  When a light beam passes through a cascade of biaxial crystals with aligned
optic axes, the resulting transverse intensity pattern consists of multiple
concentric rings. We provide a simple formulation for the pattern formation for
both circularly and linearly polarized input beams, that could be applied for a
cascade of an arbitrary number of biaxial crystals. We have experimentally
investigated multiple ring formation with up to three cascade biaxial crystals,
showing that the theoretical formulation is in full agreement with the
experimental results.
