Enhanced transmission of light through subwavelength nanoapertures by far-field multiple-beam interference

Subwavelength aperture arrays in thin metal films can enable enhanced transmission of light waves. The phenomenon relies on resonant excitation and interference of the plasmon-polariton waves on the metal surface. We show a mechanism that could provide great resonant and nonresonant transmission enhancements of the light waves passed through the apertures not by the surface waves, but by the constructive interference of diffracted waves (beams generated by the apertures) at the detector placed in the far-field zone. In contrast to other models, the mechanism depends on neither the nature of the beams (continuous waves and pulses) nor material and shape of the multiple-beam source (arrays of one- and two-dimensional subwavelength apertures, fibers, dipoles, and atoms). The Wood anomalies in transmission spectra of gratings, a long standing problem in optics, follow naturally from the interference properties of our model. The point is the prediction of the Wood anomaly in a classical Young-type two-source system. The mechanism could be interpreted as a non-quantum analog of the super-radiance emission of a subwavelength ensemble of atoms (the light power and energy scales as the number of light-sources squared, regardless of periodicity) predicted by the well-known Dicke quantum model.