40m QIL Cryo_Lab CTN SUS_Lab TCS_Lab OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop
  40m Log, Page 59 of 344  Not logged in ELOG logo
ID Date Author Typeup Category Subject
  9733   Mon Mar 17 20:14:34 2014 KojiSummaryGeneralIFO recovery / confirmed ETMX in trouble

I tried to take the photos of the magnets from outside. So far most suspicious was LL.
Otherwise, the magnets are OK.
(The SD magnet is the one with most reasonable response.)
Steve will try to take much more zoomed photo with Olympus. But the LL coil already showed some response in my observation in the morning.

ETMX_UL.JPGETMX_UR.JPGETMX_LR.JPGETMX_LL.JPG

  9739   Tue Mar 18 21:19:22 2014 KojiSummaryIOOMC spot positions checked

MC spot sposition script was ran

/opt/rtcds/caltech/c1/scripts/ASS/MC/mcassMCdecenter

Found no notable beam position change before and after the earthquake

 

Attachment 1: MCASS.png
MCASS.png
  9740   Wed Mar 19 21:37:45 2014 manasaSummaryLSCAttempt to lock PRMIsb with REFL165I&Q

I tried to repeat Koji's PRMI lock using REFL165I/Q. I was not able to lock PRMI stably. All I could get was momentary PRMI sb locks (few seconds) using AS55Q for MICH and REFL165Q for PRMI. I tried to transition MICH locks from AS55Q to REFL165I/Q and this did not work well; I lost even the momentary locks.

The demod phases for both AS55 and REFL165 were also very different. 

Input ports:
AS55       WHTN: 21dB  demod phase -78.7deg
REFL165 WHTN: 45dB demod phase -80.7deg

Input matrix:
AS55Q x1.00 MICH

REL165Q x+0.14

Triggers:
MICH POP110I 100up/10down / FM Trig FM2/3/6/7/9 35up 2down 5sec delay
PRCL POP110I 100up/10down / FM Trig FM2/3/6/9 35up 2down 0.5sec delay

Servo:
MICH OFS 0.0 / Gain -10 / Limiter ON
PRCL OFS 0 / Gain -0.023 / Limiter ON

Output matrix:
MICH ITMX -1.0 / ITMY +1.0
PRCL PRM 1.0

 

  9751   Wed Mar 26 11:16:59 2014 ericqSummaryLSCComposite Error Signal for ARms (3)

Extending the previous model, I've closed a rudimentary CESAR loop in simulink. Error signals with varying noise levels are combined to bring a "cavity" to lock.  

simlink.pdf

There are many things that are flat out arbitrary at this point, but it qualitatively works. The main components of this model are:

  • The "Plant": A pendulum with f0 = 2Hz, Q = 10
  • Some white force noise, low passed at 1Hz before input to the plant.
  • The Controller: A very rough servo design that is stable...
  • ALS signal: Infinite range Linear signal, with a bunch of noise
  • Transmission and PDH signals are computed with some compiled C code containing analytic functions (which can be a total pain to get working), have less noise than ALS
  • Some logic for computing linearized PDH and SqrtInv signals
  • A C code block for doing the CESAR mixing, and feeding to the servo

And it can lock! 

simulatedCESARLock.pdf

 

Right now, all of the functions and noise levels are similar to the previous simulation, and therefore don't tell us anything about anything real...

However, at this point, I can tune the parameters and noise levels to make it more like our interferometer, and thus maybe actually useful. 

  9753   Wed Mar 26 14:54:32 2014 KojiSummaryLSCPRMIsb locked with REFL165I&Q again

[Manasa, Eric, Koji]

PRMIsb was locked with REFL165I&Q.


- Aligned the arms with ASS. The misaligned ETMX and ETMY

- Configured PRMIsb with IFO_Configure screen

- Immediately PRMIsb was locked with REFL55I&Q

- Checked the REFL165 phase in terms of the REFL165Q vs PRCL. It was already well adjusted at -82.5deg. We tuned the phase a bit more and got -83.5deg.

- With DTT, relative gain between REFL55I and REFL165I was measured. REFL165I is about x10 higher than REFL55I and has the same sign.

- The transition of PRCL with the input matrix was just easy.

- With DTT, relative gain between REFL55Q and REFL165Q was measured. REFL165Q is about x3 higher than REFL55Q and has the same sign.

- The transition of MICH was flakey, but after careful adjustment of the PRM alignment, ~10s lock was achieved. It seemed that the PRM alignment fluctuation
  was bug enough to unlock the interferometer.

- Eric went into the lab and aligned all of the oplevs except for the SRM's one.

- Now the lock with REFL55 and also with REFL165 became more robust. Less MICH offset and darker AS port.


Input ports:
REFL55   WHTN: 45dB demod phase +45.0deg
REFL165 WHTN: 45dB demod phase -83.5deg

Input matrix: for acquisition:
REFL55I x 1.0 -> PRCL
REFL55Q x 1.0 -> MICH

Input matrix: PRCL Transition:
REFL55I x 1.0 + REFL165I x 0.0 -> x0.5 + x0.0 -> x0.5 + x0.05 -> x0.3 + x0.05 -> x0.2 + x0.05 -> x0.1 + x0.05 -> x0.0 + x0.05

Input matrix: MICH Transition:
REFL55Q x 1.0 + REFL165Q x 0.0 -> x0.5 + x0.0 -> x0.5 + x0.3 -> x0.3 + x0.3 -> x0.2 + x0.3 -> x0.1 + x0.3 -> x0.0 + x0.3

Triggers:
MICH POP110I 100up/10down / FM Trig FM2/3/9 35up 2down 5sec delay
PRCL POP110I 100up/10down / FM Trig FM2/3/6/9 35up 2down 0.5sec delay

Servo:
MICH OFS 0 / Gain 1.3 / Limitter ON
PRCL OFS 0 / Gain -0.04 / Limitter ON

Output matrix:
MICH PRM -0.2625 / BS 0.5
PRCL PRM 1.0

  9754   Wed Mar 26 21:51:42 2014 ericqSummaryLSCPRMIsb locked with REFL165I&Q again

Incidentally, while messing around with transfer functions and sensing matrix elements this evening, I was able to sideband lock straight onto REFL33 I&Q.  The settings were all identical to Koji's ELOG, with the following differences:

Input ports:
REFL33   WHTN: 30dB demod phase +125.5deg (tweaked from 135.5 to minimize MICH in I)

Input matrix:

REFL33I x +1.0 -> PRCL
REFL33Q x +3.0 -> MICH

Servo:
MICH OFS 0 / Gain 1/ Limitter ON (Oscillations occurred at 1.3)
PRCL OFS 0 / Gain -0.04 / Limitter ON

Output matrix:

MICH ITMX -1.0 / ITMY 1.0
PRCL PRM 1.0

 

  9758   Fri Mar 28 17:22:55 2014 KojiSummaryLSCPRMIsb locked with REFL165I&Q again

While I'm looking at the PRM ASC servo model, I tried to use the current servo filters for the ASC
as Manasa aligned the POP PDs and QPD yesterday. (BTW, I don't find any elog about it)

I found no issue for locking PRMIsb with the REFL165I&Q signals if the PRM ASC is employed.
See this entry for the IFO settings.

It is just stable. The IFO is ready for the arm scanning.

=== ASC setting ===

PRCL_PITCH: FM1/3/9 x-0.004
PRCL_YAW: FM1/3/9 x-0.001

The PRM OPLEV has to be off when the PRM ASC is engaged. Actually, it turned out that we don't need OPLEV for locking.

  9759   Fri Mar 28 20:23:02 2014 ranaSummaryIOOMC2 moved

I aligned MC2 suspension by 0.01 in pit and yaw to align the MC better to the PSL beam. Then I turned the WFS back on. The beams are not centered on the WFS heads.

Nic and Gabriele ought to send their SURF some example code (in April) for how to start redesigning the WFS telescopes so that we can order some optics in early June.

I've also turned on the MC2 TRANS path to gather some data over the weekend on how well or bad it works. Please turn it off on Monday.

  9764   Mon Mar 31 11:34:00 2014 manasaSummaryIOOMC2 moved

Quote:

I've also turned on the MC2 TRANS path to gather some data over the weekend on how well or bad it works. Please turn it off on Monday.

 MC2_TRANS path in WFS servo turned OFF.

  9765   Mon Mar 31 13:15:55 2014 manasaSummaryLSCAlignment update

Quote:

While I'm looking at the PRM ASC servo model, I tried to use the current servo filters for the ASC
as Manasa aligned the POP PDs and QPD yesterday. (BTW, I don't find any elog about it)

 Guilty!!

POP path

The POP PD was showing only ~200 counts which was very low compared to what we recollect from earlier PRMI locks (~400 counts). Also, the POP ASC QPD was also not well-aligned.
While holding PRMI lock on REFL55, I aligned POP path  to its PD (maximize POP DC counts) and QPD (centered in pitch and yaw).

X and Y green

The X green totally lost its pointing because of the misaligned PZTs from last week's power failure. This was recovered.
Y arm green alignment was also recovered.

  9767   Mon Mar 31 17:47:57 2014 ericqSummaryLSCMICH sensing oddities in REFL 3F

Last week, while I had the PRMI locked on REFL33, I did some poking around with mirror excitation to RFPD quadrature transfer functions. I got some indication of weird things with sensing MICH with the 3F REFL signals, but it should be explored more before taken as a real thing. I just figured I would show what I saw. 

With that disclaimer out of the way, here's what I did:

  • Locked PRMI on PRCL:REFL33_I and MICH:REFL33_Q, as detailed in my earlier ELOG
  • Created PRCL and MICH excitations at two different frequencies, notched said frequencies out of the control filters
  • Took transfer functions from mirror LSC output signals to 33 I, 33 Q, 165 I, 165 Q in DTT
  • For each DOF, look at the measured transfer functions only at the excitation frequency. (Assuming good coherence, which was there)

The basic idea was, some PRCL motion (for instance), has a transfer function to both the I and Q quadratures at a given PD. As the PRCL excitation sine wave goes through one cycle, the REFL signals at the excitation frequency go through some coherent cycle. Thus, the excitation traces out some trajectory in the I vs. Q plane. I believe this is analogous to the typical "radar plot" that we make for sensing matrix elements. 

However, the straight line that we normally plot in the radar plots assumes a certain phase relationship between the DOF-> I and DOF->Q transfer functions that results in a straight line. Here are the trajectories I actually measured, normalized by the excitation amplitudes.

REFL_33_traj.pdfREFL_165_traj.pdf

The plotted traces are (x,y) = (H_prcl->I * prcl, H_prcl->Q * prcl) and  (x,y) = (H_mich->I * mich, H_mich->Q * mich) where H_prcl->I is the measured complex transfer function from prcl to REFL I, for instance, and prcl and mich are the excitation signals, normalized to unit amplitude.

PRCL looks like a nice straight line in both of these, and pretty well phased, but not only is MICH not very orthogonal to PRCL, there is quite a bit of ellipticity present, which means we can't fully decouple the two DOFs, even if they were nominally orthogonal. 

I'm not sure what may cause this. To back up this measurement/interpretation, I tried to take measurements of these transfer functions across different excitation frequencies via swept sine DTT, but seismic activity kept me from staying locked long enough...

  9768   Mon Mar 31 21:23:30 2014 GabrieleSummaryLSCMICH sensing oddities in REFL 3F

I'm not sure what may cause this. To back up this measurement/interpretation, I tried to take measurements of these transfer functions across different excitation frequencies via swept sine DTT, but seismic activity kept me from staying locked long enough...

I guess that you get an ellipse when the transfer functions to I and Q have a different phase. One mechanism could be that when driving MICH we make some residual PRCL and this couples with a different transfer function to both I and Q. However, I would expect no phase lag in the PRMI configuration, since there is no enough optical delay in the system to give significant dephasing at few hundreds Hz. This effect might come from mechanical resonances.

It is worth measuring the optical transfer functions from both PRCL and MICH to REFL signals at all frequencies, to see if we have strange features in the TFs.

  9769   Mon Mar 31 23:57:22 2014 KojiSummaryASCPRM ASC characterization / design

A series of measurements / calculations for the PRM ASC characterization and servo design

1) Actuator characterization

The actuator responses of the PRM in pitch and yaw were measured (attachment figure 1). I believed the calibration of the oplev QPD to be
1 count/urad. The oplev servo loops were turned off at the FM inputs, and the filter banks were turned off so that the response has the open
loop transfer function except for the servo filter.

The measured transfer functions were fitted with LISO. The LISO results (c.f. the source codes) were shown in the figure. The responses also
include the 60Hz comb filter present in the input filters. The responses are well approximated by the single pendulum with f0 of 0.6-0.8 and q of 3.5 and 6.3.

From this measurement, the actuator responses of the PRM at DC are estimated to be 2.2 urad/cnt and 1.8 urad/cnt in pitch and yaw, respectively.

2) Sensor response of the POP QPD

As we already know how the actuators respond, the QPD optical gain can be characterized by measuring the actuator response of the QPD
(attachment figure 2). The QPD signals are such noisy that the response above 1Hz can't be measured with sufficient coherence. Below 1Hz,
the response is well represented by the actuator response measured with the oplev. From this measurement, the optical gains of the QPD
with respect to the PRM motion are 650 cnt/urad and 350 cnt/urad.

3) Open loop transfer function of the current ASC servo

By combining the above information with the servo setting of the servo filters, the open loop transfer functions of the PRM QPD ASC loops
were estimated (attachment figure 3). Actually the expected suppression of the fluctuation is poor. The yaw loop seems to have
too low gain, but in fact increasing gain is not so beneficial as there is no reasonable phase margin at higher frequency.

With the estimated openloop transfer functions and the measured free-running angular fluctuation, the suppressed angular spectra can be
estimated (attachment figure 4). This tells us that the suppression of the angular noise at around 3Hz is not sufficient in both pitch and yaw.
As there is no mechanical resonance in the actuator response at the frequency, intentional placement of poles and zeros in the servo filter is necessary.

4) Newly designed ASC filter

Here is the new design of the QPD ASC servo (attachment figure 5). The target upper UGF is 10Hz with the phase margin of 50 to 60deg.
The servo is AC coupled so that we still can tweak the alignment of the mirror.

As this servo is conditionally stable, at first we should close the loops with stable filter and then some boosts should be turned on.
Estimated suppressed fluctuation is shown in the attachment figure 6. We can see that the fluctuation was made well white between 0.5Hz to 10Hz.

The filter design is shown as follows:


Pitch
FM1: zero at 0Hz, pole at 2000Hz, gain at 2000Hz = 2000

FM3: (boost)
zero: f: 0.5Hz q: 1  /  4.5Hz, q: 1 / f: 1Hz, q: 3
pole: f: 2Hz q: 3  / f: 2.7Hz, q: 2  / f: 1Hz, q: 15

FM9: (HF Roll-off)
pole: f: 40Hz q: 1.7
 
Servo gain: -0.028

Yaw
FM1: zero at 0Hz, pole at 2000Hz, gain at 2000Hz = 2000

FM3: (boost)
zero: f: 0.7Hz q: 2  /  3Hz, q: 7 / f: 2Hz, q: 6
pole: f: 1.02Hz q: 10  / f: 4.5Hz, q: 0.8  / f: 1.5Hz, q: 10

FM9: (HF Roll-off)
pole: f: 40Hz q: 1.7
 
Servo gain: -0.0132


 

Attachment 1: PRM_OPLEV.pdf
PRM_OPLEV.pdf
Attachment 2: PRM_QPD.pdf
PRM_QPD.pdf
Attachment 3: OLTF_design.pdf
OLTF_design.pdf
Attachment 4: QPD_spe.pdf
QPD_spe.pdf
Attachment 5: OLTF_design2.pdf
OLTF_design2.pdf
Attachment 6: QPD_spe2.pdf
QPD_spe2.pdf
Attachment 7: 140328.zip
  9772   Tue Apr 1 21:45:01 2014 JenneSummaryLSCPRM violin notch not at correct freq?

Koji and I have the PRMI locked right now, and we hear a very strong violin mode ringing up, at 628Hz.  This is, according to Koji's elog 9634, what we expect the PRM's violin mode to be.  However, the current PRM violin mode notch is really more of a bandstop filter, between 622-670Hz.  At 628Hz, it has a suppression of about -20dB.  If I try to increase the width of this notch by making it 612-670Hz, the PRMI won't hold lock.

We're leaving this as a daytime task for tomorrow, since we're in the middle of taking data to show that Koji's new ASC filter design (slightly tuned from his elog 9769) works well.

Edit:  I have moved the PRM violin notch frequency over to 612-660 Hz, and after letting it sit for a while (while locked on PRMI), the violin mode has settled down.  Interestingly, if I compare the spectrum with and without the 1st order violin mode notch, it looks like the 2nd order mode changes from 1256Hz to 1303Hz.  I don't know what is going on here, but we already have notches for both of those frequencies.

  9773   Tue Apr 1 22:03:44 2014 KojiSummaryASCNew PRM ASC is running

[Koji Jenne]

New PRM ASC was implemented. [to be cnt'd]

  9777   Wed Apr 2 19:50:12 2014 KojiSummaryASCNew PRM ASC is running

As the designed ASC filters in this entry had too little phase margins (~10deg), I had to compromise the servo design.

The design was modified and tested again. This will be reported by a following entry.

Incidentally, I have adjusted the demodulation phases of REFL33/55/165 for PRMIsb so that the PRCL is eliminated from the Q signals.

REFL33    125.5 deg -> +136.5 deg
REFL55      45.0 deg -> +  25.0 deg
REFL165   -79.5 deg -> +  44.5 deg

This change of the demod phase for REFL165 was a bit surprising.
I did not check the sign, so it could be -135.5 deg. But still this is a bit change.

  9779   Wed Apr 2 23:08:51 2014 KojiSummaryASCNew PRM ASC is running

The new PRM ASC design


Pitch
FM1: zero at 0Hz, pole at 2000Hz, gain at 2000Hz = 2000

FM5: (boost)
zero: f: 0.5Hz q: 1  /  4Hz, q: 2 / f: 1Hz, q: 3
pole: f: 2Hz q: 3  / f: 2.7Hz, q: 2  / f: 1Hz, q: 15

FM9: (HF Roll-off)
pole: f: 40Hz q: 1/Sqrt(2) (2nd order butterworth)

Servo gain: -0.023

Yaw
FM1: zero at 0Hz, pole at 2000Hz, gain at 2000Hz = 2000

FM5: (boost)
zero: f: 0.5Hz q: 1  /  4Hz, q: 2 / f: 1.5Hz, q: 10
pole: f: 1.02Hz q: 10  / f: 3Hz, q: 5  / f: 2Hz, q: 6

FM9: (HF Roll-off)
pole: f: 40Hz q: 1/sqrt(2)
 
Servo gain: -0.027


The loop gains were adjusted to have the UGFs of 10Hz. The measured openloop transfer functions were compared with the model.
The transfer functions for yaw are well matched. However, the pitch ones don't. It seems that the pitch loop has extra low pass
which I can't locate. The possibility is the analog electronics of the pitch loop.


The effect of the control between 0.3Hz to 3Hz are well represented by the model. The attachment 2 shows the free running
angle fluctuation, the ones with the control engaged, and the estimated spectra. Indeed, the estimated spectra well represent
the measured angular spectra.

Attachment 1: PRM_QPD.pdf
PRM_QPD.pdf
Attachment 2: QPD_spe.pdf
QPD_spe.pdf
  9784   Thu Apr 3 18:55:10 2014 ericqSummaryLSCSome CARM related modeling

 The other day, Jenne and I were comparing my MIST simulation to her Optickle simulation for the CARM transfer functions I posted some days ago. She told me that the arms are not exactly where they should be for the whole "PRC length tuning to account for sideband reflection phase off resonant cavity" deal. 

Specifically, as in the wiki (but with newer modulation frequencies), I calculated the ideal arm length to be 37.795 m some time ago, when doing PRC length simulations, and Jenne has told me that the X arm is more like 37.6m, and Y is 37.9. So, I updated my simulations, and found the following:

This does weird things to the f2 sideband buildup on resonance in the PRFPMI configuration:

asIsPRCRes.pdf idealPRCRes.pdf

(POP is way huger than than the TR's, because the POP pd's are artificially "inside" the cavity, whereas TRX/Y is actually transmitted through an ETM)

This is not necessarily directly something to worry about, but I think the following may be. It looks like this arm length mismatch actually causes the PRCL demodulation phase in REFL 165 to change dramatically with the CARM offset. (REFL33 seems fine, though. 5 degrees causes less than a 1% effective gain change.) 

 3fPrclAnglesCarm.pdf

My simulations don't include any signal recycling yet, so I don't have anything to show if there is a similar effect for SRCL, but it wouldn't surprise me... 

 

  9785   Fri Apr 4 18:51:29 2014 ericqSummaryLSCMORE CARM related modeling

In today's ISC call, Kiwamu was comparing two ways to approach resonance: 

  • "C-Type": The scheme we currently think about; zero DARM offset and slowly reduce the CARM offset
  • "D-Type": Start with no CARM offset, but a DARM offset and reduce that. 

D-type might be interesting to check out, since things change a little less dramatically when you reduce the DARM offset. Maybe this makes signal hopping easier? Signal recycling may complicate things, though. 

So, I've simulated CARM and DARM offset effects on CARM and DARM signals. (As with the previous plots, this is for the PRFPMI configuration.) From moving both offsets around, it looks like the resonance peak is about 5x wider in DARM than in CARM, so I simulated a 50pm offset range for CARM and a 250pm offset range for DARM. 

Here are some CARM signal transfer functions subject to CARM offsets in the top plot, and DARM offsets in the bottom plot. 

 carm2REFL11.pdfcarm2REFL55.pdf

carm2REFLDC.pdfcarm2TRX.pdf

 

It's looks like the DARM offset changes cause much less dramatic changes in the CARM plant features. It's conceivable that this would make CARM locking easier. 

Here are some DARM plant transfer functions. 

 darm2AS11.pdfdarm2AS55.pdf

darm2ASDC.pdfdarm2TRX.pdf

In these plots, I did something kind of artificial: when we move the CARM offset, it changes the proper demodulation phase to get DARM in the Q of the AS 1F RFPDS. So, at each CARM offset, I re-phased the AS 1F demodulators, to show the total DARM information available at the AS RFPDs at each offset, rather than what one would actually see in them with a static demod phase. 

ASDemodAngles.pdf 

  9794   Thu Apr 10 10:52:15 2014 manasaSummaryIOOMC2_TRANS path in WFS servo

Quote:

Quote:

I've also turned on the MC2 TRANS path to gather some data over the weekend on how well or bad it works. Please turn it off on Monday.

 MC2_TRANS path in WFS servo turned OFF.

[From yesterday]

The MC had not been stable lately with WFS drifting constantly. I checked the servo and found that the MC_TRANS path was still running. It turned out that the autolocker script enables the TRANS path in the locking process. I have turned the MC_TRANS path servo inputs OFF and now it is no more a part of the WFS servo.

P.S. Jenne fixed the PMC alignment mostly in pitch to bring it up to 0.81 from 0.77. But the temperature fluctuations have still not got us to the sweet spot for optimum PMC trans.

  9837   Mon Apr 21 23:33:57 2014 ranaSummaryGreen LockingHP 8591E reads low by 140 Hz out of 10 MHz

To check the basolute frequency stability of the old monochrome HP 8591E RF Spectrum analyzer that we're using for the ALS beat readout, I hooked its 10 MHz reference output (from its rear panel) into the A channel of the SRS SR620 frequency counter. The SR620 is locked to the FS 720 Rubidium clock via the 10 MHz connections in their rear panels.

So, we can assume that this is a good absolute readout. It reads 9.999860.7 +/- 0.3 Hz. So its 139.1-139.4 Hz lower than 10 MHz. The +/- 0.3 is just a slow drift that I see over the course of 10 minutes.

So, let's say that the analyzer is low by 10 ppm, so the arm length estimates are short by ~0.4 mm. A negligible correction, so there's no need to use atomic clocks to measure our arm lengths.

  9857   Fri Apr 25 23:08:57 2014 ranaSummaryIOOMC2_TRANS QPD Servo re-re-engaged again

We turned on the MC2_TRANS paths for both PIT/YAW tonight.

I turned off the BLP200 and turned on the RLP7 (RLP always are better than BLP). G_PIT = -0.111, G_YAW = 0.111. On Monday, let's let Steve look at the trends and determine if this centering servo is bad or good.

  9858   Sat Apr 26 13:19:59 2014 ericqSummaryIOOMC2_TRANS QPD Servo re-re-engaged again

Quote:

We turned on the MC2_TRANS paths for both PIT/YAW tonight.

I should've included this in my Thursday night ELOG... That evening, I aligned the mode cleaner with reasonable MC1/3 spot positions, and the MC2 spots very close to centered, and recentered the WFS and MC2 Trans QPDs. The mode cleaner held up very well over the course of that evening, even when actuating CARM on MC2 with WFS engaged (which previously wasn't very stable when the WFS weren't well aligned).

  9869   Mon Apr 28 15:47:57 2014 manasaSummaryIOOMC2_TRANS QPD Servo trend

Quote:

We turned on the MC2_TRANS paths for both PIT/YAW tonight.

I turned off the BLP200 and turned on the RLP7 (RLP always are better than BLP). G_PIT = -0.111, G_YAW = 0.111. On Monday, let's let Steve look at the trends and determine if this centering servo is bad or good.

The MC was showing slow but periodic alignment drifts and eventually unlocked around noon. I looked up the alignment trend (Attach: 2 day trend)

MC_TRANS_PIT_ERR and MC_TRANS_Y_ERR show that the MC_TRANS servo slowly drifted the IMC alignment causing it to lose lock from time to time (mostly in yaw).

To confirm that the drift was NOT due to off-centering in the MC2_TRANS QPD, I turned off the WFS servo, moved MC2 to recenter the trans beam on the QPD, and re-enabled WFS servo.

MC_TRANS path in WFS is still left enabled.

Attachment 1: MC_TRANSservoApr28.png
MC_TRANSservoApr28.png
  9871   Mon Apr 28 20:31:38 2014 ranaSummaryIOOMC2_TRANS QPD Servo trend

This is a 4-day trend. I don't see any difference here which is significant. My guess is that the MC_TRANS servo gain is so low that its not really doing anything.

I'll turn it on periodically this week and then on Monday people can look at the trend again to see if they can identify when the servo is ON and when its OFF.

Attachment 1: Untitled.png
Untitled.png
  9886   Wed Apr 30 21:57:07 2014 ranaSummaryIOOMC2_TRANS QPD Servo now on for real

dolphin.pngMC2_QPD_trend.png

During a lull in Koji vs. The Arm, I switched on the MC2_TRANSQPD feedback path to check out its UGF. In the past months, when its been on, it has had a gain of ~0.03 - 0.1.

Today, I found that with the gain turned up to 11, it has a ~1 minute step response time (as you see in the above Strip chart). So its had a UGF of ~2 hours or so during the times when we thought it might be doing bad or good or magic.

I leave it on now to see if it behaves well over the next days. Let's see if Steve thinks its good or not based on his trend monitoring.

** also touched up the PMC pointing (using the PMC REFL image / please never align the beam into the PMC without this camera image)

  9925   Wed May 7 23:09:06 2014 rana, jamieSummaryComputer Scripts / ProgramsOttavia back on network

After Jamie fixed the third party repo issue with Ottavia, he was able to upgrade it to Ubuntu 12.04 Precise Pangolin. But its network stopped working.

I tried to fix its issues by ifconfig and GUI, but what it really wanted was for me to put the network cable back into its eth0 slot. The eth1 network card appears not be working anymore.

All seems fine now. Next I will mount the shared user disk from linux1 and put in a .bashrc.

  9932   Thu May 8 17:00:56 2014 rana, QSummaryLSCREFL_DC handoff didn't work last night

Last night after checking cabling and turning on ISS, we tried several times to handoff to REFL_DC but it didn't work at all.

Some issues:

  1. The ISS was injecting a lot of very low frequency power fluctuations because of bad AC coupling.
  2. The SR560 @ LSC rack was saturating a lot with the x10 gain that Jenne and Rana put in; we turned it back to G = 1.
  3. The ISS was also saturating a lot. We turned it off around 4 AM, but still no success.
  4. The ALS sequence for finding the Red Resonance takes too long (~2 minutes), so we're trying a faster scheme tonight.
  9934   Fri May 9 01:36:28 2014 ranaSummarySUSOptical Lever QPD Sum trends: they're almost all too weak

 We want there to be ~16000 cts of signal per quadrant on the optical levers. I think that most of the QPDs have been modified to have 100k transimpedance resistors.

From the attached 90 day trend, you can see that the ETMX, BS, PRM, and SRM are really low. We should figure out if we need to change the lasers or if the coating reflectivities are just low.

Steve, can you please measure the laser powers with a power meter and then reply to this entry?

Another possibility is that we are just picking a dim beam and a brighter one is available.

Attachment 1: OLtrend.png
OLtrend.png
  9936   Fri May 9 04:51:13 2014 ericqSummaryLSCREFL_DC handoff didn't work last night

Quote:

Last night after checking cabling and turning on ISS, we tried several times to handoff to REFL_DC but it didn't work at all.

Some issues:

  1. The ISS was injecting a lot of very low frequency power fluctuations because of bad AC coupling.
  2. The SR560 @ LSC rack was saturating a lot with the x10 gain that Jenne and Rana put in; we turned it back to G = 1.
  3. The ISS was also saturating a lot. We turned it off around 4 AM, but still no success.
  4. The ALS sequence for finding the Red Resonance takes too long (~2 minutes), so we're trying a faster scheme tonight.

 Still no success tonight

  • We took CARM OLTFs at various CARM offsets and could clearly see the peak in the optical TF (in once case ~2.5kHz), which gave us an indication of our offset (~200pm)
  • REFLDC effectively sees the same plant TF as the transmission signals plus a zero at ~110 Hz, at all offsets under 1nm, from my simulations; this pushes up the optical resonance and causes a loop instability when we try to handoff. 
  • We need to make the CARM OLTF steeper to suppress this instability, but also to make a good crossover with the AO path, which otherwise has too similar of a slope around the UGF, as we saw with our one arm test. 
  • We're thinking of trying to turn the AO path on with REFLDC while keeping the arms on SQRTINV signals. This may be tricky, but if we can get the loop bandwidth above the optical peak, it'll be a lot easier to deal with, and transfer digital control to REFLDC as well. 
  9942   Mon May 12 22:42:19 2014 ranaSummarySUSOptical Lever QPD Sum trends: they're almost all too weak

For some reason or another, I decided that we should see if the optical lever servos were injecting too much noise into the test masses. The ITMs are much worse than the ETMs and I am afeared that they might be making the main noise for our arms in the 20-40 Hz region. Jenne is checking up on these feedback loops to see what's up.

To estimate the actuator gains of the mirrors, I turned on 1 count drives from LSC/CAL oscillators into the LSC drives of each test mass at the frequencies shown in the plot with the resulting peaks showing up in in POX/Y with the single arm locks in red. I will leave these going permanently, but with 0.1 count ampltiudes; we need to make it so in the scripts.

Attachment 1: OL-FB.png
OL-FB.png
Attachment 2: arms_140512.pdf
arms_140512.pdf
  9943   Mon May 12 22:52:59 2014 JenneSummarySUSOptical Lever Filters are all different

We need to go back and have a look at all of our optical lever control filters, and make sure they make sense. 

In particular, we should have a look at the ITMs, since they have a huge amount of motion around 10Hz. 

Notes:  ETMX shouldn't have that lower notch.  The bounce mode Qs should be lowered.

OpLevFilters.pdf

  9946   Tue May 13 13:27:58 2014 SteveSummarySUSOptical Lever Servos setting table

Quote:

For some reason or another, I decided that we should see if the optical lever servos were injecting too much noise into the test masses. The ITMs are much worse than the ETMs and I am afeared that they might be making the main noise for our arms in the 20-40 Hz region. Jenne is checking up on these feedback loops to see what's up.

To estimate the actuator gains of the mirrors, I turned on 1 count drives from LSC/CAL oscillators into the LSC drives of each test mass at the frequencies shown in the plot with the resulting peaks showing up in in POX/Y with the single arm locks in red. I will leave these going permanently, but with 0.1 count ampltiudes; we need to make it so in the scripts.

 I'm in the process of filling this table

OPLEV

SERVO     

300 ^

2:0

BR

16,24

Hz

ELP RLP BOOST RES

GAIN

QPD

COUNTS

 

QPD

mW

QPD

beam

OD

HE/NE

output

mW

%

back

on QPD

                                
ETMY PIT  FM1  FM5    55      -30 8,200 0.2   3.3  
        YAW  FM1  FM5    55      -28          
ETMX PIT  FM1  FM5  35        4.4 900 0.2   1.7  
       YAW  FM1  FM5  35        2.1          
ITMY PIT  FM1  FM5        3.3   52 14,400 0.4   9.5  
      YAW  FM1  FM5        3.3  -46          
ITMX PIT  FM1  FM5  50      3.3   30 7,400 0.17   2.8  
       YAW  FM1  FM5  50      3.3  -20          
BS  PIT  FM1  FM5  35      3.3   9 2,800 0.05   2.8  
    YAW  FM1  FM5  35      3.3  -9          
PRM  PIT FM1  FM5  55   FM7  3.3  7 3200 0.06   2.8  
       YAW FM1  FM5  55   FM7  3.3  -5          
SRM  PIT  FM1            -20       9.5  
       YAW  FM1            20          

 I should replace ETMX He/Ne laser

Attachment 1: OLsums.png
OLsums.png
  9947   Tue May 13 17:03:05 2014 SteveSummarySUSETMX oplev laser replaced

Quote:

Quote:

For some reason or another, I decided that we should see if the optical lever servos were injecting too much noise into the test masses. The ITMs are much worse than the ETMs and I am afeared that they might be making the main noise for our arms in the 20-40 Hz region. Jenne is checking up on these feedback loops to see what's up.

To estimate the actuator gains of the mirrors, I turned on 1 count drives from LSC/CAL oscillators into the LSC drives of each test mass at the frequencies shown in the plot with the resulting peaks showing up in in POX/Y with the single arm locks in red. I will leave these going permanently, but with 0.1 count ampltiudes; we need to make it so in the scripts.

 I'm in the process of filling this table

OPLEV

SERVO     

300 ^

2:0

BR ELP RLP BOOST RES

GAIN

QPD

COUNTS

 

QPD

mW

QPD

beam

OD

HE/NE

output

mW

%

back

on QPD

                                
ETMY PIT  FM1  FM5    55      -30 8,200 0.2   3.3  
        YAW  FM1  FM5    55      -28          
ETMX PIT  FM1  FM5  35        4.4 900 0.2   1.7  
       YAW  FM1  FM5  35       2.1  1,750  0.33    2.8  
ITMY PIT  FM1  FM5        3.3   52 14,400 0.4   9.5  
      YAW  FM1  FM5        3.3  -46          
ITMX PIT  FM1  FM5  50      3.3   30 7,400 0.17   2.8  
       YAW  FM1  FM5  50      3.3  -20          
BS  PIT  FM1  FM5  35      3.3   9 2,800 0.05   2.8  
    YAW  FM1  FM5  35      3.3  -9          
PRM  PIT FM1  FM5  55   FM7  3.3  7 3200 0.06   2.8  
       YAW FM1  FM5  55   FM7  3.3  -5          
SRM  PIT  FM1            -20       9.5  
       YAW  FM1            20          

 I should replace ETMX He/Ne laser

 

  9948   Tue May 13 17:31:32 2014 JenneSummarySUSETMX oplev laser replaced: New oplev gains set

I took loop measurements of ETMX pit and yaw, and set the upper UGF to be ~6Hz for both.  This required a pitch gain of 25, and a yaw gain of 16.

The spectra look similar to what they were before Steve did the swap.

OLerr_13May2014.pdf

OLfb_13May2014.pdf

  9950   Tue May 13 22:55:57 2014 JenneSummarySUSETMX oplev: cleanup

I believe that the Xend aux laser was turned off earlier today, for Steve's work swapping out the oplev.  When I went down there, the red "off" LED was illuminated, and the LCD screen was showing something.  I pushed the green "on" button, and I immediately got green.

Also, I saw that the 24Hz roll mode was very rung up on ETMX.  I looked at the FM5 "bounce roll" filter, and it had some old values, 12Hz and 18Hz for the resonant gains.  All other optics have the proper 16Hz and 24Hz frequencies.  I copied the BS oplev bounce roll filter over to ETMX pit and yaw (both were wrong), and loaded them in.  The mode is starting to ring down.

  9952   Wed May 14 10:04:06 2014 SteveSummarySUS oplev laser and temperature

 ETMX oplev qpd gain has to be increased.

 

Attachment 1: TempRules.png
TempRules.png
  9973   Tue May 20 09:12:25 2014 SteveSummarySUSETMX oplev qpd board

Quote:

 ETMX oplev qpd gain has to be increased.

 

 Atm3, Oplev sum read 12,000 counts when the qpd was disconnected ?

           Dark qpd was zero and normal He/Ne incident on qpd was 1,730 counts.

Attachment 1: ETMXOLQPD121.jpg
ETMXOLQPD121.jpg
Attachment 2: ETMXOLQPDface121.jpg
ETMXOLQPDface121.jpg
Attachment 3: ETMXolSUM.png
ETMXolSUM.png
  9975   Tue May 20 15:54:39 2014 ranaSummarySUSETMX oplev qpd board

 This QPD circuit (D980325-C1 ) uses the nice OP497 Quad FET opamp as the transimpedance amplifier. It has a low enough current noise, such that we can increase the resistors (R1-4) up to 100k and still be Johnson noise limited. We should also make sure that the compensation caps (C3-6) are ~2.2 nF so as to not destabilize the opamp. f_low = 1/2/pi/R/C = 730 Hz.

I will do the swap later today unless someone else gets to it first. (note: check for oscillations w/ fast scope probe after installing)


I did these modification tonight. The slideshow of some images is attached. Instead of 100k, I used 97.6k thin film, since this seemed like an oddball size that doesn't get used otherwise. I forgot to measure the dark noise of the quadrants before doing the swap, but comparing the pit/yaw/sum before/after the swap shows that the signal is basically unchanged (since pit/yaw is normalized by SUM), but that the noise is lower by a factor of a few above 100 Hz due to being above ADC noise now. Previously, it was bottoming out at ~10 prad/rHz. Since the signal is unchanged, I guess that the calibration and therefore the loop gain should not have changed either...

And the sum went up by almost 10x as expected from the resistor change.

  10009   Mon Jun 9 10:55:48 2014 NichinSummaryElectronicsBBPD D1002969-v8 transimpedence measurement

My SURF week-1 work...

Motivation:

To measure the transimpedence of  the Broadband photodiode (D1002969-v8), using a New focus photodiode (1611) as reference. The amplitude modulated Jenne Laser (1.2mW) was used. 

The steps involved in getting the transimpedence are as follows:

Acquiring data

  • Get 2 sets of data from Network Analyzer Agilent 4395: One set of data will be for the transfer function of Ref PD over RF out. The other set for Test PD over Ref PD.
  • The following conditions were set:

1) Frequency sweep range: 1MHz to 200 MHz.

2) Number of Points sampled in  the range: 201

3) Type of sweep: Logarithmic

  • Set the NA to give the corresponding transfer function values in dB and also Phase response in degrees.
  • Save the data into floppy disk for processing on the computer (The wireless way of acquiring data was not working when the experiment was conducted )

Plotting

  • The matlab code attached (TransimpedencePlot.m) will then give plots for the absolute values of transimpedence in V/A.
  • Logic involved in the code:
    • Transimpedence = Voltage response / (Responsivity of the photodiode * Power incident) 
    • Responsivity for BBPD is taken as 0.1 A/W and for NF1611 as 0.68 A/W as given in their datasheets.
    • Voltage response of Test PD w.r.t RF output of NA (in dB) = Voltage response of Test PD w.r.t Ref PD (in dB) + Voltage response of Ref PD w.r.t RF output of NA (in dB) 

 Results

The Plots of transimpedence obtained are attached (results.pdf) . The results obtained for BBPD is consistent with the ones obtained before, but the same method and code gives a different transimpedence for 1611.

The transimpedence of NF 1611 was obtained to be around 4-5 V/A which is very much off-track compared to the one given in the datasheet (elog: 2906).

 

The transimpedence of  Broadband photodiode (D1002969-v8) was around 1200 - 1300 V/A for most of the range, but the value started falling as the frequency approached 100 MHz. This result is consistent with DCC document: T1100467-v2.

 

Attachment 1: PD_transimpedence_measurement.png
PD_transimpedence_measurement.png
Attachment 2: results.pdf
results.pdf results.pdf
Attachment 3: code_and_data.zip
  10012   Mon Jun 9 16:55:31 2014 KojiSummaryElectronicsBBPD D1002969-v8 transimpedence measurement

How is the modulation depth assumed in the calculation?

If you don't know the modulation depth, you can't calibrate the transimpedance of each PD individually.

  10042   Mon Jun 16 12:58:50 2014 manasaSummaryIOORingdown recap

A recap of the ringdown measurements made at the 40m in mid 2012, the hardware that was installed for the same and results from the measurements.

IMC ringdown:

Hardware installed 
A trans PD was installed (elog 7122).
This PD does not exist in the trans path anymore.

Measurements
The polarity in the MC servo was flipped with the MC WFS disabled and the PD trans signal was used to look at the cavity ringdown. 
Ringdown time = 13 us
Cavity finesse from the measurement = 453 (inconsistent with actual finesse). 

Attachment: Ringdown measurement and fits

PMC ringdown:

Hardware installed
The AOM was installed before the PMC. The AOM was driven by the driver installed on the PSL table. (RF power ~1.5W @ 80MHz @1.0V modulation input). An RF switch was installed to control the AOM driver input. ZASWA-2-50DR+ was installed.
Note: The AOM was used by the ISS crew after this. So the RF switch has been removed and the AOM is no more a part of the ringdown setup.

Measurements
No measurements were made as we could not obtain relevant TTL signals to control the switch remotely.

Attachment 1: Ringdown_815.pdf
Ringdown_815.pdf
Attachment 2: MCringdown_cum.pdf
MCringdown_cum.pdf
Attachment 3: cum_plot.png
cum_plot.png
  10043   Mon Jun 16 15:32:12 2014 ranaSummaryIOORingdown recap

 

To do this better:

1) Just step the analog input to the AOM (i.e. no RF switch) and measure the PMC trans output with a fast DC coupled PD. IMC should be unlocked and disable during this part. We want the PMC ringdown to be faster than 1 us.

2) Re-install a fast PD in the MC trans path without disrupting the existing MC trans QPD setup.

3) Measure IMC ringdown and fit the data to find the cavity losses.

4) Think about how to use the Isogai, et. al (2013) technique to better measure the losses, taking into account the mirror transmissions.

  10097   Wed Jun 25 02:01:21 2014 NichinSummaryGeneralWeekly Report

 Attached is the weekly work plan / equipment requirement / lab expert's presence needed for the upcoming week.

Attachment 1: Nichin_Week4_update.pdf
Nichin_Week4_update.pdf Nichin_Week4_update.pdf
  10193   Mon Jul 14 13:03:23 2014 AkhilSummaryElectronicsTiming Issues of Mini Circuits UFC-6000: Solved

Main Problem:

The frequency counter (FC) takes in an analog RF input(signal) and outputs the frequency of the signal(Ranging from 1 MHz- 6000 MHz) in the digital domain (into a processor). The FC samples the data with a given sample rate( user defined) which ranges from 0.1 s to 1 s(faced problems in fixing this initially).  For data acquisition, we have been using a Raspberry Pi(as a processor) which is connected to the martian network and can communicate with the computers inside the 40m.  The ultimate challenge which I faced( and been knocking my head off from past two-three weeks) is the synchronization of clocks between the Raspberry Pi and the FC i.e the clock which the FC uses to sample and dump data( every 'x' s) and the clock inside the raspberry pi( used  in the loop to wait for a particular amount of time the frequency counter takes to dump successive data).

 

Steps Taken:

  • To address this problem, first I added an external clock circuit which monitors the Raspberry Pi and the FC to dump and read data at a particular rate(which is equal to the sampling rate of the FC)In detail: http://nodus.ligo.caltech.edu:8080/40m/10129. 
  • While doing so, at first the level trigger algorithm was used which means that the external clock frequency was half as that of  the reciprocal of the sampling rate and a trigger was seen every time the level shifts from +DC to -DC(of the external square wave).
  • But this did not completely mitigate the issues and there were still few issues on how quickly the ADC reads the signal and R Pi processes it.
  • To minimize these issues completely, an edge trigger algorithm which detects a pos edge(rising)  of the clock was used. The clock  frequency is now equal to the reciprocal of the sampling rate. This algorithm showed better results and greatly minimized the drift of the sampling time.

Psuedo Code(code attached):

open device : FC via USB-HID;

open device : ADC via I2C;

always(for t= recording time):

            read data from ADC(external clock);

            if pos edge detected:

                    read data from FC and store it in a register;

             else read data from ADC;

end

write data stored in the register to a file( can be an Epics channel or a text file);

 

Results:

The attached are the plots showing the time between samples for a large number of samples taken for different sampling times of the FC. The percentage error is the percentage of standard error in the timing between two samples for the data for the entire measurement. It can be inferred that this error has been cut down to the order of ms.

 

To do next:

  • I have started taking phase measurements( analysis and plots will follow this elog) and also the PSD plots with the improved timing characteristics.

 

 

 

             

 

Attachment 1: 0.2timinganalysis.png
0.2timinganalysis.png
Attachment 2: 0.3timinganalysis.png
0.3timinganalysis.png
Attachment 3: 0.5timinganalysis.png
0.5timinganalysis.png
Attachment 4: 1stiminganalysis.png
1stiminganalysis.png
Attachment 5: pdf.zip
  10194   Mon Jul 14 14:28:27 2014 KojiSummaryElectronicsTiming Issues of Mini Circuits UFC-6000: Solved

Looks good. Now you have the internal timer to verify the external clock.
If you can realize the constant rate sampling without employing the external clock, that's quite handy.

  10199   Tue Jul 15 01:31:13 2014 AkhilSummaryElectronicsTiming Issues of Mini Circuits UFC-6000: Solved

The attached are the PSD plots with improved FC timing(with the same code as in http://nodus.ligo.caltech.edu:8080/40m/10151). More plots(Phase and PSD) to follow.

 

 

 

Attachment 1: qnoise.png
qnoise.png
Attachment 2: qnoise.pdf
qnoise.pdf
  10209   Wed Jul 16 01:18:02 2014 ranaSummaryLSCPython Wavelet peak finding for dramatic ALS - Red Resonance finding speedup

New script called scripts/ALS/findRedResonance.py finds the IR resonance in less than 20 seconds.

  1. Do a ~2 FSR scan of the arm over 10 seconds using the Phase Tracker servo offset ramp. (dt = 10 s)
  2. Load the frame data for the TR_OUT and the Phase Tracker phase. (dt = 2 s)
  3. Use Python (modern) SciPy to find all peaks with moderate SNR (dt = 3 s)
  4. Take the top 3 peaks (all presumably TEM00) and choose the one closest to zero and go there.

The above is the gist of what goes on, but there were several issues to overcome to get the code to run.

  1. None of our workstations have a modern enough Python distro to run either the ipython notebooks or the new SciPy with wavelets, so I installed Anaconda Python in the controls home directory.
  2. In order to get the peak finder function to work well I gave it a range of peak widths to look for. If we change the speed of the ALS scan by more than 3x, we probably have to change the width array in the function.
  3. I've used the find_peaks_cwt function in SciPy. This uses a Ricker ('Mexican Hat') wavelet to find peaks by doing multi-res transforms and looking for ridges in the wavelet space (I think)
  4. To make the code run fast, I downsample from 16 kHz to 1 kHz right at the top. Would be better if we had downsampling in v2 of the getData function.

 

Attachment 1: findRedResonance.pdf
findRedResonance.pdf
  10211   Wed Jul 16 01:35:16 2014 KojiSummaryLSCPython Wavelet peak finding for dramatic ALS - Red Resonance finding speedup

From the last plot:

- Subtracting the offset of 0.0095, the modulation depth were estimated to be 0.20 for 11MHz, 0.25 for 55MHz

- Carrier TEM00 1.0, 1st order 0.01, 2nd order 0.05, 3rd order 0.002, 4th order 0.004

==> mode matching ~93%, dominat higher order is the 2nd order (5%).

Eric: now we have the number for the mode matching. How much did the cavity round-trip loss be using this number?

  10219   Wed Jul 16 19:38:37 2014 manasaSummaryPSLAOM alignment issues and removed from beam path

AOM removed from the beampath and PMC relocked. 

AOM alignment:

1. Measured the initial power after PMC as 1.30W and reduced it down to 130mW.
2. Checked the power in the AOM zero order transmission before touching it. For 0-1V modulation input, the power dropped from 125uW to 98.3uW.
3. Steered the mirror right before the AOM to increase AOM zero order transmission and then carefully moved the AOM around to obtain maximum power attenuation. I repeated this a few times and the maximum attenuation that I could obtain was 125uW to 89.2uW (~30% attenuation).
Although this is not the right way to align the AOM, we do not have much options with the current setup as there is not enough separation between the zero order and first order beams and the AOM is on a fixed rigid mount.
4. I tried to dump the first order beam from the AOM and it wasn't satisfactory as well. There is barely any separation between the zero order and first order beams.

PMC relocking:

1. SInce the alignment to the PMC was disturbed by moving the AOM and the steering mirror in front of it, the PMC alignment was lost.
2. I could not relock the PMC at low power or high power. Rana had to come to rescue and fixed the alignment so that we could see flashes of PMC on the trans camera (This was done by aligning refl beam to the PMC REFL PD while giving a triangular ramp to the PMC PZT voltage).
Also I should not have tried to lock the PMC at high power as I could have been steering the beam at high power to the edges of the PMC mirrors that way and burning stuff easily.
3. Before fine tuning the alignment, I decided to remove the AOM from the beam path as there needs some work done on it to make it useful.
4. I removed the AOM from the beam path and relocked the PMC. 
5. PMC is relocked with 0.79 counts in TRANS and I measured the power after PMC 1.30W

Attachment: picture showing AOM removed from the beampath.

Attachment 1: AOMremoved.jpg
AOMremoved.jpg
ELOG V3.1.3-