The attached plot shows the beam scans of the beam leaking from the back mirror of the PMC to the BS cube that first turns the S-pol beam 90 deg to the AOM and then transmits the AOM double passed and polarization rotated P-pol beam to the reference cavity. The beam from the PMC is mode matched to the AOM using a single lens f=229 mm. The ABCD file is attached. The data were taken with VCO control voltage at 5 V. We then reduced the voltage to 4 V to reduce the astigmatism. Tara has the data for the beam scan in this configuration in his notebook.

The beam from AOM is mode matched to the reference cavity using a single lens f=286.5 mm. The ABCD file is attached.

The RefCav is locked and aligned. I changed the fast gain sign by changing the jumper setting on the TTFSS board. The RefCav visibility is 70%. The FSS loop ugf is about 80 kHz (plot attached. there is 10 dB gain in the test point path. this is why the ugf is at 10 dB when measured using in1 and in2 spigots on the front of the board.)  with FSS common gain max out at 30 dB. There is about 250 mW coming out of the laser and 1 mW going to RefCav out of the back of the PMC. So the ugf can be made higher at full power. I have not made any changes to account for the PMC pole (the FSS is after the PMC now). The FSS fast gain was also maxed out at 30 dB to account for the factor of 5 smaller PZT actuation coefficient - it used to be 16 dB according to the (previous) snap shot. The RefCav TRANS PD and camera are aligned. I tuned up the phase of the error signal by putting cables in the LO and PD paths. The maximum response of the mixer output to the fast actuator sweep of the fringe was with about 2 feet of extra cable in the PD leg.

I am leaving the FSS unlocked for the night in case it will start oscillating as the phase margin is not good at this ugf.

 Notes:

- NPRO injection current 1.0 A

- PMC losses ~32%

- FSS AOM diffraction efficiency ~52%

The attached plots show the PMC cavity line width measurement with 1 mW and 160 mW into the PMC. The two curves on each plot are the PMC transmitted power and the ramp of the fast input of the NPRO. The two measurements are consistent within errors - a few %. The PMC line width  3.5 ms (FWHM) x 4 V / 20 ms (slope of the ramp) x 1.1 MHz / V (NPRO fast actuator calibration from Innolight spec sheet) = 0.77 MHz.

Here is the output of the calculation using Malik Rakhmanov code:

modematching =  8.4121e-01

transmission1 =   2.4341e-03

transmission2 =   2.4341e-03

transmission3 =   5.1280e-05

averageLosses =  6.1963e-04

visibility =  7.7439e-01

 The PMC mode matching was initially done at low power ~150 mW. It was expected and found that at full power ~2 W (injection current 2.1 A) the mode matching got much worse:

the visibility degraded from 80% to 50% (1 - refl locked/refl unlocked) . The thermal lensing could be in the laser, EOM, or FI.

The first attached plot shows the scan of the beam after the EOM at low and full laser power. At full power the waist position is 10 mm after the turning mirror after the EOM and the waist size is 310 um.

The second plot shows the ABCD calculation for the mode matching solution.

I removed the MM lens PLCX-25.4-77.3-C and placed the PLCX-25.4-180.3-UV about 20 mm after the first PMC periscope mirror (the second mirror after the EOM).

The PMC visibility improved to 94% and the power through the PMC, as measured by the PMC transmission PD, went up by a factor of 2.

Now that we have increased the range of the AA to +/- 10 V I have increased the PRM side OSEM transimpedance from 29 kV/A to 161 kV/A by changing the R64 in the satellite box. The first attached plot shows the ADC input spectrum before and after the change with analog whitening turned off. The PD voltage readback went up from 0.75 to 4.2 V. The second attached plot shows the sensor, ADC, and projected shot noise with analog whitening turned on and compensated digitally. The ADC calibration is 20 V/ 32768 cts. The PRM damping loops are currently disabled.

I checked for oscillation by looking at the monitor point at the whitening board. There was no obvious oscillation on a scope - the signal was 20 mV p-p on 1 us scale which was very similar to the LL channel.

We missed a factor of 2 in the ADC calibration: the differential 16 bit ADC with +/-10 V input has 20 V per 32768 counts (1 bit is for the sign). I confirmed this calibration by directly measuring ADC counts per V.

So the ADC input voltage noise with +/-10V range around 100 Hz is 6.5e-3 cts/rtHz x 20V/32768cts =  4.0 uV/rtHz. Bummer. 

The ADC quantization noise limit is 1/sqrt(12 fs/2)=1.6e-3 cts/rtHz. Where the ADC internal sampling frequency is fs=64 kHz. If this would be the limiting digitization noise source then the equivalent ADC input voltage noise would be 1 uV/rtHz with +/-10 V range.

 I measured the SRM OSEM (no magnets at the moment) noise out of the satellite box with a SRS785 spectrum analyzer. I inserted a break out board into the cable going from the satellite box to the whitening board. The transimpedances of the SRM OSEMs are still 29.2 kOhm. The DC voltages out of the SRM satellite box are about 1.7 V. The signal was AC coupled using SR560 with two poles at 0.03 Hz and a gain of 10.

The noise is consistent with the one measured by the ADC except for the 3 Hz peak which does not show up in the ADC spectrum from Sunday. The peak appears in several channels I looked at. The instrument noise floor was measured by terminating the SR560 with 50 Ohm.

I recommend to change all OSEM transimpedance gains from 29 to 161 kV/A. Beyond this gain one will rail the AA filter module when the magnet is fully out of the OSEM.

The OSEM noise at 1 Hz is about factor of 10 above the shot noise. The damping loops impress this noise on the optics around the pendulum resonance frequency. Also the total contribution to the MC cavity length is sqrt(12) time the single sensor as there are 12 OSEMs contributing to MC length. The ADC noise is currently close but never the less not limiting the OSEM noise below 100 Hz. It can be further reduced by getting an extra factor of 2-3 in whitening gain above ~0.3 Hz. The rms of the ADC input of the modified PRM SD (R64 = 161 kOhm) channel is 10-20 cts during the day with damping loop off and whitening on.

The transimpedance amplifier LT1125CS is also not supposed to be limiting the noise. At 1 Hz the 1/f part of the noise: In<1pA/rtHz and Vn<20nV/rtHz.

I have been editing and reloading the c1ioo model last two days. I have restarted the frame builder several times. After one of the restarts on Sunday evening the fb started having problems which initially showed up as dtt reporting synchronization error. This morning Kiwamu and I tried to restart the fb again and it stopped working all together. We called Joe and he fixed the fb problem by fixing the time stamps (Joe will add details to describe the fix when he sees this elog).

The following changes were made to c1ioo model:

- The angular dither lockins were added for each optics to do the beam spot centering on MC mirrors. The MCL signal is demodulated digitally at 3 pitch and 3 yaw frequencies. (The MCL signal was reconnected to the first input of the ADC interface board).

- The outputs of the lockins go through the sensing matrix, DOF filters, and control matrix to the MC1,2,3 SUS-MC1(2,3)_ASCPIT(YAW) filter inputs where they sum with dither signals (CLOCK output of the oscillators).

- The MCL_TEST_FILT was removed

The arm cavity dither alignment (c1ass) status:

- The demodulated signals were minimized by moving the ETMX/ITMX optic biases and simultaneously keeping the arm buildup (TRX) high by using the BS and PZT2. The minimization of the TRX demodulated signals has not been successful for some reason.

- The next step is to close the servo loops REFL11I demodulated signals -> TMs and TRX demodulated signals -> combination of BS and PZTs.

The MC dither alignment (c1ioo) status:

- The demodulated signals were obtained and sensing matrix (MCs -> lockin outputs) was measured for pitch dof.

- The inversion of the matrix is in progress.

- The additional c1ass and c1ioo medm screens and up and down scripts are being made.

I put the PMC last mode matching lens (one between the steering mirrors) on a translation stage to facilitate the PMC mode matching.

Currently 4% of incident power is reflected by the PMC. But the reflected beam does not look "very professional" on the camera to Rana - meaning there is too much TEM20 (bulls eye) mode in the reflected beam.

I locked the  PMC  on bulls eye mode and measured  the ratio of the TEM20/TEM00 in transmission to be 1.3%. Thus the PMC mode matching is ~99% and the incident beam HOM content is ~3%.

While working on the PMC I found that the source of PMC "blinking" is not the frequency control signal from MC to the laser (the MC servo was turned off) but possibly some oscillation which could be affected even by a small change of the pump current 2.10 A to 2.08 A. I showed this behaviour to Kiwamu and we decided to leave the the current at 2.08 A for now where things look stable and investigate later.

 I made several scripts to handle the mcass configuration and sensing measurements:

- The scripts and data are in the scripts/ASS directory

- The mcassUp script restores the settings for the digital lockins: oscillator gains, phases, and filters. The MC mirrors are modulated in pitch at 10, 11, 12 Hz and in yaw at 10.5, 11.5, and 12.5 Hz. The attached plot shows the comb of modulation frequencies in the MCL spectrum.

- The mcassOn and mcassOff scripts turn on and off the dither lines by ramping up and down the SUS-MC1_ASCPIT etc gains

- The senseMCdecenter script measures the response of the MCL demodulated signals to the decentering of the beam on the optics by imbalancing the coil gains by 10% which corresponds to the shift of the optic rotation point relative to the beam by 2.65 mm (75mm diameter optic) and allows calibration of the demodulated signals in mm of decentering. The order of the steps was MC1,2,3 pitch and MC1,2,3 yaw. The output of the script can be redirected to the file and analyzed in matlab. The attached plot shows the results. The plot was made using the sensemcass.m script in the same directory.

- The senseMCmirror script measures the response of the MCL demodulated signals to the mirror offsets (SUS-MC1_ASCPIT etc filter banks). The result is shown below (the sensemcass.m script makes this plot as well). There is some coupling between pitch and yaw drives so the MC coils can use some balancing - currently all gains are unity.

- The senseMCdofs scripts measures the response to the DOF excitation but I have not got to it yet.

- The next step is to invert the sensing matrix and try to center the beams on the mirrors by feeding back to optics. Note that the MC1/MC3 pitch differential and yaw common dofs are expected to have much smaller response than the other two dofs due to geometry of this tree mirror cavity. We should try to build this into the inversion.

The attached plot shows the 30 day trend of the MC3 UL PD signal. The signal dropped to zero at some point but now it is close to the level it was a few weeks ago. There still could be a problem with the cable.

The rest of the MC1,2,3 PD signals looked ok.

The attached plot shows 2 day trends of the PMC and MC reflected and transmitted power, the PSL POS/ANG QPD signals, and the temperature measured by the dust counter.

The power step in the middle of the plot corresponds to Koji/Jenne PMC realignment yesterday.

It looks like everything is following the day/night temperature changes.

 After Kiwamu set the REFL11 phases in the PRMI configuration (maximized PRM->REFL11I reesponse) I tried to measure the MC length and the 11 MHz frequency missmatch by modulating the 11 MHz frequency and measuring the PM to AM conversion after the MC using the REFL11Q signal. The modulation appears in the REFL11Q with a good snr but the amplitude does not seem to go through a clear minimum as the 11 MHz goes through the MC resonance.

We could not relock the PRMI during the day so I resorted to a weaker method - measuring the amplitude of the 11 MHz sideband in the MC reflection (RF PD mon output on the demod board) with a RF spectrum analyzer. The minimum frequency on the IFR is 11.065650 MHz while the nominal setting was 11.065000 MHz. The sensitivity of this method is about 50 Hz.

I tried to run the scripts/senseMCdecentering to check the centering of the MC beam spots on the mirrors. The script (csh) produces a lot of error messages on the control room machines. They are machine dependent combination of "epicsThreadOnce0sd epicsMutexLock failed", "Segmentation fault", "FATAL: exception not rethrown". Most of ezcawrite commands fail but not all(?). After running the mcassUp script couple of times all the dither lines came on. The MCL responses to dither lines look qualitatively similar to what it was in February (plot attached). The overall MCL spectrum looks ~100 times lower, presumably due to the analog gain reallocation.

Before that I realigned the beam into the PMC, recentered the PSL QPDs, and the beam into the MC to bring the MC RFPD_DC from ~3 to ~1.5 VDC then tweaked MC2 to bring the MC RFPD_DC from ~1.5 to ~1 VDC.

The mcass dither lines are off now and the loops are disabled.

 Kiwamu told me that the CDS matrix notation has changed and the 40m front end code has changed since February. I changed the senseMCdecentering script to reflect that. The other problems were: the "-" sign in ezcastep on ubuntu is not recognized - I used the known workaround of using "+-" instead; the echo command in csh script on ubuntu does not make a new line - but the echo " " does. The script ran on ubuntu with one error message "FATAL: exception not rethrown" but it finished nevertheless. The data appeared ok.  On centos machine the script produced "Segmentation fault'. The matlab script sensemcass.m now calculates the position on the MC mirrors in mm. The attached table shows the MC spot positions in mm:

I had to rephase the lockin digital phases by tens of degrees. I don't know why this should happen at ~10 Hz.

 

The attached plot shows 7 day trends of the MC and PMC power levels, PSL QPDs, and temperature. The MC stayed locked for ~40 hours over the weekend. The temperature swings were somewhat smaller over the past couple of days but one should remember to turn the PSL HEPA down after working on the table. Steve turned the HEPA flow from 100% down to 20% on Thursday and posted the reminder signs on the PSL enclosure.

Kiwamu, Koji, Valera

We centered the beam on MC2 in pitch by moving the MC1,2,3 in the following combination [-9,+3,-7]. This actuation vector mostly moves the spot on MC2 vertically. The attached plot shows the dither before and after the centering. We monitored the demodulated signals and saw the reduction of the MC2 pit response from -1.0 to -0.22 which corresponds to the beam spot position change from 9 to 2 mm. Thus all the spots on MC mirrors are within 2 mm of the center. We estimate based on the distance between the MC1-MC3 of 20 cm, the distance from the center between MC1 and MC3 to the end of the Faraday isolator of 80 cm, and the aperture of the FI of 12 mm, the maximum angle out of MC of 3/200 rad. Which implies the maximum differential spot motion of 3 mm not to be limited by the FI aperture.

Yesterday we found that MC3 OSEM LL PD did not have a sensible signal - the readback was close to zero and it was making MC move around. I disabled the PD LL so that the damping is done with just three face plus side PDs. There still no signal from MC3 LL PD today. It needs debugging.

This is what was done in past two days:

- The ETMY and ITMY pitch and yaw dofs are modulated at 40, 44, 42, 46 Hz respectively (oscillator A=30). The c1ass lockin numbers are 12, 14, 27, 29.

- The NAS55I signal is demodulated at the above frequencies. The demodulated I/Q signal phase is set to shift all signal into I-phase. The lockin inputs are bandpassed around respective frequency f with butter("Bandpass",2,f-0.5,f+0.5). The demod signals are then additionally low passed with butter ("Lowpass",4,0.5) so the servo ugf has to be below 0.5 Hz. The servo filter is p:z 0.0001:0.1.

- The ETMY demodulated signal is fed back to ITMY and visa versa.

- With the above 2x2 servo running we moved the input beam PZTs by hand to follow the cavity.

- At the end we offloaded the servo control signals to the SUS biases again by hand.

- The beam spot centering was estimated by unbalancing the ETMY/ITMY pitch/yaw coil combinations intentionally by 5%, which produces 1.3 mm shift of the node, and comparing the response to the residual signals.

- The dof set up currently is: ETMY pitch lockin 12 -> dof2, ITMY pitch lockin 14 -> dof4, ETMY yaw lockin 27 -> dof7, ITMY yaw lockin 29 -> dof9

- The next step is to demodulate the TRY(X) and servo the input beam PZTs

Here the status of the dither alignment or c1ass:

- Both pitch and yaw centering on ETMY/ITMY were closed simultatenously with ugf of ~1/30 Hz.

- I made a medm screen with beam positions as measured by the dither system.The snapshot is attached. There are visual perimeter alarms (red box around the display) to warn about arm power being low or the dither lines not being on. The screen has a pull down menu with 4 scripts:

. assUp - sets up the gains, phases and matricies for the dither system (both the spot centering and the input beam alignment)

. assOn - turns on the dithers and servo - just the Y-arm centering part at the moment

. assOff - turns off the servo and dither lines

. assDitherOn - turns on the dither lines but does not turn on the servo

- All scripts are in scripts/ASS and the medm screen is in medm/c1ass/master/

Still to do:

- Commission the input beam and X-arm servos

- Make scripts for X-arm

I closed all 8 dither loops for the Y arm initial alignment: 2x2 centering servo (this worked before) and 2x2 input beam servo for both pitch and yaw.

So far it looks pretty good - the error points go to zero and the arm power goes up to 1.

The offloading to the alignment biases and the PZTs is not yet automated.

Today the PMC, MC, and Y arm were very cooperative and a pleasure to work with.

I changed optics in the ETMX transmon path to remove clipping (which made a false QPD signal).

During the weekend I found that there was an offset in X arm c1ass pitch servo, which derives the signal by demodulating the arm cavity power, coming from the beam clipping in the transmon path.

The clipping was on the pair of the 1" mirrors that steer the beam after the 2" lens (see attached picture). The beam is about 5-6 mm in diameter at this distance from the lens and was not well centered.

I moved the steering mirrors downstream by about 8" where the beam is about 2-3 mm (the attached picture shows the mirrors in the new location). The Y arm layout is different from X arm and I didn't find any obvious clipping in transmon path.

The max X arm buildup went up from 1.3 to 1.5. I changed the TRX gain from -0.003 to -0.002 to obtain the normalized X arm power of 1 in this state. The MC refl DC is 1.6 out of 4.9 V and the Y arm buildup is ~0.9 so the TRX(Y) gains will have to be adjusted once the MC visibility is maximized.

 The current status of the dither alignment system:

- Both Xarm and Yarm alignment are working. The scripts are: scripts/autoDither/alignX(Y). Each script sets up the respective arm, turns on the dither lines and servos for 66 sec, offloads the control signals to TM alignment biases and PZT sliders in case of  Yarm, and to TM and BS alignment biases in case of Xarm, and finally turns off and clears the servo filters and turns off the dither lines.

- Jammie witnessed the final tests of both scripts - both X and Y arm power went up from 0.6-0.7 to close to 1 and the AS beam became symmetric. Also Jammie wanted me to leave the ETMY oplev in its current non-nominal but more stable state i.e. the oplev signals go to the ADC from the D010033 card not the D020432 one. The scripts can now run from the CONFIGURE medm screen.

- Both arms use signals derived from modulating ITM and ETM in pitch and yaw dofs and demodulating the arm power (TRX or TRY) and the cavity length signal (AS55I). The Yarm actuation has 8 dofs - pitch and yaw of the ITM, ETM, and two input beam PZTs so all the sensed dofs are controlled. The Xarm actuation has only 6 dofs - pitch and yaw of the ITM, ETM, and BS. The Xarm servo is set up to servo the beam position on the ETMX and the relative alignment of the cavity and the input beam. The ITMX spot position is unconstrained and provides the null test. The residual displacement on the ITMX is 0.2-0.3 mm in yaw and 0.9-1.0 mm in pitch. The I phases of the beam centering lockins, which are also the error points of corresponding DOF filters, are calibrated in mm by unbalancing the TM coils by known amount. The attached snap shot of the medm screen now has both X and Y arm calibrated beam spot positions and uncalibrated input beam indicators. The input beam angle and position signals can/should be calibrated by tapping the signals digitally and applying the proper matrix transformation - this will require the model change.

- Currently there is no lock loss catching in the model. We should add a trigger on arm power (or an equivalent mechanism) to turn off the inputs to prevent the spurious inputs.

I mounted the optoisolator on the DIN rail and connected the 3 first channels

to the optoisolator inputs 1,3,4 respectively. I connected the +15V input voltage into the input(+) of the optoisolator.

The outputs were connected to DB9F-2 where those channels were connected before.

I added DB9F-1 to the front panel to accept channels from the RTS. I connected the fast channels to connectors 1,2,3 from DB9F-1 to DB9F-2 according to the wiring diagram. The GND from DB9F-1 was connected to both connector 5 of DB9F-2 and the output (-).

I tested the channels: I connected a DB9 breakout board to DB9F-2. I measured the resistance between the RTS GND and the isolated channels while switching them on and off. In the beginning, when I turned on the binary channels the resistance was behaving weird - oscillating between low resistance and open circuit. I pulled up the channels through a 100Kohm resistor to observe whether the voltage behavior is reasonable or not. Indeed I observed that in the LOW state the voltage between the isolated channel and slow GND is 15V and 0.03V in the HIGH state. Then I disconnected the pull up from the channels and measured the resistance again. It showed ~ stable 170ohm in the HIGH state and an open circuit in the LOW state. I was not able to reproduce the weird initial behavior. Maybe the optoisolator needs some warmup of some sort.

We still need to wire the rest of the fast channels to DBF9-3 and isolate the channels in DBF9-4. For that, we need another optoisolator.

There is still an open issue with the BI channels not read by EPICS. They can still be read by the Windows machine though.

3  fsr =  33 195 439 Hz
12 fsr = 132 781 756 Hz
15 fsr = 165 977 195 Hz
18 fsr = 199 172 634 Hz

• Replace the cables from the board to the front panel connectors if this hasn't already been done.
  
• Replace the input opamps with 4131's. Be sure to test both positive and negative input signals.
  
• Check that all the compensation capacitors are in place and are 68 pF
  
• Make sure all the feedback loops have high frequency rolloff
  
• The ISS board reads the PDs differentially; make sure the PD sends differentially.
  
• Add a big (ie 10uF tantalum) capacitor to the PD to suppress power supply noise
  
• Add bigger power supply bypass caps to the ISS

# On Linux, "ezcastep" will interpret negative steps as command line arguments,
# because the GNU library interprets anything starting with a dash as a flag.
# There are two ways around this.  One is to set the environment variable
# POSIXLY_CORRECT and the other is to inject "--" as a command line argument
# before any dashed arguments you don't want interpreted as a flag.  The former
# is easiest to use here:

if (`uname` =~ m/Linux/) {
    # Add an environment variable for child processes
    $ENV{'POSIXLY_CORRECT'} = 1;
}

pushd /cvs/cds/caltech/users/tf/build/labca_2_1/bin/linux-x86
setenv PATH ${PATH}:`pwd`
cd /cvs/cds/caltech/users/tf/build/labca_2_1/lib/linux-x86
setenv LD_LIBRARY_PATH ${LD_LIBRARY_PATH}:`pwd`
popd

addpath /cvs/cds/caltech/users/tf/build/labca_2_1/bin/linux-x86/labca
help labca
foo = lcaGet('C1:PSL-FSS_RCTRANSPD')