Summary:

The beam was likely very close to the right edge of ETMY since Friday, and this was due to the fact that we were only using TMS angle for the input beam pointing. We fixed this problem by using QPD servo and started over from scratch.

Now we're back to the point where we see some interference, and the good news is that the demod signal is much bigger than before (1V pp). Also we're seeing some change in the reflected DC power due to interference, unlike yesterday.

We still seem to be getting ultra higher order modes all over the place, and we don't see anything on the camera, so we need to refine alignment tomorrow.

The ETM and ITM are wobbling too much at about 1Hz, though. Due to this, the reflected beam seems to be clipped by either the Faraday aperture or the PDH diode aperture, and as a result the DC level of the PDH diode is changing by 30 to 50% constantly. This is not an interference effect (it changes even if you misalign ITM).

Also today the CM board A was not working at all. No output, fast and slow, regardless of the Beckhoff setting.

Alignment details:

When we started playing around with the alignment today, the demod output was the biggest when some light blob was hitting the right cage  bar of ETMY.  We tried many things but we always got back to this position. The likely cause of this is the fact that we only used TMS for initial pointing.

Since we initially only used the TMS angle to point the injection to the center of ITMY without using the PZTs on the ALS table, and since we needed to rotate the TMS so much, actually the ALS beam was falling off of one of the green QPDs. This means that there was a very high chance that the beam is not going through the center of the TMS primary.

Elli and I finished the QPD servo (a servo that uses PZT-driven steering mirrors so the beam from the ALS table is centered on two in-vac QPDs on the TMS) quickly so we didn't have to worry about QPDs. See Elli's alog entry.

After this, of course the pointing of TMS changed, so we started over by first aligning the TMS (with QPD servo on) to the center of the ITMY using baffle diodes, then aligning ITMY to the center of the ETMY using cage bars, then aligning ETMY to center the second beam on ITMY using baffle diodes.

Now we're getting much larger demod signal than before, and we can see that something is going on in the DC level (that is different from the clipping). And we don't see any light blob on the cage bars, so we know that the thing is not close to the edge any more. That's as far as we got today.