I feel it's too hasty to use the PRMI.
I support the idea of the half-PRC test, to make an apple-to-apple comparison.

Make haste slowly.

It seems that the cavity trans looks much better than before. Cool.

At least the optical gain is ~x5 of the previous value. This means what we did was something good.

Looking forward to seeing the further analysis of the caivty...

The comment itself was added by me.
The difference between the previous and new measurements should be described by Riju.

In the entry 7984, the description has several PDs mixed up. The measurement was done with the MCREFL PD.
But the DC transimpedance of the thorlabs PD (5e3) was used, according to the text.
I first wonder if this is only a mistake not in the calculation but only in the elog due to a sloppy copy-and-paste.
But the resulting shot-noise-intercept current was 50uA, which is way too small
compared with a realistic value of 0.1~1mA. I have never seen such a good value with
C30642 at the resonant freq ~30MHz. That's why I said "hard to believe". I guessed this wrong
DC transimpedance was actually used for the calculation. 

You may wonder why this 50uA is unreasonable number.
Basically this is just my feeling and probably is same as Rana's feeling.
But "my feeling" can't be a scientific explanation. Here is some estimation.

Looking at my note in 2010:
https://wiki-40m.ligo.caltech.edu/40m_Library (Comparisons of the PD circuits by KA)

The expected shot noise intercept current (idc) is

idc = 2 kB T / (e Rres),

where Rres is the impedance of the resonant circuit at the resonant freq.

This Rres is expressed as

Rres = 1/(4 pi^2 fres^2 Cd^2 Rs),

where Cd and Rs are the capacitance and series resistance of the diode.

If we input realistic numbers,

Cd = 100pF
Rs = 10 Ohm
fres = 30MHz

We obtain, Rres ~ 300Ohm, and idc = 0.2mA

In other words, Rs needs to be 2~3Ohm in order to have idc = 50uA.
This is too small from the previous measurements.
Test Results for C30642 LSC Diode Elements by Rich Abbott

How about to measure the AR reflectivity at larger (but small) angles the extrapolate the function to smaller angle,
or estimate an upper limit?

The spot separation is

D = 2 d Tan(\phi) Cos(\theta), where \phi = ArcSin(Sin(\theta) * n)

D = 2 d Tan(\phi) Cos(\theta), where \phi = ArcSin(Sin(\theta) / n)         (<== correction by Manasa's entry)

\theta is the angle of incidence. For a small \theta, D is propotional to \theta.

So If you double the incident angle, the beam separation will be doubled,
while the reflectivity is an even function of the incident angle (i.e. the lowest order is quadratic).

I am not sure until how much larger angle you can use the quadratic function rather than a quartic function.
But thinking about the difficulty you have, it might be worth to try.

Don't  Shouldn't you apply a small misalignment to the input beam? Isn't that why the peak for the 1st-order is such small?

I, by chance, found  that my windows partition has Vision32 installed.
So I run my usual curvature characterization for the TT phasemaps.

They are found under this link
https://nodus.ligo.caltech.edu:30889/40m_phasemap/40m_TT/（requires: LVC credentials)
or
/cvs/cds/caltech/users/public_html/40m_phasemap/40m_TT

asc/ (ascii files) --> .asc files are saved in Wyko ascii format.
bmp/ (screen shots of Vision32)
mat/ (Matlab scripts and results)
opd/ (Raw binary files)

Estimated radius of curvature

Mirror / RoC from Vision32 / RoC from KA's matlab code
G&H "A" 0864 / -527.5 m / -505.2 m
G&H "B" 0884 / -710.2 m / -683.6 m
LaserOptik SN1 / -688.0 m / -652.7 m
LaserOptik SN2 / -605.2 m / -572.6 m
LaserOptik SN3 / -656.7 m / -635.0 m
LaserOptik SN4 / -607.5 m / -574.6 m
LaserOptik SN5 / -624.8 m / -594.3 m
LaserOptik SN6 / -658.5 m / -630.2 m

The aperture for the RoC in Vision32 seems a bit larger than the one I have used in the code (10mm in dia.)
This could be the cause of the systematic difference of the RoCs between these, as most of our mirrors
has weaker convex curvature for larger aperture, as seen in the figure. (i.e. outer area is more concave
after the subtration of the curvature)

I did not see any structure like Newton's ring which was observed from the data converted with SXMimage. Why???

>> "What has changed since:"

Recently the REFL path has been rearranged after I touched it just before Thanksgiving.
(This entry)

If the lenses on the optical table is way too much tilted, this astigmatism happens.
This is frequently observed as you can find it on the POP path right now.

Also the beam could be off-centered on the lens.

I am not sure the astigmatism is added on the in-air table, but just in case
you should check the table before you put much effort to the in-vacuum work.

For the hexagonal one, insert one of the glass plate only half. Use a 1"x.5" piece if exists.

For the diamond one, you don't need the forth glass piece.

I undertook the investigation of the AS55 PD. I found the PD is not broken.

I tested the PD on the PD test bench and it works just fine.

I attatched the characterization result as there has been no detailed investigation of this PD as far as I remember.

The transimpedance gain at 55MHz is 420Ohm, and the shotnoise intercept current is 4.3mA.

10010 Ohm for POP55 vs 50 Ohm for AS55 (cf. http://nodus.ligo.caltech.edu:8080/40m/4763)

I wonder if you used an LED flash light, which emits no IR.

[Steve, Yuta, Koji]

The ETMX heavy door was removed.

[Rana, Yuta, Koji]

21:05 at the pressure of 10torr
V3 closed. RV1 manually closed. RPs were turned off. And the bellows between RV1 and the rughing pumps are disconnected.

apache has been restarted.
How to: search "apache" on the 40m wiki

- IMC PDH demodulation phase adjustment

- Permanent setup for green transmission DC PDs  on the PSL table

One of the biggest issues we had was that any Q signals (i.e. the quadrature where PRCL is absent.) of REFL11/33/55/(165) haven't been consistent each other.
i.e. We never had reliable lock of MICH with REFL_any_Q, regardless of the resonant condition. This is definitely one of the things to be tried in order to prepare for the full lock.

We don't trust any demodulation phases of any PDs any more as the previous PRC mode (or say, absence of the stable mode) was unreasonable to determine any of the demodulation phases.

I remember that the POP DC saturates at 27000. You may need to reduce the gain switch again.

The AS OSA and/or POP BBPD would be useful for the sideband PR gain estimation.

How much is the exact resonant frequency?

And what's the unit of the plot? The resonant "transimpedance" in the unit of Ohm can not be ~10⁰.

VERY GOOD!
This is how the carrier lock PRMI should look like.

- There is more room to improve the differential ITM alignment to make the dark port more dark, then you will gain more PRG

- The AS spot is definitely clipped.

- What about normalizing POPDC to indicate the carrier recycling gain?

- When you align the PMC, confirm FSS SLOW DC is around zero. Some region of the slow thermal actuation makes the laser source emit at multiple frequencies. In the case, the cavity visibility get worse.

- Do you guys think we can determine if the TT is longitudinally quiet enough? Is there any comparison between the simple Michelson and the PRC motion in m/rtHz?

At the time you, den and I worked together, we could not lock the X-arm on TEM00 with the FM1s of the POX11 on.
We could lock the arm only on the higher order mode but he gain was low. Once we turned off the FM1s, we immediately
locked the cavity on TEM00.

Don't you have the direct measurement of the TF with FM1 on and off?

PRMI for the sidebands may have different situation. Investigate our wiki to find our the simulation result.

Also I'm not confident how much is the modulation depth at 55MHz is.

Last night I measured the modulation depth of the MC incident beam.

Method:

The beam is taken from one of the  PO beam at the wedge plate before the IMC.
After removing the knife edge to dump this beam, the beam is sent to the west side
of the PSL table and put into the OSA cavity.
[The beam dump was returned after the measurement.]

I had some confusion and after all I use the OSA labeled as AS OSA rather than the one on the PSL table.
[The AS OSA was returned to the AP table.]

The transmission was detected by PDA255 and filtered by ITHACO 1201 preamp with G=10, no HPF, 30kHz LPF.
It was confirmed that the peak amplitudes are not reduced by the LPF filter. The resulting time series
was recorded by an oscilloscope.

Three measurements have been taken. The 11MHz peaks are offset by the carrier peak. They appropriately
removed. The ratio of the sideband and carrier peaks is converted to the modulation depth using the following formula.

P_sb / P_ca = [J1(m)/J0(m)]^2

Measurement

The modulation depth for the 11MHz: 0.190 +/- 0.003

The modulation depth for the 55MHz: 0.2564 +/- 0.0003

The three scans showed very similar numbers. That's why the statistical error is such small.
I don't think the systematic error is not such good.

This number is much different form the previous meaurement by Mirko.

http://nodus.ligo.caltech.edu:8080/40m/5519 m=0.14 (11MHz) & 0.17 (55MHz)
but the measured voltages and the modulatio depths are inconsistent.

http://nodus.ligo.caltech.edu:8080/40m/5462 m=0.17 (11MHz) & 0.19 (55MHz)

Probably the modulation depths should be checked by the IMC again.
However, it is certain that the 55MHz modulation exists, and even larger than the 11MHz one.

The next is to confirm that the modulation frequency is matched with the IMC FSR.
It is to make sure that the modulation is transmitted to the main IFO without attenuation.

How to calculate the accumulated round-trip Gouy phase (and namely the transverse mode spacing) of a general cavity
only from the round-trip ABCD matrix

T1300189

I took a look at the laser. It is probably the LD TEC (DTEC) failure.
As the temperature of the LD (DTMP) gradually deviated from 25degCish,
the DTEC voltage also went up from 2Vish to 2.1, 2.2... 

When DTEC reaches 3V, it stopped lasing. This cools the diode a bit, and
it start lasing but repeat the above process.

I am not sure which of the head and controller has the issue.

The situation did not improve much by reducing the pumping current (ADJ: -15).

BTW, Turning on/off the noise eater did not change the situation.

I think the head/controller set should be sent out to JDSU and find how they will say.

1) Annalisa is going to start  working on mode profiling and beat note search for the old MOPA NPRO.

2) In the meantime, Manasa is working on the end table items. This will be reviewed by KA in the afternoon.

The laser at ATF is moved to the 40m when the status of 1) and 2) is determined by KA to be reasonable.

We also make the beat note measurement for the ATF laser too.
 

Give us more info on the elog:
What PD are you using? How much power the beams on the recombining BS are? What kind of BS is it?
How are you looking for the beat note? (on the scope? or spectrum analyzer?)
What was the scanned temp range?

Three points to be checked:

- Polarization

- Alignment

- Temperature

I've tested Perkin-Elmer InGaAs PDs at OMC Lab.

- The diode impedances were measured with the impedance measurement kit. Reverse bias of 5V was used.

- Diode characteristics were measured between 10MHz and 100MHz.

- 4-digit numbers are SN marked on the can

- Ls and Rs are the series inductance and resistance

- Cd is the junction capacitance.

- i.e. Series LCR circuit o--[Cd]--[Ls]--[Rs]--o

C30665GH, Ls ~ 1nH

0782 Perkin-Elmer, Rs=8.3Ohm, Cd=219.9pF
1139 Perkin-Elmer, Rs=9.9Ohm, Cd=214.3pF
0793 Perkin-Elmer, Rs=8.5Ohm, Cd=212.8pF

C30642G, Ls ~ 12nH

2484 EG&G, Rs=12.0Ohm, Cd=99.1pF
2487 EG&G, Rs=14.2Ohm, Cd=109.1pF
2475 EG&G glass crack, Rs=13.5Ohm, Cd=91.6pF
6367 ?, Rs=9.99Ohm, Cd=134.7pF
1559 Perkin-Elmer, Rs=8.37Ohm, Cd=94.5pF
1564 Perkin-Elmer, Rs=7.73Ohm, Cd=94.5pF
1565 Perkin-Elmer, Rs=8.22Ohm, Cd=95.6pF
1566 Perkin-Elmer, Rs=8.25Ohm, Cd=94.9pF
1568 Perkin-Elmer, Rs=7.83Ohm, Cd=94.9pF
1575 Perkin-Elmer, Rs=8.32Ohm, Cd=100.5pF

C30641GH, Perkin Elmer, Ls ~ 12nH

8983 Perkin-Elmer, Rs=8.19Ohm, Cd=25.8pF
8984 Perkin-Elmer, Rs=8.39Ohm, Cd=25.7pF
8985 Perkin-Elmer, Rs=8.60Ohm, Cd=25.2pF
8996 Perkin-Elmer, Rs=8.02Ohm, Cd=25.7pF
8997 Perkin-Elmer, Rs=8.35Ohm, Cd=25.8pF
8998 Perkin-Elmer, Rs=7.89Ohm, Cd=25.5pF
9000 Perkin-Elmer, Rs=8.17Ohm, Cd=25.7pF

Note:  Calculated Ls&Rs of straight wires
  1mm Au wire with dia. 10um -> 1nH, 0.3 Ohm
20mm BeCu wire with dia. 460um -> 18nH, 0.01 Ohm

I'm still waiting for the follow-up analysis of the modulation freq tuning.

Please add the discussions on the cavity absolute length (and its change, adjustment precision),
identification of the peaks, before/after comparison of the plot, the effect of the MC REFL PD response,
and comparison of the cavity linewidth vs deviation of the 55MHz SBs from the resonance.

> The two REFL55 signals

Wow! It's a good news.
I think this is our first ever lock of PRMI with the REFL I/Q signals.

We kept having difficulty to obtain MICH from the REFL beam.

Next time could you make calibration of REFL55 MICH and AS55 MICH and compare the ratio with any simulation?

Breadboards may not be suitable for a reliable work. Why don't you switch to any protoboard and real soldering?

Beautiful double peaks. I don't see the triple zero-crossings. Is this because you adjusted the phase correctly (as predicted)?

Don't you want to have a positive number for POP22? Should we set the demod phase in the configuration script for the positive POP22, shouldn't we?

When I came to the 40m, I found most of the FB signals are dead.

The suspensions were not dumped but not too much excited. Use watchdog switches to cut off the coil actuators.

Restarted mxstream from the CDS_FE_STATUS screen. The c1lsc processes got fine. But the FB indicators for c1sus, c1ioo, c1iscex/y are still red.

Sshed into c1sus/ioo, run rtcds restart all . This made them came back under control.

Same treatment for c2iscex and c1iscey. This made c1sus stall again. Also c1iscey did not come back.

At this point I decided to kill all of the rt processes on c1sus/c1ioo/c1iscex/c1iscey to avoid interference between them.
And started to restart from the end machines.

c1iscex did not come back by rtcds restart all.
Run lsmod on c1iscey and found c1x05 persisted stay on the kernel. rmmod did not remove the c1x05 module.
Run software reboot of c1iscey. => c1iscey came back online.

c1iscey did not come back by rtcds restart all.
Run software reboot of c1iscex. => c1iscex came back online.

c1ioo just came back by rtcds restart all.

c1sus did not come back by rtcds restart all.
Run software reboot of c1sus => c1sus came back online.

This series of restarting made the fb connections of some of the c1lsc processes screwed up.
Run the following restarting commands => all of the process are running with FB connection.
rtcds restart c1sup
rtcds restart c1ass
rtcds restart c1lsc

Enable damping loops by reverting the watchdog switches.

All of the FE status are green except for the c1rfm bit 2 (GE FANUC RFM CARD 0).

Еру ьс шы тщц дщслув фтв фдшптувю

Фдыщ ш кфт еру ащддщцштп ыскшзе ещ щаадщфв еру ЬС ЦАЫ ыукмщю

I blame Den for russian keyboard installation on the control machines.

ezcaservo -r 'C1:SUS-MC2_ASCPIT_OUT16' -g '0.00001' -t 60 C1:SUS-MC2_PIT_COMM&
ezcaservo -r 'C1:SUS-MC2_ASCYAW_OUT16' -g '0.00001' -t 60 C1:SUS-MC2_YAW_COMM&
ezcaservo -r 'C1:SUS-MC1_ASCPIT_OUT16' -g '0.00001' -t 60 C1:SUS-MC1_PIT_COMM&
ezcaservo -r 'C1:SUS-MC1_ASCYAW_OUT16' -g '0.00001' -t 60 C1:SUS-MC1_YAW_COMM&
ezcaservo -r 'C1:SUS-MC3_ASCPIT_OUT16' -g '0.00001' -t 60 C1:SUS-MC3_PIT_COMM&
ezcaservo -r 'C1:SUS-MC3_ASCYAW_OUT16' -g '0.00001' -t 60 C1:SUS-MC3_YAW_COMM&

PMC aligned. C1:PSL-PMC-PMCTRANSPD improved from 0.72ish to 0.835ish.

I tried to reproduce the locking situation described in this entry tonight.
The momentary lock was regularly seen but there was no stable lock.

I wonder why the actuators are always saturated. The feedback signals have the dominant component at ~400Hz.

It would also be nice if the servos have some immunity to gain fluctuation.

I didn't check how the situation of the AP table is. I'll look into some details tomorrow.

The FE web view seems not up-to-date, does it? ( maybe for a year)

https://nodus.ligo.caltech.edu:30889/FE/c1mcs_slwebview_files/index.html

The fibers should be routed beneath the electrical cables.
They should be fixed on the table for strain relieving.
The slack of the fibers should be nicely rolled and put together at the splitter side.

These are expected to be done next time when the fiber team work around the table.

We also expect to have the table photo every time the work of the day is finished.

Last night I worked on the several locking configurations:

General preparations / AS table inspection

- The AS beam looked clipped. I went to the AP table and confirmed this is a clipping in the chamber.
  This may be fixed by the invacuum PZTs.

Modulation frequency tuning

RFPD Mon of the MC demodulator was check with the RF analyzer. Minimized the 25.8MHz (=55.3-29.5MHz) peak by changing the marconi freq.
This changed the modulation freq from 11.066147MHz to 11.066134MHz. This corresponds to the change of the MC round-trip length from
27.090952m to 27.090984m (32um longer).

Michelson tests

- I wonder why I could not see good Michelson signal at REFL ports.

- I roughly aligned the Michelson. On the AP table, the RF analyzer was connected to the REFL11 RF output.
  By using "MAX HOLD" function of the analyzer, I determined that the maximum output of the 11.07MHz peak
  was -61.5dBm.

- I went to the demodboard rack. I injected -61dBm from DS345 into the RFEL11 demodboard. This produced
  clean sinusoidal wave with the amplitude of 4 count. The whitening gain was 0dB.

- The output from the PD cable was -64.0dBm. So there is ~2.5dB loss in the cable. Despite this noise, the demodulation
  system should be sufficiently low noise. i.e. the issue is optical

- The Michelson was locked with AS55Q. And the REFL11 error signals were checked.Fringe like feature was there.
  This suggested the scattering from the misaligned PRM. The PRM was further misaligned. Then some reasonable
  (yet still noisy) Michelson signal appeared. (Usual misaligned PRM is not at the right place)

  Q. How much scattering noise (spurious cavity between PRM and the input optics) do we have when the PRM is aligned?
  Q. Where should we put the glass beam dumps in the input optics?
  Q. Can we prepare "safe" misaligned place for the PRM with the beam dump?

- The Michelson was locked with REFL11Q. From the transfer function measurement, the gain difference between AS55Q (whitening gain 24dB)
  and REFL11Q was 32dB. The whitening gain was 0dB. In fact I could not lock the Michelson with the whitening gain 33dB (saturation???)
  The element in the Input matrix was 1, The gain of the servo was +100. BS was actuated.

Coupled cavity tests

- At least REFL11 is producing reasonable signals. So what about the other REFL ports? The Michelson signals in the other frequencies
  were invisible. So I decided to use three-mirror coupled cavity with the loss PRC.

- Aligned X arm, Misaligned ETMX, ITMY. Aligned PRM.

- Locked the PRM-ITMX cavity with REFL11 and REFL33.

- Aligned ETMX. If I use REFL11I for the PRC locking, I could not lock the coupled cavity. But I could with REFL33I.
  This is somewhat familiar to me as this is the usual feature of the 3f signal.

- The coupled cavity could be locked "forever". To realize this I needed to tweak the normalization factor from 1.0 to 1.6.
  Q. How does the coupled cavity change the response of the cavity? Can we compensate it by something?
  Q. Measure open loop transfer functions to check if there is any issue in the servo shapes.

- Transmission during the lock is 3.2 while the nominal TRX with PRM misaligned was 0.93.
  This corresponds to power recycling gain of 0.17.

 - X arm:

    - Source: POX11I, phase 79.5 deg, whitening gain 36dB
    - Input matrix: POX11I->1.0->XARM, Normalization TRX*1.60
    - XARM servo gain +0.8, actuation ETMX
    - XARM trigger 0.25 up, 0.05 down. XARM Filter trigger untouched.

- PRC: (sideband locking)
    - Source: REFL33I, phase -34.05 deg, whitening gain 30dB
    - Input matrix: REFL33I->1.0->PRCL, Normalization None
    - PRCL servo gain +4.0, actuation PRM
    - PRCL trigger None

- Same test for the Y arm. At the moment ETMY did not have the OPLEV.
  Same level of transmission (~3.3)

 - Y arm:

    - Source: POY11I, phase -61.00 deg, whitening gain 36dB
    - Input matrix: POY11I->1.0->YARM, Normalization TRX*2.1
    - YARM servo gain +0.25, actuation ETMX
    - YARM trigger 0.25 up, 0.05 down. YARM Filter trigger untouched.

- PRC: (sideband locking)
    - same as above

Sideband PRMI attempt

    - Now I got some kind of confidence on the REFL33 signal.
    - So I tried to get any stable setup for sb PRMI, then to find any reasonable MICH signals anywhere else than AS55Q.
    - With REFL33I(PRCL) & AS55Q(MICH), I got maximum ~10sec lock. It regularly locked. It was enough long to check
      the spectrum on DTT. But it was not enough long to find anything about the MICH signals at the REFL ports.

    - I tried REFL33Q for MICH. The lock was even shorter but could lock for 1~2 sec.

    Q. What is the cause of the lock loss? I did not see too much angluar fluctuation. The actuation was also quiet (below 10000).

- PRCL: (sideband locking)
    - Same as above except for
      - the PRCL servo gain +0.05, No limitter at the servo output.
      - Trigger POP22I (low pass filtered by LP10) 20 up, 3 down

- MICH:
    - AS55Q -24.125 24dB -> x1.0 -> MICH -0.7, No limitter -> ITMX/Y differential
    or
    - REFL33Q -34.05dB -> x2.0 -> MICH same as above
    - For both case, trigger POP22I (low pass filtered by LP10) 20 up, 3 down

At this point Jenne came back from dinner. Explained what I did and handed over the IFO.

No.... what I told was to put the roll next to the splitter, not on the table.
The table area is more precious than the rack space.

Koji> The slack of the fibers should be nicely rolled and put together at the splitter side.

I contacted Den about malfunctioning of the Yarm ASS.

He found the scripts were modified during the attempt to make it available for Xarm (cf. a related elog entry)
So far, he could manage to make the current scripts being modified to run.
A striptool file is still missing but this is what we can handle locally.

I thank Den for the remote caring of the issue despite the limited network bandwidth.

When I talked with Den via phone, he recommended to use the trigger and normalization with POP110I.
So I decided to try this approach. Also I investigated how the REFL33 signals are useful.

I could find the state where the PRMI(sb) locks regularly, although the lock is ~1min at most.

PRCL: REFL33I
whitening gain 30dB, -14.0deg (finely tuned in lock)
-> x1.0 -> Triggered by POP110I (20up, 1down)
-> Normalized by POP110I x0.04
-> Gain 0.2~0.12 FM3, 4, 5, 6 always on, no triggered FMs
-> PRM

MICH: REFL33Q
whitening gain 30dB, -14.0deg (finely tuned in lock)
-> x1.0 -> Triggered by POP110I (20up, 1down)
-> Normalized by POP110I x0.04
-> Gain -20 FM4, 5 always on, no triggered FM
-> ITMX (-1.0) and ITMY (+1.0)

I needed to tune the phase very precisely to reach this state. Also the alignment of the michelson and PRM
was very crtiical to acquire the lock.

Later in the same night I was plagued by PRM alignment drift. It seems that the PRM alignment is bistable or
slightly drifting in pitch. I had to align PRM continuously. When the PRMI is locked, the alignment fluctuation
was mainly in yaw. This was as people commented before.

Prior to the locking trials...

scripts/LSC/LSCoffset script had behaved peculiarly:

This script spawns LSC/offset3 in order to remove the dark offset from the channels.
How ever the offsets had been nulled every other PDs
(i.e. The offsets REFL11 I&Q were nulled.
The offsets REFL33 I&Q had been left untouched
The offset REFL55 I&Q had been nulled
and so on.)

I found that the script run many instances of "offset3" scripts in background.
It seemed that tdsavg did not like too many averaging channels at once.

So the "&"s in the LSCoffsets were removed and now the script runs much more slowly,
but works for all of the PDs listed.

I think I have never seen the offsets in REFL33 and REFL165 nulled down to this level before.

Today the locking was not as easy as that was last Friday.
So I tried something new. Today Rana talked about the ASDC locking with POPDC normalization.
This technique was tried. (This is somewhat similar to DC readout.)

PRCL
Signal source: REFL33I / Normalization POP110I x 0.04 / Trigger POP110I 20up 3down, otherwise  untouched from Friday locking
Servo: input matrix 1.00 -> PRCL Servo FM3/4/5/6 Always ON G=+0.06
Actuator: output matrix 1.00 -> PRM

MICH
Signal source: ASDC Offset -109.5 (nominal of the day -49.5) / Normalization POPDC x 1.00 / Trigger POP110I 20up 3down
Servo: input matrix 1.00 -> MICH Servo FM5 Always On G=+10000
ActuaroL output matrix -1.00 -> ITMX / +1.00 -> ITMY

Observation

- POP110I was ~120 during the lock (cf 170 on Friday). So there is some small leakage from the dark port.

- Lock was easier when FM4 of the MICH loop was turned off.

- During the lock horizontal motion of the intracavity mode was visible as usual.

Q. How much Schnupp asymmetry we want in order to improve the signal ratio between PRCL/MICH in REFL ports?

Q. How much can we increase Schnupp asymmetry in the practical constraints?

Q. How PRCL/MICH ratio is different the REFL ports?
=> My modeling (many years ago) shows the ratio of {115, 51, 26, 23} for REFL{11, 33, 55, 165}.
These numbers should be confirmed by modern simulation of the 40m with updated parameters.
I should definitely use 55MHz but also prepare better 165MHz too.

Q. How the TT/PRM motions are affecting the lock stability? How can we quantify this effect? How can we mitigate this issue?

Q. Can we somehow change the sensing matrix by shifting the modulation frequency?

Q. Is normalization by POP22 or POP110 actually working well?
=> Time series measurement of error signals & servo inputs

[Jenne Koji]

- Today the spots were moving more than the usual. The OPLEV screens showed that the spots are too much off from the center.

- Each vertex OPLEVs were checked and OPLEV wonderland was discovered: Other than the usual misalignment of the spots,
it was found that PRM/ITMX/ITMY beams were clipped somewhere in the paths, BS/PRM oplevs had many loose components
including the input lenses (they are still clamped by a single dog clamp THIS SHOULD BE FIXED ASAP).

- On the ITMY table there were so many stray optics. They were removed and put on the wagon next to the ITMY table.
THIS SHOULD BE CLEARED ON THE WEDNESDAY CLEANING SESSION.

- During this OPLEV session, LSCoffset nulling was run.

- After the OPLEV session, the locking became really instantaneous. We wonder which of the OPLEV cleaning, LSC offset nulling,
and the usual seismic activity decay in the evening was effective to make it better.

- Initially the lock was attempted with REFL33I/Q and some ~10sec lock streches were obtained. During this lock,
  the optical gain of AS55Q was measured in relative to REFL33Q. In deed they were calibrated to be the same
  gain at the input matrix.

- After the MICH signal source was switched to AS55Q, the lock streches became more regular and the minutes long.
We precisely tuned the phase of AS55 and REFL55 in terms of the differential excitation of ITMX/Y using lockin (FREQ 250, AMP 1000).

- We noticed that the AS port spot with AS55Q MICH was darker than the REFL33Q MICH. This suggests the existence of residual offset
in REFL33Q. In deed we observed +30cnt offset in REFL33Q when the PRMI is locked with AS55Q MICH.

- Phases and relative gains of the signals were as follows:

PRCL: REFL33I 1.00 =REFL55I +0.4
MICH: AS55Q 29deg x1.00 = REFL33Q -14deg x1.00 = REFL55Q 118deg 0.03?

- We tried to lock PRMI with AS55Q. The acquisition was not as easy as that with REFL33I. This might be from the saturation of the
REFL55I signal. This configuration should tested with different whitening gain. Handing off using the input matrix went well once the
lock was obtained by REFL33I.

- Handing off from AS55Q to REFL55Q was not successful.

- At the end of the session, Jenne told me that the POP PD still has a large diameter beam. (and a steering mirror with a peculiar reflection angle.)
==> THIS SHOULD BE FIXED ASAP because the normalization factor can be too much susceptible to the misalignment of the spot.

- The configuration of the filters:

PRCL FM3/4/5/6 G=+0.05 / NORM 0.04 POP110I
MICH FM4/5 G=-5.00 / NORM 0.01 POP110I (or none)

- Routine alignment

Locked the arm cavties. Ran ASS. As this was not enough precise alignment for PRMI locking, Yarm alignment was re-adjusted by sliders.
Xarm was also aligned in the same way.

- OPLEV alignment

Once the arms were aligned, OPLEV spots were adjusted. For this adjustment, PRM had to be aligned and OPLEV servos needed to be turned off.

- LSC offset nulling

While Jenne was measuring the dark output of the POP PD, LSC offset nulling script was executed.

- Compensation of the POP spot size fix

As Jenne reported the POP path now has a lens and the denominator for the normalization got bigger.
To compensate this change, PRMI(sb) was locked by the same configuration as yesterday (i.e. AS55Q for MICH, REFL33I for PRCL). 
After some try and error, configuration for stable locking was found. 

PRCL
Signal source: REFL33I / Normalization POP110I x 1.00 / Trigger POP110I 80up 10down
Servo: input matrix 1.00 -> PRCL Servo FM3/4/5/6 Always ON G=+8.00
Actuator: output matrix 1.00 -> PRM

MICH
Signal source: AS55Q / Normalization POP110I x 0.01 / Trigger POP110I 80up 10down
Servo: input matrix 1.00 -> MICH Servo FM4/5 Always On G=-30
Actuator output matrix -1.00 -> ITMX / +1.00 -> ITMY

This suggests that POP110I signal is 5~6 times more than before the lens was installed. 

- SQRTing option for POP110I was implemented

The PRMI optical gain is derived from (Carrier)x(1st order Sideband) or (2nd order SB)x(1st order SB).
Here the carrier and the 2nd order sidebands are nonresonant.
Therefore the optical gain is proportional to the amplitude power recycling gain of the 1st order sidebands.
On the other hand, POP 2f signals are derived from the product of the 1st and -1st order sidebands.
This means that we should take a sqrt of the POP signals to compensate the recycling gain fluctuation.

- Locking with SQRT(POP110I)

PRCL
Signal source: REFL33I / Normalization SQRT(POP110I) x 10 / Trigger POP110I 10up 3down
Servo: input matrix 1.00 -> PRCL Servo FM3/4/5/6 Always ON G=+8.00
Actuator: output matrix 1.00 -> PRM

MICH
Signal source: AS55Q / Normalization SQRT(POP110I) x 0.1 / Trigger POP110I 10up 3down
Servo: input matrix 1.00 -> MICH Servo FM4/5 Always On G=-30
Actuator output matrix -1.00 -> ITMX / +1.00 -> ITMY

The lock seems not so different from the ones without SQRTing.

The spot was still moving in yaw direction. If I chose a correct alignment, I could minimize the modulation of the internal power
by misalignment. As you can see in the following plot.

When the alignment was deviated from the optimum, the misalignment induced RIN was much worse although this was the longest lock I ever had with the PRMIsb. (more than 8 min)

- Locking with other signal sources

REF55I/Q trial:

Demodulation phase was adjusted to make the difference of the peak heights for MICH maximized.
After the lock is acquired, I tried to swap the signal source at the input matrix. PRCL swapping was successful but
MICH swapping was not successfull.

It is much more hard to lock the interferometer with REFL55I compared with REFL33I.

REFL165I/Q trial:

As REFL165 PD never produced any useful signal, I tried to swap it with the BBPD used in the green setup.

- Borrowed the PD, power supply from the green setup.

- Put REFL165PD aside. Placed the BBPD in the path. The DC output was 0.8V. This corresponds to the input power of ~5mW.

- Checked the signal but it was very litte (several counts even at the maximum whitening gain).

- Decided to use the power reduction pick off to introduce much more light on the PD.
  This PO mirror is 90% reflector. Therefore I had to be careful no to fry the diode.
  Currently there are OD1.3 (x1/20) power attenuator to reduce the input power down to 6.5V (40mW).

- The resulting signal is very wiered suggesting the saturation of the PD at the RF stages.

- Probably I need to make a new PD circuit which has the high pass filter to reject other low frequency components.

Output matrices are added to ASS. Currently ASS is based on the mirror bases.
I prefer to have the actuator bases as the coils are more stable than the sensors.

At this point, the output matrices are identity. So Den's scripts are still working.

Striptool settings were also fixed.

No.

While the peak in the PRM OPLEV was more than 10 times higher than the spectrum level without the excitation,
we only saw small peaks in the RIN spectra. This suggests that the PRM angular motion did not contribute to the RIN spectra.

You should divide the POP110I and POPDC spectra by 400 and 450, which was the DC values of these channels, in order to convert them into RIN (1/rtHz)
The OPLEV spectra is calibrated to be urad/rtHz (is this true?) so you can obtain the conversion factor from OPLEV to RIN (1/urad)
by matching the peaks. This way you make a angular noise projection.

Yes we should do that. BTW what should be pushed?

To change the MC length is not the point.

If we can improve the length sensing by the intentional shift of the modulation frequency from the MC FSR, that's worth to try, I thought.

But that is tough as the freq difference is 18kHz that is ~x4 of the line width of the MC.
Not only the 55MHz sidebands, but also the 11MHz sidebands will just be rejected.

Nevertheless: Is there any possibility that we can improve anything by shifting the modulation frequency by ~1kHz?

Summary:

c1rfm / c1lsc / c1ass / c1sus were modified. They were recomplied and installed. They are running fine
and confirmed PRMI locking (attempt), arm locking, and Yarm ass with the new codes.

Motivation:

1a. SQRTing switching for POP110 was wrong. 0 enabled sqrting, 1 disabled sqrting. I wanted to fix this.
1b. Sqrting for POP22 was not implemented.

2. Preparation for the shadow sensor control with POPDC.

3. ASS had only an input. I want to run two ASS for the X and Y arms.

SQRTing for POP110/22:

- Flipped the input of the bypass switch. Correspoding MEDM indicators are fixed on the power normalization screen.
- Copied the sqrting structure from POP110 to POP22. Correspoding MEDM buttom was made on the power normalization screen.

- The function of the sqrting buttons were confirmed.

Additional ASS output:

- The output path "NPRO" was removed. Corresponding RFM channels have also removed.
- The previous NPRO path was turned to the "ASS1" path. The previous "ASS" path was turned to "ASS2".
- Corresponding shared memory channel are created/renamed.
- c1ass was modified to receive the new ASS shared memory channels. ASS1 is assigned to the X arm. ASS2 is assigned to the Y arm
- The output matrix screen and the lockin screen were modified accordingly.
- Only script/ASS/Arm_ASS_Setup.py was affected. The corespoding lines (matrix assignment) was fixed.

- The function of Den's version of  ASS was confirmed.

LSC->PRM ASC path

- We want to connect POPDC to PRM ASC. POPDC is acquired on c1lsc.
- So, for now we use the LSC input matrix to assign POPDC to one of the servo bank.
- The last row of the LSC output matrix was assigned to the PCIE connection to c1sus.
- This PCIE connection was connected to the PRM ASC YAW input.

- The connection between LSC and SUS was confirmed.

- During this process I found that there are bunch of channels transferred from LSC to SUS via RFM.
  These channels are transferred via PCIE(dolphin) and then via RFM. But LSC and SUS are connected
  with dolphin. So this just adds additional sampling delay while there is no benefit. I think we should remove the RFM part.
  Note that we need to use RFM for the end mirrors but this also should use only the RFM connection.

Rebuilding the codes

- Prior to the tests of the new functionalities, the codes were rebuild/installed as usual.
- The suspension were shutdown with the watch dogs before the restart of the realtime codes.
- Once the realtime codes were restarted successfully, the watch dogs were reloaded.
- As we removed/added the channels, fb was restarted.
- c1rfm / c1lsc / c1ass / c1sus codes were checked-in to svn