- Jason measured the beam after the 70W amplifier, for mode matching
- He and I measured power before and after the AOM, and he has the details, I recall there's about a 5W drop in power
- From after the AOM, almost no power drop to the PMC, and Jason has power measurements from after the PMC
- I took a measurement just before the bottom periscope mirror
- A request of 2W gave 2.4W on the power meter
- A request of 10W = 11.4W on the power meter
- A request of 20W = 23.1W on the power meter
- A request of 30W = 35.0W on the power meter
- A request of 38.5W = 45.5W on the power meter, this is the rotation stage max power, at 20.02deg
- real max power was found at the angle 20.5deg, at 45.9W
- All measurements taken with the ISS off
- All measurements take with the water cooled power meter
At 19:10TUC, I'd restored the ISS and FSS to locking. At 19:22UTC, unlocked, Mark and Keita are out making measurements.
On 9/3/18, P. King tweaked the mode matching into the 70W amplifier. As Cheryl says, yesterday I took a beam propagation measurement for mode matching into the PMC. To give an idea what the beam now looks like, I've attached a picture of the beam profile taken ~695mm from the 70W amplifier.
As there is a power drop somewhere between the 70W amplifier and the PMC, we did a quick a power budget using the water-cooled power meter; all measurements were done with the ISS OFF:
The largest power loss is at the ISS AOM, where we lose 3.4W. We had suspected clipping at this AOM, and it looks like that is the case. We will have to re-think our PMC mode matching scheme to get the beam smaller at the ISS AOM.
With the 70W beam looking better, I wanted to get an idea of where we are now in regards to PMC mode matching. Without changing the mode matching scheme for the PMC, I took a quick measurement of the PMC visibility using the locked and unlocked voltage from the PMC locking PD. This was also done with the ISS OFF:
Simply by cleaning up the 70W beam (via Peter's 70W amp mode matching tweak), we are at >80% visibility. This is, however, somewhat disconcerting. Looking at the above power budget, we are only transmitting ~73% of the power incident on the PMC, so something isn't quite adding up here. Something to think about before next Tuesday.