TJ, Sheila
This morning/afternoon we ( Keita, Jeff K, TJ, me, Lisa, Alvaro and Calum) realized that the riser for ZM2 (the squeezing TT in HAM5) is too tall, since it is set to match the height difference between HAM 5+ HAM6 at L1, which is not the same at H1.
TJ and I went to the chamber to make some sanity checks that the discrepancy is about what we should expect based on drawings. We first set up a laser pointed that was mounted on a small breadboard in the cleanroom by HAM3 in the back of HAM6, pointing towards HAM5. We leveled this by measuing the distance of the beam off the table near the laser pointer and again at the far edge of HAM6, roughly a meter away. With our final tin foil adjustment we got the beam parallel to the table to within a mm over this distance. The laser beam was 99 mm off of the HAM6 table top, and 203 off of the HAM5 table top, so we estimate the difference this way to be 104mm, or 4.1 inches.
We also measured the height of the center of the ZM2 mirror to be 223 mm off of HAM5, or 8.78 inches. That means that the center of ZM2 is 8.78-4.1 = 4.69 inches above the level of HAM6, them beam height in HAM6 is 4 inches. Calum looked at drawings earlier and said that the riser height should be 0.76 inches too tall for H1 if it is based on L1 heights.
We also attempted to measure the height of the center of the output aperture of the OFI off HAM5, which was a little difficult with our too short ruler and an akward angle. We measured 3 times and got 207.5 mm, 205 mm, and 209.5mm. (8.16 inches average, so 0.617 inches below ZM2).
It seems like these measurements are in agreement with what Calum found in the drawings, within the precision of this measurement technique.
Polarization rotation due to geometric effect won't be too bad even if we don't fix the height error.
If we don't correct the wrong height of ZM2, the polarization of the beam coming from VOPO is rotated when it goes into OFI. Wrong polarization is a loss.
I did a simple calculation and it seems like the rotation angle due to this is about 3.5 degrees and the loss is about 0.4%. This is small enough, we could choose NOT to fix the height of ZM2 though it will somewhat complicate the initial alignment procedure. OTOH, it seems as if it's possible to modify the raiser relatively quickly.
I eyeballed the positions of OFI steering mirrors and ZM2 in the horizontal plane on HAM5 from D0901134 and D1700472.
Similarly I eyeballed the position of ZM1 and the direction of the beam connecting VOPO and ZM1 on HAM6 from D1700464.
I used D0901920 to determine HAM5-HAM6 distance.
I assumed that ZM2 is 0.76 inches higher than everything else and that ZM1-VOPO beam is level.
I started with a perfectly level S-pol light reflected by the first steering mirror on OFI, and propagated it through the second OFI steering mirror, ZM2, ZM1, and finally to VOPO.
Quick and dirty Matlab scripts are attached.