Stefan, Sheila, Alexa, Kiwamu

We locked the IMC on a 00-mode this evening. The next step is to wait for the pump-down to finish and  perform a ring-down measurement to check if the absorption is not too high.

Preparation:

After talking to Mike and John, we agreed that we can do an IMC-related interferometry with a low power laser even though we are not yet on the turbo pump.The pressure at that time was below 10 torr according to John. The PSL power was decreased to 56 mW by using the rotational stage because we needed to be lower than 100 mW which is the limit for the in-air IMC locking. We then locked the rotational stage such that we won't accidentally exceed the limit. Also I had a chance to talk to Dennis about this laser power issue and he agreed that we can do some interferometry with a low power laser. Thank you for the discussion, Mike, John and Dennis !

Initial Alignment:

To recover a good alignment, we started from the PZT input pointing. We checked the spot position of the scattered beam from the HAM1 viewport, projected on the wall of the PSL enclosure. The beam was lower than the previous marking, by 5 mm or so. We then touched up the input PZT to bring the beam back to the previous making position. The PZT count in PIT had been 679.6 and after this alignment it became 683.6 counts. The we checked the alignment on the table, but surprisingly, we did not have to touch any optics at this point. This means that Bubba and company placed the IOT2L table very precisely, maybe with a precision of a few mm. Thank you, Bubba !

We then placed an analog camera in the transmission path because the GigE was not functioning for some reason. At the beginning the alignment seemed off largely in pitch. So we started tweaking the things. Starting with the PZT again, we could not get a decent 00-mode. We decided to touch the MC mirrors. We touched MC2 in pitch and was able to see a decent 00-mode flash. Good.

Locking and further tweak:

As soon as we turned on the IMC board with a high gain, it grabed a 00-mode. We then did a futher alignment  on MC2 to coarsely maximize the power-buildup. The visibility was 75 %. In lock, the reflection was about 40 and unlocking We then re-centered the WFSs beam by hand on the table and tried the ASC servo. But, after an hour of struggling, we realized that the MC2 TRANS QPD did not have a good enough signal-to-noise ratio. So we need to crank up the laser power once the pumping is over. This is now preventing us from engaging the ASC loops.

An enigma:

Signals from the IMC_REFL_DC signal occasionally behaved quite funny -- the REFL_DC signals went up by a facto of 5 or so, while the WFS DC signals remained the same. At this point, we have no idea what was going on. We will investigate a bit more tomorrow.