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 the 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 calculation of entropy. We deduce the resolution from the characteristics of the wavelet, which leads to an automatic and numerical evaluation of the resolution in near-field data. (C) 1999 Optical Society of America.