The way to usually do image subtraction is to:
1) Turn off the room lights.
2) Take 500 images with no beam.
3) Use Mean averaging to get a reference image.
4) Same with the beam on.
5) Subtract the two averaged images. If that doesn't work, I guess its best to just take an image of the green beam on the mirrors using the new DSLR.
PRM and SRM OSEM LL 1.5V are they misaligned?
We have two ready for vacuum 1.5" mirror mounts with pico motors in our hands.
Steve's elog 7682 is in response to the conversation we had at group meeting re: Jamie's proposed idea of re-purposing the active tip tilts.
What if we use the active TTs for the PR and SR folding mirrors, and use something else (like the picomotors that Steve found from the old days) for our input steering?
Steve's elog 7682 is in response to the conversation we had at group meeting re: Jamie's proposed idea of re-purposing the active tip tilts.
I think we will still need two active steering mirrors for input pointing into the OMC, after the SRC, so I think we'll still need two of the active TTs there.
My thought was about using the two active TTs that we were going to use as the input PZT replacements to instead replace the PR2/3 suspensions. Hysteresis in PR2/3 wouldn't be an issue if we could control them.
With static input pointing, ie. leaving PZT2/3 as they are, I think we could use PRM and PR2/3 to compensate for most input pointing drift. We might have to deal with the beam in PRC not being centered on PRM, though.
Koji's suggestion was that we could replace the PZTs with pico-motors. This would give us all the DC input pointing control we need.
So I guess the suggestion on the table is to replace PZT1/2 with pico-motor mounts, and then replace PR2/3 with two of the active tip-tilts. No hysteresis in the PRC, while maintaining full input pointing control.
With Picos, we lose the ability to dither the input beam as well as align the beam with the IFO locked. And the active TT will still have hysteresis, but also actuators. Once in vacuum, I'm not sure how we adjust them - what's the error signal for PR2/PR3 ?
If the interferometer is aligned, why not just pump down now? I'm not sure that we have evidence of TT hysteresis issues once people stop touching them.
[Jenne, Jamie, Manasa, Ayaka]
Flipped mount of OM2, moved OM2 behind POY pickoff so we're out of the way of POY. Adjusted and recovered rest of AS path.
We found that IPANG was not on its photodiode, but determined that it was centered on all of the in-vac mirrors, and that it was just a little bit of steering on the ETMY end out-of-vac table that needed to be done.
Got green flashes in Yarm, moved down periscope to the north by ~1 inch in order to get y green out to PSL table. This also involved moving the steering mirror on the IOO table immediately after the down periscope to match. We measured the MC spot positions before and after touching the periscope, and there was no significant change.
Aligned X green to X arm (centered on ITMX, ETMX, although no flashes since we didn't move ETMX's biases around), then made sure it was centered on all of its steering mirrors, and came out of the vacuum.
Manasa took photos of all test mass chambers and the BS chamber, so we can keep up-to-date CAD drawings.
Oplevs and IPPOS/IPANG are being centered as I type. Manasa and Ayaka are moving the lens in front of IPANG such that we have a slightly larger beam on the QPD.
In the morning, Jamie is going to put apertures back on 2 of the suspended mirrors for one last check that moving things on the IOO table didn't do anything bad, but since the AS and REFL beams on those cameras didn't move significantly, we think things are fine.
Heavy doors go on in the morning, and access connector at ~1pm, if not before lunch. Then Steve will start pumping early Monday morning! Hooray!
PS, for reference,
" We found that IPANG was not on its photodiode, but determined that it was centered on all of the in-vac mirrors, and that it was just a little bit of steering on the ETMY end out-of-vac table that needed to be done."
The lens in front of IPANG on the out-of-vac table was moved to get a larger beam giving reasonable signals at the QPD.
IPPOS did not need much adjustment and was happy at the center of the QPD.
All oplevs but the ETMY were close to the center. I had to move the first steering mirror about half an inch on the out-of-vac table to catch the returning oplev beam from ETMY and direct it to the oplev PD.
* We have taken reasonable amount of in-vac pictures of ETM, ITM and BS chambers to update the CAD drawing.
Oplevs and IP ANG are still centered. Why do the SRM and PRM move 5X more ? I could not check the sensing voltages because the computer failed.
AS and REFL are looking the same as last night.
ALL LOOKING GOOD!
I didn't make any concrete progress today. AS and REFL cameras are in place, and Manasa has put ND 0.5 filters on both. I used a
camera to look at the back of the Faraday, and aligned PRM such that it was retroreflecting, and then tried to align ITMY to have once
fringes with the PRM at that place. I failed in this, since the AS beam on the AS table was starting to dall off the first mirror on the table.
I then restored all the suspensions to where they were before I started touching them today.
I moved ETMY face camera so that it is looking at the front of the black glass, but it's hard to tell where the beam is. I was thinking
about setting up a temporary camera to look at the back of ITMY to help guide PZT steering, but I haven't done this yet.
Koji and I then talked about the several different options I have for references, and how many different knobs I can turn. I'm sleeping
on it for now, and hopefully I'll have more insight on what to do tomorrow.
We aligned accurately 00 green in yarm, changed voltage on PZT2 to see red flashing at TRY at the normalized level 0.2-0.3. The plan was to lock yarm using POY11 and green from other side, maximize red TRY by adjusting PZT2. But POY11 does not go out of the vacuum, so we adjusted TRY by flashing. 2 DOFs of PZT2 is not enough to match 4 DOFs of red beam so we adjusted both PZT2 and cavity mirrors. TRY flashing is 0.5-0.6 and green is still locking to 00 though its transmission is not maximized. We'll fix it later by adjusting input green beam.
Next we wanted to get red beam on TRX PD. Beam steering was done by BS only. We misaligned BS in pitch and excited BS angle motion by 1000 counts. We could see red beam moving on the wall of ETMX chamber. We moved it to ETMX mirror frame, estimated position of the mirror center and moved BS to this position. The beam should be approximately in the middle. For now we can not see red beam on the camera at ETMX table, more work is needed.
POY11 does not go out of the vacuum
It does but slighty low and does not get on mirrors. We need to change optic mounts to adjust the height. Red is flashing in yarm at 00 and 10 modes. TRY is ~0.4-0.5.
I've adjusted BS angle, camera and TRX PD at ETMX table so I can see red flashing at 03 mode while green is locked to 00 and its transmission is maximized. I thought that by adjusting BS angle, I will be able to align red to 00 not disturbing green, but this was not the case. Maximum TRX I could get was 0.1. I've adjusted POX to get into PD and I can see PDH signal though I can't lock as cavity is still misaligned for red.
You have constraints for the IR beams (i.e. one PZT and one BS for 8 dofs), so now you need to align the arms for the input IR beams.
The PZT and BS should be aligned so that you have the beam spots as center as possible with the above restrictions.
Then realign end greens for the given arm alignment. You can replace the mounts if necessary to align the end green.
Even if you lose the coarse alignment of the green, realignment is not difficult as you know now
We put the POY beam onto the POY PD. The Yarm is currently locked on IR with ~0.65 transmission.
Today at 11:13 AM the stack of invacuum BS table was kicked and IFO misaligned. We adjusted PZT2 voltage by ~20 V in yaw such that IPPOS was restored. Then we could lock arms.
For those of you who like to do work on the interferometer without reporting it in the elog because you think that what you did doesn't affect anything, this is your example of how our time can be wasted by such laziness.
I'm taking full responsibility for this action and I told them after lunch Friday.
HOW NOT TO:
The BS isolation stack supported by two beam tubes and they can pivot around the pivot point.
BS chamber seemed to be kicked again around 10:00 am today.
I moved PZT mainly in YAW and locked both arms. I adjusted the beam to be almost on the center of both ETM by sights.
Today I've set c1ass model to improve alignment of X and Y arms. I've added all measured parameters to ASS scripts. I've also added a script to c1ass.adl that downloads calculated OFFSETs to corresponding ASC filter banks and blocks outputs. It should be called after alignment convergence.
XARM phase rotation and sensing matrix
Output gains were (-0.5, 0.5, -0.25, -0.25). XARM Gain was set to 0.5.
YARM phase rotation and sensing matrix
Output gains were (-0.25, 0.25, 0.7, -0.7). YARM Gain was set to 0.8.
This looks like a good performance tuning for these. It would be good if you can codify this procedure in the wiki so that even unexperienced people can tune up the system after reboots or vacuum work.
Is it possible to have some python scripts automatically measure and set the phases and matrices? If so, can we also run them iteratively so that after the second run we can confirm that they have converged? Then the script can output a short report of numbers telling us how well the system is now tuned.
I suppose that there is also a similar system possible to align the arms in a continuous way; i.e. low level drives and very low bandwidth. Also something fast / slow for the the DRMI.
c1ass was really useful today when we slowly aligned PZT and servo kept arms aligned to the input beam. I think it is possible to automate phase and matrix measurements. DRMI servo will be very useful.
Today I tried to investigate the mode in PRCL and MICH. I locked them but power build-up was only 27. The beam on the POP camera looked like interference of 00 mode and a long strip of fringes. (I wanted to make videocaptures but script is not working - the problem is that it is looking for /usr/lib/*.so.4 libraries but they were updated to *.so.5, I made a few links .so.4 -> .so.5 but this kept going for many libraries, so this should be fixed in a better way).
We looked at PRM and BS faces and they had the same shape - interference of a circle with a strip. There were also a lot of bright spots all over the frames. Loops were closed and circle was not moving. Strip was oscillating at ~1Hz and also its position significantly changed with alignment. Looking at PRM face camera we made a conclusion that the length of the strip is ~5 cm and width ~1cm. Interesting that strip has plenty of power - approximately 10 times of transmitted beam when cavity is not locked. As a result POYDC was oscillating at the same frequency as a strip.
I have setup cameras looking at the back of PR3 (through the north viewport on the MC chamber) and the face of PR2 (through the north viewport on the ITMX chamber). We would like a view of the face of PR3, but that isn't possible without placing another in-vac mirror. The best we can do is the current PRM_BS camera setup, which sees a small portion of the PR3 face. Most of the face is obscured by the PRM itself.
I have taken images with the PRM misaligned. The spot near the top of PR2 is the first reflection from the pitch-misaligned PRM, so it should be ignored for the purposes of trying to see the straight-shot, no PRM beam.
Images are taken with my videocapture50 script, in ..../scripts/general/videoscripts. This takes 10 sets of 50 images and saves them. Then ImageBkgndSubtractor.m located in the same folder takes the images (you must edit the beginning of the script to tell it where the images are), averages the noBeam images (PSL shutter closed), and averages the withBeam images, and subtracts them. Results below:
Koji and Jamie locked the PRMI, and then Jamie and I took some videos.
Video 1: https://www.youtube.com/watch?v=jszTeyETyxU shows the face of PR2.
Video 2: https://www.youtube.com/watch?v=Tfi4I4Q3Mqw shows the back of PR3, the face of PR2, as well as REFL and AS.
Video 3: https://www.youtube.com/watch?v=bLHNWHAWZBA is the camera looking at the face of PRM and (through a viewing mirror) BS.
If you watch video 1, you'll see how large the beam gets on the face of PR2. The main spot, where the straight-through, no-cavity beam is, is a little high of center. The rest of the inflated beam swirls around that point.
Video 2 shows the same behavior, but you also see that we're much too high on PR3, and too close to the right (as seen on the video) side.
Video 3 is very disconcerting to me. The main, stationary beam spot seems nicely centered, but the resonant beam, since it inflates and gets big, is very close to the right side of the PRM (as seen on the video).
It wouldn't surprise me if, were we able to quantify the beam clipping loss on PR3 and PRM, the clipping were the reason we have a crappy PRC gain. This doesn't explain why we have such a weird inflated beam though.
[Jenne, Manasa, Jamie]
Now that we're up to air we relocked the mode cleaner, tweaked up the alignment, and looked at the spot positions:
The measurements from yesterday were made before the input power was lowered. It appears that things have not moved by that much, which is pretty good.
We turned on the PZT1 voltages and set them back to their nominal values as recorded before shut-down yesterday. Jenne had centered IPPOS before shutdown (IPANG was unfortunately not coming out of the vacuum). Now we're at the following value: (-0.63, 0.66). We need to calibrate this to get a sense of how much motion this actually is, but this is not insignificant.
List of things to do, in order:
* Remove BS heavy door. Steve, please remove the BS door as soon as you have enough people to do so. I will be a little late, since I have a dentist appointment, but please don't wait for me. Jamie and Manasa can help you. Put on a light door.
* Remove MC light doors, make aluminum foil tube (not light access connector, yet).
* Open laser shutter, lock PMC. (Required slight tweaking of input steering.) Confirm power level into vacuum <100mW.
* Lock MC and check spot positions of MC (quickly. this shouldn't take all day, hopefully).
------------------------------- End of work for Monday. See following elog ------------------------------------------------
* Move TT1 to be as close as possible to the location indicated on the diagram, then align it.
* Make sure beam out of Faraday is hitting the center of the optic.
* Make sure beam reflected off of TT1 hits center of PZT2. Only use actuators for the final alignment, then confirm that they aren't close to the edge of their ranges.
* Lock down TT1 with dog clamps.
* Put light access connector on MC.
* Swap PZT2 out with TT2. Should be at correct spot, according to diagram, and beam should be hitting center of optic. Alignment only to the ~few degree point here.
* Re-level BS table.
* Fix oplevs that need fixing. (Manasa should have the plan on one of the diagrams).
* Put target on PRM cage.
* Align TT2 so that beam goes through PRM target.
* Open ITMX heavy door. (Probably Tuesday morning).
* Place freestanding target in front of PR2. Ensure TT2 is aligned to go through PRM target, and hit center of PR2. Again, save actuators for fine-tuning.
At this point, I think we should (temporarily) install one of the G&H mirrors as a flat mirror facing the PRM, and see if we can lock that cavity using REFL. We will want to have already created a model for this case, to compare our observations to. Or we could align the full PRMI, and try to lock that in air.
[Jenne, with backup from Koji and Steve]
TT1 was installed without a riser, optic is too low, riser we have doesn't fit, cannot proceed with alignment. Sadface.
I had gotten to the point of checking that the beam coming out of the Faraday was hitting the center of TT1, when I realized that we had forgotten to install the risers. The TTs are designed for 4" beam height, but we have a beam height of 5.5" in-vac. This means that the beam out of the Faraday was hitting the top of the optic / the optic holder.
Steve showed me where all of the active TT equipment is stored (down the X arm, almost all the way to the flow bench...there is a plastic tub full of baked items (individually wrapped and bagged)), and I got one of the 1.5" risers.
Upon opening the riser package, and comparing it with the base plate of the active tip tilt, the screw holes don't match!
It looks like for the passive tip tilts, we had holes machined at the far corners of the base plate, then had these risers made. You can see in the photo of SR3 below that the original holes are there, but we are using 1/4-20 holes at the far corners of the base plate.
Unfortunately, without checking the base plate, I had asked Steve to get 4 more of the same risers we used for the passive tip tilts. So, now the base plate holes and the riser holes don't match up. In a perfect world, we would have installed the risers on the TTs as soon as they were baked and ready, and would have discovered this a while ago....but we don't live in that world.
The reason we had originally chosen to put the new 1/4-20 holes on the corners of the passive tip tilts was so that when we tightened the screws, we wouldn't bend the base plate, due to the groove at the bottom of the base plate being directly under the screws. Since the new aLIGO TT base plates have the groove underneath going the opposite direction, we didn't need to move the holes to the corners.
Also, you can't really see this from the photos, but the active TT base plate is slightly longer (in the beamline direction) than the riser, but only by a little bit. Koji is currently trying to measure by how much from the CAD drawings.
Also, also, because of the way TT1 will hang off the table, I'm concerned about the underneath groove on the riser being the direction it is. I'm concerned that the grooved part will be what wants to touch down on the back corner of the table, such that either the TT is insufficiently supported, or it is tilting backwards. Neither of these will be acceptable.
I propose that we re-make the risers quickly. We will have the holes match the active TT base plate, the size of the riser should match the size of the active TT base plate, and the underneath groove should be perpendicular to the way it is in the current version.
[Jenne, EricQ, Nic, MattA]
* TT1 is in place, aligned so beam hits center of TT1, hits center of MMT1 (used pitch biases to finish pitch).
* Riser installed, dogged down with 1 dog.
* TT1 sitting on top of riser, 3 dogs holding TT to table, with riser squished in between.
* IOO table leveled.
* Almost all of the weights on the IOO table were just sitting there, not screwed down! One didn't even have a screw, 3 had screws, but they were totally loose. 2 of those screws were in as far as they could go, but they weren't holding the weight. This means the screw was too long, and should have been replaced (which I did today). Just because the existing screw was too long, doesn't mean it should be left as-is. Everything in the chambers must be tightly clamped down, as soon as work on that item is complete! Anyhow, after finalizing the leveling, I tightened down all of the weights on the IOO table.
* MMT1 tweaked so beam hits center of MMT2.
* MMT2 tweaked so beam hits center of PZT2.
* Light access connector installed.
* I dropped a Class B golden-colored 3/16 allen key to the bottom of the IOO chamber. I can't see it, but Nic thinks he might be able to see it with a mirror, from the BS chamber. We should look for it when we look for the IR card that is still down there.
* We have an ant in the IOO chamber. Unfortunately my hands were on the TT1 optic holder ring when I saw it, so I couldn't dash quickly enough to grab it. I saw it run over the side of the table, and down, but looked under the table and couldn't find him. Not so good, but I don't know what to do about it right now. If anyone sees it, get it out please.
PZT2 was removed from the BS table, and packed away in a foil-lined plastic box.
PRM oplev path has been altered, including installation of a 3rd mirror, to accommodate TT2, which is larger than PZT2.
* Unfortunately, PR3 is a few mm more north than is indicated in the CAD drawing, so I wasn't able to place the oplev mirrors exactly as Manasa indicated in elog 7815.
* We came up with a different layout. Photos were taken. We will need to confirm that the IPPOS, AS, and GreenX beams all clear past the oplev mirrors, but by imagining straight lines between mirrors for those beams, I think we should be okay. but we must confirm when we have real beams.
TT2 was installed, according to the placement in the diagram. Dogged down just as TT1 - one dog for the riser, 3 dogs for the TT base which also squish the riser. You should be able to see this in the photos. Without having installed the PRM target, it looks like the input beam is hitting pretty close to the PRM's center. Tomorrow Jamie The Tall can install the PRM target for us so we can confirm.
Photos - I'm posting them on Picasa here. The new camera, and the fact that you can rotate the viewfinder, is amazing for overhead in-chamber photos. Seriously, it's much easier to take useful photos. It's great.
We remove the ITMX door first thing. If Steve isn't here, we'll ask Koji or Bob to help us with the crane.
First thing on the alignment list is to finalize TT2's pointing. Put a target in front of PR2, put on the PRM target, etc, etc. We're basically back to the same alignment procedure as we've been doing the last few vents.
Item for meditation:
Do we trust ourselves, or do we want to think about installing a 'bathroom mirror' so we can see the face of PR3 while we are pumped down?
I had asked Q to write this down on a piece of paper, but then I forgot to transcribe it into the elog....
The TT screen matrix, at least for TT1, is flipped or something. When Eric moved the pit slider, the optic moved in yaw, and vice versa.
We need to fix this, but for now, here's the situation when TT1 was pointed correctly at MMT1:
TT1 Pit slider | 1000 1000 | ---> 700 UL
0 | -1000 1000 | ---> 700 LL
TT1 Yaw slider | 1000 -1000 | ---> -700 UR
0.7 | -1000 -1000 | ---> -700 LR
The confusing thing is that Koji and I confirmed (by plugging in the correct cable to the correct sensor) that "UL" on the screen goes to the UL coil, and the same for the other 3 coils. This needs investigation / fixing.
[Bob, Manasa, Jenne]
We opened the ITMX heavy door. Before getting too far, we realized that we had to do the fancy pin swapping before we can activate TT2. So....
We followed the instructions in elog 7869, and the associated Picasa album, and swapped the pins for the in-vac connector that will go to TT2. Pretty easy, since the procedure was already well documented.
We then looked at the beam location on PR2, and the beam is ~2 inches up and to the left (as viewed from the front) from the center of the optic. This is very easily correctable with the actuators, so we're leaving TT2 as it is.
We started off to try and get TT2 working. We used the cables Jamie had already prepared while working on TT1 and used them to connect TT to the channels in 1Y3.
There were sma cable connectors already running between the channels 5-8 on the board to the UL,LL,UR and LR. Triggering the UL LL UR LR matrix on epics did not show any analog voltage at the output analog channels on the board. Talking to Jamie over phone, we inferred that the SMA cables that were already left connected corresponded to channels assigned for TT4 in epics. So we set the connections right and could see analog voltage outputs corresponding to epics triggers.
We connected the ribbon cables running from the board to the TT. But changing pitch and yaw did not do anything to the TT2 mirror. We opened the BS door and checked if the tt cables were connected to the post. We beeped the cable running from the board to TT (we also traced the cable's trail through the cable rack pile from 1Y3 to BSC). Using a function generator at the board end of the cable, we could not observe anything at the TT end of the cable.
We ran out of options on what can be done next and closed the doors. We hope Jamie can fix the problem once he returns next week.
Was the connection between the feedthrough (atmosphere side) and the connector on the optical table confirmed to be OK?
We had a similar situation for the TT1. We found that we were using the wrong feedthrough connector (see TT1 elog).
The major problem that Manasa and I found was that we weren't getting voltage along the cable between the rack and the chamber (all out-of-vac stuff). We used a function generator to put voltage across 2 pins, then a DMM to try to measure that voltage on the other end of the cable. No go. Jamie and I will look at it again today.
Everything was fine. Apparently these guys just forgot that the cable from the rack to the chamber flips it's pins. There was also a small problem with the patch cable from the coil driver that had flipped pins. This was fixed. The coil driver signals are now getting to the TTs.
Investigating why the pitch/yaw seems to be flipped...
[Jamie, Manasa, Jenne]
We started by verifying that the tip-tilts were getting the correct signals at the correct coils, and were hanging properly without touching.
We started with TT2. It was not hanging freely. One of the coils was in much further than the others, and the mirror frame was basically sitting on the back side yaw dampers. I backed out the coil to match the others, and backed off all of the dampers, both in back and the corner dampers on the front.
Once the mirror was freely suspended, we borrowed the BS oplev to verify that the mirror was hanging vertically. I adjusted the adjustment screw on the bottom of the frame to make it level. Once that was done, we verified our EPICS control. We finally figured out that some of the coils have polarity flipped relative to the others, which is why we were seeing pitch as yaw and vice-versa. At that point we were satisfied with how TT2 was hanging, and went back to TT1.
Given how hard it is to look at TT1, I just made sure all the dampers were backed out and touched the mirror frame to verify that it was freely swinging. I leveled TT1 with the lower frame adjustment screw by looking at the spot position on MMT1. Once it was level, we adjusted the EPICS biases in yaw to get it centered in yaw on MMT1.
I then adjusted the screws on MMT1 to get the beam centered at MMT2, and did the same at MMT2 to get the beam centered vertically at TT2.
I put the target at PRM and the double target at BS. I loosened TT2 from it's base so that I could push it around a bit. Once I had it in a reasonable position, with a beam coming out at PR3, I adjusted MMT1 to get the beam centered through the PRM target. I went back and checked that we were still centered at MMT1. We then adjusted the pitch and yaw of TT2 to get the transmitted beam through the BS targets as clear as possible.
At this point we stopped and closed up. Tomorrow first thing AM we'll get our beams at the ETMs, try to finalize the input alignment, and see if we can do some in-air locking.
The plan is still to close up at the end of the week.
Just for reference! The changes made to the TT matrix in order to fix the polarity problem:
The old matrix values are mentioned in elog!
PIT YAW New
Pit slider | -100 -100 | UL
0 | -100 100 | LL
Yaw slider | 100 -100 | UR
0 | 100 100 | LR
[Jamie, Jenne, Manasa]
Yesterday's goal was to get the input beam centered on the PRM, the BS and ETMY simultaneously.
Steve helped us remove the ETMY door first thing in the morning. We then iterated with TT1, MMT1 and TT2 to try to get the beam centered on all the optics. We were using MMT1 instead of TT1 for a while, so that we could keep TT1 in the center of its range, so that we had more range to use once we pump down. Also, at one point, the beam was high on PRM, centered on BS, and high on ETMY, so Jamie poked PR3 a little bit. This helped, although we closed up for lunch / group meeting soon after, so we didn't finalize any alignment stuff.
We decided to leave the rest of the full IFO alignment alone until after the PRM-flat test.
We had to work on redesigning the oplev layout in BSC when I found that the positions of the mirrors were clipping IPPOS and the green beam while updating the CAD layout.
To avoid any clipping, the prm oplev beam is steered into the vacuum by an oplev mirror and out of vacuum through 3 steering mirrors. The table weights had to be moved to allow room for the oplev mirrors. Hence table had to be re-leveled. I will update the CAD drawing with the current position of the mirrors and will reconfirm that the new mirrors are not in the way of any of the beams. In-vac photos are updated in picasa.
Jenne and I got the half PRC flashing. We could see flashes in the PRM and PR2 face cameras.
We took out the mirror in the REFL path on the AP that diverts the beam to the REFL RF pds so that we could get more light on the REFL camera. Added an ND filter to the REFL camera so as not to saturate.
We tweaked up the alignment of the half PRC a bit. Koji started by looking at the REFL and POP DC powers as a function of TT2 and PRM alignment.
He found that the reflected beam for good PRC transmission was not well overlapped at REFL. When the beam was well overlapped at REFL, there was clipping in the REFL path on the AS table.
We started by getting good overlap at REFL, and then went to the AS table to tweak up all the beams on the REFL pds and cameras.
This made the unlocked REFL DC about 40 count. This was about 10mV (=0.2mA) at the REFL55 PD.
This amazed Koji since we found the REFL DC (of the day) of 160 as the maximum of the day for a particular combination of the PRM Pitch and TT2 Pitch. So something wrong could be somewhere.
We then moved to the ITMX table where we cleaned up the POP path. We noticed that the lens in the POP path is a little slow, so the beam is too big on the POP PD and on the POP camera (and on the camera pick-off mirror as well).
We moved the currently unused POP55 and POP22/110 RFPDs out of the way so we could move the POP RF PD and camera back closer to the focus. Things are better, but we still need to get a better focus, particularly on the POP PD.
We found two irides on the oplev path. They are too big and one of these is too close to the POP beam. Since it does not make sense too to have two irides in vicinity, we pulled out that one from the post.
Other things we noticed:
After the alignment work on the tables, we started locking the cavity. We already saw the improvement of the POPDC power from 1000 cnt to 2500 cnt without any realignment.
Once PRM is tweaked a little (0.01ish for pitch and yaw), the maximum POPDC of 6000 was achieved. But still the POP camera shows non-gaussian shape of the beam and the Faraday camera shows bright
scattering of the beam. It seems that the scattering at the Faraday is not from the main beam but the halo leaking from the cavity (i.e. unlocking of the cavity made the scattering disappeared)
Tomorrow Jenne and I will go into BS to tweak the alignment of the TEMP PRC flat mirror, and into ITMX to see if we can clean up the POP path.
Yuta, Manasa, Jamie, Jenne, Steve, Rana
Starting this morning, we removed the temporary half PRC mirror in front of BS and started to align the IFO in prep for an in-air lock of the PRMI.
This morning, using the new awesome steerable active input TTs, Jenne and I centred the beam on PRM, PR2/3, BS, ITMY and ETMY.
After lunch, Yuta and Manasa aligned the Y ARM, by looking at the multi-pass beam. The X-end door was still on, so they roughly aligned to the X ARM by centring on ITMX with BS. They then got fringes at the BS, and tweaked the ITMs and PRM to get full fringes at BS.
We're currently stuck because the REFL beam appears to be clipped coming out of the faraday, even though the retro-reflected beam from PRM is cleanly going through the faraday output aperture. The best guess at the moment is that the beam is leaving MC at an angle, so the retro-reflected beam is coming out of the faraday at an angle. We did not center spots on MC mirrors before we started the alignment procedure today. That was dumb.
We may be ok to do our PRMI characterization with the clipped REFL, though, then we can fix everything right before we close up. We're going to need to go back to touch up alignment before we close up anyway (we need to get PR2 centered).
Yuta and Manasa are finishing up now by making sure the AS and REFL beams are cleanly existing onto the AS table.
Tomorrow we will set up the PRM oplev, and start to look at the in-air PRMI. Hopefully we can be ready to close up by the end of the week.
We should check MC spot positions to see what they are.
Also, I'm not thrilled about the idea of a clipped REFL beam. Haven't we played that game before, and decided it's a crappy game? Can we recenter the MC, and recover quickly with TT1?
Lot's of alignment work, still no AS beam. REFL is clipped by Faraday output aperture......
Our guess is that this is because we skipped MC centering.
Alignment procedure we took:
1. AM work: Aligned input beam using TT1/TT2
such that the beam hits ETMY and ITMY at the center.
2. Coarsely aligned ITMY
such that the ITMY retro-reflected beam hits BS at the center.
3. Aligned ETMY (we didn't actually move ITMY)
such that Y arm flashes.
This tells you that ITMY is aligned well to the incident beam.
4. Aligned BS
such that the beam hits ITMX at the center.
5. Aligned ITMX
such that the ITMX retro-reflected beam hits BS at the center.
At this point, we saw MI fringes at AS port.
6. Fine alignment of ITMX:
MI reflected beam was not overlapping in front of BS after it was reflected by PRM.
We used this longer REFL path to tune alignment of ITMX to ITMY reflected beam.
We saw MI fringe at REFL port coming out of the chamber, but it was clipped.
7. Aligned PRM
by looking at REFL beam from PRM on the back face of Faraday (video FI_BACK).
We fine tuned the alignment such that PRM retro-relfected beam hits BS at the center and REFL beam from PRM overlaps with the MI fringes at the back face of Faraday.
8. Clipping of REFL at the Faraday output aperture:
We confirmed that the shape of the REFL beam from PRM was OK at the back face of Faraday. But some how, it was clipped at the output aperture. So, REFL beam coming out of the chamber is clipped now.
9. Tried to get AS beam out of the chamber:
We tweaked steering mirrors after SRM to get AS beam out of the chamber. But, we lost the AS beam between the very last folding mirrors (OMPO and OM6) in the OMC chamber......
1. Why clipping at the Faraday output aperture?
In principle, if PRM reflects the incident beam at normal incidence, it should pass the Faraday unclipped. But it's not!
Our guess is that the incident beam does not go well centered through the apertures of the Faraday. I think we have to do MC centering to get good pointing to the Faraday.
We also see that MI fringe at the back face of the Faraday is at the edge of its aperture, after all of these alignment work (we even used Y arm!). This tells you that some thing is wrong.
2. Why did you guys lose the AS beam?
AS beam is too weak after reflecting off of OMPO. The beam was neither visible on IR cards nor IR viewers. The beam is weaker than usual because PMC transmission is ~0.7 and MC REFL is getting high (~ 0.7). We didn't want to realign MC after all of this work today.
Tomorrow (my suggestion):
1. Align PMC (for higher power).
2. MC centering.
3. Input beam steering using TTs and redo the same alignment procedure (it shouldn't take longer than today).
==> Center beam on PR2 (Added by Manasa)
4. Maybe we should better check PRM reflection at REFL port after the Faraday, before doing the full alignment work.
5. Align AS, REFL, POP PDs/cameras.
6. Setup PRM/BS/ITMX/ITMY oplevs.
7. Balance the coils on these mirrors.
8. Lock PRMI.
What needs to be done before pumping down:
1. PRMI characterization: PR gain and g-factor
How can we do the g-factor measurement? Use additional laser? Kakeru method (elog #1434; we need to calibrate mirror tilt to do this)?
2. Glitch study in PRMI locking. If still glitchy, we have to do something. How is beam spot motion? (elog #6953)
3. Fine alignment of the flipped PR2.
4. Fine alignment of IFO using both arms.
We need to calculate whether this level of astigmatism is expected from the new active TT mirrors, but I claim that the beam is not clipped.
As proof, I provide a video (PS, why did it take me so long to be converted to using video capture??). I'm just showing the REFL camera, so the REFL beam as seen out on the AS table. I am moving PRM only. I can move lots in pitch before I start clipping anywhere. I have less range in yaw, but I still have space to move around. This is not how a clipped beam behaves. The clipping that I see after moving a ways is coincident with clipping seen by the camera looking at the back of the Faraday. i.e. the first clipping that happens is at the aperture of the Faraday, as the REFL beam enters the FI.
Also, I'm no longer convinced entirely that the beam entering the Faraday is a nice circle. I didn't check that very carefully earlier, so I'd like to re-look at the return beam coming from TT1, when the PRM is misaligned such that the return beam is not overlapped with the input beam. If the beam was circular going into the Faraday, I should have as much range in yaw as I do in pitch. You can see in the movie that this isn't true. I'm voting with the "astigmatism caused by non-flat active TT mirrors" camp.
Let's wait for astigmatism calculation.
In either case(clipping or astigmatism), it takes time to fix it. And we don't need to fix it because we can still get LSC signal from REFL.
So why don't we start aligning input TTs and PRMI tomorrow morning.
Take the same alignment procedure we did yesterday, but we should better check REFL more carefully during the alingment. Also, use X arm (ETMX camera) to align BS. We also have to fix AS steering mirrors in vacuum. I don't think it is a good idea to touch PR2 this time, because we don't want to destroy sensitive PR2 posture.
Calculations need to be done in in-air PRMI work:
1. Explanation for REFL astigmatism by input TTs (Do we have TT RoCs?).
2. Expected g-factor of PRC (DONE - elog #8068)
3. What's the g-factor requirement(upper limit)?
Can we make intra-cavity power fluctuation requirement and then use PRM/2/3 angular motion to break down it into g-factor requirement?
But I think if we can lock PRMI for 2 hours, it's ok, maybe.
4. How to measure the g-factor?
To use tilt-and-measure-power-reduction method, we need to know RoC of the mirror you tilted. If we can prove that measured g-factor is smaller than the requirement, it's nice. We can calculate required error for the g-factor measurement.
After using alamode to calculate the round-trip mode of the beam at the Faraday exit after retro-reflection form the PRM, I'm not able to blame the MMT and TT curvature for the beam ellipticity.
I assume an input waist at the mode cleaner of [0.00159, 0.00151] (in [T, S]). Propagating this through the MMT to PRM, then retro-reflecting back with flat TTs I get
w_t/w_s = 0.9955, e = 0.0045
If I give the TTs a -600 m curvature, I get:
w_t/w_s = 1.0419, e = 0.0402
That's just a 4% ellipticity, which is certainly less than we see. I would have to crank up the TT curvature to -100m or so to see an ellipticity of 20%. We're seeing something that looks bigger than 50% to me.
Below are beam size through MMT + PRM retro-reflection, TT RoC = -600m:
[Yuta, Manasa, Jenne, Jamie, Steve]
0. Measured MC centering (off by 5mrad) before getting the doors off.
1. Got the TTs to 0.0 in pitch and yaw.
2. Using the MMTs, the beam was centered on the TTs.
3. TT1 was adjusted such that the incident beam was centered at PRM (with target).
4. TT2 was adjusted such that the beam passed through the center of BS (with target).
5. Centered the beam on PR2 by sliding it on the table.
6. Moved PR2 and tweaked TT2 to center the beam on ITMY and BS respectively.
7. Using TTs, we got the beam centered on ETMY while still checking the centering on ITMY.
8. ITMY was adjusted such that it retro-reflected at the BS.
9. ETMY was aligned to get a few bounces in the arm cavity.
10. Centered on ITMX by adjusting BS and then tweaked ITMX such that we retro-reflected at BS.
11. At this point we were able to see the MI fringes at the AS port.
12. Tweaked ITMX to obtain reflected MI fringes in front of MMT2.
13. By fine adjustments of the ITMs, we were able to get the reflected MI to go through the faraday while still checking that we were retro-reflecting at the BS.
14. Tweaked the PRM, such that the PRM reflected beam which was already visible on the 'front face back face of faraday' camera went through the faraday and made fine adjustments to see it fringing with the reflected MI that was already aligned.
15. At this point we saw the REFL (flashing PRMI) coming out of vacuum unclipped and on the camera.
16. Started with alignment to get the AS beam out of vacuum. We tweaked OM1 and OM2 (steering mirrors in the ITMY chamber) to center the beams on OM4 and OM3 (steering mirrors in the BSC) respectively.
17. We then adjusted steering mirrors OM5 and OM6 (in the OMC chamber) such that the beam went unclipped out of vacuum.
18. Note that we took out the last steering mirror (on the AS table) in front of the AS camera, so that we can find the AS beam easily. This can be fixed after we pump down.
0. REFL still looks like an egg, but leave it .
1. Align PRMI (no more in-vac!) .
2. Align POP/REFL/AS cameras and PDs.
3. Setup PRM/BS/ITMX/ITMY oplevs.
4. Balance the coils on these mirrors.
5. Lock PRMI.
Yuta and Manasa, you guys are awesome!
Small, inconsequential point: The camera image in the upper right of your video is the *back* of the Faraday in our usual nomenclature. The camera is listed in the videoswitch script as "FI_BACK". The camera looking at the "front" of the Faraday is just called "FI".
We set up POP camera and POPDC PD, and centered REFL PDs.
We also tried to center AS55 PD, but AS55 seems to be broken.
What we did:
1. POP path alignment:
Shot green laser pointer from ITMX table at where POPDC PD was sitting and centered green beam at optics in the POP path. Steered POPM1/M2 mirrors in the ITMX chamber to make green laser overlap with the PRM-PR2 beam as far as I can reach from ITMX chamber. We removed some ND filters and a BS for attenuating POP beam because POP power was somehow so low. Currently, POP is pick-off of the beam which goes from PRM to PR2.
2. POP camera and PD:
We first used camera to find the beam at where POPDC PD was sitting because it is much easier to find focused beam. Put an iris in front of the camera, and put POP DC behind it. Steered a mirror in front of PD to maximize DC output.
3. REFL PDs:
Steered mirrors in the REFL path to center the beam and maximized DC outputs, as usual.
AS55 was not responding very much to the flashlight nor AS beam. C1:LSC-ASDC_OUT looked funny. By swapping the ribbon cables of AS55, REFL55, and REFL165, I confirmed that AS55 PD itself is broken. Not the ribbon cable nor PD circuit at LSC rack. I don't know what happened. AS55 was working on Feb 8 (elog #8030).
We aligned PRMI coarsely. POP(right above) looks much better than before. REFL (left below) still looks elliptic, but ellipticity differs with the position on the camera. Some astigmatism is happening somewhere. AS (right below) looks pretty nice with MI aligned.
1. Fix AS55? Or replace it with POP55 PD, which is currently unused.
2. Confirm we are getting the right error signals or not, and lock PRMI.
We will start preparing for pumping down. Main goal for this is to demonstrate PRFPMI using ALS.
Here are to-dos before we pump down.
Feb 18 eveing
- check input beam and Y arm alignment again
- IPPOS/IPANG alignment
- check all oplevs
Feb 19 morning
- open ETMX chamber heavy door
- align BS to X end
- adjust OSEM values (added by YM)
- center beam on all AS optics
- make sure AS/REFL is clear
- take picture of flipped PR2 (added by YM)
- make sure green is not clipped by new PRM oplev mirrors (added by YM)
- center all oplevs
Feb 19 afternoon - Feb 20 morning
- close PSL shutter
- close all heavy doors and put the access connector back
- start pumping down
Feb 20 evening
- start aligning IFO