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ID Date Author Type Category Subject
  2946   Tue May 18 14:30:31 2010 josephbUpdateCDSLSC.mdl problem found and fixed

After having checked old possibilities and deciding I wasn't imagining the lsc.mdl file not working, but working as another name, I tracked Alex down and asked for help.

After scratching our heads, we finally tracked it down to the RCG code itself, as opposed to any existing code.

Apparently, the skeleton.st file (located in /home/controls/cds/advLigoRTS/src/epics/util/) has special additional behavior for models with the following names: lsc, asc, hepi, hepia, asc40m, ascmc, tchsh1, tchsh2.

Alex was unsure what this additional code was for.  To disable it, we went into the skeleton.st file, and changed the name "SEQUENCER_NAME_lsc" to "SEQUENCER_NAME_lsc_removed" where ever it occured.  These names were in #ifdef statements, so now these codes will only be used if the model is named lsc_removed.  This apparently fixed the problem.  Running startlsc now runs the code as it should, and I can proceed to testing the communication to the lsp model.

Alex said he'd try to figure out what these special #ifdef code pieces are intended for and hopefully completely remove them once we've determined we don't need it.

  2945   Tue May 18 12:04:13 2010 robUpdateIOOFirst steps toward MC mode measuring

Quote:

Another note: Don't trust the PSL shutter and the switch on the MEDM screens! Always use a manual block in addition!!! We discovered upon closeup that hitting the "Closed" button, while it reads back as if the shutter is closed (with the red box around the buttons), does not in fact close the shutter.  The shutter is still wide open.  This must be fixed.

 Has anyone tried pushing the "reset" button on the Uniblitz driver?

  2943   Tue May 18 11:54:29 2010 steveConfigurationSAFETYpsl mechanical shutter is not working

As we learned yesterday, the PSL laser power out put mechanical shutter is not working in the remote mode. It only works in local manual mode.

Do not rely on the MEDM screen monitor readout! The position is only changing on the monitor. The main beam must be blocked before the output periscope.

  2942   Tue May 18 01:40:56 2010 KojiUpdateIOOFirst steps toward MC mode measuring

OK. Don't worry. This is just an initial confusion which we also had for the suspensions a while ago.

The faraday must be clamped. It shakes the table terribly but it is fine. The leveling may change a bit but should be small enough. Otherwise, just tweak the weights. In fact, the faraday has enough large apertures and we hope we don't need to move it again, as far as the MC incident beam is not moved. But if necessary, we don't move the mirrors but move the faraday itself.

Usually the alignment of the MC is taken by MC2/MC3 such that we don't  move the refl. But if you think what have moved is the MC1/MC3 (i.e. activity in the IMC chamber), take the alignment of the MC1/MC3.

It is just a matter of time to get TEM00. If you get TEM11, it is already close. If you align for TEM11, it is enough aligned to lock TEM10 or TEM01. Once you got better mode, align for it again. Eventually you will get TEM00.

The leveling may change by moving the optics and the weight again. But once the leveling is recovered by arranging the weights somewhere else,
the pointing must be fine again. If necessary, You can remove two optics for squeezing injection (strange motorized rotating mirror and a mount sticking out from the table to south.)

Yes, we need to move the PZT mirror. For the connection, only Steve can give us the right way to do it. If it is too much hussle, just move only the mirror and ignore the wiring for now.

I will update how the mirrors should be migrated from the table to the table.

 

  2941   Mon May 17 19:42:11 2010 JenneUpdateIOOFirst steps toward MC mode measuring

[Jenne, Kevin, Steve]

We made some progress toward getting the MC's beam profile measured.  In the end, no changes were made to anything today, but we're more prepared to go for tomorrow.

What we did:

* Grabbed the scanning slit beam scan from the PSL lab.  It's the same kind as we had here at the 40m, so Kevin was able to hook it up to the computer, and confirmed that it works.

* Opened the IOO and OMC chamber doors, and locked the MC.  Unfortunately the MC mode was awful in Yaw.  Awful like TEM(0,10+). But it still locked.  

* Confirmed that the beam went through the Faraday.  I looked at the beam before and after the Faraday on a card, and it was the same nasty beam both before and after.  So it looks like Zach did a good job aligning the Faraday and everything else.  I was going to clamp the Faraday, but I didn't yet, since I wanted to see the nice happy TEM00 mode go through without clipping before risking moving the Faraday during clamping (I don't know how heavy it is, so I'm not sure how much it might potentially move during clamping.)

* Noticed that there is a whole lot of crap on both the OMC and BS tables that's going to have to move.  In particular, one of the weights leveling the OMC table is right where I need to put MMT2.  Steve suggested putting the optic there, in its approximate place, before doing too much other stuff, since it could potentially affect the leveling of the table, and thus the input pointing to the MC.  Unfortunately, to do that I'll need to move the weight, which is definitely going to change things.  Sad face.  Moving the weight will likely be one of the first things I do tomorrow, so that all 3 profile measurements have the same configuration. 

* Before closing up, I tried to align the MC, to get back to TEM00, to no avail.  I got as far as achieving TEM11 flashing, along with a bunch of other crappy modes, but didn't get 00.  That's also on the to-do list.

What we're going to do:

* Open the chambers, and align the MC to TEM00 (using the sliders on the MC align screen).

* Check with an IR card that the beam goes through the Faraday.

* Clamp the Faraday, reconfirm.

* Remove the weight on the OMC table.

* Place MMT2 on the OMC table in it's approximate final location.

* Realign the MC, and make sure the beam goes through the Faraday.  If this doesn't happen smoothly, I may need more instruction since I've never dealt with aligning the Faraday before.  What are the appropriate mirrors to adjust? 

* Move the PZT flat steering mirror from the BS table to the IOO table.  (Thoughts on this?  This will change the table leveling, and also includes the trickiness of needing to move the connectors for the PZT.)

* Place a flat mirror on the BS table to route the MC beam out to the BS/PRM/SRM oplev table. 

* Measure the mode using the beam scan: on the BS oplev table, on the POX table, and then perhaps by shooting the beam through the beamtube on the ETMY (new convention) table.

* Place MMT1 on the BS table, use flat mirrors to get it out of the chambers, repeat measurements.

* Place MMT2 in the correct position, use flat mirrors to get it out of the chambers, repeat measurements.

All of this may require some serious cleaning-up of the BS table, which is going to be ugly, but it has to happen sometime. Hopefully I can get away with only moving a minimal number of things, in order to get these measurements done.

 

Another note: Don't trust the PSL shutter and the switch on the MEDM screens! Always use a manual block in addition!!! We discovered upon closeup that hitting the "Closed" button, while it reads back as if the shutter is closed (with the red box around the buttons), does not in fact close the shutter.  The shutter is still wide open.  This must be fixed.

  2940   Mon May 17 17:17:49 2010 josephb, steve, alberto, kiwamuUpdateCDSNew CDS computers now in racks.

We placed 3 new computers in the racks.  One in 1X4 (machine running SCX) and 2 in 1Y4 (LSC and SUS).  These are 1U chassis, 4 core machines for the CDS upgrade.  I will be bringing over 2 IO chassis and their rails over tomorrow, one to be placed in 1Y4, and 1 in 1X4.

We still need some more 40 pin adapter cables and will send someone over this week to make them.  However, once we have those, we should be able to get two to three machines going, one end computer/chassis and the SUS computer/chassis.

After tomorrow we are still going to be owed 1 computer, another dolphin fiber, a couple of blue boxes, and the LSC, IO, and Y end IO chassis.  We also realized we need further fiber for the timing system.  We're going to need to get and then run fiber to both ends, as well as to 1X3, where the LSC IO chassis will be.

 

  2939   Mon May 17 10:57:16 2010 steveConfigurationSUSdamping restored to ETMYs

ETMY-south sus damping was restored

  2938   Mon May 17 02:10:10 2010 KojiConfigurationIOOHow to lock / align the MC

Let me remind you how to lock and align the IMC

To lock

1. Open the doors for the IMC/OMC chambers. Open the manual shutter of the PSL just in front of the optical window

2. Run scripts/MC/mcloopson

3. Set the MC length path gain 0.3 / Set the MC total gain "+20"

4. If you want to avoid excitation of the mirrors by air turbulence, put a big plastic film and put three posters on the top and both the sides on the floor to block the wind go into the chamber.

To shut down

1. Run scripts/MC/mcloopsoff

2. Close the manual shutter, Remove the wind blockers, and the light door of the chambers

To align the MC

1. Tweak MC2 and MC3 to get maximum transmittion and/or minimum reflection.

  2937   Sun May 16 19:25:45 2010 KojiUpdateGreen Lockingreflected beam at PD

Don't make a short cut. The beam size at a single place does not tell you anything.
Measure the mode of of the beam at multiple points. Calculate the mode matching ratio.

Align the mirrors precisely. Try to see the DC fringe. Predict the size of the DC fringe.

Test the demodulation system with a function generator. Find the 200kHz signal using the spectrum analyzer to find the signal and the optimal alignment.

Put the DC signal and the AC signal to the oscilloscope as X&Y.

Good luck.

 

  2936   Sun May 16 12:51:08 2010 kiwamuUpdateGreen Lockingreflected beam at PD

Mode matching to the cavity has been done.

Now the reflection from the cavity is successfully going into the PD.

However I could not see any obvious error signal.

I should compute and re-check the expected signal level.

 


(mode matching of the crystal)

On the last Wednesday, Kevin and I measured the mode profile before the PPKTP crystal,  and we found the Gaussian beam at the crystal is focused too tightly (w = 38 um).

In order to achieve the best conversion efficiency the waist size should be 50.0 um. So we moved a lens, which was located before the crystal, to 7 cm more away from the crystal. Eventually we obtained a better focus (w = 50.1 um).

Thanks, Kevin. You did a good job.

 

(mode matching of the cavity)

I put a lens with f=-50 mm after the crystal to diverge the green beam more quickly. Then the beam is going through the Faraday of 532 nm, two final modematching lenses and ETMY at last.

By shifting the positions of these lenses, I obtained the reflection from ITMY with almost the same spot size as that of the incident. This means modemathing is good enough.

I put two more steering mirrors before its injection to the ETM, this allows us to align the beam axis against the cavity.

I aligned the axis by using the steering mirrors and now the green beam are successfully hitting the center of both the ETM and the ITM.

Then the alignment of the ETM and the ITM was adjusted from medm, so that both reflection goes in the same path as that of the incident.

And then I put a PD (Thorlabs PDA36A) to see the reflection rejected by the Faraday.

Connecting a mixer and a local oscillator (Stanford func. generator) with f=200kHz, but I couldn't see any obvious PDH signal....

Since the PD is DC coupled, the signal is almost dominated by DC voltage. Even if I inserted a high pass filter to cut off the DC, the AC signal looks very tiny..

  2935   Sat May 15 04:13:33 2010 KojiSummaryIOOMC table leveled

Fixing at the next time is absolutely OK.

Quote:

Ah... no, I didn't. That explains why there were loose dogclamps on the table. I wrapped them in foil and put them on the clean cart. Can this wait until the next time we open the tank (i.e. to measure the beam profile), or should I go over there and clamp it down today? 

 

  2934   Fri May 14 16:19:22 2010 JenneUpdatePEMGuts of a Guralp

[Jenne, Rana]

We took apart and examined one of the Guralp seismometers this afternoon.  For the most part we think we understand how it works. The horizontal sensors are a little more confusing, since we didn't end up finding the moving masses.  The vertical sensor is a flat rectangle, hinged at one edge.  There are capacitive sensors above and below the rectangle.  The hinged end is connected to a leaf spring. 

The PCBs are packed full of old-school 80's components.  We probably need an actual schematic to figure out where the preamp circuit is, which is what we'd want to think about fitzing with, if we were to try to improve the noise of the seismometer.  For now, we put it all back together, and back out on the granite slab. 

There was a wee bit of confusion when putting the N/S marker-spikes back on as to where they should go.  The solution is that the handle of the seismometer is aligned with the North/South axis, so the spikes should be aligned with the handle.  The lid of the seismometer is uniquely aligned to the stuff inside by the ribbon cable connector, as well as the holes in the lid for accessing the centering potentiometers.  So, align the lid to the pots, and then align the spikes to the handle.

Photos are on Picasa.

  2933   Fri May 14 16:14:37 2010 KevinUpdateGreen LockingGreen Laser Beam Profile

Quote:

Strange. I thought the new result became twice of the first result. i.e. w0=32um or so.

Can you explain why the waist raidus is estimated to be three times of the last one?
Can you explain why the measured radius @~70mm is not 0.8mm, which you told us last time,
but is 0.6mm?

The measurements have been done at the outside of the Rayleigh range.
This means that the waist size is derived from the divergence angle

theta = lambda / (pi w0)

At the beginning you used diameter instead of radius. This means you used twice larger theta to determine w0.
So if that mistake is corrected, the result for w0 should be just twice of the previous wrong fit.

 

 

I was off by a factor of sqrt(2). The correct fit parameters are

for the vertical beam profile:

reduced chi^2 = 3.28

x0 = (-87 ± 1) mm

w0 = (32.59 ± 27) µm

for the horizontal beam profile

reduced chi^2 = 2.02

x0 = (-82 ± 1) mm

w0 = (32.23 ± 20) µm

In the following plots * denotes vertical data points and + denotes horizontal data points. The blue curve is the fit to the vertical data and the purple curve is the fit to the horizontal data.

Attachment 1: profile.png
profile.png
Attachment 2: residuals.png
residuals.png
  2932   Fri May 14 12:14:26 2010 josephbUpdateCDSNeed to track down old code for lsc system and remove them

I'm currently in the process of tracking down what legacy code is interfering with the new lsc model.

It turns out if you change the name of lsc file to something else (say scx as a quick test for example), it runs fine.  In fact, the lsc and scx GDS_TP screens work in that case (since they're looking at the same channels).  As one would expect, running them both at the same time causes problems.  Note to self, make sure the other one is killed first.  It does mean the lsc code gets loaded part way, but doesn't seem to communicate on EPICs or to the other models.  However, I don't know what existing code is interfering.  Currently going trhough the target directories and so forth.

  2931   Fri May 14 10:33:01 2010 ZachSummaryIOOMC table leveled

Ah... no, I didn't. That explains why there were loose dogclamps on the table. I wrapped them in foil and put them on the clean cart. Can this wait until the next time we open the tank (i.e. to measure the beam profile), or should I go over there and clamp it down today?

 

  2930   Fri May 14 08:18:46 2010 steveUpdateGreen LockingReflection from ETM and ITM !

I stopped AWG  1 Hz drive to ITMYs. ITMXe was also driven or oscillating. ITMXe damping was off, so I turned it on. It did not effect it's oscillation

Attachment 1: itmx1hzos.jpg
itmx1hzos.jpg
  2929   Fri May 14 03:30:45 2010 KojiSummaryIOOMC table leveled

Thanks Zach.This was a great job.

It was not mentioned but: was the Faraday clamped down on the table?

 

  2928   Thu May 13 23:59:46 2010 ZachSummaryIOOMC table leveled

 After the recent removal of the old IMMT and the relocation of the Faraday isolator, the MC table was tilted a bit (southward and slightly westward---as of when I opened the chamber this afternoon). I re-leveled it by putting an extra two rectangular ballast blocks on the stack that was already hanging off the NNE edge of the table (there are a total of 4 in the stack now). I also screwed down the circular block that Koji and I put between the Faraday and SM1 on Tuesday, and re-mounted the two wire harness towers onto the table.

Needless to say, this threw the MC way out of alignment. I spent the rest of the afternoon reacquiring alignment and getting it to lock robustly. Here is a summary:

  • I adjusted MC3 until I got the 2nd, 3rd+ pass beams to overlap with the input beam between MC1&3, then I adjusted MC2&1 semi-methodically until I got something flashing at the transmitted end. This took some time.
  • I went back into the control room, engaged the loops and acquired lock on the TEM00 mode, whereupon I found that the beam spot was WAY off center on MC2 (due to my meddling with all the mirrors to get resonance flashes). I began using the MC2_spot_up (etc) scripts we wrote the other day to re-center it.
  • After a few iterations, the lock became weak, and eventually gave out. This is because the REFL beam was falling off the RFPD (and being clipped by the iris on the AP table), so I moved the iris and re-centered the beam on the diode.
  • With that, I was able to get the MC2 spot more or less centered, but then I noticed that---though the lock was clearly strong as evidenced both by the REFL power dip and visually via the camera on MC2---it looked like crap on the CCD. It seemed like there was some higher order mode structure sloshing around on top of the 00 spot, which didn't make any sense, until I realized that it was just a diffraction pattern from the TRANS beam getting clipped somewhere on the way out of the vacuum system.
  • I went back to the AP table, where I noticed that the TRANS beam was hitting near the edges of several of the mirrors on the way back to the PSL table, including the first one out of the viewport, so I turned IM4 to center the beam on this mirror, then proceeded to center the beam on each mirror downstream and then onto the CCD.
  • After getting a clear picture of the transmission on the CCD, centering the spot even better on MC2, then fine-tuning MC2&3 to strengthen the lock, I went back to the MC table to check that the transmitted beam was still passing through the center of the Faraday, which, by none other than an act of God, it was.
  • Having done the necessary work in the tank, I ran the A2L_MC2 script to fine-tune the centering of the spot on MC2. It needed a couple steps up and to the side, but after that the actuator gains for pitch and yaw were both balanced again to within ~2%, which is only slightly above the measurement error. We will probably need to adjust this continually, especially during the upgrade, so I didn't bother with getting it better than that.

After that, I shut off the loops, blocked the beam, and put the light doors back on the tanks. Then I went to the parking lot, then I got in my car, etc, etc, etc.

  2927   Thu May 13 15:19:44 2010 josephbUpdateCDSTrying to get lsc.mdl and lsp.mdl working

I had a chat with Alex this morning and discovered that the dcu_ids 13,14,15,16 are reserved currently, and should not be used.  I was told 9-12 and 17-26 were fine to use.  I pointed out that we will eventually have more modules than that.  His response was he is currently working on the framebuilder code and "modernizing" it, and that those restrictions will hopefully be lifted in the future although he isn't certain at this time what the real maximum gds_id number is (he was only willing to vouch for up to 26 - although the OMC seems to be currently working and set to 30).

Alex also suggested running an iop module to provide timing (since we are using adcSlave=1 option in the models).  Apparently these are x00.mdl, x01.mdl, x11.mdl files in the /home/control/cds/advLigoRTS/src/epics/simLink/ directory.  I saved x00.mdl as io1.mdl (I didn't want to use io0 as its a pain to differentiate between a zero and 'O'.  This new IOP is using gds_node=1, dcu_id=9.  I modified the approriate files to include it.

I modified /etc/rc.d/rc.local and added io1 to shmem line.  I modified /cvs/cds/caltech/target/fb/daqdrc to use dcu_id 9 as the controller (this is the new iop model dcu_id number).  In that same directory I modifed the file master by adding /cvs/cds/caltech/chans/daq/C1IO1.ini as well as uncommenting tpchn_C1 line.  I modified testpoint.par in /cvs/cds/caltech/target/gds/param to include C-node0, and modified the prognum for lsc and lsp to 0x31001003 and 0x31001005.

So I started the 3 processes with startio1, startlsc, startlsp, then went to the fb directory and started the framebuilder.  However, the model lsc.mdl is still having issues, although lsp and io1 seem to be working.  At this point I just need to track down what fundamentally is different between lsc and lsp and correct it in the lsc model.  I'm hoping its not related to the fact that we actually had a previous lsc front end and there's some legacy stuff getting in the way.  One thing I can test is changing the name and see if that runs.

 

  2926   Thu May 13 05:06:43 2010 ranaUpdate40m Upgrading216 MHz resonance in the POY11 PD killed

 

 This idea was tried before by Dale in the ~1998 generation of PDs. Its OK for damping a resonance, but it has the unfortunate consequence of hurting the dynamic range of the opamp. The 100 Ohm resistor reduces the signal that can be put out to the output without saturating the 4107.

I still recommend that you move the notch away from the input of the 4107. Look at how the double notch solution has been implemented in the WFS heads.

  2925   Wed May 12 23:31:17 2010 AlbertoUpdate40m Upgrading216 MHz resonance in the POY11 PD killed
It turned out that the resonance at 216 MHz in the 11MHz PD that I showed in the elog entry 2902 was casued by an instability of the of the MAX4107 opamap' feedback loop.
As the datasheet of the opamp shows, the close-loop gain has a peak at about 200-250MHz, in presence of even small capacitive loads.
In my case, perhaps either the capacitance of the BNC cables plugged to the RF output of the PD box, or the shunt capacitance of the circuit parts after the opamap (traces and resistors) might have introduced capacitance at the output of the amplifier.
 
LISO had failed in predicting the resonance because it has only ideal transfer functions of the opamps. In particular the open-loop gain of the opamaps in the library is just a function with a simple pole.
 
At RF frequencies the output impedances of the opamp starts having a non-negligible inductance that interacts with the load capacitance, generating a typical LC-circuit resonance.
 
In cases like this, such effect can be mitigated by introducing an "isolating" resistor at the output of the opamp.
 
So I did that and modified the circuit as in this simplified schematic here:
 
POX11.png
 

The choice of 100 Ohm for the isolating resistor was mainly empirical. I started with 10, then 20 and 50 until I got a sufficient suppression of the resonance. Even just 10Ohm suppressed the resonance by several tens of dB.

2010-05-12_POY11_CalibratedOpticalResponse0-500MHz.png

 

In that way the gain of the loop didn't change. Before that, I was also able to kill the resonance by just increasing the loop gain from 10 to 17.  But, I didn't want to increase the closed-loop gain.

One thing that I tried, on Koji's suggestion, was to try to connect the RF output of the PD box to an RF amplifier to see whether shielding the output from the cable capacitance would make the resonance disappear: It did not work.

  2924   Wed May 12 17:10:16 2010 AlbertoUpdate40m UpgradingRF frequency generation box - step 0

I started putting together the components that are coint to go inside the frequency generation box. Here's how it looked like:

DSC_1499_small.JPG

The single component are going to be mounted on a board that is going to sit on the bottom of the box.

I'm thinking whether to mount the components on an isolating board (like they did in GEO), or on an aluminum board.

I emailed Hartmut to know more details about his motivations on making that choice.

  2923   Wed May 12 12:58:26 2010 josephbConfigurationCDSSetup fb to handle lsc, lsp models on megatron

I modified /cvs/cds/caltech/target/fb and changed the line "set controller_dcu=10" to "set controller_dcu=13" (where 13 is the lsc dcu_id number).

I also changed the set gds_server line from having 10 and 11 to 13 and 14 (lsc and lsp).

The file /cvs/cds/caltech/fb/master was modified to use C1LSC.ini and C1LSP.ini, as well as tpchn_C2.par (LSC) and tpchn_C3.par (LSP)

testpoint.par in /cvs/cds/caltech/target/gds/param was modified to use C-node1 and C-node2 (1 less then the gds_node_id for lsc and lsp respectively).

Note all the values of gds_node_id, dcu_id, and so forth are recorded at http://lhocds.ligo-wa.caltech.edu:8000/40m/Electronics/Existing_RCG_DCUID_and_gds_ids

  2922   Wed May 12 12:32:04 2010 josephbConfigurationCDSModified /etc/rc.d/rc.local on megatron

I modified the /etc/rc.d/rc.local file on megatron removing a bunch of the old test module names and added the new lsc and lsp modules, as well as a couple planned suspension models and plants, to shared memory so that they'll work.  Basically I'm trying to move forward into the era of working on the actual model we're going to use in the long term as opposed to continually tweaking "test" models.

The last line in the file is now: /usr/bin/setup_shmem.rtl lsc lsp spy scy spx scx sus sup&

I removed mdp mdc mon mem grc grp aaa tst tmt.

  2921   Wed May 12 12:25:11 2010 KojiUpdateGreen LockingRe: Reflection from ETM and ITM !

??? I still don't understand. What principle are you rely on?

I could not understand why you rotated the HWP to the "minimum" transmission
and then minimized the transmission by rotating the output PBS. What is optimized by this action?

Probably there is some hidden assumption  which I still don't understand.
Something like:
Better transmission gives best isolation, PBS has some leakage transmission
of the S-pol light, and so on.

Tell me what is the principle otherwise I don't accept that this adjustment is "to get a good isolation with the Faraday".

P.S. you could flip the faraday without removing it from the V-shaped mount. This does not roll the Faraday.

Quote:

The procedure you wrote down as a standard is right.   I explain reasons why we didn't do such way. 

For our situation, we can rotate the polarization angle of the incident beam by using a HWP in front of the Faraday.  

This means we don't have to pay attention about the PBS_in because the rotation of either PBS_in or the HWP causes the same effect (i.e. variable transmission ). This is why we didn't carefully check the PBS_in, but did carefully with the HWP.

Normally we should take a maximum transmission according to a instruction paper from OFR, but we figured out it was difficult to find a maximum point. In fact looking at the change of the power with such big incident (~1W) was too hard to track, it only can change 4th significant digit ( corresponds to 1mW accuracy for high power incident ) in the monitor of the Ophir power meter. So we decided to go to a minimum point instead a maximum point, and around a minmum point we could resolve the power with accuracy of less than 1mW.

After obtaining the minimum by rotating the HWP, we adjusted the angle of PBS_out to have a minimum transmission.

And then we was going to flip the Faraday 180 deg for fine tuning, but we didn't. We found that once we remove the Faraday from the mount, the role angle of the Faraday is going to be screwed up because the mount can not control the role angle of the Faraday. This is why we didn't flip it.

Quote:

I could not understand this operation. Can you explain this a bit more?

It sounds different from the standard procedure to adjust the Faraday:

1) Get Max transmittion by rotating PBS_in and PBS_out.

2) Flip the Faraday 180 deg i.e. put the beam from the output port.

3) Rotate PBS_in to have the best isolation.

 

 

 

  2920   Wed May 12 10:33:32 2010 kiwamuUpdateGreen LockingRe: Reflection from ETM and ITM !

The procedure you wrote down as a standard is right.   I explain reasons why we didn't do such way. 

For our situation, we can rotate the polarization angle of the incident beam by using a HWP in front of the Faraday.  

This means we don't have to pay attention about the PBS_in because the rotation of either PBS_in or the HWP causes the same effect (i.e. variable transmission ). This is why we didn't carefully check the PBS_in, but did carefully with the HWP.

Normally we should take a maximum transmission according to a instruction paper from OFR, but we figured out it was difficult to find a maximum point. In fact looking at the change of the power with such big incident (~1W) was too hard to track, it only can change 4th significant digit ( corresponds to 1mW accuracy for high power incident ) in the monitor of the Ophir power meter. So we decided to go to a minimum point instead a maximum point, and around a minmum point we could resolve the power with accuracy of less than 1mW.

After obtaining the minimum by rotating the HWP, we adjusted the angle of PBS_out to have a minimum transmission.

And then we was going to flip the Faraday 180 deg for fine tuning, but we didn't. We found that once we remove the Faraday from the mount, the role angle of the Faraday is going to be screwed up because the mount can not control the role angle of the Faraday. This is why we didn't flip it.

Quote:

I could not understand this operation. Can you explain this a bit more?

It sounds different from the standard procedure to adjust the Faraday:

1) Get Max transmittion by rotating PBS_in and PBS_out.

2) Flip the Faraday 180 deg i.e. put the beam from the output port.

3) Rotate PBS_in to have the best isolation.

 

 

  2919   Wed May 12 09:16:29 2010 steveUpdateGreen LockingReflection from ETM and ITM !

 

 Now I know why Rana was wearing his bright green pants yesterday. It is nice to see the green beam in the 40m IFO again. It calls for celebration!

I stopped AWG 1Hz drive of ITMYs (south-arm) I still see unblocked beams at the ETMYs table. We have plenty of cleaned razor beam traps to be used. Please block Faraday rejects etc

  2918   Wed May 12 03:56:54 2010 KojiUpdateIOOFaraday aligned

Zach and Koji

The old small MMT was removed and wrapped by Al foils.

The steering mirror IM2-IM4 were displaced and aligned.

The Faraday isolator block is moved and aligned.

The MC is realigned and resonatng TEM-00.

Now the MC has slightly miscentered beam on the mirrors owing to change of the stack leveling.
OSEMs are also in a strange state. We should check this later.

  2917   Wed May 12 03:52:54 2010 KojiUpdateGreen LockingReflection from ETM and ITM !

I could not understand this operation. Can you explain this a bit more?

It sounds different from the standard procedure to adjust the Faraday:

1) Get Max transmittion by rotating PBS_in and PBS_out.

2) Flip the Faraday 180 deg i.e. put the beam from the output port.

3) Rotate PBS_in to have the best isolation.

Quote:

* To get a good isolation with the Faraday we at first rotated the polarization of the incident beam so to have a minimum transmission. And then we rotated the output polarizer until the transmission reaches a minimum. Eventually we got the transmission of less than 1mW, so now the Faraday should be working regardless of the polarization angle of the incident beam. As we predicted, the output polaerizer seems to be rotated 45 deg from that of the input.

  2916   Wed May 12 03:42:38 2010 KojiUpdateGreen LockingGreen Laser Beam Profile

Strange. I thought the new result became twice of the first result. i.e. w0=32um or so.

Can you explain why the waist raidus is estimated to be three times of the last one?
Can you explain why the measured radius @~70mm is not 0.8mm, which you told us last time,
but is 0.6mm?

The measurements have been done at the outside of the Rayleigh range.
This means that the waist size is derived from the divergence angle

theta = lambda / (pi w0)

At the beginning you used diameter instead of radius. This means you used twice larger theta to determine w0.
So if that mistake is corrected, the result for w0 should be just twice of the previous wrong fit.

Quote:

 

I recalculated the fits using the radius of the beam instead of the diameter of the beam at 13.5% full-width with the following results:

For the vertical beam profile:

reduced chi^2 = 3.25

x0 = (-86 ± 1)mm

w0 = (46.01 ± 0.38)µm

For the horizontal beam profile:

reduced chi^2 = 2.05

x0 = (-81 ± 1)mm

w0 = (45.50 ± 0.28)µm

 

  2915   Wed May 12 02:35:13 2010 Koji, Rana, KiwamuUpdateGreen LockingReflection from ETM and ITM !

We succeeded in getting the reflected green beam from both ITMY and ETMY.

After we did several things on the end table, we eventually could observe these reflections.

Now the spot size of the reflection from ITMY is still big ( more than 1 cm ), so tomorrow modematching to the 40m cavity is going to be improved by putting mode matching telescopes on right positions.

An important thing we found is that, the beam height of optics which directly guides the beam to the cavity should be 4.5 inch on the end table.

 


(what we did)

* Aidan, Kevin and Kiwamu set the beam to be linearly polarized by rotating a QWP in front of the Innolight. This was done by monitoring the power of the transmitted light from the polarizer attached on the input of the Faraday of 1064 nm. Note that the angle for QWP is 326.4 deg.

* We put some beam damps against the rejected beam from the Faraday

* To get a good isolation with the Faraday we at first rotated the polarization of the incident beam so to have a minimum transmission. And then we rotated the output polarizer until the transmission reaches a minimum. Eventually we got the transmission of less than 1mW, so now the Faraday should be working regardless of the polarization angle of the incident beam. As we predicted, the output polaerizer seems to be rotated 45 deg from that of the input.

* Rana, Koji and Kiwamu aligned the PPKTP crystal to maximize the power of 532 nm.  Now the incident power of 1064 nm is adjusted to 250mW and the output power for 532 nm is 0.77mW. Actually we can increase the laser power by rotating a HWP in front of the Faraday.

* We injected the green beam to the chamber and aligned the beam axis to the ETMY without the modematching lenses, while exciting the horizontal motion of the ETM with f=1Hz from awg. This excitation was very helpful because we could figure out which spot was the reflection from the ETM.

* Once we made the reflected beam going close to the path of the incident beam, we then put the modematching lenses and aligned the steering mirrors and lenses. At this time we could see the reflected beam was successfully kicked away by the Faraday of 532 nm.

* Koji went to ITMY chamber with a walkie-talkie and looked at the spot position. Then he told Rana and Kiwamu to go a right direction with the steering mirrors. At last we could see a green beam from ITM illuminating the ETM cage.

* We excited the ITMY with f=2Hz vertically and aligned the ITM from medm. Also we recovered a video monitor which was abandoned around ETMY chamber so that we could see the spot on the ETM via the monitor. Seeing that monitor we aligned the ITM and we obtained the reclection from the ITM at the end table.

* We also tried to match the mode by moving a lens with f=400mm, but we couldn't obtain a good spot size.

 

  2914   Wed May 12 02:21:56 2010 ranaHowToElectronicsMarconi phase noise measurement setup

Finally got the 3-cornered-hat measurement of the IFRs done. The result is attached.

s12, s23, & s31, are the beat signals between the 3 signal generators.

s1, s2, & s3 are the phase noise of the individual generators made by the following matlab calculation:

%% Do the hat
s1 = sqrt((s12.^2  + s31.^2 - s23.^2) / 2);
s2 = sqrt((s12.^2  + s23.^2 - s31.^2) / 2);
s3 = sqrt((s31.^2  + s23.^2 - s12.^2) / 2);

As you can see, there is now an estimate of the individual noises. We can do better by doing some fitting of the residuals.

The real test will be to replace the noise one here with the good Wenzel oscillator and see how well we can estimate its noise. If the 11 MHz crystals don't show up, I can just try this with the 21.5 MHz one for the PSL.

Attachment 1: pn.png
pn.png
  2913   Tue May 11 18:58:49 2010 ranaHowToElectronicsMarconi phase noise measurement setup

Just a little while ago, at 2330 UTC on 5/11, I swapped the phase noise setup to use another Marconi - this time its the 3rd one from the top beating with the 4th one from the top (2nd from the bottom).

After a little while, I swapped over to beat the 33 w/ the 199. I now have all the measurements. For the measurement of the last pair, I inserted BALUN 1:1 transformers on the outputs of both signal generators'.

This last pair appears to be the quietest of the 3 and also has less lines. The lines are mainly at high frequency and are harmonics of 120 Hz. Probably from the Sorensen switching supplies in the adjacent rack.

I double checked that the 10 MHz sync cable was NOT plugged in to any of these during this and that the front panel menu was set to use the internal frequency standard. In the closed loop case, the beat frequency between the 33/199 pair changes by less than ~0.01 Hz over minutes (as measured by calibrating the control signal).

 

Attachment 1: Untitled.png
Untitled.png
  2912   Tue May 11 17:02:43 2010 KevinUpdateGreen LockingGreen Laser Beam Profile

 

Quote:

Hey, what a quick work!

But, wait...

1) The radius of the beam was measured by the razor blade.

2) The diameter of the beam (13.5% full-width) at each point was measured by Beam Scan. The one at z=~7cm was consistent with 1)

3) The data 2) was fitted by a function w = sqrt(w0^2+lambda^2*(x-x0)^2/(pi*w0)^2). This is defined for the radius, isn't it?

So the fitting must be recalculated with correct radius.
Make sure that you always use radius and write with a explicit word "radius" in the record.

I recalculated the fits using the radius of the beam instead of the diameter of the beam at 13.5% full-width with the following results:

For the vertical beam profile:

reduced chi^2 = 3.25

x0 = (-86 ± 1)mm

w0 = (46.01 ± 0.38)µm

For the horizontal beam profile:

reduced chi^2 = 2.05

x0 = (-81 ± 1)mm

w0 = (45.50 ± 0.28)µm

Attachment 1: vbp.jpg
vbp.jpg
Attachment 2: vbp_residuals.jpg
vbp_residuals.jpg
Attachment 3: hbp.jpg
hbp.jpg
Attachment 4: hbp_residuals.jpg
hbp_residuals.jpg
  2911   Tue May 11 16:38:16 2010 josephb,rana,rolfUpdateCDSCDS questions and thoughts

1) What is c1asc doing?  What is ascaux used for?  What are the cables labeled "C1:ASC_QPD" in the 1X2 rack really going to?

2) Put the 4600 machine (megatron) in the 1Y3 (away from the analog electronics)  This can be used as an OAF/IO machine.  We need a dolphin fiber link from this machine to the IO chassis which will presumably be in 1Y1, 1Y2 (we do not currently have this fiber at the 40m, although I think Rolf said something about having one).

3) Merge the PSL and IOOVME crates in 1Y1/1Y2 to make room for the IO chassis.

4) Put the LSC and SUS machines into 1Y4 and/or 1Y5 along with the SUS IO chassis.  The dolphin switch would also go here.

5) Figure out space in 1X3 for the LSC chassis.  Most likely option is pulling asc or ascaux stuff, assuming its not really being used.

6) Are we going to move the OMC computer out from under the beam tube and into an actual rack?  If so, where?

 

Rolf will likely be back Friday, when we aim to start working on the "New" Y end and possibly the 1X3 rack for the LSC chassis.

 

  2910   Tue May 11 14:39:17 2010 AidanUpdateGreen LockingGreen Laser Beam Profile

 

 Here's a photo of the set-up used. The beam profile is measured relative to the f=-100mm lens.

Attachment 1: P5110057_beams.jpg
P5110057_beams.jpg
  2909   Mon May 10 22:25:03 2010 KojiUpdateGreen LockingGreen Laser Beam Profile

Hey, what a quick work!

But, wait...

1) The radius of the beam was measured by the razor blade.

2) The diameter of the beam (13.5% full-width) at each point was measured by Beam Scan. The one at z=~7cm was consistent with 1)

3) The data 2) was fitted by a function w = sqrt(w0^2+lambda^2*(x-x0)^2/(pi*w0)^2). This is defined for the radius, isn't it?

So the fitting must be recalculated with correct radius.
Make sure that you always use radius and write with a explicit word "radius" in the record.

Quote:

Kiwamu and Kevin measured the beam profile of the green laser by the south arm ETM.

The following measurements were made with 1.984A injection current and 39.65°C laser crystal temperature.

 

Two vertical scans (one up and one down) were taken with a razor blocking light entering a photodiode with the razor 7.2cm from the center of the lens. This data was fit to

b + a*erf(sqrt(2)*(x-x0)/w) with the following results:

scan down: w = (0.908 ± 0.030)mm  chi^2 = 3.8

scan up:      w = (0.853 ± 0.025)mm   chi^2 = 2.9

giving a weighted value of w = (0.876 ± 0.019)mm at this distance.

 

The beam widths for the profile fits were measured with the beam scanner. The widths are measured as the full width at 13.5% of the maximum. Each measurement was averaged over 100 samples. The distance is measured from the back of the lens mount to the front face of the beam scanner.

distance (cm) vertical w (µm) horizontal w (µm)
3.2 ± 0.1 1231 ± 8 1186 ± 7
4.7 ± 0.1 1400 ± 4 1363 ± 6
7.4 ± 0.1 1656 ± 5 1625 ± 9
9.6 ± 0.1 1910 ± 10 1863 ± 9
12.5 ± 0.1 2197 ± 8 2176 ± 8
14.6 ± 0.1 2450 ± 12 2416 ± 10
17.5 ± 0.1 2717 ± 12 2694 ± 14
20.0 ± 0.1 2973 ± 16 2959 ± 8
22.4 ± 0.1 3234 ± 12 3193 ± 14

This data was fit to w = sqrt(w0^2+lambda^2*(x-x0)^2/(pi*w0)^2) with lambda = 532nm with the following results:

For the vertical beam profile:

reduced chi^2 = 3.29

x0 = (-87 ± 1)mm

w0 = (16.30 ± 0.14)µm

For the horizontal beam profile:

reduced chi^2 = 2.01

x0 = (-82 ± 1)mm

w0 = (16.12 ± 0.10)µm

 

  2908   Mon May 10 20:33:29 2010 KojiSummaryCDSFinished

This IPC stuff looks really a nice improvement of CDS.

Please just maintain the wiki updated so that we can keep the latest procedures and scripts to build the models.

Quote:

So I finished writing a script which takes an .ipc file (the one which defines channel names and numbers for use with the RCG code generator),  parses it, checks for duplicate channel names and ipcNums, and then parses and .mdl file looking for channel names, and outputs a new .ipc file with all the new channels added (without modifying existing channels). 

The script is written in python, and for the moment can be found in /home/controls/advLigoRTS/src/epics/simLink/parse_mdl.py

I still need to add all the nice command line interface stuff, but the basic core works.   And already found an error in my previous .ipc file, where I used the channel number 21 twice, apparently.

Right now its hard coded to read in C1.ipc and spy.mdl, and outputs to H1.ipc, but I should have that fixed tonight.

 

  2907   Mon May 10 20:03:22 2010 KevinUpdateGreen LockingGreen Laser Beam Profile

Kiwamu and Kevin measured the beam profile of the green laser by the south arm ETM.

The following measurements were made with 1.984A injection current and 39.65°C laser crystal temperature.

 

Two vertical scans (one up and one down) were taken with a razor blocking light entering a photodiode with the razor 7.2cm from the center of the lens. This data was fit to

b + a*erf(sqrt(2)*(x-x0)/w) with the following results:

scan down: w = (0.908 ± 0.030)mm  chi^2 = 3.8

scan up:      w = (0.853 ± 0.025)mm   chi^2 = 2.9

giving a weighted value of w = (0.876 ± 0.019)mm at this distance.

 

The beam widths for the profile fits were measured with the beam scanner. The widths are measured as the full width at 13.5% of the maximum. Each measurement was averaged over 100 samples. The distance is measured from the back of the lens mount to the front face of the beam scanner.

distance (cm) vertical w (µm) horizontal w (µm)
3.2 ± 0.1 1231 ± 8 1186 ± 7
4.7 ± 0.1 1400 ± 4 1363 ± 6
7.4 ± 0.1 1656 ± 5 1625 ± 9
9.6 ± 0.1 1910 ± 10 1863 ± 9
12.5 ± 0.1 2197 ± 8 2176 ± 8
14.6 ± 0.1 2450 ± 12 2416 ± 10
17.5 ± 0.1 2717 ± 12 2694 ± 14
20.0 ± 0.1 2973 ± 16 2959 ± 8
22.4 ± 0.1 3234 ± 12 3193 ± 14

This data was fit to w = sqrt(w0^2+lambda^2*(x-x0)^2/(pi*w0)^2) with lambda = 532nm with the following results:

For the vertical beam profile:

reduced chi^2 = 3.29

x0 = (-87   ± 1)    mm

w0 = (16.30 ± 0.14) µm

For the horizontal beam profile:

reduced chi^2 = 2.01

x0 = (-82   ± 1)    mm

w0 = (16.12 ± 0.10) µm

Note: These fits were done with the beam diameter instead of the beam radius. The correct fits to the beam radius are here: http://nodus.ligo.caltech.edu:8080/40m/2912

Attachment 1: vbp.jpg
vbp.jpg
Attachment 2: vbp_residuals.jpg
vbp_residuals.jpg
Attachment 3: hbp.jpg
hbp.jpg
Attachment 4: hbp_residuals.jpg
hbp_residuals.jpg
  2906   Mon May 10 19:29:33 2010 AlbertoHowToElectronicsNew Focus 1811 PD calibrated against New Focus 1611 PD
I measured the output impedance of the New Focus 1611 PD (the 1GHz one) and it is 50 Ohm for both the DC and the AC output. It turns out that the transimpedance values listed on the datasheet are the following:
T1611_dc = 1e4 V/A (1MOhm referred)
T1611_ac = 700 V/A (50 Ohm)
The listed transimpedances for the 1811 PD (the 125 MHz PD) are the following:
T_dc = 1e3 V/A (??)
T1811_ac = 4e4 V/A (50 Ohm)
I measured the output impedances of the 1811 and they are: 50 Ohm for the AC output, ~10 Ohm for the DC output.
It's not clear which input impedance the DC transimpedance should be intended referred to.
So I measured the transimpedance of the 1811 using the 1611 as a (trusted) reference. It turns out that for the AC transimpedance to match the listed value, the DC transimpedance has to be the following:
T1811_dc = 1.7e3 V/A (1MOhm)
  2905   Mon May 10 19:09:45 2010 ranaUpdateElectronicsUnexpected oscilaltionin the POY11 PD

Quote:

Where did you get the 55nH based notch from? I don't remember anything like that from the other LSC PD schematics. This is certainly a bad idea. You should remove it and put the notch back over by the other notch.

 Why is it a bad idea?

You mean putting both the 2-omega and the 55MHz notches next to each other right after the photodiode?

  2904   Mon May 10 18:56:53 2010 ranaUpdateElectronicsUnexpected oscilaltionin the POY11 PD

Where did you get the 55nH based notch from? I don't remember anything like that from the other LSC PD schematics. This is certainly a bad idea. You should remove it and put the notch back over by the other notch.

  2903   Mon May 10 17:47:16 2010 josephbSummaryCDSFinished

So I finished writing a script which takes an .ipc file (the one which defines channel names and numbers for use with the RCG code generator),  parses it, checks for duplicate channel names and ipcNums, and then parses and .mdl file looking for channel names, and outputs a new .ipc file with all the new channels added (without modifying existing channels). 

The script is written in python, and for the moment can be found in /home/controls/advLigoRTS/src/epics/simLink/parse_mdl.py

I still need to add all the nice command line interface stuff, but the basic core works.   And already found an error in my previous .ipc file, where I used the channel number 21 twice, apparently.

Right now its hard coded to read in C1.ipc and spy.mdl, and outputs to H1.ipc, but I should have that fixed tonight.

  2902   Mon May 10 16:59:35 2010 AlbertoUpdate40m UpgradingUnexpected oscilaltionin the POY11 PD

The measured transimpedance of the latest POY11 PD matches my model very well up to 100 MHz. But at about ~216MHz I have a resonance that I can't really explain.

2010-05-10_POY11_CalibratedOpticalResponse0-500MHz.png

 

 The following is a simplified illustration of the resonant circuit:

POX11.png

 

Perhaps my model misses that resonance because it doesn't include stray capacitances.

While I was tinkering with it, i noticed a couple of things:

- the frequency of that  oscillation changes by grasping with finger the last inductor of the circuit (the 55n above); that is adding inductance

- the RF probe of the scope clearly shows me the oscillation only after the 0.1u series capacitor

- adding a small capacitor in parallel to the feedback resistor of the output amplifier increases the frequency of the oscilaltion

  2901   Sun May 9 20:02:23 2010 ranaConfigurationSUSSUS filters deleted again to reduce CPU load on c1susvme2 again

On Friday, I deleted a bunch of filters from the c1susvme2 optics' screens (MC1,2,3 + SRM) so as to reduce the CPU load and keep it from going bonkers.

This first plot shows the CPU trend over the last 40 days and 40 nights. As you can see the CPU_LOAD has dropped by 1 us since I did the deleting.

40.png400.png

In the second plot (on the right) you can see the same trend but over 400 days and nights. Of course, we hope that we throw this away soon, but until then it will be nice to have the suspensions be working more often.

  2900   Sat May 8 03:09:15 2010 KojiUpdateIOOSteering around MC

After the MZ-removal work:

- I found that the input steering (IM1) was right handed. This was different from the CAD layout. This was the main reason why the MC trans was kicked by the mount.
- Removed the mount from the post and converted it to a keft handed.
- Align IM1 so that we can get TEM00 lock. Align IM1 further.

- After the IM1 was optimized for the TEM00, move the periscope mirrors to have best alignment.

- Checked the beam spot positions. They looks quite good (MC2 is not the matter now).

C1:SUS-MC1_ULPIT_GAIN = 0.998053
C1:SUS-MC1_ULYAW_GAIN = 0.992942
C1:SUS-MC2_ULPIT_GAIN = 1.00856
C1:SUS-MC2_ULYAW_GAIN = 1.04443
C1:SUS-MC3_ULPIT_GAIN = 0.99868
C1:SUS-MC3_ULYAW_GAIN = 1.00041

  2899   Sat May 8 02:38:08 2010 KojiSummaryIOOMC incident power

As per Steve's request I checked the MC incident power as a function of time.

The output is negative: the lower voltage, the higher power.

Before I put the attenuator the incident power was 1.1W. It appear as -5V.

Now the output is -0.1V. This corresponds to 22mW.

 

Attachment 1: MC_input.png
MC_input.png
  2898   Fri May 7 21:55:59 2010 kiwamuUpdatePSLremove Mach-Zehnder

[Koji, Kiwamu]

The Mach-Zehnder on the PSL table was removed.

A path for 166 MHz modulation in the Mach-Zehnder (MZ) was completely removed, the setup for another path remains the same as before.

Also the photo detector and the CCD for the PMC transmittion were moved to behind the PZT mirror of PMC. 

 


Before removing them, we put an aperture in front of the PD for MC REFL so that we can recover the alignment toward MC by using the aperture.

After the removal we tried to re-align the EOM which imposes the sideband of 29MHz for MC.

We eventually got good alignment of 97% transmissivity at the EOM ( the power of the incident beam is 1.193W and trans was 1.160W )

And then we aligned the beam going to MC by guiding the reflected beam to the aperture we put. This was done by using the steering mirrors on the periscope on the corner of the PSL table.

Now MC got locked and is successfully resonating with TEM00.

Attachment 1: NO_MachZehnder_s.jpg
NO_MachZehnder_s.jpg
  2897   Fri May 7 19:02:27 2010 ranaUpdate40m UpgradingNew improved design for the 11MHz photodiode

To measure the width of a resonance, the standard method is to state the center frequency and the Q. Use the definition of Q from the Wikipedia.

As far as how much phase is OK, you should use the method that we discussed - think about the full closed loop system and try to write down how many things are effected by there being a phase slope around the modulation frequency. You should be able to calculate how this effects the error signal, noise, the loop shape, etc. Then consider what this RFPD will be used for and come up with some requirements.

  2896   Fri May 7 18:18:02 2010 AlbertoUpdate40m UpgradingNew improved design for the 11MHz photodiode

Quote:

How much is the width?

Quote:

 This should be better. It should also have larger resonance width.

 

 The transfer function phase drops by 180 degrees in about 2MHz. Is that a good way to measure the width?

ELOG V3.1.3-