The camera used in this set-up is found to be tilted today. Fig.1 shows that this tilt is introduced through the interface between camera and post.

During the alignment, we use camera to characterize cavity HG modes shapes. When the beam and camera height is aligned, we found beam appears not in the center of screen as Fig.2. We suspect the tilt between camera and post is the cause of the cavity modes mis-center as Fig.2.

Note that Fig.2 shows the non-ideal alignment of crystal, which has a black defect.