Today after the cavity has been aligned, by hitting the center of the NE and NI mirrors (using the dithering lines), and the B7 diodes have been centered the input beam has been aligned by changing the offset on the error signal of the PR vertical control.

The power drops of a factor 4 for a PR vertical displacement of ~ 100 um. The control of the beam in the cavity alignment can be done with the vertical position of PR.