Nobody can understand this alog unless he/she is familiar with https://dcc.ligo.org/LIGO-T1100603-v1 , but the basic message is that we're OK, some problem was identified in the mechanical/optical design of the installation tooling but a new procedure was developed to work around it.

At first things weren't good.

• We had the new F1 steering mirror from Newport, which was orders of magnitude better than anything from the past.
• Telescope path was aligned using two auto collimators, AC1 looking from the primary (i.e. the arm) side and AC2 from the secondary (i.e. the ISC table) side. Note that AC2 is installed on the telescope plate using a specially machined class-B sleeve that ensures that the  auto collimator barrel contacts with the inside surface of the sleeve by two lines.
• For laser injection, two irises were installed, one inside the telescope path and the other on the injection table ("pedestal" in the case of Hanford).
  • The first iris was centered using AC2.
  • The second one was set up after flipping the direction of AC2 inside the sleeve mentioned before.
  • Then the injected beam was centered on the irises using video cameras.
• An 8-inch flat mirror was placed downstream of the primary mirror and the angle was set up using AC1.
• We injected the laser beam and started analyzing the return beam.
• We saw a huge astigmatism/ellipticity in the return beam.
  • All flat mirrors (FM1, FM2 and 8" retro mirror) were rotated and exonerated.

After putting a clean wipe on the primary and taking a picture of the IR beam position, it turned out that the beam had a huge offset like an inch or more. This shouldn't have been the case since the procedure is designed specifically to prevent such a thing from happening. Anyway, we should use IR-sensitive DSLR camera  to determine the beam position on the primary.

On further investigation it turned out that flipping AC2 in the sleeve was not a good idea. When we removed the 8" reflector in front of AC1, in the view of AC1 the iris on the injection table was totally off centered by half inch or so, though it was quite well centered in the view of the flipped AC2.

Apparently AC2's optical axis depends on the direction the AC is inserted into the sleeve. The angle repeatability of this sleeve was not that good to start with in the past, maybe that alone explains this, or maybe the AC2's optical axis is not quite colinear with the barrel. Regardless of the real cause, we changed the procedure such that the iris on the injeciton table is set up by AC1.

After this change, the beam shape started to look reasonable. We were able to tune the telescope in such a way that the errors are spread in two directions, and we're already good (see attached).

However, after the tuning is done, the beam is still off-centered on the primary by half inch or so. After Cheryl took the picture of the beam position on the iris in the telescope path, it seems that it is off-centered by maybe 0.5mm or so even though it looked perfectly centered using video cameras. Since the magnification of the telescope is 20, this agrees with the beam position on the primary (half inch = 12.7mm).

We will center the injected beam on two irises using IR camera, tighten all of the actuator tensioning screws for the mirror holders (which, sadly, will change the alignment), make an adjustment if necessary, take the last scan and we'll move to the mating of the telescope and the ISC table.