We leveled the optical path from the laser to the first MCL PZT mirror, but things didn't improve much.
The first Faraday transmission is fine (first picture, EOM and the second Faraday removed from the path, picture taken in front of the second lens).
EOM transmission is ugly when the beam passes through the middle of the input and output aperture (second picture).
After fiddling around with the EOM alignment using 4 DOF stage, we always ended up with the beam very high on the input side. (no picture).
After the EOM, when the second Faraday was inserted, it makes many ghost beams /halo in PIT (third picture). This vertical pattern doesn't change much with alignment.
Using an iris, we can get rid of most of the ghost beams (last picture). The central part of the beam is not totally round, this comes from the EOM. This looks somewhat better than OAT days (sadly).
Anyway, since it is convenient to open up the iris to see the retro reflected beam from ETMY, we left all irises wide open.
The Faraday makes many ghost beams for the refl beam too, but all of these seem to fall on the PD.
We measured the power level right at the laser, downstream of the first Faraday, downstream of the EOM and downstream of the second Faraday. Jax will post the numbers.
We have removed some unused optics from ALS table.
One 50/50 green splitter (labeled as such on the mount) and one green high reflector (ditto) were put in the ISC cabinet in the squeezer bay together with things labeled "ALS WFS stuff".
One green high reflector didn't have any label, but it was easy to see that it was a high reflector. To avoid future confusion, I removed the optic and put it back in the original mirror box from Precision Photonics.
It seems like there are other unlabeled optics in "ALS WFS stuff" bunch, and maybe on our tables, but we should do better. PP optics are not labeled anywhere, the only visual clue for the reflectivity is the color of the coating, and some people might have a difficulty identifying which is which.
Make labels and put them on mirror holders or posts.
Power measurements as promised:
From laser: 42.5 mW
After first Faraday isolator: 35.5 mW
After EOM: 31 mW
After 2nd Faraday isolator: 28 mW
After 2nd PZT mirror: 26.3 mW - after inserting another iris this measured 27 mW, likely within the bounds of measurement error.
Note that there is a 10% pick-off for Hartman sensor path between the 2nd PZT mirror and the periscope.
All in all, the efficiency from the laser to the chamber is something like 0.9*27mW/42.5mW = 57%, which is consistent with June 2012 alog (61%) as well as July 2012 alog (0.9*20mW/30mW=60%, note that the measurement was done upstream of 10% pick off in July 2012).