Ryan called and walked me through unsticking the green QPD loops at the Y end, which had become railed.

We're leaving the rest of the work for the morning.

I and Alexa looked at the video image of ETMY and ITMY.

We confirmed that the green and the IR are on top of each other on ITMY when the alignment was good-ish for green and IR. There's no particularly bright spot.

We couldn't tell if the green and the IR are on top of each other on ETMY. But there are two bright spots on the ETMY camera that only appear when the arm is locked. See attached images (green was misaligned for these images so you only see IR).

The ETMY camera is looking at the ETMY from HR side. These spots could be something on the HR coating itself, or could be an image of something else (e.g. some scattering and ACB or some unknown ghost beam hitting near by structure?) reflected by the HR coating. This cannot be behind the HR coating, but it's still not impossible that these are some ghost beams from TMS structure taking strange path and coming into the camera at a large angle.

While Dave was walking the beam in PIT, the high spot became brighter or weaker but the lower spot didn't change much (the first three images).

When the beam was moved in YAW the lower spots got brighter (the 4th image).

Update:

This morning I locked green to Y arm without IR, and I can see bright spots on the same position (5th picture), so now it seems more likely that they are on the HR of the mirror.

The sixth picture is taken with green and IR both locked.

If these are on the mirror, the low spot is somewhat low and somewhat to the right  left  to the center of the HR.

Update 2: Is the loss by shmutz big?

To see if the loss caused by the shmutz is significant, Alexa and I moved the beam about +-3cm in YAW on the ETMY without moving ITMY position: (ITMY, ETMY)= (-7.5, +5.88) urad in YAW moves the beam on ETMX to the right, flip the sign to move to the left.

We saw an improvement in both of the cases but it was better when we moved to the left. This is probably because the shmutz is to the right to the center of the mirror.

Alexa will post the StripTools plot, Dave is working on the loss number.

In the attached picure, the first one is when the beam was moved to the right, the next one is when it was moved to the left. Ignore the bright thing at the center of the shmutz as that's just green, look at the halo, and you can see that the IR is indeed dimmer than the last picture from my previous entry.

Keita and I had intentionally misaligned the green PZTs to examine the ETMY and ITMY camera with only the IR beam, and we never realigned it. This is why Evan found the EY green QPDs railed.

Also I found that one of the two IR input pointing WFS had not been cleared, which also explains why the IR beam was not flashing in the cavity.

The above tables lists the positions and the counts on ASAIR. When the IR is not resonanting in the arm, ASAIR reads about 1360 cnts.

In the StripTool I have shown ASAIR_LF_OUTPUT which we are using to measure the power loss, and LSC-Y_TR_A_LF_OUT which measures the IR transmitted power.

At -75 min the IR is flashing in the arm cavity, and ASAIR is about 1360 cnts. Shortly after the IR locks, and then the input pointing WFS engage, as seen by the power build up in IR.

At -70 min we have full IR buildup (TR is about 11 counts), meanwhile ASAIR has dropped to about 1068 cnts. 

At -45 min I begin to move the beam to the right; this is completed at about -40 min. At this point the transmitted power has remained the same and ASAIR is now up to around 1117 cnts

Shortly after we lose lock, and I recover the lock.

At -30 min I begin to move to the left; this is completed at about -20min. Again the tranmistted power has stayed the same, and now ASAIR is at 1129 cnts. Eventually we lose lock again.

Mirror cage outline and guesstimated mirror center line.

Note that we are looking the mirror from the left at a big-ish angle.

Blue lines are inner edges of the cage.

Rick sent us this picture of Pcal camera. We can clearly see bright spots, which I assume is caused by the IR.

Note that pcal camera is looking at the optic from the right.

I managed to find the missing data frames on the Caltech cluster.  The results for a lock on 3 Oct 2014 at around 23:18 UTC (1096413500) are very much the same:

H1:LSC-ASAIR_A_LF_OUT_DQ
locked = 1057.0
unlocked = 1226.4
ratio = 0.86

H1:LSC-ASAIR_B_LF_OUT_DQ
locked = 303.2
unlocked = 357.5
ratio = 0.85
 

A plot of the channels is attached (the x-axis is seconds).  So, it seems the y-arm losses have not significantly changed in the past two months.

Can you please post PDFs of the plots as well?

If beam mis-centering on the TMs is the cause of all the extra loss, it will have to be quite a big mis-centering. I did a quick calculation, and to get 750ppm loss at the ETM, the beam has to be offset from the center by about 6cm (roughly one beam size). The attached plots show the intensity spill over for a 62mm radius beam on a 163mm radius coating, with no offset and with a 6cm offset. The proportions of beam power outside the coating, with no offset and 6cm offset, are 0.991ppm and 762ppm respectively.

Just in case someone wants a plot ...

Dave has a calculation which makes some assumptions about mode-mismatch and sideband power for the X arm.

Suppose the power in the sidebands is 6% of the incident beam, and 15% of the incident carrier doesn't enter the cavity because of mode matching issues; i.e., about 20% of the light is nonresonant. Then the equivalent power reflection is (1155 - 236) / (1180 - 236) = 0.974. This gives a loss of 108 ppm in the X arm.