I started mode matching of the beam going to IMC. The work is still going on.
According to Rana's calculation (see here), I put the first lens (f=200mm) in between two steering mirrors after PMC.
The distance from PMC to the first lens was adjusted by using a metal ruler. So I believe the accuracy is something like 1mm.
I aligned the beam path going through the broadband EOM and the mode matching lenses.
I could find the optimum position for the second lens (f=-150mm) by sliding the position of the lens and measuring the mode after it.
But the optimum position looked a bit far from the EOM. It's off by about 3-4 inch from the designed position.
Somehow I feel that the beam before the second lens goes with a smaller divergence angle than that of designed.
So tomorrow I am going to restart the work from checking the mode before the second lens.
Maybe at first I should measure the mode without going through the EOM because it changes the waist position and makes the system not straightforward. |