Here I show two photos of the latest ABSL (ABSolute Length measurement) setup.
Figure.1 : A picture of the ABSL setup on the AP table.
The setup has been a little bit modified from the before (#4923).
As I said on the entry #4923, the way of sampling the ABSL laser wasn't so good because the beam, which didn't go through the faraday, was sampled.
In this latest configuration the laser is sampled after the faraday with a 90% beam splitter.
The transmitted light from the 90% BS (written in pink) is sent to the PSL table through the access tube which connects the AP and PSL table .
FIgure.2: A picture of the ABSL setup on the PSL table.
The 10% sampled beam ( pink beam in the picture) eventually comes to the PSL table via the access tube (the hole on the left hand side of the picture).
Then the ABSL beam goes through a mode matching telescope, which consists of a combination of a concave and a convex lens.
The PSL laser (red line in the picture) is sampled from a point after the doubling crystal.
The beam is combined at a 50 % BS, which has been setup for several purposes( see for example #3759 and #4339 ) .
A fast response PD (~1 GHz) is used for the beat-note detection.