 ε^2  ɑ^2 J1^2 TPRM  = 8.0e-9   25 ɑ^2 J1^2 TPRM = 2.0e-7  16 ɑ^2 J1^4 TPRM = 3.2e-10

LO phase @44MHz: LO 11 x AS 55 = Sqrt(2.5e-6 * 2.0e-7)  = 7.1e-7
                 LO CA x AS 44 = Sqrt(1.0e-3 * 3.2e-10) = 5.7e-7

AS MICH  @55MHz: AS CA x AS 55 = Sqrt(0.05 * 2.0e-7) ε  = 1.0e-4 ε
AS MICH  @BHD:　 LO CA x AS CA = Sqrt(1.0e-3 * 0.05) ε  = 7.1e-3 ε

PRMI (Carrier Resonant)

   Carrier              11MHz                     55MHz                      44MHz
LO PRG TPR2 = 0.3       J1^2 APRG TPR2 = 2.5e-7   J1^2 APRG TPR2   = 2.5e-7  J1^4 PRG TPR2 = 1.9e-6
AS PRG ε^2  = 15 ε^2    ɑ^2 J1^2 APRG  = 8.0e-10  25 ɑ^2 J1^2 APRG = 2.0e-8  16 ɑ^2 J1^4 PRG = 9.6e-8

LO phase @44MHz: LO 11 x AS 55 = Sqrt(2.5e-7 * 2.0e-8)  = 7.1e-8
                 LO CA x AS 44 = Sqrt(0.3 * 9.6e-8)     = 1.7e-4
AS MICH  @55MHz: AS CA x AS 55 = Sqrt(15 * 2.0e-8) ε    = 5.5e-4 ε
AS MICH  @BHD:　 LO CA x AS CA = Sqrt(0.3 * 15) ε       = 2.1 ε
 

PRMI (Sideband Resonant)

   Carrier               11MHz                     55MHz                      44MHz
LO APRG TPR2 = 1e-4      J1^2 PRG TPR2 = 7.5e-4    J1^2 PRG TPR2   = 7.5e-4  J1^4 APRG TPR2 = 6.3e-10
AS APRG ε^2  = 5e-3 ε^2  ɑ^2 J1^2 PRG  = 2.4e-6    25 ɑ^2 J1^2 PRG = 6.0e-5  16 ɑ^2 J1^4 APRG = 3.2e-11

LO phase @44MHz: LO 11 x AS 55 = Sqrt(7.5e-4 * 6.0e-5)  = 2.1e-4
                 LO CA x AS 44 = Sqrt(1e-4 * 3.2e-11)   = 5.7e-8
AS MICH  @55MHz: AS CA x AS 55 = Sqrt(5e-3 * 6.0e-5) ε  = 5.5e-4 ε
AS MICH  @BHD:　 LO CA x AS CA = Sqrt(1e-4 * 5e-3) ε    = 7.1e-4 ε

PRFPMI

   Carrier             11MHz                     55MHz                      44MHz
LO PRG TPR2 = 0.3      J1^2 PRG TPR2 = 7.5e-4    J1^2 PRG TPR2   = 7.5e-4   J1^4 APRG TPR2 = 6.3e-10
AS PRG ε^2  = 15 ε^2   ɑ^2 J1^2 PRG  = 2.4e-6    25 ɑ^2 J1^2 PRG = 6.0e-5   16 ɑ^2 J1^4 APRG = 3.2e-11

LO phase @44MHz: LO 11 x AS 55 = Sqrt(7.5e-4 * 6.0e-5)  = 2.1e-4
                 LO CA x AS 44 = Sqrt(0.3 * 3.2e-11)    = 3.1e-6
AS MICH  @55MHz: AS CA x AS 55 = Sqrt(15 * 6.0e-5) ε    = 3.0e-2 ε  ==> DARM@55MHz 9.0 ε
AS MICH  @BHD:　 LO CA x AS CA = Sqrt(0.3 * 15) ε       = 2.1 ε     ==> DARM@BHD   6.3e2 ε

I'm checking Koji + Yuta's not-so-naive calculations using finesse.

PRMI Carrier resonant:
- The HD phase signal @44 MHz is estimated to be 386.5 times stronger.
- The MICH signal @BHD_DIFF is estimated to be enhanced by a factor of 299.75.

PRMI Sideband resonant:
- The HD phase signal @44MHz is estimated to be () stronger.
- The MICH signal @BHD_DIFF is estimated to be suppressed by a factor of

PRFPMI: Now the carrier and the 11 and 55MHz sidebands are resonant.
- The HD phase signal @44MHz is estimated to be ().
- The MICH signal @BHD_DIFF is estimated to be the same level as the one with PRMI Carrier resonant.

The frree swinging test was successful. I ran the input matrix diagonalization code (scripts/SUS/InMAtCalc/sus_diagonalization.py) on the LO1 free swinging data collected last night. The logfile and results are stroed in scripts/SUS/InMatCalc/LO1 directory. Attachment 1 shows the power spectral density of the DOF bassis data (POS, PIT, YAW, SIDE) before and after the diagonalization. Attachment 2 shows the fitted peaks.

0.12

0.137

0.338

0.321

0.004

1.282

1.087

-0.57

-0.375

-0.843

1.07

-0.921

-1.081

0.91

0.098

-0.042

0.383

0.326

-0.099

0.857

The new matrix was loaded on LO1 input matrix and this resulted in no control loop oscillations at least. I'll compare the performance of the loops in future soon.

We tracked the issue of LO1 LLCOIL not actuating LO1, and found that the DB9 cable from the coil driver to the sat amp was loose.
I tightened the screws and now it is working.
Never ever connect cables without screwing the connectors tightly!

What I did:
 - Measured the resistance and the inductance of each coil with BK PRECISION LCR meter, as I did for ITMY (Attachment #1, 40m/16896). The result is the following and it shows that LLCOIL is there.

Feedthru connector: LO1 1
Pin 3-15 / R = 16.0Ω / L = 3.27 mH (UL)
Pin 7-19 / R = 15.8Ω / L = 3.27 mH (UR)
Pin11-23 / R = 15.7Ω / L = 3.27 mH (LL)

Feedthru connector: LO1 2
Pin 3-15 / N/A
Pin 7-19 / R = 15.6Ω / L = 3.22 mH (SD)
Pin11-23 / R = 15.9Ω / L = 3.30 mH (LR)

 - Swapped the DB25 cable which goes to the feedthru LO1 1 and feedthru LO1 2. LLCOIL could be drived from LR coil driver and LRCOIL could not be drived from LL coil driver. SD and UR worked fine with the swap. This means that there is something wrong with the LL driving.
 - Went to see the rack which have coil drivers and sat amp for LO1, and immediately found that the DB9 cable was loose (Attachment #2). Tightened them and the issue was fixed.
 - C1:SUS-LO1_TO_COIL matrix gains were reverted to default values (Attachment #3).

I tuned the local damping gains for LO1, LO2, AS1, and AS4 by looking at step responses in the DOF basis (i.e. POS, PIT, YAW, and SIDE). The procedure was:

1. Grab an ndscope with the error point signals in the DOF basis, e.g. C1:SUS-LO1_SUSPOS_IN1_DQ
2. Apply an offset to the relevant DOF using the alignment slider offset (or coil offset for the SIDE DOF) while being careful not to trip the watchdog. The nominal offsets found for this tuning are summarized below:

3. Tune the damping gains until the DOF shows a residual Q with ~ 5 or more oscillations.
4. The new damping gains are below for all optics and their DOFs, and Attachments #1-4 summarize the tuned step responses as well as the other DOFs (cross-coupled).

Note that during this test, FM5 has been populated for all these optics with a BounceRoll (notches at 16.6, 23.7 Hz) filter, apart from the Cheby (HF rolloff) and the 0.0:30 filters.

I used the open light level output of 908 for ITMX side OSEM from 40m/16549 to roughly calibrate cts2um filter module in LO1 OSEM input filters. All values were close to 0.033. As the calibration reduces the signal value by about 30 times, I increased all damping gains by a factor of 30. None of loops went into any unstable oscillations and I witnessed damping of kicks to the optic.

In-loop power spectrum

I also compared in-loop power spectrum of ETMX and LO1 while damping. ETMX was chosen because it is one of the unaffected optics by the upgrade work. ITMX is held by earthquake stops to avoid unnecessary hits to it while doing chamber work.

Attachment 1 and 2 show the power spectrum of in-loop OSEM values (calibrated in um). At high frequencies, we see about 6 times less noise in LO1 OSEM channel noise floor in comparison to ETMX. Some peaks at 660 Hz and 880 Hz are also missing. At low frequencies, the performance of LO1 is mostly similar to EMTX except for a peak (might be loop instability oscillation) at 1.9 Hz and another one at 5.6 Hz. I'll not get into noise hunting or loop optimization at this stage for the suspension. For now, I believe the new electronics are damping the suspensions as good as the old electronics.

[Paco, Anchal]

Today we invested some time in the DW filters for LO1 supension. We discovered that the binary DW enable/disable channels were not connected, and we had basically postponed testing this final bit on the chain of new SUS electronics since the upgrade took place. A quick noise spectrum of error and control points (uncalibrated) show that outside of the ~ 40 Hz control bandwidht, the LO phase noise rms is dominated by line noise (mostly 180 Hz) (Attachment #1).

We checked the BIO inputs, but failed to make them work from the c1su2 model and Anchal spotted an error in the model; so maybe to speed up the proper dewhitening tests, we override the acromag enabling BIO interface and just short the coil driver BI to always enable the Analog DW filter. Then, using the measured DW transfer function with z = [130 + 0j; 233+0j], p=[10+0j; 2845+0j], k=2.0, we corrected the FM9 and FM10 in the coil outputs (this is different from the other DW filters). Today we just did this for LO1, but the next step is to replicate this for the other BHD SOS so that we have a consistent test.

So for now, the LO1 coil drivers at 1Y0 have shorted binary inputs to enable watchdog + Analog dewhitening filters. This needs to happen on LO2, AS1 and AS4, and then the noise spectra should be measured again.

We added the DB9 short connectors to all coil drivers in the BHD suspensions and updated FM9-FM10 for LO1, LO2, AS1, AS4, SR2, PR2 and PR3 to match the work on LO1 yesterday. We then locked the LO phase using BH55 and took noise spectra for the error and control points; Attachment #1 shows the comparison before and after these changes were made.

LO1 is set to go through a free swinging test at 1 am tonight. We have used this script (scripts/SUS/InMatCalc/freeSwing.py) reliably in the past so we expect no issues, it has a error catching block to restore all changes at the end of the test or if something goes wrong.

To access the test, on rossa, type:

Then you can kill the script if required by Ctrl-C, it will restore all changes while exiting.

[Yehonathan, JC]

Yehonathan and I attempted to align the LO2 beam today through the BS chamber and ITMX Chamber. We found the LO2 beam was blocked by the POKM1 Mirror. During this attempt, I tapped TT2 with the Laser Card. This caused the mirror to shake and dampen into a new postion. Afterwards, when putting the door back on ITMX, one of the older cables were pulled and the insulation was torn. This caused some major issues and we have been able to regain either of the arms to their original standings.

I checked the state of the LO2 suspension. I found that the coil driver Enable Mon was all red. Meaning, the actuation signals were not delivered to the coil driver. I wasn't sure if this was intentional or not.

Enabled the coils with "WD Master" Shutdown -> Normal.

Immediately I saw the OSEMS flipped the sign because there was an (non-intentional) alignment offset in pitch. I've adjusted the pitch offset so that all the OSEM PDs have the voltages 4~5V.

That's it.

[Anchal, Yuta]

In the weekend, I ran a free swing test on all optics. During this test, LO2 magnets got stuck to the coil because LO2 PIT alignment was very high, making its lower OSEMs almost fully dark and upper OSEMs almost fully bright. Today we realized that LO2 is actually stuck and is not coming off even when we dither PIT alignment. We tried several ways but could not get this off.

Do we have any other method to get magnets off in vaccum?

It will be pretty bad if we try anything related to BHD with LO beam reflecting off a stuck mirror. Does anyone have any suggestions other than venting and fixing the issue?

Good job guys. What I did was saying "I don't know", "Maybe", and "Ants...".

Now you can proceed to measurements for the visibility and the cavity pole! 

 I'm going to do it right now.

It is a 4^th order filter with cut of frequency of 120 kHz.

Design

Measurement

My ls plant compiled!! The RCG code can now be found in /opt/rtcds/rtscore/tags/advLigoRTS-2.5. I uploaded a copy of c1lsp.mdl onto the svn.

The weird "failed to connect" error was due to the fact that I named my inputs the same thing as my goto/from tags, so the RCG got confused. Once I renamed my inputs, it worked! I'm not sure what happened to the original "not enough parts" error; it didn't appear a single time during the rebuilding process. Anyway, I made the PDH block much neater, though the lines between PDH and ADC are looking wonky (this is purely an aesthetic problem, not a "oh god my simulation will DIE right now if I don't fix it" problem). I'll fix it in the morning; screenshot attached!

The original c1lsp was kind of sad. I updated it extensively and brought it into the modern era with color. The original c1lsp.mdl should also be on the svn. Tommorow, I'll get started on figuring out how to get LIGO specific noises from white noise.