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ID Date Author Type Category Subject
6298   Tue Feb 21 04:30:02 2012 kiwamuUpdateLSCY arm + PRMI

I tried the "Yarm + PRMI" configuration to see what happens.
The Y arm was locked at a resonance and held with the ALS technique.
On the other hand, the X arm was freely swinging.

I briefly tried severl demod signals to calm down the central part, but didn't succeed.
Now I feel I really want to have the X arm locked with the ALS technique too.
Give me the beat-box !

The attached screen shot shows the transmitted light of both arms as a function of time.
TRY is always above 1, since it was kept at a resonance.
Sometimes TRY went to 50 or so.

6302   Tue Feb 21 22:06:18 2012 jamieUpdateLSCbeatbox DFD installed in 1X2 rack

I have installed a proto version of the ALS beatbox delay-line frequency discriminator (DFD, formally known as MFD), in the 1X2 rack in the empty space above the RF generation box.

That empty space above the RF generation box had been intentionally left empty to provide needed ventilation airflow for the RF box, since it tends to get pretty hot.  I left 1U of space between the RF box and the beatbox, and so far the situation seems ok, ie. the RF box is not cooking the beatbox.  This is only a temporary arrangement, though, and we should be able to clean up the rack considerably once the beatbox is fully working.

For power I connected the beatbox to the two unused +/- 18 V Sorensen supplies in the OMC power rack next to the SP table.  I disconnected the OMC cable that was connected to those supplies originally.  Again, this is probably just temporary.

Right now the beatbox isn't fully functioning, but it should be enough to use for lock acquisition studies.  The beatbox is intended to have two multi-channel DFDs, one for each arm, each with coarse and fine outputs.  What's installed only has one DFD, but with both coarse and fine outputs.  It is also intended to have differential DAQ outputs for the mixer IF outputs, which are not installed in this version.

The intended design was also supposed to use a comparator in the initial amplification stages before the delay outputs.  The comparator was removed, though, since it was too slow and was limiting the bandwidth in the coarse channel.  I'll post an updated schematic tomorrow.

I made some initial noise measurements:  with a 21 MHz input, which corrseponds to a zero crossing for a minimal delay, the I output is at ~200 nVrms/\sqrt{Hz} at 5 Hz, falling down to ~30 nVrms about 100 Hz, after which it's mostly flat.  I'll make calibrated plots for all channels tomorrow.

The actual needed delay lines are installed/hooked up either.  Either Kiwamu will hook something up tonight, or I'll do it tomorrow.

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.

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.

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.

(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.

6315   Fri Feb 24 18:37:13 2012 ranaUpdateLSCY arm + PRMI part II

 Quote: 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.

Isn't the point that the 11 and 55 MHz signals have the carrier effect, but the 3f signals are better?

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.

 Quote from #6313 The figure below shows the time series of the Y arm + PRMI trail.

6318   Fri Feb 24 19:25:43 2012 jamieUpdateLSCALS X-arm beatbox added, DAQ channels wiring normalized

I have hooked the ALS beatbox into the c1ioo DAQ.  In the process, I did some rewiring so that the channel mapping corresponds to what is in the c1gcv model.

The Y-arm beat PD is going through the old proto-DFD setup.  The non-existant X-arm beat PD will use the beatbox alpha.

Y coarse I (proto-DFD) --> c1ioo ADC1 14 --> C1:ALS_BEATY_COARSE_I
Y fine   I (proto-DFD) --> c1ioo ADC1 15 --> C1:ALS_BEATY_FINE_I
X coarse I (bbox alpha)--> c1ioo ADC1 02 --> C1:ALS_BEATX_COARSE_I
X fine   I (bbox alpha)--> c1ioo ADC1 03 --> C1:ALS_BEATX_FINE_I


This remapping required coping some filters into the BEATY_{COARSE,FINE} filter bank.  I think I got it all copied over correctly, but I might have messed something up.  BE AWARE.

We still need to run a proper cable from the X-arm beat PD to the beatbox.

I still need to do a full noise/response characterization of the beatbox (hopefully this weekend).

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.

 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.

6335   Tue Feb 28 16:44:56 2012 ranaUpdateLSCMICH and PRCL signals in a simulation

### Like I said, this is possible if you fail to set up the OSA to look at the sidebands at BOTH the AS and REFL ports at all times. Don't waste your time - set up an OSA permanently!

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.

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
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
6358   Mon Mar 5 18:12:00 2012 KeikoUpdateLSCRAM simulation update

I wrote an RAM simulation script ... it calculates the LSC signal offset and the operation point offset depending on the RAM modulation index.

Configuration : RAM is added on optC1, by the additional Mach-Zehnder ifo before the PRM.

Both are for PRCL sweep result. Note that REFL33I is always almost zero. Next step: Check the LSC matrix with matrix at the offset operation point.

6359   Mon Mar 5 20:31:33 2012 KojiUpdateLSC22/110MHz path for POP

This a kind of self record...

We need an RF setup at POP to extract 22 and 110 MHz components separately.

I am planning to work on this in the daytime on Tuesday.

6360   Mon Mar 5 23:47:15 2012 keikoConfigurationLSCND2 at REFL OSA

ND filter ND3 (which is at the REFL port to the REFL OSA) is removed. Don't forget to put it back when you restore PRM!!!

6361   Tue Mar 6 00:13:20 2012 keikoUpdateLSCASI signal offset

AS55Q and AS55I signals. AS55Q is around zero while AS55I has a large offset which is about the signal amplitude. It is likely because of the RAM?

keiko, kiwamu

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.

6363   Tue Mar 6 15:22:02 2012 KeikoUpdateLSCRAM simulation update

 Quote: I wrote an RAM simulation script ... it calculates the LSC signal offset and the operation point offset depending on the RAM modulation index. Configuration : RAM is added on optC1, by the additional Mach-Zehnder ifo before the PRM.  Both are for PRCL sweep result. Note that REFL33I is always almost zero. Next step: Check the LSC matrix with matrix at the offset operation point.

On the right figure, you see the non-zero operation points even when RAM mod index = 0. Apparently they come from non-zero loss of the model.  (Each mirror of 50ppm loss was assumed).

6366   Tue Mar 6 22:23:04 2012 KojiUpdateLSC22/110MHz path for POP

As par Kiwamu's request, RF filters for POP22 and POP110 were installed. They are not really nice. We need to replace it with more fancy electronics.
More to come later.

6374   Wed Mar 7 15:56:36 2012 KojiUpdateLSC22/110MHz path for POP

The RF separator installed comprises of the Minicircuits filters cascaded as in the figure below.
This has one input and 4 output ports for 11, 22, 30-60, and 110MHz signal.
As seen in this entry #6167, we have 22 and 110MHz signals together with 11, 44, 66MHz signals.
They may be demodulated via a harmonic characteristic of the mixers. (Remeber mixers are not multipliers.)

Of course the big concern is the impedance matching for those signals as usual.
The 2nd attachment shows measured impedance of the circuits with all of the ports terminated.
From the complex impedance, we can calculate the reflection coefficient. The 44 and 110MHz
components look correctly matched while the others seems largely reflected.
This certainly is not a nice situation, as the reflection can make the amplifier next to the PD unhappy
(although the reflected power is tiny in our case).

In our case more eminent problem is that the amplitude of the 22MHz signal can vary depending on the cable length by
factor of 10 in amplitude. (c.f. VSWR on the 2nd attachment.)

The transmission to each port was measured. The separation of the signals looks good. But the attenuation of the
targetted signals (i.e. insertion losses) are qulitatively consistent with the impedance. Again these losses are depend
on the cable length.

Attachment 2: impedance.pdf
Attachment 3: transmission.pdf
6375   Wed Mar 7 16:32:09 2012 keikoUpdateLSCOSA

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.

6376   Wed Mar 7 17:39:40 2012 keikoUpdateLSCMICH noise budget on 5 Mar

This is the calibrated MICH noise budget on Mar 5. There was a sharp peak at 1Hz and a blob on 3 Hz. The demod phase was adjusted for AS55Q.

Attachment 1: Mar5-MICHbudget.png
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.

 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.

6379   Wed Mar 7 20:06:23 2012 KojiUpdateLSCREFL OSA : how the signal look like

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

6380   Wed Mar 7 20:53:13 2012 keikoUpdateLSCMICH noise budget on 5 Mar

This is the MICH noise budget on 6th March. 1Hz peak got a bit better as the BS sus control gain was increased.

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.

6384   Wed Mar 7 23:29:28 2012 keikoUpdateLSCREFL OSA observation

kiwamu, keiko

We measure the REFL OSA spectrum when (1) direct reflection from the PRM (2) CR lock at PRC (3) SB lock at PRC. When CR lock, both SBs are reflected from the PRC and when SB lock (ref line), some SB is sucked by PRM and looked lower than the other two lines.

6385   Thu Mar 8 00:57:48 2012 keikoUpdateLSCMICH noise budget on Mar 5, Mar 6, and old

Here is the recent two noise budgets of MICH, with the old measurement by Jenne. The most latest Mar 6 data is quite close to the old data, even better around 20-30 Hz. Probably some scattering source was improved?

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
6393   Fri Mar 9 13:34:13 2012 keikoUpdateLSCupdate on the locking activity

We tried to measure the sensing matrix for MICH and PRCL last night. They look too much mixed as we expect... the matrix may be posted later. We suspect the IX and IY of the MICH excitation is not balanced very well, although Kiwamu adjusted that about two weeks ago, and it is mixing the dof. We'll try to balance it again, ans see the matrix.

Keiko, Kiwamu

 Quote: [Keiko / Kiwamu]  Some updates on the locking activity: Started summarizing the data of the Michelson lock in a wiki page: https://wiki-40m.ligo.caltech.edu/Interferometer_Characterization/Michelson_Noise_Budget Some careful analysis of the OSA signals are missing Besides the analysis we need to work on the mode matching to get a better resolution as Mirko achieved. 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

6398   Sat Mar 10 02:00:03 2012 keikoUpdateLSCupdate on the locking activity

ITMX and ITMY balance for the MICH excitation (lockin) is adjusted again. Now it's ITMx = -0.992, ITMy = 1 for MICH (lockin output matrix values).

RA: what were the old values? Does this change make any difference for the signal mixing noticed before?

6400   Mon Mar 12 01:04:18 2012 keikoUpdateLSCRAM simulation update, RAM LSC matrix

I calculated the DRMI RAM LSC matrix with RAM and the operation point offsets.

• configuration: C1 DRMI
• RAM is added by an Mach-Zehnder ifo placed before the PRM
• demodulation phases are optimised for each DoF
• the operation points offset from the PDH signals are calculated and added to the optical configuration as mirror position offsets
• Then the matrix is calculated with the offsets and the RAM
• The set of the scrips are found as RAMmatrix.m, normMAT.m, newGetMAT.m,  on CVS/ifomodeling/40m/fullIFO_Optickle. They are a bit messy scripts at this moment.

Results:

(1) No RAM LSC matrix

 PRCL MICH SRCL REFL11I 1 -0.001806 -0.000147 AS 55Q 0.000818 1 0.000474 AS 55 I 1.064561 902.292816 1

(2) With 1% RAM mod index of PM (normalised by (1) )

 PRCL MICH SRCL REFL11I 1.000618 -0.001837 -0.000163 AS 55Q 0.000919 1.000521 0.000495 AS 55 I 1.169741 924.675187 1.018479

(3) With 5% RAM mod index of PM (normalised by (1) )

 PRCL MICH SRCL REFL11I 0.999986 -0.001812 -0.000150 AS 55Q 0.000838 1.000028 0.000479 AS 55 I 1.084598 906.83668 1.003759

6401   Mon Mar 12 18:57:58 2012 keikoUpdateLSCRAM simulation update, RAM LSC matrix

Quote:

I calculated the DRMI RAM LSC matrix with RAM and the operation point offsets.

• configuration: C1 DRMI
• RAM is added by an Mach-Zehnder ifo placed before the PRM
• demodulation phases are optimised for each DoF
• the operation points offset from the PDH signals are calculated and added to the optical configuration as mirror position offsets
• Then the matrix is calculated with the offsets and the RAM
• The set of the scrips are found as RAMmatrix.m, normMAT.m, newGetMAT.m,  on CVS/ifomodeling/40m/fullIFO_Optickle. They are a bit messy scripts at this moment.

Results:

(1) No RAM LSC matrix

 PRCL MICH SRCL REFL11I 1 -0.001806 -0.000147 AS 55Q 0.000818 1 0.000474 AS 55 I 1.064561 902.292816 1

(2) With 1% RAM mod index of PM (normalised by (1) )

 PRCL MICH SRCL REFL11I 1.000618 -0.001837 -0.000163 AS 55Q 0.000919 1.000521 0.000495 AS 55 I 1.169741 924.675187 1.018479

(3) With 5% RAM mod index of PM (normalised by (1) )

 PRCL MICH SRCL REFL11I 0.999986 -0.001812 -0.000150 AS 55Q 0.000838 1.000028 0.000479 AS 55 I 1.084598 906.83668 1.003759

Adding some more results with more realistic RAM level assumption.

(4) With 0.1% RAM mod index of PM (normalized by (1) )

 PRCL MICH SRCL REFL11I 0.99999 -0.001807 -0.000148 AS 55Q 0.000822 1.000002 0.000475 AS 55 I 1.068342 906.968167 1.00559

(5) With 0.5% RAM mod index of  PM (normalized by (1) )

 PRCL MICH SRCL REFL11I 0.999978 -0.001810 -0.000149 AS 55Q 0.000830 1.000010 0.000476 AS 55 I 1.075926 904.321433 1.001677

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.

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.

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 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.
• 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.

(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)
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.

(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.

6417   Wed Mar 14 16:33:20 2012 keikoUpdateLSCRAM simulation / RAM pollution plot

In the last post, I showed that SRCL element in the MICH sensor (AS55I-mich) is chaned 1% due to RAM.

Here I calculated how is this 1% residual in MICH sensor (AS55 I-mich) shown in MICH sensitivity. The senario is:

(1) we assume we are canceling SRCL in MICH by feed forward first (original matrix (2,3) element).

(2) SRCL in MICH (matrix(2,3) is changed 1% due to RAM, but you keep the same feed forward with the same feedforward gain

(3) You get 1% SRCL residual motion in MICH sensor. This motion depends on how SRCL is quiet/loud. The assumed level is

Pollution level = SRCL shot noise level in SRCL sensor  x  SRCL closed loop TF  x  1% residual .... the following plot.

AS sensor = AS55I-mich  --- SN level 2.4e-11 W/rtHz ------- MICH SN level 6e-17 m/rtHz

SRCL sensor = AS55 I-SRCL --- SN level 2e-11 W/rtHz ---  SRCL SN level 5e-14 m/rtHz

Quote:

Adding some more results with more realistic RAM level assumption.

(4) With 0.1% RAM mod index of PM (normalized by (1) )

 PRCL MICH SRCL REFL11I 0.99999 -0.001807 -0.000148 AS 55 Im 0.000822 1.000002 0.000475 AS 55 Is 1.068342 906.968167 1.00559

Attachment 1: Mar14pollution.png
6419   Wed Mar 14 21:01:36 2012 keikoUpdateLSCevolution of the sensing matrix in PRMI as a function of time

This is the simulated signals to compare with the original post #6403

PRMI configuration, PRCL signal

 [W/m] Simulation Measured REFL11 575440 ~10000 REFL33 4571 ~50 REFL55 288400 ~5000 REFL165 891 NA AS55 71 70

PRMI configuration, MICH signal

 [W/m] Simulation Measured REFL11 2290 ~600 REFL33 36 ~4 REFL55 5623 ~200 REFL165 17 NA AS55 6456 ~200

Simulated DC REFL power is 9mW (before the attenuator). AS DC is 0.3mW.

They don't agree. I suspect the PR gain for the SBs are somehow different. It is about 40 (or a bit less) in the simulation for 11MHz.

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