[Joe Gleason, Chris Mueller, Alberto]

Yesterday we set the lenses on the ALS path on the PSL for mode matching to the ISCT1 table.

The ideal solution had a R=75mm lens and a R=257mm lens placed after the ALS Farady and separated by about 60cm (see LIGO-T1200471-v5 for details). Ideally this should have given us a waist of 68um radius between thw two lenses and a collimated beam of 3mm radius after the second lens. In actuality we measured a waist radius of 75um between the two lenses and becasue of this the second lens was placed at a different distance than designed. The beam coming out of the second lens had the desired size, however, due to the limited room on the table to do a long range beam scan, it was not easy to assess whether the beam was actually colimated, rather than diverging/diverging.

To be sure that the beam would not further diverge on its path to ISCT1, we set the second lens such that the beam would slightly converge over the 50cm or so that it covered over the table.

When the ISCT1 table is installed, someone will have to finely tune the position of this lens, if the beam size at its arrival on the table is not as desired. 

Mode matching on ISCT1 is designed to accept basically any relatively large beam (~>1mm) which arrives to the table almost collimated.