Keita, Ryan, Georgia, Craig

This afternoon we worked on the POP path, for HAM1 layout refer to page 4 here. Keita used a laser pointer to verify that the wedge on the existing mirror was oriented correctly (the transmitted ghost beam was diverging from the main beam, did not cross the main beam, and was parallel to the table). To get a reference measure of the transmissivity of M12 we installed a temporary steering mirror on the REFLAIR path, after M7 and steered the REFLAIR beam onto the POP_A diode, the power and dark offset on POP_A with the current M12. The temporary steering mirror didn't seem to be highly reflective at 1064nm but it was good enough for this relative measurement.

The old M12 (90/10 splitter) was engraved with a reference number: IO820-09. The new M12 (95/5 splitter) is E1000671-v1-02. Unfortunately the old mirror was 1/2" thick while the new mirror is 0.375" thick, this resulted in a translating of the beam on the POP diode and a shift of the beam onto the POPAIR path. We steered the beam onto the POP_A diode using the pico-mirror directly before it (M15), it was a bit off-center in pitch after the swap, indicating that the beam is not level on the M10-M15 path.

The powers before and after the swap are in the table below. The dark noise increasing between measurements it strange, since we turned off the room light for the second measurement we expected it to go down (or not change). Fromm this measurement the power on POP_A is now 54% what it was before.

The thickness difference of M12 will translate the POPAIR path, but we didn't touch it, we think we'll be able to compensate for the alignment shift using the top periscope mirror on ISCT1. The POPAIR path comes out about 6cm to the -X of the REFLAIR beam, it seems like it will clear the viewport.

We removed the temporary steering mirror (but left dog clamps marking its location incase we want to put REFL on POP again), and did the final alignment of M15 using PRMI flashes. The peak PRMI flashes after the swap (~1338844651) are ~ 50% of the flashes we were seeing this morning (~1338853945), though this is really hard to eyeball since the brightest flashes are few and far between.

Keita noted that the beam is about 1/2" off-center on the lens before POP_A (L2) in the -Y direction. That's not too close to clipping, since it is a 2" lens, but it is bad and something we are considering fixing. It's fairly well-centered on M15, and a bit offset on M12. He also noted the pitch picometer on M15 was getting close to the edge of its range.

Tomorrow we plan to swap M2 on the REFL path and swap the REFL_A WFS.