As the suspension work winds down (we'll be completely done once the ETMs arrive, are suspended, and then are placed in the chambers), I'm going to start working on the RF system. 

Step 1: Figure out what Alberto has been up to the last few months.

Step 2: Figure out what still needs doing.

Step 3: Complete all the items listed out in step 2.

Step 4: Make sure it all works.

Right now I'm just starting steps 1 & 2.  I've made myself a handy-dandy wiki checklist: RF Checklist.  Hopefully all of the bits and pieces that need doing will be put here, and then I can start checking them off. Suggestions and additions to the list are welcome.

[Jenne, Suresh, Thanh (Bram's Grad Student)]

When we removed the grippers from the magnets on the PRM, one of the face magnets broke off.  This time, the dumbbell remained glued to the optic, while the magnet came off.  (Usually the magnet and dumbbell will stay attached, and both come off together).  I had 3 spare magnet-dumbbells, but only one of them was the correct polarization.  The strength of the spare magnet was ~128 Gauss, while the other magnets glued to the PRM are all ~180 Gauss.  We considered this too large a discrepancy, and so elected to reuse the same magnet as before. 

We removed the dumbbell from the optic using acetone.  After the epoxy was gently removed, we drag wiped the AR face of the optic (Acetone followed by Iso, as usual), being careful to keep all the solvent away from all the other glue joints.  We cleaned off the magnet with acetone (it didn't really have any glue stuck on it...most of the glue was stuck on the dumbbell), and epoxied it to a new dumbbell. 

The PRM, as well as the magnet-dumbbell gluing fixture are in the little foil house, waiting for tomorrow's activities.  Tomorrow we will re-glue this magnet to the optic, and Thursday we will balance the optic.  

This still leaves us right on schedule for giving the PRM to Bob on Friday at lunchtime, so it can bake over the weekend.

Since MC2_TRANS is, in fact, MC2 Transmission, and not an oplev at all (it's not red, and it's not a lever, although it does use a QPD), I propose that the name be changed to something sensical, since calling it an oplev is completely non-sensical.  The name change should happen sooner rather than later, to avoid confusion.

DTT has only SUS and "X02" channels under C1 in the drop down channel selection menu.  Basically, we can't measure any fast channels with DTT.  I keep getting the error: "Unable to select testpoints."  Sadface.

Similar things are true for DataViewer.  The same limited number of fast channels, and no data found:

Server error 13: no data found
datasrv: DataWriteRealtime failed: daq_send: Illegal seek

Is this a framebuilder problem?  Is this something that the CDS team has on the to-do list?

[Suresh, Jenne]

We took a look-see at the PRM after the gluing from last night.  The balance is still okay.  The reflected beam is a teeny bit below the laser aperture (center of the beam maybe ~2mm below, so ~1mRad low).  This is within our okay range, since the DC offset that the OSEMs will give will be even more, and the coils can definitely handle this kind of offset.

We took the optic out of the tower, and gave it to Bob and Daphen to bake over the weekend.

[Jenne, Joonho]

At Koji's request, we disassembled 2 of the old Green suspension towers that have been sitting along the X-arm forever (read that last word in a 'Sandlot' voice.  Then you'll know how long the suspensions have been sitting there).

They are now hanging out in plastic trays, covered with foil.  They will now be much easier to store.

We should remember that we have these, particularly because the tables at the top are really nice, and have lots of degrees of freedom of fine adjustment.

Steve:

Atm1, there is one more of these old suspension towers

Atm2, disassembled

[Jenne, Suresh]

Over the weekend, Bob and Daphen gave the PRM a 48hr. vacuum bake.  This afternoon Suresh and I placed it back in the wire in the tower.  We used the microscope-on-translation-stage technique to make sure the scribe lines on each side of the optic are at the same height, and then secured the PRM using all of the EQ stops.  It is wrapped in foil, and ready for its journey into the IFO room.  When we next have the BS chamber open, we should put the PRM in, and move the current PRM to its final place on the ITMY table as the SRM.

Dear whomever setup the camera on the SW corner of the PSL table,

It would be handy if, even for temporary setups, all cables went underneath the white frame around the PSL table.  As it is now, the cables are in the way of the door.  The door is pretty much closed all the way, but if someone were to open other doors, the far door can easily be pushed all the way to the end of the track, thus squishing the cables.  Squished cables are bad cables.

Thanks!

Joon Ho and I took a look at the RF stuff that Alberto left, and we determined that we've got most everything that we need.  On Monday, Joon Ho will list off the stuff that we're missing, and we'll have Steve order it.

Joon Ho also replaced the temporary front panel to the RF generation box with Alberto's fancy new panel.  Pics are here (although you have to sign in as foteee to see them). 

Work on the frequency distribution box will continue on Monday.

[Suresh, Jenne]

We have put together the new-old ETM towers.  These are the ones which were hanging out on the flow bench down the arm for years and years, and have recently been re-baked.  Interestingly, these are predominantly steel, whereas the newer ones are mostly aluminum.  This caused momentary drama while we scrounged for the correct screws (we needed more silver-plated screws than anticipated, since we were screwing into steel and not aluminum), however the miscellaneous clean hardware collection came to the rescue.  We did however use up all of the 1/4-20 3/4" silver plated screws, so hopefully no one else needs more later...

We only found 5 (enough for one of the two towers) spring plungers which are used to hold the OSEMs in place.  Suresh is sending an email to Steve to ask him to buy some more, so we can get them cleaned in time for use.  This is important, but not super urgent, since we have ~ 2 weeks before the ETMs will be ready for installation. 

Koji has not yet had a chance to inspect the ETM data sheets and choose for us which pair of ETMs to use (ATF sent the 4 ETMs in matched pairs).  So we will not begin the "arts and crafts" until tomorrow-ish.

[Valera, Jenne]

We pondered the idea of clamping the PRM optic to measure the OSEM noise.  So we opened up the BS tank to give this a try.  We rediscovered that Jenne is too short to reach the other side of the PRM tower, so we couldn't fully clamp the optic (when is Jaime coming again? He's kind of tall...)  If we only did the back 2 EQ stops, the optic would still be able to rock, and thus defeat the purpose of clamping anyway.  So we didn't go for it. 

While we were in there we saw that the SRM OSEMs were just hanging out on the table, and decided to go with them.  See Valera's elog for details on our measurement.  We closed up the tank without making any changes to anything.

In other news, we still need to figure out how to change up the connectors to get those OSEMs over to the ITM table.  This needs to happen pretty soonish. 

[Steve, Jenne, Suresh, Koji]

The remaining test mass chambers have been opened, and have light doors in place.  Now we can do all of the rest of the IFO alignment, and then (hopefully) button up before the New Year.

[Jenne, Suresh]

Today has been a downright miserable day in the world of suspension work. Thumbs down to that: 

Yesterday, we had glued 2 full sets of magnets to dumbbells.  Today, half of those broke.  I think I put too thin of a layer of glue on the magnets when gluing them to the dumbbells.  All magnet/dumbbell assemblies should pass the test of being picked up by the dumbbell while the magnet is stuck to the optical table or a razor blade.  6 of the 12 magnets failed this test. Suresh soaked the dumbbells that had been used in acetone, and scrubbed them, so we can reuse them when we reglue things tomorrow.  By some miracle, we have exactly one full set intact (for each set of 6, we need 4 of one direction and 2 of the other).  This was frustrating, but not yet a deal-breaker.  That part comes next....

I got ETMU05 nicely aligned in the magnet gluing fixture, and then was on my last check of whether the side magnets would be glued in the correct place when I realized that the fixture is all wrong for the ETMs.  This final check was added to the procedure after the drama with the ITMs of having the side magnets glued incorrectly as a result of the fixture being specific to the wedge angle of the optic.  Kiwamu and I had set the fixture to be just right for the ~1deg wedge corner station optics, but the ETMs have a 2.35deg wedge (according to the Coastline spec sheet, which is consistent with our measurements when placing the guiderod and standoffs).  Suresh and I need to reset the height of the optic in the fixture using more teflon sheets, but we don't have a whole lot of options ready in the cleanroom.  We're going to cut some more pieces and ask Bob to clean them tomorrow.  Since the way the fixture holds the teflon is a little hoaky, Suresh suggested just resting the optic on teflon pads, rather than screwing the teflon to the fixture, and then putting the optic on the pads.  We'll try Suresh's method tomorrow, and hopefully it will be pretty easy. 

At least the guiderods and standoffs were successfully glued to the optics....

Here's the updated Status Table.  I don't think we're going to be able to have an ETM ready for the chambers early next week, but we should still be able to have both ready for the Monday after Thanksgiving.  The spring plungers arrived today, and were given immediately to Bob and Daphen for cleaning.

[Jenne, Suresh]

Suresh and I glued the intact-from-the-first-round magnets to ETMU05.  I accidentally got too much glue on one of the dumbbells (the glue was connecting the dumbbell to the gripper - bad news if we let that dry), and while I was cleaning it, the magnet broke off.  So I used one of the ones that Suresh had re-glued last night, and he is putting that one back together after some cleaning. 

To set the fixture, Suresh had the great idea of using small pieces of foil underneath the teflon pads to set the height of the optic in the fixture.  The optic still rests on the teflon pads, but with the foil we have finer control over how the optic sits.  Neat.  Since both ETMs are the same, we shouldn't have to do any more adjustment for the other ETM.

The updated Status Table:

[Suresh, Jenne]

A story about minor disasters, and crises averted:

Once upon a time, in a cleanroom not so far away..... there lived an optic.  To preserve anonymity, we shall call him "ETMU05".  This optic had a rough day.  When removing the grippers from the magnet-to-optic fixture, 4 out of 6 magnets broke off the dumbbells (the dumbbells were still securely glued to the optic...these had come out of the same batch that had problems last week, same problem).  The remaining 2, LL and LR, were sadly of the same polarity.  This is bad, because it means that the "humans" taking care of "ETMU05" didn't check the polarity of the face magnets properly, and ensure that they were laid out in an every-other pattern (LL and UR having the same polarity, and LR and UL having the opposite).  So, the humans removed all magnets and dumbbells from ETMU05.  All remaining glue was carefully scrubbed off the surfaces of ETMU05 using lens paper and acetone, and the magnets and dumbbells were sonicated in acetone, scrubbed with a lint-free wipe, sonicated again, and then scrubbed again to remove the glue.  ETMU05 had a nice cleansing, and was drag wiped on both the AR and HR surfaces with acetone and iso.  ETMU05 is now on vacation in a nice little foil hut.

His friend, (let's call him ETMU07) had a set of magnets (with polarities carefully confirmed) glued to him.  The cleaned magnets and dumbbells removed from ETMU05 were reglued to their dumbbells, and should be dry by tomorrow. 

.....And then they lived happily ever after.  The End.

The revised schedule / status table:

Joe showed me what was what with adding DAQ channels, and I have begun building a simulink model to acquire the PEM channels. 

My models is in: /cvs/cds/rtcds/caltech/c1/core/advLigoRTS/src/epics/simLink/c1pem.mdl

Next on the to do list in this category: test which input connector goes with which channel (hopefully it's linear, exactly as one would think), and give the channels appropriate names. 

[Koji, Jenne]

ETMU07 had its wire winched to the correct height, was balanced, standoff glued.  Can be ready for going into the oven tomorrow, if an oven is available.  (One of Bob's ovens has a leak, so he's down an oven, which puts everything behind schedule.  We may not be able to get anything into the oven until Monday).

ETMU05 had magnets glued to the optic.  Hopefully tomorrow we will winch the wire and balance the optic, and glue the standoff, and be ready to go into the oven on Monday.

The spring plungers were sonicated, but have not yet been baked.  I told Daphen that we'd like the optics baked first, so that we can get ETMX in the chamber ASAP, and then the spring plungers as soon as possible so that we can install ETMY and put the OSEMs in.

The updated status table:

[Jenne, Koji]

We removed ETMU07 from the suspension tower, after confirming that the balance was still good.  Bob put it in the oven to bake over the weekend.  The spring plungers and our spare magnets are all in there as well. 

I tried to remove the grippers from ETMU05, and when I did, both side dumbbells came off of the optic.  Unfortunately, I was working on getting channels into the DAQ, so I did not clean and reglue ETMU05 today.  However Joe told me that we don't have any ETMY controls as yet, and we're not going to do Yarm locking (probably) in the next week or so, so this doesn't really set any schedules back. 

The cleaning of ETMU05 will be tricky.  Getting the residual glue off of the optic will be fine, but for the dumbbells, we'd like to clean the glue off of the end of the dumbbells using a lint free wipe soaked in acetone, but we don't want to get any acetone in the magnet-to-dumbbell joint, and we don't want to break the magnet-to-dumbbell joint.  So we'll have to be very careful when doing this cleaning. 

The Status Table:

I have made a little bit of progress on the PEM channels.  I have begun writing up detailed instructions in the DAQ Wiki page on how to add a channel to the new DAQ system.  I have followed those instructions thus far, and can see my channels in the .ini file (and in the daqconfig gui thing), but I don't have any channels in Dataviewer or DTT. 

There are some tricky "gotchas" involved in creating new models and channels.  Some examples include:  No use of the characters "DUMMY" in any channel name.  The makefile is specifically hardcoded to fail if that string of characters is used.  Also, you must have at least 2 filter banks in every model.  Why? No one knows.  You just do.  The model won't compile unless you have 2 or more filter banks. 

My efforts today included ~3 reboots of the frame builder, and ~2 reboots of c1sus.  When Kiwamu and I rebooted c1sus, we burt restored to some time in the last 24 hrs.  Some of the SUS filters on some of the optics were not set correctly (things like the bounce roll filter), so we turned all of them on, and reset all of the input and output matricies to be the correct combination of +1 and -1's to make Pit, Pos and Yaw.  The tuning seems to happen now-a-days in the gains for each DOF, and the gains were set correctly by the burt restore for every optic except PRM.  We made some educated guesses for what the gains should be based on the other optics, and PRM is damping pretty well (these guesses included reducing the SIDE gain by ~10 from the BS SIDE value, since the analog gain of the PRM SIDE sensor is much higher than others).  We'll have to fine tune these gains using some Yuta-developed method soon.  Or find a burt snapshot that had some non-unity values in there.

[Jenne, Kiwamu]

We put ETMX back in its tower, and confirmed its balance.  It might be pointing a teensy bit upward, but it is way less than the DC pointing offset we see when we put the OSEMs in the towers (since the PDs and LEDs have some magnetic bits to them).

Discussions are ongoing as to where the ETM should sit on its table, but we'll probably toss it into the chamber later this evening.

I took ETMY out of the magnet gluing fixture, and put it in a ring, in the foil house.  It is ready to have the wire winched and get balanced at our convenience.

The updated status table:

[Suresh, Jenne]

We Finished!!!

ETMU05 (ETMY) had its wire winched to the correct height, was balanced, and had the standoff glued.  Since it's kind of like final exam week at Caltech, Suresh had his suspension exam today, and did most of this work himself, with me hanging around and watching. 

As you can see in my almost entirely green table, all that is left to do with the whole suspensions project is bake the optic (hopefully Bob has time / space this week), and then stick it in the chamber!  Hooray!!! (Can you tell I'm excited to not spend too much more time in the cleanroom?)

The table:

The Backstory:

Kevin was working on characterizing all of our RF photodiodes for the upgrade, and he discovered that REFL11 didn't work, as described in elog 3890.  Rana was working on fixing it, but then he went off to Japan.

Today's Activities:

I visually inspected the components inside the RF cage on the REFL 11 circuit board inside the PD.  Most of them were okay, but the connection between L5 and C33 (the big tunable inductor and the next capacitor in the path) was totally flaky.  the leg of the inductor had been soldered directly to the trace on the PCB, and the inductor was a little bit tipped over, and pulling the trace off the board.  I wiggled it a little while trying to see what was going on, and the trace broke.  Since there is nothing going on between L5 and C33, just the trace, I used a piece of resistor lead to attach the two.  The connection now seems very robust.  I'm a little worried about the connection between the inductor and the board on the other side, but I can't see it since it's under the inductor itself.

Also, the soldering of L4 (a standard surface mount component type body) to the board seemed totally shoddy.  I was desoldering the first side, and the whole inductor popped off.  It was clear that the inductor was making a physical connection to the board, but not a nice solid electrical connection.  So I resoldered it on.  (On Alberto's schematics, it is listed as a 633nH inductor.  I can't find any of this value, so I just put the same one back on.  The best I could do to confirm the component was still okay was measure its resistance, and compare that to a similar inductor of a similar value.  It seemed okay.)

After that I powered up the PD, and took an electrical transfer function, just to have a look-see.  It seems kind of okay, although the resonance seems to be closer to 13MHz than 11MHz. 

Since we would like to remove the capacitor that is in parallel with the diode itself, which will then change all of the resonant conditions on other components, I didn't worry too much about the resonant peak for tonight.  We're going to have to look in on this though.

Also, I'm leaving the optical check-out for Kevin, so he will let us know if I magically fixed the PD, or if it needs some more work.

Photos of the circuit board (mostly Alberto's mods) before and after I fitzed with it are on Picasa

The Future:

More testing. Probably more fixing.

[Joe, Jenne]

The nightly backup of the frames and the /cvs/cds directories is back up and running.  We are free again to do crazy stuff at will, and it will all be saved for eternity.

[Koji, Jenne]

I wish I could use a bigger font for this, but, the suspension work is totally done for the upgrade!!!

Now, nobody break any suspensions, or we're not going to be friends for a while. 

Koji and I put ETMY back in its tower, and made sure that both scribe lines are at the correct height.  We also confirmed that the balance is good (as Suresh mentioned in a previous elog, since we balanced using the AR surface, the HR surface is pointing downward a little bit, but it's well within the OSEMs ability to correct.

While we were in there, we also looked at Tip Tilt number 002.  As mentioned in elog 3645, the pitch pointing was off by a little bit.  Since the TTs don't have actuators, the pointing has to be pretty good.  We tweaked the balancing, and now the reflected beam goes completely back into the laser aperture, so it's as balanced as it's going to get.  This TT is now ready for installation onto the ITMY table as part of the SRC.

Kiwamu confirmed that he's going to install these optics tomorrow, since he's doing some other alignment work today.

Just for good measure, the Table:

The Seismometer channels are once more being recorded.  Alastair brought Gur1 back from the ATF the other day, and today I put it in its place below MC2 (yeah, the numbers are backwards.  But they always have been.) 

I checked the matching between BNC inputs on the breakout box to the ADC channels as labeled in the SimuLink diagram.  To do this I had all 32 channels activated, and I put a 1Hz, 1Vpp sine wave into various BNC inputs to see what channel they showed up as.  At first things were a bit backwards (BNC channels 1-16 going to ADCs 16-31, and BNCs 17-32 going to ADCs 0-15), but then Joe quickly flipped the cables on the adapter board in the back and things are in the correct order now.  Channel 1 on the BNC board corresponds to channel 0 on the ADC, etc. 

I checked that jumping near each seismometer made the signals spike, which they did. 

I then changed the channel names in the c1pem.mdl SimuLink diagram to match the old channel names for the Guralps and the accelerometers, and deleted all of the other channels that aren't being used.  There's a table in the diagram to indicate what goes with what, as of today.  If you do anything to the PEM diagram, please update the table so it's easy to look things up.

I recompiled the code, but have not yet restarted the frame builder since Zach and Kiwamu are working on some things in the chamber, and I don't want to be annoying (so the channels aren't actually being recorded quite yet). 

Edit, 7:15pm:  Just kidding.  Something didn't work, and I have to track down what.  I'm not getting any data yet.

Tuesday

• If still everythig is fine, put the BS heavy door.

- Do the following list for all of the testmass chambers.

• Check if the OSEMs and the OPLEV are still fine. (ITMX and ITMY were not done on Monday, so need extra care.)
• Inspect the surface of the mirror with a laser pointer or a fiber coupled halogen light.
• Blow the mirrors by the ionization gun.
• Inspect the mirror surface again.
• Move the suspension tower close to the door.
• Make a single drag-wipe with iso
• Move the SOS tower at the original place.
• Check the OSEMs and the OPLEVs. Adjust the alignment.
• Put the heavy door.

- Start slow pumping

[Kiwamu, Jenne, Koji, Osamu]

We have mostly prepared the IFO for pump down. 

After lunch [Steve, Bob, Koji, Kiwamu, Jenne, Joe, Joon Ho, Vladimir, Osamu] put the access connector back in place.  Hooray!  Steve still has to check the Jam Nuts before we pump down.  Kiwamu checked the leveling of the IOO table, and fixed all of the weights to the table.

For all 4 test masses, bars (upside-down dog clamps) were placed to mark the alignment of 2 sides of the suspension tower.  All test mass tables were re-leveled, and the weights fixed to the tables.  

For ETMY, PRM, BS, SRM, we confirmed that the OSEMs were close to their half-range.  ETMX was already fine.  ITMY (the screens and the optics wiki are still old-convention, so this is listed as ITMX! No good!) OSEMs are pretty much fine, but ITMX desperately needs to be adjusted.  Unfortunately, no one can find the standard screwdriver (looks like a minus), to adjust the ITM OSEMs.  All the other towers had hex-key set screws, but the ITMs need a screwdriver.  We will ask Bob to sonicate a screwdriver in the morning. 

What was the point:

I twiddled with several different things this evening to increase the power into the Mode Cleaner.  The goal was to have enough power to be able to see the arm cavity flashes on the CCD cameras, since it's going to be a total pain to lock the IFO if we can't see what the mode structure looks like.

Summed-up list of what I did:

* Found the MC nicely aligned.  Did not ever adjust the MC suspensions.

* Optimized MC Refl DC, using the old "DMM hooked up to DC out" method.

* Removed the temporary BS1-1064-33-1025-45S that was in the MC refl path, and replaced it with the old BS1-1064-IF-2037-C-45S that used to be there.  This undoes the temporary change from elog 3878.  Note however, that Yuta's elog 3892 says that the original mirror was a 1%, not 10% as the sticker indicates. The temporary mirror was in place to get enough light to MC Refl while the laser power was low, but now we don't want to fry the PD.

* Noticed that the MCWFS path is totally wrong.  Someone (Yuta?) wanted to use the MCWFS as a reference, but the steering mirror in front of WFS1 was switched out, and now no beam goes to WFS2 (it's blocked by part of the mount of the new mirror). I have not yet fixed this, since I wasn't using the WFS tonight, and had other things to get done.  We will need to fix this.

* Realigned the MC Refl path to optimize MC Refl again, with the new mirror.

* Replaced the last steering mirror on the PSL table before the beam goes into the chamber from a BS1-1064-33-1025-45S to a Y1-45S.  I would have liked a Y1-0deg mirror, since the angle is closer to 0 than 45, but I couldn't find one.  According to Mott's elog 2392 the CVI Y1-45S is pretty much equally good all the way down to 0deg, so I went with it.  This undoes the change of keeping the laser power in the chambers to a nice safe ~50mW max while we were at atmosphere.

* Put the HWP in front of the laser back to 267deg, from its temporary place of 240deg.  The rotation was to keep the laser power down while we were at atmosphere.  I put the HWP back to the place that Kevin had determined was best in his elog 3818.

* Tried to quickly align the Xarm by touching the BS, ITMX and ETMX.  I might be seeing IR flashes (I blocked the green beam on the ETMX table so I wouldn't be confused.  I unblocked it before finishing for the night) on the CCD for the Xarm, but that might also be wishful thinking.  There's definitely something lighting up / flashing in the ~center of ETMX on the camera, but I can't decide if it's scatter off of a part of the suspension tower, or if it's really the resonance.  Note to self:  Rana reminds me that the ITM should be misaligned while using BS to get beam on ETM, and then using ETM to get beam on ITM.  Only then should I have realigned the ITM.  I had the ITM aligned (just left where it had been) the whole time, so I was making my life way harder than it should have been.  I'll work on it again more today (Tuesday). 

What happened in the end:

The MC Trans signal on the MC Lock screen went up by almost an order of magnitude (from ~3500 to ~32,000).  When the count was near ~20,000 I could barely see the spot on a card, so I'm not worried about the QPD.  I do wonder, however, if we are saturating the ADC. Suresh changed the transimpedance of the MC Trans QPD a while ago (Suresh's elog 3882), and maybe that was a bad idea? 

Xarm not yet locked. 

Can't really see flashes on the Test Mass cameras. 

I undid Yuta's temporary setup, and put beam back on both WFS.  Since Koji had just aligned the Mode Cleaner, I centered the beam on the WFS using the WFS QPD screen, while watching the WFS Head screen, to make sure that the beam was actually hitting the QPD, and not off in lala land. 

[Kiwamu, Jenne]

We successfully aligned the X arm.  No big deal.  Nothing to write in giant colorful letters about.  If we thought it was tricky, we'd be excited.  But since we're rockstar grad students, we can do this anytime, with one hand behind our back.

The details:

Earlier this evening, Kiwamu put a PD at the dark port.  After starting with the usual steering beams around and approximately centering them by finding the beam on the SUS tower, we saw that we could see the fringes on a 'scope hooked up to the dark port's new PD.  We could make the dip in the scope trace go away by misaligning the ETM, so we were confident that it was due to some kind of resonance in the arm.  We then fine-tuned our beam centering by moving the optics in either pitch or yaw until the fringe went away, wrote down the number, then moved the other direction until the fringe went away, and then put the optic back in the middle of those two numbers.  We did the ETM first, then the ITM (because the beam on the PD is sensitive to the ITM pointing, so we didn't want to have to move the ITM very far).  We saw that the cavity had a visibility of ~56% when we had finished with this method.

We then went to look for the flashes transmitted through the ETM.  We were not able to see them on a card, but when we looked with an IR viewer at the back face of the ETM, we could see the flashes. We stole a spare CCD camera found on the PSL table, and the camera power supply from the RefCav Refl camera, and set up a CCD camera with telephoto lens on the ETMX Trans table, looking directly at the back of the ETM.  We hooked the camera up to the regular ETMX camera cable, so we can see the flashes in the control room.  You can see them here:

While the cavity was aligned, here were the slider positions:

Correct.  We can see the flashes clearly on our new ETM camera, but we see absolutely nothing on the ITM.

Unfortunately, the camera is in the path of the green beam, so we'll have to figure out a more permanent plan.  Right now the laser at the end is shuttered.

Measuring the power now....

[Kiwamu, Jenne]

We have a measely 465mW going into the MC.  We lose a boatload of power on the PZT mirror that is part of the last zigzag for steering into the MC.  Just before this mirror, we measure 1.21W .  Just after this mirror, we measure ~475mW.  Then a teeny bit gets picked off for the PSL POS/ANG.  But we're losing a factor of 3 on this one mirror.  Need to fix!!!!!!!!!

[Kiwamu, Jenne]

We went this evening in search of a beat note signal between the Xarm transmitted green light and the PSL doubled green light. 

First, we removed our new ETMX camera (we left the mount so it should be easy to put back) from the other day.   We left the test masses exactly where they had been while flashing for IR, so even though we can no longer confirm, we expect that the IR beam axis hasn't changed.  We used the steering mirror on the end table to align the green beam to the cavity.  We turned on the loop to lock the end laser to the cavity, and achieved green lock of the arm.

Then we went to the PSL table to overlap the arm transmitted light with the PSL doubled light.  We made a few changes to the optics that take the arm transmitted light over to the PD.  We found that the arm transmitted light was very high, so we changed from having one steering mirror to having 3 (for table space / geometry reasons we needed 3, not just 2) in order to lower the beam axis.  We also found that the spot size of the arm transmitted beam was ~2x too small, so we changed the mode matching telescope from a 4x reducer to a 2x reducer by changing the 2nd lens from f=50mm to f=100mm (the first lens is f=200mm).  We made the arm transmitted beam and the PSL green beam overlap, but we saw no peak on the spectrum analyzer. 

We checked the temperature of the PSL and end lasers, and determined that we needed to adjust the set temp of the end laser.  However, we still didn't find any beat note.

We then tweaked the temperature of the doubling oven at the end station, to maximize the power transmitted, since Kiwamu said that that had worked in the past.  Alas, no success tonight.

We're stopping for the evening, with the success of reacquiring green lock of the Xarm.

[Larisa and Jenne]

We wanted to get rid of the awkward cart that was sitting behind the 1Y1 rack.  This cart was supplying a +5V offset to the PZT driver, so that we could use the MC length signal to feedback to lock the laser to the MC cavity.  Instead, we put the offset on the last op amp before the servo out on the Mc Servo Board.  Because we wanted +5V, but the board only had +5, +15, -15V as options, and we needed -5 to add just before the op amp (U40 in the schematic), because the op amp is using regular negative feedback, we made a little voltage divider between -15V and GND, to give ourselves -5V.  We used the back side of the voltage test points (where you can check to make sure that you're actually getting DC voltage on the board), and used a 511Ohm and 1.02kOhm resistor as a voltage divider. 

Then we put a 3.32kOhm resistor in ~"parallel" to R124, which is the usual resistor just before the negative input of the op amp.  Our -5V goes to our new resistor, and should, at the output, give us a +5V offset. 

Sadly, when we measure the actual output we get, it's only +2.3V.  Sadface.

We went ahead and plugged the servo out into the PZT driver anyway, since we had previously seen that the fluctuation when the mode cleaner is locked was much less than a volt, so we won't run into any problems with the PZT driver running into the lower limit (it only goes 0-10V).

Suresh has discovered that the op amp that we're looking at, U40 on the schematic, is an AD829, which has an input impedance of a measely 13kOhm.  So maybe the 3.32kOhm resistors that we are using (because that's what had already been there) are too large.  Perhaps tomorrow I'll switch all 3 resistors (R119, R124, and our new one) to something more like 1kOhm.  But right now, the MC is locked, and I'm super hungry, and it's time for some arm locking action.

I've attached the schematic.  The stuff that we fitzed with was all on page 8.

My goal this afternoon was to measure the quantum efficiency of the MC WFS.  In the process of doing this, I discovered that when I reverted a change in the MCWFS path (see elog 4107 re: this change), I had not checked the max power going to the WFS when the MC unlocks.

Current status:

MC locks (is locked now).  No light going to WFS at all (to prevent MC WFS french-fry action).  Quantum Efficiency measured.

The Full Story:

Power to WFS:

Rana asked me to check out the quantum efficiency of the WFS, so that we can consider using them for aLIGO.  This involves measuring the power incident on the PDs, and while doing so, I noticed that WFS1 had ~160mW incident and WFS2 had ~240mW incident while the mode cleaner was unlocked.  This is bad, since they should have a max of ~10mW ever.  Not that 200mW is going to destroy the PD immediately, but rather the current out, with the 100V bias that the WFS have, is a truckload of power, and the WFS were in fact getting pretty warm to the touch.  Not so good, if things start melting / failing due to extended exposure to too much heat.

The reason so much power was going to the WFS is that it looks like Yuta/Koji et. al., when trying to use the WFS as a MC1 oplev, changed out 2 of the beam splitters in the MC WFS / MC Refl path, not just one.  Or, we've just been crispy-frying our WFS for a long time.  Who knows?  If it is option A, then it wasn't elogged.  The elog 3878 re: BS changeout only mentions the change of one BS.

Since the MC Refl path has a little more than ~1W of power when the MC is unlocked, and the first BS (which was reverted in elog 4107) is a 10% reflector, so ~100mW goes to the MC Refl PD, and ~900mW goes to the MC WFS path.  In front of a Black Hole beam dump was sitting a BS1-33, so we were getting ~300mW reflected to be split between the 2 WFS, and ~600mW dumped.  The new plan is to put a W2 window in place of this BS1-33, so that we get hopefully something like 0.1% reflected toward the WFS, and everything else will be dumped.  I could not find a W2-45S (everything else is S, so this needs to be S as well).  I found a bunch of W2-0deg, and a few W2-45P.  Does anyone have a secret stash of W2-45S's???  To avoid any more excessive heat just in case, for tonight, I have just left out this mirror entirely, so the whole MC WFS beam is dumped in the Black Hole.  The WFS also have aluminum beam dumps in front of them to prevent light going in.  None of this affects the MC Refl path, so the MC can still lock nice and happily.

Quantum Efficiency Measurement:

I refer to Jamie's LHO elog for the equation governing quantum efficiency of photodiodes: LHO 2 Sept 2009

The information I gathered for each quadrant of each WFS was: [1] Power of light incident on PD (measured with the Ophir power meter), [2] Power of light reflected off the PD (since this light doesn't get absorbed, it's not part of the QE), and [3] the photo current output by the PD (To get this, I measured the voltage out of the DC path that is meant to go to EPICS, and backed out what the current is, based on the schematic, attached). 

I found a nifty 25 pin Dsub breakout board, that you can put in like a cable extension, and you can use clip doodles to look at any of the pins on the cable.  Since this was a PD activity, and I didn't want to die from the 100V bias, I covered all of the pins I wasn't going to use with electrical tape.  After turning down the 100V Kepco that supplies the WFS bias, I stuck the breakout board in the WFS.  Since I was able to measure the voltage at the output of the DC path, if you look at the schematic, I needed to divide this by 2 (to undo the 2nd op amp's gain of 2), and then convert to current using the 499 Ohm resistor, R66 in the 1st DC path.  

I did all 4 quadrants of WFS1 using a 532nm laser pointer, just to make sure that I had my measurement procedure under control, since silicon PDs are nice and sensitive to green.  I got an average QE of ~65% for green, which is not too far off the spec of 70% that Suresh found.

I then did all 8 WFS quadrants using the 1064nm CrystaLaser #2, and got an average QE of ~62% for 1064 (58% if I exclude 2 of the quadrants....see below).  Statistics, and whatever else is needed can wait for tomorrow.

Problem with 2 quadrants of WFS2?

While doing all of this, I noticed that quadrants 3 and 4 of WFS2 seem to be different than all the rest.  You can see this on the MEDM screens in that all 6 other quadrants, when there is no light, read about -0.2, whereas the 2 funny quadrants read positive values.  This might be okay, because they both respond to light, in some kind of proportion to the amount of light on them.  I ended up getting QE of ~72% for both of these quadrants, which doesn't make a whole lot of sense since the spec for green is 70%, and silicon is supposed to be less good for infrared than green.  Anyhow, we'll have to meditate on this.  We should also see if we have a trend, to check how long they have been funny.

The MC WFS have had beam dumps in front of them for the past ~2 weeks, until I could find the appropriate optic to put in the WFS path, to avoid melting the WFS' electronics. 

Koji noted that Steve had a W2-45S in a secret stash near his desk (which Steve later had put into the regular optics storage shelves down the Yarm), so I used that in front of the black hole beam dump on the AS table.  Now the beam is ~1W reflected from the unlocked mode cleaner, and ~100mW goes to the MC REFL PD.  The other 900mW now goes to this W2, and only ~5mW is reflected toward the MC WFS.  Most of the 900mW is transmitted through the window and dumped in the black hole.  There is a ghost beam which is reflected off the back surface of the wedged window, and I have blocked this beam using a black anodized aluminum dump.  I will likely change this to a razor dump if space on the table allows.  I have aligned the beam onto WFS1 and WFS2, although I did not re-align the mode cleaner first, so this alignment of the WFS will likely need to be redone. 

WFS1 has about 2mW incident, and WFS2 has about 3mW incident, when the mode cleaner is unlocked.  I have not yet measured the power incident when the MC is locked, although obviously it will be much smaller.

Except that I might temporarily remove one of the WFS for more quantum efficiency measurements later today, the WFS should be ready to turn back on for alignment stabilization of the mode cleaner. 

Back in the days when we were talking about getting a new 2W PSL, I was given naming rights by Rana for this new laser. 

Today, the 40m PSL was given its new name: Edwin.

Here he is, with his shiny new label:

Mystery solved!

I removed WFS2 from the AP table (after placing markers so I can put it back in ~the same place) so that I could take some reflectivity as a function of angle measurements for aLIGO WFS design stuff.

I was dismayed to discover, upon glancing at the diode itself, that half of the diode is covered with some kind of oil!!!.  The oil is mostly confined to quadrants 3 and 4, which explains the confusion with their quantum efficiency measurements, as well as why the readback values on the MEDM WFS Head screen for WFS2 don't really make sense. 

The WFS QPD has a piece of glass protecting the diode itself, and the oil seems to be on top of the glass, so I'm going to use some lens tissue and clean it off.

Pre-cleaning photos are on Picasa.

Update:  I tried scrubbing the glass with a Q-tip soaked with Iso, and then one soaked in methanol.  Both of these failed to make any improvement.  I am suspicious that perhaps whatever it is, is underneath the glass, but I don't know.  Rana suggested replacing the diode, if we have spares / when we order some spares.

I sat down in the control room to find that ETMX and PRM's watchdogs had been tripped.  I don't know how long they've been crazy, but there was a big something that showed up in the seismometers around 16:30UTC, or ~11:30 this morning.  I don't find any significant earthquakes on the USGS site for that time though, so it might be more local, i.e. work next door or trucks or whatever.

I take back the suggestion that it was that seismic event.  Clearly the PRM and the ETMX were kicked at different times, neither of which is the same as the seismic action. Mystery.  You can see they have been ringing down for a while though, which is neat. 

I did a yum-install of the latest ldg-client (to get onto the LIGO Clusters) on Rossa. 

I followed the instructions on the wiki page, and everything seemed to work nicely.

I think the new ldg client installs somewhere on the local computer, so if anyone wants cluster access on any other computer, they should follow the same directions.

Using a stray beam that is generated as the transmitted green beam from the Xarm goes through the viewport to the PSL table, I installed a fast lens (because I was constrained for space) and a Thorlabs PDA36 photodiode on the PSL table.

The BNC cable runs along the edge of the PSL table, up the corner hole with the huge bundle of cables, and over to IOO_ADC_0. It's channel 3 on the simulink model, which means that it is plugged into connector #4.

With the green resonating TEM00, I have ~1.4V output from the photodiode, as seen on a voltmeter. This corresponds to ~1500 counts on the MEDM screen.

Note to self:  Switch to a ~1cm diode with a boatload of gain (either from the 40m or Bridge), and use transmission through a steering mirror of the actual beat note path, not the jittery viewport pickoff.  Want RIN noise level to be about 1e-5, only care about below ~100Hz so don't need broadband.

[Larisa and Jenne]

A few weeks ago (on the 28th of January) I had tried to measure the quantum efficiency of one quadrant of the WFS as a function of angle.  However, Rana pointed out that I was a spaz, and had forgotten to put a lens in front of the laser.  Why I forgot when doing the measurement as a function of angle, but I had remembered while doing it at normal incidence for all of the quadrants, who knows?

Anyhow, Larisa measured the quantum efficiency today.  She used WFS2, quadrant 1 (totally oil-free), since that was easier than WFS1.  She also used the Jenne Laser (with a lens), since it's more stable and less crappy than the CrystaLasers.  We put a 50 Ohm terminator on the RF input of the Jenne Laser, since we weren't doing a swept sine measurement.  Again, the Ophir power meter was used to measure the power incident on the diode, and the reflected power, and the difference between them was used as the power absorbed by the diode for the quantum efficiency measurement.  A voltmeter was used to measure the output of the diode, and then converted to current as in the quote below. 

Still on the to-do list:  Replace the WFS2 diode.  See if we have one around, otherwise order one.  Align beams onto WFS so we can turn on the servo.

QE = (h*c)/(lambda*e) * (I/P)

Where I = (Volts from Pin1 to GND)/2 /500ohms
P = Power from laser - power reflected from diode.
h, c, e are the natural constants, and lambda is 1064nm.

Also, I/P = Responsivity

Larissa is going to put her data and plots into the elog shortly....

Just in case anyone has encountered this / knows how to fix it....

I'm running NDS2 on Rossa, trying to get a bunch of raw data from S5.  I get 10min of data at a time, and it goes through ~200 iterations successfully, and then throws the following error:

Getting new data
Connecting.... authenticate ... done
daq_recv_id: Wrong length read (0)
Error reading writerID in daq_recv_block
Warning: daq_request_data failed
 
??? Error using ==> NDS2_GetData
Fatal Error getting channel data.

Error in ==> getDARMdataTS at 37
oot = NDS2_GetData({...

Error in ==> SaveRawData_H1_DARM at 40
    oot = getDARMdataTS(t0s(ii), strideDuration, srate);

[Valera, Jenne]

After Steve and Valera switched out the PMC, the Mode Cleaner resonance needed to be brought back.  We spent some time playing with the 2 steering mirrors directly after the PMC, to get the beam through the EOM, and to achieve flashing in the MC.  Valera then adjusted those 2 steering mirrors to minimize MC_REFL_DC.  I did a little bit more, and it's kind of close now, but we're only at ~half normal transmitted power.  Since the 2 steering mirrors after the PMC are so close together, the beam alignment is pretty sensitive to even small touches.  So it's probably time to move on to using the last zigzag steering mirrors on the PSL table, since they're farther apart. 

I have to head out for a little while, but I'll be back in a few hours. Kiwamu said he might continue the alignment into the MC, if he needs the IFO.  Also, we should measure the power before and after the EOM, just to confirm that we're getting through it optimally.  The beam looks good after the EOM, and the MC is resonating, so it should be fine, but it can't hurt to check.

So.... Kiwamu and I were concerned (still a little concerned) that ETMY is not damping as nicely as it should be.  (It's fine, but the UL rms is ~5, rather than ~1 or less. BURT restores by Kiwamu didn't change anything.) Anyhow, I was heading out to push the annoying ribbon cables more firmly into the satellite adapter board things that are tied to the racks in various places (The back of 1X5 for the corner optics and the end station racks for the ETMs).  The point was to push in the ETMY one, but while I was out in the lab and thinking about it, I also gave all of the corner connectors (MC1, MC2, MC3, ITMx, ITMY, BS, PRM, SRM) a firm push. 

Kiwamu noticed that when I did this, the Mode Cleaner alignment got a little bit worse, as if the connection to the satellite adapter boards hadn't been great, I pushed the connectors in and the connection got better, but we also got a bit of a DC offset in the MC alignment.  Anyhow, the MC_TRANS power went down by ~2, to about the place it had been before Kiwamu adjusted the position of the lens in between the zigzag mirrors.  (I don't know if Kiwamu elogged it earlier, but he scooted the lens a teensy bit closer in the optical path to the Mode Cleaner). 

To counteract this loss in MC transmitted power as a result of my connector actions, I went back to the PSL table and fiddled with the zigzag steering mirrors that steer the beam from the PSL table over to the mode cleaner.  I got it a little better, but it's still not perfect.

Kiwamu has noted that to improve the mode matching into the Mode Cleaner with the new PMC in place, we might have to move the lens which is currently between the zigzag steering mirrors, and put it after the second mirror (so in between the last steering mirror and the pickoff window that sends a piece of the beam over to PSL_POS and PSL_ANG).  This will make the waist between MC1 and MC3 tighter. 

Moral of the story:  To improve IMC mode matching we need to move the last lens closer in the optical path to the mode cleaner waist. Twiddle with zigzag steering mirrors to optimize.

I worked a little bit more on optimizing the mode matching to the MC, but it's still not great.  I've only gotten a visibility of ~45%, but Koji said that it used to be ~87%.  So there is a long way to go.  Kiwamu said he can work with the lower-power configuration for a few days, and so my next step will be to measure the beam profile (stick a window in the path, and look at the refl from the window....that way we don't get thermal lensing from transmission through an optic), and redo the mode matching calculation, to figure out where the last lens should actually sit.

Just in case anyone else wants to access it, we now have 30 days of H1 S5 DARM data sitting on Rossa's harddrive.  It's in 10min segments.  This is handy because if you want to try anything, particularly Wiener Filtering, now we don't have to wait around for the data to be fetched from elsewhere.

 I'm going to take the easy question - What are the pink data points??

I (think) I have finished the new PMC base riser.  The eDrawing of it (so you can view it on any computer) has been uploaded to the PMC wiki page.

I also attach it here, for comments.