Plan C finally worked. We have 1.454mW of AUX X light at the PSL table (2mW incident on the fiber coupler).
Attached is the layout of the telescope.
What I did:
I stuck in Lens 1 (f=200mm) and measured the beam width after the focus of the lens at several points. I fit the data and calculated the beam waist and its position after this lens.
I used the calculated waist and matched it with an appropriate lens and target (fiber coupler) distance. I calculated the maximum coupling efficiency to be 77% for Lens 2 with f=50mm and the fiber coupler placed at 20cm from the waist of Lens1. I was able to obtain 72% coupling after putting the telescope together.
I locked the arms, ran ASS and brought back GTRX to its usual optimum value of ~0.5 counts after closing. We also have the X arm beatnote on the spectrum analyzer.
There are still a couple of things to fix. The rejected beam from the beam sampler has to be dumped using a razor blade.