40m QIL Cryo_Lab CTN SUS_Lab TCS_Lab OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop
  40m Log, Page 94 of 344  Not logged in ELOG logo
ID Date Authorup Type Category Subject
  2354   Sat Dec 5 01:40:11 2009 KojiUpdateoplevsOplevs centered, IP_POS and IP_ANG centered

We restarted daqd and it did restored the problem
http://lhocds.ligo-wa.caltech.edu:8000/40m/Computer_Restart_Procedures#fb40m
Then restart the 'daqd' process:'telnet fb40m 8087', type "shutdown" at the prompt. The framebuilder will restart itself in ~20s.

 

It did not related to the problem, but we also cleaned the processes related to dtt, dataviewer by pkill

After that the alignment scripts started to work again. As a result, we got some misalignment of the oplevs.
I am going to come on Sunday
- Align the optics
- Align the oplevs again
- Take snapshots for the suspensions
- Align the IP_POS, IP_ANG
- Align the aux laser for the absolute length
- Align PSL table QPDs, and MCT QPD

  2358   Sat Dec 5 18:23:48 2009 KojiUpdateoplevsOplevs centered, IP_POS and IP_ANG centered

NOTE: HEPA is on at its full.

[[[OK]]] Align the suspended optics (by Rob)
[[[OK]]]
Align the oplevs again
[[[OK]]] Take snapshots for the suspensions/QPDs/IO QPDs/PZT strain gauges
[[[OK]]] Align the IP_POS, IP_ANG
[[[OK]]] Align the PSL table QPDs, the MC WFS QPDs, and the MCT QPD
[[[OK]]] Align the aux laser for the absolute length 


Alignment of the aux laser

o Go to only ITMX mode:
Save the alignment of the mirrors. Activate X-arm mode. Misalign ITMY and ETMX.

o Inject the aux beam:
Open the shutter of the aux NPRO. Turn the injection flipper on.

o Look at the faraday output:
There are several spots but only one was the right one. Confirm the alignment to the thorlabs PD. Connect the oscilloscope to the PD out with a 50Ohm termination.
Thanks to the Alberto's adjustment, the beat was already there at around 10MHz. After the PD adjustment, the DC was about 600mV, the beat amplitude was about 50mVpp.

o Adjust the aux beam alignment:
Adjust the alignment of the aux beam by the steering mirrors before the farady isolator. These only change the alignment of the aux beam independently from the IFO beam.
After the alignment, the beat amplitude of 100mVpp was obtained.

o Closing
Close the shutter of the NPRO. Turn off the flipper mirror. Restore the full alignment of the IFO.

Attachment 1: Screenshot_091205_1830.png
Screenshot_091205_1830.png
  2360   Mon Dec 7 09:38:05 2009 KojiUpdateVACVent started

Steve, Jenne, Koji

The PSL was blocked by the shutter and the manual block.
We started venting
at 9:30

09:30  25 torr
10:30 180 torr
11:00 230 torr

12:00 380 torr

13:00 520 torr
14:30 680 torr - Finish. It is already over pressured.

  2366   Tue Dec 8 13:03:26 2009 KojiUpdateCOCETMY drag wiped

Jenne, Kiwamu, Alberto, Steve, Bob, Koji

We wiped ETMY after recovery of the computer system. We take the lunch and resume at 14:00 for ITMX.
Detailed reports will follow.

  2369   Wed Dec 9 00:23:28 2009 KojiUpdateSUSfree swinging spectra of ETMY and ITMX

Where is the plot for the trend?
It can be either something very important or just a daydream of you.
We can't say anything before we see the data.

We like to see it if you think this is interesting.

... Just a naive guess: Is it just because the seismic level got quiet in the night?

 

P.S.

You looks consistently confused some words like damping, Q, and peak height.

  • Q is defined by the transfer function of the system (= pendulum).
     
  • Damping (either active or passive) makes the Q lower.
     
  • The peak height of the resonance in the spectrum dy is determined by the disturbance dx and the transfer function H (=y/x).

dy = H dx

As the damping makes the Q lower, the peak height also gets lowered by the damping.
But if the disturbance gets smaller, the peak height can become small even without any change of the damping and the Q.

Quote:

By the way I found a trend, which can be seen in all of the data taken today and yesterday.

The resonances of pitch and yaw around 0.5Hz look like being damped, because their height from the floor become lower than the past.

I don't know what goes on, but it is interesting because you can see the trend in all of the data.

 

  2373   Wed Dec 9 18:01:06 2009 KojiUpdateCOCWiping finished

[Kiwamu, Jenne, Alberto, Steve, Bob, Koji]

We finished wiping of four test masses without any trouble. ITMY looked little bit dusty, but not as much as ITMX did.
We confirmed the surface of the ITMX again as we worked at vertex a lot today. It still looked clean.

We closed the light doors. The suspensions are left free tonight in order to check their behavior.
Tomorrow morning from 9AM, we will replace the door to the heavy ones.

  2375   Thu Dec 10 00:46:15 2009 KojiUpdateSUSRe: free swinging spectra of ETMY and ITMX

Well, I get the point now. It could be either seismic or change in the suspension Q.

The pendulum memorizes its own state for a period of ~ Q T_pend. (T_pend is the period of the pendulum)
If the pendulum Q is very high (>104), once the pendulum is excited, the effect of the excitation can last many hours.

On the other hand, in our current case, we turned on the damping once, and then turned off the damping.
Again it takes ~Q T_pend to be excited. 

In those cases, the peak height is not yet before in equilibrium, and can be higher or lower than expected. 

So, my suggestion is:
Track the peak height along the long time scale (~10hrs) and compare between the previous one and the current one.
This may indicate whether it is equilibrium or not, and where the equilibrium is.

Quote:

If such variation of the peak heights is cased by the seismic activity, it means the seismic level change by several 10 times. It sounds large to me.

 

  2381   Thu Dec 10 09:56:32 2009 KojiUpdatePSLRCPID settings not saved

Note: The set point C1:PSL-FSS_RCPID_SETPOINT is 37.0 on C1PSL_FSS_RCPID.adl.

Now the temp is recovering with its full speed. At some point we have to restore the value of the FSS SLOW DC as the temp change drag it up.

Quote:

Koji, Jenne, Rob

We found that the RCPID servo "setpoint" was not in the relevant saverestore.req file, and so when c1psl got rebooted earlier this week, this setting was left at zero.  Thus, the RC got a bit chilly over the last few days.  This channel has been added. 

Also, RCPID channels have been added (manually) to conlog_channels. 

 

Attachment 1: RC_TEMP.png
RC_TEMP.png
  2395   Fri Dec 11 09:30:09 2009 KojiConfigurationLSC166 LO Disconnected

They must not be dBm, must be dB

Quote:

Quote:

I temporarily disconnected the Heliax cable that brings the 166MHz LO to the LSC rack.

I'm doing a couple of measurement and I'll put it back in as soon as I'm done.

 These are the losses I measured on a RG-174 cable for the two frequencies that we're planning to use in the Upgrade:

@11MHz Loss=0.22dBm/meter

@55MHz Loss=0.41dBm/meter

(The cable was 2.07m long. The input signal was +10dBm and the output voltages at the oscilloscope where: Vpk-pk(11MHz)=1.90V, Vpk-pk(11MHz)=1.82V )

 

  2399   Fri Dec 11 14:19:22 2009 KojiConfigurationVACpumpdown has started

Wait, Wait, Wait. You are moving too fast. Go one by one.

Check the PZTs, the MC, initial pointings, IFO mirrors, some of the partial locks, and maybe some momentary full locks?
Once the recover of the IFO is declared, you can proceed to the measurements.

I hope the grad students can take this precious opportunity to have their fun time for restoring everything by themselves.

Quote:

 I'm leaving the lab now for less than 2 hours. I should be back in time for when the pumping is finished so that I can measure the finesse again.

 

  2408   Mon Dec 14 00:37:28 2009 KojiOmnistructureEnvironmentAnts in the coffee maker

I made a short stop at the 40m on Sunday night and found that hundreds ants are in the coffee maker.
I removed ants around the sink and washed the coffee maker.

It looked the ants were everywhere in the lab tonight. They seemed to prefer warm places like in the coffee maker and below the coffee mill.
So, I recommend that Steve should confirm there is no ants in the coffee maker again before the first coffee of the week is made.
Othewise they will add some more acidity to your cup.

 

  2411   Mon Dec 14 13:08:33 2009 KojiUpdateTreasureLOCKSTARS

Good job guys. What I did was saying "I don't know", "Maybe", and "Ants...".

Now you can proceed to measurements for the visibility and the cavity pole! 

Quote:

[Jenne, Kiwamu, Koji]

We got the IFO back up and running!  After all of our aligning, we even managed to get both arms locked simultaneously.  

  2416   Mon Dec 14 22:32:56 2009 KojiUpdateGeneralArm cavity loss ~ result

I like to ask someone to review the calculation on the wiki.

In the calculation, the round trip loss and the front mirror T are the unknown variables.
The end mirror T of 10ppm was assumed. (End mirror T)+(Round trip loss) is almost invariant, and T_end does not change the other results much.

Arm cavity loss measurement (Dec. 14, 2009)

X Arm:
  • Arm visibility (given): 0.897 +/- 0.005 (20 pts) (2.5%UP!!)
  • Cut off freq (given): 1616 +/- 14 [Hz] (2.1%UP!!)
  • Finesse (derived): 1206 +/- 10 (2.1%UP!!)
  • Round Trip loss (estimated): 127 +/- 6 [ppm] (28%DOWN!!)
  • Front Mirror T (estimated): 0.00506 +/- 0.00004
Y Arm:
  • Arm visibility (given): 0.893 +/- 0.004 (20 pts) (2.1%UP!!)
  • Cut off freq (given): 1590 +/- 4 [Hz] (8.2%UP!!)
  • Finesse (derived): 1220 +/- 3 (8.2%UP!!)
  • Round Trip loss (estimated): 131 +/- 6 [ppm] (37%DOWN!!)
  • Front Mirror T (estimated): 0.00500 +/- 0.00001 

Previous measurement (Oct 07, 2009 & Nov 10, 2009)

X Arm:  

  • Arm visibility (given): 0.875 +/- 0.005 (34 pts)
  • Cut off freq (given): 1650 +/- 70 [Hz]
     
  • Finesse (derived): 1181 +/- 50
  • Round Trip loss (estimated): 162 +/- 10 [ppm]
  • Front Mirror T (estimated): 0.0051 +/- 0.0002

Y Arm: 

  • Arm visibility (given): 0.869 +/- 0.006 (26 pts)
  • Cut off freq (given): 1720 +/- 70 [Hz]
     
  • Finesse (derived): 1128 +/- 46
  • Round Trip loss (estimated): 179 +/- 12 [ppm]
  • Front Mirror T (estimated): 0.0054 +/- 0.0002
  2419   Tue Dec 15 17:16:22 2009 KojiUpdateGeneralTable distance measurements

During the vent we have tried to measure the distances of the optical tables for BS-ITMX and BS-ITMY.
We need to take into account the difference between the AutoCAD drawing and the reality.

X direction distance of the table center for BS and ITMX:
84.086" (= 2135.8mm)
(This is 84.0000" in AutoCAD drawing)

Y direction distance of the table center for BS and ITMX:
83.9685" (= 2132.8mm)
(This is 83.5397" in AutoCAD drawing)

We used two scales attached each other in order to measure the distance of the certain holes on the tables.

We got more numbers that were estimated from several separated measurements.
I think they were not so accurate, but just as a record, I also put the figure as an attachment 2.

Attachment 1: Table_distance_by_metal_scale.pdf
Table_distance_by_metal_scale.pdf
Attachment 2: Table_distance_by_chambers.pdf
Table_distance_by_chambers.pdf
  2431   Fri Dec 18 15:40:33 2009 KojiUpdateIOOMC2 spot centered / MCT QPD issue

This afternoon I felt like saying hello to the input mode cleaner. So I decided to center the spot on MC2.

Motivation

MC has 6 alignment dofs. 4 of them are controlled by the WFSs. Remaining 2 appears at the spot position on MC2.
If the spot on the MC2 is fixed, the beam hits the same places of three mirrors. If the mirrors are completely fixed
in terms of the incident beam, I suppose the reflected beam is also fixed. This makes the WFS spots more stable.
Then I feel better.

Today's goal is to confirm the behaviour of MC such as dithering amplitude, response of the couplings to the alignment,
behavior of the WFS, and the transmitted power.


Method

1) Turned off MC auto locker. Turned off MC WFS as the WFS servos disturbs my work.
2) Dithered MC2 in Pitch and Yaw using DTT. There looks elliptic filter (fc=28Hz) in the ASC path, I used 20Hz-ish excitations.
- C1:SUS-MC2_ASCPIT_EXC 100cnt_pk@19Hz
- C1:SUS-MC2_ASCYAW_EXC 100cnt_pk@22Hz
3) Looked at C1:SUS-MC2_MCL_OUT to find the peaks at 19Hz and 22Hz. These are caused by alignment-length coupling.
If they are minimized I assume the spot is somehow centered on MC2.
Note: This may not be the true center. The suspension response should be investigated. But this is a certain reporoducible spot position.
Note: I should use ezcademod in order to obtain the phase information of the dither result.

4) Move MC2 Pitch for certain amount (0.01cnt) by the alignment slider. Align MC1/MC3 to have max transmittion.
5) If the Pitch peak got lower, the direction of 4) was right. Go further.
5') If the Pitch peak got higher, the direction of 4) was wrong. Go the other direction.

6) Repeat 4)&5) for Yaw.


Result

After the adjustment, the couplings got lower about 10 times. (Sorry! The explanation is not so scientific.)
Next time I (or someone) should make a script to do it and evaluate the coupling by the estimated distance of the spot from the center of the mirror (the center of the rotation).
I have not seen visible change in the spectrum of C1:SUS-MC2_MLC_OUT.


MCT QPD issue

By the spot centering, I could expected to see some improvement of the transmittion. But in reality, there was no change.
In fact, the transmittion power was getting down for those weeks.

I checked WFS and MCT paths. Eventually I found that a couple of possible problems:
1) MCT Total output varies more than 10% depending on the spot position on MCT QPD.
2) Just before the QPD, there is a ND1 filter.
This may suggest that:
a) Four elemtns of the MCT QPD have different responses.
b) The ND filter is causing a fringe.

So far I aligned the ND filter to face the beam. The reflection from the filter was blocked at a farther place.
Still the output varies on the spot position. Probably I have to look at the QPD someday.

So far the spot on the QPD was defined so that I get the maximum output from the QPD. This is about 8.8.
As I touched the steering mirrors, the X and Y outputs of the QPD are no longer any reference.

For now, I closed the PSL table. The full IFO was aligned.

  2432   Sat Dec 19 14:33:25 2009 KojiConfigurationComputersPDFlib lite / gnuplot 4.2.6 on Rosalba/Allegra

In order to enable 'set terminal pdf' in gnuplot on Rosalba/Allegra, I installed PDFlib lite and gnuplot v4.2.6. to them.
(PDFlib lite is required to build the pdf-available version of gnuplot)


Installation of PDFlib lite:

  • Building has been done at rosalba
  • Download the latest distribution of PDFlib lite from http://www.pdflib.com/products/pdflib-7-family/pdflib-lite/
  • Expand the archive. Go into the expanded directory
          tar zxvf PDFlib-Lite-7.0.4p4.tar.gz
          cd ./PDFlib-Lite-7.0.4p4
  • configure & make
          ./configure
          make
  • install the files to the system / configure the dinamic linker
          sudo make install
          sudo ldconfig

Installation of gnuplot:

  • Building has been done at rosalba
  • Download the latest distribution of gnuplot form http://www.gnuplot.info/
  • Expand the archive. Go into the expanded directory
          tar zxvf gnuplot-4.2.6.tar.gz
          cd ./gnuplot-4.2.6.tar.gz
  • configure & make
          ./configure --prefix=/cvs/cds/caltech/apps/linux/gnuplot
          make
          make install
  • Create symbolic links of the executable at
          /cvs/cds/caltech/apps/linux/bin
          /cvs/cds/caltech/apps/linux64/bin
  • Note: Although the original (non-PDF) gnuplot is still at
          /usr/bin/gnuplot
    new one is active because of the path setting
          rosalba:linux>which gnuplot
          /cvs/cds/caltech/apps/linux64/bin/gnuplot

 

  2433   Sun Dec 20 14:34:24 2009 KojiUpdateSUSETMY watchdog tripped Sunday 5:00AM local

It seemed that the ETMY watchdog tripped early Sunday morning.
The reason is not known. I just looked at ETMX, but it seemed fine.

I called the control room just in case someone is working on the IFO.
Also I did not see any elog entry to indicate on going work there.

So, I decided to reset the watchdog for ETMY. And it is working fine again.

Attachment 1: Y.png
Y.png
  2448   Wed Dec 23 16:34:25 2009 KojiUpdateIOOMCT QPD/MC REFL QPD disabled

For a certain investigation of the sum/diff module for MCT QPD/MC REFL QPD, I removed it from the system.

 

  2451   Thu Dec 24 19:13:29 2009 KojiUpdateIOOMCT QPD investigation

I found that MCT QPD has a dependence of the total output on the position of the spot. Since the QPD needs the supply and bias voltages from the sum/diff amp, I could not separate the problems of the QPD itself and the sum/diff amplifier by the investigation on Tuesday. On Wednesday, I investigated a generic quad photodiode interface module D990692.

...I was so disappointed. This circuit was left uninvestigated and used so long time with the following sorrowful conditions.
- This circuit has 4 unbuffered inputs with input impedance of 300~400 Ohm. It's way too low!
- Moreover, those channels have different input impedances. Ahhhh.
- Even worse, the QPD circuit D990272 has output impedance of 50 Ohm.
- The PCB of this circuit has four layers. It is quite difficult to make modifications of the signal route.
- It is a headache: this circuit is "generic" and used in many places.

D990692 has 4 channel inputs that are not buffered. Each channel has two high impedance buffers but they are used only for the monitors. The signal paths have no buffer.

The differential amplifier is formed by R=1k Ohm. The inverted side of the input has 1kOhm impedance. The non-inverted side has 1.5kOhm impedance.

CH1: 10K // 1.5k // 1.5k // 1k = 411 Ohm
CH2: 10K // 1.5k // 1k // 1k = 361 Ohm
CH3: 10K // 1k // 1k // 1k = 323 Ohm
CH4: 10K // 1k // 1.5k // 1k = 361 Ohm

Considering the output impedance of 50Ohm for the QPD, those too low input impedances result in the following effect:
- Because of the voltage division, we suffer absolute errors of 10.8~13.4%. This is huge.
- Because of the input impedance differences, we suffer a relative error of 1.5%~3%. This is also huge.

Unfortunately, the circuit has no room to modify; the signal paths are embedded in the internal layer.

I decided to replace the resistors of the sum/diff amps from 1k to 10k. Also the input impedance of the buffer was removed as the input is terminated by the sum/diff amps in any case.This changes the input inpedance to the followings:

CH1: 15k // 15k // 10k = 4286 Ohm
CH2: 15k // 10k // 10k = 3750 Ohm
CH3: 10k // 10k // 10k = 3333 Ohm
CH4: 10K // 15k // 10k = 3750 Ohm

These yield the absolute error of 1.2-1.5%. The relative error is now 0.3%. I can accept these numbers, but later I should put additional terminating resistors to compensate the differencies.

So far I have modified the resistors for the MCT as the modification for a QPD needs 17 10k resistors.
Next thing I have to check is the dependence of the QPD outputs on the spot positions.

-----------------------------------------------

Edit: Feb 11, 2010

I talked with Frank and he pointed out that the impedances are not the matter but the gains of the each channels are the matters (after considering the output impedance of the QPD channels).
If we assume the ideal voltage sources at the QPD and the symmetric output impedances of 50Ohm, the gain of the each circuit are affected but the change should be symmetric.

He found that several things:
- The analog switch (MAX333) used in the QPD unit adds more output impedance (somewhat randomly!).
- The resistance of the sum/diff circuits may vary each other unless we use 0.1% resistors.

 

Attachment 1: D990692.png
D990692.png
  2452   Sat Dec 26 19:22:13 2009 KojiSummaryGeneralMode coupling of two astigmatic beams

In this note, amplitude and power couplings of two astigmatic (0,0)-th order gaussian modes are calculated.

Attachment 1: mode_coupling.pdf
mode_coupling.pdf mode_coupling.pdf
  2455   Mon Dec 28 01:17:01 2009 KojiUpdateElectronicsMCT QPD investigation

Unfortunately, the signals for individual segments also suffer from the voltage drop as all of the low impedance amplifiers are hung from the same input.
In order to utilize the individual channels, we anyway have to remove the resistors for the VERT/HOR/SUM amps.
That is possible. But does it disable some fast channels for future ASC purposes?

 

Quote:

 This is indeed sad. But, we can perhaps bypass all of this by just using the individual segment outputs. According to the circuit diagram and the c1iool0 .db file, we should be able to just do the math on the segments and ignore the VERT/HOR/SUM signals completely. In that case, we can just use high impedance for the sum/diff buffers as Koji says and not suffer from the calibration errors at all I think.

 

  2458   Mon Dec 28 12:45:55 2009 KojiUpdateSUSMC2 is having a bad day

The MCL path of MC2 was in a strange state as the filters were activated as if it is in lock even though we had no lock. So I manually ran "mcdown". This reset the filters of the MCL path.

Quote:

MC2 is having a bad day, and I'm not yet sure why.  It's to do with the damping though.  When the damping is off, after a little while it will settle to ~30mV or so on the Watchdog screen.  When I enable all of the outputs and then turn on the damping, the optic gets kicked up.  It's like there's a minus sign error somewhere, maybe in a bad burtrestore?  This has been going on since I did my morning bootfest.

It's started to sit down and play nicely now.  Is someone doing magic remotely that is fixing things that I hadn't figured out yet?

 

  2481   Wed Jan 6 03:44:41 2010 KojiConfigurationIOOElusive Mode Matching Solution found!

I am in the way to get a reasonable optical layout.
Please calculate the final results with the following conditions.

"Result" =
- mode overlapping with astigmatism
- alignment matrix (m/rad, rad/rad) for Pitch and Yaw
- alignment orthogonality
- sensitivity of the mode overlapping to the perturbations
  * histgram
  * individual scan of the optic positions

Optics chain: MC3 - SM1(flat) - MMT1(f=-5m) - MMT2(f=+8m) - SM2(flat) - PRM

Incident angles: SM1 24deg, MMT1 3deg, MMT2 1deg, SM2 44.5deg

Distances:
MC3 HR - SM1: 884mm
SM1 - MMT1: 1058.2mm
MMT1 - MMT2: 1890mm
MMT2 - SM2: 2007.9mm
SM2 - PRM HR: 495.6mm

It has ~200mm deviation from the solution. I can move only MMT1 for final optimization.
Give us the numbers if it can improve the performance.
Note that this move changes SM1-MMT1 and MMT1-MMT2 simultaneously.

Quote:

I think I have finally found a Mode Matching solution for our new Input Mode Matching Telescope!  And after looking at the layout diagram with Koji and Raffaele, it seems like all of the optics will fit into the chambers / onto the tables (not true as of last week). 

3. RoCMMT1 is -5m
   RoCMMT2 is 8m,
   with the MMTs 1.89m apart.
   This is a 1.6x telescope.
   MMT2 is 2.2641m from the PRM
   MMT1 is 2m from MC3.
   The Condition Number for this optical chain is 89219047.5781.

This layout is very similar to the one that Koji posted on the wiki yesterday:  Upgrade09/Optical Layout.  The difference is that I want to move MMT1 ~20cm closer to the MC13 table, so just on the other side of the main red beam that goes directly to PRM.  There is plenty of space there, so it should be all good.  The tricky bit is that the flat steering mirrors fit into things now while they are piezos, but they will be trickier to fit if we make them into Tip Tilts.  But I have full faith in Koji's amazing optical table layout skills, that he can make it happen. 

Unless there are major objections, I think this is the MMT that we're going to go with. (So speak now or forever hold your peace.)  The angle between tilt and translation isn't quite what we'd like it to be (at ~18deg), but it's not too terrible.  And we still have 99.5% overlap which is very important.

 

  2495   Sun Jan 10 15:47:26 2010 KojiUpdateSUStransfer function measurement of the quadrant maglev circuit

1. Why do all of the BNCs have no GND connection? Each should have the individual cables to the ground. Each signal line and the corresponding ground line should be twisted together.

2. This looks the (usual) oscillation of the V-I conversion stage but I can't tell anything as I don't have the circuit diagram of the whole circuit.

3. In a certain case, putting some capacitance at the feedback may help. Read P.11 of the data sheet of LT1125. Try to put some capacitors from 20pF to some larger one whether it changes the situation or not. I suppose the bandwidth of your sensor can be ~1kHz. So putting a capacitance less than 10nF still has no effect to the servo.

  2498   Sun Jan 10 17:15:25 2010 KojiUpdateSUStransfer function measurement of the quadrant maglev circuit

1. Yes. That is the bad. You should eventually replace the BNCs to the isolated ones.

2. OK. I like to emphasize again that everyone works on electronics should read data sheets more carefully and seriously because they have many important practical instructions to exploit full performance of the components. 

Quote:

Quote:

1. Why do all of the BNCs have no GND connection? Each should have the individual cables to the ground. Each signal line and the corresponding ground line should be twisted together.

2. This looks the (usual) oscillation of the V-I conversion stage but I can't tell anything as I don't have the circuit diagram of the whole circuit.

3. In a certain case, putting some capacitance at the feedback may help. Read P.11 of the data sheet of LT1125. Try to put some capacitors from 20pF to some larger one whether it changes the situation or not. I suppose the bandwidth of your sensor can be ~1kHz. So putting a capacitance less than 10nF still has no effect to the servo.

 1. They are all connected to the box which has a single connection to the board ground. If I connect each of them to the ground, there would be many small loops

of ground. Of course, I should have replaced all the connectors such that the they are disconnected to the box as point out by Robert.

2. The oscillation disappears after I add 5 nF capacitor in parallel to the existing resistor. Thank you very much for pointing this out.

 

  2526   Tue Jan 19 02:40:38 2010 KojiUpdateElectronicstriple resonant circuit for EOM

The design looks very good. I have some questions.

1. As far as I remember, you've got the gain of slightly worse than 10 for a 55MHz single resonant case. Why your expectation of the gain (G=11) for the highest resonance better than this?

Supposing the loss exists only on the EOM, the other part of the LC network for the triple work as an inductor at the resonant frequency. This is just equivalent as the single resonant case. So the expected gain at 55MHz should coincides with what we already have. Probably, the resistance of 4 Ohm that is used here had too rough precision???

2. How can you adjust the resonances precisely?

Do we need any variable components for Cs and Ls, that may have worse quality than the fixed one, generally speaking.
I myself has no experience that I had to tune the commercial EOM because of a drift or whatever. I hope if you can adjust the resonance with a fixed component it should be fine.

3. Changing Cp. What does it mean?

Do you put additional cap for Cp?

4. The resonances for the lower two look very narrow. Is that fine?

This will show up in a better shape if we look at the transfer function for the gain. Is this right?

If we have BW>100kHz, it is sufficient.

5. Impedance matching for the lower two resonances.

Yep. You know this problem already.

 

  2527   Tue Jan 19 03:04:14 2010 KojiUpdateElectronicstriple resonant circuit for EOM

Self-follow:

I got the answer of Q3 from the follow-up entry.

For Q4, once you get the impedance of the LC network lower than n^2*50, the EOM gain will be quite low. This means that the resonance is anyway narrow.
I did some simple calculation and it shows that the width of the resonance will be 100kHz~500kHz. So it maybe OK.

Quote:

The design looks very good. I have some questions.

1. As far as I remember, you've got the gain of slightly worse than 10 for a 55MHz single resonant case. Why your expectation of the gain (G=11) for the highest resonance better than this?

Supposing the loss exists only on the EOM, the other part of the LC network for the triple work as an inductor at the resonant frequency. This is just equivalent as the single resonant case. So the expected gain at 55MHz should coincides with what we already have. Probably, the resistance of 4 Ohm that is used here had too rough precision???

2. How can you adjust the resonances precisely?

Do we need any variable components for Cs and Ls, that may have worse quality than the fixed one, generally speaking.
I myself has no experience that I had to tune the commercial EOM because of a drift or whatever. I hope if you can adjust the resonance with a fixed component it should be fine.

3. Changing Cp. What does it mean?

Do you put additional cap for Cp?

4. The resonances for the lower two look very narrow. Is that fine?

This will show up in a better shape if we look at the transfer function for the gain. Is this right?

If we have BW>100kHz, it is sufficient.

5. Impedance matching for the lower two resonances.

Yep. You know this problem already. 

 

  2528   Tue Jan 19 03:20:28 2010 KojiUpdateElectronicsdesign complete --- triple resonant circuit for EOM ---

First I was confused, but now I think I understood.

My confusion:
If the k get bigger, L get smaller, C get bigger. This makes R(L) smaller and R(C) smaller. This sounds very nice. But why smaller k is preferable in the Kiwamu's result?

Explanation:
The resultant impedance of the network at a resonance is determined by Zres = L/(R C) or something like that. Here R = R(L)+R(C). (I hope this is right.)

Here larger Zres is preferable. So smaller R is nice.

But If the speed of reduction for R is slower than that of L/C (which is proportional to k^-2), increasing k does not help us to increase of Zres. And that's the case.

This means "if we can put the LC network in the box of EOM, we can do better job!" as we can reduce Cp.

Quote:

scaling.png


   Loss for Capacitor :  R(C) = 0.5 (C / 10pF)^{-0.3} Ohm

   Loss for Inductor :    R(L) = 0.1 ( L / 1uH) Ohm

  2535   Thu Jan 21 10:09:27 2010 KojiSummaryIOOPhotos of the optical tables

I made a wiki page dedicated for the photos of the optical tables.
The current layouts were uploaded.

http://lhocds.ligo-wa.caltech.edu:8000/40m/Optical_Tables

  2536   Thu Jan 21 10:31:13 2010 KojiUpdateABSLSome preliminary results from measuring PRC's transmissivity for an amplitude modulated beam

Nice and interesting plot.

I suppose slight decrease of the Schnupp asymmetry (in your model) adjusts the discrepancy in the high freq region.
At the same time, it will make the resonance narrower. So you need to put some loss at the recombination (=on the BS)?

...of course these depends on the flatness of the calibration.

  2559   Tue Feb 2 13:14:09 2010 KojiHowToIOOAnatomy of New Focus Resonant EOM

Joe let me use the resonant EOM for GigE phase camera for a while.
Then, I immediately started to open it :)

it uses the MiniCIrcuits T5-1T transformer and a TOKO RCL variable inductor.

The photos are on the Picasa 40m album.

http://lhocds.ligo-wa.caltech.edu:8000/40m/40m_Pictures

  2564   Wed Feb 3 01:17:19 2010 KojiUpdatePSLIFO isn't playing nice tonight

I checked the situation from my home and the problem was solved.

The main problem was undefined state of the autolocker and the strange undefined switch states, being associated with the bootfest and burtrestore.

- MC UP/DOWN status shows it was up and down. So I ran scripts/MC/mcup and scripts/MC/mcdown. These cleared the MC autolocker status.

- I had a problem handling the FSS. After mcup/mcdown above, I randomly pushed the "enable/disable" buttons and others, and with some reason, it recovered the handling. Actually it acquired the lock autonomously. Kiwamu may have also been working on it at the same time???

- Then, I checked the PSL loop. I disconnected the loop by pushing the "test" button. The DC slider changes the PZT voltage only 0~+24V. This is totally strange and I started pushing the buttons randomly. As soon as I pushed the  "BLANK"/"NORMAL" button, the PZT output got back under the control.

- Then I locked the PMC, MZ, and MC as usual.

Alberto: You must be careful as the modulations were restored.

Quote:

[Jenne, Kiwamu]

It's been an iffy last few hours here at the 40m.  Kiwamu, Koji and I were all sitting at our desks, and the computers / RFM network decided to crash.  We brought all of the computers back, but now the RefCav and PMC don't want to lock.  I'm a wee bit confused by this.  Both Kiwamu and I have given it a shot, and we can each get the ref cav to sit and flash, but we can't catch it.  Also, when I bring the PMC slider rail to rail, we see no change in the PMC refl camera.  Since c1psl had been finicky coming back the first time, I tried soft rebooting, and then keying the crate again, but the symptoms remained the same.  Also, I tried burt restoring to several different times in the last few days, to see if that helped.  It didn't.  I did notice that MC2 was unhappy, which was a result of the burtrestores setting the MCL filters as if the cavity were locked, so I manually ran mcdown.  Also, the MC autolocker script had died, so Kiwamu brought it back to life.

Since we've spent an hour on trying to relock the PSL cavities (the descriptive word I'm going to suggest for us is persistent, not losers), we're giving up in favor of waiting for expert advice in the morning.  I suppose there's something obvious that we're missing, but we haven't found it yet......

 

  2587   Wed Feb 10 23:15:37 2010 KojiUpdateElectronicstriple resonant EOM ---- preliminary result

Hey, this looks nice, but can you provide us the comparison of rad/V with the resonant EOM of New Focus?

Quote:

I have made a prototype circuit of the triple resonant EOM.

The attached is the measured optical response of the system.

The measured gains at the resonances are 8.6, 0.6 and 7.7 for 11MHz, 29.5MHz and 55MHz respectively.

I successfully got nice peaks at 11MHz and 55MHz. In addition resultant optical response is well matched with the predicted curve from the measured impedance.

However there is a difference from calculated response (see past entry) (i.e. more gains were expected)

Especially for the resonance of 29.5MHz, it was calculated to have gain of 10, however it's now 0.6. Therefore there must a big loss electrically around 29.5MHz.

I am going to re-analyze the impedance and model the performance in order to see what is going on.

 

  2588   Wed Feb 10 23:44:56 2010 KojiSummaryCOCPhase Map Analysis

In the middle of the last month, Kiwamu and I went to Garilynn's lab to measure the phase maps of the new ITMs and SRMs.

Analysis of the phase map data were posted on the svn directory:
https://nodus.ligo.caltech.edu:30889/svn/trunk/docs/upgrade08/cocdocs/PhaseMaps/

The screen shots and the plots were summarized in a PDF file. You can find it here:
http://lhocds.ligo-wa.caltech.edu:8000/40m/Upgrade_09/Main_Optics_Phase_Maps

The RoCs for all of the PRMs are turned out to be ~155m. This is out of the spec (142m+/-5m) although the actual effect is not understand well yet..

These RoCs are almost independent from the radus of the assumed gaussian beam.
In deed, I have checked the dependence of the RoC on the beam spot position, and it turned out that the RoCs vary only little.
(In the SRMU01 case, for example, it varies from 153.5m to 154.9m.)
The beam radius of 3mm was assumed. The RoCs were calculated 20x20mm region around the center of the mirror with a 2mm mesh.
 

Attachment 1: SRM01_HR_RoC_rad_15mm.png
SRM01_HR_RoC_rad_15mm.png
Attachment 2: SRM01_HR_RoC_scan.png
SRM01_HR_RoC_scan.png
  2602   Sat Feb 13 13:21:53 2010 KojiUpdateElectronicstriple resonant EOM --- liniaryity test

Looks good. I just thought of the idea that we also can use Alberto's PLL setup to sense the modulation with more sensitivity.  ;-)

Quote:

I have measured the linearity of our triple resonant EOM (i.e. modulation depth versus applied voltage)

The attached figure is the measured modulation depth as a function of the applied voltage.

The linear behavior is shown below 4Vrms, this is good.

Then it is  slowly saturated as the applied voltage goes up above 4Vrms.

However for the resonance of 29.5MHz, it is difficult to measure below 7Vrms because of the small modulation depth.

Our triple resonant EOM looks healthy

 - - - - result from fitting - - -

11MHz: 910mrad/Vrms+20mrad

29.5MHz: 46mrad/Vrms+6.2mrad

55MHz:820mrad/Vrms+10mrad

 

  2611   Wed Feb 17 19:36:05 2010 KojiUpdateCOCArm visibility

I have measured the arm visibilities.
I did not see any change since the last wiping. Our vacuum is not contaminating the cavity in the time scale of 2 months.

It is very good.


Arm visibility measurement ~ latest (Feb. 17, 2010)

X Arm: 0.898 +/- 0.003
Y Arm: 0.892 +/- 0.006

Arm visibility measurement after the vent (Dec. 14, 2009)

X Arm: 0.897 +/- 0.005
Y Arm: 0.893 +/- 0.004

Arm visibility measurement before the vent (Nov 10, 2009)

X Arm: 0.875 +/- 0.005
Y Arm:
0.869 +/- 0.006

  2615   Fri Feb 19 02:38:32 2010 KojiConfigurationoplevsIntsant green oplevs for ITMs shooting from the ends

I set up instant green oplevs for ITMs.

A green laser pointer has been set on each end table. It illuminates the ITM center. The beam goea through the ETM substrate.
The reflected green beam returns to the ETM if the ITMs are aligned. Even though the reflected beam to the end is too big, this can
be a rough reference for each ITM.

Note: The green laser pointer at the ETMX were borrowed from Frank. We must return it to him when we finish the work.

  2617   Fri Feb 19 13:28:44 2010 KojiUpdateGeneralPrep for Power Supply Stop

- ETMX/ETMY oplev paths renewed. The nominal gain for ETMY YAW was reversed as a steering mirror has been put.
- Oplevs/QPDs cenrtered except for the MCT QPD.
- SUS snapshots updated
- QPD/Aligment screenshots taken

40m Wiki: Preparation for power supply stop

Attachment 1: screen_shot.png
screen_shot.png
  2625   Mon Feb 22 11:42:48 2010 KojiUpdateGeneralPrep for Power Supply Stop

Turned on the power supply for the oplev lasers.
Turned on the power of the aux NPRO.
Turned on some of the Sorensen at 1X1.
Fixed the thermal output to round -4.0.
Locked PMC / MZ.

Waiting for the computers recovering.

  2630   Tue Feb 23 06:47:57 2010 KojiUpdateGeneralIFO situations / low power MC lock

Work on 22nd Monday:

[MC recovery]

- Tried to lock MC after the computer recovery by Joe.
- A lot of higher modes. I can touch the input periscope or the MC mirrors.
- First tried to align the MC mirrors. MC1 was aligned against the MC REFL PD. MC2/3 was aligned to maximize the transmitted power.
- After the alignment, I got the MC Trans Sum ~8V. Also I saw the flashing of the arm cavities. I decided to take this alignment although the beam looks little bit clipped by the faraday.

[IFO alignment recovery]

- Aligned the arms for TEM00 manually.
- Arm alignment script seems not working now. This could come from the move of the end QPDs
- PRMI/DRMI were aligned. All alignment values saved.

[Low power MC]

[Optical config]

- I fixed the MCT CCD camera. It is quite useful to align the MC.

- Inserted HWP+Cube PBS+HWP combo in the MC incident path.
- First HWP and PBS adjust the light power. The second HWP is fixed at 342deg such that it restores the poralization to S.
- The incident power was measured by the SCIENTECH power meter. Offset of 3mW was subtracted in the table below.

HWP1 angle P_MC_incident comment
126deg 1.03W Max
100 0.39  
90 0.098 Low power max
85 0.021 Low power nominal

- HWP1 85deg is the nominal.

- I needed to touch the steering mirror (indicated by the picture) to obtain TEM00.
  The alignment of the HWPs and the cube PBS didn't change the mode. Thermal lense of the cube?

- I could not lock the MC with the incident power below 100mW. So the BS in the MC REFL path was replaced by a total reflector (Y1-45S).
- This increased the power on the MC REFL PD x10 of the previous. NOW WE ARE CONSTRAINED BETWEEN 81deg~90deg. DON'T ROTATE FURTHER!
- The original BS was stored on the AP table as shown in the picture.
- This total reflector disabled the MC WFS QPDs. We can't use them.

[Lock of the MC with 20mW incident]
- Disable the MC autolocker.
- Disable the MC WFS.
- Run
  /cvs/cds/caltech/scripts/MC/mcloopson
- Turn on the MCL servo.
- Set the MCL gain to 1.5 (it was nominally 0.3 for the high power)
- Just wait until lock.

[Gain boost after the lock] ...If you like to have more gain
- There was almost no room to increase the MCL gain.
- MC_REFL_GAIN can be increased from +6dB to +20dB
  ezcawrite "C1:IOO-MC_REFL_GAIN" 20
- MC_VCO_GAIN can be increased from -3dB to +2dB
  ezcawrite "C1:IOO-MC_VCO_GAIN" 2
- Crank the FSS gains
  ezcawrite C1:PSL-FSS_MGAIN `ezcaread -n C1:PSL-STAT_FSS_NOM_C_GAIN`
  ezcawrite C1:PSL-FSS_FASTGAIN `ezcaread -n C1:PSL-STAT_FSS_NOM_F_GAIN`

[If lock is lost]
- Run
  /cvs/cds/caltech/scripts/MC/mcdown

Attachment 1: MC_incident.png
MC_incident.png
Attachment 2: MC_REFL.png
MC_REFL.png
  2637   Wed Feb 24 12:08:31 2010 KojiUpdateComputersRFM goes red -> recovered by the nuclear option

Most of the RFM went red this morning. I took the nuclear option and it seemed to be recovered.

  2639   Thu Feb 25 11:21:06 2010 KojiUpdateGeneralTanks opened

[Steve, Bob, Joe, Zach, Alberto, Kiwamu, Koji]

We opened the OMC-IMC access connector, ITMX North door, and ITMY West door.
We worked from 9:30-11:00.
The work was quite smooth thanks to the nice preparation of Steve as usual.

Thank the team for the great work!

 

  2641   Thu Feb 25 19:59:50 2010 KojiConfigurationSUSITMX OSEMs

Koji, Steve

ITMX OSEM CONFIGURATION

 

Attachment 1: osem_config_ITMX.png
osem_config_ITMX.png
  2643   Fri Feb 26 11:48:36 2010 KojiUpdateGeneralMC incident beam shift

Last night I worked on the MC incident beam such that we can hit the center of the MC mirrors.

Steve and I checked the incident beam on MC1. We found the beam is ~5mm south.
This was not too critical but it is better to be realigned. I moved the steering mirror on the OMC
table (in vac). We kept the MC resonated. After the maximization of the resonance, I realigned the
MC1 and MC3 such that the resonance in dominated by TEM00.

Jenne, Kiwamu, and I then closed the light door on to the OMC/IMC.

I will make more detailed entry with photos in order to explain what and how I did.

  2651   Tue Mar 2 23:11:43 2010 KojiUpdateSUSITMX hung

Jenne and Koji

We successfully hung ITMX on the SOS. Side magnet is ~2mm off from the center of the OSEM. ITMX aligned using the QPD. The OSEMs changes the alignment. It looks that something magnetic is inside the OSEM PD or LED.

Reguled ITMY side magnet.

Cleaned up the lab for the safety inspection.

  2664   Tue Mar 9 09:32:31 2010 KojiSummaryGeneralWideband measurement of Fast PZT response

I have measured a wideband response of the fast PZT in the LWE NPRO 700mW in the Alberto's setup.
This is a basic measurement to determine how much phase modulation we can obtain by actuating the fast PZT,
primarily for the green locking experiment.

RESULT

  • Above 200kHz, there are many resonances that screws up the phase.
     
  • Modulation of 0.1rad can be easily obtained even at 10MHz if the modulation frequency is scanned.
     
  • Change of the laser frequency in DC was observed depending on the modulation frequency.
    i.e. At the resonance the laser frequency escaped from the RF spectrum analyzer.
    This may induced by the heat dissipation in the PZT causing the temperature change of the crystal.
     
  • Some concerns: Is there any undesired AM by the PZT modulation?

---

METHOD

1. Locked the PLL of for the PSL-NPRO beating at 20MHz.

2. Added the modulation signal to the NPRO PZT input.
I used the output of the network analyzer sweeping from 100kHz to 1MHz.

3. Measured the transfer function from the modulation input to the PLL error signal.
The PLL error is sensitive to the phase fluctuation of the laser. Found that the first resonance is at 200kHz.
The TF is not valid below 3kHz where the PLL suppresses the modulation.

4. Single frequency modulation: Disconnected the PLL setup.
Plug Marconi into the fast PZT input and modulate it at various frequencies.
Observing with the RF spectrum analyzer, I could see strong modulation below 1MHz.
It turned out later that the TF measurement missed the narrow peaks of the resonances due to the poor freq resolution.

Also the modulation depth varies frequency by frequency because of the resonances.
Scanned the frequency to have local maximum of the modulation depth. Adjusted the
modulation amplitude such that the carrier is suppressed
(J0(m)=0 i.e. m~2.4). As I could not obtain
the carrier suppression at above 1MHz, the height of the carrier and the sidebands were measured.

The modulation frequency was swept from 100kHz to 10MHz.

5. Calibration. The TF measured has been calibrated using the modulation depth obtained at 100Hz,
where the resonance does not affect the response yet.

The responce of the PZT was ~10MHz/V below 30kHz. Looks not so strange although this valure is
little bit high from the spec (2MHz/V), and still higher than my previous experience at TAMA (5MHz/V).
Note that this calibration does not effect to the modulation depth of the single freq measurement as they are independent.

Attachment 1: PZT_response.png
PZT_response.png
  2668   Thu Mar 11 17:51:04 2010 KojiUpdateSUSRecent status of SOSs

Jenne, Koji

Recent status of SOSs:

We completed one of the suspension (ITMY).

ITMX: 6 Magnets, standoffs, and guide rod glued / balance to be confirmed / needs to be baked
ITMY: 6 Magnets, standoffs, and guide rod glued / balance confirmed / needs to be baked
SRM: 6 Magnets, one standoff, and guide rod glued,  / waiting for the release from the gluing fixture.
PRM: one standoff, and guide rod glued / waiting for the magnet gluing. 

We think we solved all the problems for hanging the suspensions.

--- Magnet gluing fixture ---

  • There is the two kinds of fixtures. Neither does work propery in the original form!
  • The height of the side magnets should be finely adjusted by changing the teflon sheets beneath the optics in the fixture.
  • Be aware of the polarity of the fixture in terms of the side magnets
  • Wrongly glued magnets (and others) can be removed by a razor blade with some amount of acetone.
  • The pickle picker frequently knocks the magnets down during the release. Don't s be down in the dumps too much.

--- Suspending the mirror ---

  • The wire winches must be carefully attached to the suspension tower such that the wires are not streached during fastening the clamps.
  • There are a couple variations of the drawings for SOS. The one we have has #4-40 for the earthquake stops at the bottom.
    Zach and Mott made the EQ stops with the right size.
  2679   Thu Mar 18 10:46:51 2010 KojiUpdateABSLPLL reconstructed

Last night (Mar 17) I checked the PLL setup as Mott have had some difficulty to get a clean lock of the PLL setting.

  • I firstly found that the NPRO beam is not going through the Faraday isolator well. This was fixed by aligning the steering mirrors before the Faraday.
     
  • The signal from the RF PD was send to the RF spectrum analyzer through a power splitter. This is a waist of the signal. It was replaced to a directional coupler.
     
  • Tee-ing the PZT feedback to the oscilloscope was producing the noise in the laser frequency. I put the oscilloscope to the 600Ohm output of the SR560, while connectiong the PZT output to the 50Ohm output.
     
  • In addition, 6dB+6dB attenuators have been added to the PZT feedback signal.

Now the beating signal is much cleaner and behave straight forward. I will add some numbers such as the PD DC output, RF levels, SR560 settings...

Now I am feeling that we definitely need the development of really clean PLL system as we use PLL everywhere! (i.e. wideband PD, nice electronics, summing amplifiers, stop poking SR560, customize/specialize PDH box, ...etc)

  2681   Thu Mar 18 13:40:35 2010 KojiUpdateABSLPLL reconstructed

We use the current PLL just now, but the renewal of the components are not immediate as it will take some time. Even so we need steady steps towards the better PLL. I appreciate your taking care of it.

Quote:

Quote:

Last night (Mar 17) I checked the PLL setup as Mott had some difficulty to get a clean lock of the PLL setting.

  • I firstly found that the NPRO beam is not going through the Faraday isolator well. This was fixed by aligning the steering mirrors before the Faraday.
     
  • The signal from the RF PD was send to the RF spectrum analyzer through a power splitter. This is a waist of the signal. It was replaced to a directional coupler.
  • Tee-ing the PZT feedback to the oscilloscope was producing the noise in the laser frequency. I put the oscilloscope to the 600Ohm output of the SR560, while connectiong the PZT output to the 50Ohm output.
  • In addition, 6dB+6dB attenuators have been added to the PZT feedback signal.

Now the beating signal is much cleaner and behave straight forward. I will add some numbers such as the PD DC output, RF levels, SR560 settings...

Now I am feeling that we definitely need the development of really clean PLL system as we use PLL everywhere! (i.e. wideband PD, nice electronics, summing amplifiers, stop poking SR560, customize/specialize PDH box, ...etc)

I also had noticed the progressive change of the aux NPRO alignment to the Farady.

I strongly agree about the need of a good and robust PLL.

By modifying the old PDH box (version 2008) eventually I was able to get a PLL robust enough for my purposes. At some point that wasn't good enough for me either.

I then decided to redisign it from scratch. I'm going to work on it. Also because of my other commitments, I'd need a few days/1 week for that. But I'd still like to take care of it. Is it more urgent than that?

 

  2683   Thu Mar 18 19:00:04 2010 KojiSummaryElectronicsadvantege of our triple resonant EOM

Did you find what is the merit of their impedance matching technique?

Quote:

In this LVC meeting I discussed about triple resonant EOMs with Volker who was a main person of development of triple resonant EOMs at University of Florida.

Actually his EOM had been already installed at the sites. But the technique to make a triple resonance is different from ours.

They applied three electrodes onto a crystal instead of one as our EOM, and put three different frequencies on each electrode.

For our EOM, we put three frequencies on one electrode. You can see the difference in the attached figure. The left figure represents our EOM and the right is Volker's.

Then the question is; which can achieve better modulation efficiency ?

Volker and I talked about it and maybe found an answer,

 We believe our EOM can be potentially better because we use full length of the EO crystal.

This is based on the fact that the modulation depth is proportional to the length where a voltage is applied onto.

The people in University of Florida just used one of three separated parts of the crystal for each frequency.

 

ELOG V3.1.3-