[Koji and Kiwamu]

 We did some more vacuum works today. It is getting ready to pump down.

 (what we did) 

 - alignment of the POY mirrors. Now the beam is coming out from the ITMY chamber successfully

  - leveling of the tables (except for the IOO and OMC chamber)

  - realigned the beam axis down to the Y arm because the leveling of the BS table changed the alignments.

 - installed IP_POS mirrors

 - aligned the green beam and made it overlap with IR beam path.

 - repositioned green steering mirrors since one of them are too close to the dark beam path

  Last Saturday I succeeded in damping the ETMY suspension eventually.

This means now ALL the suspensions are happily damped. 

It looked like some combination of gains and control filters had made unstabie conditions.

  I actually was playing with the on/off switches of the control filters and the gain values just for fun.

Then finally I found it worked when the chebyshev filters were off. This is the same situation as Yuta told me about two months before.

Other things like the input and the output matrix looked nothing is wrong, except for the sign flips at ULSEN and SDSEN as I mentioned in the last entry (see here).

So we still should take a look at the analog filters in order to make sure why the signs are flipped.

 [Jenne and Kiwamu]

 We wiped all the test masses with isopropyl alcohol.

They became apparently much cleaner.

(how to)

 At first we prepared the following stuff:

  * syringe

  * isopropyl alcohol 

  * lens papers

  * cleaned scissors

  Then we cut the lens papers into the half by the scissors such that the long side can remain.

This is because that the SOSs have relatively narrow spaces at their optic surfaces for putting a piece of paper. 

   We did vertical and horizontal wiping using the lens paper and appropriate amount of isopropyl alcohol.

Each wiping (vertical and horizontal) requires two or three times trials to appropriately remove dusts.

Amount of isopropyl:

   * vertical 15 [ul]

   * horizontal 10 [ul]

In addition to this, we also used the ionizer gun for blowing big dusts and fiber away from the surface.

(surface inspection)

   Before wiping them, all the test masses had small dusts uniformly distributed on the HR surfaces.

Especially ETMX was quite dirty, many small spots (dusts) were found when we shined the surface with the fiber illuminator.

ETMY was not so bad, only a couple of small dusts were at around the center.  ITMX/Y had several dusts, they were not as dirty as ETMX, but not cleaner than ETMY.

   After we wiped them,  we confirmed no obvious dusts were around the centers of the optics. They looked pretty good !

I stopped the pumping at 9:30 pm. Now we are at 29 torr.

I gave a christmas present to a doubling oven who has been sitting on the PSL table.

The below is a picture of the present I gave. It's a base plate for the doubling oven, made from a block of aluminum, and black-anodized.

The size and the shape are nicely tailored for the combination of the Newfocus kinematic mount and the Covesion oven.

The design had been done by using Solid Works 2010

Here is a picture before he got the present.

Now he looks pretty happy.

Found exactly the same error messages at the end of the log file.

I replaced the final steering mirror (Y1-1037-45-S) in the zig-zag path on the PSL table by a 0 deg mirror Y1-1037-0.

With a sensor card I confirmed the transmission reduced a lot after the replacement.

As we expected, the replacement of the mirror caused a mis-alignment of the incident beam axis to the MC, so I compensated it by touching the angle of the mirror a little bit.

After the alignment of the mirror, the MC is still resonating at TEM00.

We will check the spot positions more accurately by A2L technique.

I connected PZT1 and PZT2 to a slow front end machine c1iscaux.

Now we are able to align these PZTs from the control room via epics.

   Since we removed C1ASC that was controlling the voltage applied on the PZTs, we didn't have the controls for them for a long time.

So Rana and I decided to hook them up to an existing slow front end machine temporarily.

(probably the best solution is to connect them to C1LSC, which is fast enough to dither them.)

We actually found that c1iscaux is the proper machine, because it looked like it used to control the PZTs a long long time ago.

Moreover, c1iscaux still has DAC channels named like C1:LSC-PZT1_X, and so on.

  Below shows a screen shot of the medm screen for controlling the PZTs, invoked from a button on sitemap.adl ( pointed by a black arrow in the picture below)

The current default values are all zero at the right top sliders.

I checked the spot positions on MC1 and MC3 by running Yuta's A2L script.

The amounts of the off-centering were good except for YAW of MC1.

 So we have to adjust the YAW alignment of the beam axis by steering the mirrors at the PSL table.

- - - (measured off-centering) - - - 

MC1_PIT  =  -0.711 mm

MC1_YAW =  1.62 mm

MC3_PIT  =   -0.0797 mm

MC3_YAW  =  - 0.223 mm

This is a connection diagram for the input PZTs (i.e. PZT1 and PZT2).

As drawn in the diagram, the signals don't go through the anti-imaging filter D000186 in the current configuration.

 I checked the triple resonant box for the broadband EOM this afternoon, and found it was healthy.

So I installed it again together with a power combiner and succeeded in locking the MC.

Since the box has a non-50 Ohm input impedance at 29.5 MHz, so it maybe needed to adjust the phase of the LO for the demodulation of the PDH signal.

A good thing is that now we are able to impose the other sidebands (i.e. 11 MHz and 55MHz) via the power combiner.

[Jenne, Zach, Kiwamu]

 We made some efforts to lock the X arm cavity with the infrared beam.

We eventually obtained the PDH signal from a photo diode at AS port, we are still in the mid way of the lock.

The PDH signal now is going into c1lsc's ADC.

We have to make sure which digital channel corresponds to our PDH signal,

(what we did)

- split the LO signal, which comes from a Marconi, just before the EOM into two path.

     One is going to the EOM and the other is going to the AP table for the demodulation, The driving frequency we are using is 11MHz.

- put RF amplifiers to make the RF signal bigger. The raw signal was small, it was about ~-50 dBm in the spectrum analyzer.

   So we connected two ZLN amplifiers. Now the RF signal is at about 0 dBm

- connected the LO and RF signals to a mixer.  Additionally we put a 9.5-11.5 MHz bandpass filter at the LO path since there was some amounts of 29.5MHz due to the RF reflection at the EOM resonant box.

     After a low pass filter by SR560 the signal shows typical PDH behaviors.

- strung a BNC cable which connects the demodulated signal and c1lsc.

    In order to connect the signal to the current working ADC, we disconnected AS166_I from a whitening board and plug our cable on it.

- tried checking the digital signal but we somehow couldn't configure DAQ setting, So actually we couldn't make sure which channel corresponds to our signal.

[Suresh, Kiwamu]

 We eventually succeeded in locking X arm with the infrared beam.

The PDH signal is taken at MCL's ADC instead of c1lsc's, and fedback to MC2_POS through the MCL path.

Right now the lock is not so stable for some reasons, so we need to investigate it more.

(what we did)

 - strung a long BNC cable to connect the demodulated signal and the ADC of c1ioo.

          We didn't touch anything on the demodulation system, so the setup for the demodulation is exactly the same as that of yesterday (see here).

 - disconnected the actual MCL cable from the ADC breakout board at 1X2 rack. And put the demodulated signal onto it.

 - checked the analog dewhitening filter state for the MC2 coil driver, found the analog filter are always off.

  So we just made simDW and invDW always on.

- changed the gain of the MCL loop to have a stable lock for the X arm.

    right now a reasonable setup in the MCL filters are:

         FM1:ON, FM10:ON, G=0.1

 - In fact the lock of the MC is not so stable compared to before, frequently an attempt of locking the X arm leads to the unlock of the MC.

[Rana, Kiwamu]

Here is the list for the daytime tasks of tomorrow, Jan. 12th.

The daytime task is a work basically to be done or quitted before the sun goes down.

Along with the tasks, we roughly assigned the people who are responsible for it.

The tasks below are basically separated from each other, so we can work in parallel.

--- 1.  LSC analog interface check (Joe/Koji)

   * check whitening filter

   * demodulation board check

    * check ADC connections

--- 2.  MC2 coil Dewhitening (Joe)

    * fix binary outputs.

    * FM9 must be the trigger of the binary outputs instead of FM10.

--- 3. 11MHz modulation depth (Kiwamu)

   * investigate why the depth is so low

--- 4. PEM DAQ name issue (Jenne)

   * change the name of seismic channels properly so that we can deal with the calibrated stuff

--- 5. phase adjustment for MC-PDH locking (Suresh)

--- 6. medm screens for C1LSC ()

    * make screens

I briefly checked the MC2 analog dewhitening filters.

It turned out that the switching of the dewhitening filters from epics worked correctly except for the UR path.

I couldn't get a healthy transfer function for the UR path probably because the UR monitor at the front panel on either the AI filter or the dewhitening filter maybe broken.

Need a check again.

 [Koji, Kiwamu]

 We succeeded in locking the X arm with the C1LSC digital control.

As we did on the day before yesterday, the feedback signal goes to MCL (#4141), but this time the signal is transfered from C1LSC through the RFM.

 (key points) 

- checking the state of the analog whitening filters at C1LSC rack.

   We took the transfer function of them and found that they were always on regardless of the clicking any buttons on medm.

To cancel the filter shape of the whitening, we put an unWhitening filter so that these transfer functions becomes flat in total.

The whitening filter approximately has : pole:150Hz, pole:150Hz, zero:15Hz, zero:15Hz (although these numbers came from by our eye ball fitting)   

 - demodulation phase adjustment

   We performed the same measurement as that of Suresh and Koji did yesterday (#4143) to adjust the phase of the PDH demodulation.

By changing the cable length we roughly adjusted the I-phase to eventually ~10 deg, which is close enough to 0 deg.

(probably some more efforts should be made as a part of daytime tasks)

Note that we are currently using the REFL33 demodulation board for this purpose (#4144). The LO power we put is about 16dBm.

The angle between I and Q at 11MHz is actually almost 90 deg.

This fact has been confirmed by putting a sinusoidal signal with a slightly different frequency (~100Hz) from that of the LO onto the RF input.

 - attenuation of RF signal

  Since the PDH signal taken by C1LSC's ADC had been saturated somewhat, we introduced a ND filter of 10 on the photo diode to attenuate the RF signal.

As a result the amplitude of the PDH signal on dataviewer became more reasonable. No more saturations.

(some notes)

 unWhitening filter           pole:15Hz. pole:15Hz, zero:150Hz, zero:150Hz

 C1LSC_MC_FM1   pole:1kHz, zero:10Hz

 Gain in digital control       G ~ -1

measured UGF  ~  200-300 Hz

 measured RFM delay ~ 125 usec 

Here shows a plot of the expected open loop transfer function (TF) for the X arm locking.

I assume that the delay time of the digital system associated with the ADC/DAC and the digital filtering process is ~100 usec independently from the RFM delay according to Yuta's measurement (#3961).

Also I assume the MC2 pendulum has a pole at 1Hz with Q of ~5, and the X arm has its cavity pole at ~3kHz.

When the lock acquisition takes place, we used the red curve shown above in order to avoid a big DC feedback onto MC2.

Once the X arm became resonant at TEM00, we manually switched FM3 on, which is a boost filter containing a pole at  1Hz and a zero at 50Hz in order to suppress the residual motion below 1Hz.

The expected curve for the boosted state is drawn by the blue curve in the plot. 

With this open loop TF, the UGF can be realized only around 100-300 Hz due to the phase margin condition.

This expectation of the UGF is consistent with our measurement because we obtained the UGF around 200-300Hz.

In fact above 300Hz we observed that the control became unstable and started oscillating.

 I summarized how we proceed our green locking in this month on the wiki.

Since step1 and 2 shown on the wiki are mostly done apparently, so we will move on to step 3-D and 3-E.

A short term target in the coming couple of days is to phase lock the VCO to the beat note.

Here is another trick for the DAQ setup when you add a DAQ channel associated with a new front end code.

 Once you finish setting up the things properly according to this wiki page (this page ), you have to go to 

      /cvs/cds/rtcds/caltech/c1/target/fb

and then edit the file called master. 

This file contains necessary path where fb should look at, for the daqd initialization.

Add your path associated with your new front end code on this file, for example:

        /opt/rtcds/caltech/c1/chans/daq/C1LSC.ini

       /opt/rtcds/caltech/c1/target/gds/param/tpchn_c1lsc.par

After editing the file, restart the daqd on fb by the usual commands:

             telnet fb 8088

             shutdown

 I found that c1scy was not running due to a daq initialization error.

 I couldn't figure out how to fix it, so I am leaving it to Joe.

 I connected the PLL signal to the ADC on c1ioo. 

So now we are able to take the data into the digital world, and will be able to feedback signals to the suspensions.

 The output signal from the VCO box goes to a black beakout board on 1X2 rack though a BNC cable.  

Then the signal comes out from the back side of the board with DB39 style, so I put a DB39 to SCSI adapter so that we can take it to the IO chasis.

Now the SCSI is connected to ADC_1 (the second ADC card) on the IO chasis at 1X1. 

  Additionally I modified the green locking simulink model, C1GCV, in order to pick the right ADC channels.

A medm screen for green locking is now under the construction. I put a link on the sitemap screen, so anyone can look at the half-baked green locking screen.

Any comments and suggestions are really welcome.

I realized that the black AA board I mentioned on the last entry has the same range issue as Valera reported before (see #3911). 

Basically our ADC card has +/- 10V input range, but on the other hand the AA board is already limited by approximately +/- 2V.

We have to fix it.

 [Suresh, Kiwamu]

  We did the following things:

     - installed a 1/10 voltage divider such that the signal won't be saturated at the AA board (see here)

     - put a Ithaco preamplifier 1201 as a whitening filter

     - checked the entire beat detection system without using the real beat note

Here are some items to be done before the sun goes down tomorrow:

       - calibration of ADC and the interfaces including the voltage divider and the whitening filter.

     - fine matching of unwhitening filter at the digital side

         - PLL response measurement ( freq to voltage response ) over the frequency range of interest

         - plotting an well calibrated spectrum of the PLL output 

(whitening filter)

The Ithaco 1201 was setup to have a zero at 0 Hz and two poles at 0.1 Hz and 10 Hz in order to emphasize the signal over the frequency range of interest.

Around 1Hz it is supposed to have a gain of 1000. These settings have done by tweaking the knobs on the front panel of the Ithaco 1201.

In addition to that, we made an unwhitening filter in digital filter banks. This filter was designed to cancel the analog whitening filter.

(system check) 

 To check the entire beat detection system, we phase-locked the VCO to a Marconi running at 80 MHz, which is the center frequency of the VCO.

Then we imposed a frequency modulation on the Marconi to see if the signal is acquired to ADC successfully or not. It's quite healthy.

According to the spectra corrected by the unwhitening filter, we confirmed that the noise floor at 1Hz is order of 1Hz/sqrt Hz, which is already quite good.

Then we took several spectra while putting a modulation on the Marconi at a different frequency in each measurement.

The peak due to the artificial modulation essentially works as a calibration peak in the spectra.

So in this way we briefly checked the flatness of the response of the system in the frequency domain.

As a result we found that the response is not perfectly flat in the range of 0.05 - 30Hz, probably due to a mismatch of the combination of the whitening and unwhitening filters.

We will check it tomorrow.

[Rana, Suresh, Kiwanu]

 We did the following things:

   *  taking the VCO stability data from the error signal instead of the feedback

   *  tried calibrating the signal but confused

   *  increased the modulation depth of the green end PDH.

--

 We found that a cable coming out from the VCO box was quite touchy. This cable was used for taking the feedback signal.

When we touched the cable it made a big noise in the feedback. So we decided to remove the cable and take the signal from the error point (i.e. just after the mixer and the LPF.)

In order to correct that signal to the one in terms of the feedback signal, we put a digital filter which is exactly the same as that of the PLL (pole at 1.5 Hz, zero at 40 Hz, G=1) .

However for some reasons the signal shown in the digital side looked completely mis-calibrated by ~ 100. We have no idea what is going on.

Anyway we are taking the data over tonight because we can correct the signal later. The 2nd round data started from AM1:40

I succeeded in green-locking the X arm by feeding back the beat signal to ETMX.

Here are some quick reports. Some more details will be posted tomorrow.

The below shows a time series data of the PLL feedback signal when the servo was acquiring the lock.

At t = -2 sec. I started feeding back the signal to ETMX with the gain 50 times smaller than its nominal.

Then at t = 0 sec.I switched on a low frequency boost (pole 0.1Hz and zero 1Hz) to make it more robust.

At t = 3 sec. I increased the gain to the nominal.

Finally the UGF became ~ 60 Hz according to my open loop measurement by diaggui.

However I couldn't make the UGF higher than 60Hz because the more gain caused a instability for some reasons.

Here is a diagram for the green locking.

I used the same VCO box as we setup on the last Friday (see #4189).

Well, the diagram I drew is true. I also have been confused by this 1/f^2 issue in our PLL.

As Rana pointed out, the open-loop TF should become 1/f^2 over most of the frequency range, but it still remains 1/f above 5kHz for some reasons. 

 Need more investigations.

 At the beginning I tried phase-locking the VCO to the beat note without any external filters (i.e. SR560 see here), but I never succeeded.

It was because the hold-in range of the PLL was not sufficiently wide, it could stay locked within frequency range of less than +/- 1MHz from the center frequency of 80 MHz.

This is obviously not good, because the beat note typically fluctuates by more than +/- 3MHz in time scale of 1 sec or so.

  So I decided to put an external filter, SR560,  in order to have a larger DC gain and a higher UGF.

Somehow I unconsciously tuned the SR560 to have a pole at 1Hz with the gain of 2000, which shouldn't work in principle because the open-loop will be 1/f^2.

However I found that the PLL became more robust, in fact it can track the input frequency range of +/- 5MHz.

The open-loop TF is shown above. For comparison I plotted also the open-loop TF wehn it's without the SR560.

I checked the frequency of the VCO output when it was phase-locked to a Marconi, it was healthy (i.e. the same frequency as the input signal from Marconi).

 I haven't yet taken any data for the IR fluctuation when the Xarm is locked by the green locking.

You are right, the DC drift was due to a lack of the DC gain. But don't worry about that, because this issue has been solved.

(DC gain issue)

  The lack of DC gain was because I put an IIR filter called ''DC block" that I made. It has 1/f shape below 30mHz and becomes flat above it.

The purpose of this filter was to avoid a DC kick when it starts feeding back to ETMX.

Usually the output signal from the PLL has an offset, typically ~5V, then this offset is also acquired into the ADC and eventually kicks ETMX through the feedback.

So when I took the time series data I enabled the 'DC block', that's why it drifts slowly.

 After taking the time series, I found that without this 'DC block' technique, the lock can be achieved by appropriately subtracting the offsets with epics numerical values.

This subtraction technique, of course, gave me more stable lock at DC.

(open loop transfer function)

Here is the open-loop TF of the arm locking I measured last night:

The IIR filter chain has the following poles and zeros:

     pole 0.1Hz, 1000Hz,

   zero 1Hz, 30Hz

For the fitting I assume that the ETMX pendulum has a resonance at 1Hz with Q of 5. Also I put the cavity pole at 24 kHz, assuming the finesse is 80 at 532 nm.

I just fitted the gain and the time delay by my eyes.

If I believe the result of the fitting, whole time delay is 330 usec, which sounds pretty large to me.

I scanned the X arm by changing an offset for the feedback to ETMX while the arm stayed locked by the green locking.

But the resultant plot is still far away from a beautiful one.

Changing the offset broke the lock frequently, so eventually I couldn't measure the stability of the IR-PDH signal at the resonance. 

 The plot above is a result of the scanning. You can see there is a clear resonance at the center of the plot.

However the lock frequently became unstable when I was changing the offset.

It looked like this unstability came from the end PDH lock. I guess there are two possible reasons:

  (1)  feedback range for the laser PZT is not wide enough. Right now the range is limited by a SR560, which has been used for a summing amplifier.

  (2)  Length to Alignment coupling. Pushing ETMX causes a misalignment.

The issue (1) can be easily solved by engaging the temperature feedback, which helps actuating the laser frequency a lot at DC.

The issue (2) will be also solved by well align the IR beam, the arm cavity and the green beam.

Here are some tasks that I want someone to work on during my absence.

1. Y-arm alignment for IR

 Basically we gradually have to move onto the Y-arm locking at some point.

Prior to it we need to align the Y arm for IR. Probably we have to touch PZT1 and PZT2.

It would be very nice if the X-arm alignment also gets improved together with this work. 

2. Temperature feedback with a digital control for X end PDH lock

  Need a temperature feedback not with an analog way but with a digital way because we want to put an offset and the feedback signal at the same time (#4198).

 Right now the temperature control input of the laser is connected to a slow DAC (#3850).

Probably we should plug the feedback signal from the PDH box to the fast ADC (i.e. c1iscex), and then connect a fast DAC to the laser temperature.

This entry maybe helpful.

3. Calibration of optical gain for IR arm locking

 In order to evaluate the performance of the green locking, one of the key points is the IR PDH signal.

Because it tells us how much the motion of the X arm is suppressed at IR when the green lock is engaged.

To get this information in m/sqrtHz, we need to know the optical gain.

4. MC servo characterization and PSL frequency noise measurement

 SInce the green beat note tells us the frequency difference between the MC and the arm in the current configuration, we should know how the MC servo is.

Along with this work, I need someone to measure the PSL frequency noise, when it is locked to the MC over the frequency range from 0.01Hz to 1kHz.

5. PLL characterization 

 Solve this issue (#4195) and make it reliable.

 Yesterday I moved the whole green electronics stuff, which had been sitting on the floor at the X end,  into a new electronics rack.

The rack now is placed under the cable rail close to the ETMX chamber.

 I repeated the same measurement as that Koji did before (see here) with the mixer-based frequency discriminator.

The frequency fluctuation of the beat note is now 50 kHz in rms integrated down to 0.1 Hz, which is a bit better than before.

However there still is the same undesired structure in the spectrum below 10 Hz.

Fig.1 power spectra of the green beat note fluctuation in terms of frequency fluctuation.

   Red curves were taken when the IR was locked to the MC, and the green was locked to the X arm.

Blue curves were taken when both the IR and the green were locked to the X arm.

Black curve was also the one taken when the IR and the green were locked to the X arm, but showing the lower noise level.

I have no idea what exactly was going on when I took the black curve, but this noise level sometimes showed up.

The discrepancy may come from a kind of calibration error although I kept using the same calibration factor to convert the data from count to frequency.

Need more investigations.

 Additionally Koji and I took the coherence between the beat fluctuation and the transmitted lights of both the IR and the green.

It showed a strong coherence at 1 Hz, which is one of the dominant noise of the beat note.

This probably indicates that the 1 Hz peak is produced by a coupling from amplitude fluctuation.

 For monitoring the green transmitted light, I used the Jenne's PD (see here)

The amounts of the X arm's beam off-centering have been measured by the A2L technique.

So now we are able to start aligning the IR beam axis in a quantitative way.

(motivation)

 Since we saw big residual motions at 1 Hz, 16 Hz on both the green beat note signal and the IR PDH signal (see #4268 and #4211),

we are suspecting that these noise come from an angle to length coupling.

In order to minimize the angle to length coupling, one thing we can do is to bring the beam spots to the center of ITMX and ETMX more precisely.

To do it, we have to quantitatively know how well the beam spots are on the center of the optics. Therefore I started measuring the amount of the beam off-centering.

(method)

 The A2L technique was used to measure the off-centering with the real-time lockin system, which has been recently embedded in the real-time code by Joe (see #4265).

The idea is the same as Yuta did before (see #3863).

But this time the excitation signal from the real-time oscillator was injected directly to the coil matrix on either ITMX or ETMX, at 18.13 Hz with the amplitude of about 400 cnt.

When the IR laser stays locked to the X arm, the LSC feedback signal is demodulated with the oscillator signal.

This demodulated signal gives the amount of the off-centering.

For this purpose I modified Yuta's A2L script such that we can use it also for the X arm.

(results)

 I obtained the following values:

     - ETMX

         PIT  = -1.61 mm

         YAW =  -0.918 mm

    - ITMX

         PIT = -3.76 mm

        YAW = -2.24 mm

I used the same calibration factor as that of Koji calculated (see #3020) for MC, in order to convert the results from the coil gain to the off-centering.

These values are consistent with the spots appearing on the CCD monitors.

I found that the ADC channels for IP_ANG had been assigned to a wrong machine.

IP_ANG is supposed to be acquired at c1auxey (east end), but actually it had been at c1auxex (south end).

This is the reason why we couldn't see any signals from IP_ANG.

So I fixed it by editing the db files (i.e. ETMXaux.db and ETMYaux.db). Now it seems working fine.

This mistake obviously came from the X-Y name swapping business. Something else might be still wrong.

It turns out there are no reasonable signal from the segment 1 on the IP_ANG QPD.

For right now I can still use it as a funny QPD, but I absolutely need somebody to check and fix it in a daytime.

Rana and I found that the QPD for the optical lever at X end are showing small signals.

At this moment each of the segments exhibits approximately 200 counts when the oplev beam is centered.

These small numbers may be due to the coating of ETMX, but we are not sure.

Probably we have to increase the gain of the QPD depending on situations.

So a set of the tomorrow's daytime task is:

   1. check the trend data of the QPD outputs to see how much signals were there in the past.

   2. check the whitening filters to make sure if it's on or off.

   3. If it's necessary, increase the gain of the QPD to have reasonable readouts.

I am going to ask somebody to do this task.

I tried aligning the IR beam axis for the X arm to have good beam centering on ITMX and ETMX.

As a first attempt, I started translating the beam upward by steering PZT1 and PZT2, since the pitch was quite off from the center on ITMX.

As a result I could decrease the pitch off-centering down to about 0.5 mm on ITMY, but on the other hand TRX decreased a lot (by a factor of 4).

I am worrying if something in the central part of IFO might be clipping the beam.

(notes)

When I was touching PZT1 and PZT2, I payed attention on IP_ANG so that I don't lose a beam spot on IP_ANG.

As long as the beam is on the IP_ANG QPD, the angle of the beam should not be so much different.

Each time after I touched the PZTs, I realigned ITMX and ETMX to maximize the transmitted light.

In this way I proceeded the alignment by changing the PZT offsets little by little while keeping the X arm locked always.

At the beginning, all the PZT offsets were zero. And at the end of this work they became:

 C1:LSC-PZT1_Y = 1.880

 C1:LSC-PZT2_Y = -1.699

But during this alignment work TRX gradually decreased eventually down to 0.25, which had been 1 at the beginning (TRX is calibrated by dividing it by its maximum power).

Along with this TRX reduction, I found that the optical gain also decreased by a factor of about 5.

This fact has been confirmed by intentionally increasing the filter gain such that the servo oscillates at the UGF.
 

I think this week is going to be an "alignment week".

The goal is to get a good alignment on X arm for both the green and the IR beam in order to reduce a2l couplings.

Today's missions are :

 - fixing the oplev channel names (see here)

 - fixing the oplev gain issue (see here)

 - engage the oplev servos

 - f2p adjustment

 - make a realtime lockin model for the f2p measurement and the dithering technique

 - alignment of the MC incident beam  (because we installed a new PMC this morning)

 - manual alignment of the IR beam by steering PZT1 and PZT2 (this procedure will be replaced by an automatic way soon)

 - bounce roll filters (see here)

[Jenne and Kiwamu]

 This time we aligned the vertical angle (not the translation) of the IR beam so that the transmitted light from BS shoots the center of ETMY.

The idea is to use ETMY as a beam pointing reference instead using IP_ANG, assuming the translation is not so bad.

As a result it looks like we are wining. A quick A2L test on ITMX_PITCH showed a small off-centering at sub-milimeter level.

 We are concluding that the initial beam after PZT2 had been pointing downward somehow.

Before doing this whole job, we checked the spot shape on IP_POS to see if the beam is clipped or not. It was a round shape, which means no clipping around MMT.

But on the other hand, the spot on IP_ANG had been clipped more than half of its bottom as Suresh reported on his elog (see here).

I found that this clipping is able to be fixed by moving the beam angle upward. I guess the clipping happened at one of the steering mirror in the ETMY chamber.

According to these information, we imagined that the beam was somehow pointing downward after PZT2.

So we started aligning the beam by touching only PZT2 for vertical direction. Then we found a beam spot on ETMY's suspension frame, and brought it to the center.

Then we aligned BS and X arm for this new beam axis. The it resulted a small off-centering on pitch.

Once the MC fully gets back, we will examine the TRX degradation with this configuration.

Let's share our tasks !

==== daytime ===

 . mode matching for MC  (Jenne/Koji)

 . mode matching for doubling crystal on PSL table (Suresh/Koji)

 . f2p adjustment (Kiwamu)

 . fix daq and CDS issues (Joe)

 . increase oplev gain (low priority)

 . make ITMY camera nicer (Steve)

 . c1ass simlink model (Valera/Joe)

 . Bounce Roll notches (Suresh)

==== nighttime (after 7pm) ====

 . align everything   (at first green beam, then X arm cavity and finally IR beam)

 . update the noise spectrum of the green locking

 . estimate the noise from angle to length coupling

THANK YOU, JOE !!! 

DAYTIME

  -  more precise F2P measurement and modify lockin simlink model (Kiwamu)

  -  run  C1ASS to check it (Valera)

  -  take care of CDS (Joe)

  -  MC mode matching (Jenne/Koji)

   -  RF stuff  (Suresh)

  -  mode matching for doubling crystal at PSL table (low priority)

  -  OPLEV (low priority)

NIGHITTIME

 -  update the noise spectra of green locking

 -  make noise budgets

[Koji and Kiwamu]

 We took transfer functions (TF) from the angle excitations at ETMX and ITMX to the green beat note signal (i.e. angle to length TF).

It turned out that the coupling from ETMX_PIT is quite large.

I wonder how f2p of the ETMX changes this coupling. We'll see.

The plot above shows a set of the transfer functions from the angle excitation to the green beat note.

Note that the y-axis has not been calibrated, it is just a unit of counts/counts.

You can see that the TF from ETMX_PIT to the beat (red cruve) is larger than the others by about a factor of 10 over most of the frequency range.

This means that any PIT motions on ETMX can be coupled into the green beat signal somewhat over the wide frequency range.

It looks having a resonance at 1.5 Hz, but we don't exactly know why.

At that time the coil gains on only ITMX were tuned by applying f2p filters, but ETMX wasn't because of a technical reason coming from epics.

- - - - measurement conditions

  * PSL laser was locked to X arm by feeding back the IR PDH signal to MC2.

  * the green laser was locked to Xarm as usual.

  * took the green beat note signal (approximately 0 dBm) into Rana's MFD with the cable length of about  6 m.

  * the output from the MFD was connected to XARM_COARSE channel without a whitening filter.

  * excitation signal was injected into either ASC_PIT or ASC_YAW. The excitation was Gaussian noise with frequency band of 10 Hz and amplitude of 300 counts.

  * only ITMY had the f2p filters, which balance the coil gains all over the frequency.

The f2p measurements are done on ETMX and ITMX with the real time lockin systems.

I don't explain what is the f2p measurement in this entry, but people who are interested in it can find some details on an old elog entry here or somewhere on DCC.

So far the resultant filters looked reasonable compared with the previous SRM f2p filters.

- backgrounds -

  Some times ago I found that the coils on ETMX had not  been nicely balanced, and it made a POS to angle coupling when I tried green locking (see here).

In addition to that, accuracy of A2L kind of measurement including the dithering techniques depend on how well the coils are balanced.  Therefore we need to balance the coils basically at all the suspended optics.

There used to be a script for this particular purpose, called f2praio.sh. This script does measure the imbalances and then balance the coils.

However this time I used the realtime lockin system to measure the imbalances instead of using the old f2p script.

One of the reasons using the real time system is that,  some of the ezca and tds commands for the old script don't work for some reasons.

Therefore we decided to move on to the real time system like Yuta did for the A2L measurement a couple of months ago.

The f2p measurement finally gives us parameters to generate a proper set of filters for POS and also the coil gains. We apply those filters and the gains in order to eliminate the POS to angle coupling and to balance the coils.

- results -

The followers are the resultant filters and coil gains.

The plots below show new f2p filters according to the measurement.

ITMX (assuming pendulum POS has f0 = 1 Hz and Q = 1)

ULPOS  fz = 1.009612   Qz = 1.009612 

URPOS fz = 1.125965   Qz = 1.125965  

LLPOS  fz = 0.873725   Qz = 0.873725    

LRPOS  fz = 0.974418   Qz = 0.974418  

C1:SUS-ITMY_ULCOIL_GAIN      -1.103044

C1:SUS-ITMY_URCOIL_GAIN      0.884970

C1:SUS-ITMY_LLCOIL_GAIN      0.950650

C1:SUS-ITMY_LRCOIL_GAIN      -1.060326

ETMX (assuming pendulum POS has f0 = 1 Hz and Q = 1)

ULPOS  fz = 1.055445   Qz = 1.055445   

URPOS  fz = 1.052735   Qz = 1.052735   

LLPOS  fz = 0.944023   Qz = 0.944023   

LRPOS  fz = 0.941600   Qz = 0.941600   

C1:SUS-ETMX_ULCOIL_GAIN      -0.887550

C1:SUS-ETMX_URCOIL_GAIN      1.106585

C1:SUS-ETMX_LLCOIL_GAIN = 1.07233

C1:SUS-ETMX_LRCOIL_GAIN      -0.931013

The precision of the coil gains looked something like 1% because every time I ran the measurement script, the measured imbalances fluctuated at this level.

The precision of the filter gain at DC (0.01 Hz) could be worse, because the integration cycles for the measurement are fewer than that of the coil gains done at high frequency (8.5 Hz).

Of course we can make the precisions by increasing the integration cycles and the excitation amplitudes, if we want to.

 The plot below shows how the f2p filters work.

At -2 min I turned on the f2p filters.

New noise spectra of the green locking have been updated.

The plot below shows the in-loop noise spectra when the beat signal was fedback to ETMX.

The rms noise integrated from 0.1 Hz to 100 Hz went down to approximately 2 kHz.

The red curve was taken when the beat was controlled only by a combination of some poles sand zeros on the digital filter banks. The UGF was at 40Hz.

This curve is basically the same as that Koji took few weeks ago (see here). Apparently the rms was dominated by the peaks at 16 Hz and 3 Hz.

The blue curve was taken when the same filter plus two resonant gain filters (at 16.5 Hz and 3.15 Hz) were applied. The UGF was also at 40Hz.

Due to the resonant gain filter at 16.5 Hz, the phase margin became less, and it started oscillating at the UGF as shown in the plot.

Two different measurement have been performed for a test of the green locking last night.

Everything is getting better. yes. yes.

[ measurement 1 : IR locking]

The X arm was locked by using the IR PDH signal as usual (#4239,  #4268) .

The in-loop signal at from the IR path and the out-of-loop signal at from the green beat note path were measured.

Let us look at the purple curve. This is an out-of-loop measurement by looking at the green beat note fluctuation.

The rms down to 0.1 Hz used to be something like 60 kHz (see here), but now it went down to approximately 2 kHz. Good.

This rms corresponds to displacement of about 260 pm of the X arm. This is barely within the line width. The line width is about 1 nm.

[ measurement 2 : green locking]

The motion of the X arm was suppressed by using the green beat signal and feeding it back to ETMX.

After engaging the ALS servo, I brought the cavity length to the resonance by changing the feedback offset from epics.

Then took the spectra of the in-loop signal at the beat path and the out-of-loop signal at the IR PDH path.

 Here is a time series of TRX after I brought it to the resonance.

TRX was hovering around at the maximum power, which is 144 counts.

Since I put one more 10:1 filter to suppress the noise around 3 Hz, the rms of the in-loop beat spectrum went to about 1 kHz, which used to be 2 kHz (see #4341).

But the out-of-loop (IR PDH signal) showed bigger noise by a factor of 2 approximately over frequency range of from 2 Hz to 2 Hz. The resultant rms is 2.7 kHz.

The rms is primarily dominated by a peak at 22 Hz (roll mode ?).

I calibrated the IR PDH signal by taking the peak to peak signal assuming the finesse of the cavity is 450 for IR. May need a cooler calibration.

I forgot to mention about the whitening filter for the ALS digital control system.

As usual I used a whitening filter to have a good SNR against ADC noise, but this time our whitening scheme is little bit different from the usual our systems.

I used two ADC channels for one signal and put a digital summing point  and digital filters to keep good SNR over the frequency range of interest.

It's been working fine but it's still primitive, so I will study more about how to optimize this scheme.

     The diagram above shows our scheme for the signal whitening.

Basically the SNR at DC is bad when we use only a whitening filter as shown on the bottom part of the diagram because the signal is quite tiny at DC.

On the other hand if we take raw signal into ADC as 'DC path'  shown above, the SNR is better at DC but not good at intermediate frequencies (30 mHz - 1kHz).

So the idea to keep the good SNR over the frequency range of interest is to combine these 'DC path' and 'AC path' in a clever way.

     In our case, the 'DC path' signal is not as good as the 'AC path' signal above 30 mHz, so we cut off those high frequency signals by using a digital low pass filter.

In addition to it, I put a gain of 1000 in order to match the relative gain difference between 'DC path' and 'AC path'.

Then the resultant signal after the summing point keeps the good SNR with a flat transfer function up to 1 kHz. 

In this past weekend I replaced a summing amplifier for the end green PDH locking by a home-made summing circuit box in order to increase the control range.

It's been working well so far.

However due to this circuit box, the demodulation phase of the PDH locking is now somewhat different from the past, so we have to readjust it at some point.

(background)

    At the X end station, the voltage going to the NPRO PZT had been limited up +/- 4 V because of the summing amplifier : SR560.

Therefore the laser was following the cavity motion only up to ~ +/- 4 MHz, which is not wide enough. (it's okay for night time)

So we decided to put a passive circuit instead of SR560 to have a wider range.

(summing box)

   We made a passive summing circuit and put it into a Pomona box.

The circuit diagram is shown below. Note that we assume the capacitance of the 1W Innolight has the same capacitance as that of the PSL Innolight (see #3640).

The feedback signal from a PDH box goes into the feedback input of the circuit.

Then the signal will be low passed with the corner frequency of 200 kHz because of the combination of RC (where R is 681 Ohm and C is capacitance of the PZT).

Because of this low pass filter, we don't drive the PZT unnecessarily at high frequency.

On the other hand the modulation signal from a function generator goes into the other input and will be high passed by 50 pF mica capacitor with the corner frequency of 200 kHz.

This high pass filter will cut off noise coming from the function generator at low frequency.

In addition to it, the 50 pF capacitor gives a sufficient amount of attenuation for the modulation because we don't want have too big modulation depth.

Here is a plot for the expected transfer functions.

You can see that the modulation transfer function (blue curve) has non-zero phase at 216 kHz, which is our modulation frequency.

-- Alignment

     - C1ASS

     - MC WFS 

    - OPLEVs

-- Optimization of Suspended Optics

  - diagonalizations

  - damping control

  - upgrading of electronics

   - weekly check

-- Input Optics

   - PMC

         * mode matching
         * epics LO HI values

   - FSS and ISS

        * recover FSS
        * make ISS working

   - EOM

   - doubling and RFPD for green

-- Length Sensing and Control

   - digital system and electronics

-- Green Locking

    - X end station

    - Y arm green locking ==> Suresh/Bryan

    - digital control systems

      - noise budget

   - cavity scan and handing off

-- misc.