After installation we characterized the waist of the bright alignment beam out of the telescope. The first plot in attachment shows the beam radius versus propagation distance (in blue) as compared with the corresponding measurement of the B1 beam from the ITF reflected from the SDB1 Faraday isolator towards the SQZ bench (in red). The positive direction of the propagation distance in the plot goes from SDB1 towards the squeezer. Solid lines represent a fit with the propagation law for Gaussian beams. The new BAB waist radius is 1.01+/-0.02 mm, and the waist position is at 1.7+/-0.07 m from the last steering mirror on the SQZ bench, i.e. very close to SDB1. The second plot shows the measured waist radius versus waist position for the two beams, i.e. B1 and BAB; error bars are given by the standard error from least-squares fitting. The differences between the two beams in terms of waist radius and waist position are now comparable with the overall measurement errors.
The new configuration also implies a longer optical path on the SQZ bench. For this reason the double stage Faraday isolator will have to be displaced from the previous position.
We have moved the double stage Fardaay isolator this morning. The BA beam is well centered on all the optics and is still passing weel through the pinhole installed after the first piezo alignment mirror.
The camera looking at the beam reflected off the output polarizer will have to be realigned with the beam coming from the ITF.