Apparatus for establishing a visible plane or fan of light

Claim 1

An optical apparatus for projecting a sweep laser beam, to thereby define a reference plane, the apparatus including, a. a source of visible laser light, b. a generally rectangular housing supporting and containing said laser source, c. a leveling mechanism supporting said housing, d. rotatable reflecting surface means for intercepting a laser beam from said laser source and causing the beam to repeatedly sweep out a light plane over angular areas, said rotatable reflecting surface means contains a plurality of reflecting surfaces and rotates about an axis extending along one wall of said housing, whereby a portion of said rotatable reflecting surface means extend beyond the plane of said one housing surface, e. a generally semi-cylindrical wall attached to and extending out from said one housing surface, the axis of rotation of said rotatable reflecting surface means being substantially coincident with the longitudinal axis of said semi-cylindrical wall, whereby the rotatable reflecting surface means is housed by both the housing and the semi-cylindrical wall, f. an optical window in said semicylindrical wall to permit egress of the laser light and to thereby sweep out 180* without interference from the housing.