Local spectral information in the near field with wavelet analysis and entropy

In near-field optical microscopy the resolution is strongly related to the experimental illumination conditions and to the separation between tip and sample. Therefore the spectral information in near-field data (related to t he resolution in images) can be described only locally as a function of the tip-sample position. To make a local study of the spectral information in near-field data, we use wavelet decomposition that is associated with the c alculation of entropy. We deduce the resolution from the characteristics of the wavelet, which leads to an automatic and numerical evaluation of the r esolution in near-field data. (C) 1999 Optical Society of America.