THEORY OF PROBING A PHOTONIC CRYSTAL WITH TRANSMISSION NEAR-FIELD OPTICAL MICROSCOPY

While near-field scanning optical microscopy (NSOM) can provide optica l images with resolution much better than the diffraction limit, analy sis and interpretation of these images is often difficult. We present a theory of probing with transmission NSOM that includes the effects o f tip field, tip/sample coupling, light propagation through the sample , and light collection. We apply this theory to analyze experimental N SOM images of a nanochannel glass (NCG) array obtained in transmission mode. The NCG is a triangular array of dielectric rods in a dielectri c glass matrix with a two-dimensional photonic band structure. We dete rmine the modes for the NCG photonic crystal and simulate the observed data. The calculations show large contrast at low numerical aperture (NA) of the collection optics and detailed structure at high NA consis tent with the observed images. We present calculations as a function o f NA to identify how the NCG photonic modes contribute to and determin e the spatial structure in these images. Calculations are presented as a function of tip/sample position, sample index contrast and geometry , and aperture size to identify the factors that determine image forma tion with transmission NSOM in this experiment.