The aLIGO Beamsplitter and ITM elliptical baffle alignment procedure was attempted along the ITM-Y to SR3 path.  

The alignment beam was centered at ITM-Y.  Some rework of the tooling is required, so the error in centering at the ITM for this measurement is estimated to be less than 2.5 mm - corresponding to the alignment beam radius.
There was no target at SR3, so we tilted the alignment laser to center the spot on the Beamsplitter Baffle alignment tool D1200901 just to see what it looked like there.
Upon removal of the alignment tool, the beam was seen to be about half way between center and edge of the SR3.  High and right as viewed from ITM-Y.
An error of ~ 66 mm at SR3 would correspond to 13 mm of error of the BS HR baffle position - assuming the alignment spot was well centered at the BS target and ITM-Y



Some useful numbers:
SR3 diameter: 265 mm
Distance from ITMY to BS HR 5,167 mm
Distance from BS HR to SR3 19,432 mm
Alignment spot size at  ITMY 5 mm diameter



Alignment Procedure draft
https://dcc.ligo.org/E1700341-v1

GariLynn Billingsley
Jason Oberling
October 12, 2017