Beam projection system having a light curtain system for detecting obstacles

The plurality of emitters and the plurality of detectors form a light curtain that is patterned about the beam, and are positioned to surround the beam. The plurality of emitters each have a centerline and each have a divergence angle centered on the centerline. The placement and orientation of the plurality of emitters about the acceptance centerline of the beam receiver are configured to align the centerlines of the plurality of emitters substantially parallel to the incoming beam. The detection of one or more of the plurality of emitters by one or more of the plurality of detectors depends on the divergence angles of each of the plurality of emitters and the tilt of the beam receiver relative to the beam centerline.