Evan, Kiwamu, Stefan

Today we tried to measure the PRC cavity length using the single-shot time-delay method. Despite an estimated accuracy of about 2mm, we only achieved a precision of about 1cm variation between measurements.

Measurement details:
- We put a 3400Hz, 7.5V (25000cts using LSC-EXTRA) signal into the IMC offset.
- We intentionally detuned the modulation frequency to generate maximal AM at 3400Hz in the mode cleaner.
- We then demodulated this signal after a single bounce off the PRM, ITMX and ITMY respectively to get a time-of-flight measurement.
- Before we started we made sure the REFLAIR demodulation was exactly 90deg (with an error of about 1e-3deg), and the relative gain was balanced to 1 part in 1e4. We achieved this by adding a 45MHz band-pass into the PD RF path of the demodulator (to get rid of any higher harmonics contributions), and then adding a test signal exactly 3.4kHz offset. Using this test signal we balanced the gain and phase response. All this was done at a fixed whitening gain. (The 45MHz band-pass was taken out again at the end of the measurement.)
- With this setup we achieved a phasing precision for PRM of about 0.02deg, and about 0.1deg for the IMTs. However there were large q-offsets, so we had to be careful to tune the audio-demodulation phase for the 3.4kHz signal. Probably our biggest systematic error came from this.
- From the measured phase difference we can calculate the expected PRX length (and PRY and Schnupp length in the same way) using the following script:

MATLAB script to calculate the length:
f=9099483; % sideband frequency
c=299792459;
lambda=c/5/f;
degX=-9.356;    % demodulation phase for ITMX
degPRM=-10.311; % demodulation phase for PRM
dX=degPRM-degX;
Lx=(17.5+dX/360)*lambda/2

- To verify the result, we then calculated the frequency which should be exactly anti-resonant, and repeated the measurement. Unfortunately the results only were good to about 1deg in phase difference, or about 1cm:
      f (Hz)  PRM phase   ITMX phase   PRx length   new f (Hz)
1st) 9101734   73.87deg    72.311deg    57.6557m     9099483
2nd) 9099483  -10.311deg   -9.356deg    57.6469m     9100863

The two results disagree my 8.8mm. While we did measure PRY too, we had different whitening gain settings for PRM and ITMY, so we didn't trust those numbers.

We did however measured the Schnupp-asymmetry using the same technique: we got 8.9cm for Lx-Ly. Again, this number probably has about 1cm of systematic error.

For reference, the design PRC length is 57.6557m (T1000298). With an 8cm Schnupp-asymmetry we expect PRx to be 57.6957m.

As we might need feedback loops from the optical lever to stabilize the motion of the test mass of ETMX and ITMX, the simulink models were temporary modified to include a link from the optical lever to the PUM and UIM masses.

This was done by copying over what has been done for the beamsplitter optical lever :

• FOUROSEM_STAGE_MASTER.mdl was modified to include two oplev inputs going through the OLDAMP filter bank (copied from BS). cf FOUROSEM_STAGE_MASTER_before/after.png.
• The new part was copied and renamed : FOUROSEM_STAGE_MASTER_oplevfeedback.mdl
• QUAD_MASTER.mdl was also copied and renamed QUAD_MASTER_oplevfeedback.mdl  and points to the new FOUROSEM_STAGE_MASTER_oplevfeedback.mdl part for L1 and L2 stages (cf QUAD_MASTER_before/after.png)

A backup of the models h1sus{etmx/itmx}_Feb3rd2013.mdl was made under /opt/rtcds/userapps/release/sus/h1/models

Today I used the nanoscan to measure the ITMX direct reflected beam size that makes it through the REFL path onto ISCT1.

I had previously done some more preparation for this measurement (since aLOG entry 9633), measuring the ITMX direct reflected beam power again on ISCT1 to be 31.6uW. This time the green beam was misaligned at the TMS, so was not coming through the X-arm. Also, ITMY was misaligned, and ETMX was misaligned, so there shouldn't  have been anything that was adding to the measured power. It seems that either the green light, or X-arm flashes were contributing to the ~50uW I measured last time.

At the same time, I measured the PRM direct reflected beam size using the nanoscan. However, the capture settings I used for logging the data were probably not ideal for this measurement, so I would like to retake this data at some point. In any case, the preliminary measured PRM direct reflected beam sizes were wx=1949um and wy=2094um. These can be compared to the numbers I expect from my model: wx=2170um and wy=2138um.

At this time I tried taking a measurement of the ITMX direct reflected beam, but the nanoscan software kept complaining that the detector was "saturating". At 30uW this seemed unlikely to me, but it prompted me to turn off frame averaging. As soon as I turned off the averaing I saw that the beam was swinging around on the nanoscan, with peak to peak motion of roughly a beam size. This seemed like too much motion to get a decent measurement so I decided to wait until we had some quieter optics in the path between ITMX and ISCT1.

Today I went back into ISCT1 and looked again at the nanoscan data for the ITMX direct reflected beam. The ALS beam was misaligned at TMS, ITMY, ETMX  and PRM were all misaligned. The beam motion seemed significantly less for the most part, although I did see it go through quiet and loud times. I logged data at 10Hz for around a minute, which I then averaged offline to get ITMX direct reflected beam sizes of wx=2525um and wy=2510um. The attached plot shows the beam sizes at this location that I expect from my model, for a range of different ITMX lens cases and PR2-PR3 distances. In the cold state, I expect that the ITMX direct reflected beam sizes should be on the cyan line. A naive interpretation at this stage is therefore either that the PR2-PR3 distance is longer than designed, or the ITMX on-thermal lens is weaker than we thought, but there are many variables which still need to be accounted for.

In the top panel of the attached, red is the ETMX OL PIT, pink is the dark noise (this is ETMX OL PIT when there's no light on the OL, but a fake offset of 9900 counts was applied to OL SUM so the scaling of red and pink become the same).

The RMS of the red line for f>0.1Hz is about 0.15urad (that's about 0.5 urad pk-pk). The dominant hump at 0.4-0.5Hz is about 0.12urad RMS, but it seems like the microseism is adding another 0.9urad RMS, resulting in sqrt(0.09^2+0.12^2)=0.15urad RMS.

Dark noise is well below the PIT signal up to a few Hz.

Green is the OL SUM normalized by OL SUM DC, and then scaled by H1:SUS-ETMX_L3_OPLEV_PIT_GAIN. If  the green stays on top of the red for some frequency band you'd be suspicious that the OL quadrants are measuring some noise that is incoherent across the quadrants (shot, dark), but that's not the case.

So OL seems to be measuring the angle at least for f<1Hz, probably we don't have to worry too much about injecting more noise than we want by using OL damping. Even if the actual PIT noise floor is as big as green (which is not likely), the RMS due to noise injection is not bigger than brown dashed curve.

OTOH, at least for the time when the measurement was done, it seems like the damping for 0.4-0.5Hz hump is not good enough, microseismic should be attacked too.

Commissioners remain in the control room.  Earlier, Richard went to EX to investigate the dust monitor that Patrick reported below.  The DM's behavior remains unresolved.

Doug and Jason are out of EY, leaving the station in laser hazard.

With uncontrolled position/controlled target differences of 10 & 13urads in Rx & Ry, the turn on of HEPI rings up the trilliums and makes ISI turn on (especially when HEPI trips) not one button.  Are these tilts really needed?

Andres, Scott, & Jeff

   The H1-SR2 suspension has been installed in HAM4. No significant issues or problems were encountered during the installation. 

   A big thank you to the Apollo crew for all their support with the prep work and the installation. 

(Alexa, Sheila, Stefan, Evan)

Using the picomotors, we have centered the beam onto both POP A and POP B QPD. For reference... with a whitening gain of 45dB, H1:ASC-POP_A_SUM_OUTMON = 11450 cnts, H1:ASC-POP_B_SUM_OUTMON = 10436 cnts.

We have also calculated how many counts we expect on each quadrant: We have 8.8W into MC. There is 15% loss due to input optics losses (IMC and faraday), 3% transmission of PRM and 230ppm from PR2. This gives about 6.4uW for each quadrant of the QPD. With a responsivity of .8 A/W, a transimpedance of 1kOhm and a gain of 45dB, there is 1V on each quadrant. This amounts to about 3000 counts on each quadrant, which is consistent with what we see.  

As a prep for the PRC length measurements, I hooked up a DAC cable of LSC, CAB_H1_ISC_421, to the Dsub breakout board D1201450 at the 18th floor of the ISC rack R4 as specified in E1200408-v14. It is connected to the right half of the breakout unit.

Then I connected a TNC cable from the 2nd output port of the breakout board to the A excitation of the IMC servo board. This is a temporary configuration and allows us to remotely excite the IMC length using the LSC_EXTRA_AO_2 signal (see T1100242-v11 for the signal assignment).

Jeff and Andres report that SR2 now sits inside HAM4.  The installation arm remains on the chamber and will come off Tuesday morning.

I noticed last week that the IPC receive errors at all end station SUS and HEPI for the LSC signals is non-zero. Following the discovery of LLO LSC transmit errors to the end stations due to CPU overrun on the LSC model, I verified that our errors are also due to the LSC model running longer than its average of 40uS. The attached plot shows the error going to ONE at the time the LSC cpu increased to 44uS. The error latches, which is why we don't see any indication of the subsequent 45 and 44uS excursion.
I am running a script which clears the diagnostics on H1SUS-ETMX every minute. The next time an IPC error is seen it will reset after a minute ready for the next event.
All the error rates I've seen so far are only for ONE transmission of the 16384 sent that second. So the error rate is about 3 in an hour or 5.e-6 %

Currently underway (~1:30PM local):

** Doug is transitioning EY to laser hazard for IAS.  Betsy and Travis have been at EY this morning and might return this afternoon depending on Doug's results.
** Rich continues to test BS ISI.  He's pausing while Filiberto attends to a CPS cable at BSC2.
** A semi from LLO carrying storage containers, etc. has driven down the X arm.

This morning I finished rolling out available guardian updates for suspension (following alog 9733)

• Created and started a guardian process for : MC1 MC3 PR2 BS ITMY ITMX ETMX ETMY TMSX TMSY using the commands :

guardctrl create SUS_MC1

guardctrl start SUS_MC1

• Saved the alignment offsets to their current values (except PRM which is in parking position), in order to test if the align_save_burt python script is properly saving, and the guardian properly restoring those offsets.
• Table below summarizes those offsets :

• Modified the overview screens quad/hsts/hlts/tmts/bsfm to make the link to the guardian work

changed the command of the guardian button from  /ligo/apps/ubuntu12/guardian/bin/guardmedm to -> guardmedm

• What still needs to be improved / fixed :

- The sitemap needs to be started from a terminal in order to either save the offsets, or open a guardian medm screen.

- Managing the way the offsets are saved. For now there is 4 txt files per suspension under /opt/rtcds/userapps/release/sus/h1/burtfiles.

one .req file defining the two offset epics channels, one snap file for the aligned value, one snap file for the misaligned value, one file saving all the aligned offsets with the date it was changed.

 Spent some time looking at the noise of the CPS on the BSC after rerouting the sync signals

  One figure is a matlab plot of some calibrated signals using a fixed target on which there are some VERY bad BS channels

  the second plot is a dtt screen of all of the BSC CPS channels in counts, (BS-V3 is looking at a fixed target, all other channels are looking at motion) with all of the ISIs OFF.

  there are a number of icky channels

Stefan, Kiwamu

The PRMI lock is now quite solid. After we engaged a dither alignment system for ITMY, we turned on the ring heater on ITMY with a hope it is going to improve the mode matching.

• We set the modulation frequency back to 9099471 Hz which is the nominal value. This was for making sure that the separation of MICH and PRCL is good in REFLAIR_RF45. Although, we didn't do any quantitative assessment. So we have to revisit this.
• Both stages of BS-ISI and stage2 of ITMY-ISI were turned off because they were found to be too loud at low frequencies around 0.5 Hz and also at around 10 Hz (for some reason). Disabling them made the PRY noise quitter and the length RMS improved by a factor of 2 or 3.
• We successfully locked the PRMI with the sideband resonant with the settings shown in the attached screenshot.
• We found four oscillations very close to each other at around 300 Hz which are believed to be the BS wire violin modes. Two of them were so big and 6 orders of magnitude bigger than the noise floor.
• We put a double notch filter in LSC-MICH and PRCL filter banks. This let the mode ring down slowly.
• Also, at the same time we saw a power drop over a time scale of 2 minutes which seemed to be correlated to with the peak height of the violin modes. This behavior went away after the notch filters were installed.
• The PRMI lock was so stable that it did not spontaneously unlock.
• We set up an audio output path in LSC-DARM and used Chris's cool script, rockifo to listen to the sound of PRCL and MICH.
  • It is available in /ligo/home/christopher.wipf/Public/bin
  • For example, rockifo H1:LSC-DARM_OUT_DQ 16384 100
• We imported LLO's dither alignment stuff, but we realized that it only dithered the common mode of the power recycling cavity while we wanted to stabilize the ITMY angle drift. So we decided not to use it.
• We temporarily disconnected the cable for the ITMY green transmitted power and instead plugged in QMON of POPAIR_B_RF18. We used an SR560, AC coupled at 0.1 Hz with a gain of 5000 to whiten the signal.
• We then used the Y-arm dither alignment system to keep ITMY well aligned. We chose 1.7 and 2.4 Hz for pitch and yaw excitations respectively.
• We could close both pitch and yaw loop, probably with a UGF of 0.1 Hz for both.
• We turned on the ring heater at around 00:08 in local time with 10 W in both upper and bottom heaters of ITMY.

I made a calibration of the IM4trans and MC2trans SUM channels into uW.

The conversion from W incident on the PDs to counts registered on IMC-IM4_TRANS_SUM_OUTMON is as follows:

[counts/W] = responsivity [0.16 A/W] x transimpedance gain [1000V/A] x differential to single input gain [2V/V] x whitening gain [36dB=63.1 V/V] x ADC gain [1.6384x10^3 cts/V].

This is actually the same for both MC2trans QPD and IM4trans QPDs: 2.087x10^9 [counts/W]

I used this calibration factor to calculate the power on IM4trans and MC2trans currently:

IM4trans counts ~= 57890 counts, which converts to 1.75mW. Comparing this with the expected power on IM4trans:

8.73W into IMC * 0.85 IO throughput * 2400ppm IM4 transmission * 0.1 transmission of BS between IM4 and IM4trans QPD = 1.78mW

MC2trans counts ~= 2.17x10^4 counts, which converts to 655uW. Comparing this with the expected power on MC2trans:

8.73W into IMC * (IMC gain = IMC Finesse/pi = 166 ) * 5.1x10^-6 MC2 transmission * 0.1 transmission of BS between MC2 and MC2trans QPD = 740uW.

Both these estimates for the power incident on each PD agree pretty well so I'll go ahead and add a new filter called "cts2uW" in the SUM_OUTMON paths to give the outputs in uW incident on the PDs.