I'm just on an elog roll this morning...
Again while poking around inside the IFO room, I noticed that they have replaced all of our incandescent lights with CFLs. Do we care? The point of having the incandescent lights on a separate switch from the big fluorescent lights was so that we could have only 60Hz lines, not wide-band noise if we want the lights on while locking.
I'm not sure that we actually care, because more often we just turn off all the lights while trying to do serious locking, but if we do care, then someone needs to ask the custodial staff (or someone else?) to undo the change.
[Jenne, Zach, Frank]
Frank helped Zach and I cable up at PT-100 RTD, and make sure it worked with the Newport Model 6000 Laser Diode Controller. We're using this rather than the Newport 3040 Temperature Controller because Dmass says the output of that isn't working. So we're using just the temp control part of the Laser Diode controller.
The back of the controller has a 15-pin D-sub, with the following useful connections. All others were left Not Connected.
1 & 2 (same) - Pin 2 is one side of TEC output (we have it connected to one side of a resistive heater)
3 & 4 (same) - Pin 4 is the other side of the TEC output (connected to the other side of the resistive heater)
7 - connected to one side of PT-100 temp sensor
8 - connected to other side of PT-100 temp sensor
I used aluminum tape to attach the sensor and heater to the 40m's EOM, and we plugged in the controller. It seems to be kind of working. Zach figured out the GPIB output stuff, so we can talk to it remotely.
I don't think I touched/adjusted/whatever anything, but I did open the PSL table ~5-10min ago to measure the size of the Kiwamu-Box, so if the RFAM stuff looks funny for a few minutes, it was probably me. Just FYI.
DO NOT CHANGE THE IFO ALIGNMENT UNTIL TOMORROW MORNING OR FURTHER NOTICE.
We're playing with the MC OAF, so we're actuating on MC2. Again, FYI.
Gave the elog its afternoon / tea-time reboot, since it was hanging yet again.
I turned it back on, maybe around 11am? Definitely a little while before the 12:30 meeting.
EDIT by KI:
Sorry, it's me. I was checking if AC was doing something bad on the ALS noise.
Here is a drawing of where the monitors are coming from:
Since we can't put current into the ADC, the heater drivemon is measuring the input of the OP27, which is related to the amount of current sent to the heater.
EOM TEMPMON and HEATER DRIVEMON have been hooked up to the the following channels.
Here is 5 days of trend of the EOM temp sensor and the heater driver monitor. Unfortunately, it looks like we're regularly railing the heater. Not so awesome.
Some of the funniness is some kind of mysterious interaction between 2 filter modules in the filter banks. Just FM1 (30:0.0) or just FM4 (Cheby, which is 2 cheby1's) has reasonable coherence. Both FM1 and FM4 together doesn't do so well - the coherence goes way down.
Just FM1 (30:0.0)
Just FM4 (Cheby)
Both FM1 and FM4
All the coherences plotted together
You'd think that the signal encounters FM1, gets filtered, and that result is the signal sent to the next active filter module, FM4, so the 2 filter modules shouldn't interact. But clearly there's some funny business here since engaging both makes things crappy.
Matlab investigations to replicate this behavior offline are in progress.
I'm picking points off of this no-magnet OSEM plot, and I thought I'd write them down somewhere so I don't have to do it again when I lose my sticky note...
1e-2 Hz 1.05e-2 um/rtHz
1e-1 Hz 3.4e-3 um/rtHz
1 Hz 1.3e-3 um/rtHz
10 Hz 2.5e-4 um/rtHz
60 Hz 7.5e-5 um/rtHz
100 Hz 7e-5 um/rtHz
400 Hz 7e-5 um/rtHz
The new EOM adapter plate and riser just got back from the shop. I just had Mike do the milling, and I'll drill and tap them tomorrow after the TAC. Then we can remount the EOM to see if stiffening the mount helps at all.
Activities in a far, far away land called PSL lab...
We are looking at the RFAM from the detuned ACAV refl pd in the red trace. Red trace is the demodulated RFAM output. RCAV was locked, so on a ~min time scale the freq drift follows, so we stay detuned.
Heater and temp sensor are taped to EOM, no foam box.
Around when the red trace starts, we turn on the heater to stabilize the temp. After a while we reach the set point (no longer railing the heater), and start seeing temp stabilization. The RFAM fluctuations clearly go down. Neato.
No calibrations, no RIN, no nothing. Get over it.
Green trace is the DC level of a different PD, which should also be sensitive to RFAM.
This is using a fancy-pants temp controller chip that Frank found. It works, so that's handy.
I've added filter banks for correction path in the C1OAF model to use AA filters. I compiled and installed the new version. I runs but does not sync. Probably, I've made a mistake in the some names of epics channels. Leave it for now, figure out tomorrow. If someone needs an old version, it is in the /opt/rtcds/caltech/c1/userapps/trunk/isc/c1/models/c1oaf_BACKUP20111204.mdl file. Corresponding medm screen is in the /opt/rtcds/caltech/c1/userapps/trunk/isc/common/medm/OAF_OVERVIEW.adl file.
The general rule in the 40m is that if it's not an 'emergency', i.e. something is wrong with the computers and preventing the main locking work, no model recompiling-type activities at nighttime.
Also, if you do things and recompile, you need to do an svn check-in. That's where backups are kept. We don't want to clutter folders with backups anymore.
I have drilled all the holes necessary, and have tapped all but 4 of the holes for the new EOM mount. The adapter plate is finished and ready to go (including a 10-min iso sonic bath). The riser that goes between the table and the 9082 mount is drilled but not yet tapped.
EOM is remounted on the fancy-pants new mount that I crafted. EOM is also aligned. 2 green mirrors (the first ones to see the beams coming onto the PSL table from the arm transmissions) had to be moved so I could fit the mount in, since the new mount is bigger than the old one. I put them back, and approximately realigned them, but didn't do any fine alignment. This must be done before looking at beatnotes again.
After playing with the EOM, the MC was flashing on higher order modes. The PSL beam has been realigned to make the MC lock on TEM00, and Suresh helped me center on the WFS and MC2T.
Things look okay for now. Next step: Kiwamu needs to find his happy mode cleaner place, and we'll realign the PSL beam to the MC. The PSL-MC axes were mismatched pretty badly according to Suresh anyway, so this had to be done no matter what.
There were 2 open outputs on the splitter in the RAMmon (formerly known as Stochmon) box underneath the BS oplev table. The input to the splitter comes from the Thorlabs PD that we're using as our RAM monitoring PD. 2 of the outputs go to the RMS detection of 11 and 55 MHz. Now the other 2 (previously terminated) outputs go over to the LSC rack via SMA cable. The signal on both channels is ~200mV pk-pk, so -10dBm. One is plugged into the AS11 demod board (which didn't have a PD input yet), and the other goes to POP55's demod board, so POP55 is not what you think it is for now.
Koji is working on checking out the Rich box, which has 4 demodulators, which we will use eventually. Right now we're just using the already-plugged-in demod boards so we can start looking at some trends of RAM. We're going to need to find some channels when we're ready for the switchover.
Zach is nearing completion of the mini-update to the temp sensing system. Once we have the new more sensitive temp sensor in place, we can have a look-see at the similarities between EOM temperature and RAM levels.
Monitoring good, but remember that the EOM alignment must be done carefully to minimize the RAM before we can use these trends.
I temporarily diverted the output of the RAMmon PD to a spectrum analyzer (4195 in Spectrum Analyzer mode), and tweaked the EOM alignment until I minimized the 11 and 55 MHz peaks as much as possible. It was possible to get each individual peak to disappear into the noise (about -70dBm), but to get both minimized simultaneously I wasn't able to get both down into the noise. I left the 11MHz at about -55dBm, and the 55MHz at about -60dBm. If Kiwamu's simulation tells us that one is more significant than the other (55, because we use it for MICH?), then we can decide to favor putting that peak in the noise and sacrifice ~10dB in the other peak.
When I first plugged the PD into the analyzer, I saw 22MHz and 44MHz (small) peaks, but they went away after the first bit of tweaking.
Before having used the analyzer, I was trying to minimize the demodulated signals via StripTool, but that was a slow process. The spectrum analyzer was obviously much faster.
The PD has been returned to the regular RAMmon electronics.
Next up: putting in the new demod box that Koji tested last night.
* New demod box has been placed in the LSC rack.
* An extra set of +\- 24V has been prepared at the terminal block where all the Crates get their power on the LSC rack. The grounds were all connected up, but the hot wires weren't. So there were extra spots available, but none that were pre-wired with my voltages.
* To do this I turned off all the power supplies in the short rack, since I decided to be a live chicken rather than a dead duck. After hooking up the new terminal block slots, I turned on the power supplies.
* Make a power cable to go from the terminal block to the box
Still to do:
* Connect the spare 55MHz LO and the POP (or POX or POY) unused 11MHz LO to the back of the box
* Move the PD inputs to the new demod box rather than the borrowed AS11 and POP55 boards
* Plug the I & Q outs for each freq into some spare ADC channels - must first make sure we have 4 open channels.
* See if it works.
I was looking at the trends from the RAMmon, since I did the EOM alignment yesterday, and wanted to compare them to the MC trans, just to make sure the MC was locked during the times I'm examining. I was dismayed to discover that the MC has lost its oomph, starting around 11:30 this morning. Den was the only person in the lab to my knowledge at that time, and he claims that he didn't touch the MC until well after lunch. As you can see from the 8 hour trend attached, we went from normal ~26000 counts to ~15000, and we're slowly decaying from there.
MC refl looks pretty bad on the camera, particularly in YAW. Investigations are beginning now....
Edit, ~10min later... I enabled the WFS (I don't know why they were off...when the MC fell out of lock and relocked itself, the WFS didn't come on), and things went basically back to how they should be. However, the sans-WFS alignment is still totally crappy, so the PSL beam probably needs to be aligned to the MC. I don't really want to touch the alignment though without an okay from Kiwamu, so I'll wait for him to come in and confirm that he's happy with the current MC.
I checked the power regulators on the Rich demod box (according to the schematic, D1000217). The positive one is LM2941CT, and the negative one is LM2991T. Both accept input voltage up to +26V or -26V respectively. So my use of +\- 24V to be regulated down to +\- 15V isn't too crazy. It's a little crazy, but not too crazy. They recommend having only a 3V difference between the input and output voltages. We don't have any 18V or 20V power supplies in the regular LSC power supply rack, so Rana suggested using the 24's.
When I plug in and turn on the Rich box, the current on the +24V power supply goes up by about 0.8A, and the -24V supply goes up by about 0.3A. That seems like kind of a lot. Is that too much? Do I need to find a better plan that involves +\- 18V? Thoughts?
For now, the Rich box is off, just in case.
Kiwamu and I discussed, and looking at the AS camera with the PRM and SRM misaligned, but MCWFS engaged, things look good. This means that it's probably the MC that has drifted, and we want to align the MC back to the PSL beam.
Foam house installed on EOM a few min ago. We'll leave it until ~tomorrow, then try out the heater loop.
PMC trans was only ~0.79, where it should be ~0.84 something. The MC was also not stellar.
I aligned the beam to the PMC, and am now getting PMC trans 0.837 .
Then I aligned the PSL zigzag to the MC, and got MC Refl down to ~0.6 .
I then aligned the WFS to the unlocked MC, and the MC Trans QPD to the locked MC.
Things seem good. MC axis is still in a good place, since we get good michelson fringes at the AS port.
Dataviewer couldn't connect to the framebuilder, so I checked the CDS status screen, and all the fb-related things on each model went white, then red, then computer-by-computer they came back green. Now dataviewer works again. Is someone secretly doing shit while not in the lab??? Not cool man!
EOM was aligned to minimize the 11 and 55 MHz peaks in the RAMmon PD the other day (elog 6089), and was left with just the temperature sensor attached, no heater, no foam box.
Here is a 4 day trend:
I don't have a whole lot to say about this, other than there's a lot of stuff going on. The craziness at the end is me realigning the PMC and MC since, as you can see, MC trans was way down. The foam box was put on earlier today (elog 6104), so we'll see how that changes things over night.
Now we've got another day of data, with the foam box on for the last 24hrs.
First plot is a 5 day trend so you can see that the RAM has gotten a little bit smaller, as has the temperature drift, but not by a whole lot.
Second plot is the last 19 hours (so excluding much of the time while I was realigning beams on the PSL table yesterday), to zoom in on just the time when the foam box was installed.
After lunch Zach and I are going to engage the heater to temperature stabilize the system, to see how that affects things.
In other news, the MC looks like it was fine for a good long time, and ~3 hours ago it went bad. The mode that's flashing is really bad in both pitch and yaw. I don't know what happened, but something is not so awesome. Edit: Steve said that he opened the PSL table at some point this morning to look around but not touch, and also it's Janitor Day, and Kevin comes in around 8ish. That doesn't mean I know the actual cause, but those are the only things that happened in the IFO room this morning that anyone is aware of.
The Rich demod box wants 10dBm for the local oscillator inputs, so I measured the values that we have coming out of the distribution box. I'm using the "Spare 55MHz" and the "POP11" outputs, both of which had terminators so were not in use.
The 55MHz had ~600mV peak, so between 5 and 6 dBm.
The 11MHz had ~800mV peak, so about 8 dBm.
This is not enough dBm for either. Going in search of RF amplifiers now...
Actually, the LO inputs to the IQ boards have AP1053 (Cougar) amps on them. These are 10 dB amps and so putting 10 dBm in puts us on the very maximum of the LO range at 20 dBm.
I think the distribution box levels are fine.
I'm not sure I agree with your conversions, BUT:
The IQ boards use a PE4140, fancy MOSFET array as the mixer, and according to Peregrine (manufacturer), they can be operated with 0-20 dBm LO drive. I'm not recommending we drive them at 0 dBm, but perhaps the numbers you mentioned are OK.
Yeah, I looked and saw that it's a semiconductor mixer, so it doesn't have to be as perfect.
Everything is plugged in now to the new demod board. More details soonly...
The I & Q outs are plugged into whitening filter #3, channels 5-8. 11MHz I = chan 5, 11MHz Q = chan 6, 55MHz I = chan 7, 55MHz Q = chan 8. These channels are probably already recorded, but I haven't checked yet. Hopefully I'll have time tonight after I pack for my trip. But Zach, can you look into it tomorrow just to check?? Backup plan is to just go back to using the AS11 and POP55 boards and channels if the new board isn't doing what it's supposed to.
I disconnected the 3rd and 4th channels of the demod box since they were drawing unnecessary current, and making the box hot. Now the box is just warmish.
Is there a reason the framebuilder status light is red for all the front ends?
Also, I reenabled PRM watchdog.
I realigned the incident beam to PMC at 23:30. The transmitted light went up from 0.78 to 0.83.
Do we have PSL pos and ang QPD trends? We should start watching them, because the PMC drifted back down to 0.76 transmission, ~3.5 days after Kiwamu realigned it (his elog is from last Thurs). Not so awesome.
I walked through the control room just now and found both PMC and MC unlocked. They're both locked now, but with PMC transmission 0.76, MC transmission ~24,500.
Bob, Callum and Daphen noted that our keeping a JDSU HeNe (max power <4mW) is against somebody's SOP. So I cleared everything that relates to 40m SOS suspending to the bottom shelf of the 2nd cabinet in the cleanroom (the back set of cabinets nearest the flow benches). The door has a nifty label. Things that are in there include:
QPD and micrometer mount
microscope and micrometer mount
Al beam block
Magnet gluing fixture
dumbbell gluing fixture
The electronics that we use (HeNe's power supply, 'scope, QPD readout) are still on the roll-y thing under the flow bench.
The mode cleaner is super unhappy. It's rocking around at ~1Hz.
I turned off the WFS and turned them back on after the MC was locked, and it seems a little happier now. At least it's not falling out of lock ~1/minute.
Sitting down to start cavity measurements, I found both ITMs tripped. It must have happened a while ago (I didn't bother to check dataviewer trends) because both had rms levels of <5 counts, so they've had a while to sit and quiet down.
The Yarm green laser really wanted to lock on a 01/10 mode, so Kiwamu suggested I go inside and realign the green beam to the arm. I did so, and now it's much happier locked on 00 (the Yarm is resonating both green and IR right now).
The mode cleaner is a little misaligned in pitch, and is very misaligned in yaw. The lowest order mode that is flashing is TEM11.
I had a look-see at the SUS sensors, to see if there were any big jumps. There were moderately sized jumps on all 3 mode cleaner optics.
The MC's lockloss was at ~8:22am this morning, and went along with a giganto kick to the optics. Steve tells me that Den might have been kicking up optics while doing computer things this morning, before Steve reminded him to shut off the watchdogs. However, Steve was also taking phots/measuring things near MC Refl, so maybe he's not totally absolved of blame. But this really looks like the optics settled to different places after big kicks.
I'm going to try to align the MC mirrors to get back to the sensor numbers from early this morning before chaos began.
Reminder / Moral: Everything cannot be considered to be "working fine" if the MC isn't locking. See if you can figure out why, and especially if it's something that you screwed up, either fix it, or better yet, ask for help and learn how to fix what you broke.
We moved the MC approximately back to where the sensors for each optic used to be (mostly touching MC2, but a little bit of MC1 to help the refl get back to its max value). MC is now locked, and with the help of the WFS it's back to nominal. I forgot to disable the WFS, so I think we aren't perfectly aligned, but we're close enough for the WFS to get us the rest of the way. We're heading over to JClub right now, so we're going to leave it as-is.
Kiwamu and Steve maybe don't know about how to trend seismic noise. If you just take the mean of the time series, you don't prove that the seismic noise got any higher. The STS has a nominally zero DC output, so the long period level shifts that you see tell you just that there was a DC offset.
This is NOT an increase in seismic noise. To see a seismic trend you should plot the trend of the BLRMS channels that we made especially for this purpose.
So, none of our PEM BLRMS channels are recorded as of right now. All we have for long-term record is the StripTool on the wall. The 0.1-0.3Hz and 0.3-1 Hz traces both show these weirdo things, but the 1Hz and up BLRMS don't have any unusual noise.
Seems like a problem to solve on Monday so that we don't end up without trends like this again.
Tragically, this is more tricksy than I would have thought. The channels we need are "cdsEpicsOutput"s in the model. They don't show up in Dataviewer (fast or slow channels) or the regular fast channel .ini file. Jamie and I don't remember where these channels live and how to get them saved to frames. I'm on top of it though.
I did notice however, that the striptool for seismic trends is showing the wrong channels for 3-10 and 10-30 Hz. The other 3 channels are correctly the output after the sqrt is taken, but those two (orange and red on striptool) are before the sqrt, but after the bandpass and low pass. I'll fix that now...
We extracted the fiber that Suresh and Sonali laid over the summer, for the IR beat for the Ygreen laser, and Frank took it back to Bridge to be used in the new fiber distributed reference laser setup.
Power Spectral Density plot using PyNDS, comparing 5 fast data channels for ETMX.
Is there any stuff to install, etc? Y'know, for those of use who don't really know how to use computers and stuff....
Xarm is aligned for both IR and green.
Here is a photo of the beam paths of the PSL beat setup. I want to make sure that the X-green BBPD sees a nice beam from both the PSL and the Xarm, without disturbing the currently working Y setup. I keep getting confused with all the beamsplitters, especially the green PBSes, which operate at ~56deg, not 45deg, so I made a diagram.
Meh. I've searched in steps of 20 counts in C1:GCX-SLOW_SERVO2_OFFSET units (16 bit +\- 10V DAC, and 1GHz/V coeffecient for the Xgreen aux laser means this is ~0.6MHz per 20 count step). I went from -400cts to +800 cts and haven't found the beatnote yet. Meh.
Both PSL green and Xgreen beams are going to the Xgreen BBPD. Both beams are easily visible, so while I didn't actually measure the power, it should be sufficient. The arm is being re-locked in green for each step, but it's not locked in IR, but that doesn't matter for just finding the beatnote.
I've got the output of the BBPD directly connected to the 50 ohm input of the HP8591E spectrum analyzer, with the freq span from 10MHz to 120MHz. The BBPD is supposed to be good up to ~100MHz, so I should catch any beatnote that's there. I have to head out, so I guess I'll continue the search tomorrow.
One of Kiwamu's suggestions was that, since no one is using the Ygreen concurrent with my fiddling, I rotate the waveplate after the PSL doubling oven so that max power goes to the Xgreen path, thus giving myself a bigger signal. I'll try that tomorrow. Today, I didn't ever touch the waveplate.
The actual temperature of the Xend laser is 0.02 C higher than anticipated based on the formula in elog 3759. Both the PSL and the Xend laser are at their nominal diode currents (2.100 A for the PSL, 2.003 A for Xend), so the curves should be used as they are. The PSL temp (when the slow servo offset is ~0) is 31.71 C. Using curve 2 from elog3759, the Xend laser should be 37.78, which I found was +10 counts on the Xgreen slow servo offset.
Right now the Xend laser is at 37.80 C, and the beat is around 30 MHz. This is +80 counts on the Xgreen slow servo. +60 counts gave me ~80 MHz. When (a few minutes ago) the MC unlocked and relocked, it came back to a slightly different place, so the temp of the Xend laser had to go up a few 10's of counts to get the same beat freq. Right now the PSL slow servo offset is 0.076 V.
The HP8591E is set with ResBW=100kHz, Ref Level= -39dBm (so I'm not attenuating my input signal!). The largest peak I see for the beatnote is -66dBm. The nose floor around the peak is -83dBm. Trace (trace button!) A is set to MaxHoldA, and Trace B is set to ClearWriteB, so B is giving me the actual current spectrum, while A is remembering the peak value measured, so it's easier to see if I went past the peak, and just didn't see it on the analyzer.
Also, I went back and realigned the beams earlier, to ensure that there was good overlap both near the BS which combines the PSLgreen and Xgreen beams, and at the PD. The overlap I had been looking at was okay, but not stellar. Now it's way better, which made the peak easier to see. Also, also, the waveplate after the doubling oven on the PSL table is still rotated so that I get max power on the Xgreen side of things, and not much at all on the Ygreen side. I'll need to rebalance the powers, probably after we make sure we are seeing the beatnote with the BeatBox.
Lay a cable from the BBPD to the BeatBox in 1X2, make the BeatBox do its thing.
Use the dichroic locking to do a sweep of the Xarm.
ND filter ND3 (which is at the REFL port to the REFL OSA) is removed. Don't forget to put it back when you restore PRM!!!
I don't know what tripped the PRM watchdog, but it was unhappy. I manually moved the sliders on the IFO align screen away from the positions of the save file before turning on the damping, to make sure that I wouldn't be sending oodles of power to the REFL port, since the ND filter is still removed. So PRM is damped now, but misaligned.
Has default inmat:
Has fancy inmat:
BS, ITMY, SRM (but side is non-fancy), ETMX, ETMY, MC1, MC2, MC3
So it's likely that the MICH problems (giganto 1Hz peak) Keiko and Kiwamu were seeing last night had to do with ITMX having the non-optimized input matrix. I'll try to figure out where the data from the last freeswing test is, and put in a fancy diagonalized matrix.
The Xgreen PD now has a cable going over to the beatbox. Once beatbox characterization is done I can re-find the beat, and we can do some stuff with the beatbox.
Here is a picture of the small black breadboard on which I have put together the PD characterisation setup. It would be great if we can retain this portable set up as it is, since we keep reusing it every couple of weeks. It would be convenient if we can fiber couple the path to the PD under test with a 2m long fiber. Then we will not have to remove the PD from the optical table while testing it.
This is totally sweet Suresh! I don't remember how much more fiber is coiled up under the plate that has the "Jenne Laser" label, but there's a reasonable amount. It's not 2m, but maybe we can just extend the blue snakey thing some?
I'd like to know what we expect for these numbers. I've added to Kiwamu's drawing some more distances, so I can calculate the expected beam size at the IPPOS port.
I'm meditating over the mode matching from the mode cleaner to the ITMs, and I had another thought:
Have we changed the pointing of the MC significantly enough that we are no longer on the center of the MMT mirrors? To be this significant, we would probably also have had to scoot the Faraday a bit too, since it's skinny like a straw. It looks like our measurements of the input beam have been the following:
MC waist, 21 May 2010
After MMT2, 18 June 2010 (a few days before this, we flipped the MMT2 mount to 'perfect' the mode matching up to 99.3%, so I don't think the MMT has moved since then.)
After MMT2, 26 March 2012
There's a big o' ~2 year gap between our measurements, and we've been in and out of the vacuum a few times since then. I'll flip through the elog, but does anyone have any memory of us moving the Faraday after June 2010? When was the last time we made sure that we were at least close to the center of the MMT mirrors?
This is wrong! See following elog for corrected plot (and explanation)
I'm not done meditating on what's going on, but here's what I've got right now:
This is a beam profile, using the distances from the combined Kiwamu / Jenne sketch earlier today.
0 meters along the horizontal axis is meters from the Mode Cleaner waist. (Yes, I was bad and forgot to label it. Get over it.)
The pink and green dots to the left of the plot are the MC fitted waist measurements that we made in May 2010.
The pink and green dots in the ~center of the plot are the fitted waist measurements that Suresh and Keiko took yesterday, of the IPPOS path, so after the MMT.
The black dot is where we would like our non-astigmatic beam to be. This is the calculated waist size of the cavity mode, using the new ~37.76m distance, after we moved the ETMs to their current positions. The black dot indicates 3.036 mm at the ITM (averaged between the BS-ITMX and BS-ITMY distances).
The moral of the story that I'm getting from this plot: something funny is going on.
The distances Kiwamu quoted on the sketch are very close to the ones that I used for designing and checking the MMT in the first place, which were based off of measurements using rulers etc to measure distances. Steve said he looked at photos today, and agreed that Kiwamu's numbers looked reasonable also.
Something that we haven't done lately is measure the position of each optic from every other optic, along the beam path. I propose we come up with a clever way to put a target on top of / next to mirrors, and then a way to hold the laser distance measure-er at an optic, so that we can go thorough systematically and measure the actual path that our beam is seeing. Maybe this is too much work, and not worth it, but it would make me happier. In my head, these 'fixtures' are just small pieces of cleaned aluminum, one that can sit on a mirror mount, and one which we can use to align the laser ruler to approximately the front of an optic. Nothing fancy.