Three-beam-interference lithography: contrast and crystallography

Specific configurations of three linearly polarized, monochromatic plane waves have previously been shown to be capable of producing interference patterns exhibiting symmetry inherent in 5 of the 17 plane groups. Starting with the general expression for N linearly polarized waves, three-beam interference is examined in detail. The totality of all possible sets of constraints for producing the five plane groups is presented. In addition, two uniform contrast conditions are identified and discussed. Further, it is shown that when either of the uniform contrast conditions is applied and the absolute contrast is maximized, unity absolute contrast is achievable.