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ID Date Authorup Type Category Subject
  6303   Wed Feb 22 01:53:57 2012 kiwamuUpdateLSCupdate on glitch table

I tried SRMI. The glitch rate wasn't as high as that of PRMI but it happened once per 10 sec or so.

 

 

 Yarm

(POY11 -->

ETMY)

Xarm

(POX11 --> ETMX)

MICH

(AS55-->BS)

or

(AS55 --> ITMs)

Half PRMI

(REFL11 --> PRM)

or

(REFL33 --> PRM)

low finesse PRMI

(ASDC --> ITMs)

(REFL33 --> PRM)

PRMI (carrier)

(AS55 --> ITMs)

(REFL33 --> PRM)

PRMI (sideband)

(AS55 --> ITMs)

(REFL33 --> PRM)

SRMI(NEW)

(AS55-->ITMs)

(REFL11I --> SRM)

DRMI
AS55 NO NO NO NO glitch (depends on finesse)
glitch glitch glitch glitch
REFL11 NO NO NO NO glitch (depends on finesse)
glitch glitch glitch glitch
REFL33 NO NO NO NO - glitch glitch glitch glitch
REFL55 NO NO NO NO glitch(depends on finesse) glitch glitch glitch glitch
REFL165 NO NO NO - - - - - -
POX11 - NO NO NO  - glitch glitch - glitch
POY11 NO - NO NO  - glitch glitch - glitch
POP55 - - - -  -  - -   -
                   

 

Quote from #6284

I updated the table which I posted some time ago (#6231). The latest table is shown below.

It seems that the glitches show up only when multiple DOFs are locked.

 

  6304   Wed Feb 22 13:28:22 2012 kiwamuUpdateLSCY arm + central part locking

Last night I tried the "Y arm + central part" locking again. Three different configuration were investigated :

  •  Y arm + DRMI
  •  Y arm + PRMI
  •  Y arm + MICH

In all the configurations I displaced the Y arm by 20 nm from the resonance.

As for the DRMI and PRMI configurations I wasn't able to acquire the locks.

As for the MICH configuration, the MICH could be locked with AS55. But after bringing the Y arm to the resonance point the lock of MICH was destroyed.

  6306   Wed Feb 22 19:45:33 2012 kiwamuUpdateLSChow much length offset do we need ?

I did a quick calculation to see if the offset of the arm length which I tried last night was reasonable or not.

The conclusion is that the 20 nm offset that i tried could be a bit too close to a resonance of the 55 MHz sidebands.

A reasonable offset can be more like 10 nm or so where the phases of all the laser fields don't get extra phases of more than ~ 5 deg.


 

The attached plot shows where the resonances are for each sideband as a function of the displacement from the carrier's resonance.

armresonance.png

The red solid line represent the carrier, the other solid lines are for the upper sidebands and the dashed lines are for the lower sidebands.

The top plot shows the cavity power and the bottom plot shows how much phase shift the fields get by being reflected by the arm cavity.

Apparently the closest resonances to the the main carrier one are that of the 55 MHz sidebands, and they are at +/- 22 nm.

So if we displace the arm length by 22 nm, either of the 55 MHz sidebands will enter in the arm cavity and screw up the sensing matrix for the 55 MHz family.

Quote from #6304

In all the configurations I displaced the Y arm by 20 nm from the resonance.

  6310   Fri Feb 24 03:58:13 2012 kiwamuUpdateLSCY arm + PRMI part II

I tried the Yarm + PRMI configuration again.

The PRMI part was locked, but it didn't stay locked during the Y arm was brought to the resonance point.

I will post the time series data later.

 

(locking of the PRMI part)

Tonight I was able lock the PRMI when the arm was off from the resonance by 10 nm (#6306).

This time I used REFL11Q to lock the MICH instead of the usual AS55Q because the MICH didn't stay locked with AS55Q for some reason.

The PRCL was held by REFL33I as usual.

Also I disabled the power normalization for the error signals because it could do something bad during the Y arm is borough to the resonance.

In order to reduce the number of the glitches, PRM was slightly misaligned because I knew that the lower finesse gives fewer glitches.

  6311   Fri Feb 24 04:12:44 2012 kiwamuUpdateSUSfreeswing test
The following optics were kicked:
MC1 MC2 MC3 ETMX ETMY ITMX ITMY PRM SRM BS
Fri Feb 24 04:11:15 PST 2012
1014120690
 
Steve (or anyone), can you restore the watchdogs when you come to the lab in the morning ?

Quote from #6305

Kiwamu (or whoever is here last tonight): please run the free-swing/kick script (/opt/rtcds/caltech/c1/scripts/SUS/freeswing) before you leave, and I'll check the matrices and update the suspensions tomorrow morning.

  6313   Fri Feb 24 15:01:31 2012 kiwamuUpdateLSCY arm + PRMI part II

The figure below shows the time series of the Y arm + PRMI trail.

time_series.png

(Top plot )

  Normalized TRY (intracavity power). It is normalized such that it shows 1 when the arm is locked with the recycling mirrors misaligned.

(Middle plot)

ASDC and REFLDC in arbitrary unit.

(Bottom plot)

The amount of the arm length detuning observed at the fine frequency discriminator.

 

(Sequence)

At t = 20 sec, the amount of detuning was adjusted so that the cavity power goes to the maximum. At this point the PRM was misaligned.

At t = 30 sec, the cavity length started being slowly detuned to 10 nm. As it is being detuned the intracavity power goes down to almost zero.

At t = 45 sec, the alignment of PRM was restored. Because of that, the REFLDC and ASDC diodes started receiving a large amount of light.

At t = 85 sec, the PRCL and MICH were locked. The REFLDC signal became a high value as the carrier light is mostly reflected. The ASDC goes to a low value as the MICH is kept in the dark condition.

At t = 100 sec, the length started being slowly back to the resonance while the PRMI lock was maintained.

At t = 150 sec, the lock of the PRCL and MICH were destroyed. With the arm fully resonance, I wasn't able to recover the PRMI lock with the same demod signals.

Quote from #6310

I tried the Yarm + PRMI configuration again.

The PRMI part was locked, but it didn't stay locked during the Y arm was brought to the resonance point.

I will post the time series data later.

 

  6317   Fri Feb 24 19:18:28 2012 kiwamuUpdateLSCY arm + PRMI : how they should look like

I calculated how the DC signals should look like in the Y arm PRMI configuration.

The expected signals are overlaid in the same plot as that of shown in #6313.

You can see there are disagreements between the observed and expected signals in the plot below at around the time when the arm is brought to the resonance.

 

(expected behaviors)

  •  TRY: At the end it should be at 1 (remember TRY is normarlized) and should not go more than that, since the power-recycling is in a weird situation and it is not fully recycling the power.
  •  ASDC: It should become brighter at the end because the arm cavity flips the sign of the reflected light and hence the dark port must be on a bright fringe.
  •  REFLDC: It will decrease a little bit because the arm cavity and MICH try to suck some amount of the power into the interferometer.

 

expected_time_series.png

Quote from #6313

The figure below shows the time series of the Y arm + PRMI trail.

  6319   Fri Feb 24 23:14:09 2012 kiwamuUpdateCDStdsavg went crazy

I found that the LSCoffset script didn't work today. The script is supposed to null the electrical offsets in all the LSC channels.

I went through the sentences in the script and eventually found that the tdsavg command returns 0 every time.

I thought this was related to the test points, so I ran the following commands to flush all the test point running and the issue was solved.

[term]> diag              
[diag]>open               
[diag]> diag  tp clear *  
 

EDIT, JCD 11June2012:  3rd line there should just be [diag]> tp clear *

  6320   Sat Feb 25 00:37:42 2012 kiwamuUpdateSUSoplev spectra during PRMI lock

Somehow the angular stability of the central part have not been so great.

Also the angular motions look fluctuating a lot and they seem to be related with the glitches.

I took the oplev spectra when the PRMI is locked and unlocked to see whether if something obviously crazy is going on or not.

They seem ok to me except that the PRM pitch shows an extra bump at around 2-3 Hz when the PRMI is locked. But I don't think it's prominent.

 


- The attached files show the oplev spectra. When the PRMI is locked the PRM and both ITMs are under the length control.

(red) pitch when PRMI is locked

(blue) yaw when PRMI is locked

(orange) pitch without any length controls

(cyan) pitch without any length controls

 

Attachment 1: oplev_PRMI.pdf
oplev_PRMI.pdf oplev_PRMI.pdf oplev_PRMI.pdf oplev_PRMI.pdf
  6321   Sat Feb 25 14:27:26 2012 kiwamuUpdateLSCglitches in the RFPD outputs

Last night I took a closer look at the LSC analog signals to find which components are making the glitches.

I monitored the RFPD output signals and the demodulated signals at the same time with an oscilloscope when the PRMI was kept locked.

Indeed the RFPD outputs have some corresponding fast signals although I only looked at the RELL11 I and Q signals.

(REFL33 didn't have sufficiently a high SNR to see the glitches with the oscilloscope.)

I will check the rest of channels.

  6330   Tue Feb 28 12:00:54 2012 kiwamuUpdateLSCinstalled anti-whitening filters

I found that none of the filter banks in the LSC input signals have the precise anti-whitening filters.

I installed the precise filters on REFL11, REFL33, REFL55 and AS55 based on Jenne's measurement (#4955)

After installing them I briefly checked the REFL11 sensing matrix with the PRMI locked, but it didn't change so much from what I got (#6283).

But I felt that the PRMI became more robust after that ... I just felt so ...

 


(Background)

The lock of the PRMI doesn't look healthy, especially the sensing matrix doesn't make sense at all (#6283).
A very staring thing in the sensing matrix is that the REFL11 and REFL55 didn't show the 90 degree separation between MICH and PRCL.
So I suspected some electronics, particularly the demodulation boards.
 

(What I did)

I checked the anti-whitening filters shape to see if they are ok or not.
I found that they all had the default filters of two zeros at 150 Hz and two poles at 15 Hz. So they weren't quite tuned.
I thought this could be a problem when I measure the sensing matrix because I usually excite the length DOFs at a high frequency of 283.1 Hz
and the mismatches between the anti-whitening and whitening filters may lead to something funny at such a high frequency.
 
So I installed the precise filters on REFL11, REFL33, REFL55 and AS55.
After that I did a orthogonality test on each I-Q pair of the demod signals to correct the D-phases and the relative gain between I and Q.

 

(Next ?)

 Rana and I discussed the plan and decided to go back to a simple Michelson which should be easy enough to understand what is going on and should allow us a complete set of measurements.
Our big concern behind it is that we maybe locking the PRMI at a funny operation point.
In order to assess the issue I will do the following actions on the Michelson at first and then apply the same things on the PRMI later :
  • Check  the amount of of the sidebands using the OSA
  • Check the amount of the DC light
  • Check the sensing matrix to see if the absolute values in watt / meter make sense or not
    • This work needs calibrations on all the demodulated board (this is equivalent to measuring the conversion losses of the mixers in the demod boards).
  • Measure the contribution from the RAMs (it must be measurable by some means)
  6331   Tue Feb 28 15:48:32 2012 kiwamuUpdateLSCinstalled anti-whitening filters

I installed the rest of the precise anti-whitening filters. Now all of the LSC sensors have the right filters.

Quote from #6330

I found that none of the filter banks in the LSC input signals have the precise anti-whitening filters.

I installed the precise filters on REFL11, REFL33, REFL55 and AS55 based on Jenne's measurement (#4955)

  6334   Tue Feb 28 16:39:25 2012 kiwamuUpdateLSCMICH and PRCL signals in a simulation

I briefly ran a Optickle code to see how the PRC macroscopic length screws up the sensing matrix in the PRMI configuration.

Especially I focused on the optimum demodulation phases for the MICH and PRCL signals to see how well they are separated in different PRC length configuration.

It seems that the demod phases for MICH and PRCL are always nicely separated by approximately 90 degree regardless of how long the PRC macroscopic length is.

If this is true, how can we have such a strange sensing matrix ??

 


(Simulation results)

 The plots below show the simulation results. The x-axis is the macroscopic length of PRC in a range from 6.3 meter to 7.3 meter.
The y-axis is the optimum demodulation phases for MICH (blue) and PRCL (black).
The red line is the difference between the MICH and PRCL demodulation phases.
The left plot is for the REFL11 signals and the right plot is for the REFL55 signals.
When the difference is 90 degree, it means we can nicely separate the signals (i.e. REFL11I for PRCL and REFL11Q for MICH).
Obviously they are always nicely separated by ~ 90 deg.

 

REFL11_PRMI.pngREFL55_PRMI.png

Quote from #6330
The lock of the PRMI doesn't look healthy, especially the sensing matrix doesn't make sense at all (#6283).
A very staring thing in the sensing matrix is that the REFL11 and REFL55 didn't show the 90 degree separation between MICH and PRCL.

 

  6336   Tue Feb 28 20:49:33 2012 kiwamuUpdateLSCinsalling OSA

I am installing an OSA on the AP table and it's ongoing.

I am leaving some stuff scattered on the AP table and I will resume the work after I come back.

  6340   Wed Feb 29 04:23:14 2012 kiwamuUpdateLSCREFL OSA installed

I placed the OSA (Optical Spectrum Analyzer) on the AP table and this OSA will monitor the REFL beam.

Tomorrow I will do fine alignment of the OSA.

 

(some notes)

- a new 90% BS in the REFL path for limiting the REFL beam power

 I installed a 90 % beam splitter in the REFL path so that this BS limits the maximum power in the downstreams because we don't want to damage any more RFPDs.
The REFL beam has a power of about 610 mW and the BS has R = 94 % (the spec says 90 +/- 4 % ), resulting in a power of ~37 mW in the transmitted light.
Then the transmitted beam goes through the combination of a half-wave plate and PBS, which allows a fine adjustment of the power.
After passing through the lambda/2 + PBS, the beam is branched to four ways and each beam goes to the REFL RFPD, i.e. REFL11, 33, 55 and 165.
In the end each RFPD receives a laser power of 9 mW at maximum, which is reasonably lower than the power rate of the photo diodes (~17 mW ).
The new OSA uses the reflected light from the 90% BS.

- Squeezed the ABSL (ABSolute length Laser) path

 I squeezed the path of the ABSL in order to accommodate the OSA.
I tried to keep the same optical distances for some lenses, but I guess their mode matching must be different from what they used to be.
So be aware of it.
 

- Modification of the AS OSA path

 I have also modified the optical path of the AS OSA because there had been an extra zig-zag path which made the path more complex in unnecessary way.
Since I have squeezed the ABSL path, it allowed me to simplify the optical path. So I modified the path.

Quote from #6336

I am installing an OSA on the AP table and it's ongoing.

  6350   Mon Mar 5 03:22:54 2012 kiwamuUpdatePSLPMC realigned

I realigned the steering mirrors for the PMC. The trans value went up from 0.79 to 0.83.

The misalignment was largely in the pitch direction.

  6351   Mon Mar 5 03:50:49 2012 kiwamuUpdateIOOPZT1 PITCH railing

PZT1 started railing in the pitch direction and because of this TRY doesn't go more than 0.7. I will leave it as it is for tonight.

Tomorrow I will shift the alignment of the MC to make the PZT1 happier.

Quote from #6300

PZT1, the one with Koji's custom mid-HV driver (#5447), is getting degraded.

 

  6352   Mon Mar 5 05:39:36 2012 kiwamuUpdateLSCREFL OSA installed

The OSA for the REFL beam is now fully functional.

The only thing we need is a long BNC cable going from the AP table to the control room so that we can monitor the OSA signal with an oscilloscope.

The attached picture shows how they look like on the AP table. Both AS and REFL OSAs are sitting on the corner region.

Quote from #6340

I placed the OSA (Optical Spectrum Analyzer) on the AP table and this OSA will monitor the REFL beam.

Tomorrow I will do fine alignment of the OSA.

Attachment 1: APtable.png
APtable.png
  6353   Mon Mar 5 06:11:08 2012 kiwamuSummaryLSCplans

Plans:

  •  DRMI (PRMI) + one arm test before the LVC meeting
  •  Study of the funny sensing matrix and the RAM offset effects before the LVC meeting
  •  Glitch hunting

Action items:

  • MC beam pointing 
    • to make the PZT1 pitch relax
  • OSA setup
    •    a long BNC cable for monitoring the signal in the control room
  • Power budget on the AP table
    • in order to ensure the laser power on each photo diode
  •  POP22/110 sideband monitor
    • installation of an RF amp
    • building a diplexer
    • connect the signals to the demod boards 
  •  Calibration of the demod boards
    • calibrate the conversion loss of the mixers to calibrate all the LSC signals to watts / meter
  •  (1+G) correction for the glitch time series data
  • Simulation study for the RAM offset
    • How much offset do we get due to the RAM ? and how do the offsets screw up the sensing matrix ?
  •  A complete set of the MICH characterization
    •   DC power
    •   Sensing matrix
    •   Noise budget
    •   OSA
    •   Estimation of the RAM offset 
    •  Summarize the results in the wiki
  •  A complete set of the PRMI/DRMI characterization
    •  The same stuff as the MICH characterization
  •  DRMI + one arm test
    •   Monitor the evolution of the sensing matrix during the arm is brought to the resonance

   
 

  6354   Mon Mar 5 13:11:06 2012 kiwamuUpdateLSCinstalled a long BNC cable for REFL OSA

A long BNC cable was installed and now the REFL OSA signal is happily shown on an oscilloscope in the control room.

Quote from #6352

The OSA for the REFL beam is now fully functional.

The only thing we need is a long BNC cable going from the AP table to the control room so that we can monitor the OSA signal with an oscilloscope.

  6355   Mon Mar 5 14:10:35 2012 kiwamuUpdateLSCpower budget on the AP table

I checked the laser powers on the AP table and confirmed that their powers are low enough at all the REFL photo diodes.

When the HWP( which is for attenuating the laser power with a PBS) is at 282.9 deg all of the REFL diodes receives about 5 mW.

This will be the nominal condition. 

If the HWP is rotated to a point in which the maximum laser power goes through, the diodes get about 10 mW, which is still below the power rate of 18 mW (#6339).

I used the Coherent power meter for all the measurements.

The table below summarizes the laser powers on the REFL diodes and the OSA. Also the same values were noted on the attached picture.

 

 nominal power [mW]

(when HWP is at 282.9 deg)

expected max power [mW]

(when HWP is at a point where the max power goes through)

REFL11 5.5 10
REFL33 4.5 10
REFL55 5.3 10
REFL165 4.8 10
REFL OSA 0.7 0.7

 

A note:
I found that the OSA for the REFL beam was receiving a unnecessary bright laser.
So I put an ND1 attenuator stacked on the existing ND2 attenuator. The laser power entering in the OSA is currently at 0.7 mW.
Attachment 1: power_budget.png
power_budget.png
  6357   Mon Mar 5 17:07:58 2012 kiwamuUpdateIOOrealigned MC

I have slightly shifted the MC beam pointing to relax the PZT1 PITCH. As a result the TRY value went to 0.97 in a first lock trial.

However another issue arose:

   The polarity for controlling the PZT1 PITCH seems to have flipped for some reason.

Since it is still sort of controllable, I am leaving it as it is.

If I remember correctly, sliding the PZT1 pitch value to the positive side brought the beam spot upward in the AS CCD. But now it moves in the opposite way.

Also the ASS feedback looks tending to push the PZT1 pitch to the wrong direction.

I am not 100 % sure if the polarity really flipped, but this is my current conclusion.

 

 

(MC pointing)

  1. Locked the Y arm and aligned ITMY and ETMY with the ASS servos such that the beam spot on each test mass is well centered on the test mass.
    • With this process the eigen axis of the Y arm cavity is well prepared.
  2. Checked the beam positions of the prompt reflection light and cavity leakage field in the AS CCD.
    • It looked the incident beam needed to go upward in the CCD view.
  3. Offloaded the MC WFS feedback values to the MC suspension DC biases in a manual way.
  4. Disabled the MC WFS servos. The MC transmitted light didn't become worse, which means the suspensions were well aligned to the input beam
  5. Changed the DC bias in the MC2 PITCH, to bring the beam spot upward. I changed the DC bias by ~ 0.1 or in the EPICS counts.
  6. Aligned the zig-zag steering mirrors on the PSL table to match the incident beam to the new MC eigen beam axis.
    • The transmitted DC light and reflected DC values went back to 27000 counts and 0.58 counts respectively without the WFS servos.
  7. Re-engaged the WFS servos.

Quote from #6351

PZT1 started railing in the pitch direction and because of this TRY doesn't go more than 0.7. I will leave it as it is for tonight.

Tomorrow I will shift the alignment of the MC to make the PZT1 happier. 

 

  6362   Tue Mar 6 01:35:03 2012 kiwamuUpdateLSCMICH characterization

[Keiko / Kiwamu]

 Update on the MICH characterization:

  • The OSAs weren't so great because the 11 MHz sidebands were covered by the carrier's tail
    • It seemed that the frequency resolution depended on the mode matching. We will try improving the mode matching tomorrow.
  • The noise budget looked very bad
    • There were huge peaks at 1 Hz, 3 Hz, 16.5 Hz and 23 Hz. Something is crazy in the vertex suspensions.
    • Keiko will post the calibrated noise budget.
  • The MICH response at AS55Q was measured and we will calibrate it into watts / meter.

 

  6369   Wed Mar 7 04:08:48 2012 kiwamuUpdateSUSBS SIDE gain was too low

The BS SIDE damping gain seemed too low. The gain had been 5 while the rest of the suspensions had gains of 90-500.

I increased the gain and set it to be 80.

 

I did the "Q of 5" test by kicking the BS SIDE motion to find the right gain value.

However there was a big cross coupling, which was most likely a coupling from the SIDE actuator to the POS motion.

Due to the cross coupling, the Q of 5 test didn't really show a nice ring down time series. I just put a gain of 80 to let the Q value sort of 5.

I think we should diagonalize the out matrices for all the suspensions at some point.

  6378   Wed Mar 7 19:10:06 2012 kiwamuUpdateLSCREFL OSA : how the signal look like

Just a quick report on the REFL OSA.

The attached plot below shows the raw signal from the REFL OSA which Keiko installed in this afternoon.

When the data was taken the beam on the REFL OSA was a direct reflection from PRM with the rest of the suspended mirrors misaligned.

One of the upper and lower 11 MHz sidebands is resolved (it is shown at 0.12 sec in the plot) while the other one is still covered by the carrier tail.

The 55 MHz upper and lower sidebands are well resolved (they are at 0.06 and 0.2 sec in the plot).

One of the oscilloscopes monitoring the OSA signals in the control room has a USB interface so that we can record the data into a USB flash memory and plot it like this.

OSArefl.png

Quote from #6375

 I swap an OSA at PSL and OSA at REFL. It was because the PSL-OSA had a better resolution, so we place this better one at REFL. The ND filter (ND3) which was on the way to REFL OSA was replaced by two BSs, because it was producing dirty multiple spots after transmitting.

 

  6382   Wed Mar 7 22:04:05 2012 kiwamuUpdateLSCREFL OSA : how the signal look like

I was also wondering about the same thing, comparing with what Mirko obtained before with the same OSA ( #5519).

Quote from #6379

I'm puzzled why the 11MHz peak can be such high considering 1.7~2 times smaller the modulation depth.

 

  6386   Thu Mar 8 04:13:12 2012 kiwamuUpdateLSCupdate on the locking activity

[Keiko / Kiwamu]

 Some updates on the locking activity:

  • Started summarizing the data of the Michelson lock in a wiki page:
  • Gradually moving on to the PRMI lock
    • The lock stays for reasonably a long time (~20 min or more)
    • POP22/110 demod signals seemed just ADC noise.
    • A first noise budget is in process
      • The glitches make the noise level worse above 40 Hz or so in both the MICH and PRCL budgets.
    • Sensing matrix will be measured tomorrow
    • The data will be also summarized in a wiki page
  6388   Thu Mar 8 23:37:03 2012 kiwamuUpdateIOOdither Y arm dither script

I disabled the feedback to the PZT1 PITCH in the Y arm dithering scripts so that it won't push the beam away from the good point.

Currently one has to do a manual alignment only for the PZT PITCH but the rest of DOFs are still able to be automatically aligned with the script.

Quote from #6357

 The polarity for controlling the PZT1 PITCH seems to have flipped for some reason.

  6403   Tue Mar 13 07:04:55 2012 kiwamuUpdateLSCevolution of the sensing matrix in PRMI as a function of time

The punch line is -- the sensing matrix still looks strange in the PRMI configuration.

 

I have been measuring the sensing matrix of the PRMI configuration because it didn't make sense (#6283).

One strange thing I have noticed before was that all the I-phase signals showed a weird behavior -- they fluctuate too much in time series.

Tonight I measured the sensing matrix again but this time I recorded them as a function of time using the realtime LOCKINs in the LSC front end.

The attached plots are the responses (optical gains) of PRCL and MICH in watts / meter at various sensors in time series.

I will explain some more details about how I measured and calibrated the data in another elog entry.

 

PRCL.png

 MICH.png

 

  6405   Tue Mar 13 16:40:06 2012 kiwamuUpdateLSCevolution of the sensing matrix in PRMI as a function of time: details

Here I describe the measurement of the sensing matrix.

 

Motivations

  There were two reasons why I have been measuring the sensing matrix :

  1.  I wanted to know how much each element in the sensing matrix drifted as a function of time because the sensing matrix didn't agree with what Optickle predicted (#6283).
  2.  I needed to estimate the MICH responses in the 3f demodulated signals, so that I can decide which 3f signal I should use for holding MICH.

 I will report #2 later because it needs another careful noise estimation.

 

Measurement

 In order to measure the sensing matrix, the basic steps are something like this:

  1. Excite one of the DOF at a certain frequency, where a notch filter is applied in the LSC servos so that the servos won't suppress the excitation signal.
  2. Demodulate the LSC signals (e.g. C1:LSC-REFL11_I_ERR and etc.,) by the realtime LOCKINs (#6152) at the same frequency.
  3. Calibrate the obtained LOCKIN outputs to watts/meter.
In the actual measurement I choose the frequency of the excitation signal to be at 283.1 Hz,
at which any of the LSC servos don't have gains of more than 1 and there were no particular structures in the spectra.
For the amplitude of the excitation, I usually choose it to be 1000 - 2000 counts.
Because all the actuators have response functions of approximately 10-9 / f^2 meter/counts  (#5637), the actual displacement in the excited DOF should be about 10 pm level.
Therefore the excited displacements must be always in the linear ranges and also the amplitude in counts is reasonably smaller than the DAC range.
 

LOCKIN detection

The attached cartoon below shows how the LOCKIN system works for the MICH response measurement.
In the case of the PRCL response measurement, the setup is the same except that only PRM is shaken.
Here is some notes about the LOCKIN detection.
  • The LOCKIN oscillator excites ITMs differentially
    • In order to purely excites the MICH DOF, the actuation coefficients were precisely adjusted (#6398).
    • Currently ITMY has a gain of 1, and ITMX has a gain of -0.992 for the pure MICH excitation. Those numbers were put in the output matrix of the LOCKIN oscillator.
  • The demodulation phase of the LOCKIN system was adjusted to be -22 deg at the digital phase rotator.
    • This number maximizes the in-phase signals while the quadrature-phase signals give almost zero.
    • This number was adjusted when the simple MICH configuration was applied.
  • In the demodulations, the LO signals have amplitude of 100 counts to just make the demodulated signals readable numbers.

 

lockins_MICH.png

 

Calibration of the LOCKINs

  The calibration of the LOCKIN detectors is easy because all the processes takes place in the digital land, where we know all the parameters.
In this phase the goal is to calibrate the signals into counts / meter.
To calibrate the LOCKIN output signals, the following equation is used :
 
 [The obtained LOCKIN output in counts ] = H x ADOF x CLO x CEXC x 1/2  ,
 
 where H is the response of a sensor (e.g. AS55_I, AS55_Q and so on) against a particular DOF in unit of counts / m and this the quantity which we want to measure here,
ADOF is the actuator efficiency of the DOF at the excitation frequency in unit of m/counts,
CLO is the amplitude of the local oscillator signal for demodulating the sensor signals in unit of counts,
CEXC is the amplitude of the excitation signal in unit of counts,
the last 1/2 term comes from the fact there is a low pass filter in each demodulation path. 
Therefore once we measure the response of a sensor, dividing the obtained LOCKIN output by ADOF x CLO x CEXC x 1/2 gives the calibrated response in unit of counts/meter.
  ADOF are well known as they have been measured several times (#5637).
For the MICH actuator I assumed that AMICH = 2 x (ITMY response) since they are balanced through the actuation coefficients.
Note that a confirmation of this calibration has been done
when the configuration is in the simple Michelson, where we can easily estimate the response of a sensor by letting the MICH freely swing.
 

Calibration of the responses to watts/meter

  With the calibration process described above, we obtain the sensor responses in unit of counts/m.
 Then we need to do another calibration to make them into unit of W/m.
If we think about how the RFPD signal flows, we get the following gain chain.
 
[raw response in counts/m ] = Hopt x CADC x Ldemod x GWF x Ztrans x RPD
 
Hopt  is the optical gain at a sensor which we want to calibrate. It is in unit of W/m.
CADC  is the conversion factor of the ADCs and the value is CADC = 1638.4 counts/m because their resolution is 16 bit and the range is +/-20 V.
Ldemod is the conversion efficiency of the demodulation boards in unit of V/V. I used the values which Suresh measured yesterday (#6402).
GWF is the gain of the whitening filter in unit of V/V,
Ztrans is the transimpedance gain of an RFPD in unit of V/A and I used the values summarized in (the wiki),
and RPD is the responsivity of the photo diodes and I assumed RPD = 0.75 A/W for all the RFPDs.
 
Therefore the calibration can be done by dividing the raw response value by the entire gain chain of CADC x Ldemod x GWF x Ztrans x RPD.
 

Settings and parameters

  •  LSC RF demodulation phases
    •  AS55 = 17.05 deg (minimizing the PRCL sensitivity in the Q-phase)
    •  REFL11 = -41.05 deg (maximizing the PRCL sensitivity in the I-phase)
    • REFL33 = -25.85 deg (maximizing the PRCL sensitivity in the I-phase)
    • REFL55 = 4 deg (maximizing the PRCL sensitivity in the I-phase)
    • REFL165 = 39 deg (random number)
  •  Whitening filters
    • AS55 = 30 dB
    • REFL11 = 0 dB
    • REFL33 = 42 dB
    • REFL55 = 30 dB
    • REFL165 = 45 dB
  • MICH servo
    • AS55_Q for the sensor
    • G = -5 in the digital gain
    • FM2, FM3, FM5 and FM9 actiavted
    • UGF ~ 100 Hz
    • Feedback to ITMs differentially
  • PRCL servo
    • REFL33_I for the sensor
    • G = 1 in the digital gain
    • FM2, FM3, FM4, FM5 and FM9 activated
    • UGF ~ 100 Hz
    • Feedback to PRM

Quote from #6403

Tonight I measured the sensing matrix again but this time I recorded them as a function of time using the realtime LOCKINs in the LSC front end.

I will explain some more details about how I measured and calibrated the data in another elog entry.

  6406   Tue Mar 13 16:56:19 2012 kiwamuUpdateLSCevolution of the sensing matrix in PRMI as a function of time

Next steps:

  • Compare the obtained sensing matrix with an Optickle model. Particularly I am interested in the absolute strengths in watts/meter
  • Noise estimation of the REFL33_Q as a MICH sensor to see if this sensor is usable for holding MICH.

Quote from #6403

Tonight I measured the sensing matrix again but this time I recorded them as a function of time using the realtime LOCKINs in the LSC front end.

The attached plots are the responses (optical gains) of PRCL and MICH in watts / meter at various sensors in time series.

  6407   Tue Mar 13 19:14:40 2012 kiwamuUpdateLSCNoise estimatino in the REFL33Q as a MICH sensor

A feasibility study of the REFL33Q as a MICH sensor was coarsely performed from the point view of the noise performance.

The answer is that :

  the REFL33Q can be BARELY used as a MICH sensor in the PRMI configuration, but the noise level will be at only sub-nano meter level.

  Tonight I will try to use the REFL33Q to control the MICH DOF to see what happens.

 

(Background)

  I neeeeeeeed a 3f signal which is sensitive enough to hold the Michelson in the PRMI configuration so that I can test the single arm + PRMI configuration.
Based on the data I got in the sensing matrix measurement (#6403) I wanted to see how noises in the REFL33Q look like.
 

(Noise analysis)

  I did a coarse noise analysis for the REFL33Q signal as shown in the attached plot below while making some assumptions as follows.

  •  Optical gain for MICH = 0.8  W/m (#6403)
    • In the plot below, I plotted a unsuppressed MICH motion which had been measured the other day with a different sensor. This is for a comparison.
  •  Shot noise due to DC light on the REFL33 photo diode
    •  With a power of 5.0 mW (#6355)
    • Assume that the responsivity is 0.75 A/W, this DC light creates the shot noise in the photo current at a level of 35 pA/sqrtHz.
    • Then I estimated the contribution of this shot noise in terms of the MICH displacement by calibrating the number with the optical gain and responsivity.
    • It is estimated to be at 60 pm/sqrtHz
  • Dark current
    • I assumed that the dark current is 0.52 mA. (see the wiki)
    • In the same manner as that for the shot noise, the dark current is estimated to be at 20 pm/sqrtHz in terms of the displacement
  • Whitening filter input referred noise
    • I assumed that it is flat with a level of 54 nV/sqrtHz based on a rough measurement by looking at the spectrum of the LSC input signals.
    • The contribution was estimated by applying some gain corrections from the conversion efficiency of the demod board, transimpedance gain, responsivity and the optical gain.
    • This noise is currently the limiting factor over a frequency range from DC to 1 kHz.
  • ADC noise
    • I did the same thing as that for the whitening filter noise.
    • I assumed the noise level is at 6 uV/sqrtHz and it is flat (I know this not true particularly at mHz region the noise becomes bigger by some factors)
    • Then I applied the transfer function of the whitening filter to roll off the noise above 15 Hz.

 NB_REFL33.png

(Some thoughts)

  •   Obviously the limiting noises are that of ADC and the whitening filter.
    • These noise can be easily mitigated by installing an RF amplifier to amplify the RF signals from the REFL33Q RFPD.
    • Therefore this is not the real issue
  • The real issue is that the shot noise is already at a level of 60 pm/sqrtHz, and we can't suppress the MICH motion less than that.
    • In order to decrease it, one possibility is to increase the modulation depth. But it is already at the maximum.
    • If the REFL165 RFPD is healthy, it is supposed to give us a bigger MICH signal. But it didn't look healthy ... (#6403)
  6409   Wed Mar 14 03:34:44 2012 kiwamuUpdateSUSAdjustment of BS suspension output matrix : coupling from SIDE to POS

[Rana / Kiwamu]

 We put some elements in the BS output matrix to mitigate the actuator coupling from SIDE to POS.

As a result the degree of the coupling reduced by a factor of 2 or so.

Rana did the "Q of 5" test on the SIDE damping servo after putting the elements and set the gain to be 40.

 

The attached screen shot is the new elements that we put in the suspension output matrix.

Untitled.png

 

(How to)

  • Excite the SIDE motion by AWG at 3 Hz.
  • Monitor the POS signal in DTT
  • Try some numbers in the matrix elements until the peak at 3 Hz in the POS signal is minimized

Quote from #6369

The BS SIDE damping gain seemed too low. The gain had been 5 while the rest of the suspensions had gains of 90-500.

I increased the gain and set it to be 80.

 

I did the "Q of 5" test by kicking the BS SIDE motion to find the right gain value.

However there was a big cross coupling, which was most likely a coupling from the SIDE actuator to the POS motion.

Due to the cross coupling, the Q of 5 test didn't really show a nice ring down time series. I just put a gain of 80 to let the Q value sort of 5.

I think we should diagonalize the out matrices for all the suspensions at some point.

 

  6410   Wed Mar 14 04:03:37 2012 kiwamuUpdateIOOPZT1 and associate extra works

As the PZT1 has not been functional, I have been aligning the Y arm to the input beam instead of aligning the beam to the Y arm.

It turned out that this procedure leads to two extra works everytime after alignments of the Y arm:

  1. The Y green beam must be always aligned to the Y arm
    • The amount of the misalignment was found to be relatively big compared with how it used to be.
  2. The PSL beat note setup must be always realigned because the Y green path is determined by the orientation of the Y arm.
    • In the past I didn't often realign the beat note path, but currently it needs to be pay more attentions.

Sad ..

Quote from #6357

   The polarity for controlling the PZT1 PITCH seems to have flipped for some reason.

 

  6411   Wed Mar 14 04:19:51 2012 kiwamuUpdateLSCREFL33Q for MICH control : not good

 I tried the REFL33Q for controlling MICH in the PRMI configuration (#6407)

The result was --

 It was barely able to lock MICH in a short moment but didn't stay locked for more than 10 sec. Not good.

 

The attached screenshot below shows a moment when the PRMI was locked with REFL33I and REFL33Q for PRCL and MICH respectively.
Apparently the lock was destroyed after 10 sec or so and it was locked again.
Untitled.png

 

(Tricks)

 At the beginning I tried minimizing the PRCL signal in the Q phase by rotating the demodulation phase because the PRCL signal was always huge.
However it turned out that the rotation of the demodulation phase didn't completely eliminate the PRCL signal for some reason.
 
This could be some kind of imbalance in the electronics or somewhere between the I and Q signal paths.
So instead, I tried blending the I and Q signals by a linear combination through the LSC input matrix.
Then I was able to eliminate the PRCL signal.
I put a gain of -0.1 for the I signal and 1 for the Q signal to get the good blend when the demodulation phase was at -17.05 deg.
  6414   Wed Mar 14 13:16:50 2012 kiwamuUpdateLSCA correction on Noise estimatino in the REFL33Q

A correction on the previous elog about the REFL33Q noise:

 Rana pointed out that the whitening filter's input referred noise should not be such high (I have estimated it to be at 54 nV/sqrtHz).
In fact the measurement was done in a condition where no laser is on the photo diode by closing the mechanical shutter at the PSL table.
Therefore the noise I called "whitening filter input referred noise" includes the voltage noise from the RFPD and it could have such a noise level.
So the noise curve drawn in the plot should be called "whitening filter + RFPD electronics noise".

Quote from #6407

A feasibility study of the REFL33Q as a MICH sensor was coarsely performed from the point view of the noise performance.

  • Whitening filter input referred noise
    • I assumed that it is flat with a level of 54 nV/sqrtHz based on a rough measurement by looking at the spectrum of the LSC input signals.
    • The contribution was estimated by applying some gain corrections from the conversion efficiency of the demod board, transimpedance gain, responsivity and the optical gain.
    • This noise is currently the limiting factor over a frequency range from DC to 1 kHz.

 

  6426   Fri Mar 16 16:03:03 2012 kiwamuUpdateIOOMC alignment servo : put some offsets in the TRANS QPD signal

The MC alignment servo wasn't great in the last 1 hour or so as it kept disturbing the MC lock. It was found to be due to some offsets in the MC trans QPD signals.

I put some values to cancel the offsets and then the lock became stable.

This is a first aid. So we need to take a closer look at the QPD signals and also probably the spot position on the QPD.

 


The symptom was that every time the alignment servo was engaged, at the beginning the amount of the transmitted light went to 27000 counts, which is good.

However, then the amount of the transmitted light slowly decreased in a time scale of ~ 20 sec or so, ending up with destruction of the MC lock.

According to the time scale I suspected that the servos using the trans QPD signals were doing something bad because their control width had been designed to be slow and slower than the rest of the servo loops.

I switched off the servos, called C1:IOO-TRANS_PIT and C1:IOO-TRANS_YAW and found the MC stayed locked stably with 27000 counts of the transmitted light.

Leaving the trans QPD servos off, I zeroed the offsets and then switched them on. It worked.

 

The values below are the current offset that I put.

                C1:IOO-MC2_TRANS_PIT_OFFSET = -0.115203
                C1:IOO-MC2_TRANS_YAW_OFFSET = -0.0323576
 

  6436   Thu Mar 22 16:45:06 2012 kiwamuUpdateCDSc1scx and c1scy not properly running

It seems that neither c1scx nor c1scy is working properly as their ADC counts are showing digital-zeros.

However the IOPs, c1gcx and c1gcy look running fine, and also the IOPs seem successfully recognizing the ADCs according to dmesg.

Also there is one more confusing fact : c1scx and c1scy are synchronizing to the timing signal somehow.

I restarted the c1scx front end model to see if this helps, but unfortunately it didn't work.

As this is not the top priority concern for now, I am leaving them as they are now with the watchgods off.

(I may try hardware rebooting them in this evening)

Quote from #6434

The power was turned back on at 4pm It took some time for Suresh to restart the computers. We have damping but things are not perfect yet. Auto BURTH did not work well.

 

  6437   Thu Mar 22 17:35:59 2012 kiwamuUpdateLockingmode profiles of the POP and POX beams : not bright enough

I tried to measure the beam profiles at the POP and POX ports as Koji mentioned in his entry (#6421).

However it turned out that the beam powers were too small to be measured with our beam scan at those ports.

So I will move on to measurements at the REFL port as Rana suggested because the laser power is much larger than that of POP and POX.

(If the data of the POP and POX beam profiles turn out to be very necessary, we will do the razor blade technique with a more sensitive photo diode)

Quote from #6421

More precise analysis can be done with quantitative analysis of those two spots with Beamscan. This could happen tomorrow.

 

  6440   Fri Mar 23 01:59:59 2012 kiwamuUpdateIOOREFL beam currently unavilable

[Suresh / Kiwamu]

Currently the REFL beam is bypassed by additional mirrors and blocked by a razor blade dump.

Therefore the signals associated with the REFL ports (e.g. REFL11, REFLDC and etc.) are unavailable.

Just be aware of it.

  6444   Mon Mar 26 15:15:16 2012 kiwamuUpdateIOOexpected beam profile of PRM reflection

I have estimated how the mode profile of the PRM reflection should be, as shown in the plot blow.

A conclusion here is :

   we should be able to constrain the PRM curvature situation if measurements are precise and accurate enough with a level of less than ~ 100 um

 

In the calculation two cases are considered :

      (1) PRM has the correct curvature of  +122 m. This is shown as solid curves in the plot.

      (2) PRM has a wrong curvature of - 122 m (mirror is flipped) This is shown as dashed curves in the plot. 

expected_edit.png

The plot above shows beam radii of the PRM reflections for vertical and horizontal profiles in each case.
The x-axis is distance from PRM in meter and the y-axis is the beam radii in mm.
As for the initial beam parameter, I used the measured values (see the wiki), which are that of after the beam exits from the mode matching telescope and before it goes to PRM.
 
(1) If PRM has the correct curvature, the reflection after it passes MMT1 will have ~ 1.6 mm beam radii.
This is intuitively correct because the beam profiles should match to that of the MC exiting beam  (see the wiki), which has waist size of 1.5 - 1.6 mm if everything is perfect.
(2) When PRM is flipped, the beam starts converging at the beginning as PRM act as a convex mirror, resulting in smaller beam sizes after it comes out from the telescope.
Roughly speaking the waist sizes will be different by ~ 5 mm between those two cases, so our measurement should be more precise and accurate than this number.

Note:

 I have omitted the effect from the PRM thickness. Therefore PRM is dealt as just a curved reflector with RoC of +/- 122 m in the calculation.

 

  6445   Mon Mar 26 16:25:44 2012 kiwamuUpdateIOOexpected v.s. measured beam profile of PRM reflection

[Suresh / Kiwamu]

 We did the 2nd round of the PRM reflection mode scan on Friday.

It seems that the PRM curvature maybe correct if we look at the vertical mode, however but the horizontal mode doesn't seem to agree with any of the expected lines.

In order to increase the reliability of the measurement, we need to confirm the beam profile of the incident beam by looking at the IP-POS beam.

Right now Suresh and Keiko are mode-scanning the IP-POS beam.

 

 


The plot below shows both the expected beam profiles (see the detail in #6444) and the actual data. 

PRMreflection.png

This plot is the same as one shown in the previous entry (#6444) with newly added actual data.
The errorbar in each data point is the standard deviation obtained by 100 times of averaging.
In this plot I made the error bars 10 times bigger in order to let them visible in the plot, so the actual deviation is much lesser than they appear.
 

(Discussion)

 The vertical profile (shown in red) seems to be close to the curve for the correct PRM case.
However the horizontal profile has a bigger waist size of about  2 mm.
While measuring the waist size Suresh and I have noticed that the rotational angle of the scan head affects the measurement by 10% or so.
Of course in each data point we tried making the incident beam normal to the scan head by rotating the scan head.
But this 10% is not big enough to explain the discrepancy in the horizontal mode.
There are some possible scenario which can distort the beam shape in the horizontal direction:
  • Clipping at some optics. (Since the beam shape looked very Gaussian, the amount of the clipping could be very slight ?)
  • Astigmatism at some optics. (Possibly in the telescope ?)

(Some distances)

DSC_4001_small.jpg
 

(Some notes)

We did the following things prior to the measurement.

  • Put a boost filter in the PRM_OLYAW to suppress the beam jitter below 1 Hz.
  • Checked the MC WFS servo loop although it looked healthy.

Quote from #6444

I have estimated how the mode profile of the PRM reflection should be, as shown in the plot blow.

A conclusion here is :

   we should be able to constrain the PRM curvature situation if measurements are precise and accurate enough with a level of less than ~ 100 um 

 

  6446   Mon Mar 26 18:04:43 2012 kiwamuUpdateIOOmode scan at the REFL port

For those who are interested in the actual data, I attache the actual data in zip file together with a python plot code.

The distance was set such that the 1st steering mirror (the one at the very left in the previous cartoon diagram #6445 ) in the REFL path is positioned at zero.


mode_profile.png

 

- - - Fitting results (chi-square fitting done by gnuplot):

All values are in unit of meter

# PRM (v) (Last tree points are excluded as the beam were clipped at the aperture of the beam scan)

w0          = 0.0015114        +/- 2.192e-05    (1.451%)
z0           = -4.46073         +/- 0.05605      (1.256%)

# PRM (h)

w0           = 0.00212796       +/- 1.287e-05    (0.6049%)
z0           = -2.53079         +/- 0.1688       (6.668%)

# ITM (v) (Last two points are excluded as the beam were clipped at the aperture of the beam scan)

w0           = 0.00190696       +/- 4.964e-05    (2.603%)
z0           = -8.09908         +/- 0.1525       (1.882%)

# ITM (h)

w0           = 0.0032539        +/- 4.602e-05    (1.414%)
z0           = -1.89484         +/- 1.524        (80.42%)

 

Attachment 2: REFLmodescan.zip
  6450   Tue Mar 27 02:46:28 2012 kiwamuUpdateIOOREFL beam available

The dump and some temporary mirrors were removed and now the REFL beam is available again.

I locked PRMI with REFL signals, it locked as usual.

Quote from #6440

Currently the REFL beam is bypassed by additional mirrors and blocked by a razor blade dump.

  6471   Fri Mar 30 10:20:51 2012 kiwamuUpdateLSClocking last night

I was trying to make the DRMI lock more robust.

Increasing the gains of the oplev on SRM helped a lot, but the lock is still not solid enough for measurements.

According to some line injection tests, the SRCL and MICH signals show up in AS55Q with almost the same amplitudes.

I tried to diagonalize the input matrix (particularly MICH-SRCL in AS55) based on the result of the line injection tests, but I ran out the time.

Work continues.

  6474   Sat Mar 31 08:01:07 2012 kiwamuUpdateLSCDRMI measurement

I have measured the sensing matrix of the DRMI although the lock still doesn't stay for a long time.

As for the noise budget, it looks very tough as there are more glitches than that in the PRMI.

In this weekend I will take some more trials in the DRMI lock until I am satisfied.

  6488   Thu Apr 5 06:27:51 2012 kiwamuUpdateLSCAS110 sideband monitor installed

[Jenne / Kiwamu]

 We have installed a broad band PD in the AS path in order to monitor the 110 MHz signal associated with the SRC.

The PD is currently connected to the POP110 demodulation board and it seems working fine.

I know this is confusing but right now the signal appears as "POP110" in the LSC front end model.

 


  • Installed a 50% BS at the AS path
    • The AS beam is split to two path - one goes to AS55 and the other goes to the OSA.
    • The new BS is installed on the way of the OSA branch therefore AS55 isn't affected by the new BS.
  • Installed a PDA10A
    • This is a silicon diode with a bandwidth of 150 MHz, and is fast enough to detect the 110 MHz signals.
    • The 110 MHz signal seems going up to approximately -40 dBm according to a coarse measurement with an RF spectrum analyzer.
    • Also a SMA-style high pass filter, HPF-100, was attached to the output to cut off unnecessary sidebands (e.g. 11, 22 MHz and etc.)
  • Put a long BNC cable, which goes from the PD to LSC rack.
    • The end of the cable at the LSC rack was directly connected to the POP110 demod board.
    • The actual POP110 signal path is currently terminated by a 50 Ohm load and therefore this signal  is unavailable.
  • Adjustment of the demodulation phase
    • The demod phase was adjusted to be 7 deg in the EPICS screen. This phase minimize the Q-signal.
    • Locking PRMI with sidebands resonating makes the AS110 signal ~ a few counts and this level is still noticeable.
    • Perhaps we may need to put an RF amplifier to get the signal bigger.
  6489   Thu Apr 5 07:19:16 2012 kiwamuUpdateLSCDRMI locking

 I tried locking the DRMI to the signal-extraction condition with the new trigger by AS110.

A first thing I tried was : flipping the control sign of the SRCL while keeping the same control setups for the PRCL and MICH.

Occasionally the DRMI was "sort of" locked and hence I believe this setup must be a good starting point.

As a next step I will try some different gains and demodulation phase to make it more lockable.

 


(Time series)

DRMI_2012Apr4_edit.png

 The picture above is time series of some signals when the DRMI was barely locked.
The red arrows indicate the durations when the DRMI was sort of locked.
 (Green curve) REFLDC becoming a high value state, which indicates that the carrier is anti-resonant.
 (Red curve) ASDC becoming dark, which indicates the MICH is in the vicinity of the dark condition.
 (Brown curve) AS110 becoming a high value state, which means the 55 MHz sidebands got amplified by the SRCL.
 (Blue curve) POP22 becoming a high value state, which indicates that the 11 MHz sidebands are resonating in the PRC.
 
According to the measurement of AS110 when PRMI was locked (#6488), the AS110 signal went up to ~ 1 counts or so.
On the other hand when the DRMI was locked the AS110 went to up more than 10 counts as shown in the plot above.
Therefore at least some kind of signal amplification is happening for the 55 MHz sidebands in the SRC.
Looking at the AS CCD, I found that the beam looked like a TEM01 mode (two beam spots at top and bottom) every time when the DRMI was locked.
 
(settings)
  • REFL33I => PRCL  G = -0.2
  • AS55Q => MICH    G = -6
  • AS55I => SRCL     G = 1   (G = -50 for the signal recycling condition)
  • AS55 demod phase = 17 deg
  6506   Sat Apr 7 01:56:05 2012 kiwamuUpdateLSCOSA signal in DRMI condition

It wasn't a dream or illusion -- I was locking the DRMI to the right condition last Wednesday (#6489).

Here is a snap shot of the AS-OSA signal taken today when the DRMI was locked with the same control settings (#6489).

The blue curve is data taken when the PRMI was locked for comparison.

You can see that both the upper and lower 55 MHz sideband are amplified by the SRC.

OSA.png

 

(Some notes)

Currently SRM is slightly misaligned such that the MICH optical gain at AS55Q doesn't increase so much with the presence of SRM.

With this condition I was able to acquire the lock more frequently than how it used to be on the Wednesday.

The next step is to gradually align SRM, to optimize the controls and to repeat this process several times until SRM is fully aligned.

Quote from #6489

A first thing I tried was : flipping the control sign of the SRCL while keeping the same control setups for the PRCL and MICH.

Occasionally the DRMI was "sort of" locked and hence I believe this setup must be a good starting point.

  6508   Sat Apr 7 06:58:34 2012 kiwamuUpdateLSCDRMI lock : lost good alignment

Somehow I lost the good alignment, where the lock can be frequently acquired and hence I didn't go further ahead.

I will try locking the DRMI during the weekend again. My goal is to take time series when the DRMI is being locked and sensing matrix.

Quote from #6506

Currently SRM is slightly misaligned such that the MICH optical gain at AS55Q doesn't increase so much with the presence of SRM.

With this condition I was able to acquire the lock more frequently than how it used to be on the Wednesday.

The next step is to gradually align SRM, to optimize the controls and to repeat this process several times until SRM is fully aligned.

 

ELOG V3.1.3-