E.M.S. Hitzer
Closed Light Paths in Equiangular Spiral Disks
Advances in Applied Clifford Algebras 10(2), 225 (2000).

Abstract: A new type of deformation for microscopic laser disks, the equiangular spiral deformation is proposed. First a short review of the geometry of light paths in equiangular spirals in the language of real two-dimensional geometric calculus is given. Second, the constituting equations for closed paths inside equiangular spirals are derived. Third, their numerical solution is performed and found to yield two generic types of closed light paths. Degenerate closed paths that exist over large intervals of the deformation parameter, and nondegenerate closed paths which only exist over relatively small deformation parameter intervals spanning less than 1% of the nondegenerate intervals. Fourth, amongst the nondegenerate paths a stable asymmetric bow-tie shaped light trajectory was found.

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