Local signal processing to evaluate resolution in SNOM images, using 1D wavelets

The near-field optical images are known to be inhomogeneous due on the one hand to the piezo decay and on the other hand to the scanning process. Both can induce a variation of the tip-sample distance between the beginning an d the end of the scanning in constant height mode and steps between consecu tive scanning lines. Moreover, the tip often rubs on the sample and induces artifactual, local high variations of the recorded signal. Therefore, a lo cal characterization of spectral information in the signal could be useful in defining the separation power of the setup. This paper proposes a conven ient method to evaluate this local spectral information in terms of local c haracterization of spatial frequency power in the recorded signal. The loca tion of the spatial frequencies is achieved by using the discrete wavelet t ransform method. (C) 2000 Elsevier Science B.V. All rights reserved.