should compare side by side with the ITM PRMI radar plots to see if there is a difference. How do your new plots compare with Gautam's plots of PRMI?
Here is a side by side comparison of the PRMI sensing matrix using PRM/BS actuation (attachment 1) and ITMs actuation (attachment 2). The situation looks similar in both cases. That is, good orthogonality on REFL55 and bad seperation in the rest of the RFPDs.
The He-Ne laser which has been used for the PRM and BS oplevs were found to be dead.
According to the trend data shown below, it became dead during the dolphin issue.
(During the dolphin issue the output from the oplev QPDs are digitally zero)
JDSU 1103P died after 4 years of service. It was replaced with new identical head of 2.9 mW output. The power supply was also changed.
The return spots of 0.04 mW 2.5 mm diameter on qpds are BS 3,700 counts and PRM 4,250 counts.
The laser below is dead. JDSU 1103P, SN P845655 lived for 3.5 years.
It was replaced by JDSU P/N 22037130,( It has a new name for 1103P Uniphase ) sn P919639 of mfg date 12-2014
Beam shape at 5 m nicely round. Output power 2.8 mW of 633 nm
BS spot size on qpd ~1 mm & 60 micro W
PRM spot size on qpd ~1 mm & 50 micro W
Recently, Steve replaced the HeNe which was sourcing the BS & PRM OL. After replacement, no one checked the beam sizes and we've been living with a mostly broken BS OL. The beam spot on the QPD was so tiny that we were seeing the 'beam is nearly the size of the segment gap' effect.
Today I removed 2 of the lenses which were in the beam path: one removed from the common PRM/BS path, and one removed from the PRM path. The beams on both the BS & PRM got bigger. The BS beam is bigger by a factor of 7. I've increased the loop gains by a factor of 6 and now the UGFs are ~6 Hz. The loop gains were much too high with the small beam spots that Steve had left there. I would prefer for the beams to be ~1.5-2x smaller than they are now, but its not terrible.
Many of the mounts on the table are low quality and not constructed stably. One of the PRM turning mirror mounts twisted all the way around when I tried to align it. This table needs some help this summer.
In the future: never try locking after an OL laser change. Always redo the telescope and alignment and check the servo shape before the OL job is done.
Also, I reduced the height of the RG3.3 in the OL loops from 30 to 18 dB. The BS OL loops were conditionally stable before and thats a no-no. It makes it oscillate if it saturates.
[ Jenne, Koji and Kiwamu]
We have installed the PRM and the tip-tilt (TT) in the BS chamber.
We have started the in-vac work which takes about a week.
Today's mission was dedicated to installing the PRM and two TTs, one for the PRC and the other for the SRC, on the BS table in the chamber.
The work has been smoothly performed and we succeeded in installation of the PRM and a TT for the PRC.
But unfortunately the other TT got broken during its transportation from Bob's clean room.
(what we did)
- Prior to this work we screwed down the earthquake stops so that the mirror is fixed to the tower. Also we disabled the watchdog.
- When moving it we used an allen key as a lever with an screw as a fulcrum. This idea was suggested by Jenne and it really worked well.
The reason why we used this technique is that if we slide the tower by hands the tower can't go smoothly and it may sometimes skips.
After that we checked the postion from some reference screw holes by using a caliper and we made sure that it was on the right position.
- After this removal the mirrors were wrapped by aluminum foils and put in a usual clear box.
- These were also wrapped by aluminum foils and put in the box. Later we will put them back to the BS table.
- The position of the PRM were coarsely aligned since we still don't have any 1064 beam going through the PRM.
- The position of the installed TT was coarsely adjusted.
- After we brought them we removed the aluminum foils covering the TTs and we found the wire of a TT got broken.
It may have been damaged during its transportation from Bob's room because it was fine before the transportation.
(7) closed the door
(the next things to do)
* Installation of the OSEMs to the PRM
* Installation of the pick off mirror and its associated optics
* Arrangement of the pzt mirror
I measured PRM angular motion spectra (in daytime today).
PRM angular motion is ~ 10 urad in RMS when undamped and ~1 urad in RMS when damped.
If PR2/PR3 angular motions are something like this, and their motion are not enhanced when PRC is locked, measured g-factor of PRC looks OK. But considering the error we have, maybe we are not OK yet. We need calculation.
We have positioned the guide rod and the wire-stand-off on the optic in the axial direction.
We have selected six magnets whose magnetic strength is +/-5% of their mean strength (180 Gauss). The measurement was made as follows:
1) each magnet was placed on its end, on the top of a beaker held upside down.
2) The Hall probe was placed directly under the magnet touching the glass from the other side (the inside of the beaker).
This ensures that the relative position of the magnet and the probe remains fixed during a measurement. And ensures that their separation is the same for each of the magnets tested.
With this procedure the variation in the measured B field is less than +/- 10% in the sample of magnets tested.
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.
I realized I hadn't checked the PRM actuator as thoroughly as I had the others. I used the Oplev as a sensor to check the coil balancing, and I noticed that while all 4 coils show up with the expected 1/f^2 profile at the Oplev error point, the actuator gains seem imbalanced by a factor of ~5. The phase isn't flat because of some filters in the Oplev electronics I guess. The Oplev loops were disabled for the measurement, and the excitations were small enough that the beam stayed reasonably well centered on the QPD throughout. This seems very large to me - the values in the coil output filter gains lead me to expect more like a ~10% mismatch in the actuation strenghts, and similar tests on other optics in the past, e.g. ETMY, have yielded much more balanced results. I'm collecting some free-swinging PRM data now as an additional check. I verified that all the coils seem actuatable at least, by applying a 500 ct step at the offset of the coil output FM, and saw that the optic moved (it was such a test that revealed that MC1 had a busted actuator some time ago). If the eigenmode spectra look as expected, I think we can rule out broken magnets, but I suppose the magnets could still be not well matched in strength?
PRM coil gains and f2a filters are adjusted for PRMI work.
It seems like UR/LL coil gains were ~10 % larger than others, and f2a filters changed by few %.
What I did:
1. Tried to lock PRMI but when I turn on PRCL lock, PRM reflection looked like it tends to go up and left in REFL camera (last night).
2. So, I set up PRM oplev back, by steering PRM oplev mirrors on the BS table (last night).
3. Turned PRM oplev sero on, f2a filters off, and ran
> /opt/rtcds/caltech/c1/scripts/SUS/F2P_LOCKIN.py -o PRM
I had to fix F2P_LOCKIN.py because it assumed some OUTPUT buttons in LOCKIN1 filters to be ON.
Also, I had to restore filters in LOCKIN1 (8.5 Hz bandpass filter etc.) because their names were changed. To do this, I copied filters needed from /opt/rtcds/caltech/c1/chans/filter_archive/c1sus/C1SUS_110916_162512.txt, renamed LOCKIN1_(I|Q|SIG) with LOCKIN1_DEMOD_(I|Q|SIG), and pasted to the current filter bank file. I checked that they look OK with foton after editing the file.
This measurement takes about 30 minutes. I ran several times to check consistency. There was ~ 0.1 % standard deviation for the measurement results.
4. By putting measured coupling coefficients and PRM pendulum frequency (f0=0.993 Hz) to /opt/rtcds/caltech/c1/scripts/SUS/F2Pcalc.py, I got new f2a filters.
5. Overwrote f2a filters in C1:SUS-PRM_TO_COIL_(1-4)_1 FM1 with new ones, and turned new f2a filters on.
Below is the DC gain adjustment result from F2P_LOCKIN.py;
multiplier factors are :
UL = 1.141525
UR = 0.879997
LR = 1.117484
LL = 0.860995
Set C1:SUS-PRM_ULCOIL_GAIN to 1.04990177238
Set C1:SUS-PRM_URCOIL_GAIN to -0.983396190716
Set C1:SUS-PRM_LRCOIL_GAIN to 0.954304254663
Set C1:SUS-PRM_LLCOIL_GAIN to -0.971356852259
So, UR/LL coil gains somehow got ~10 % larger than other two since last coil balancing.
Measured coupling coefficients from F2P_LOCKIN.py were
- measured coupling coefficients are :
P2P(POS=>PIT) = 0.014993
P2Y(POS=>YAW) = 0.001363
New f2a filters are plotted below. They look fairly different compared with previous ones.
We need better F2P_LOCKIN.py:
Some one should make F2P_LOCKIN.py better. The main problem is the sudden gain change when starting diagonalization at low frequency. It sometimes trips off the watchdog.
Some elogs related:
Kiwamu made f2a filters in Sep 2011: elog #5417
Koji adjusting DC gains in Jan 2013: elog #7969
> /opt/rtcds/caltech/c1/scripts/SUS/F2P_LOCKIN.py -o PRM
- measured coupling coefficients are :
P2P(POS=>PIT) = 0.014993
P2Y(POS=>YAW) = 0.001363
I will check out the AS55 situation tomorrow. Just put it on my desk.
MC Autolocker was disabled - I enabled it.
For the F2P.py, you should look at how we did this with the script written 8 years ago in csh. There we stored the initial values in a file (so they don't get blow away if someone does CTRL-C). Your python script should have a trap for SIGINT so that it dies gracefully by restoring the initial values. In order to have the smooth value adjustment, you must first set the TRAMP field for all the coil gains to 2 and then switch. Make sure that the lockin ignores the first few seconds of data after making this switch or else it will be hugely biased by this transient.
For the PRM OL use as a F2A reference, you also have to take into account that the OL beam is hitting the PRM surface at non-normal incidence. IF it is a large angle, there will be a systematic error in the setting of the F2Y values.
We tried to lock half-PRC tonight, but we couldn't. Why?? I could lock yesterday.
It locks for ~ 1 sec, but it beam spot motion freaks out mainly in yaw.
I tried to balance PRM coils, but oplev beam was clipped by MMT1......
What I did:
1. Found elog #5392 and found F2P_LOCKIN.py
2. Modified F2P_LOCKIN.py because LOCKIN channel names are some how changed like this;
LOCKIN1_I -> LOCKIN1_DEMOD_I
LOCKIN1_Q -> LOCKIN1_DEMOD_Q
LOCKIN1_SIG -> LOCKIN1_DEMOD_SIG
/opt/rtcds/caltech/c1/scripts/SUS/F2P_LOCKIN.py -o PRM
should adjust (UL|UR|LR|LL)COIL_GAINs by putting some gain imbalance and shaking the mirror in different frequencies. It uses LOCKIN to OL(PIT|YAW).
4. Since there was no PRM oplev beam coming out from the vacuum, I quickly looked into BS-PRM chamber. Oplev beam was clipped by MMT1. If I adjust PRM slider values to avoid clipping, the beam will be clipped by mirrors on oplev table. What happened to the PRM oplev?
5. I also made bunch of /opt/rtcds/userapps/trunk/sus/c1/medm/templates/SUS_SINGLE_LOCKIN(1|2)_DEMOD_(I|Q|SIG).adl because there were missing screens.
We need to restore the PRM oplev and balance the coils. See, also, elog #7679
/opt/rtcds/caltech/c1/scripts/SUS/F2P_LOCKIN.py -o PRM
We tried actuating on PRM so that we go through fringes in a known, linear way. We used C1:SUS-PRM_LSC_EXC and awggui. It seems that we get a lot of angular motion when we actuate....we need to look into this tomorrow.
EDIT/UPDATE: Last night we tried several combinations of frequency and amplitude, but just for an idea, we were using 2Hz, 1000cts. Using Kiwamu's calibration in elog 5583 for the PRM actuator of 2e-8/f^2 m/cts, this means that we were pushing ~5nm. But when we pushed much harder (larger amplitude) than that, we saw angular fringing.
[Koji, Jamie, Jenne]
Koji did this, while we actuated on PRM in pos, and watched the oplev. Empirically, he found the following values for the POS column of the output matrix:
UL = 1.020
UR = 0.990
LL = 1.000
LR = 0.970
SD = 0.000
(The nominal values are all +1, except for Side, which is 0).
Actuation of PRM was through C1:SUS-PRM_LSC_EXC, f=0.1Hz, A=100 counts.
Ed by KA:
This means UL and UR are increased by 2% and UR and LR are decreased by 3%. More precisely UR should be 1.02*0.97.
This is just a quick hack which works only for the DC.
PRM sus damping recovered and PMC locked.
The PRM sus damping restored. C1:SUS-PRM_SDPD_VAR is still 20-30mV and going up. Side gain turned on. This pulled it down to 5-8 mV
Why is the side osem sensing voltage 4.4V ? It can not be higher than ~2.4V.......something is rotten in the state of Denmark?
Edit by KI:
It's because Valera increased the transimpedance gain of the PRM SIDE OSEM to match the signal level to the new ADC range (#3913 ).
The PRM sus damping was restored. It's side rms motion came down from 35 to 4 mV immediately. Lab air quality is back to normal.
The PRM watchdogs were tripped. The side was kicked up to 180mV Damping was restored.
The PRM damping was restored at side sensor var 1050
The PRM sus damping restored.
The PRM lost damping about a day ago. It was restored.
Yuta claims he fixed the PRM oplev by centering it the other day, but no one has left it on and watched it for a long while, to make sure it's okay. We watched it now for ~2 min, and it was good, but we're leaving the oplevs off anyway for the night. Tomorrow we should restore PRM (it's currently restored), turn on the oplevs, and let it sit to make sure it doesn't go crazy.
PRM oplev servo was turned on with PITgain 0.5 and YAWgain -0.7
Note: gain settings were PIT 1.0 and YAW --0.5 on Jun 1, 2012 that I measured Feb 23, 2012
It is still oscillating. Gains turned down to zero.
Earthquake test our suspensions PRM damping restored. Oplev servo gains turned to zero.
The PRM damping restored. Oplev PIT gain 0.15 and YAW gain -0.3 turned to zero.
PRM oplev gains set to zero from PIT 0.15 and YAW -0.3 and damping restored
PRM oplev servo turned off. OLPIT servo gain 0.15 and OLYAW -0.3 set to ZERO. PRM damping restored
The PRM side was kicked up
Local earthquake 3.8 Mag tripped only PRM
Vac monitor is not communicating.
PSL HEPA turned on
PRM suspension damping restored after 4.1 Mag Ludlow earthquake.
Recent EQ 4.8 mag San Felipe, Mexico trips PRM sus damping.
PRM damping restored. PMC locked.
Local earth quake 3.7 mag trips PRM
What about the MC?
What not to do:
The PRM oplev servo was left on and it was driving this oscillation overnight.
Oplev servo turned off and sus damping restored. What is kicking up the PRM?
Local m3.8 eq shakes PRM lose.
A few things tonight. Locked both arms simultaneously (IR only). Locked MICH, Locked PRMI, although it doesn't like staying locked for more than a minute or so, and not always that long.
Locking PRCL was possible by getting rid of the power normalization. We need to get some triggering going on for the power norm. I think it's a good idea for after the cavity is locked, but when PRCL is not locked, POP22 is ~0, so Refl33/Pop22 is ~inf. The PRCL loop kept railing at the Limit that was set. Getting rid of the power normalization fixed this railing.
I took some spectra of PRM's oplev, while PRMI was locked, and unlocked. The PRM is definitely moving more when the cavity is locked. I'm not sure yet what to do about this, but the result was repeatable many times (~6 or 7 over an hour or so). The OpLev spectra when PRMI was locked didn't depend too strongly on the PRM's alignment, although I think that's partly because I wasn't able to really get the PRM to optimal alignment. I think POP22I is supposed to get to 7 or so...last week with Koji it was at least flashing that high. But tonight I couldn't get POP22I above 4, and most of the time it wouldn't go above 3. As I was aligning PRM and the circulating SB power increased, POP22I fluctuations increased significantly, then the cavity unlocked. So maybe this is because as I get closer, PRM gets more wiggly. I tried playing 'chicken' with it, and took spectra as I was aligning PRM (align, get some improvement, stop to take spectra, then align more, stop to take spectra....) but usually it would fall out of lock after 1-2 iterations of this incremental alignment and I'd have to start over. When it relocked, it usually wouldn't come back to the same level of POP22I, which was kind of disappointing.
In the PDF attached, pink and light blue are when the PRMI is locked, and red and dark blue are no PRCL feedback. The effect is more pronounced with Pitch, but it's there for both Pitch and Yaw.
Also, I need to relook at my new restore/misalign scripts. They were acting funny tonight, so I'm taking back my "they're awesome, use them without thinking about it" certification.
Is this enhancement of spectrum caused by the lock? Or by the actuation?
If this is also seen with approximately same amount of actuation to PRM POS,
this is just a suspension problem.
If this is only seen with the PRM locked, this is somehow related to the opt-mechanical coupling.
The PRM oscillation stopped by turnig off oplev servo.
Do not turn Oplev Servo on when PRM is missaligned !
Set the PRM OL servo gains to zero until someone can take care of this. Turning off the buttons doesn't help anything if people run the alignment scripts.
C1:SUS-PRM_OLPIT_GAIN 1.0 -> 0
C1:SUS-PRM_OLYAW_GAIN -0.7 -> 0
* Still need to finish calculating what could be causing our big arm power fluctuations (Test mass angular motion? PRM angular motion? ALS noise?) (Calculation)
I think that our problem of seeing significant arm power fluctuations while we bring the arms into resonance during PRMI+arms tests is coming from PRM motion. I've done 3 calculations, so I will describe below why I think the first two are not the culprit, and then why I think the PRM motion is our dominant problem.
ALS length fluctuations
Arm length fluctuations seem not to be a huge problem for us right now, in terms of what is causing our arm power fluctuations.
What I have done is to calculate the derivative of the power in the arm cavity, using the power buildup that optickle gives me. The interferometer configuration I'm using is PRFPMI, and I'm doing a CARM sweep. Then, I look at the power in one arm cavity. The derivative gives me Watts buildup per meter CARM motion, at various CARM offsets. Then, I multiply the derivative by 60 nm, which is my memory of the latest good rms motion of the ALS system here at the 40m. I finally divide by the carrier buildup in the arm at each offset, to give me an approximation of the RIN at any CARM offset.
I don't know exactly what the calibration is for our ALS offset counts, but since we are not seeing maximum arm cavity buildup yet, we aren't very close to zero CARM offset.
From this plot, I conclude that we have to be quite close to zero offset for arm length fluctuations to explain the large arm power fluctuations we have been seeing.
AS port contrast defect from ETM motion
For this calculation, I considered how much AS port contrast defect we might expect to see given some ETM motion. From that, I considered what the effect would be on the power recycling buildup.
Rather than doing the integrals out, I ended up doing a numerical analysis. I created 2 Gaussian beams, subtracted the fields, then calculated the total power left. I did this for several separations of the beams to get a plot of contrast defect vs. separation. My simulated Gaussian beams have a FWHM of 1 unit, so the x-axis of the plot below is in units of spot motion normalized by spot size.
Unfortunately, my normalization isn't perfect, so 2 perfectly constructively interfering beams have a total power of 0.3, so my y-axis should all be divided by 0.3.
The actual beam separation that we might expect at the AS port from some ETM motion (of order 1e-6 radians) causing some beam axis shift is of the order 1e-5 meters, while the beam spot size is of the order 1e-3 meters. So, in normalized units, that's about 1e-2. I probably should change the x-axis to log as well, but you can see that the contrast defect for that size beam separation is very small. To make a significant difference in the power recycling cavity gain, the contrast defect, which is the Michelson transmission, should be close to the transmission of the PRM. Since that's not true, I conclude that ETM angular motion leading to PRC losses is not an issue.
I still haven't calculated the effect of ITM motion, nor have I calculated either test mass' angular effect directly on arm cavity power loss, so those are yet to be done, although I suspect that they aren't our problem either.
I think that the PRM moving around, thus causing a loss in recycling gain, is our major problem.
First, how do I conclude that, then some thoughts on why the PRM is moving at all.
theta = 12e-6 radians (ref: oplev plot from elog 9338 last week)
L = 6.781 meters
g = 0.94
a = theta * L /(1-g) = 0.0014 meters axis displacement
w0 = 3e-3 meters = spot size at ITM
a^2/w0^2 = 0.204 ==>> 20% power loss into higher order modes due to PRM motion.
That means 20% less power circulating, hitting the ITMs, so less power going into the arm cavities, so less power buildup. This isn't 50%, but it is fairly substantial, using angular fluctuation numbers that we saw during our PRMI+arms test last week. If you look at the oplev plot from that test, you will notice that when the arm power is high (as is POP), the PRM moves significantly more than when the carrier buildup in the cavities was low. The rms motion is not 12 urad, but the peak-to-peak motion can occasionally be that large.
So, why is that? Rana and I had a look, and it is clear that there is a difference in PRM motion when the IFO is aligned and flashing, versus aligned, but PSL shutter is closed. Written the cavities flash, the PRM gets a kick. Our current theory is that some scattered light in the PRC or the BS chamber is getting into the PRM's OSEMs, causing a spike in their error signal, and this causes the damping loops to push on the optic.
We should think a little more on why the PRM is moving so much more that any other optic while the power is building up, and if there is anything we can do about the situation without venting. If we have to, we should consider putting aluminum foil beam blocks to protect the PRM's OSEMs.
Interesting results. When you compute the effect of ETM motion, you maybe should also consider that moving around the arm cavity axis changes the matching of the input beam with the cavity, and thus the coupling between PRC and arms. But I believe this effect is of the same order of the one you computed, so maybe there is only one or two factors of two to add. This do not change significantly the conclusion.
Instead, the numbers you're giving for PRM motion are interesting. Since I almost never believe computations before I see that an experiment agrees with them, I suggest that you try to prove experimentally your statement. The simplest way is to use a scatter plot as I suggested the past week: you plot the carrier arm power vs PRM optical lever signals in a scatter plot. If there is no correlation between the two motions, you should see a round fuzzy ball in the plot. Otherwise, you will se some non trivial shape. Here is an example: https://tds.ego-gw.it/itf/osl_virgo/index.php?callRep=18918
Nic and Evan put the ISS together (elog 9376), and we used an injection into the error point (?) to modulate the laser power before the PMC (The AOM had a bias offset, but there is no loop). This gives us some RIN, that we can try to correlate with the PRM OSEM sensors.
We injected several lines, around 100, 200, 500 and 800 Hz. For 100, 200 and 800 Hz lines, we see a ratio between POPDC and the OSEM sensors of 1e-4, but at 500 Hz, the ratio was more like 1e-3. We're not sure why this ratio difference exists, but it does. These ratios were true for the 4 face OSEMs. The side OSEM saw a slightly smaller signal.
For these measurements, the PRMI was sideband locked, and we were driving the AOM with an amplitude of 10,000 counts (I don't know what the calibration is between counts and actual drive, which is why we're looking at the POPDC to sensor *ratio*).
To get a more precise number, we may want to consider locking the PRMI on carrier, so we have more power in the cavity, and so more signal in the OSEMs.
These ratios look, by eye, similar to the ratios we see from the time back on 30 Oct when we were doing the PRMI+2arms test, and the arms were resonating about 50 units. So, that is nice to see some consistency.
This time series is from 1067163395 + 27 seconds, from 30 Oct 2013 when we did the PRMI+2arms.
Ideas to go forward:
We should think about chopping the OSEM LEDs, and demodulating the PD sensors.
We should also take a look in the chamber with a camera from the viewport on the north side of the BS chamber, to see if we see any flashes in the chamber that could be going into the OSEMs, to see where we should maybe put aluminum foil shields.
Some more words about the ISS -> OSEM measurement:
The calibration of the OSEMs have been done so that these channels are each in units of microns. The SIDE channel has the lower noise floor because Valera increased the analog gain by 5x some time ago and compensated with lower digital gain.
The peak heights in the plot are:
So that tells us that the coupling is not uniform, but mostly coming in from the left side (which side is the the SIDE OSEM on?).
Jenne and I discussed what to do to mitigate this in the loops. Before we vent to fix the scattering (by putting some covers around the OSEMs perhaps), we want to try to tailor the OSEM damping loops to reduce their strength and increase the strength of the OL loops at the frequencies where we saw the bulk of the instability last time.
Jenne is optimizing OL loops now, and I'm working on OSEM tweaking. My aim is to lower the overall loop gains by ~3-5x and compensate that by putting in some low Q, resonant gain at the pendulum modes as we did for eLIGO. We did it here at the 40m several years ago, but had some troubles due to some resulting instability in the MC WFS loops.
In parallel, Steve is brainstorming some OSEM shields and I am asking around LIGO for some AC OSEM Satellite modules.
The returning spot diameter on the qpd ~10 mm. In order to reduce the spot size I moved the f 1145 mm lens toward the PRM ~ 25 cm. The spot size was reduced to ~8 mm, 3200 counts.
I'll try to find an other lens tomorrow.
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.
PRM oplev beam was not hitting on the QPD since Jun 1, so I centered it. I reverted the oplev servo gains and now oplev servo looks fine.
C1:SUS-PRM_OLPIT_GAIN = 1.0
C1:SUS-PRM_OLYAW_GAIN = -0.7
There's SIDE to UL/UR/LL/LR coil element in PRM TO_COIL matrix. They were 0 until Mar 31, 2012, but someone changed them to -0.160. I couldn't find elog about it.
Same thing happened to BS on Mar 13, 2012 (see elog #6409), so I think somebody did the same thing to PRM.
After last week's work on the BS/PRM oplev table, I think the PRM oplev got centered while the PRM was misaligned. With the PRM aligned, the oplev spot was not on the QPD. It has been centered.