Ushiba, Akutsu
We installed an optical lever (oplev) for the marionette stage of the cryopayload in the EYC chamber at the Y end. There are several issues still remaining, but we can say finished the installation.
Issues
- The island on which those oplev setup is set is relatively easy to bend, as the island is supported by the one side like a cantilever. It seems sufficiently stiff for support stuffs on it, while the effect of the bending can become obvious when the light beam going from the transmitter comes reflected back from the reflector on the marionette stage; well, that is the oplev, sensitive to such tilting effect.
- About the height of the transmitter (and the receiver, of course). During the installation work, we found the height of the oplev beam from the top of the island must be about 1-inch more than my design so that the reflected beam can be the same height of that of the input beam.... otherwise the reflected beam was screened by the apeture! Today I just added 1-inch pedestals to the legs of the transmitter and the receiver, but both I and Ushiba-kun had no idea why this happened.
- Beam height on the reflector. The marionette reflector will come to the center of the ICF152 viewport window after the payload will be totally cooled down, while the payload (and the marionette) is located 9-10 mm below the position in the room temperature. To cope with this situation, the design was done so that the marionette oplev's beam should be pointing 5-mm below of the center of the ICF152 viewport; the height of the center of the ICF152 viewport from the island is 150mm, so this means the height of the beam should be 150-5=145mm.
- No good space to locate the light source unit. So far I just put on the box bottom, and breifly fixed with a tape. The optical fiber should be fixed in more sophisticated way (see the attached photos!).
- Probably need to replace the legs; with 25 mm diameter pedestals, it is too tall to support very stable someting in about 150mm (or plus 1inch) height. I prepared some resolutions today but I missed some small parts so I cannot complete to try the resolution.
Anyway, now the reflected beam from the marionette reflector is hitting the QPD!
Discussion
We firstly suspected the height inc was due to the unexpective bowing (pitching) of the marionette reflector, but we are not sure. It is difficult to see the reflector with illuminating the reflector by the oplev beam due to the cryostat structure; probably using a dental mirror would be one of the solution, but today we did not have it. One good thing is that the reflector on the marionette can be seen from the viewport window somehow; note that the actual clear aperture for the oplev beams are very limitted due to the complicated structure of the cryostat and the shields in it. Anyway, need to keep the investigation. And note that the cryopayload is still not well re-aligned so that it reflects the interferometer's beam back to the BS. After the re-alignment, the marionette oplev should be reset again!!
