cheryl.vorvick@LIGO.ORG - posted 21:20, Tuesday 26 March 2013 - last comment - 09:28, Wednesday 27 March 2013(5898)
Alignment of PRM in angle is complete - REFL goes to HAM1 - REFL to it's parking spot is not fully reachable.
- Joe, Giacomo, Cheryl, Keita Tonight we started by revisiting the retro-reflected beam between PR3 and PRM. We used fringes to tweak the alignmet of the second reflection from the PRM to be aligned to the transmitted beam at PR2, which we estimated to be good to the beam radius of 6mm. PRM was estimated to be aligned to within 0.1mrads in pitch and yaw. Good PRM alignment is: pitch = +2000 on the slider yaw = -4000 on the slider With this alignment of PRM, the REFL beam clears all apertures and goes to HAM1! REFL to it's parking spot out of the top viewport is not reachable. Full bias in yaw, meaning we are saturating the output, gets the beam fully onto the steering mirror and onto the SiC baffle, but there is not enough drive to get the beam through the baffle aperture. PRM is at -4000 in it's a aligned position, and we had to drive it farther from zero to get the beam on the steering mirror, and saturated at -7800 on the slider. REFL can reach the SiC baffle but not the aperture position is pitch = +3000 on the slider yaw = -7800 on the slider Our suggestion is that we relieve/recenter yaw for the PRM at some point, so we can reach the baffle aperure, but that it's not necessary to do this immediately. For IO, Alignment checks and power measurements continue in HAM2 tomorrow. There is a steering mirror in HAM2 for Keita to use to set up the green beam for HAM3 alignment.
PRM angle estimate breakdown:
Two irises over 16m: This is our primary reference. 2mm over 16m = 0.1mrad, there are two irises and in the worst case these add up to 0.2mrad.
Retro reflected beam going back to PRM: The beam becomes big at PRM, and it's difficult to center on the iris with 2mm accuracy. I'd say 5mm over 16m = 0.3mrad but this might be pessimistic.
PRM alignment itself: We formed a FP cavity by PRM and the retro reflecting mirror, and aligned PRM to the point where the fringe spacing was 1cm (when we were in HAM2) to 5mm (when we moved to HAM3, don't know if this is the wave front curvature coming into play, or if this is simply that the alignment of things were drifting around at this level), so the angle here is 1um/1cm to 1um/0.5cm or 0.1 to 0.2mrad.
All in all, even if these things all add up in the same sign, we're still within 0.7mrad.
After removing the retro reflector mirror in the path, we were able to see the beam from PR3 coming into HAM3 and hitting the cover of the North opening of HAM3.
I'd say the position of the beam was somewhat off to the East from the center of HAM3, maybe about 4 inches or so but I cannot say for sure.
Anyway it seems like we already know the good ball park numbers for alignment offsets of all PRs. The question is if we tare off these offsets.