3-D FDTD image analysis in transmission illumination mode of scanning near-field optical microscopy

Tunnel scanning near-field optical microscopy (tunnel SNOM or TNOM) detects not only the regularly transmitted waves but also radiation coupled via evanescent waves to the classically forbidden directions (angles larger than the angle of total internal reflection). Forbidden light can, in general, provide images with higher contrast and resolution than those of allowed-light images. However, the full use of the forbidden-light information requires better understanding of the SNOM imaging process. While the multiple multipole method (MMP) has been proven to be useful for 2-D modeling of SNOM, it seems to be unsuitable for more realistic 3-D simulations due to difficulties in dealing with complicated inhomogeneous material geometries.