The AC response of the SRM actuator has been calibrated.

 

For a comparison, the length fluctuation of Signal-Recycled ITMX (SRX) and ITMY (SRY) have been measured.

Roughly speaking the length motion of SRX and SRY are as loud as that of PRCL.

Some details about the measurement and data analysis can be found in the past elog entry (#5582).

In the process of converting the raw spectra to the calibrated displacements the SRM actuator was assumed to have a resonance at 1Hz with Q = 5.

(Notes on SRX/Y locking)

The efficiency of the mode matching (MM) to PRC (Power-Recycling Cavity) has been estimated by using the interferometer.

The estimated MM efficiency is about 74 % when losses in the cavity are assumed to be zero.

(Motivation)

(Measurement)

(Analysis)

(Results)

Here are the measured values in REFLDC

Anyways the estimated MM efficiency with the sidebands effect included and without loss effect is

        MM efficiency = 73.7 +/- 1.7 % (1 sigma error)  or +/- 8.7 % (5 sigma error)

"^2"s are missing in the second equation, but the calculation results seem correct.

PRX and PRY have different mode matching because of the Michelson asymmetry.
Are individually estimated mode matching indicates any sign of reasonable mode mismatch?
(The difference can be very small because the asymmetry is not so big.)

 How does it make sense that the motion at 0.1 Hz of PRC is 10x larger than MICH?

EDIT by KI:

[Mirko, Kiwamu]

I tried to answer two questions regarding the IMC:

1. What is the coupling of fluctuations in the SB freq. to SB transmitted power?
2. What (if any) is the influence of the IMC on the AM?

I ran into some weird things regarding the corresponding optickle simulations:
1. There seems to be some artifact at the beginning of every simulation sweep.
2. The position of features depends on the parameters of the sweep.

I mailed Matt asking if he sees some error in the simulations

- Thank you for the correction. The missing square operation has been added correctly on the last entry (#5639).

[Koji Suresh]

The steering mirrors for PMC were aligned. The transmission went up from 0.779 to 0.852.

 I lost UL osem voltage this morning when I was checking the actual connection at rack ETMY

This after noon I disconnected  the 64 pins IDE connector from satelite amp at the rack, and the two 25 pins Dsubs at this juction board.

UL OSEM recovered after reconnecting these three connectors.

Atm3, bad connection.........noisy UL

The angle of incidence of light is for some mirrors on the YARM end table different from 45° even though the mirrors are coated for 45°.

The mirrors below are useful if there are plans to replace these mirrors by properly coated ones.

* This is the new mirror as decribed on http://nodus.ligo.caltech.edu:8080/40m/5623

[Kiwamu, Koji, Suresh]

After correcting several errors in the WFS loops, we turned them on today and saw them working!

A while back (last week actually) I noticed that the WFS1 and WFS2  QPD segments were numbered in a different order but that their input matrices did not reflect this change.  As result the WFS pitch and yaw definitions were pretty much mixed up.  However even after clearing this up the signals still showed significant amount of cross couplings. 

This problem was finally traced to the relative phase between I and Q channels of the WFS segments.  Koji suggested that I check the relative phase between all the segments to be sure.  I then repeated the procedure that Valera and I followed in our earlier elog # 5321 , and found that the phases indeed required to be adjusted.  The excitation of MCL was at 6Hz, 100mVpp, as before.   The WFS response after this was much improved i.e.  the pitch yaw cross couplings were not visible when we misalign the MC with sliders in MC_ALIGN.  And the magnitude of the response also increased since the signal was transferred from the Q to I channels.  The the phases were tweaked by hand till Q< 1% of I.  However when I repeated this measurement an hour later (I wanted to save the plots) I found that the phases had changed by a few percent! 

Koji noticed that the MC_REFL camera image showed significant intensity fluctuations and advised that we try a higher frequency and lower amplitude to avoid nonlinear effects in the WFS and in the MCL to PSL lock.  So we repeated the process at 20Hz and 20mVpp, introduced at the IN2 of the MC_Servo.  The fig below shows the level to which we reduced the signal in Q.

We then checked the relative phase between various quadrants by looking at the time series in dataviewer.  WFS2 Seg4 phase had to be flipped to bring it into phase with all the rest. 

After this I tried to see the WFS response to moving the MC1 and MC3 with the sliders and determined the following relations:

Disregarding the MC2 for now and assuming arbitrary gains of 1 for all elements we inverted these matrices inserted them into the WFS_servo_outmatrix.  We then found that the with a sign flip on all elements the loops were stable.  In the servo filters we had turned on only the filter modules 3 and 4.  There was no low frequency boost.   We gradually increased gain till we saw a significant suppression of the error signal at low frequencies as shown below.  There was also an associated suppression of Intensity noise at REFL_DC after a single bounce from PRM.

To see if the locks can actually realign the MC if it were manually misaligned, we turned the loops off and misaligned MC by moving MC3 pitch by 0.05 (slider position), and then turned on the loops.  The locks were reengaged successfully and the MC regained alignment as seen on the StripTool below:

We can now proceed with the fine tuning the servo filters and understand the system better:

Q1:    Does the WFS (I to Q) phase drift rapidly?  How can we prevent it?

Q2:   How is that we do not see any bounce or roll resonances on the WFS error signals?

Q3:  How do we include the MC2 QPD into the WFS Servo?

I will proceed with determination of the actual transfer coefs between the MC DoF and the WFS sensors. 

The response of the BS actuator in a low frequency regime has been measured.

(Measurement)

 + With free swinging MICH, the sensor (AS55_Q) was calibrated into counts/m.

     => The peak-peak counts was about 110 counts. So the sensor response is about 6.5x10⁸ counts/m

 + Locked Michelson with AS55_Q and the signal was fedback to BS.

 + Set the UGF high enough so that the open loop gain below 10 Hz is greater than 1.

 + With DDT's swept sine measurement, C1:LSC-MICH_EXC was excited with a big amplitude of 40 counts.

 + Took a transfer function from C1:LSC-MICH_OUT to C1:LSC-MICH_EXC.

 + Calibrated the transfer function into m/counts by dividing it with the sensor response.

This seems like an error prone method for DC responses due to the loop gain uncertainty. Better may be to use the fringe hopping method (c.f. Luca Matone) or the fringe counting method

I think the precision due to the loop gain uncertainty is something like 0.1% at 0.1 Hz. It's not the issue.

The real issue was the loud motion of MICH, which degrades the coherence of the measurement.

Also last night I tried the fringe hopping technique and gave it up for several reasons.

(uncertainty due to the loop gain)

(Effect from the MICH motion)

After analyzing the cleaner data, I get the following:

Y_Length_long  =  37.757 meters

X_Length_long  =  37.772 meters
 

As stated in the wiki, the goal arm length was  L = 37.7974 m for each arm. 

So we're within 2cm for X, and within 4cm for Y.

According to Kiwamu's awesome tolerance calculation, we need to be within 2cm for each arm.  Given that we started out 20cm wrong for X and 25cm wrong for Y, we're a lot closer now, even though we aren't meeting our Yarm requirement yet.

Probably some Optickle action is in order, to see what these new lengths give us in terms of sideband phase and other stuff.

If you want more digits on my calculated numbers (which are probably meaningless, but I haven't done a careful error analysis), in my directory ...../users/jenne/Xarm and ..../users/jenne/Yarm run Xarm_find_peaks_and_length.m and Yarm_find_peaks_and_length.m  respectively.  These will output the lengths.

The TRY (TRansmitted light from Y arm ) path was a bit realigned because there had been a small clipping.

This clipping was introducing offsets on the error signals of the C1ASS servo.

(Story)

During I was running the C1ASS servo on the Y arm I found every time after the auto-alignment is done there still remained a slight offset in the beam pointing,

I looked at the CCD camera which looks at the transmitted light and then introduced an intentional misalignment in ETMY in order to find an obvious clipping.

Indeed there was a clipping in horizontal direction. I checked through the optics on the Y end optical bench.

On the second mirror (beam splitter) the beam was on a very edge. So I steered the first steering mirror to fix it,

In addition to that an iris which is placed between the first and second mirror was also clipping the beam,

So I fully opened the aperture of the iris.

 Atm2 is before optical path adjustment. The idea was to remove possible clipping in vacuum.

Coherense significantly reduced below 4 Hz

Today I will replace the He/Ne laser 1125P with 1103P

An update on calibration of the BS actuator : A fitting has been done.

(Fitting)

(Fitting result)

There was a 60 Hz and 120 Hz oscillation on the green PDH photo diode output. After a long search, I could identify that

the source was a broken BNC cable which was connected to the photo diode. I exchanged that BNC cable and the 60 Hz

and 120 Hz are gone :-)

With the new cable the PD output was less noisy so that it was easier to achieve a better alignment of the light to the cavity.

The reflected power could be reduced from 40% to 30%. For perfect alignment the reflected power would be 20%.

The mini circuit power splitter ZFRSC-42S+ used at the YARM has no balanced output as it should have according to the data sheet.

@ 0.05MHz  the amplitude unbalance should be 0.03 dB

A quick measurement shows that there is a LO amplitude dependent unbalance:

So my question is, shall I replace the power splitter just in case it is further degrading?

- status update on LSC activity :

The measurement of the LSC sensing matrix has begun. But no useful results yet.

 The measurement script (#4850) ran pretty well after I did some modifications to adopt the script to the latest LSC model.

However the SNR weren't so great particularly in REFL33 in the PRMI configuration.

So I will tune the amplitude of excitations and integration times tomorrow.

Currently the excitation is at 238.1 Hz, where no disturbing structures are found in the spectra.

 I replaced the JDSU-Uniphase 1125P by 1103P He/Ne laser. This new laser had 2.8 mW output yesterday. It degraded to 0.5 mW by this morning.

The beam size on the QPD is ~3 mm  This should give us  better sensitivity. These are not the perfect lenses at all, but we have them here.

On the other hand, there are still some coherence below 1 Hz, so the laser intensity noise or clipping dominating  this  part of the spectrum.

It is a 4^th order filter with cut of frequency of 120 kHz.

Design

Measurement

[Rana, Koji, Mirko]

We looked into the CDS RMS block c-code as described in Rolfs RCG app guide. Seems the block uses a first order LP filter with a corner freq. / time of 20k execution cycles. There are also some weird thersholds at +-2000counts in there.

I was looking into implementing a hand-made RMS block, by squaring, filtering, rooting. The new RMS (left) seems nicer than the old one (bottom right). Signal was 141counts sinus at 4Hz.

Filters used: Before squaring: 4th order butterworth BP at given freq. & (new) 6th order inverse Chebyshew 20dB at 0.9*lower BP freq. and 1.1*upper BP freq. => about 1dB at BP freq.

                       After squaring: 4th order butterworth LP @ 1Hz.

C1PEM execution time increased from about 20us to about 45us.

Made a new medm screen with the respective filters in place of the empty C1PEM_OVERVIEW. Should go onto the sitemap.

Original RMS LP is slower than 0.1Hz, see below for single LP at 0.1Hz in the new RMS. Original RMS is faster than single LP @ 0.01Hz

Some of the channels are recorded as 256Hz DAQ channels now. Need to figure out how to record these as 16Hz EPICS channls.

I already have reported in this entry that REFL165 shows too high DC output which does not depend on the light level on the diode.
Today I removed REFL165 from the table and inspected it.

The diode has been burnt as shown in the first picture (left).
The window is smoked, and the photo sensitive surface has been removed from its base. It moves in the can.

The burnt diode was replaced to the new one.
The new one shows ~30% better capacitance of ~50pF and I had to increase the inductance from 14nH (i.e. 15nH//220nH) to 18nH.
After some struggles to increase/decrease the stray inductance by moving the SMD capacitors a little, the resonance is reasonably tuned to 166MHz.

The comprehensive test will be performed shortly.

The lock of DRMI wasn't stable enough to measure the sensing matrix. Failed.

PRMI and SRMI were okay and in fact they could stay locked robustly for a long time.

I added a new option in the C1IFO_CONFIGURE screen so that one can choose Signal-Recycled Michelson in carrier resonant condition.

 Additionally the orthogonalization of the I-Q signals on REFL55 should be done because it hasn't been done.

I offered to help Kiwamu with some of the 40m work. The first task was to figure out why the ETMX side OSEM monitor was so low, since we know that the depth is about right. It was showing ~0.13 V to the others' ~0.7 V.

TL,WR: There was a wire disconnected from the breakout panel on the side of the rack

I started by pulling the board out and checking to make sure that it was working properly. I injected a sine wave to the SIDE IN and found that it showed up in the signal coming out of the back (into the crate) just fine (see below). One strange thing I noticed while testing the board is that both inputs for each used channel of the MAX333 switches on the board are shorted to their respective outputs. That is, the switches seem to be open to BOTH 0 and 1 logic states. This seems counterintuitive, but perhaps there's something about how these work that I don't know.

Then I went about tracing the signal from the back of the crate to the breakout panel on the side of the rack. I opened it up, verified that the ribbon cable was transmitting correctly, and as I went to plug it back in I noticed that one of the wires---the correct one---had come completely undone.

The screw clamp appeared to be a bit finicky, as I had to loosen and tighten it a few times before it finally seemed to grab hold of the wire. It probably just wasn't tight in the first place and the wire was pulled out. Anyway, things are working now:

 Good job ! Thank you so much

After we had a rough idea of what the output matrix looks like (see this elog),
I tried to measure the transfer function coefs (TFCs) between mirror degrees of freedom and the WFS sensors (WFS1, WFS2 and MC_Trans QPD)
I found that the TFCs that I obtained at 10.15 Hz did not have any resemblance to the previously identified output matrix.
The problem, I realised, arises because the various lockins used
in the C1IOO model do not have the same relative phase; So if we try to excite a mirror with one of them
and demodulate a sensor signal on any of the other lockins the resulting output would not have the correct phase
(relative to the 1st lockin output). As a result unless we can reset the phase of all the lockins
simultaneously, we cannot demodulate multiple signals at the same time. (Joe/Jamie, Is it possible to
reset/reinitialise the phase of the CLK signals of the lockings? )

To get around this problem Koji suggested that I use just one lockin and determine all the 36 elements of the transfer matrix with it one at a
time rather than six at a time.  When I did that, I got results consistent with the previoulsly determined outmatrix. It, of course, takes six times longer.

The matrix I first got is this one

Note that when MC2 is excited all the sensors showed a response about 75 deg out of phase with the reference (MC1 --> WFS1_PIT ) This was traced to the fact that while there is a 28Hz Elliptic LP filter on

both MC1 and MC3, while it is absent on MC2.  The Transfer functions  below show the difference in the phase of their response

Since the MC2 POS is used in servos involving MCL we cannot afford to install a 28 Hz LP filter into the MC2 coil drivers.  However a module with the 28 Hz ELP was switched on, in each of the

 MC2 PIT and YAW filter banks.   I then checked to see if this has affected the relative phase of variour sensors.  The Phase angle between I and Q on each sensor channel was checked and corrected. 

Below are the spectra with the "before" and "after" correction of phases.

Before:

Obviously this needed adjustment to reduce Q phase.   

  After twealkng the angle "R":

And again determined the transfer matrix (below). 

This time the signals are all nearly in the same phase and in agreement with the  outmatrix estimate made earlier.

I plugged these TFCs into the matrix inversion code: wfsmatrix2.m.   And get the following inverse:

I have ignored the MC2_Trans_P and Y sensors for now.

In order to save time and sanity, you should not measure the pitch ->yaw and yaw-> pitch. It makes things too complicated and so far is just not significant. In the past we do not use these for the matrix work.

i.e. there should just be a 3x3 pitch matrix and a 3x3 yaw matrix. Once the loops are working we could investigate these things, but its really a very fine tweak at the end. There are quite a few other, more significant effects to handle before then.

To make things faster, I think we can just make a LOCKIN which has 3 inputs: it would have one oscillator, but 6 mixers. Should be simple to make.

 I think the idea of having multiple inputs in a LOCKIN module is also good for the LSC sensing matrix measurement.

Because right now I am measuring the responses of multiple sensors one by one while exciting a particular DOF by one oscillator.

Moreover in the LSC case the number of sensors, which we have to measure, is enormous (e.g. REFL11I/Q, REFL33I/Q, REFL55I/Q, ... POY11I/Q,...) and indeed it has been a long-time measurement.

Test results of new REFL165 (the first attachment)

- The resonant freq 166.2MHz, Q=57 (previous Q was ~7)

- If we believe the TF measurement, the transimpedance at the resonance is 7.8k [V/A] and the shotnoise intercept current of ~1mA.
The linearity of the peak was confirmed by changing the modulation level of the beam.

- There is a riddle: the white light test indicates 4.5k [V/A] and 2.8mA for those numbers.
There are big descrepancies from those by the TF measurements.

Further analysis of the descrepancies:

Using the noise measurements with different DC current levels, the transimpedance for each frequency can be reconstructed.

Does this indicate the satiration by the white light???

- The TF measurement shows consistent mag&phase relationship at the resonance (c.f. LISO fit).
So this steep resonance is not an artifact by a noise or glitch but the real structure of the electronics.

- The TF measurement has been done with the photocurrent of ~0.3mA, while the transimpedance measurement
with the white light illumination has the practical effect only when the DC photocurrent is larger than 1mA
because of the circuit noise. Does this higher photo current affected the resonance?

- The off-resonant transimpedance agree with the TF measurement as far as we can see with those measurements.
This may mean that the actual resonant structure has been affected in the white light measurement.
(i.e. not the saturation of the RF opamp which causes the change of the gain at any freq.)
Is the above mentioned higher DC current causing the change of the diode capacitance or other property of the diode or the inductors???

REFL165 was installed on the AP table last night.

Meanwhile I found the DC power level at the REFL PDs were 0.8~1.2V if the PRM is aligned and the IFO is not locked.
This corresponds to 16~24mA (20~30mW). This is too big.

The HWP of the REFL path were adjusted so that we have 6~10mA (8~12mW) on each PDs.

Unless the bias feedback circuit has been tuned for the 1 mm diode, its possible that you are seeing some C(V) effects. Its easy to check by looking at the phase response at 165 MHz v. the DC photocurrent. Then the feedback or feedforward gain can be tuned.

 Doesn't work on pianosa either. Has someone changed the python environment?

pianosa:SUS_SUMMARY 0> ./setSensors.py 1000123215 600 0.1 0.25
Traceback (most recent call last):
  File "./setSensors.py", line 2, in <module>
    import nds
ImportError: No module named nds

I want to make changes to c1rfm. Found uncommited changes to it from Sept 27. Since we recompiled it since then it should be safe to commit them, so I did. See svn log for details.

Changed, recompiled, installed and restarted c1rfm and c1oaf to get the MC1-3 Pitch and Yaw data into the c1oaf model.
Also changed c1oaf to use MCL as a witness channel (as well as an actuator).
Added the changes to svn.

REFL165 removed from the table for the C(V) test

 Channels are now going into EPICS channels (e.g. C1:PEM-ACC1_RMS_1_3 ). Adapted the PEM_SLOW.ini file. Channels don't yet show up in dataviewer. Probably due to other C1PEM maschine

 ETMX oplev had 6 mm diameter beam on the qpd.  I relayed the beam path with 2 lenses  to get back  3 mm beam on the qpd

BRC 037  -100 Bi _concave lens and PCX 25  200 VIS do the job. Unfortunately the concave lens has the AR 1064.

The PD was returned on the table.

The C(V) compensation path was modified and the change of the resonant freq was cancelled.
A more precise analysis comes later.

To get to the bottom of the RFAM mystery, we've got to resurrect the StochMon to trend the RFAM after the IMC.

We will put an 1811 on the MC_TRANS or IP_POS beam (the 1811 has an input noise of 2.5 pW/rHz).

Then the Stochmon has an input pre-amp, some crappy filters, and then Wenzel RMS->DC converters. We will replace the hand-made filters with the following ones from Mini-Circuits which happen to match our modulation frequencies perfectly:

11 MHz     SBP-10.7+

55 MHz     SBP-60+

29.5 MHz   SBP-30+

[Rana, Suresh]

     To see if the loops will stay locked when the Integrators in the servo are switched on, we stayed with the same simple output matrix (just 1 or -1 elements) and switched on the FM1 on all WFS servo filter banks.  We monitored the time domain error signals to see if engaging the locks made the error signals go to zero.  Most of the error signals did go to zero even when an intentional offset was introduced into the MC pitch of the suspension.

      We need to include TestPoints just before the Input Servo Matrix so that we can monitor the error signals without being affected by the gain changes in the WFS_GAIN slider.   These are currently not present in the C1IOO model and the position of the WFS_GAIN also has to be shifted to the other side of the Input matrix.

      The C1IOO_WFS_MASTER screen has been changed to the new one.  This incorporates filter banks for the MC_TRANS_P and _Y channels.  The screen is not yet fully functional but I am working on it and I it will continue to improve it.

I made some attempts to measure the sensing matrix of the central part.

I could measure the matrix in the PRMI configuration but wasn't able to measure the matrix in the DRMI configuration.

   => I will report the result of the PRMI sensing matrix tomorrow.

The main reason why I couldn't lock DRMI was that the suspensions were touchy and especially the SRM suspension wasn't good.

Some impacts due to the feedback during the lock acquisition completely kicks SRM away. 

The watchdogs' RMS monitor on SRM easily rang up to more than 10 counts once the acquisition started.This is quite bad.

Also the stability of the PRMI lock was strongly depending on the gains of the PRM oplevs.

I guess I have to revisit the vertex suspensions more carefully (i.e. f2a coupling, actuator output matrix, damping gains, input matrices, oplev filters)

otherwise any LSC works in the vertex will be totally in vain.

The original REFL165 had ~50MHz/A dependence on the DC photocurrent.
The resistr R21, which was 2670 Ohm contrary to the original drawing, was replaced to 532 Ohm
to increase the feedforward gain by factor of 5.

The resulting dependence is reduced to ~0.5MHz/A although it has Q reduction of ~20% at 6mA.

Some concerns:

These transfer functions were measured between TEST IN and RF OUT while the diode was illuminated with the white light from a light bulb.

There looks some thermal effect on the resonant freq. If the white light illumination is suddenly removed, the bias compensation
is immediately removed but the resonance takes some time (~min) to come back to the original freq.

I am afraid that the light bulb gave too much heat on the surrounding PCB and lead unnecesarily high level dependence of the resonant freq on the DC current.

Or, if this thermal effect comes from the power consumption on the diode itself, we need to characterize it for aLIGO.

In order to check this, we need a test with the 1064nm illumination on the diode in stead of the light bulb.

In keeping with the current protocol,  I have started to move all the user-built medm screens associated with C1IOO into the $screens$/c1ioo/master/ directory. 

I then edited the menu button in the sitemap.adl to point to the screens in the ..c1ioo/master/ directory.  All the screens in $screens$/c1ioo/ directory have been backed up into bak/.  I plan to edit the c1ioo model soon and at that time I will delete all the screens in the $screens$/c1ioo directory and let only the automatically regenerated screens  stay there.   If there are broken links to user-built screens associated with c1ioo, please copy the relevant screen to the master/ directory and edit the path in the menus.

The following optics were kicked:
SRM
Wed Oct 19 04:22:53 PDT 2011
1003058589
 

I made some efforts to fix the situation of SRM but it is still bad.

The POS motion wasn't well damped. Something is wrong either (maybe both) sensing part or actuation part.

I am going to check the sensing matrix with the new free swinging spectra (#5690)

(Symptom)

 When I was trying to lock SRMI I found that the fringes observed at the AS camera didn't show spatial higher order modes, which is good.

So I thought the SRM suspension became quiet, but it actually wasn't. Because the RMS monitor of the SRM OSEMs already went to about 30 counts.

At the same time the opelev error signals were well suppressed. It means some DOFs which were insensitive to the oplev were ringing up, namely POS and SIDE.

According to the LSC error signal and the ASDC signal, I believe that the POS was going wild (although I didn't check the OSEM spectra).
 

(Some efforts)

 + Readjusted the f2a filters (see the attachment).

 + Tried to eliminate a coupling between the POS and SIDE drives by tweaking the output matrix.

    => In order to eliminate the coupling from the POS drive to SIDE sensor, I had to put a comparable factor into an element.

     So it might be possible that the POS sensor was showing the SIDE signal and vice versa.

      In order to check it I left SRM free swinging (#5690).

Sorry Kiwamu, I realized too late that you were freeswigging. Hopefully 4 hrs was enough.