Optical depolarization induced by arrays of subwavelength metal holes

We present a symmetry-based theory of the depolarization induced by subwavelength metal hole arrays. We derive the Mueller matrices of hole arrays with various symmetries (in particular square and hexagonal) when illuminated by a finite-diameter (e.g., Gaussian) beam. The depolarization is due to a combination of two factors: (i) polarization-dependent propagation of surface plasmons along the surface of the array and (ii) a spread of wave vectors in the incident beam.