J. Oberling, E. Merilh, P. King

Today we installed the new 35W Front End power monitor pick-off.  We removed the unused AOM port from the back wall of the FE (1st attachment), wired the pick-off, and installed it in front of the output of the MOPA (2nd attachment).  The half-wave plate in front of the FE FI was adjusted to minimize the NPRO power delived to the MOPA and the NPRO current was decreased from 2.222A to 1.0A.  This was to minimize the output of the FE while adjusting and aligning the new pick-off.  Using a WinCAM, we positioned the pick-off such that it was not clipping the beam, and aligned it using the 3 set screws (can be seen on the 2nd attachment) to maximize the signal seen by Beckhoff; this was a very tedious and time-consuming process.  Once the PD output was aligned we slowly increased the NPRO current back to its nominal operating value of 2.222A.  All being good, we then adjusted the half-wave plate to deliver the maximum NPRO power to the MOPA.  Once again, there were no issues with the beam profile and the output power of the MOPA read 36.2 W.  We calibrated the new pick-off to this value.

On Monday, we will recover the alignment to the PMC if necessary (the new pick-off could potentially change this alignment), then proceed with installation of the new PBSC and half-wave plate.  These 2 components replace the mirror that is currently being used to direct the beam into the HPO, and allow us to change the beam path either toward the 70W amplifier or toward the HPO; the latter will allow operation of the just the 35W FE laser, if necessary.