Helicon waves: Propagation-invariant waves in a rotating coordinate system

The concept of propagation-invariance is extended to discrete-distance propagation-invariant waves, i.e., waves whose intensity distributions are periodic with propagation distance. A new type of wave is presented which has an intensity pattern which rotates at a constant rate about the optical axis as it propagates, but is otherwise unchanged. These waves consist of superpositions of different higher-order Bessel waves. The new waves are referred to as a 'helicons' as their lines of constant intensity trace out helices about the optical axis. Methods to produce 'helicon' waves are described based upon established techniques for producing Bessel waves approximations with computer-generated holograms. Several such helicon elements are fabricated and tested, and the experimental results are presented. Possible practical applications of such waves, which include alignment and distance/speed measurements are discussed briefly.