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.

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.

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?

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., w_0ix ≠ w_0iy, z_0ix ≠ z_0iy) and allows for transforming to an elliptical waist  (i.e., w_0fx ≠ w_0fy, but z_0fx = z_0fy). It would be straightforward to allow for z_0fx ≠ z_0fy, 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 .

 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

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

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

Adding some more results with more realistic RAM level assumption.

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

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

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

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

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.

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.

LOCKIN detection

• The LOCKIN oscillator excites ITMs differentially
  • In order to purely excites the MICH DOF, the actuation coefficients were precisely adjusted (#6398).
  • Currently ITMY has a gain of 1, and ITMX has a gain of -0.992 for the pure MICH excitation. Those numbers were put in the output matrix of the LOCKIN oscillator.
• The demodulation phase of the LOCKIN system was adjusted to be -22 deg at the digital phase rotator.
  • This number maximizes the in-phase signals while the quadrature-phase signals give almost zero.
  • This number was adjusted when the simple MICH configuration was applied.
• In the demodulations, the LO signals have amplitude of 100 counts to just make the demodulated signals readable numbers.

Calibration of the LOCKINs

Calibration of the responses to watts/meter

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

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.

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)

(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.

(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)

[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.

(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

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 ..

 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.

(Tricks)

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]

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.

A correction on the previous elog about the REFL33Q noise:

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.

 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.

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

 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. 

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

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

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.

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.

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 R_PRM R_MI
(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.

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 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

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.

 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.

 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?

 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 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
 

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.

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

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.

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.

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.  

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.

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

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)

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)

 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. 

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.

[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.

[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.

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

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...

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

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

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. 

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.

[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. 

(Discussion)

• 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)

(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.