Yokogawa, Sugimoto, Akutsu; see here as well.
After pico-ing the steering mirros around PR2, the green beam reached the Yend (EYT) very well. Actually due to sudden berserk BS, the green beam is not so stable, but somehow could be used for a reference.
- As wirtten in the above link, we found the beam after the 2nd BRT lens seems shifted to -X in 10mm (Fig. 5 and 6) and tilted in pitch by -0.03 rad (Fig 3 and 4); using a lase level.
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Apart from the shift, the tilt could be due to originally -1/300 tilt of the input beam (see the above link or note *1 below), assuming the BRT was sitting horizontally sufficiently
. - We hooked up the BRT slightly after slightly loosening the screws that fix the foots of the BRT to the fixed stage, and changed the lengths of the three legs so that BRT got tilted in -1/300 pitch (-Y get lower).
With those, what we found today are:
- The BRT can actually be aligned with the above method. This was the first time to do tilt-and-fix work (in short, alignment) of an BRT! I was relieved.
- The pitch tilt of the beam seemed successfully canceled by the tilt alignment of the BRT; needs more detailed check.
For the detailed check, we must have a stable BS so that the beam becomes stable...
(*1) To put it breifly, the beam reducing telescope (BRT) has a 10-times magnification (a definition of a word is difficult... it is 10 times reduction of a beam's diameter). Assume a ray is entering into such an optic with a small but non-zero angle, then the angle of the emitting gets 10 times leverage (oh, another oplev!), so a 1/300-rad will increase to 1/30-rad.
...By the way, you know, the fact that the beam can pass through even the 2nd BRT lens is kind of surprising to me, considering the tough works of the alignement in Mitaka.
... and you can find a ghost beam of green in Fig 5 and 6. Ok, it's green, but I now need to consider the IR case... Anyway, from where the ghost came? From the wedge of the ETMY?? As it is also focused, this story would have high possibility. Probably we can esitimate with measuring the distance from the main beam.
