J. Oberling, C. Vorvick, C. Grey
Today we did a power budget of the main beam on the PSL table, from the lower periscope mirror all the way back to the output of the 35W Front End laser, using the water-cooled 300W power meter; all measurements were done with the ISS OFF. I've attached the results as a .pdf file.
It should be noted that we had to hold the power meter by hand for several (roughly half) of the measurements due to space constraints (there was not enough room to hard-mount the power meter to the table). I've noted these measurements as such in the spreadsheet. Because of this, these measurements are not as accurate as they would be if we could have hard-mounted the power meter (slight movement of the meter, location of beam on the meter, and angle of incidence all effect the measurement). In a few instances this caused the measured power to not make much sense compared to other measurements; red entry text denotes these instances (they are included for completeness).
Where appropriate we also measured the power in certain pickoff paths; these measurements are noted using a green text for the entry.
Despite some oddities with some of the measurements, by and large things make sense and we don't seem to be losing large amounts of power anywhere in the main beam path (the loss between the ISS AOM and the PMC is explained by the ISS AOM diffracted beam; this beam is separated out and dumped shortly after the ISS AOM).
Note: The PMC transmitted power was low because the enclosure environmental controls were ON (since we were in the enclosure); air currents from the fans and cold air from the AC slightly change the mode matching to the PMC. After we left and things settled down, with the ISS ON (2nd loop OFF) the PMC was outputting 53.8W. An alignment tweak could possibly increase the transmitted power; the reflected power is now at 11.3W, and we've had it as low as 10.0W in the recent past (at the end of the vent). I'll plan on tweaking the beam alignment into the PMC during the next maintenance window.
