J. Kissel

We're really getting pummelled by ground motion, especially the past few days. I attach plots of the band-limited RMS in the Z direction of PEM ground inertial sensors in the corner station and the X end station over the past 48 hours. We've been hit by earthquakes (in the 30-100 [mHz] band), high-micro seism from windstorms and spring ocean activity (in the 100-300 [mHz] band), and gusts of wind and anthropogenic noise (in the 1-3 and 3-10 [Hz] bands). I think this is an excellent representation of why we've had so much trouble trying to find a configuration of the isolation systems that "just works" -- the characteristics of the input motion radically change constantly on a ~3-hour timescale. Not to mention there are times (like in the middle of the plot, 2014-03-16 21:50 UTC) where the earth is just down right angry with all three bad things at the same time.

I apologize for the ambiguity in calibration, I have an email out to Robert asking the proper calibration into physical units. The FOMs with these channels on the wall suggest that the channels are calibrated into "[decaum/s]" in the frames (which I think is 10 * 1e-6 [m/s]) but with no calibrations in the DMT template (and none on the data viewer trace, obviously), I get different numerical values. pem.ligo.org suggests that both the corner-station and endx should be 0.0076e-6 [m/s]. I think whatever units they are, they're at least self-consistent. I'll take spectra at choice times to gather the diversity; stay tuned.

After getting TF's Thursday night that look much better than the previous ones, I've been able to make pretty good progress on ETMY. Friday afternoon I was able to install damping and blend filters. This morning/afternoon I installed a level one controller, then copied it to the level two and three slots, much like we did at HAM4 for the guardian testing. I still have a couple of tests to run on the ISI (no more than a couple of hours total) and write the report for approval, but we have most of what we need and I think it looks pretty good. The attached screenshots are two sets of seismometer transfer functions from thursday night and a set sensor spectra from this morning.

After Travis had notified me of a problem on ETMy where the copper clamps on the ring heater were touching when it was moved into final position I went in chamber and made some adjustments to keep the upper and lower clamps separated. Decided to check if the same problem existed on ITMx and ITMy. Unfortunately, ITMy had part of its macor break while I was adjusting the copper clamps. ITMx had the glass former break sometime after it's installation onto the lower quad. Both lower ring heaters have been removed.

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Please save or publish all log entries prior to the outage.

A reminder entry will be posted to the logbook tomorrow.

Here is the list of commissioning task for the next 7-14 days:

Green team:

• Look for clipping in green transmission.
• Look for 1-10Hz noise.
• Make a mode scan of the red resonances.
• Test the length feedback path to the ETM top suspension point to suppress microseism.

Red team:

• Center the red QPDs in EX.
• RF REFLAIR45 whitening.

Blue team (ALS WFS):

• Remeasure alignment sensing matrix.
• High bandwidth WFS.
• Automate drift alignment.

Blue team (ISCTEY):

• PLL fiber locking.
• Commission PZTs.
• Cut panel and install light pipe.
• Prepare noise eater remote switch. 
• Add WFS.

TMS:

• ETMY beam alignment in final position.

SEI/SUS team: 

• Testing ITMX/ETMX angle drive at higher frequencies. 
• ETMY diagonalization.

I think that when we reworked the X arm input path on Friday, was done with the ETM badly misalinged (by 250urad in pitch).   With the ETM realigned we still have a reflected beam on the LSC PDs and on the WFS.

The mode matching seems to have improved, we see flashes of up to 1000 counts, which is the most we expect given the ETM reflectivity. The lock is verry unstable right now, possibly because of the large motion of the optics.  I have raised the locking threshold for the arm autolocker.

Today we have a different type of interesting seismic time, the low frequency ground motion due to the earth quake has subsided, but we still have microseism well above the 90th percentile (the wind has also died down).  While the microseism is high, it seems like these might be conditions we want to be able to ride out in the long run.  ETMX and ITMX are both isolated with Tcrappy (no sensor correction), both have pitch fluctuations of about 0.3urad, but yaw fluctuations of more than 1 urad.  Right now it is UTC 1:28. 

A screenshot of the ground motion and Op Levs are attached, the .xml file which also includes SEI sensors is available here

Is this ground motion just too much for us to ride out, or is there a configuration for the ISIs that would be better under these conditions?

(Jax, Alexa)

Things that went well this weekend:

1. Alignment of components: the components on ISCTEY are largely in good alignment, with one exception - we ran out of time to align PD4 (faraday rejection/green laser power). 

2. Fiber polarization is adjusted fairly well.

3. Beam scan of green input beam was taken for a baseline measurement for possible beam quality issues in the future. This scan was taken after PZT2 (wanted more points but getting the beam to nanoscan height was being difficult with what I had at the end station). 

Things that did not go well this weekend:

1. PZT mirrors: the PZT mirrors move, but not as desired - there's some p/y coupling, especially in PZT2. The readbacks look questionable as well. Needs follow-up.

2. Acquisition of PLL beatnote: despite some pretty exhaustive alignment to the BBPD, there's no appreciable beatnote. Lots of alignment tweaks and laser temperature adjustments only led to us finding something weak on the laser at 750kHz. 

Our working theory was that we're not getting enough power out of the fiber. 

To the table: 75 uW

Onto the table: 65 uW

After PBS: 45 uW

After the splitter that brings it to the main path: 22 uW

This may or may not be enough power. Sheila suggested we might be saturating the PD with the laser light, but we're planning on taking a closer look at possible causes tomorrow.

In summary, lots of work got done, but there's lots left.

I redid the baffle PD alingment today:

Baflle PD 1: 203.4 Pit -236 YAW

Baffel PD 4: 272.4 PIT -297.1 YAW

Aligned: 237.9 PIT -266.5 YAW

This is only a 3 urad change in Pitch from the save values, 1 urad in yaw.  I saved these new positions.

I also wanted to see if we can use the ITMX Gig E camera instad of the baffle PDs for TMS pointing.  I unlocked the IMC and misalinged MC2, and mislianged the PZTs on ISCEX.  In this situation there should be no IR or Green on ITMX, but I still see some spots on the camera, maybe these are from an OPLEV?  The pixel sum is between 900 and 1600. (exposure is set to 100000).  At least in single shot, it doesn't seem like we can use the camera to replace the baffle PDs. 

I moved PR3 by about 1 urad in TAW and half a urad in pitch to center the beam on the ISCT1 camera. 

Then an earth quake hit (maybe 6.7 in Chile).  The 0.03-0.1Hz seismic band has been above the uper limit of the FOM chart for about an hour.

(Jax, Alexa)

Yesterday we observed that the transmitted light from the fiber was entirely the wrong polarization. This morning, we started out by changing the settings on the MPC.

Settings for X-bound fiber: +18.75 -60.00 -4.50

Initial Y-bound settings: +5.70 -25.35 -56.85

The PD on the fiber monitor path is likely misaligned so we had to optimize based on minimizing power on the fiber polarization PD. Given that criteria, we started with the X-end settings and adjusted to a nominal condition.

Y-bound settings: +18.6 -61.35 -42.30

No guarantees we won't be commenting on this entry later with updated settings.

I haven't caught up on logs now but I'll report what I've found.

Pretty easy--All HEPIs are isolating with Position loops.

All BSC ISIs are Isolating at Lvl3 with TCrappy Blends; HAM 2 & 3 are running Lvl3 controllers with 01-28 blends.  HAM4 is running a Fake Lvl3 with 250 Blend.

Summary: moving both red and green beams to a single periscope seems to have greatly reduced the periscope contribution to the RMS. In HIFO-Y the contribution was about 7 Hz while in HIFO-X, after the move, it is roughly 0.5 Hz. About half of the current HIFO-X periscope peak contribution comes from the periscope on ISCT1 (65-75, 95-105 Hz in the spectrum) with the rest coming from the periscope inside HAM1 (the 68 Hz sharp peak). The forest of peaks between 250 and 700 Hz come from optic supports along the beam paths on ISCT1.

I investigated vibrational noise in the current HIFO-X spectrum. Figure 1 shows coherence between H1:LSC-REFL_SERVO_SLOW_OUT_DQ and the environmental sensors with the most coherence, accelerometers on the ISCTEX table at EX, and the PSL and ISCT1 periscopes at the corner station. Vibration is the source of most of the signal 60 - 900 Hz, and may also become dominant at lower frequencies as other noise sources are reduced. Of course vibrational levels in the region around 100 Hz are now roughly a factor of two or three above what we hope they will be in science mode.

I tap tested ISCT1 while the arm was locked to confirm that the broad peaks in the HIFO-X spectrum at 65-75 Hz and 95-105 Hz were due to the ISCT1 red/green periscope. They do not closely follow the shape of the periscope peak in the accelerometer on the periscope (Figure 1), probably because the features in the HIFO-X spectrum are produced by differences in periscope motion along the red and green path, not total motion. Tap testing also showed that the forest of peaks between 250 and 700 Hz is mainly due to individual optic supports along the red and green paths on ISCT1.

Tap testing did not excite the sharp 68 Hz peak that sits on top of the ISCT1 periscope peaks. Figure 2 shows that I was instead able to excite it with a frequency-sweeping shaker on a blue cross beam of HAM1. The lower plot in Figure 2 shows that the shaker could not have been exciting HAM2 or ISCT1 enough to produce the peak, supporting the conclusion that the peak is due to motion inside HAM1. A very likely source of the 68 Hz peak is the tall periscope inside HAM1 (shown in Figure 3) used to direct the beams to the red/green periscope on ISCT1. Other optic supports in HAM1 should have much higher frequencies.

Moving the two beams onto a single periscope, suggested by Stefan, seems to have worked very well. In HIFO-Y the red and the green ISCT1 periscopes added about 7 Hz to the HIFO-Y RMS (here). In Shiela’s calibrated H1:LSC-REFLBIAS_OUT spectrum, with the calibration thought to be good to a factor of a couple at this frequency, the 65-75, 95-105 Hz portion of the ISCT1 periscope peak adds about 0.20 Hz to the RMS. The 68 Hz HAM1 periscope peak adds about 0.17 Hz (it added a lot more before the clean room was turned off). 

Jax and I went to EY to start up the ISCTEY table, and found that there was no fiber power coming to EY. The cable in the MSR from the MPC to EY is double ended and the wrong end was plugged in to the end station. This has now been fixed. I crudely measured the following powers:

Input of MPC @ MSR ~ 300uW

To EY @ MSR ~224uW

Into ISCTEY patch panel ~ 90uW

I made no adjustments to the MPC; the controller is still off.

We mounted the second green Faraday on a 4-axes mount and reworked the Green injection path to make the beam shape less clipped. We needed to go close to the edge of the EOM and Faraday aperture to get the best beam quality.

As for the EOM, the best beam shape was achieved when the beam is very close to the top edge of the output aperture, maybe it was already touching the hole. We backed off the height adjustment screw (closer to the output) of the EOM mount by half turns so there's no apparent clipping but it's still very close. With this backed off position the beam shape was not as good but we called it good anyway as we couldn't do anything about it.

Anyway, since the center of the aperture for Faraday as well as EOM is NOT the best position as far as the beam quality is concerned, Faraday and EOM should be on adjustable mount. The first Faraday is still fixed, and this means that the beam is not horizontal along the beam path through the first Faraday, which is OK but not ideal (e.g. the beam is not completely centered on the first lens).

We still don't know if this new beam path arrangement is any better  or worse than before.

We took some beam profile measurements, which Sheila will post later. Quality of the injected beam is better, the beam coming back to WFSA looked better than before, WFSB was worse.