J. Oberling, P. King, J. Bartlett

This morning we transitioned the PSL to 35W Front End (FE) operation only, per LHO WP 7329: 

• A HR mirror was installed in front of the HPO ouput coupler.
• Mode matching lenses L02 and L03 were moved back to their 35W FE positions.
• Mirror HPO_M5 was adjusted to recapture the alignment out of the HPO enclosure.
• Mirrors M06 and M07 were adjusted to re-align the beam to the PMC.
• Various half-wave plates in the FSS path were adjusted to maximize the transmitted power of the FSS Reference Cavity.
• Tweak beam alignment into the FSS RefCav.

It should be noted that we did not remove the HPO from the cooling loops, therefore water is still flowing through the HPO.  This will be done prior to the start of the 70W amplifier installation.

The beam alignment to the PMC was tweaked to maximize the transmitted power; with the ISS ON, the PMC is transmitting 22.3 W and reflecting 3.0 W.  I took a quick visibility measurement:

• PMC unlocked: -0.505 V
• PMC locked: -0.040 V
• Visibility: 92.1%

With the visibility >90%, no further mode matching work was done at this time.  To get the ISS stable, the reference voltage had to be raised to -0.40 V.  In addition, the FSS Reference Cavity TPD is reading 1.34 V, and we measured ~10 mW in the ALS path being fed into the ALS fiber.

There are a couple more things that need to be done prior to the start of the 70W amplifier installation:

• Undo ISS changes made for the HPO
  • Put ISS PDA back in the ISS box.
  • Remove the beam splitter installed in place of the final ISS steering mirror and re-install the original mirror.
• Remove the extra high power attenuation stage installed before the PMC.
• Fine tune PMC mode matching if necessary.
• Remove the HPO crystal and laser head water circuits from the PSL cooling loops.

The PSL is now good to go for tomorrow's X-arm peek and any further commissioning required for this week; 70W amplifier prep work begins in earnest next week.  This closes LHO WP 7329.