In situ technique for measuring the orthogonality of a plane wave to a substrate

A new compact in situ method of measuring the perpendicularity of a plane wave to a substrate is proposed. Off-axis cylindrical Fresnel lenses are used to focus a portion of the incident plane wave onto target lines. The displacement of the focal line from the targets is determined by the degree of angular misalignment. The proposed design has been incorporated into a 10-mm-thick fused-silica module, which enables us to obtain an alignment precision of better than 0.0083 degrees. This method is designed for use in optical assembly procedures that require an incident collimated beam that is normal to the alignment features. Experimental results are presented.