Maybe Stefan turned these off, I didn't catch such in the alog.  I thought I left these in some Isolation state yesterday as Stefan wanted PRMI asap.

ITMY is damping with a Stage2 trip from GS13 limits.  The BS has no trip indicator but is damping only.

The HEPIs here are running normally.

Stefan and I found that the BS oplev was oscillating because of probably a loop instability. Disabling and enabling them at H1:SUS-BS_M2_OLDAMP_P(Y) made it stable again. It had been oscillating for more than 15 hours. The attached is the trend.

Stefan and I lowered the threshold value of the ref cav transmitted light because it was preventing FSS from a smooth recovery. It is now 0.4.

Stefan, Lisa, Kiwamu,

Our goal tonight was to lock PRMI with the 3f signals. However we didn't reach that point yet because of a (perhaps new) issue in the PRMI locking.

A good news is that the power build up was high because of the ring heater on ITMY which had been set at 4 W in total. POPAIR_B_RF18 went to 8000 counts.

40 Hz unidentified oscillation in PRMI signals:

After some tweak of alignment and gains, we managed to lock PRMI with the sidebands being resonant. However the PRMI lock was fragile for some reason. In particular, it lost the lock frequently when we changed the PRC gain. We took spectra of the signals and were surpprised by a huge peak in both PRC and MICH signals. This was causing a DAC saturation in the M2 stage of PRM which made the PRC loop unstable. This is something we didn't see before. We looked at some previous spectra from the last long stretch of 3rd of February (alog 9809) and confirmed that there was no such oscillation at that time. The attached shows spectrum of various signals from tonight. It is obvious that there is a broad and prominent oscillation at around 40 Hz in each signal. Note that when I took this data, I had a notch in PRM M2 stage to mitigate the saturation and that's why the PRM_M2 signal look a bit suppressed at around 30 Hz.

We tried to lower the UGF of PRCL, but the oscillation persisted. In fact the peak moves as we changes the UGF. For example, lowering the UGF also brings the peak frequency lower. We suspected a gain peaking and tried to move the UGF, but somehow the gain margin was so narrow that we could not move around so much. According to a quick swept sine measurement, the UGF was at around 40 Hz.. Another thing we suspected was a roll mode which is usually at around 40 Hz in the case of the small triple suspension. Since we failed to lower the UGF, we could not really try a notch technique to minimize unwanted excitation. We also looked at MC_F because we suspected the roll mode of MC2, but there was no visible oscillation at all. I also quickly tried the PRX locking to see if it still persists, but I didn't see any oscillation in PRX.

We are still unable to identify this oscillation.

Stefan, Lisa, Kiwamu,

The X arm is now quiter due to the oplev on ETMX and we are now becoming able to assess the noise performance.

Since Stefan got the oplev active loop running on ETMX and made the arm quitter, we wanted to measure the ALS infrared frequency noise by locking the PSL to the X arm using the green beatnote. The hand off process was very smooth tonight and we could try many times to bring the PSL frequency close to the arm resonance. Stefan engaged the additive offset path on top of the MCL feedback. We measured the UGF to be 3.6 kHz with a phase margin of about 64 deg.

It seems that the CARM noise is now suppressed to ~ a few 100 Hz which is unfortunately still greater than the arm linewidth of about 84 Hz. Because the fringe moved more than its linewidth, we could not confine it within the linear range. The below is a screenshot of the PDH signal in StripTool. You can see that the PDH signal, which in blue, goes back and forth around a resonance, resulting in a periodic funny shape. Also it looked like we need to have some more gain at low frequencies because we saw a low frequency excursion in the error signal.

Even though the PDH signal was pretty much out of the linear range, we calibrated REFLAIR_A_RF45 using Alexa's formula (see alog 7054) and tentatively made a noise spectrum which, of course, underestimated the actual noise due to a low optical gain. One thing we immediately noticed was that there is a 70 Hz broad peak which maybe a vibration of the periscope on ISCT1. It looks quite similar to what we had in HIFO-Y. We are not sure what this is at this point.

I finally got a script working to step the alignment offsets on the IMC mirrors and record the transmitted power drop with MC2trans and IM4trans QPDs. 

The idea behind this was to compare the quadratic function for power drop with misalignment with the theoretical function, giving us a means of accurately calibrating the alignment offsets.

The reason I'm interested in calibrating these offsets accurately is for beam jitter measurements using the coupling from jitter to RIN in transmission of a misaligned IMC [see e.g. LHO aLOG entry 8190]. The coupling factor is determined by the slope of the quadratic function, so we can't calibrate jitter measurements made in this way any better than we can calibrate the DC alignment offset.

The first attached plot shows the normalized transmitted power obtained for each individual mirror DOF, from both IM4trans QPD and MC2trans QPD, over "intended" alignment offset. Also included is a plot of the normalized transmitted power from a Finesse model of the IMC over "real" misalignment offset. From these plots we can see that in general the alignment offsets actually applied to the MC mirrors are larger than the intended alignment offsets. However, the measured data is not always symmetric (especially for IM4). This could be due to clipping at the QPDs. The centering on IM4trans is not as good as the centering on MC2trans, so I would be more confident in the numbers from MC2trans.

I fitted a quadratic function P=A(x-h)^2+k to each of the curves. The calibration is then done by scaling the alignment offsets applied to the actual suspensions by sqrt(Amodel/Adata). The second attached plot shows each DOF again, but this time with the x-axis scaled for the measured data to fit the model. I used the scaling factors calculated from MC2trans data since the centering on this QPD was better. For the most part I'd say the data matches the model well after this scaling.

These scaling factors are:

I would propose to include these scaling factors in the calibration of the MC mirror offsets.

The script can be run again at any time to check for any possible changes in e.g. the OSEM coil driver gains over time. It might be beneficial to take more data points at some point too, but the script takes 15mins or so to run as it is (mainly due to the time given for optics to settle between changes of offset). Another improvement would be to step MC1 and MC3 pitch over a larger range, since the transmitted power is actually fairly insensitive to these DOFs. Both these things can be edited in the top few lines of the script.

In case anyone is interested in running this script in future, it is located at opt/rtcds/userapps/release/ioo/h1/scripts/imc/pfulda/IMC_align_calibrate.py

Be sure to run the mcWFSrelieve script located in opt/rtcds/userapps/release/ioo/h1/scripts/imc/ first though!

I attach the analysis scripts here too, including the measured data, Finesse model and results, and other functions used.

Stefan, Lisa

Now that the mirrors move less and the arm cavity locks stably, we want to actually measure the frequency noise between the red and green.

When trying to do the green CARM hand off, we found that we didn't have a signal. 
We tracked it down to a bad alignment between the green beam from the SHG and the one from the arm.
We used Sheila's numbers  as reference: the beat note was supposed to be around 28 mV, it was just a few mV. We realigned the green arm beam on ISCT1, and we brought the beat note back to about 22 mV. 

I tried to add back the Beckhoff channels and then remove the ones that I thought were updating too frequently. It still seemed to be updating too much (from watching H1:CDS-CONLOG_QUEUE_SIZE). I reverted back to the list without the Beckhoff channels.

Sheila, Paul

Yesterday while in the PSL we aligned the Thorlabs PDA55 known as IO_AB_PD_3. This PD sees the beam picked off from the main beam after the EOM by the wedge IO_MB_WG1. The PD was already on the table and connected to the DAQ, but the final steering mirror steering onto it was not present. The post was in place (labelled as IO_MB_WG1, though I think this should be labeled IO_AB_W1) but there was no mirror mount on top. I borrowed a HR turning mirror already mounted that I found in the IO shelf in the PSL ante-room and mounted this on the post and aligned the beam onto the PD. 

The design actually calls for this PD to be placed behind a window (IO_AB_W1), but I did not find this window so I left it in reflection from an HR mirrror as a temporary setup.

The power incident on the PD was 1.17mW, and it gave a DC reading of 5.56V. The PDA55 switchable gain was at its lowest setting (1.5E4).

This roughly makes sense: using the previously estimated PDA55 responsivity of 0.325A/W we get an expected voltage of 0.325A/W * 1.5E4 V/A * 1.17E-3 W = 5.8V. This looks like the responsivity is a little lower than the other PDA55 (IO_AB_PD_1), so I adjusted the responsivity in the LSC DCPD medm screen until the voltage and power matched the measurement. The channel H1:PSL-EOM_A_DC_POWER is now calibrated in mW incident on this PD. I don't know the pick off fraction of that wedge exactly, so if anyone wants to calibrate it in terms of power leaving the EOM it might be best to measure the main beam power on the PSL table before the IO power control stage.

1: Pilot unit beam diverter was replaced with a production unit.

IR high reflector on the old diverter was put in the new one, but we removed a translucent-ish black glass and installed a standard black glass.

2. TMS ISC table + telescope was reattached to the top mass and suspended.

Some circus of putting the tele+table on a bench and then picking it up from the opposite side was necessary due to space constraint under the test end. As a result, one Genie lift is right now trapped between the roll up door side of the clean room and the TMS/ETM. I hope this doesn't bother others.

One of the TMS tele F2 mirror clamp was pressed against the tele lift tooling when we're lowering the tele/table.

After the tele/table was freed and was suspended, I inspected F2 mirror. All clamps were still touching the mirror, and all ball point contacts (three from the side and three from the back) were all touching the mirror sourface also. Looks good.

3. Fall protection wire and temporary alignment stabilization tooling were installed.

4. For tomorrow: Cable up QPDs, picos and beam diverter, balance the entire structure, and completely free up everything.

That could be a day's job. After that, we need IAS to measure the position of the TMS input aperture. We need to find the right tooling for that at EX lab. The one we used for EX probably doesn't work as EY is a pilot unit and it has somewhat different screw hole locations, so we need to find the old tooling.

Evan, Paul

Yesterday we took beam size measurements on ISCT of the beam directly reflected from ITMY. I didn't get around to processing the data until later, hence the late post.

The results were: ITMY direct reflected beam size = 2329um (x-axis), 2398um (y-axis)

As expected, the ITMY direct relfected beam size is smaller than the ITMX direct reflected beam size, but only by 6% or so. I will check against my model to see if the difference in sizes makes sense quantitatively, though the unknown non-thermal lens in ITMY may make it difficult to draw a strong conclusion from this.

I attach again plots of the ASD of the beam spot centroid position and radius throughout the first 60 seconds of logging.

Rich, Jim and Hugh

The ETMX BSC-ISI is running a level 2 controller (~25Hz UUG) with low frequency blend filters (~40Mhz stage 1 and ~250mHz on stage 2)

We were to able to turn on the level three controllers mostly due to an excessive amount of 60Hz pick in the GS13s and L4Cs, this needs to get looked

 We still need to finalize the tilt decoupling

Everyone


- ITMX motion has been largely reduced by the seismic teem, now the motion at 0.5 Hz is around 0.03 urad, A LOT less than before;

- The tuning of the ETMX is still in progress, but in the meantime Stefan implemented a 'dirty' optical lever feedback which reduced the ETMX PIT motion by about a factor of 5 at 0.5 Hz. With the OL feedback on, ETMX PIT @ 0.5 Hz is around 0.1 urad. There is some gain peaking around 1 Hz.

- In this state, the one arm is stably locked on green with 32 uW (calibration to be confirmed) in transmission (~840 counts in ALS-C-TRX_A_LF_OUT) power fluctuations are small, around 5%. We are not seeing the 01 coming into resonance, so we can make a measurement of the frequency noise red/green. (P.S.: Sheila says that ~800 counts is a good number, corresponding to a good cavity alignment.)

(Sheila, Alexa)

1. We wanted to re-visit the EX PLL shot noise measurement we had previously done.

• From the direct output of the pre-ampifier we measured the beatnote signal to be -33dB at 39.8MHz with 100 Hz BW
• The RF spectrum analyzer had a noise floor of -126dbm with 100 Hz BW (no attenuation)
• From the direct output of the pre-amp with the BBPD blocked, we measured an electronic noise of -118dbm at 100 Hz BW from the PD
• With the fiber blocked we measured noise of -114dBm at 100 Hz BW
• We meaured the power at the BBPD to be 5.8mW with a DC reading of 1.04V --> .52mA at the PD. We calibrated the PD responsivity to be .09 A/W
• To confirm we were measuring shot noise, we increased the optical power by a factor of 2, and saw that the noise with the fiber blocked increased to -111dBm at 100 Hz BW. We expected this increase, so are confident we were measuring shot noise.

2. WIth the EX PLL locked, the arm cavity well aligned, and the green beam flashing, we looked at the PDH error signal out of the demod IMON and measured the peak-to-peak of the signal to be 230mVpp

3. We went on to investigate the fringe wrapping we saw in the PDH amplitude spectrum at the error point. With the arm locked, we only saw a slight difference in the spectrum with the HEPA fans on or off (Sheila will attach pictures). There did not seem to be fringe wrapping, and the acoustic noise seemed minimal. I will look at the PDH shot noise again when I can misalign ITMX and see if the fringe wrapping is still there..