The regular ~1nm variations in ETM coating thickness cast a diffraction ring onto baffles that may produce excess noise through modulation of retro-reflected light (https://dcc.ligo.org/T1300354). A test of whether this scattering noise may limit our sensitivity could be made by shaking a beam tube baffle in the region where the maximum light power falls on the baffles, about 2375 m from the vertex. Because only one or a couple out of many baffles would be affected by shaking and because the LLO sensitivity is still about 3 orders of magnitude away from the goal at the most troubling beam tube resonance (~14 Hz), the increase in motion over normal would have to be at least 4 orders of magnitude for the present LLO sensitivity.

In order to see if I could increase motion of the beam tube by this much I made a pusher system and tried it out here at LHO. Figure 1 shows the voice coil shaker and the coupling rod that has interchangeable springs to optimize force. A universal joint is required to minimize non-axial forces on the voice coil plunger and the coupling rod. The system was powered by a 150 W inverter in an Uplander LT van. Figure 2 shows the relative positions of, at the left, the accelerometers, in the middle, the shaker, and, on the right, a beam tube enclosure door.

Figure 3 shows that the shaker increased the axial beam tube motion at the accelerometer by 4 orders of magnitude at 14 Hz. The noise floor for the shaking injection is higher than for non-shaking because I had to reduce the gain by 10. The injection is not as monochromatic as I would like. This version 2 is better than the first version, but there are still peaks injected at higher frequencies from slight rattling of bolts, springs and other components in the rod. Nevertheless, it looks like it could be used for a test as long as we are focusing on direct (vs. upconversion) coupling. 

model restarts logged for Sun 28/Sep/2014
2014_09_28 06:27 h1fw1
2014_09_28 17:53 h1fw1

unexpected restarts of h1fw1

Last night I used the good alignment of the OMC from the dither loops to sweep the cavity with a single-bounce beam from ITMX and ITMY.  The result is that I think the modulation depth mystery is gone (Gamma2 = 0.077, for the 45MHz sidebands; in hindsight my earlier calculation was wrong) and we see a difference in the mode-matching to the OMC between ITMX and ITMY that matches what we expect from the as-built optical parameters.  So, maybe life makes sense again...

===== Modulation Depth =====

The short story is that I mis-identified the peaks from the 45MHz sidebands in the measurement from Sep 19th.  Probably I was looking at the 1st and 4th order carrier modes; with the good alignment the 1st order mode is much smaller, and there's no way to mistake that the 4th order peak doesn't have a matching peak at the other end of the FSR.  The two plots attached show the cavity sweeps of ITMX and ITMY; the peaks used to calculate the modulation depth are marked with black crosses.  There are five sweeps for each optic. The peak heights are averaged and used to calculate J1(Gamma), and the value of Gamma that returns J1(Gamma) is calculated using the scipy.special.jn() function.  The result is:

Gamma1 (9MHz) = 0.211

Gamma2 (45MHz) = 0.077

These results are consistent for the upper and lower sidebands of each modulation frequency, and are the same for ITMX and ITMY.  The variation from one sweep to the next is small (usually less than 0.001).  Also, this measurement of the modulation depth for the 45MHz sidebands agrees with a measurement from last December.  No modulation mystery after all?

(I hope that Koji will check these results with his more-sophisticated peak-calibration code.  If you are comparing my plots to his, note that my data use up-going sweeps of the PZT, while his are down-going (for example here), and so the order of the peaks is flipped between the two.  The latest (Sep 28th) sweep data are here.)

===== Mode Matching =====

Using the mode scans we can make an estimate of the mode-matching of the single bounce beam into OMC.  Following Koji's calculation I use the peak height of the 2nd-order carrier mode to make a rough estimate of the mode overlap, using the expression MM = 1 - (CR_TEM20/CR_TEM00).  This calculation is rough, in that it ignores the power in the higher order modes, and just uses the peak height; I will try to include the HOMs and integrate the peaks later, but the answer should be the same to within a percent or two.  For each ITM we get:

ITMX = 0.884

ITMY = 0.913

The magnitude of the mode mismatch, and the difference between the ITMs, is in agreement with predictions from the beam-propagation.  Good alignment matters!  I suppose the next step will be to check that we can improve things with TCS.  (Again, someone should make an independent calculation using this sweep data...)

===== Other Stuff =====

• Last week I plugged in the picomotor controller for the in-vacuum HAM6 picos.  It was an easy job to figure out which pico driver was which: channels 1-3 are AS_A, B, and C; channels 5 and 6 are the picos in front of the OMC REFL QPDs.  I centered the beam on AS_A,B,C with the OMC in its good-alignment state, and unless something dramatically changes with the SRC alignment I think they will stay centered.  Now that there is beam on AS_A and AS_B we can use them for initial alignment.  (OMCR_A and B are not centered, this is kind of tricky since the picos for that beam path are upstream of both QPDs, and there are two lenses between the picos and the diodes, so there's a lot of degeneracy in the actuation.  I'll need to spent an hour or two pico-ing this week.  Heh, maybe the ISS team wants to help?)
• I fixed the channel swap in the AC and DC monitor channels for OMC PZT1 and PZT2, now all the readbacks make sense.
• We need to commission a shutter for the OMC.  For the moment all we can do is use PZT1 to kick the cavity length when the trigger diode (AS_C? how to get this signal out of the analog electronics?) goes over the threshold.
• I remeasured the OMC QPD and dither alignment loops.  The QPD loops all have a UGF around ~12Hz, the dither is around 0.1Hz.  Both have plenty of phase.
• With the beam aligned to the OMC and the AS WFS, I measured the {OM1,2,3} --> {OMC QPD, AS WFS} sensing matrix.  This is in preparation for setting up a combined OMC/WFS centering servo.  The matrix needs to be inverted and the control topolgy chosen (tricky, with four sensors and three actuators), but before we can do anything we need to add the inputs from the ASC model to the SUSHTTS model.  Right now the OMs get their ISC inputs from the OMC model.  For comparison, Livingston is sending the AS_B signal to OM1 (with low bandwidth), and the OMC QPD signal to OM2 and OM3.

This afternoon I wrote a short slider offload script to use with the alignment guardians that Sheila & Gabriele commissioned yesterday.

The script is ~userapps/release/asc/common/scripts/offload_M1_LOCK_ALIGN.py.  It moves the outputs of the M1 DRIVEALIGN matrix to the alignment sliders, taking care to check the calibration gain that comes after the sliders on some optics.  It should work for most any optic that has an M1 stage; I tried it on the PRM and SRM and it did the trick.  The syntax is, for example:

./offload_M1_LOCK_ALIGN.py -o PRM

Not sure how to best get this into the ISC_DOF guardian.  Don't forget to save those aligned slider values!

After touching up the alignment of PRX, SRY, and MICH I was able to get the DRMI to lock at 1W a few times, for a few minutes.  The gain settings were:

MICH: 30

PRCL: 22

SRCL: -400

...and FM8 (ELP70) engaged on the MICH bank rather than FM9 (ELP40), although I didn't have a chance to measure the MICH loop to see if it made a difference.  A loop measurement of PRCL is attached; the red curve is today, the black curve is a reference.

no restarts reported

Gabriele, Dan, Sheila

• We have locked DRMI at 1 Watt.
• We got WFS loops running for PRX and SRY, and added to the guardian the Xarm IR locking and wfs for inital alignment.
• We have focused several of the cameras, and now have better views of many optics.

We did several things today and last night...

First we worked on focusing the cameras on the input arm, ETMX, and both ITMs.  Now we have a much clearer view of our interferometer.  I also copied the code to align TMSX using the GigE camera from the IAS guardian into the ALS guardian, and tried it out with the cavity locked on green.  This kind of works, although the camera centroid is noisy, the noise roughly coresponds to 3 urad of TMS angle.  We probably want to get a mask going on the camera to see if that helps. 

We are using refl WFS for SRY and PRX.  We also attempted this for MICH on the dark fringe, but the signal was too noisy to work well.  For all the asc loops, we used FM1+2.  For PRX we used REFL B 9 with a gain of -0.0003 for Pitch and 0.003 for Yaw.  For SRY we used REFL A 9 with a gain of 0.03 for both pitch and yaw.  All of these states are now added to the guardian currently called ISC_DOF ( we will think of a better name).  This currently has the states that were in the DRMI guardian that are actually used for initial alingment, plus the arm IR locking states.   The graph for this guardian is attached.

After running though the parts of the inital laignment sequence that we have working so far, we locked PRMI at 10 Watts, and steped the power down using the rotation stage, manually correcting the power in DC PWR IN using the offset, and increaseing our gains.  We locked 2.8 Watts with a PRCL gain of 50.4 and a MICH gain of 10, and at 1 Watt with MICH at 110 and PRCL at 22 (we measured the loops and adjusted the gains to keep our MICH ugf around 12 Hz and PRCL around 80Hz, suprisingly the PRCL gain had to be increased by less than a factor of 10 to keep the same gain with a factor of 10 decrease in the power.) 

We then took some guesses at the gains to use for DRMI at 1 Watt based on Anamaria's document, what we had originally used, and what we needed for PRMI with 1 Watt.  After some adjustment, we locked with the parameters shown in the screen shot.  DRMI was locked on the sideband at 1 Watt from about 1:57 UTC September 28th to 2:21 when we tried to change a filter and it dropped lock. 
 

Yesterday afternoon we reconnected the ADC to the whitened signals for PD5-8. Now the status is the following:

• PD1-4: we are acquiring the direct output of the transimpedance, before the whitening. We can use those signals to check the DC level, but we can't see the AC noise
• PD5-8: we are acquiring the whitened output of the boards. We can see the AC noise, but no DC signal

I wanted to compare the RIN meaured by the first loop photodiodes PDA and PDB with was is measured by the second loop photodiodes. However, looking into the way PDA_REL and PDB_REL are reconstructed, I found a couple of strange things, and I'm quite convinced that the estimated RIN was wrong. Peter King computed the whitening transfer function of the PDA and PDB box. Comparing this with what was implemented in the PD?_CALI_AC, I found a quite large discrepancy I could not understand. Therefore I implemented an inverse of the expected whitening, which is good between 1 Hz and few kHz, as shown in the first plot. I also found that the low pass filter used in the PD?_CALI_DC was giving me a strange notch at about 10 Hz in the PD?_REL signals, so I changed it into a simple low pass, as visible in the second plot. For both the AC and DC parts, the old filters are still there.

The second loop photodiode PD5-8 outputs are dewhitened as explained in a previous entry. The output is calibrated in V, and the DC level that we measured before changing the ADc connection is about 3 V.

The third plot shows the RIN as visible in both the first and second loop photodiodes when the first ISS loop is open. In particular, we see that the second loop photodiodes are in good agreement with the first loop photodiodes, at least above 100 Hz. This is a cross check that the calibration in terms of RIN is, if not correct, at least self consistent.

The fourth plot shows what happens when the first loop is closed. As expected the out of loop PDB shows a flat RIN that I guess should correspond to the shot noise level, even though I don't know right now how much pwoer is getting into the diode, so I can't teel if the absolute level is correct. Looking at the second loop photodiodes, it is clear that we have a huge excess of noise with respect to the level obtained at the output of the first loop. At this point we can't tell if this is real intensity noise, or just jitter noise that couples to the second loop PDs. Recall that we didn't optimize at all the coupling of jitter to RIN for the second loop photodiodes. For sure, there's still a lot of work to do...

model restarts logged for Fri 26/Sep/2014
2014_09_26 13:05 h1dc0
2014_09_26 13:07 h1broadcast0
2014_09_26 13:07 h1fw0
2014_09_26 13:07 h1fw1
2014_09_26 13:07 h1nds0
2014_09_26 13:07 h1nds1
2014_09_26 23:12 h1fw1

unexpected restart of h1fw1. DAQ restart to include TCS HWS channels and new DMT chan list.

1. I tuned up the input pointing ASC loop which I closed yesterday (alog 14162).
   • see the attached for the loop parameters.
2. Locked PRMI and found POPAIR_RF18 at a high value of 200 uW.
   • One difference from the past is that IM4 had been servoed to a small bias in pitch (~11000 urad) by the IM4/PR2 loop.

No working green WFS with centering yet.

1. WFSB segment 3 demod signal is a factor of 10 weaker than the others when the beam is centered.

Giving the WFS centering servo a YAW offset (+0.4 in YAW so the beam stays at -0.4) would recover the balance. But at that point we're already almost railing MCL PZT.

2. Difference between good alignment (H1:ALS-C_TRY_A_LF_OUT_DQ=870-900) and not-terrible (smaller than 800) is big on WFS centering.

We made the centering servo work when the alignment is not that bad, but later when I manually aligned the arm, the servo started railing.

So, one of the problems seems to be that we don't have much range for MCL PZT mirror.

The screenshot shows the demod phase setting and RF WFS error signal, and you can see that the WFSB seg3 signal is very small. The reason why WFSB spectra look washed out is because the WFS centering kept railing during the measurement (sorry).

Next step would be to go to the end station, manually releave the PZTs, and repeat the measurements. I'll leave the centering servo disabled for now.

Attached see the TFs--Comparing these to the most recent in the matlab SVN (August 2013,) these look just fine.  There is a new little extra wiggle on some dofs at 0.7 & 1hz that I'd say are the table top components.

Sure, I know Jim beat me but he's young..  Of course we were both waiting for the filter loading/saving scripts to get fixed.  In the end, Jim fixed them.

Anyway, I got the controller on HAM4 now too.  Attached are two plots of calibrated spectra, top from 23 Sept with the Level1 controllers and the lower from this afternoon with the Level3 controllers.  Certainly compromises in place but good between 1 & 10 hz.   I'll look for the plotting tool jim used to compare to HAM3.

LVEA is LASER HAZARD

08:00 Hugh running TFs on HAM6 - folks should steer clear of that are for the next several hours

08:18 Peter King out of LVEA

08:40 Danny out to West bay to work on quad. Also helping Aiden with removing viewport cover for more precision TCS alignment

08:53 Aiden out to HAM4 for TCS/HWS

09:29 Danny into LVEA- this time for real.

09:30 Mode cleaner locked on wrong mode. Re locked on correct mode

10:16 Andres to End-X to search for parts in lab

10:30 Sheila out to focus cameras. X/Y arm

11:03 Aiden back out to LVEA

12:36 Peter out to H2 enclosure

12:59 Sheila to X-End to focus camera(s)

13:04 DAQ restart

13:05 Andres back to End-X searcing for parts

13:15 Danny out to X-End to search for parts

13:45 Danny out to Y-end to search for parts

14:24 Sheila back from focusing cameras

15:00 Sheila - locked X-Arm and going out to focus cameras in corner

15:07 Andres - back from End-X

15:35 Jim reports that everything seems fine with HAM5 HEPI/ISI. Gaurdian was placed back into the managed state and it seems happy as well.

15:50 Robert to beam tube enclosure between Mid-Y and End-Y

Peter K, Sudarshan, Gabriele

All the eight photodiodes are now acquired with the temporary break out box, allowing us to measure the direct output of the transimpedance. 

We could finally find what we believe is the real beam, since we got high power on all photodiodes and also on the quadrant. However, we've not been able to find a position that simultaneously center the QPD and maximize all the photodiode signals. We can either center the QPD or maximize one or few of the photodiode signals.

For reference, we have now

QPD = 22000 cts, 13 V

PD1 = 4170 cts = 2.54 V = 2.1 mW
PD2 = 4500 cts = 2.75 V = 2.7 mW
PD3 = 4620 cts = 2.81 V = 2.3 mW
PD4 = 5000 cts = 3.05 V = 2.5 mW
PD5 = 4840 cts = 2.95 V = 2.4 mW
PD6 = 4320 cts = 2.63 V = 2.2 mW
PD7 = 5120 cts = 3.13 V = 2.6 mW
PD8 = 5000 cts = 3.05 V = 2.5 mW

There is an excursion of about 20% from the minimum to the maximum. For sure, the present position does not correspond to one that minimize the jitter to RIn coupling for each diode separately. We tested that adding a slow 1 Hz modulation  in pitch or yaw on IM3 does introduce a fluctuation in the PD signals. The effect is particularly large in yaw, and much smaller in pitch.

Installed new high level controllers into the HAM5 ISI this afternoon. After some normal amounts of fiddling I have them working about as well as HAM3 (see attached performance spectra, blue is HAM3, the unlabeled red trace is HAM5). There's no feed-forward or sensor correction installed yet, so there's probably room for improvement. But for the moment, I hope it's good enough.

Aidan.

I set the SYNC frequency (the frame rate) for the H1 ITMX HWS to 1Hz rather than the default 57Hz. This was done by accessing the serial port of the camera, making sure the frame rate was set to 1Hz and then entering the command wus to "write user settings" to the camera.

I confirmed this was working by rebooting the camera and verifying that the frame rate returned to 1Hz.

See the attached screen capture of the command window I used to do this.

(I also turned off the HWSX SLED).

Aidan.

I removed the LEXAN cover to help locate the conjugate plane of the HWS by the ITM. This test was performed in the following way:

1. Removed Hartmann plate from CCD to get a simple capture of the return beam

2. Added a 50mHz, 4 micro-radian amplitude oscillation to ITMX YAW

3. Captured a series of 100 frames on the HWS, running at 1Hz. Measured the centroid of the overall intensity pattern for each frame.

4. Plotted the centroid vs time. 

5. Determined the <pk-pk> size of the oscillation in the centroid in pixels.

6. Determined the conjugate plane of the HWS near the ITM (or conversely, the conjugate plane of the ITM near the HWS).

<pk-pk>*magnification_of_HWS_optics*pixel_size = oscillation size near the ITM

The goal was to move the HWS along the optical axis until the <pk-pk> size was minimized.

The best I could do was:

<pk-pk> = 0.2 pixels

M = 17.5x

pxiel_size = 12E-6m

Therefore the oscillation size (peak to peak) by the ITM is 42 microns. The peak-to-peak angular change is 16 micro-radians for the reflected HWS beam. Therefore:

the HWS is within 2.6m of the conjugate plane of the ITM.

7. The last step was to replace the Hartmann plate on the sensor and move it an additional 10mm along the optical axis. (The Hartmann plate is mounted 10mm in front of the CCD and this action places the conjuate plane on the Hartmann plate rather than on the CCD).

These are working again. We needed to align things on the table, as it was previously done with some random alignment.

The filter gains are +500000 counts for WFSA PIT/YAW and WFSB PIT, but -500000counts for WFSB YAW.

UGF is 10-12Hz for WFSA and 8Hz-ish for WFSB with these gains.