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ID Date Authorup Type Category Subject
  4398   Thu Mar 10 14:22:58 2011 kiwamuUpdateGreen LockingIntensity noise limits the beatnote sensitivity

The next steps we should do are :

    - to investigate a cause of the intensity fluctuation
          * end green laser
          * suspensions' angular motions
          * doublecheck the RIN contribution if it's from the PSL or the X arm in the beatnote RFPD to make sure the RIN is dominated by the X arm transmitted light
    - to think about how to make the system insensitive to the intensity noise
          - bring the beat frequency to the zero cross point of the MFDs ?
          - PLL ?


We are limited by the intensity noise of the X arm transmitted green light.

  4411   Fri Mar 18 12:22:04 2011 kiwamuUpdateGreen LockingY arm plan for today

 Prior to the works on the Y end setup I propose to perform the temperature scan business like Koji and Suresh did before (see this entry).

This business will allow us to easily find a beatnote at 532nm after the installation on the Y end.

 I guess the right persons for this work are Bryan and Suresh.

Bryan will have a safety guidance from Steve in this after noon. So after that they can start working on it.


/* - - - coarse plan - - - */

* remove Alberto's laser from the AS table

* setup Alberto's laser on the PSL table

* put some stuff such as lenses, mirrors and etc. (Use the IR beam picked off after the doubling crystal for the main laser source)

* mode matching

* measurement


Which laser are we going to use,  Alberto's laser or MOPA laser ?

  4412   Fri Mar 18 14:18:00 2011 kiwamuSummaryGeneralnew laser pointers

Just for a record. We got 4 new laser pointers (2 greens, 1 blue, and 1 green and red combination). Don't lose them.

They reside in a bucket on the SP table, where IR viewers and sensor cards also reside.


  4413   Fri Mar 18 16:06:30 2011 kiwamuUpdateGreen LockingRe: Y arm plan for today

We use Alberto's laser for the Y end Green Locking.


 Which laser are we going to use,  Alberto's laser or MOPA laser ?


  4419   Mon Mar 21 16:49:11 2011 kiwamuSummaryGreen Lockingplan for this week

- Plan for this week

  * Intensity stabilization for the end green laser (Matt / Kiwamu)

  * Hand off the servo from Green to Red (Matt / Kiwamu)

  * Y end green locking (Suresh / Bryan) (rough schedule)

  * Reconnect the X end mechanical shutter to 1X9 (Kiwamu)

  * Connect the end DCPD signal to a DAC (done)

  * Make a LPF in a Pomona box for the temperature (Larisa)

  * Clean up and finalize the X end setup (Kiwamu)

  * Make a item lists for electronics. Order the electronics. (Aidan / Kiwamu)

  4420   Mon Mar 21 18:34:10 2011 kiwamuUpdateGreen Lockingadded a new ADC channel on 1X9

I added a new ADC channel for a DC signal from the X end green PD.

It is called C1:GCX-REFL_DC and connected to adc_0_1, which is the second channel of ADC_0.


By the way, when I tried connecting it to an ADC I found that most of the channels on the AA board on 1X9 were not working.

Since the outputs form the board are too small the circuits may have benn broken. See the picture below.

In addition to that  I realized that the signal from the PDH box for the temperature actuation is limited by +/- 2V due to the range of this AA board.

In fact the signal is frequently saturated due to this small voltage range.

We have to enlarge the range of this AA board like Valera did before for the suspensions (see this entry).


  4421   Tue Mar 22 00:01:25 2011 kiwamuSummaryGreen Lockingplan for daytime tasks

Some tasks for the daytime tomorrow.

  * Beam profile measurements of the Y end laser  (Suresh / Bryan)

  * Taking care of CDS and the simulated plant (Jamie / Joe)

  * Reconnect the X end mechanical shutter to 1X9 (Kiwamu)

  * LPF for the X end temperature feedback (Larisa)

  4424   Tue Mar 22 16:39:51 2011 kiwamuUpdateGreen Lockingcomaprator installed : 80 pm residual displacement

 A comparator has been installed before the MFDs (mixer-based frequency discriminator) to eliminate the effect from the amplitude fluctuation (i.e. intensity noise).

As a result we reached an rms displacement of 580 Hz or 80 pm.


(differential noise measurement)


  Here is the resultant plot of the usual differential noise measurement.

The measurement has been done when the both green and red lasers were locked to the X arm.

In the blue curve I used only MFD. In the black curve I used the combination of the comparator and the MFD.

Noise below 3 Hz become lower by a factor of about 4, resulting in a better rms integrated from 40 Hz.

Note that the blue and the black curve were taken while I kept the same lock.

A calibration was done by injecting a peak at 311 Hz with an amplitude of 200 cnt on the ETMX_SUS_POS path.



  Yesterday Koji modified his comparator circuit such that we can take a signal after it goes thorough the comparator.

The function of this comparator is to convert a sinusoidal signal to a square wave signal so that the amplitude fluctuation doesn't affect the frequency detection in the MFD.

I installed it and put the beat-note signal to it. Then the output signal from the comparator box is connected to the MFDs.

The input power for the comparator circuit has been reduced to -5 dBm so that it doesn't exceeds the maximum power rate.

  4426   Wed Mar 23 00:51:47 2011 kiwamuUpdateGreen Lockingplan for tomorrow

  - Plan for tomorrow

    * Video cable session (I need ETMY_TRNAS) (team)

    * Characterization of the Y end laser  (Bryan / Suresh)

    * LPF for the X end laser temperature control (Larisa)

    * Frequency Divider  (Matt)

    * X end mechanical shutter (Kiwamu)

  4427   Wed Mar 23 05:11:08 2011 kiwamuUpdateGreen Lockingservo handig off

Succeeded in handing off the servo from the green to the red.




(noise performance)

 This time we found that the fluctuation in the IR signals became lesser as the gain of the ALS servo increased.

Therefore I increased the UGF from 40 Hz to 180 Hz to have less noise in the IR PDH signal.

Here is a preliminary plot for today's noise spectra.


The blue curve is the ALS in-loop spectrum, that corresponds to the beat fluctuation.

The red curve is an out-of-loop spectrum taken by measuring the IR PDH signal.

Since the UGF is at about 180 Hz the rms is integrated from 200 Hz.

The residual displacement noise in the IR PDH signal is now 1.2 kHz in rms.

I am going to analyze this residual noise by comparing with the differential noise that I took yesterday (see the last entry ).

  4448   Mon Mar 28 16:24:35 2011 kiwamuUpdateGreen Lockingpower budget on PSL table

   I measured some laser powers associated with the beat-note detection system on the PSL table.

The diagram below is a summary of the measurement. All the data were taken by the Newport power meter.

 The reflection from the beat-note PD is indeed significant as we have seen.

In addition to it the BS has a funny R/T ratio maybe because we are using an unknown BS from the Drever cabinet. I will replace it by a right BS.



 During my work for making a noise budget I noticed that we haven't carefully characterize the beat-note detection system.

The final goal of this work is to draw noise curves for all the possible noise sources in one plot.

To draw the shot noise as well as the PD dark noise in the plot, I started collecting the data associated with the beat-note detection system.


(Next actions)

 * Estimation and measurement of the shot noise

 * measurement of the PD electrical noise (dark noise)

 * modeling for the PD electrical noise

 * measurement of the doubling efficiency

 * measurement of an amplitude noise coupling in the frequency discriminators

  4449   Mon Mar 28 17:06:15 2011 kiwamuUpdateGreen Lockinga mixer school

In the last week Matt and I modified the MFD configuration because the mixer had been illegally used.



Since the output from the comparator is normally about 10 dBm, a 4-way power splitter reduced the power down to 4 dBm in each output port.

In order to reserve a 7 dBm signal to a level-7 mixer, we decided to use an asymmetric power splitter, which is just a combination of 2-way and 3-way splitter shown in the diagram above.

With this configuration we can reserve a 7 dBm signal for a mixer in the fine path.

However on the other hand we sacrificed the coarse path because the power going to the mixer is now 2.2 dBm in each port.

According to the data sheet for the mixer, 1 dB compression point for the RF input is 1dBm. Therefore we put a 1 dB attenuator for the RF port in the coarse system.

In the delay line of the fine path we found that the delay cable was quite lossy and it reduced the power from 2.2 dBm to about 0 dBm.



  4451   Mon Mar 28 18:22:43 2011 kiwamuUpdateGreen Lockinga mixer school


Actually we tried looking for a level-3 or a smaller mixer, but we didn't find them at that moment. That's why we kept the level-7 mixer for the coarse path.

As you pointed out we can try an RF amplifier for it.


Using 2 dBm for a Level 7 mixer is so bogus, that I will dismantle this as soon as I come over.



  4458   Tue Mar 29 22:29:16 2011 kiwamuUpdateGeneralsome tasks tomorrow

 *  Temporary strain relief for the heliax cables on 1X2 (Steve)

 *  RF diagrams and check lists (Suresh)

      => In the lunch meeting we will discuss the details about what we will do for the RF installation.

 *  Electronics design and plan for Green locking (Aidan / Kiwamu)

      => In the lunch meeting we will discuss the details.

 *  LSC model (Koji)

 *  Video cable session (team)

 * LPF for the laser temperature control (Larisa)

  4461   Wed Mar 30 16:57:13 2011 kiwamuUpdateGeneralturned off c1aux

[Steve / Kiwamu]

 As a part of the video cable session, we reconnected some power cords on 1Y1 rack.

During the work we momentarily turned off c1aux, which handles DMF, Illumintators, mechanical shutters and the old video epics.

I think it automatically reverted the things, but we may need to check them.

  4478   Thu Mar 31 19:58:11 2011 kiwamuUpdateCDSc1iscex crashed

After I did several things to add new DAQ channels on c1iscex it suddenly became out of network. Maybe crashed.

Then c1iscex didn't respond to a ping and all the epics values associated with c1iscex became not accessible.

I physically shut it down by pushing the reset button. Then it came back and is now running fine.


(how I broke it)

Since activateDAQ.py has screwed up the 'ini' files including C1SCX.ini, I was not able to add a channel to C1SCX.ini by the usual daqconfig GUI.

So I started editing it in a manual way with an editor and changed some sentences to that shown below


Then I rebooted fb to reflect the new DAQ channels.

After that I looked at the C1_FE_STATUS.adl screen and found some indicator lights were red.

So I pushed "Diag reset" button and "DAQ Reload" button on the C1SCX_GDS_TP.adl screen and then c1iscex died.

After the reboot the new DAQ channels looked acquired happily.

This is my second time to crash a front end machine (see this entry)

  4482   Fri Apr 1 23:05:58 2011 kiwamuUpdateGreen Lockingnoise budget

I made a coarse noise budget in order to decide our next actions for the X arm green locking.

So be careful, this is not an accurate noise budget !

 Some data are just coming from rough estimations and some data are not well calibrated.


 Assuming all the noise are not so terribly off from the true values, the noise at high frequency is limited by the dark noise of the PD or it already reaches to the IR inloop signal.

The noise at low frequency is dominated by the intensity noise from the transmitted green light although we thought it has been eliminated by the comparator.

In any case I will gradually make this noise budget more accurate  by collecting some data and calibrating them.


According to the plot what we should do are :

  * More accurate PD noise measurement

  * More accurate shot noise estimation

  * Searching for a cause of the small beat signal (see here) because a bigger beat signal lowers the PD noise.

  * Investigation of the Intensity noise

  4483   Fri Apr 1 23:49:24 2011 kiwamuSummaryGreen Lockingtwo states in green beat-note

According to the measurement done by Aidan and me, there are two beat-note state.

One gave us a small beat signal and the other gave us a bigger signal by approximately 20 dB.


 A possible reason for this phenomenon is that the end laser is operating at a special temperature that somehow drives the laser with two different modes at the same time.

So that it permits the laser sometimes locked with one of the two modes and sometimes with the other mode.

For the first step we will change the temperature such that the laser can run with a single stable mode.

Then for investigating it we will put a scanning cavity on the X end table to see if it really exhibits a two modes or not.

Quote from #4472

The attached table shows the amplitude of the green beat note when the end laser was in various states. We can increase the beat note amplitude dramatically by switching to a different states.

  4491   Wed Apr 6 02:41:01 2011 kiwamuUpdateGreen Lockingnoise budget : some more noise

It turned out that the dark noise from the beat PD and the shot noise on the beat PD was overestimated.

So I corrected them in the plot of the last noise budget (#4482).

Additionally I added the end laser error signal in the plot. Here is the latest plot.


 The end laser error spectrum is big enough to cover most of the frequency range.
 (although it was taken at a different time from the other curves.)

Quote from #4482

According to the plot what we should do are :

  * More accurate PD noise measurement

  * More accurate shot noise estimation

  4504   Fri Apr 8 19:43:03 2011 kiwamuSummaryIOORF combiner eases impedance mismatching

An RF combiner should be included in the triple resonant box because it eases impedance mismatching and hence lowers undesired RF reflections.

Therefore we should use three cables to send the RF signals to the box and then combine them in the box.


(RF combiner)

 With proper terminations an RF combiner shows 50 Ohm input impedance.

But it still shows nearly 50 Ohm input impedance even if the source port is not properly terminated (i.e. non 50 Ohm termination).

This means any bad impedance mismatching on the source port can be somewhat brought close to 50 Ohm by a combiner.

  The amount of deviation from 50 Ohm in the input impedance depends on the circuit configuration of  the combiner as well as the termination impedance.

For example a resistive 3-way splitter shows 40 Ohm when the source port is shorten and the other ports are terminated with 50 Ohm.

Also it shows 62.5 Ohm when the source port is open and the other ports are terminated with 50 Ohm.

In this way an RF combiner eases  impedance mismatching on the source port.


(RF signal transfer at the 40m)

 According to the prototype test of the resonant box it will most likely have a non-50 Ohm input impedance at each modulation freqeucy.

If we install the resonant box apart from the combiner it will create RF reflections due to the mismatch (Case 1 in the diagram below)

The reflection creates standing waves which may excite higher harmonics and in the worst case it damages the RF sources.

 To reduce such a reflection one thing we can do is to install the combiner as a part of the resonant box (Case 2).

It will reduce the amount of the mismatching in the input impedance of the resonant circuit and results less reflections.

A rule we should remember is that a cable always needs to be impedance matched.



  4505   Fri Apr 8 20:43:46 2011 kiwamuSummaryIOORF combiner + resonant box : impedance and reflection coefficient

 The input impedance of the resonant box was measured when an RF combiner was attached to the box.

Indeed the combiner makes the impedance more 50 Ohm and reduces the reflection.


**** measurement conditions ****

* The output of box, where the EOM will be connected,  was open so that the box tries resonating with a parasitic capacitor instead of the real EOM.

* ZFSC-3-13, a 3-way combiner from mini circuit, was used.

* The S-port of the combiner was directly attached to the box with a short connector (~ 30 mm).

* Port 1 and 2 are terminated by 50 Ohm.

* The input impedance was measured on port 3 with AG4395A net work analyzer.

* Reflection coefficient 'Gamma' were calculated from the measured impedance 'Z' by using an equation Gamma = (50-Z)/(50+Z).


The resonances are found at 11, 29 and 73 MHz (55 MHz resonance was shifted to 73 MHz because of no EOM).

Note that the resonances are at frequencies where the notches appear in the reflection coefficient plot.

Don't be confused by a peak at 70 MHz in the impedance. This is an extra resonance due to a leakage inductance from the transformer in the circuit.

Quote: from #4504

An RF combiner should be included in the triple resonant box because it eases impedance mismatching and hence lowers undesired RF reflections.

  4517   Tue Apr 12 18:15:07 2011 kiwamuSummaryIOORF combiner is more like attenuator

I realized that my impedance matching theory on an RF combiner was wrong !

In fact an RF combiner behaves more like an attenuator according to a reflection measurement that I did today.

A 3-way combiner reduces power of an input signal by a factor of 4.8 dB because it can be also considered as a 3-way splitter.

So it is just a lossy component or in other words it is just an attenuator.


(reflection measurement)

To check my speculation that I posted on #4504 I measured reflection coefficients for both cases.

In the measurement I used a heliax cable, which goes from 1X2 rack to the PSL table with a length of about 10 m. Note that this is the cable that had been used as '33 MHz EOM'.

At the input of the heliax cable it was connected to a direction coupler to pick off reflections and the reflected signal was sampled in AG4395A.

The other end of the cable (output side of the cable) was basically connected to the resonant box.

Then I did a reflection measurement for both cases as drawn in this entry (see #4504).

  - case 1 -  the combiner was inserted at the input side of the heliax cable.

  - case 2 - the combiner was directly attached to the resonant box

On the combiner, ZFSC-3-13, the port 1 and 2 were terminated with 50 Ohm, therefore the port 3 was used as an input and the source port is the output.

Here is a resultant plot of the reflection measurements.


Note that whole data are calibrated so that it gives 0 dB when the output side of the heliax is open.

There are two things we can notice from this plot:

 (1) The reflection coefficient at the resonant frequencies (where notches appear) are the same for both cases.

 (2) Over the measured frequency range the reflections were attenuated by a factor of about 9.6 dB , which is twice as large as the insertion loss of the combiner.

These facts basically indicates that  the RF combiner behaves as a 4.8 dB attenuator.

Hence the location of the combiner doesn't change the situation in terms of RF reflections.

Quote from #4505

 The input impedance of the resonant box was measured when an RF combiner was attached to the box.

Indeed the combiner makes the impedance more 50 Ohm and reduces the reflection.



  4527   Fri Apr 15 02:17:18 2011 kiwamuUpdateLSCMichelson locked

[Koji / Kiwamu]

The Michelson was locked with the new LSC realtime code.



(what we did)

 --  Fine alignment of the Michelson, including PZTs, BS and ITMY.

  Since the X arm has been nicely aligned we intentionally avoided touching ITMX. The IR beam now is hitting the center of both end mirrors.

  At the end we lost X arm's resonance for IR. This probably means the PZTs need more careful alignments.


-- Signal acquisition

 We replaced the RFPD (AS55) that Aidan and Jamie nicely installed by POY11 because we haven't yet  installed a 55MHz RF source.

The maximum DC voltage from the PD went to about 50 mV after aligning steering mirrors on the AP table.

The RF signal from the PD is transferred by a heliax cable which has been labeled 'REFL33'.

Then the RF signal is demodulated at a demodulation board 'AS11', which is one of the demodulation boards that Suresh recently modified.

Although we haven't fully characterized the demod board the I and Q signal looked healthy.

Finally the demod signals go to ADC_0_3 and ADC_0_4 which are the third and fourth channel.

They finally show up in REFL33 path in the digital world.


-- Control

 With the new LSC code we fedback the signal to BS. We put anti-whitening filters in the I and Q input filter banks.

We found that dataviewer didn't show correct channels, for example C1LSC_NREFL33I showed just ADC noise and C1LSC_NREFL33Q showed NREFL_33I.

Due to this fact we gave up adjusting the digital phase rotation and decided to use only the I-phase signal.

Applying a 1000:10 filter gave us a moderate lock of the Michelson. The gain was -100 in C1LSC_MICH_GAIN and this gave us the UGF of about 300 Hz.

 Note that during the locking both ETMs were intentionally misaligned in order not to have Fabry-Perot fringes.

  4530   Fri Apr 15 12:17:39 2011 kiwamuUpdateLSC11MHz demod board : funny I-Q phase

During checking the 11MHz demod boards I found that the I-Q relative phase showed funny LO power dependence.

It is now under investigation.


 In the plot above the green curve represents the I-Q phase of a 11MHz demod board (see here).

It showed a strong dependence on the LO power and it changes from -60 deg to -130 deg as the LO power changes.

This is not a good situation because any power modulation on the LO will cause a phase jitter.

For a comparison I also took I-Q relative phase of a 33MHz demod board, which hasn't been modified recently.

 It shows a nice flat curve up to 5 dBm although it looks like my rough measurement adds a systematic error of about -5 deg.


 - to do -

* check RF power in every point of LO path on the circuit

* check if there is saturation by looking at wave forms.

  4533   Fri Apr 15 15:15:08 2011 kiwamuUpdateLSC11MHz demod board : 90 degree splitter

[Rana, Koji, Kiwamu]

 Moreover the amplitude of the I and Q signals are highly unbalanced, depending on the LO power again.

This implies the coil for a 90 degree splitting won't work at 11 MHz since the coil is home made and used to be designed for a specific frequency (i.g. 24.5 MHz).

We decided to use a Mini circuit 90 deg splitter instead. Steve will order few of them soon and we will test it out.


During checking the 11MHz demod boards I found that the I-Q relative phase showed funny LO power dependence.

It is now under investigation.


  4538   Mon Apr 18 13:05:57 2011 kiwamuSummaryLSCdemod board modification

Here is the idea how we upgrade the demodulation boards.

Basically we go ahead with two steps as depicted in the cartoon diagram below.

Once we finish the first step of upgrade, the board will be ready to install although the circuit won't be awesome in terms of noise performance.




* * * (details) * * *

 First of all we will replace the home-made 90 degree splitter (see this entry) by a commercial splitter, PSCQ-2-51-W+ from Mini circuit. This is the step 1 basically.

At this point the boards will be ready to use in principle. I asked Steve to get three 90 degree splitters so that we can have at least three demodulators for the dual-recycled Michelson locking.

If they work very fine we will buy some more 90 degree splitters for full locking.

While we try to lock the dual-recycled Michelson once we will get a Cougar amplifier, remove all ERA-5s and install it such that we don't have to gain up and down in the circuit. This is the last step.

  4539   Mon Apr 18 14:11:44 2011 kiwamuUpdateLSCRF status

 We will make them all green !!


Again, all the files are available in the svn.


  4540   Mon Apr 18 17:47:41 2011 kiwamuConfigurationLSCLSC rack's ADC cabling

To understand the situation of the ADC cabling at the LSC rack I looked around the rack and the cables.

The final goal of this investigation is to have nice and noise less cables for the ADCs (i.e. non-ribbon cable)

Here is just a report about the current cabling.


(current configuration)

At the moment there is only one ribbon-twisted cable going from 1Y2 to 1Y3. (We are supposed to have 4 cables).

At the 1Y2 rack the cable is connected to an AA board with a 40 pin female IDC connector.

At the 1Y3 rack the cable is connected to an ADC board with a 37 pin female D-sub connector.

The ribbon cable is 28AWG with 0.05" conductor spacing and has 25 twisted pairs (50 wires).



(things to be done)

 - searching for a twisted-shielded cable which can nicely fits to the 40 pin IDC and 37 pin D-sub connectors.

 - estimating how long cable we need and getting the quote from a vendor.

 - designing a strain relief support

  4546   Wed Apr 20 20:42:55 2011 kiwamuUpdateVIDEOtoday's video session

[Steve / Suresh / Kiwamu]

90 % of unused video cables have been removed.

Still a couple of video cables are floating around the video MUX. They will be removed in the next week's session.




  4554   Thu Apr 21 21:24:41 2011 kiwamuUpdateLSCdemod board : new 90 deg splitter

A new 90 degree splitter, PSCQ-2-51W, has arrived today and I installed it on a demod board called AS11.

Results of the I-Q phase measurement with the new splitter will be reported soon.


 * Picture 1 = before removal of the handmade coil

 * Picture 2 = after removal of the coil and the associated capacitors

 * Picture 3 = after soldering PSCQ-2-51-W




Quote from #4358

 First of all we will replace the home-made 90 degree splitter (see this entry) by a commercial splitter, PSCQ-2-51-W+ from Mini circuit. This is the step 1 basically.

  4555   Thu Apr 21 21:46:22 2011 kiwamuUpdateLSCdemod board : new 90 deg splitter

A less LO power dependence on the relative phase was found. The new 90 deg splitter works better.

From -3 dBm to 10 dBm in LO power, the relative phase is within 90 +/- 5 deg.

As a comparison I plot the phase that I measured when the handmade coil had been there (green curve in the plot).



 I will also measure amplitude unbalances between I and Q.

Quote from #4554

A 90 degree splitter, PSCQ-2-51W, has arrived today and I installed it on a demod board called AS11.

Results of the I-Q phase measurement with the new splitter will be reported soon.



  4560   Fri Apr 22 11:08:50 2011 kiwamuUpdateLSCdemod board AS11 : amplitude imbalance

Amplitude imbalance between I and Q in a demod board, AS11, with the new 90 deg splitter was measured.

It shows roughly 10% amplitude imbalance when the LO power is in a range from 0 to 5 dBm. Not so bad.


  With the handmade coil there used to be a huge imbalance (either I or Q goes to zero volt while the other keeps about 1 V rms) as the LO power decreases.

But with the new 90 deg splitter now there are no more such a huge imbalance.

The remaining 10 % imbalance possibly comes from the fact that we are using ERA-5 in each I and Q path. They may have such gain imbalance of 10%.

We should check the ERA-5 gains so that we can confidently say ERA-5 causes the amplitude imbalance.

Then our plan replacing the ERA-5s (see here) will sound more reasonable.



Quote from #4555

The new 90 deg splitter works better.

 I will also measure amplitude unbalances between I and Q.


  4562   Sun Apr 24 21:37:40 2011 kiwamuUpdateIOOreview of triple resonant EOM : model looks fine

To design a new resonant EOM box I started reviewing the prototype that I've built.

As a part of reviewing I checked an important thing that I haven't carefully done so far :

I compared the measured input impedance with that of predicted from a circuit model. I found that they show a good agreement.

So I am now confident that we can predict / design a new circuit performance.

* * * (input impedance) * * *

 Performance of a resonant circuit is close related to its input impedance and hence, in other words, determined by the input impedance.

Therefore an investigation of input impedance is a way to check the performance of a circuit. That's why I always use impedance for checking the circuit.

The plot below is a comparison of input impedance for the measured one and one predicted from a model. They show a good agreement.

(Note that the input impedance is supposed to have 50 Ohm peaks at 11, 29.5 and 55 MHz.)

* * * (circuit model) * * *

To make the things simpler I assume the following three conditions in my model:

 1. inductor's loss is dominated by its DC resistance (DCR)

 2. capacitor's loss is characterized only by Q-value

 3. Transformer's loss is dominated by DCR and its leakage inductance

All the parameters are quoted from either datasheet or my measurement. The model I am using is depicted in the schematic below.

Basically the Q-vaules for the capacitors that I used are quite low. I think higher Q capacitors will improve the performance and bring them to more 50 Ohm.


  4567   Mon Apr 25 22:38:49 2011 kiwamuUpdateLSCprepration for DRMI : Y arm flashing
This week is going to be a recycled Michelson week.
As a preparation I did several things today :
 1. Alignment of the Y arm
 2. Alignment of PRM
 3. Checking of all the pick-off ports


(Y arm alignment)
 The idea to have the Y arm aligned is that : once we lock the Y arm we will be able to align the input PZTs using the Y arm as a reference.
 I tried aligning the Y arm and successfully made the Y arm flashing with IR. I can see it flashing on ITMY camera but no flashing on ETMY camera.
(PRM alignment)
PRM has been intentionally misaligned for the single arm green locking test.
I just confirmed that we can bring PRM back to a good alignment. Now we can see the central part is flashing too.
(picked-off beams)
I went checking through all the picked off beams to see if they are available or not.
POX : lost
POY : fine
POP : very clipped
POSRM : fine
  4570   Tue Apr 26 22:56:01 2011 kiwamuUpdateLSCc1iscaux2 and c1iscaux restrated

While checking whitening filters on the LSC rack, I found some epics controls for the whitening looked not working.

So I powered two crates off : the top one and the bottom one on 1Y3 rack.

These crates contain c1iscaux and c1iscaux2. Then powered them on. But it didn't solve the issue.

  4572   Wed Apr 27 15:34:38 2011 kiwamuUpdateElectronicsAS55 demod board with new 90 deg splitter : healthy

A new 90 deg splitter, PSCQ-2-51W, has been installed on another demod board called AS55.

It shows a reasonably close 90 degree separation between the I and Q signals at 55 MHz with various LO and RF power.

So far we have ordered only three PSCQ-2-51Ws for test. Now we will order some more for the other demodulators.

 Some plots will be posted later.

  4573   Wed Apr 27 17:38:01 2011 kiwamuUpdateElectronicsRe : AS55 demod board with new 90 deg splitter : healthy


Figure.1  I-Q relative phase measurement as a function of LO power.

 Blue curve : relative phase of AS55 that I have modified today (#4572).

 Red curve : relative phase of AS11 that I had modified a week ago (#4554). Just for comparison.

 The relative phase of AS55 agrees approximately what we expected according to the datasheet of PSCQ-2-51W. We expected 85 degree.



Figure.1  I-Q amplitude imbalance as a function of LO power.

From - 5 dBm to 5 dBm in LO power the imbalance is within 3 %.

But the precision of the measurement is also about 2 % (because I used an oscilloscope). Even so the imbalance is still good.

Quote from #4572

Some plots will be posted later.


  4574   Wed Apr 27 18:14:48 2011 kiwamuUpdateLSCpreparation for DRMI locking : RF status


POX11 (see this entry) is now listed as REFL11 (on the very top row).

We will rename POY11 to POP11 for DRMI locking.

The files are on https://nodus.ligo.caltech.edu:30889/svn/trunk/suresh/40m_RF_upgrade/.

  4577   Wed Apr 27 21:19:25 2011 kiwamuUpdateLSCLSC whitening for PD1-4

On the back side of 1Y2 rack I found a cable, CAB-1X2-LSC_7, which is supposed to be connected to the whitening filter was disconnected.

I plugged it back and confirmed that the whitening filter is under control of EPICS.

Now all the gain sliders seem to be working because I can change the amplitude of signals with the sliders.



  To check if the gain sliders are working or not, I intentionally disconnected all the inputs to the whitening filter.

Then I brought a gain slider of interest to the maximum. Due to the big gain I was easily able to see noise lying above ADC noise.

Also if the gain slider is 0 dB, which is the minimum value, the spectrum becomes just ADC noise.

In this way I checked all the gain sliders from PD1 to PD4. The picture below is just an example screenshot when I was doing this test.

Note that each filer is designed to have two poles at 150 Hz and two zeros at 15 Hz.


Quote from #4570

While checking whitening filters on the LSC rack, I found some epics controls for the whitening looked not working.

So I powered two crates off : the top one and the bottom one on 1Y3 rack.

These crates contain c1iscaux and c1iscaux2. Then powered them on. But it didn't solve the issue.

  4582   Thu Apr 28 15:31:36 2011 kiwamuUpdateIOOMC PDH lock : readjustment of demodulation phase

Since Suresh has installed the RF source box and changed the cable configuration somewhat,

the demodulation phase for the MC locking became off by about 10 degree.

I changed the length of some cables and obtained a good demodulation phase by the same technique as Suresh and Koji did before (see here for detail).

I maximized the Q signal. The lock of the MC looks healthy.


Quote from #4578

RF Source box has been mounted in the 1X2 rack. 

  4586   Fri Apr 29 05:48:52 2011 kiwamuUpdateLSCY arm locked

The Y arm has been locked with the IR beam. The purpose is to use the arm as an alignment reference for the input PZTs.

Detail will be posted later. Here is a picture of ITMY suspension. You can see there is a beam spot in the middle of the test mass.


  4587   Fri Apr 29 12:18:48 2011 kiwamuUpdateLSCY arm locked : details

First of all, the conclusions / results from the exercise of the Y arm locking yesterday are:

   The position of the beam spots on both ETMY and ITMY are now not so bad ( ~ 5 mm off from the center).

   The input PZTs are coarsely aligned to the Y arm.

   Nevertheless IP_ANG is still too high to come out from the view port at the Y end station.

  After the alignments of PRM, SRM and Michelson, POP is still largely clipped.


(what I did)

  - Alignments of the Input PZTs

    First I tried letting the incident beam hit the center of ETMY by steering PZT1 and 2 as usual.
    Then I coarsely aligned the cavities to the incident beam and checked the beam flashing spots on ETMY and ITMY with the CCD monitors.
    When the spots were far from the center I went back to the alignment of PZT1 and 2 to get better beam positions. And repeated this work several times.

  - Adjustment of the demodulation phase  for the Y arm PDH.

    First I started looking at the digital signals and tried correcting the demodulation phase by the rotation matrix, but this didn't go fast because I had to do some DAQ settings, plotting and analysis.
    Instead looking at the digital signal, I observed the analog signals with an oscilloscope. I found the demodulation phase was something like 45 deg.
    Based on the analog measurement I rotated the digital matrix by 45 deg to get the I-signal maximized. Indeed this worked well. I obtained a beautiful PDH signal from the I-signal.
    Note that we are using 11 MHz mod/demod and eventually the signals come out from "REFL33" on the digital side.

  - Activation of oplev on ITMY

    Instead using ETMY I used ITMY for the length control because somehow I felt that ETMY coils were suspicious and they looked not so nice.
    One of the reason is that ETMY's coil actuation efficiencies looked low compared to the other test masses.
    For example a gain of 700 for SUSSIDE damping is needed on ETMY to get a reasonable Q. This is about 2 - 3 times larger gain than the other test masses.
    So I started using ITMY for the locking and activated the oplev to suppress unwanted excitation due to kicks from the control signal during the locking,
    The oplev has been misaligned, so I went to the ITMY optical bench and tweaked a steering mirror to let the He-Ne beam go into the QPD.
    I set the gains +2 for PITCH and -2 for YAW.

  - PDH locking

    The locking had been quite difficult even though the cavity alignment was quite good.
    It's because the beam on AS11_RFPD was almost falling off from the photo diode. This causes a big amplitude fluctuation in the PDH signal as the beam position moves.
    After aligning the beam by steering BS I got able to lock the Y arm. The PD whitening gains are all 0 dB and the feedback gain is -2, giving us a UGF of 250 Hz.


(Broken or likely broken stuff)

 * IP_ANG doesn't give a signal to the digital side.

 * ETMY coils look weak and 2 - 3 times weaker than the other test masses. (or OSEM readout gain maybe lower)

 * reload button on sitemap.adl doesn't work.

 * Farfalla, a lab laptop, seems out of network.

Quote from #4586

The Y arm has been locked with the IR beam. The purpose is to use the arm as an alignment reference for the input PZTs.

Detail will be posted later. Here is a picture of ITMY suspension. You can see there is a beam spot in the middle of the test mass.


  4588   Fri Apr 29 13:15:04 2011 kiwamuUpdateLSCY arm locked : details

As far as I know, this button works only once after the launch of MEDM...


 * reload button on sitemap.adl doesn't work. 


  4592   Sat Apr 30 00:15:26 2011 kiwamuUpdateSUSDRMI prep : suspension diagnostic

As a part of the DRMI preparation,

I leave all the suspensions free from the watchdogs for 5 hours from now.

Please DO NOT touch them.

I will check the spectra and the mechanical resonant frequencies on Monday.

Also I will renew all the input matrices of the local dampings based on these free swinging spectra.

  4594   Mon May 2 11:14:27 2011 kiwamuUpdateSUSscript : opticshutdown

Just FYI.

There is a useful script for this particular job : shutting down all the suspensions and bringing it back to operation after 5 hrs.

It is called opticshudown, which resides in /cvs/cds/rtcds/caltech/c1/scripts/SUS/.


Also I added this script on the list in the wiki where all the scripts will be listed.


If you find any other useful scripts, please add them on the wiki.

Quote from #4592

I leave all the suspensions free from the watchdogs for 5 hours from now.


  4595   Mon May 2 12:51:52 2011 kiwamuUpdateLSCPRMI locking : plan

Today we will try to lock the PRMI. Here is a plan for it.

(to be done in the daytime)

 - setup REFL11 RFPD

 - setup AS55 RFPD

 - install a demod board for 55 MHz

 - install a 3-way RF combiner on EOM.

 - prepare 55 MHz RF source (Marconi or RF source box ?)

 - adjustment of each demodulation phase

 - activation of PRM oplev


 (control topology)

- AS55_Q ==> BS

- REFL11_I ==> PRM

  4596   Mon May 2 13:30:13 2011 kiwamuUpdateSUSPRMI locking prep: PRM oplev

I had a quick look at PRM optical lever.

The He-Ne beam is still successfully coming out from the chamber and I could guide it to the QPD by using steering mirrors.

But the beam size looks too big for the QPD. We should slide the lens which is standing before the injection to get a moderately smaller beam size at the QPD.

Quote from #4595

 - activation of PRM oplev

  4598   Mon May 2 15:53:27 2011 kiwamuUpdateLSCPRMI locking prep : demodulation boards

I swapped the name of two demodulation boards (AS55 and REFL55).

Now the REFL11 and AS55 demodulation boards are ready to go for the PRMI locking.

The physical labels, which are on the front surface of the boards, are also corrected to avoid a confusion.

Here is the latest RF status.


Quote from #4574

The files are on https://nodus.ligo.caltech.edu:30889/svn/trunk/suresh/40m_RF_upgrade/.


  4600   Mon May 2 18:16:24 2011 kiwamuUpdateLSCPRMI locking : status update



  With a help from Jamie the AS55 RFPD was installed.

- 55 MHz demodulation board

  The AS55 demod board was installed on 1Y2.

- 3-way combiner

  ZFSC-3-13 has been installed. All the RF cables from the source side were connected to the combiner.


(next things)

 - installation of the REFL11 RFPD

 - DAQ check for AS55 and REFL11

Quote from #4595

(to be done in the daytime)

 - setup AS55 RFPD

 - install a demod board for 55 MHz

 - install a 3-way RF combiner on EOM.

 - prepare 55 MHz RF source (Marconi or RF source box ?)


  4601   Mon May 2 21:14:55 2011 kiwamuUpdateElectronicstoo loose Heliax connectors on 1Y2 rack

I found that all the Heliax cables landing on the bottom of 1Y2 were too loose.

Due to this loose connection the RF power at 55 MHz varies from -34 dBm to 3 dBm, depending on the angle of the Heliax's head.



The looseness basically comes from the fact the black plate is too thick for the Heliax cable to go all the way. It permits the Heliax's heads to rotate freely.

What we should do is to make countersinks on the black plate like this:



ELOG V3.1.3-