Optical near fields as photon-matter interacting systems

A quantum theoretical formulation of an optical near-field system developed using the projection operator method is shown to be applicable to conventional problems in the optical near field in a unified way, and also addresses different quantum mechanical issues such as atom manipulation and nano-fabrication. To gain a clear insight, the effective mass of exciton-polarizations is introduced; this depends on the sizes of the probe tip and sample. We calculate the optical near-field intensity detected by (a) a probe sphere and (b) tapered probe modelled by two spheres. The results show that the size of the probe tip determines the spatial resolution, while the contribution of the tapered part causes degradation of the signal contrast. A size-resonance effect between the probe and sample is predicted. Furthermore, enhancement of the signal intensity is observed at the edges of a circular aperture perpendicular to incident polarization. These results are consistent with those obtained from different methods. The approach employed is shown to be a valuable tool in physical understanding and analysis of the near-field optical phenomena as well as experimental situations.