J. Oberling, P. King, E. Merilh

Summary

Today we went into the PSL enclosure to increase the front end (FE) diode currents and tweak the PMC and FSS alignment.  We:

• Added ~2A of current to the 4 FE diodes and tweaked their operating temperature.  We now have 33.1 W out of the FE.
• Tweaked the PMC alignment and now have a transmitted power of 22.9 W, a reflected power of 2.4 W, and a visibility of 89.9%.
  • We will have to go back in at a later date and adjust the PMC mode matching lenses, L02 and L03, to improve the PMC transmitted power; we ran out of time today.
• Tweaked the FSS alignment to increase the RefCav transmission and now have a RefCav TPD reading of 1.47 V and a visibility of 72.3%.
• Checked the DBB RPD voltage to make sure it was above 9 V so we could continue to make measurements with the DBB.  It is at 9.53 V.  We also measured the power into the DBB along the 35 W laser path as 150 mW; this is >135 mW, so all is good.

Details

FE Diodes:

We added ~2A to the 4 FE diodes to increase the FE power, which had been slowly drifting down over the last several months (threshold for diode current adjustment is 5% drop, we were at ~7%).  Both power supplies are now feeding ~51A to the FE diodes.  We then had to optimize the temperature of the diodes to maximize the FE power.  Peter took before/after screenshots of the FE diode settings and will post them as a comment to this log.  We are now reading 33.1 W out of the PSL FE.

PMC:

We then proceeded to tweak the PMC alignment.  We adjusted both pitch and yaw on mirrors M06 and M07 and were able to get 22.9 W of transmitted power, with 2.4 W of reflected power.  This is obviously not ideal (we want reflected power to be <10% of transmitted power), but all we could do within the alotted maintenance window.  We will have to go back in at a later date and adjust the 2 mode matching lenses, L02 and L03.

Looking at the PMC RPD, it has a locked reading of -0.154 V and an unlocked reading of -1.52 V, giving a PMC visibility of 89.9%.

FSS:

We tweaked the alignment of the RefCav input periscope in both pitch and yaw and improved the RefCav transmission (as read from the RefCav TPD) from 0.75 V to 1.4 V.  We then adjusted the AOM in pitch/yaw to see if we could improve the TPD reading further.  We were able to improve the TPD to ~1.47 V.

Looking at the FSS RefCav RPD, it has a locked reading of 0.072 V and an unlocked reading of 0.260 V, giving a RefCav visibility of 72.3%.

DBB:

We opened the DBB shutters along the 35W laser path to measure the voltage on the DBB RPD; this has to be between 9 V and 11 V for proper DBB operation.  We measured it at 9.53 V.  We also measured the power into the DBB along the 35W laser path at 150 mW; this is >135 mW, so all is good here.