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  11970   Tue Feb 2 18:35:47 2016 gautamUpdateGreen LockingLightwave NPRO moved from PSL table to SP table

I've moved the following components that was a part of Koji's setup from the PSL table to the SP table so that I may measure the beam profile of the beam from the spare Lightwave NPRO and work on a mode-matching solution for the X-end.

  • Lightwave laser
  • Lightwave controller
  • Interlock switch (Newport)
  • HWP and PBS

I did some preliminary characterization of the beam from the Lightwave - in the power controlled mode, setting the "ADJ" parameter to 0 (which is the state recommended in the manual) gives an output power of ~240mW. I used the HWP and PBS to dump most of this into a "Black Hole" beam dump, but I was still getting about 300uW of power after this. This was saturating the CCD in the beam profiler (even though 300uW for a beam of ~1mm should be well within the recommended operating limits as per its manual - maybe the ND filter on the camera isn't really ND4.0), and so I further reduced the "ADJ" parameter on the laser controller to -20, such that I had no saturation of the CCD. I will try and take some data later today. The laser is presently in "Standby" mode, and the SP table is fully covered again.

  11971   Tue Feb 2 18:54:02 2016 KojiUpdateGreen LockingLightwave NPRO moved from PSL table to SP table

jiIn fact, it is one of the most difficult type mode profiling to measure a beam directly out from a laser source.

If you reduce the power by ADJ, this significantly changes the output mode as the pumping power varies temperature gradient of the laser crystal and thus thermal lensing in it. I'd recommend you to keep the nominal power.

If you use a PBS for power reduction, you should increase the transmission ~x10 from the minimum so that you are not dominated by possible junk polarization.

Any transmissive BK7 components where the beam is small can cause thermal lensing. In order to avoid this issue, I usually use two noncoated (or one AR coated) optical windows made of UV fused silica to pick off the beam. Once the beam power is reduced I suppose it is OK to use an additional ND filter in front of the CCD.

Another more reliable method is an old-good knife edge measurement.

  11973   Wed Feb 3 23:23:47 2016 gautamUpdateGreen LockingLightwave NPRO moved from PSL table to SP table

As Koji pointed out in the previous elog, the CCD beam profiler was ill suited for this measurement. Nevertheless, to get a rough idea of the beam profile, I made a few rearrangements to my earlier setup:

  • Kept the HWP at the same place it was, as this is roughly the configuration that is going to be used at the endtable anyways. It was ~7cm from the shutter housing on the laser head (unfortunately, I neglected to take a picture).
  • Moved the PBS downstream till it was ~40 cm away (so as to minimize the thermal lensing effect from the ~300mW beam) from the laser head. Rotated the HWP till I got about 6mW of transmitted power (dumped the rest into a black hole)
  • Installed a 95% reflecting BS to further attenuate the power to a level suitable for the CCD (dumped the reflected part onto a razor beam dump)
  • Installed the CCD beam profiler and captured an image, at ~60cm from laser head. In this configuration, I was able to get a clean image capture without the CCD saturating. Unfortunately, I could not transfer it off the laptop used to operate the beam profiler, I will upload a screen capture tomorrow once I get it. Anyways, the main observation was that the beam appeared quite elliptical (ellipticity ~0.6). It was also not clear to what extent thermal lensing at the PBS/BS was afftecting this measurement.

Following Koji's suggestion, I decided to do a knife-edge measurement as well. The measurement configuration was similar to the one described above, except the PBS/BS were removed, and a 1.0 neutral density filter was was installed ~80cm from the laser head (here the ~300 mW beam was >2mm in diameter, as judged by eye). I used the Ophir power meter, which was why I had to install an ND filter as it is rated for 100mW max power. I will put a picture up tomorrow. Thermal lensing shouldn't be of much consequence here, as we just need the whole beam to fall onto the power meter active area (verified by eye), and only the relative change in power levels as the knife edge cuts the beam matters. I took the cross-sectional profile of the beam by translating the knife in the x-direction (i.e. cut the beam "left to right" ).

Attachments 1 and 2 are the results from todays measurements. It remains to repeat by cutting the beam along the y direction, and see what ellipticity (if any) shows up. I also found some "nominal" numbers in page 4 of the Lightwave datasheet - it tells us to expect a waist 5cm from the shutter housing, with horizontal and vertical 1/e^2 diameters of 0.5mm and 0.38mm respectively. My measurement suggests a horizontal diameter of ~0.25mm (half the "nominal" value?!), and the waist location to be 8.22cm from the shutter housing. I wonder if this discrepancy is a red flag? Could it be due to the HWP? I'm reasonably sure of my calculations, and the fits have come out pretty nicely as well...

Attachment 1: KnifeEdgeScans_x.pdf
KnifeEdgeScans_x.pdf
Attachment 2: Beamscan_x.pdf
Beamscan_x.pdf
  11974   Thu Feb 4 09:16:46 2016 KojiUpdateGreen LockingLightwave NPRO moved from PSL table to SP table

I don't think the discrepancy is a serious issue as long as the mode is clean. The mode is determined by the NPRO crystal and is hard to change by anything except for the thermal lensing in the crystal.

And I never succeeded to reproduce the mode listed in the manual.

One thing you'd better to take care is that clipping of the beam produces diffraction. The diffracted beam spreads faster than the nominal TEM00 mode. Therefore the power meter should to be placed right after the razor blade. i.e. As you move the longitudinal position of the razor blade, you need to move the power meter.

  11977   Fri Feb 5 00:23:01 2016 gautamUpdateGreen LockingLightwave NPRO moved from PSL table to SP table

I've repeated the measurement for the x-direction and also did the y-direction, taking into account Koji's suggestion of keeping the power meter as close as possible to the knife edge. Attachment #1 shows a picture of the setup used. Because an ND filter is required to use this particular power meter, the geometrical constraints mean that the closest the power meter can be to the knife edge is ~3cm. I think this is okay. 

The result from the re-measured X-scan (Attachments #2 and #4) is consistent with the result from yesterday. Unfortunately, in the y-direction (Attachments #3 and #4), I don't seem to have captured much of the 'curved' part of the profile, even though I've started from pretty much adjacent to the HWP. Nevertheless, the fits look reasonable, and I think I've captured sufficient number of datapoints to have confidence in these fits - although for the Y-scan, the error in the waist position is large. The ellipticity as measured using this method is also significantly smaller than what the CCD beam profiler was telling us. 

If we are happy with this measurement, I can go ahead and work on seeing if we can arrive at a minimally invasive mode-matching solution for the X-end table once we switch the lasers out...

 

Attachment 1: Beamscan_setup.pdf
Beamscan_setup.pdf
Attachment 2: Beamscan_x.pdf
Beamscan_x.pdf
Attachment 3: Beamscan_y.pdf
Beamscan_y.pdf
Attachment 4: Zscan.pdf
Zscan.pdf
  11951   Tue Jan 26 17:50:22 2016 gautamUpdateGreen LockingLightwave frequency noise measurement

I attempted to measure the frequency noise of the extra Lightwave NPRO we have that is currently sitting on the PSL table. I did the following:

  1. Turn the Lightwave NPRO back on.
  2. Disable MC autolocker and close the PSL shutter.
  3. Checked the alignment of the pick off from the PSL beam and the beam from the Lightwave NPRO onto the PDA10CF. These seemed okay, and I didn't really have to tweak any of the steering optics. I was getting a DC signal level of ~7V (the PD should drive a 1Mohm load up to 10V so it wasn't saturated).
  4. Swept the crystal temperature on the Lightwave using the dial on the front panel of the controller. I found beatnotes at 48.1831 degrees and 45.3002 degrees. However, the amplitude of the beatnote was pretty small (approx. -40dBm on the Agilent NA). I tried playing around with the beam alignment and laser power on the Lightwave NPRO to see if I could increase the beatnote amplitude, but was unsuccessful - turning up the laser power (from the nominal level of 55mW as per the front panel display) caused the PD to saturate at 10V, while as far as I could tell, the alignment of the two beams onto the PD is reasonably good. This seems inconsistent with the numbers Koji has reported in this elog, where he was able to get a beatnote of ~1Vpp for a DC of 2.5 V. 
  5. I tried locking the PLL (in roughly the same configuration as reported here) with this small amplitude beatnote but was unsuccessful. 

I've turned the Lightwave NPRO back to standby for now, in anticipation of further trials later today. I've also restored the IMC. 

  11953   Wed Jan 27 18:19:45 2016 gautamUpdateGreen LockingLightwave frequency noise measurement

After adjusting the alignment of the two beams onto the PD, I managed to recover a stronger beatnote of ~ -10dBm. I managed to take some measurements with the PLL locked, and will put up a more detailed post later in the evening. I turned the IMC autolocker off, turned the 11MHz Marconi output off, and closed the PSL shutter for the duration of my work, but have reverted these to their nominal state now. The are a few extra cables running from the PSL table to the area near the IOO rack where I was doing the measurements from, I've left these as is for now in case I need to take some more data later in the evening...

  11956   Thu Jan 28 00:29:30 2016 gautamUpdateGreen LockingLightwave frequency noise measurement

Summary of the work done today:

Alignment and other work on PSL table

As mentioned in a previous elog, the beatnote amplitude I obtained was tiny - so I checked the alignment of the two beams onto the PD. I did this as follows:

  • Checked the alignment of the two beams on the recombination BS. Moved the steering mirror for the PSL beam until the two were aligned, as verified by eye using an IR card
  • Turn the steering mirror just before the fast focusing lens and thorlabs PD (kept the fork fixed, just loosened the screw on the post to do this) such that the far-field alignment of the two beams could be checked. I used the BS to tweak this alignment as necessary
  • Iterate the previous two steps till I was happy with the alignment
  • Return steering mirror before the PD to its original position, tweak alignment until DC level on the PD was maximized (as verified using an oscilloscope) 
  • Adjust the HWP just after the lightwave laser such that the power arriving at the PD from the PSL beam and the lightwave beam were approximately equal - verified by blocking each beam and checking change in the DC level

After doing all of this, I found a beatnote at ~-10dBm at a temperature of 45.3002 degrees on the Lightwave. The DC level was ~8V (~4V contribution from each beam). 

PLL and frequency nosie measurements:

Pretty much the same procedure as that described in this elog was followed for setting up the PLL and taking the measurements, except that this time, I used the two SR560s in a better way to measure the open loop TF of the PLL. This measurement suggested a UGF of ~ 10kHz, which seems reasonable to me. I turned the 11MHz marconi off because some extra peaks were showing up in the beat signal spectrum. I judged that the beatnote was not large enough to require the use of an attenuator between the PD and the mixer. I was able to lock the PLL easily enough, and I've attached spectra of the control signal (both uncalibrated and calibrated). To calibrate the spectrum, I did a quick check to determine the actuator gain of the spare Lightwave laser, by sweeping the fast PZT with a low frequency (0.5Hz) 1Vpp sine wave, and looking at the peak in the beat signal spectrum move on the network analyzer. This admittedly rough calibration suggests that the coefficient is ~5MHz/V, consistent with the other Lightwave. Eric suggested a more accurate way to do this would be to match up spectra taken using this method and by locking the PLL by actuating on the FM input of the Marconi - I didn't try this, but given the relatively large low-frequency drifts of the beatnote that I was seeing, and that the control signal was regularly hitting ~2V (i.e shifting the frequency by ~10MHz), I don't think this is viable with a low MHz/V coefficient on the Marconi, which we found is desirable as described here

Bottom line:

The spare Lightwave frequency noise seems comparable to the other two measurements (see attachment #2). If anything, it is a factor of a few worse, though this could be due to an error in the calibration? I'm also not sure why the shapes of the spectra from today's measurement differ qualitatively from those in elog 11929 above ~7kHz. 

 

Some random notes:

  • Do we want to do an AM/PM characterization of the spare Lightwave laser as well? It might be easier to do the PM measurement while we have this measurement setup working
  • Yesterday, I noticed some peaks in the spectrum of the PD output while only the PSL beam was incident on it, at ~35MHz and ~70 MHz. They were pretty small (~-50dBm), but still clearly discernible over the analyzer noise floor. It is unclear to me what the source of these peaks are.
Attachment 1: PLL_OLG.pdf
PLL_OLG.pdf
Attachment 2: Freq_noise_comparison.pdf
Freq_noise_comparison.pdf
  11969   Mon Feb 1 18:11:25 2016 gautamUpdateGreen LockingLightwave frequency noise measurement

Before distrubing the beat setup with the spare Lightwave laser, I wanted to see if I could resolve the apparent difference in behaviour between the measured free running noise of the spare Lightwave laser and my earlier measurements with the existing X and Y end lasers above ~5kHz. So I redid the measurement, but this time, on Eric's suggestion, while taking spectra on the SR785, I was careful to maintain the same "CH1 input range" while measuring the control signal spectrum and the measurement noise spectra. The level used was -20dBvpk. I think the measured spectrum shape now makes sense - above ~4kHz, the SR560 noise means that the SNR is poor and so we can only trust the spectra up to this value (the spectra for the end lasers are from earlier measurements where I did not take care to keep the input range constant). Anyways, I think the conclusion is that the spare Lightwave seems to have a free-running frequency noise that is approximately a factor of 3 worse than the Lightwave laser at the Y-end, though this may be because I didn't take the measurement at the optimal operating conditions (diode current, power etc). But I guess this is tolerable and that we can go ahead with the planned swapping out of the existing Innolight at the X-end with this laser. 

I will now move the Lightwave laser off the PSL table onto the SP table where I will do some beam characterization and see if I can come up with a satisfactory mode-matching solution for the swap. I've borrowed a beam profiler from the TCN lab for this purpose.

Attachment 1: Free_running_frequency_noise_comparison.pdf
Free_running_frequency_noise_comparison.pdf
  12075   Wed Apr 13 18:25:07 2016 gautamUpdateendtable upgradeLightwave health check

[Koji,gautam]

Lightwave NPRO information:

Model: 126-1064-700

Serial Number: 337

Manufactured: December 1998!!

Details of checks performed:

Koji tuned the parameters on the laser controller and we observed the following:

  1. Turning "ADJ" to +10 and the pumping current all the way up to the maximum (2.62A) allowed us to recover an output power of 300mW, at a laser crystal temperature of ~45degrees
  2. The output power increased almost monotonically as a function of the laser crystal temperature - why? We were able to see powers as high as 250mW (at ADJ=0) for the maximum crystal temperature of ~60 degrees.
  3. We checked that we could believe the readout of the power meter by measuring the power using the Scientech power meter - we saw ~270mW after the Faraday with this meter, accounting for ~10% loss through the Faraday, this corresponds to an output power of 300mW (all this was done at ADJ=+10, DC=2.62A). I suspect that the display is dodgy though, because changing the Diode Current from 2.52A to 2.62A increased the output power by almost 100mW, which seems hard to believe?
  4. The Lightwave NPRO does not have heat dissipation fins attached - could this be affecting the power output somehow? In any case, this has to be rectified. So if we decide to keep the Lightwave NPRO, the layout will still need minor changes to accommodate the heat fins. Steve, do we have these in hand?

Way forward

Ericq has begun the characterization of the repaired Innolight. We checked that it outputs 1W of power. We will now have to perform the following measurements:

  • Frequency noise using PLL
  • AM/PM response of the PZT
  • Laser power output as a function of diode current - this will be useful for diagnostic purposes in the future
  • AUX temperature vs PSL temperature at which beatnotes can be found
  • Waist measurement - the mode matching and optical layout upstream of the doubling oven at least will have to be modified significantly

All of these will have to be done before installing this laser at the endtable.

I believe the consensus as of now is to go ahead with carrying out the above measurements. Meanwhile, we will keep the Lightwave NPRO on and see if there is some miraculous improvement. So the decision as to whether to use the Innolight is deferred for a day or two.

  12079   Fri Apr 15 18:38:12 2016 gautamUpdateendtable upgradeLightwave health check - NO IMPROVEMENT

I re-measured the power levels today.

We have ~205mW out of the NPRO, and ~190mW after the Faraday. It doesn't look like the situation is going to improve dramatically. I'm going to work on a revised layout with the Innolight as soon as I've profiled the beam from it, and hopefully, by Monday, we can decide that we are going ahead with using the Innolight.

  46   Thu Nov 1 16:34:47 2007 Andrey RodionovSummaryComputersLimitation on attachment size of E-LOG

I discovered yesterday when I was attaching photos that it is NOT possible to attach files whose size is 10Mb or more. Therefore, 10Mb or something very close to that value is the limit.
  6146   Thu Dec 22 20:49:33 2011 KojiUpdateIOOLimitter activated for WFS servos

I set the limitters of the MC WFS servos not to inject the feedback more than 2000.

The residual of the WFS shakes the MC SUSs at every lock loss.

  6732   Thu May 31 16:54:12 2012 JenneUpdateGreen LockingLinks to old elogs for green beatnote laser temps

Because I keep taking a long time to search for these, since I can't remember the keywords in the different entries, here are the links:

elog 3759 : Green X end aux laser temperature setting vs. PSL laser temperature setting

elog 4439 : Green Y end aux laser temperature setting vs. PSL laser temperature setting

More words: beat note, doubling, second harmonic.

Relevant results: 

T_Xend = 8.31 + 0.9293*T_PSL

T_Yend = 6.9825 + 0.87326*T_PSL

 

Also, C1:GCY-SLOW_SERVO2_OFFSET was 29725 (twenty nine thousand seven hundred twenty five) cts when we sat down to start today.

C1:GCX-SLOW_SERVO2_OFFSET was 80 (eighty) cts when we sat down to start today.  Why the offsets are so different, I don't know.  But I was able to find the X green beatnote with this small number offset, so it is approximately correct.

  1904   Fri Aug 14 15:20:42 2009 josephbSummaryComputersLinux1 now has 1.5 TB raid drive

Quote:

Quote:

nodus was rebooted by Alex at Fri Aug 14 13:53. I launched elogd.

cd /export/elog/elog-2.7.5/
./elogd -p 8080 -c /export/elog/elog-2.7.5/elogd.cfg -D

 It looks like Alex also rebooted all of the control room computers.  Or something.  The alarm handler and strip tool aren't running.....after I fix susvme2 (which was down when I got in earlier today), I'll figure out how to restart those.

 Alex switched the mount point for /cvs/cds on Linux1 to the 1.5 TB RAID array after he finished copying the data from old drives.  This required a reboot of linux1, with all the resulting /cvs/cds mount points on the other computers becoming stale.  Easiest way to fix that he found was to do a reboot of all the control room machines.  In addition, a reboot fest should probably happen in the near futuer for all the front end machines since they will also have stale mount points as well from linux1.

The 1.5 TB RAID array mount is now mounted on /home of linux1, which was the old mount point of the ~300 GB drive.  The old drive is now at /oldhome on linux1.

 

  478   Thu May 15 10:40:21 2008 steveHowToGeneralLisa Goggin, PhD
Lisa Goggin successfully defended her thesis on May, 13 2008

"A Search For Gravitational Waves from Perturbed Black Hole Ringdowns in Ligo Data"

She started out as a surf student in the 40m.

Congratulation!
Attachment 1: lisa.JPG
lisa.JPG
  7247   Wed Aug 22 01:54:03 2012 JenneUpdateGeneralList o' things: YarmASS, ETMXTcamera, POXwhiteningTriggering

While meditating on other things, I have noticed / found the following today:

YARM ASS works okay.  Yesterday I measured the sensing matrix for the ASS for both arms (although I forgot to copy one of the matrix elements to my text file for Xarm - needs remeasuring).  I put the Yarm matrix in (after appropriate inversion, only non-zero pitch-to-pitch, yaw-to-yaw elements).  I turned on the Yarm ASS, and  the yaw converged pretty quickly (couple of minutes), with gains of -1 in the servos, overall gain of anywhere between 0.005 and 0.010.  The pitch took much longer, and I had to 'pause' several times by turning off the overall gain for the yarm ass when the MC lost lock (which has happened several times tonight - unknown cause).  Eventually, the pitch settled out, and quit changing, but the lockin outputs weren't zero, even though the error signal for the servos were almost zero (gains for the pitch servos were -0.5, overall gain ~0.005 was better than 0.01 - higher gain caused oscillations in the lockin outputs).  I think this means that I need to remeasure the yarm pitch ass matrix.  It's still much, much faster to just turn on the dithers, watch the striptool of the lockin outputs, and align the cavity by hand.

I think the ETMX Trans camera view is clipped a little bit.  I went down there, and it doesn't seem to be on the last optic before the camera, and moving the spot on the camera doesn't change the shape of the image, so I don't think it's on the camera.  We should look into this, since it's either clipping on the BS that separates some camera beam from the TRX beam, or TRX is getting a clipped beam too.  If the clipping is any earlier in the Trans path, the Trans QPD could also have some clipping.  This requires investigation.  The xarm trigger needs to be reset/disabled so we don't lose lock every time we block the TRX beam (as was happening to me).

XARM really doesn't like to relock unless the POX whitening is turned off.  Good flashes, doesn't really catch (10+ min waiting (while working on Yarm stuff) ).  After turning off the whitening, it catches almost immediately. Even though it's on the to-do list to rethink the tuning of our whitening, we should probably implement the whitening triggering now anyway.  It'll make things easier.

The double integrator that Rana implemented in the X and Y arm servo filters last week take 8 seconds to turn off (due to Foton settings), so even though they are triggered to turn off immediately upon lockloss, they sit around and integrate for 8 seconds, so have huge signals.  If the cavity flashes and the locking trigger engages during that 8 seconds, we send a huge kick to the ETMs.  I'm modeling the response of the filters to an impulse and noise, particularly in the case of ramping on the double integrators.  The problem is that a flat filter has 0deg phase, but the double integrator has 180deg phase at low frequencies, so there's some weird sign flipping that can happen as we ramp - this is part of what I'm modeling.

MC is losing lock unusually often tonight.  Everything on the servo board screen looks normal (which is good since that's all set by the autolocker).  I just disabled the test exc in, but that's been left enabled for a while now, and it hasn't (I think?) been a problem since there shouldn't be anything connected to the board there.  PMC transmission is a little low, 0.816, and FSS is starting to get near -1 on the slow actuator adjust, but we've seen locking of the PMC problems around -1.5 or -2 of the FSS, and the adjust value was at -0.8 earlier tonight and we still had MC locking problems.  I have had the seismic channels open on Dataviewer for the last several hours, and I'm not seeing any spikes in any of the Guralp channels which correspond to the times that the MC loses lock.  BLRMS don't seem particularly high, so MC lockloss cause is still a mystery for today.

The ETMX monitor selector on the VIDEO screen seems not to be switching the actual camera that's shown on the monitor.  Using the script command itself works, so my screen is wrong.

  11190   Wed Apr 1 16:52:02 2015 JenneUpdateLSCList of measurements

I'd like to get a concrete list of measurements written down, so that it's clear what needs to be done before I graduate.

Noise couplings:

  • Laser amplitude noise coupling to DARM
    • We don't have an AOM for ISS right now, but we should be able to just stick it back in the beam path, right?  I think Koji checked that the AOM was all okey-dokey recently.
    • AOM calibration should tell me how much the single-pass amplitude changes as a function of input signal.
  • Laser frequency noise coupling to DARM
    • Inject signal at the CM board input, which should be calibrated by looking at response to calibrated MC2 motion.
  • Marconi phase noise coupling to DARM
    • Marconi can produce internally or accept via BNC 0-10 rad of phase modulation.  Marconi spec sheet should give me rad/V for the input calibration.
  • Marconi amplitude noise coupling to DARM
    • Using external input of Marconi.  Marconi spec sheet should give me input calibration.
  • MICH err to DARM
    • Compare with Optickle model
  • PRCL err to DARM
    • Compare with Optickle model

Noise cancellation:

  • PRC angle
  • MICH noise removed from DARM (compare flat gain FF vs. Wiener FF)
  • PRCL noise removed from DARM (compare FF shape from model vs. Wiener FF)
  • MC length noise (equiv. to laser freq noise) removed from CARM & DARM

Are there things that I'm missing?  I've never had an IFO to characterize before.

  14582   Sun Apr 28 16:00:17 2019 gautamUpdateComputer Scripts / ProgramsList of suspension test

Here are some tests we should script.

  1. Checking Coil Vmons, OSEM PDmons, and watchdog enable wiring
    • Disable input to all the coil output filter modules using C1:SUS-<OPTIC>_<COIL>_SWSTAT (this is to prevent the damping loop control signals from being sent to the suspension)
    • Set ramptimes for these filter modules to 0 seconds.
    • Apply a step of 100 cts (~15 mV) using the offset field of this filter module (so the test signal is being generated by the fast CDS system).
    • Confirm that the step shows up in the correct coil Vmon channel with the appropriate size (in volts), and that other Vmons don't show any change (need to check the sign as well, based on the overall gain in this filter module).
    • Confirm that the largest response in the PDmon signals is for the same OSEM. There will be some cross-coupling but I think we always expect the largest response to be in the OSEM whose magnet we pushed provided the transimpedances are the same across all 5 coils (which is true except for PRM side), so this should be a robust criterion.
    • Take the step off using the watchdog enable field, C1:SUS-<OPTIC>_<COIL>_COMM. This allows us to confirm the watchdog signal wiring as well.
    • Reset ramptimes, watchdogs, input states to filter modules, and offsets to their pre-test values.
    • This test should tell us that the wiring assignments are correct, and that the Acromag ADC inputs are behaving as expected and are calibrated to volts.
    • This test should be done one channel at a time to check the wiring assignments are correct.
  2. Checking the SUS PD whitening
    • Measure spectrum of individual PD input (fast CDS) channels above 30 Hz with the whitening in a particular state
    • Toggle the whitening state.
    • Confirm that the whitened sensor noise above 30 Hz is below the unwhitened case (which is presumably ADC noise.
    • This test should be done one channel at a time to check the wiring assignments are correct.

Checking the Acromag DAC calibration is more complicated I think. There are measurements of the actuator calibration in units of nm/ct for the fast DACs. But these are only valid above the pendulum resonance frequency and I'm not sure we can synchronously drive a 10 Hz sine wave using the EPICs channels. The current test which drives the PIT/YAW DoFs with a DC misalingment and measures the response in the PDmon channels is a bit ad hoc in the way we set the "expected" response which is the PASS/FAIL criterion for the test. Moreover, the cross-coupling between the PDmon channels may be quite high. Needs some thought...

  10126   Wed Jul 2 22:58:11 2014 JenneUpdateLSCLittle Bo-Peep has found her phase

Never mind.  This is just the low pass filter that Den put in to try to deal with the moving cavity pole. 

Before I realized this, just in case it was a computer quirk, Koji and I rebooted the end station front end machines.  This had no effect other than to keep me searching and measuring until I figured it out.  If I turn off the low pass, the phase pops back up to very close to the reference.  The low pass currently comes on automatically as part of the carm_cm_up script.

  10125   Wed Jul 2 21:30:42 2014 JenneUpdateLSCLittle Bo-Peep has lost her phase
Little Bo-Peep has lost her phase,
And can't tell where to find it;
Leave it alone, and it'll come home,
Bringing its degrees behind it.
 
Seriously.  What?  I was holding CARM on sqrtTrans with arm powers of about 1, DARM was still ALS diff, PRMI on REFL33.  CARM was actuating on +ETMX+ETMX, since I kept kicking the MC out of lock, but other than that, everything was set by the carm_cm_up script, so I don't think there should be any big differences.  I took a CARM transfer function, and it seems like the phase bubble has all but disappeared compared to the reference from mid-May. 

CARM_loop_ArmPowers1_2July2014.pdf

I need to figure this out before it's worth trying any acrobatic AO path turn-on scenarios.

 

Also this evening, I went to the Yend and did another tweak-up of the green beam alignment. 

  2284   Tue Nov 17 21:09:17 2009 Jenne, ranaUpdateGeneralLittle Thorlabs Photodiode

[Rana, Jenne]

We opened up the little Thorlabs battery operated PD to see what was inside.  Rana took some pictures, and I drew a schematic (attached).  It's just a diode, biased with a battery (albeit a crazy 22.5V battery).

---------------
Comment by KA: PD is Hamamatsu S1223-01 Si PIN diode.


What a crazy battery. The main point is that it looks like this can be used for reasonable purposes: uses a load resistor on the BNC connector and you can use some pre-amp (e.g. Busby box or SR560) to have a low noise PD readout. You can also use the SR560 in its A-B mode as an 'opamp'. Ground the A input and the use a pole at 1 Hz and make the Output go into the B input through some large series resistor. The BNC from the PD gets Teed into the B input as well.

Then this becomes a transimpedance circuit readout of the diode, using the current noise of the SR560 as the limit.

Attachment 1: ThorlabsPD.png
ThorlabsPD.png
  6511   Mon Apr 9 17:03:38 2012 DenUpdateEnvironmentLms vs Wiener

I tried to figure out why offline LMS filter subtract seismic noise much better from MC_F then the Wiener filter. I did the calculations twice - with my codes and with Matlab in-build functions, the results are the same. So this is not a code error.

The coherence between GUR 1, 2 and MC_F is still poor. Wiener filter is linear and its performance is confined to the frequency ranges where we see coherence. Lms filter is non-linear and it may be possible to subtract the noise even if non-linear effects are present in the system.

gur12_mcl.png

I've checked seismometer readout box again. I've soldered 50 Ohms to plus and minus inputs to VERT 1,2 N/S 1,2, E/W 1,2 - GUR 1 and 2 use these channels. Then I put the box back and connected it to the ADC.

seismboxnoise.png

The plot shows that the readout box noise is below the ADC noise. It is possible that amplifiers introduce non-linear effects. To check this I plotted the coherence between OSEM sensors and GUR1X signal:

gur1_osem.png

The coherence between OSEM sensors and GUR1X is pretty good, so may be witness path is not responsible for low coherence at 0.1 - 0.5 Hz between MC_F and GUR 1,2. IT seems that MC_F is bad at low frequencies. I terminated the input to the Channel 1 of the Pentek Generic board, where MC_F is plugged in.

mcl_noise.jpg

ADC is also good. Something else is wrong.

  10543   Fri Sep 26 11:44:55 2014 nicolasFrogsComputer Scripts / ProgramsLoaded larry's fake filter into C1:ALS-OFFSETTER2

 Larry and Nicolas

Larry's transfer function measurements suddenly started returning 0dB 0degrees when before there was some fake filter in the C1:ALS-OFFSETTER2 filter bank.

We looked in the filter bank and his filter was gone. So I created a new filter called LARRYP in FM2. We also disabled the output so he could drive the filter bank and test his TF code.

  15633   Mon Oct 19 15:38:42 2020 KojiUpdateElectronicsLoan: A file binder "40m wiring diagram"

I'll bring a file binder "40m wiring diagram" to home at the next chance.
There is another one on the shelf in the control room.

(I thought I put it in my bag, but it looks like that I left it somewhere around the fax area)

  10122   Wed Jul 2 15:35:34 2014 ericqUpdateComputer Scripts / ProgramsLocal Chiara backups

Koji has provided a 2TB USB3 external hard drive that will get daily backups of chiara:/home/cds, the idea being that if the internal HD at /dev/sdb1 fails, we can physically open the external up, and swap the hard drive into chiara. 

We're running an rsync job on it right now, which should be done in a few hours. (USB3 is fast!)

I've also written a backup script at scripts/backup/rsync_chiara.backup which keeps its books in scripts/backup/rsync_chiara.backup.log 

I'm adding a entry to the root crontab on chiara to execute the script every day at 7am. 

 

  10236   Fri Jul 18 15:21:12 2014 ericqUpdateComputer Scripts / ProgramsLocal Chiara backups

Quote:

I've also written a backup script at scripts/backup/rsync_chiara.backup which keeps its books in scripts/backup/rsync_chiara.backup.log 

I'm adding a entry to the root crontab on chiara to execute the script every day at 7am. 

 I had some syntax errors in the script that prevented the script from doing the right thing. The backup is now up to date, and the cronjob should work. 

  15167   Tue Jan 28 17:36:45 2020 gautamConfigurationComputersLocal EPICS7.0 installed on megatron

[Jon, gautam]

We found that the caput commands were taking much longer to execute on megatron than on pianosa (for example). Suspecting that this had something to do with the fact that megatron was using EPICS binaries from the shared NFS drive which were compiled for a much older OS, I installed the latest stable release of EPICS on megatron. The new caput commands execute much faster. I also added the local EPICS directory to the head of the $PATH variable used by the MC autolocker and FSS Slow scripts, so that they use the new caput command. But mcup is still slow - maybe my new path definition isn't picked up and it is still using the NFS binaries? To be looked into...

Quote:

There were a bunch of medm processes stalled on megatron (connected with screenshot taking). To see if they were interfering with the other scripts, I killed all of the medm processes, and commented out the line in the crontab that runs the screenshots every 10 mins. Let's see if this improves stability.

  390   Fri Mar 21 17:01:21 2008 ranaConfigurationDMFLocale change on Mafalda & seisBLRMS restart
Ever since we moved the accelerometers to be around the MC and changed their names, the seisBLRMS
has not been working. I tried to restart it today after fixing the channel names in the par file
but I ran into a PERL / UBUNTU bug.
perl: warning: Setting locale failed.
perl: warning: Please check that your locale settings:
        LANGUAGE = (unset),
        LC_ALL = (unset),
        LC_TIME = "en_US.ISO8859-1",
        LC_MONETARY = "en_US.ISO8859-1",
        LC_CTYPE = "en_US.ISO8859-1",
        LC_COLLATE = "en_US.ISO8859-1",
        LC_MESSAGES = "C",
        LC_NUMERIC = "en_US.ISO8859-1",
        LANG = "en_US.UTF-8"
    are supported and installed on your system.
perl: warning: Falling back to the standard locale ("C").

I don't know how this crept up or when it started. There were a bunch of fixes on the Ubuntu
forums which didn't work.

In the end I just set the 'unset' environment variables via our cshrc.40m file and this seemed
to make ligotools/perl happy. Lets hope this lasts...I love Linux.
  9360   Thu Nov 7 14:39:49 2013 JenneUpdateLSCLock Acquisition Game Plan

Between the 40m meeting, and chatting with Gabriele, there was lots of talking yesterday about our 40m Lock Acquisition game plan. 

From those talks, here is my current understanding of the plan, in a Ward-style cartoon:

 LockAcquisition_7Nov2013.pdf(This is a 2 page document - description of steps is on 2nd page)

If you look closely, you will notice that there are several places that I have used "?" rather than numbers, to indicate what RFPD signal we should be using.  To fill these in, I need to look at some more simulations, and think more carefully about what signals exist at what ports, and what SNR we have at each of those ports.

Also, while the overall scale of the arm power plot is correct, the power level at each step is totally arbitrary right now, and should just be taken to mean places (in time) where the CARM offset is reduced a little more.


There are several things at this point that we know we need to look into:

* POP 22/110 PD and filtering electronics should be switched to a broadband PD, rather than the Thorlabs PD + Miniciruits filters. (Hardware)

* Whitening for the transmission QPDs needs to be thought about more carefully. (Calculation, then hardware)

* Chose a good SNR REFL DC signal, which may or may not be from the PD we are currently using (I think it's the DC of REFL11, but I'll have to check). (Calculation)

* For DRMI locking, what is the size of the SRCL error signal at AS55, AS165, and the REFL ports?  Do we need to lock with AS port, and then switch over to a REFL 3f port, to make acquisition easier?  (Simulation)

* Similarly, I want to make the equivalent of Figure 3 of T1000294, with our 40m parameters. (Simulation)

* To set the phase of AS110, simulate the demod phase of AS110 in both DRMI and SRMI cases.  If no (significant) change, maybe we can set the phase in the real system by misaligning the PRM, and watching the SRMI flash.  (Simulation)

* Simulate an arm sweep, up to many orders of the sidebands, to see how close to the carrier resonance any sideband resonances might be.  If something like the 4th order sideband resonates, and then beats with a 1st order sideband, is that signal big enough to disturb our 3f locking of the PRMI / DRMI?  We want to be holding the arms off resonance with ALS closer to the carrier than any "important" sideband resonances (where the definition of "important" is still undetermined).  (Simulation)

* Check if we can hand DARM from the DC transmission signals to the final RF signal while we still have a large CARM offset. Is there a point where the CARM offset is too large, and we must be still using the DC signals? (Simulation)

* At what arm power level can we transition from ALS to IR DC transmission signals for the individual arms? (Simulation)

* Still need to finish calculating what could be causing our big arm power fluctuations (Test mass angular motion?  PRM angular motion? ALS noise?) (Calculation)


Replys, and comments are welcome, particularly to help me understand where I may have (likely did) go wrong in drawing my cartoon. 

  10998   Wed Feb 11 00:07:54 2015 ranaUpdateLSCLock Loss plot

Here is a lock loss from around 11 PM tonight. Might be due to poor PRC signals.  \oint {\frac{\partial PRCL}{\partial x}}

This is with arm powers of ~6-10. You can see that with such a large MICH offset, POP22 signal has gone done to zero. Perhaps this is why the optical gain for PRCL has also dropped by a factor of 30 crying.

This seems untenable no. We must try this whole thing with less MICH offset so that we can have a reasonable PRCL signal.cool

Attachment 1: 1107673198.png
1107673198.png
  15348   Tue May 26 02:15:36 2020 gautamUpdateLSCLock acquisition portal entry

Summary:

Provided the IMC is cooperative, the input pointing isn't drifting, and the RF offsets aren't jumping around too much, the locking sequence is now pretty robust.

Details:

Most of the analysis uses data between the GPS times 1274418176 and 1274419654 that are recorded to frames.

  15349   Tue May 26 02:31:00 2020 gautamUpdateLSCLock acquisition sequence

Here, I provide some details of the sequence. Obviously, I am presenting one of the quickest transitions to the fully locked state, I don't claim that every attempt is so smooth. But it is pretty cool that the whole thing can be done in ~3 minutes.

See Attachment #1 for the labels.

  • A --- Arms are locked on POX/POY, and EX/EY lasers are also locked to their respective arms. The phase tracker outputs are averaged in preparation for transitioning control from POX/POY to ALS. 
  • B --- Aforementioned transition has been realized. CARM offset of -4 is applied. Based on this calibration, this is ~ 4 nm.
  • C --- PRM is aligned in preparation for 3f vertex locking. Between C and D, the long pause is because I also use this time to DC couple the ITM Oplev servos, which requires some averaging. 
  • D --- PRMI is locked. CARM offset reduction begins. Between D and E, I scan CARM through a resonance, and look at the necessary offset requried in the CARM_B (=RF) path. It is a mystery to me why this is required.
  • E --- Ramp CARM offset completely to 0. Twiddle CARM_A and DARM_A offsets (=ALS path) to maximize the arm transmitted powers. Between E and F, you can see that the arm powers stabilize somewhat before any RF control is engaged (more on this later), which means we are approximately in the linear regime of the CARM PDH signal, and the switchover can be effected. As I write this, I wonder if there is any benefit to normalizing the REFL_11 error signal (=CM_SLOW) by the arm transmission for a broader capture range?
  • F --- CARM_B and DARM_B (=RF) paths engaged. I ramp off the ALS servos between F and G using a 10 second ramptime.
  • G --- IFO is now under RF control, ALS control has been turned off completely.
  • H --- Rudimentary ASC is enabled. The ITMs are already running with DC coupled Oplev servos, and for the ETMs, I use the Transmon QPDs. The loop shapes/gains for this part haven't been finalized yet, but some improvement in the stability is seen.

This particular lock held for ~20 minutes so I could run some loop characterization measurements etc.

I am struggling to explain:

  1. Why POP22 goes to 0 when we zero the CARM offset? The arm length is such that the 2f fields don't experience any abrupt changes in reflectivity from the arm cavity for a wide range of offsets. This signal is the trigger signal for the PRMI LSC control - right now, I get around this problem by mixing in some amount of POP DC once the PRMI is locked. But if the lock is lost, this requires some EPICS button gynmastics to try and salvage the lock... I guess the 1f field components experience a different phase on reflection at various offsets, so maybe I should be looking at sqrt(POP22_I^2 + POP22_Q^2) instead of just POP22_I.
  2. Why is an error point offset required in the CARM RF path?
Attachment 1: PRFPMIlock_1274418200_1274418550.pdf
PRFPMIlock_1274418200_1274418550.pdf
  15360   Wed May 27 20:14:51 2020 KojiUpdateLSCLock acquisition sequence

I see. At the 40m, we have the direct transition from ALS to RF. But it's hard to compare them as the storage time is very different.

  15364   Wed Jun 3 01:34:53 2020 gautamUpdateLSCLock acquisition update portal

Highlights:

  • With better ASC servos implemented, I think the lock stability has been improved. 
  • Arm transmission of ~350 was stably maintained (PRG~20, overcoupled). It went as high as 410, so this is now very close to the highest (~425) I've ever managed to get.
  • I was trying to get the vertex transitioned to 1f control but it remains out of reach for now.  The noise at ~100 Hz is dominated by MICH-->DARM coupling (as judged by coherence, I haven't yet done the broadband noise injection characterization). I figured I'd try the 1f transition before thinking about feedforward.
  • The biggest problems remain flaky electronics (poor IMC duty cycle, jumping RF offsets, newly glitchy seismometer, ...)

Details:

  15369   Wed Jun 3 03:29:26 2020 KojiUpdateLSCLock acquisition update portal

Woo hoo!

Which 1f signals are you going to use? PRCL has sign flipping at the carrier critical coupling. So if the IFO is close to that condition, 1f PRCL suffers from the sign flipping or large gain variation.

  15371   Wed Jun 3 11:40:56 2020 gautamUpdateLSCLock acquisition update portal

For these initial attempts, I was just trying to transition MICH to REFL55Q. I agree, the PRCL situation may be more complicated.

Which 1f signals are you going to use? PRCL has sign flipping at the carrier critical coupling. So if the IFO is close to that condition, 1f PRCL suffers from the sign flipping or large gain variation.

  11443   Fri Jul 24 13:49:09 2015 SteveUpdatesafetyLock doors please !

Thursday morning I found the control room emergency exit not locked.

Please check the doors when leaving the lab , specially when you are the last one out.

  8376   Fri Mar 29 19:56:02 2013 GabrieleMetaphysicsLSCLock of PRMI on sidebands

I finally managed to get long stretches of PRMI lock, up to many minutes. The lock is not yest very stable, it seems to me that we are limited by some yaw oscillation that I could not trace down. The oscillation is very well visible on POP.

Presently, PRCL is controlled with REFL55_I, while MICH is controlled with AS55_Q. This configuration is maybe not optimal from the point of view of phase noise couplings, but at least it works quite well. I believe that the limit on the length of locks is given by the angular oscillation. I attach to this entry few plots showing some of the lock stretches. The alignment is not optimal, as visible from a quite large TEM01 mode at the dark port.

Here are the parameters I used:

MICH gain -10   PRCL gain -0.1

Normalization of both error signal on POP22_I with factor 0.004

Triggering on POP22: in at 100, out at 20 for both MICH and PRCL.

POP55 demodulation phase -9

MICH and PRCL control signal limits at 2000 counts

 

There is a high frequency (628 Hz) oscillation going on when locked (very annoying on the speakers...), but reducing the gain made the lock less stable. I could go down to MICH=-1.5 and PRCL=-0.02, still being able to acquire the lock. But the oscillation was still there. I suspect that it is not due to the loops, but maybe some resonance of the suspension or payload (violin mode?). There is still some room for fine tuning...

Lock is acquired without problems and maintained for minutes.

Have a nice week-end!

Attachment 1: lock_prmi5.pdf
lock_prmi5.pdf
Attachment 2: lock_prmi6.pdf
lock_prmi6.pdf
Attachment 3: lock_prmi7.pdf
lock_prmi7.pdf
Attachment 4: oscillation.pdf
oscillation.pdf
Attachment 5: lock_prmi8.pdf
lock_prmi8.pdf
  8378   Sun Mar 31 17:26:32 2013 ranaUpdateLSCLock of PRMI on sidebands

 

 Our first move has to be fixing the whitening switching for REFL55. That's the configuration we need to start and then move onto REFL165 to get to FPPRMI.

  8380   Mon Apr 1 09:25:35 2013 JenneMetaphysicsLSCLock of PRMI on sidebands

[Gabriele, Jenne]

I put a notch in FM10 for both MICH and PRCL at 628Hz, to try to prevent us from exciting the mode that Gabriele saw on Friday.  Since those filter banks were all full, I have removed an ELP50 (ellip("LowPass",4,1,40,50)).  I write it down here, so we can put it back if so desired.

  6509   Mon Apr 9 15:02:30 2012 JenneUpdateLSCLocked MICH

I was going to try some locking, but things are a little too noisy. 

Just so Kiwamu knows what I did today, in case he comes back....

I ran LSCoffsets, and aligned both X and Y arms and saved their positions, and aligned MICH, and saved the BS position. 

I'll play with it more later, when there aren't trucks driving around outside that I can hear / feel in the control room.

  6510   Mon Apr 9 15:09:34 2012 JenneUpdateLSCLocked MICH

Quote:

I was going to try some locking, but things are a little too noisy. 

Just so Kiwamu knows what I did today, in case he comes back....

I ran LSCoffsets, and aligned both X and Y arms and saved their positions, and aligned MICH, and saved the BS position. 

I'll play with it more later, when there aren't trucks driving around outside that I can hear / feel in the control room.

 After giving up on locking, the MC is getting unlocked every now and again (2 times so far in the last few minutes) from transient seismic stuff.

  58   Fri Nov 2 12:18:47 2007 waldmanSummaryOMCLocked OMC with DCPD
[Rich, Sam]

We locked the OMC and look at the signal on the DCPD. Plots included.
Attachment 1: 071102_OMC_LockedDCPD.gif
071102_OMC_LockedDCPD.gif
Attachment 2: 071102_OMC_LockedDCPD.pdf
071102_OMC_LockedDCPD.pdf
  4313   Thu Feb 17 11:51:14 2011 josephbUpdateCDSLockin filter names too long - broke loading

Problem:

Could not load filters into the C1:SUS-ETMX_LOCKIN1_SIG filter bank.

Reason:

Apparently the filter bank name was too long.  I'm not sure why this isn't caught by the real time code generator, I'm planning on asking Alex and Rolf about it today.

Solution:

Reduce the name of the components.  Basically LOCKIN1 needs to become something like LOCK1 or LIN1.

 

In related news, it looks like the initial filters are hard coded to be 2048 Hz.  Given that they start out empty they won't cause things to break immediately, and if you're editing the file you can update the rate as you add the filter.  I'll also bring this up with Alex and Rolf and see if the RCG can't be more intelligent about its filter generation.

 

  1316   Tue Feb 17 05:20:11 2009 YoichiUpdateLSCLocking
Since we excluded *.snap and *.req files from the svn control in the medm directory and these were not restored by the svn co, the burt part of the align/mis-align scripts were not working correctly this evening. So I recreated .req files and cooked up some mis-aligned .snap files.
After some cut-and-try work, I was able to run the dither alignment scripts fine.

Due to the above mentioned delay, the locking work started around midnight.

Tonight, the DD hand-off was not robust. I spent sometime to optimize this.
After the optimization, the locking proceeded to the DC CARM/DARM control state stably.
The CARM->MCL hand-off failed because the LSC-MC offset button was off.
I added a line to turn on the button in the ontoMCL script.
Today, the offloadMCF script worked fine.

Next, the cm_step script stumbled on the "ENGAGERIZING" of the AO path.
I got a hunch that the AO path might not be connected to the MC board.
Indeed, OMC_OSC_FM was connected to the IN2 of the MC board. Looks like it was used for the optimization of the modulation frequencies.
Probably I had the hunch because I did it Smile

I was able to increase the arm power up to 3.9.
The script failed when it tried to switch the CARM signal from TR_DC to SPOB_DC.
I haven't tackled on this issue yet.
  16247   Wed Jul 14 20:42:04 2021 gautamUpdateLSCLocking

[paco, gautam]

we decided to give the PRFPMI lock a go early-ish. Summary of findings today eve:

  1. Arms under ALS control display normal noise and loop UGFs.
  2. PRMI took longer than usual to lock (when arms are held off resonance) - could be elevated sesimic, but warrants measuring PRMI loop TFs to rule out any funkiness. MICH loop also displayed some saturation on acquisition, but after the boosts and other filters were turned on, the lock seemed robust and the in-loop noise was at the usual levels.
  3. We are gonna do the high bandwidth single arm locking experiments during daytime to rule out any issues with the CM board.

The ALS--> IR CARM handoff is the problematic step. In the past, getting over this hump has just required some systematic loop TF measurements / gain slider readjustments. We will do this in the next few days. I don't think the ALS noise is any higher than it used to be, and I could do the direct handoff as recently as March, so probably something minor has changed.

  1317   Wed Feb 18 03:17:40 2009 YoichiUpdateLSCLocking
Yoichi, Kakeru,

Last night, the cm_step script failed at the hand-off of CARM error signal from TR_DC to PO_DC.
This was fixed by reducing the PO_DC gain by a factor of 2.
Currently the script fails when changing C1:LSC-DEMOD_GAIN to zero.
To be honest, I don't fully understand the purpose of this step.
  15471   Sun Jul 12 02:42:01 2020 gautamUpdateLSCLocking (on rossa)

Main goals tonight were:

  1. Check if I can lock the interferometer by working on rossa - indeed, I could! It is much snappier than the ageing pianosa. The viewing angle of the CRT monitors from this corner isn't so good though.
  2. Measure step responses for the arm ASC loops to see if any insight can be gained into these loops. Analysis forthcoming...
Attachment 1: ASCsteps.png
ASCsteps.png
  1334   Tue Feb 24 02:23:40 2009 YoichiUpdateLockingLocking - MC board bad
Rob, Yoichi, Alberto, Kiwamu, Kakeru

We found that the OMC alignment feedback was on for the POS X loop even though the OMC was not locked.
This caused the PZT mirror to be tilted in yaw a lot. This was probably the reason for the mysterious shift in the AS beam last week, because the AS RF beam is picked up after this PZT mirror.
Rob aligned the OMC and we re-centered the AS PDs and the CCD.
This changed the DARM RF gain, so we changed it from 3 to 1. This gain used to be -1. It is still not understood why the polarity was changed.
The MC length was changed ? We should check the sideband transmission.

After this, we reached to the arm power 4. But the IFO loses lock immediately after the moving zero is turned off.
At this stage, the CARM loop bandwidth is supposed to be high enough that the moving zero is no longer necessary.
However, when we measured the MCL loop gain with several different AO path gains, the loop shape did not change at all.
This led us to suspect the AO path may not be connected. The cabling from the common mode board to the MC board seemed ok.
We tested the signal flow in the MC board using a signal generator and an oscilloscope.
Then we found that a signal injected to the IN2 (AO path) does not reach to the TP1A (right after the boost stages), though the signal is visible in the OUT2 (monitor BNC right after the initial amplifier (B-amp) for the AO path). The signal from IN1 (MC REFL) can be observed at TP1A. This means something is broken between the B-amp and the sum-amp in the AO path.
We will check the MC board tomorrow.
ELOG V3.1.3-