Kiwamu, Jenne, Alexa, Sheila, Daniel,

Today we locked ALS COMM.  We chaanged the locking sequence compared to our old sequence.  One difference is that we have moved the notches in MC2 to M2, so we can have a higher crossover between the slow and fast actuators (CARM gain is 240 now, instead of 80).  We also got rid of a z5 p20 filter we had in the CARM filter module.  The rest is the same as it was in late May.  This seems to be locking fairly robustly.  The ugf is 1 kHz, with a phase of -80 deg.  A measurement of the cross over is attached.

We also aligned the DIFF beatnote, 800mVpp.  We have locked this at low gain a few times.  We need to feedback to the top mass of the ETMs to keep the DIFF PLL within the VCO range, but we have had trouble engaging the tidal feed back.

[Jim, Fabrice]

To help comparing and finding the best of the blend configurations used at each sites, we loaded the LLO blend configuration on ITMY.  Unlike for previous transfers of filters from site to site, we did not export the filters from LLO foton files into different continuous or digital forms before to re-convert them, simplify and re-install them into LHO foton file. We directly copied and pasted the second order sections from one foton file to another. [We used the filter file logged in the repository Keith has set up (very useful!): https://daqsvn.ligo-la.caltech.edu/websvn/]. A few blend filters take two banks,  we left it that way.

We performed measurements with the initial configurations (called "before" in the figures) and with the LLO filters configuration (called "after" in the figures). The blend configurations are summarized at the end of the report.

- The first two figures show the ISI motion for each configuration. Using the LLO config (after), the X and Y motion is lower at the suspension resonances at the cost of more motion at higher frequencies (good compromise). The rotational motions appear higher at most frequencies.

- The next two figures show the suspension point motion for each configuration. In the initial configuration, the suspension point motion is dominated by ISI longitudinal motion at almost all frequencies. With the LLO blend, the RZ motion takes over around 1 Hz.

- The last two figures show the optical lever motion for each configuration. In this example the Pitch RMS motion went from 5.8 nRad (before) to 4.1 nRad (after).  The Yaw RMS motion went from 6.6 nRad to 4.2 nRad. [These numbers seem very small (calibration issue?) but the relative comparison is probably fair.] 

We leave it on for tonight for making a comparison over a longer stretch of time.

---------------

Blend configuration used for the "before"  and 'after" measurements.

DOF:            Before  /  After

Stage 1 X : Tbetter  / 45mHz

Stage 1 Y: Tbetter / 45mHz

Stage 1 RZ: TCrappy / Off

Stage 1 Z: T750mHz / 90mHz

Stage 1 RX: Tbetter  / [250a & 250b for CPS and T240, 250 for L4C]

Stage 1 RY: Tbetter  / [250a & 250b for CPS and T240, 250 for L4C]

Stage 2 X : T750mHz  / 250 mHz

Stage 2 Y: T750mHz  / 250 mHz

Stage 2 RZ: T750mHz / Off

Stage 2 Z: T750mHz / Off

Stage 2 RX: T750mHz / Off

Stage 2 RY: T750mHz / Off

After finding good whitening setting, the arm was aligned, I walked the beam on WFSB to find a good offset.

Demod phase was set after finding a good position on WFSB (PIT offset = -0.15, YAW=0). For WFSA I never set any offset.

See the first attachment for the demod phase.

See the second for the spectra after an offset of -0.15 was set for the WFSB PIT centering servo to balance the demod signal peak generated by an excitation to the PDH board EXC A.

Sudarshan, Gabriele

We significantly improved the beam centering on the ISS array: now we have good powers on all diodes, centered QPD and lower coupling of beam motion to dP/P

The procedure

1. We wrote a python script that uses the picomotor 1 to maintain the beam centered on the QPD. 
2. We moved picomotor 8, mainly in the LEFT direction. After each motion, we ran the script to recenter the beam on the QPD. We then checked that we were improving the power levels.

After a lot of steps in the LEFT direction and few in the UP direction (for picomotor 8), we could get the beam centered on the QPD and good power levels on all diodes. Actually, we believe we are quite close to the maximum power for each diode.

The results

The following table compares the power levels (in counts) before our adjustment and at the end.

Then, we measured again the coupling of beam motion to dP/P, and we got much improved numbers:

At this level it is difficult to find a better position looking only at the power levels. We might have to optmize the centering looking directly at the beam motion coupling.

Summary:

Some whitening settings for EY green WFSA  I3, Q3 and WFSB Q2 channel don't work. It's probably the whitening chassis itself as the whitening request and the readback agree with each other.

For now I'm leaving both of the chassis in place as there are some usable settings, but note that these guys have a history of many troubles due to chassis and crappy cablings (12159,  12138, 12127).

Details 1:

For WFSA I3 and WFSB Q2, the measured whitening gain doesn't match the request and the readback (attached).

You can see that in both cases one of four stages (+3dB, +6dB, +12dB and +24dB) is failing. It's the 12dB gain stage for WFSA I3 and the 6dB stage for WFSB Q2.

These were measured injecting 20mVpp signal at 100Hz using a function generator and a breakout board.

Details 2:

For WFSA Q3, the third whitening filter doesn't turn on.

For now:

I set the gain to +27dB and turned all filters off.

Alastair & Greg

Greg is running the TCS x-arm laser for a couple of hours (from 16:41 onwards) so we can start to get some data on stability at LHO.  The beam to the CP is blocked so there is no output, and the laser is being run with the table closed.

Performance plots later.  Lvl2 will be quick but later too.

9:20 am Jeff B and Andres R to X-End lab area, retrive 3-IFO TMS components.
9:35 am Danny S to CS VEA, West bay area, quad work.
12:58 pm Karen to Y-end VEA, cleaning.
FIRE DRILL.
1:25 pm Danny S to CS VEA, West bay area, quad work.
1:28 pm Richard M and Patrick T from CS control room, Beckhoff work.
1:30 pm Jeff B and Andres R to Y-End.
1:45 pm Rick S and Peter K to CS VEA, pull cables from CER to HAM2 area.
3:14 pm Danny S to CS VEA, West bay area, quad work.
3:29 pm Travis S to CS VEA, west bay area, quad work.
4:06 pm Greg G to CS VEA, TCS work.
4:12 pm John W and Bubba G to Y-End VEA, walk/inspection.

PSL Check: 9/29/2014

Laser Status:

• SysStat is good
• Output power is 33.6 W (should be around 30 W)
• FRONTEND WATCH is active
• HPO has multiple red, LOCKED, LRA, WATCH and WARNINGS.

PMC:

• It has been locked 2 days, 20 hr , and 56 minutes (should be days/weeks)
• Reflected power is 2.0 Watts and PowerSum = 25.6 Watts.
• (Reflected Power should be <= 10% of PowerSum)

FSS:

• It has been locked for 1 min (should be days/weeks), keeps glitching.
• Threshold on transmitted photo-detector PD = 1.753 V (should be at least 0.9V)

ISS:

• The diffracted power is around 9.75 % (should be 5-15%)
• Second loop is RED.
• Last saturation event was 1 d, 23 h and 20 minutes ago (should be days/weeks)

Now with added "damped" plots.  Note, the damping loops on the electronics test stand are hodge podge and so damping was poor for some regions of many loops.  As well, like I mentioned in earlier logs, the coherence of this in-air QUAD is poor at lower frequencies.  I spent some time trying to work out better excitation filtering/boosting but to no avail.  Damping works on both M0 and R0 chains of Q6.

This morning I adjusted the x-arm alignment to obtain green locking. First I misaligned ETMX, and adjusted TMSX using the ITMX baffle PDs. See table below for configuration:

NOTE: he baffle PDs read 2.4V at 0dB gain.

Then, using the ETMX camera I centered the beam on ETMX by adjusting the ITMX alignment. I found ITMX (P,Y) = (74.7, -8.2). Finally, I maximized the flashes by aligning ETMX. H1:ALS-X-TR_A_LF_OUT reached about 0.85 cnts. With this alignment we were able to lock the green beam to the arm. The alignments are saved to the guardian. 

It seems that what we see on the ISS second loop photodiodes is real intensity noise in transmission of the IMC. Indeed, as visible in the attached plot, the signal on all ISS PDs has the same shape and is very well coherent with other monitors of the IMC transmitted and reflected powers.

So, as suggested in my previous entry, the RIN at the IMC output is very large, 1e-5 at 10 Hz and 1e-6 at few hundreds Hz.

To investigate the origin of this broadband excess of noise, I had a look at some angular channels related to the IMC.

As visible in the third attached plot, the IMC transmission shows some coherence with the IMC WFS signals and with the periscope accelerometer. In particular:

• WFS_B_YAW shows the same structure at 250-280 Hz as the IMC transmission
• WFS_B_PITCH has the same structure visible at 700 Hz

There is some broadband coherence also, so maybe most of the noise floor is due to angular motion of the beam, converted to intensity noise by the IMC.

Jenne, Kiwamu,

We aligned the SHG and ALS comm paths on ISCT1 this morning. After the alignment, we obtained the following power leves:

• incident on SHG  = 200 mW @  1064nm
• second harmonic power = 1.2 mW @ 532nm
• beatnote of ALS comm = 800 mV p-p @ 80 MHz observed by a scope.

(SHG path alignment)

The beam going through the crystal had been tiled downward -- it was too high on the incident side and too low on the output side of the crystal. We tweaked a 1" steering mirror in front of the bottom periscope mirror to correct it. Also the beam was off in the horizontal direction on the first 2" lens and therfore we shifted the position of this lens to have the beam centered on the lens. We noticed that the HWP after the 2" lens was a bit too low. However, since it was not terrible too low, we left it as it was.

Then we steered a 1" mirror before the crystal to level the beam tilt. It looked like a lens and PBS after the crystal were too high by a bit. Since the first lens strongly deflects the beam, it was difficult to center the beam on both optics. We compromised the beam pointing such that it is not clipped on either of the optics.

We then steered the crystal mount in order to match the crystal to the beam pointing. A screw knob at center bottom was already all the way in and it seemed we needed to go further more, but we could get a green power of 1.2 mW in this configuration and we decided not to touch it any more. We optimized the other three knobs to maximize the green power.

(ALS comm path alignment)

We touched the following optics:

• ALS-PBS1
• ALS-M12
• ALS-BS3
• ALS-BS4
• ALS-BS5
• ALS-M6

in order to optimize the beatnote setup. Since the alignment of the X arm was not stable, we did not really optimize the beat note power. But it the maximum we saw was about 800 mV p-p observed with a scope terminated with a 50 Ohm.

(Green power monitor's feedthrough was bad)

We did not see signals in the green power monitor. We eventually found that this was due to a bad feedthrough (or perhaps the cable was not plugged all the way in). We changed the feedthrough from the top one to the bottom one and it solved the issue. Now the signal is acquired to an ADC. Good.

Install Work

Richard:  cabling for gig-E cameras

cont to build quad (finding parts)

Acceptance Reviews:  starting installation acceptance process (following LLO's lead).  This is a sizeable documentation endeavor.

Commissioning

Jenne up visiting for the week.

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.