Matteo, Simon
In order to measure absorption maps of the Sappire substrate from the "GT" company, we started to take the ETMY substrate. For this purpose, we carefully opened the container of the mirror and took-out the sample This was actually a tricky part as the sample is quite heavy and not only there were some placeholder-columns in the container which we could not remove and made it difficult to pick-up the sample, but also we realized that the sample already has the "ears" attached.
Somehow we succeeded to put the sample inside the mirror-holder and confirmed that it has a reproducable position in it by using a horizontal alignment of the ears. We can furthermore report that close to the edge, we recognized several defects which we, however, do not consider as being a problem.
Also, due to a repolishing measure which has been done after bKAGRA-phase1 (the substrates were already been used as KAGRA mirrors before), the thickness is reduced compared to the Shinkosha#7 sample (150 mm → 143 mm)
Once we set the substrate together with its holder inside the transition stage, we adjusted a little bit the position of the imaging-unit (6.7 mm → 9.7 mm) due to the reduced thickness. After that, the DC-signal was adjusted and the pump-laser power maximized.
Main Issue:
At that point we could start setting the basic limits for the transition stage with the respective LabView program.
However, the initial (default) values for the stage-position put the holder into the beam-path of the pump-laser while at maximum power!!!
→ That burnt a hole into the mirror-holder
→ Parts of the burnt hard-plastic could be found also on the sample surface
Of course, we immediately blocked the laser-power and removed the sample and its holder for inspection:
- It seems that the sample itsel is not damaged but dirty on one surface now
- With an air-blower, we removed the largest parts of the dirt), while the sample-holder has a hole on the outer side. No further damage could be reported (the sample holder is still usable).
- We put the sample back into the container-frame and put first-contact on it
Let's hope this will clean the surface enough for continuing the measurements (we will see next week...).
