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ID Dateup Author Type Category Subject
  6395   Fri Mar 9 16:00:46 2012 steveUpdateGreen Lockinglaser emergency shut down switch replaced at the south end

Over-sized local laser emergency switch was held by large C clamp at the south end. This was replaced by a smaller one and it is mounted with magnets.

The Innolight laser was turned off, while the interlock was wired.

  6396   Fri Mar 9 16:28:10 2012 Ryan FisherSummaryComputer Scripts / ProgramsAlterations to base epics install for installing aLIGO conlog:
I created a page on the wiki for the new EPICS log (conlog):
https://wiki-40m.ligo.caltech.edu/aLIGO%20EPICs%20log%20%28conlog%29

I also edited this with restart instructions:
https://wiki-40m.ligo.caltech.edu/Computer_Restart_Procedures#megatron
  6397   Fri Mar 9 20:44:24 2012 Jim LoughUpdateCDSDAQ restart with new ini file

DAQ reload/restart was performed at about 1315 PST today. The previous ini file was backed up as c1pem20120309.ini in the /chans/daq/working_backups/ directory.

I set the following to record:

The two JIMS channels at 2048:
[C1:PEM-JIMS_CH1_DQ] Persistent version of JIMS channel. When bit drops to zero indicating something bad (BLRMS threshold exceeded) happens the bit stays at zero  for >= the value of the persist EPICS variable.
[C1:PEM-JIMS_CH2_DQ] Non-persistent version of JIMS channel.

And all of the BLRMS channels at 256:
Names are of the form:
[C1:PEM-RMS_ACC1_F0p1_0p3_DQ]
[C1:PEM-RMS_ACC1_F0p3_1_DQ]

On monday I intend to look at the weekend seismic data to establish thresholds on the JIMS channels.

256 was the lowest rate possible according to the RCG manual. The JIMS channels are recorded at 2048 because I couldn't figure out how to disable the decimation filter. I will look into this further.

  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?

  6399   Sat Mar 10 15:29:47 2012 ZachHowToComputer Scripts / ProgramsModeMatchr

For your mode matching pleasure, I have added a tool called "ModeMatchr" to the SVN under /trunk/zach/tools/modematchr/

It uses the usual fminsearch approach, but tolerates a fully astigmatic input (i.e., w0ix ≠ w0iy, z0ix ≠ z0iy) and allows for transforming to an elliptical waist  (i.e., w0fx ≠ w0fy, but z0fx = z0fy). It would be straightforward to allow for z0fx ≠ z0fy, but I have never seen a case when we actually wanted this. On the other hand, the elliptical output ability is nice for coupling to wide-angle ring cavities.

It also does the looping through available lenses for you , and retains the best solution for each lens combination in an output cell, which can then be combed with another function (getOtherSol). fminsearch is incredibly fast: with a 10-lens bank, it finds all 100 best solutions on my crappy MacBook in <10s.

I have also included the functionality to constrain the length of the total MMT to within some percentage of the optimal distance, which helps to sift through the muck .

MMrLogo.png

  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
 

  6402   Mon Mar 12 22:14:56 2012 SureshUpdateRF SystemCalibration of Demod Board Efficiency.

I have completed the calibration of the demod board efficiencies.  Here is the schematic of the set-up.

 Calibration_Schematic.png

The data is given below and the data-file is attached in several different formats.

 Demod_calib.png

 

Attachment 3: Demod_calib.txt
								
	Measurements			 After corrections			Efficiency= out/in	
Demod Board	mV_ampl	mV_pk-pk	mV_pk-pk	mV_ampl	mV_ampl	mV_ampl	Vout/Vin	Vout/Vin
	PD in	Q out	I out	PD in	Q out	I out	Q out	I out
REFL33	10.6	10.0	10.0	9.4	5.0	5.0	0.53	0.53
AS11	24.0	10.0	11.0	21.3	5.0	5.5	0.23	0.26
REFL11	22.5	240.0	255.0	20.0	120.0	127.5	6.00	6.38
POX11	24.0	9.2	8.5	21.3	4.6	4.3	0.22	0.20
POY11	22.4	10.5	9.0	19.9	5.3	4.5	0.26	0.23
AS55	17.6	268.0	268.0	15.6	134.0	134.0	8.57	8.57
REFL55	19.7	15.8	15.5	17.5	7.9	7.8	0.45	0.44
POP55	18.8	278.0	274.0	16.7	139.0	137.0	8.32	8.20
REFL165	21.2	16.0	16.4	18.8	8.0	8.2	0.42	0.44
POY110	23.4	14.7	14.4	20.8	7.4	7.2	0.35	0.35
POY22	17.5	11.9	9.3	15.6	6.0	4.6	0.38	0.30
Attachment 4: Demod_calib.xlsx
  6403   Tue Mar 13 07:04:55 2012 kiwamuUpdateLSCevolution of the sensing matrix in PRMI as a function of time

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

 

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

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

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

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

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

 

PRCL.png

 MICH.png

 

  6404   Tue Mar 13 13:28:31 2012 Ryan FisherUpdateCDSDAQ restart with new ini file
Extra note: This was the ini file that was edited:
/cvs/cds/rtcds/caltech/c1/chans/daq/C1PEM.ini
  6405   Tue Mar 13 16:40:06 2012 kiwamuUpdateLSCevolution of the sensing matrix in PRMI as a function of time: details

Here I describe the measurement of the sensing matrix.

 

Motivations

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

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

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

 

Measurement

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

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

LOCKIN detection

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

 

lockins_MICH.png

 

Calibration of the LOCKINs

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

Calibration of the responses to watts/meter

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

Settings and parameters

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

Quote from #6403

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

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

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

Next steps:

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

Quote from #6403

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

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

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

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

The answer is that :

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

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

 

(Background)

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

(Noise analysis)

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

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

 NB_REFL33.png

(Some thoughts)

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

[Rana / Kiwamu]

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

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

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

 

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

Untitled.png

 

(How to)

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

Quote from #6369

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

I increased the gain and set it to be 80.

 

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

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

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

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

 

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

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

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

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

Sad ..

Quote from #6357

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

 

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

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

The result was --

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

 

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

 

(Tricks)

 At the beginning I tried minimizing the PRCL signal in the Q phase by rotating the demodulation phase because the PRCL signal was always huge.
However it turned out that the rotation of the demodulation phase didn't completely eliminate the PRCL signal for some reason.
 
This could be some kind of imbalance in the electronics or somewhere between the I and Q signal paths.
So instead, I tried blending the I and Q signals by a linear combination through the LSC input matrix.
Then I was able to eliminate the PRCL signal.
I put a gain of -0.1 for the I signal and 1 for the Q signal to get the good blend when the demodulation phase was at -17.05 deg.
  6412   Wed Mar 14 05:26:39 2012 interferomter tack forceUpdateGeneraldaytime tasks

The following tasks need to be done in the daytime tomorrow.

  • Hook up the DC output of the Y green BBPD on the PSL table to an ADC channel (Jamie / Steve)
  • Install fancy suspension matrices on PRM and ITMX [#6365] (Jenne)
  • Check if the REFL165 RFPD is healthy or not (Suresh / Koji)
    • According to a simulation the REFL165 demod signal should show similar amount of the signal to that of REFL33.
    • But right now it is showing super tiny signals [#6403]
  6413   Wed Mar 14 10:06:26 2012 steveUpdateGreen Lockingdichroic mirror quotes

Dichroic mirror quotes are in the wiki.

ATF is pricy.

We got a good price from Laseroptik, but the wedges are 5 arcminutes. The fused silica grade is 0F, meaning the  homogeneity is 5 ppm instead of 1ppm.  I requested an other large wedge quote on the substrates.We may have to get substrates from somebody else and ship it to Germany

MLT quote is outrageously high

REO is not interested in this low volume job.

 

  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.

 

  6415   Wed Mar 14 13:27:15 2012 ZachHowToComputer Scripts / ProgramsModeMatchr

I have added to ModeMatchr the capability to fix the total MMT distance. This is nice if you are coupling to a cavity some fixed distance away. The blurb from the help:

% Note: for any total length constraint dtot_tol > 0, ModeMatchr will use
% fminsearch to find the best solutions near your nominal dtot, and then
% omit solutions whose dtot lie outside your tolerance. For dtot_tol = 0,
% ModeMatchr actively constrains dtot to your value, and then finds the
% best solution. Therefore, set dtot_tol = 0 if you have a fixed distance
% into which to put a MMT.

Quote:

For your mode matching pleasure, I have added a tool called "ModeMatchr" to the SVN under /trunk/zach/tools/modematchr/

It uses the usual fminsearch approach, but tolerates a fully astigmatic input (i.e., w0ix ≠ w0iy, z0ix ≠ z0iy) and allows for transforming to an elliptical waist  (i.e., w0fx ≠ w0fy, but z0fx = z0fy). It would be straightforward to allow for z0fx ≠ z0fy, but I have never seen a case when we actually wanted this. On the other hand, the elliptical output ability is nice for coupling to wide-angle ring cavities.

It also does the looping through available lenses for you , and retains the best solution for each lens combination in an output cell, which can then be combed with another function (getOtherSol). fminsearch is incredibly fast: with a 10-lens bank, it finds all 100 best solutions on my crappy MacBook in <10s.

I have also included the functionality to constrain the length of the total MMT to within some percentage of the optimal distance, which helps to sift through the muck .

MMrLogo.png

 

  6416   Wed Mar 14 14:09:01 2012 interferomter tack forceUpdateGeneraldaytime tasks

Quote:

The following tasks need to be done in the daytime tomorrow.

  • Hook up the DC output of the Y green BBPD on the PSL table to an ADC channel (Jamie / Steve)
  • Install fancy suspension matrices on PRM and ITMX [#6365] (Jenne)
  • Check if the REFL165 RFPD is healthy or not (Suresh / Koji)
    • According to a simulation the REFL165 demod signal should show similar amount of the signal to that of REFL33.
    • But right now it is showing super tiny signals [#6403]

 For ITMX, I used the values from the conlog:

2011/08/12,20:10:12 utc 'C1:SUS[-_]ITMX[-_]INMATRIX'
These are the latest values in the conlog that aren't the basic matricies.  Even though we did a round of diagonalization in Sept, and the 
matricies are saved in a .mat file, it doesn't look like we used the ITMX matrix from that time.

For PRM, I used the matricies that were saved in InputMatricies_16Sept2011.mat, in the peakFit folder, since I couldn't find anything in the Conlog other than the basic matricies.

 

UPDATE:  I didn't actually count the number of oscillations until the optics were damped, so I don't have an actual number for the Q, but I feel good about the damping, after having kicked POS of both ITMX and PRM and watching the sensors.

  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

 

 

RAMexampleplot.png

 

 

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
Mar14pollution.png
  6418   Wed Mar 14 16:39:02 2012 SureshUpdateGeneralREFL165 signal was not reaching demod board : Fixed

Quote:

The following tasks need to be done in the daytime tomorrow.

  • Hook up the DC output of the Y green BBPD on the PSL table to an ADC channel (Jamie / Steve)
  • Install fancy suspension matrices on PRM and ITMX [#6365] (Jenne)
  • Check if the REFL165 RFPD is healthy or not (Suresh / Koji)
    • According to a simulation the REFL165 demod signal should show similar amount of the signal to that of REFL33.
    • But right now it is showing super tiny signals [#6403]

 The REFL165 RF output was not reaching the Demod board.  The RF cable was disconnected.  I fixed that and then I put in a RF signal at 165MHz , 1.66 mVrms at the test input  (100Hz off set from the 165MHz LO) and saw that the 100 Hz demodulated signal was visible in the dataviewer. 

Test_CDS_Calibration.png

 

Will complete the Optical RF power -> CDS counts calibration tomorrow morning. 

  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.

 

 

 

 

  6420   Wed Mar 14 23:02:09 2012 KojiUpdateLSCLocking activity

Kiwamu and Koji

The target is to realize DRMI or PRMI + one arm with ALS.

The focus of the night is to achive stable lock of the PRMI (SB resonant) with 3f signals.
Particularly, REFL165 is back now, we are aiming to see if any of the 165 signals is useful.

We made a comparison between  REFL33Q/REFL165Q/AS55Q to find any good source of MICH.
However, none of them showed a reasonable shape of the spectra. They don't have reasonable coherence between them.

Nonetheless, we have tried to lock the IFO with those REFL signals. But any of them were useful to keep the PRMI (SB resonant).
The only kind of stable signal for MICH was AS55Q as we could keep the PRMI locked.

  6421   Thu Mar 15 04:04:23 2012 KojiConfigurationLockingPRC Matching issues

Kiwamu and Koji

We found that the intra-cavity mode of the PRC is not round although it was obvious even with the DARK and REFL port images.
We need to review the mode matching situation.

In order to look at the PRC intra-cavity mode, we reconfigured the POP CCD.

If we look at the beam reflected from the Michelson, the beam is round. However, the PRC intra-cavity mode can never be round
in any resonant conditions. (Pict 1, 2, and 3, for the sideband resonant, carrier resonant conditions and another carrier resonant
one, respactively). Particularly the mode of the carrier resonant case is very unstable and always changing.

P3150902.jpg

P3150906.jpgP3150907.jpg

By misaligning the PRM, we can compare between the spot directly reflected from the Michelson and the one after additional round trip in the PRC (Pic 4).

They looks round, but it was obvious the secondary reflection is dimmer and larger (Pic 5). The intensity difference corresponds to the factor RPRM RMI
(i.e. product of the reflectivities for the PRM and MI). It can be understand if the dimmer spot looks smaller due to the artifact of the CCD. But it is opposite.

This may mean the mode matching is not correct. We are not sure what is not right. This could be just an incorrect incident beam, the curvature error of the PRM,
beam is distortec by the TT mirrors, or some other unknown reasons.

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

P3150910.jpgP3150900.jpg

  6422   Thu Mar 15 08:48:40 2012 RyanSummaryCDSSummary of Syracuse Visit to 40m Mar 5-9 2012

JIMS Channels in PEM Model

The PEM model has been modified now to include the JIMS(Joint Information Management System) channel processing. Additionally Jim added test points at the outputs of the BLRMS.

For each seismometer channel, five bands are compared to threshold values to produce boolean results.  Bands with RMS below threshold produce bits with value 1, above threshold results in 0.  These bits are combined to produce one output channel that contains all of the results.

A persistent version of the channel is generated by a new library block that called persist which holds the value at 0 for a number of time steps equal to an EPICS variable setting from the time the boolean first drops to zero. The persist allows excursions shorter than the timestep of a downsampled timeseries to be seen reliably.

The EPICS variables for the thresholds are of the form (in order of increasing frequency):
C1:PEM-JIMS_GUR1X_THRES1
C1:PEM-JIMS_GUR1X_THRES2
etc.
 
The EPICS variables for the persist step size are of the form:
C1:PEM-JIMS_GUR1X_PERSIST
C1:PEM-JIMS_GUR1Y_PERSIST
etc.

The JIMS Channels are being recorded and written to frames:

The two JIMS channels at 2048:
[C1:PEM-JIMS_CH1_DQ] Persistent version of JIMS channel. When bit drops to zero indicating something bad (BLRMS threshold exceeded) happens the bit stays at zero  for >= the value of the persist EPICS variable.
[C1:PEM-JIMS_CH2_DQ] Non-persistent version of JIMS channel.

And all of the BLRMS channels at 256:
Names are of the form:
[C1:PEM-RMS_ACC1_F0p1_0p3_DQ]
[C1:PEM-RMS_ACC1_F0p3_1_DQ]

For additional details about the JIMS Channels and the implementation, please see the previous elog entries by Jim.

 

Conlog

I have a working aLIGO Conlog/EPICS Log installed and running on megatron.

Please see this wiki page for the details of use:
https://wiki-40m.ligo.caltech.edu/aLIGO%20EPICs%20log%20%28conlog%29

I also edited this page with restart instructions for megatron:
https://wiki-40m.ligo.caltech.edu/Computer_Restart_Procedures#megatron

Please see Ryan's previous elog entries for installation details.

Future Work

  • Determine useful thresholds for each band
  • Generate MEDM Screens for JIMS Channels
  • Add a decimation option to channels
  • Add EPICS Strings in PEM model to describe bits in JIMS Channels
  • Add additional JIMS Channels: Testing additional characterization methods
  • Implement a State Log on Megatron: Will Provide a 1Hz index into JIMS Channels
  • Generate a single web page that allows access to aLIGO Conlog/EPICS Log and State Log

 

  6423   Fri Mar 16 06:17:56 2012 SureshUpdateElectronicsREFL165 calibration : measurements

 

These are the measurements for estimating the amplitude of the signal recorded in the CDS when a known amount of modulated light is incident on the photodiode. 

I mounted the PD characterisation setup onto a small breadboard which could then be placed close AP table.  I then placed position markers for REFL165 on the AP table before moving it onto my small breadboard.  The AM laser was driven by an RF function generator (Fluke 6061A) at a frequency of 165.98866 MHz, which is 102 Hz offset from the 165MHz LO.  The power level was set at -45dBm.  This power level was chosen since anything higher would have saturated the AntiAliasing  Whitening Filters.  The counts in the CDS were converted to voltage using the ADC resolution = 20V per 2^16 counts.

  

  RF source RF power to AM laser 1611 PD 1611 PD REFL165 REFL165 CDS CDS
  power set (dBm) Actual power out (dBm) DC (V) RF out (dBm) DC (mV) RF out (dBm) Amplitude (V)   102 Hz Amplitude (V) 102 Hz
                 
1  -45  -50.6  -2.5 -58.9  10  -37.4  0.171 0.172
2  -48  -53.5  -2.5 -62.1  10  -40.3  0.122  0.121
3  -51  -56.5  -2.5 -65.0  10  -43.1  0.085  0.085

    

 When the 166MHz power is decreased by a factor of 2 the amplitude of 102Hz wave recorded in CDS goes down by sqrt(2) as expected.   The RF AM power incident on the REFL165 was estimated to be 0.011mW(rms)  (case #1 in the above table)  using the DC power ratio and using the transimpedance of the 1611 BBPD to be 700 Ohms.  This produces a 171 mV amplitude wave at 102 Hz.  I then stepped down the power by factor of 2 and repeated the measurement. 

(These numbers however are not agreeing with the power incident on REFL165 if we assume its transimpedance to be 12500.  It will take a bit more effort to make all the numbers agree.  Will try again tomorrow)

Here is a picture of the small black breadboard on which I have put together the PD characterisation setup.  It would be great if we can retain this portable set up as it is, since we keep reusing it every couple of weeks.  It would be convenient if we can fiber couple the path to the PD under test with a 2m long fiber.  Then we will not have to remove the PD from the optical table while testing it.

IMG_0552.JPG

 

  6424   Fri Mar 16 10:37:52 2012 JenneUpdateElectronicsJenne Laser

Quote:

Here is a picture of the small black breadboard on which I have put together the PD characterisation setup.  It would be great if we can retain this portable set up as it is, since we keep reusing it every couple of weeks.  It would be convenient if we can fiber couple the path to the PD under test with a 2m long fiber.  Then we will not have to remove the PD from the optical table while testing it. 

 This is totally sweet Suresh!  I don't remember how much more fiber is coiled up under the plate that has the "Jenne Laser" label, but there's a reasonable amount.  It's not 2m, but maybe we can just extend the blue snakey thing some?

  6425   Fri Mar 16 16:01:53 2012 ranaUpdateElectronicsREFL165 calibration : measurements

 To characterize the RF V to counts we need to know the state of the whitening filter board. Was the filter on or off ? What was the value of the whitening gain slider?

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

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

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

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

 


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

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

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

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

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

 

The values below are the current offset that I put.

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

  6427   Sun Mar 18 00:29:24 2012 DenUpdatePEMsts-2

I've turned off the power of the STS-2 readout box as it provides outputs with ~10 Volts DC offset! AA filter box works in the range -2 +2 Volts, so we do not have any useful information anyway. I'll adjust the mass positions in the seismometer.

  6428   Mon Mar 19 21:25:31 2012 SureshUpdateElectronicsREFL165 calibration : measurements

Quote:

 To characterize the RF V to counts we need to know the state of the whitening filter board. Was the filter on or off ? What was the value of the whitening gain slider?

 The filter was ON and the whiterning filter gain was 45dB

 

  6429   Tue Mar 20 09:59:01 2012 steveUpdateIOOLaser tripped off

Today is janitor day. It still does not explain why the 2W Innolight tripped off about an hour ago. All back to normal.

.......................................................I asked Keven later, he admitted hitting the emergency shut off next to the chemical storage cabinet.

  6430   Tue Mar 20 16:53:48 2012 steveUpdatePEMcranes maintenance & certified inspection of 2012

Fred Goodbar of Konecrane has completed the annual certified crane inspection and maintenance of our cranes as required in safety document.

They are in good working condition and safe to use.

  6431   Tue Mar 20 17:50:44 2012 SureshUpdateComputersBeam Scan machine fixed

There was something wrong with the Beam Scan PC.  The  mouse and screen were not responding and the PC was asking for drivers for any new hardware that we plugged in.  We called in the services of Junaid and co. since we do not have a Win98 Second Edition installation disk in the lab.   Junaid came with the disk, we changed the screen and the mouse and installed everything. 

We tried to get the network going on the PC so that we could update stuff easily over the net.  This didnt succeed. For now, we still have to depend on a Win98se CD to get drivers if any new hardware is connected to this machine. 

For future reference, some notes:

1)  We will get a copy of Win98SE for the lab from Junaid

2) We have to use a USB mouse from Dell. We have several spares of this. The drivers for these are present in the machine. 

 

 

The Beam Scan is working okay now.  We will proceed with the beam profile measurements.  

  6432   Wed Mar 21 10:31:28 2012 steveUpdateSAFETYAC power to ETMY turned off

ETMY sus damping was disabled. Green locking laser and associated electronics turned off. Computers and power supplies turned off at rack 1Y4

The electricians picking up ac power from 1Y4 manual disconnect box and installing conduit line to ISCT-ETMY east end optical table.

There will be no more daisy chaining this way. 

  6433   Wed Mar 21 11:32:47 2012 steveUpdateSAFETYAC power to ETMX turned off

Quote:

ETMY sus damping was disabled. Green locking laser and associated electronics turned off. Computers and power supplies turned off at rack 1Y4

The electricians picking up ac power from 1Y4 manual disconnect box and installing conduit line to ISCT-ETMY east end optical table.

There will be no more daisy chaining this way. 

 The power is back on at ETMY . c1iscey has not been restarted.

Now I'm turning ac power off at ETMX for the same job to be done.

  6434   Wed Mar 21 19:12:27 2012 steveUpdateComputersAC power back on both ends

Quote:

Quote:

ETMY sus damping was disabled. Green locking laser and associated electronics turned off. Computers and power supplies turned off at rack 1Y4

The electricians picking up ac power from 1Y4 manual disconnect box and installing conduit line to ISCT-ETMY east end optical table.

There will be no more daisy chaining this way. 

 The power is back on at ETMY . c1iscey has not been restarted.

Now I'm turning ac power off at ETMX for the same job to be done.

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

  6435   Thu Mar 22 08:14:21 2012 steveUpdateGreen Lockingdichroic mirror quotes with large wedge

Quote:

Dichroic mirror quotes are in the wiki.

ATF is pricy.

We got a good price from Laseroptik, but the wedges are 5 arcminutes. The fused silica grade is 0F, meaning the  homogeneity is 5 ppm instead of 1ppm.  I requested an other large wedge quote on the substrates.We may have to get substrates from somebody else and ship it to Germany

MLT quote is outrageously high

REO is not interested in this low volume job.

 

 The Laseroptik quote is here.The 2 degrees wedge cost is $40 on each optics!  See wiki

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

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

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

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

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

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

(I may try hardware rebooting them in this evening)

Quote from #6434

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

 

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

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

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

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

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

Quote from #6421

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

 

  6438   Thu Mar 22 17:41:15 2012 sureshUpdateCDSc1scx and c1scy not properly running

Quote:

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

Quote from #6434

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

 When Steve and I restarted the c1iscex and c1iscey computers after the power shutdown, the models within them did not start-up automatically.  I had to start them manually from a terminal in the control room. 

I also tried rebooting the FB a couple of times.  Did not make any difference.

Manually starting the c1x05, c1scy and c1x01, c1scx models (with the Burt Restore button ON) did not resolve the issue of zeros in the epics screens.  though it did re-establish timing. 

  6439   Thu Mar 22 23:43:56 2012 KojiUpdateCDSc1scx and c1scy not properly running

Did you guys checked if the simplant switch is set to "REAL WORLD" mode?

Edit by KI:

Bingo ! The input signals were bypassed to the simplant. I switched the simplant settings to REAL WORLD and now both end suspensions are working fine.

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

[Suresh / Kiwamu]

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

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

Just be aware of it.

  6441   Fri Mar 23 05:10:46 2012 SureshUpdateIOOBeam Profile measurements: Errors too large to yield good fits.

[Kiwamu, Suresh]

   Today we attempted to measure the beam profile of the REFL beam under two conditions:

              (a) with PRM aligned and ITMs misaligned 

              (b) with PRM misaligned and ITMs aligned

 

The raw data is shown below.  In each of the above conditions we measured in both the vertical (v) and horizontal (h) directions.   The measurements in the vertical direction were better than the ones in the horizontal direction because the optics had a horizontal oscillation which gave larger errors in measurement.

rawdataplot.png

 

Looking at the general trend of these lines it is clear that modes are not matched since the beam reflected by the PRM has a different divergence than that reflected from ITMs.  The beam is also astigmatic as the vertical and horizontal directions have different divergences.

I could find beam parameters only for the Blue line above (Profile in the vertical direction while PRM was aligned).   The fit is quite sensitive to the data points close to the waist, so we need to make better (lower St.Dev.) measurements near the AP table closer to the beam waist.  The intensity with only one ITM aligned is too low and also contributes to the errors.   The beam size is close to 6mm in the horizontal direction, this coupled with yaw oscillations give large errors in this measurement.

Here is the only reliable fit that could be obtained, which is for the prompt reflection from the PRM in the vertical direction

PRM-to-REFL-profile.pdf

The fit function I used is  Beam Dia = Waist { Sqrt [ 1+  ((z + z0)/zr)^2). The fit parameters we get for this data are

z0 = 7.7 m 

Waist = 2.4 mm

zr = 6.9 m

 

Will make another attempt later today...

 

 

 

 

  6442   Sun Mar 25 20:13:31 2012 ranaHowToSUSOptical Lever Servo Tuning thoughts

To start the optical lever filter design, I looked into the noise on ITMY. It should be similar to the other arm cavity optics since they have the same whitening electronics.

The RED/BLUE are with loops open. The MAGENTA/CYAN with loops closed. Looks good; the bandwidth is a few Hz and there is not much peaking,

To figure out the contribution from the dark noise I misaligned the ITMY until the sum on the QPD went to zero. Then I took the spectra of the OL{1,2,3,4}_OUT signals (they all looked the same).

To normalize them properly I took OL4, multiplied it by 2 to account for the incoherent sum of 4 channels and then divided by the nominal SUM (which was 14685 counts). I've left the OL3 un-normalized to show the ratio.

From this plot it seems that the dark noise is not a problem at any frequency (no need to amplify for the new ADCs).

I'm going to use the open loop spectra to design the optimal feedback control. The file is saved as /users/rana/dtt/ITMY_OL-120325.xml

Attachment 1: Untitled.png
Untitled.png
  6443   Mon Mar 26 12:50:24 2012 ZachUpdateelogrestarted with script

On the plus side, it was the first time I've had to do it in a while..

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

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

A conclusion here is :

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

 

In the calculation two cases are considered :

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

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

expected_edit.png

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

Note:

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

 

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

[Suresh / Kiwamu]

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

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

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

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

 

 


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

PRMreflection.png

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

(Discussion)

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

(Some distances)

DSC_4001_small.jpg
 

(Some notes)

We did the following things prior to the measurement.

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

Quote from #6444

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

A conclusion here is :

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

 

ELOG V3.1.3-