Optical nonlinearity versus mechanical anharmonicity contrast in dynamic mode apertureless scanning near-field optical microscopy

We show that the contrast mechanism in dynamic mode apertureless scanning near-field optical microscopy is in general a combination of both spatially nonlinear optical interaction and temporally anharmonic mechanical cantilever motion. Mechanical factors are found experimentally to easily overshadow the optical signal, leading to artifacts not yet well documented in the literature. Our algebraic analysis provides a systematic framework to identify and control the relative influence of the competing contrast origins. (C) 2005 American Institute of Physics.