KAGRA MIR (Absorption)
ManuelMarchio - 19:52, Thursday 30 November 2017 (606)
Pump laser alignment

after moving alle the optics of the IPC I had to realign the pump laser beam on the pinhole (at the reference position of the cross point).

First I adjusted the height of the beam on the optical table from the IPC to the periscope (128mm)
Then I removed the last focusing lens on the optical breadboard (after the periscope).
I used two positions of the pinhole along z (max and min position limits), and maximized the power transmitted by the pinhole. I moved back and forth the translation stage on those positions. On the closest position I adjusted the second stearing mirror, on the further position I adjusted the periscope mirror. For the first rough alignment I also used an optical cross.
Now the beam is parallel to the z axis of the translation stage. Then i put the last focusing lens back on its mount and I adjusted the lens position to have the maximum power transmitted by the pinhole.

Since I had optimized the IPC, now, in order to have 30mW on the imaging unit table with 0.8A of laser current, the half wave plate have to have an angle of about 22deg (before optimization it was 0deg)

Then I made a scan of the reference sample with the HeNe Imaging unit, and when I went to optimize the maximum of the AC scan (adjusting the pump focusing lens position) I found that it was already at the maximum.

Images attached to this report
606_20171130115130_20171130scanrefsurf.png