THEORY OF RESONANT SNOM (SCANNING NEAR-FIELD OPTICAL MICROSCOPY) - BREAKDOWN OF THE ELECTRIC-DIPOLE SELECTION RULE IN THE REFLECTION MODE

A theoretical study is reported about SNOM with the use of light in re sonance with the quantized levels of a mesoscopic sample. The microsco pic variation of electromagnetic field and the coherence of matter sta te are properly treated by solving the microscopic Maxwell equations a nd Schrodinger equation self consistently. A remarkable effect, i.e., the breakdown of the dipole selection rule, is shown in the reflection mode where a probe tip is used for both illumination of the sample an d collection of the signal. Namely, both dipole-active and higher-mult ipole-active levels give comparable signal intensities for appropriate probe tip positions.